HK1069196B - A method for manufacturing a heat resisting member applicable to an exhaust gas guide assembly of a gas turbocharger - Google Patents

Description

Method for manufacturing heat-resistant component applicable to exhaust guide assembly of variable geometry turbocharger

Technical Field

The present invention relates to a turbocharger used in an automobile engine or the like, and particularly to an exhaust guide assembly incorporated therein and a variable vane of a constituent member thereof.

Background

As a supercharger used as a device for achieving high output and high performance of an automobile engine, a turbocharger is known, which drives a turbine by using exhaust energy of the engine, rotates a compressor by an output of the turbine, and brings the engine to a supercharging state higher than that in a natural suction. However, in such a turbocharger, when the engine rotates at a low speed, the exhaust gas flow rate is reduced, and therefore, the operation is not smooth until the exhaust turbine rotates at a high efficiency, and a certain time is required until the turbocharger can be supercharged at a time, which makes it difficult to avoid the occurrence of a phenomenon such as so-called turbo lag. Further, in a diesel engine in which the engine speed is originally low, there is a disadvantage that it is difficult to obtain a turbo-charging effect.

For this reason, a VGS type turbocharger capable of operating with high efficiency even from a low rotation speed stage has been developed. This is a turbocharger that can achieve high output even when rotating at low speed by increasing the work done by the exhaust turbine by throttling a small amount of exhaust gas with variable vanes (blades) to increase the speed of exhaust gas, and is an effective turbocharger that can achieve high efficiency when rotating the engine from low speed, particularly in diesel engines that have recently been solving the problem of the amount of NOx in exhaust gas.

The exhaust guide unit in the variable geometry turbocharger is used in a high temperature and exhaust gas atmosphere, and materials having heat resistance, for example, heat-resistant materials such as JIS standard, SUS, SUH, SCH, and NCF super alloy, have been used for the production thereof.

In manufacturing a variable vane in a variable geometry turbocharger, a metal material (a molding material having a variable vane profile) in which a vane portion and a shaft portion are integrally formed is first formed, and the molding material is then appropriately cut and processed to be finished into a desired shape and size.

In recent years, in particular, diesel engines have been subject to very strict restrictions with respect to exhaust gas discharged into the atmosphere in view of environmental protection, and there is a strong demand for a variable geometry turbocharger that can achieve high efficiency of the engine from a low rotation speed stage to mass production, as a diesel engine having an originally low engine rotation speed, in order to reduce NOx, Particulate Matter (PM), and the like.

The present invention has been made in view of the above-mentioned background, and it has been attempted to improve the performances of the exhaust guide assembly, such as high-temperature wear resistance, oxidation resistance, high-temperature hardness, etc., of the constituent members of the exhaust guide assembly, which is used in an exhaust gas atmosphere for a long time with a heat cycle at a high temperature of 700 ℃ or higher, and to develop a novel manufacturing method by which a variable-airfoil-shaped material having a nearly clean shape can be obtained in reality by solving the problems of the above-mentioned methods such as precision casting and metal injection molding and by using these methods.

Disclosure of Invention

The method of manufacturing a heat-resistant member applicable to an exhaust guide assembly of a variable geometry turbocharger according to claim 1 of the present invention is suitable for a turbine frame having variable vanes for adjusting the flow rate of exhaust gas discharged from an engine to rotate an exhaust turbine, the variable vanes being rotatably supported on an outer peripheral portion of the exhaust turbine, and a variable mechanism for adjusting the flow rate of exhaust gas by rotating the variable vanes;

a method for manufacturing a heat-resistant member of an exhaust guide unit in a turbocharger of a variable geometry turbocharger capable of increasing the speed of exhaust gas by throttling the flow rate of exhaust gas with a variable vane and achieving high output even at low-speed rotation,

a high-alloy austenitic heat-resistant stainless steel, an iron-based superalloy, or a nickel-based superalloy is subjected to ion carburization, and then subjected to TD salt bath treatment.

According to the present invention, high-temperature hardness of the surface of the material is ensured by ion carburization and TD salt bath treatment, and a heat-resistant member having high durability can be obtained.

The method of manufacturing a heat-resistant member applicable to an exhaust guide assembly of a variable geometry turbocharger according to claim 2 of the present invention is characterized in that, in addition to the gist of claim 1 of the present invention, when the iron-based superalloy is selected as a raw material, one or more of Ti, Nb, B, Hf and Zr are contained.

Further, the method of manufacturing a heat-resistant member applicable to an exhaust guide assembly of a variable geometry turbocharger according to claim 3 of the present invention is characterized in that, in addition to the gist of claim 1 of the present invention, when a rolled material of the high-alloy austenitic heat-resistant stainless steel or the iron-based superalloy is selected as a raw material, the raw material is hot-rolled under a high pressure in a ferrite region to refine particles.

Further, the method of manufacturing a heat-resistant member applicable to an exhaust guide assembly of a variable geometry turbocharger according to claim 4 of the present invention is characterized in that, in addition to the gist of claim 1 of the present invention, a large amount of internal strain is accumulated under high stress within an allowable range in the case where the nickel-based superalloy is selected as a raw material, and a fine γ' phase is precipitated as nuclei for the strain.

Drawings

FIG. 1 is a perspective view (a) of a variable geometry turbocharger in accordance with the present invention, and an exploded perspective view (b) of an exhaust guide assembly,

figure 2 is a front and left side view of a variable vane as one component of the exhaust guide assembly,

fig. 3 is a graph showing the relationship between the temperature and the viscosity of the Ni-based heat-resistant material and the Fe-based heat-resistant material.

Detailed Description

The present invention will be explained below. The present invention has been developed in order to improve the high-temperature durability of the exhaust guide assembly a of the variable geometry turbocharger by studying various heat-resistant materials, and first, an exhaust guide assembly made of such heat-resistant materials will be described. The heat-resistant raw materials are classified into the following 8 types, i.e., embodiment 1, embodiment 2, embodiment 3, embodiment 4, embodiment 5, embodiment 6, embodiment 7, and embodiment 8.

[1] Exhaust guide assembly

The exhaust guide assembly a is used particularly for appropriately throttling exhaust gas G to adjust the flow rate of exhaust gas when the engine rotates at a low speed, and includes, as shown in fig. 1, a plurality of variable vanes 1 provided on the outer periphery of an exhaust turbine T to substantially set the flow rate of exhaust gas, a turbine frame 2 supporting the variable vanes 1 to be freely rotatable, and a variable mechanism 3 for rotating the variable vanes 1 by a predetermined angle to appropriately set the flow rate of exhaust gas G. Next, each component will be explained.

First, the variable vane 1 will be explained. As shown in fig. 1, for example, a plurality of variable vanes (about 10 to 15 variable vanes in one exhaust guide unit a) are arranged in a circular arc shape along the outer periphery of the exhaust turbine T, and the flow rate of exhaust gas is appropriately adjusted to substantially the same degree every time the variable vanes rotate. Each variable vane 1 includes a wing portion 11 and a shaft portion 12. The wing part 11 is formed to have a certain width mainly corresponding to the width dimension of the exhaust turbine T, and its cross section in the width direction is approximately airfoil-shaped so that the exhaust gas G can efficiently enter the exhaust turbine T. Here, for convenience of explanation, the width dimension of the wing part 11 is set as the fin height h. The shaft portion 12 is formed to be integrally continuous with the wing portion 11, and is a portion corresponding to a rotation shaft for rotating the wing portion 11.

Further, at the joining portion of both the wing portion 11 and the shaft portion 12, a tapered portion 13 which narrows from the shaft portion 12 to the wing portion 11 and a flange 14 having a diameter slightly larger than that of the shaft portion 12 are formed continuously with each other. The bottom surface of the flange 14 is formed on substantially the same plane as the end surface of the wing 11 on the shaft 12 side, and the smooth rotation of the variable vane 1 in the state of being attached to the turbine frame 2 can be ensured by this plane. A reference surface 15 is formed at the tip of the shaft portion 12 as a reference for the mounting state of the variable vane 1. The reference surface 15 is a portion fixed to the variable mechanism 3 by caulking or the like as described later, and is formed in a state where a plane formed by cutting out the shaft portion 12 relatively is inclined substantially at a constant angle with respect to the wing portion 11 as shown in fig. 1 and 2.

The turbine frame 2 will be explained below. This is configured as a frame member that holds a plurality of variable vanes 1 so as to be rotatable, and one example thereof is shown in fig. 1 in which the variable vanes 1 are sandwiched between a frame assembly 21 and a holding member 22. Further, the frame assembly 21 has a flange portion 23 into which the shaft portion 12 of the variable vane 1 is inserted, and a boss portion 24 on the outer periphery of which the variable mechanism 3 is fitted as described later. According to this configuration, the insertion holes 25 are formed at equal intervals in the peripheral portion of the flange portion 23, the number of which is equal to the number of the variable vanes 1.

As shown in fig. 1, the holding member 22 is formed in a disk shape with an opening at the center. The dimensions between the two members of the frame assembly 21 and the holding member 22 are maintained substantially constant (approximately the width dimension of the blade of the variable blade 1) so that the blade portion 11 of the variable blade 1 sandwiched therebetween can be smoothly rotated at all times, and the dimensions between the two members are maintained by four caulking pins 26 provided at the outer peripheral portion of the insertion hole 25, as an example. Here, holes formed in the frame assembly 21 and the holding member 22 are used as pin holes 27 so that the caulking pins 26 can be inserted.

In this embodiment, the flange portion 23 of the frame unit 21 is formed of two flange portions, i.e., a flange portion 23A having substantially the same diameter as the holding member 22 and a flange portion 23B having a slightly larger diameter than the holding member 22, and these are formed as a single member.

The variable mechanism 3 will be explained below. The mechanism provided on the outer periphery of the boss portion 24 of the turbine frame 2 is a mechanism for rotating the variable vane 1 to adjust the exhaust gas flow rate, and one example thereof is, as shown in fig. 1, provided with a rotating member 31 for substantially rotating the variable vane 1 in the module, and a transmission member 32 for transmitting the rotation to the variable vane 1. As shown in the drawing, the rotary member 31 is formed in an approximately disk shape having a hole at the center, and the transmission members 32 are provided at the same number as the variable vanes 1 at equal intervals at the peripheral portion thereof. The transmission member 32 includes a driving element 32A rotatably attached to the rotation member 31 and a driven element 32B fixedly attached to the reference surface 15 of the variable blade 1, and transmits rotation in a state where the driving element 32A and the driven element 32B are connected to each other. Specifically, the quadrangular sheet-like driving element 32A is fixed to the pivot member 31 by a pin so as to be rotatable, and the driven element 32B formed in a substantially U-shape so as to be fitted into the driving element 32A is fixed to the reference surface 15 at the tip end of the variable vane 1, and finally the pivot member 31 is attached to the boss 24, and the quadrangular sheet-like driving element 32A is fitted into the U-shaped driven element 32B, and both are engaged with each other.

In the initial state where the plurality of variable vanes 1 are attached, in order to align them in the circumferential direction, both the variable vanes 1 and the passive element 32B are attached at substantially constant angles, and in the present embodiment, this function is mainly exerted by the reference surface 15 of the variable vane 1. Further, if the rotor 31 is simply fitted into the boss portion 24, the engagement state of the transmission member 32 is released when the rotor 31 is slightly disengaged from the turbine frame 2, and in order to prevent this, a ring 33 or the like is provided to hold the rotor 31 from the other side of the turbine frame 2, and the rotor 31 is pressed toward the turbine frame 2 side.

According to this configuration, when the engine rotates at a low speed, the turning member 31 of the variable mechanism 3 is appropriately turned, and the turning is transmitted to the shaft portion 12 via the transmission member 32, so that the variable vane 1 is turned as shown in fig. 1, and the exhaust gas G is appropriately throttled to adjust the exhaust gas flow rate.

The exhaust guide module a has the above-described basic structure, and the heat-resistant material constituting the module will be described below for each embodiment.

[ embodiment 1]

Embodiment 1 is an embodiment for reducing the non-metallic substance present in the heat-resistant metal member and miniaturizing the size thereof. As a production method, there are methods such as calcium addition, heat and pressure treatment, pure oxygen converter blowing treatment, and the like for a heat-resistant metal member, and specifically, the production is performed in the following steps.

(I) Reducing non-metallic inclusions in heat resistant metal parts

By adding calcium during refining, sulfur, silicon, aluminum and the like can be excluded from the calcium compound to reduce the formation of non-metallic inclusions of sulfides (type A) and oxides (type B and type C). In addition, the non-metallic inclusions of B and C are reduced by removing oxide slag through blowing treatment of a pure oxygen converter.

(II) miniaturization of non-metallic inclusion size in Heat-resistant Metal Member

A Steckel mill or a powerful continuous hot mill operating under a large pressure, which is attached to a heating furnace at both the leading end and the trailing end of a coil, stretches (class A) and crushes (class B and class C) nonmetallic inclusions remaining after refining. Further, a large amount of oxides are uniformly formed by blowing in a pure oxygen converter to achieve a small size of the nonmetallic inclusions.

(III) manufacture of exhaust guide Assembly

The above-treated raw material is subjected to casting, forging, press working, fine blanking, punching, caulking, surface modification, etc. to manufacture the exhaust guide assembly a.

(IV) durability

Compared with non-treated materials, the high temperature/thermal fatigue, creep property, toughness, stress concentration coefficient and high temperature oxidation resistance are obviously improved to below 1/5, and the high temperature durability of the exhaust guide assembly is more than 5 times.

[ embodiment 2]

The heat-resistant member (alloy) according to embodiment 2 is produced by a general method. Specific three embodiments are shown in table 1.

The reason for limiting the respective components of the alloy is as follows.

The C content is 0.05% or less for the purpose of reducing sensitization.

Mn is 1% or more in order to retard the generation of the sigma phase.

Ni is 15% or more for increasing the free energy of formation of the sigma phase.

Cr is 30% or less for increasing the free energy of formation of the sigma phase.

Ti is 0.1% or more for forming a gamma' phase.

Al is 0.1% or more for forming a gamma' phase.

Ce or La is 0.05% or more to suppress the generation of the σ phase.

(I) Manufacture of exhaust guide assembly

The predetermined components are controlled in a converter refining step, and then the raw material is manufactured through the usual steps of continuous casting, hot rolling and cold rolling, and the exhaust guide assembly is processed and manufactured using the material.

(II) inhibition of tissue embrittlement

The tissue embrittlement inhibiting data are shown in table 1 below.

TABLE 1

Test article		Ingredient (wt%)								Test for resistance to tissue embrittlement
												C	Mn	Ni	Cr	Ti	Al	Ce	La	Resist againstSensitization	Sigma embrittlement resistance
		Steel material according to embodiment 2	①②③	0.010.050.05	2.01.51.5	252525	202020	1.5--	1.5--	-0.070.07	--0.08											○△△	○○○
Contrast steel material (SUS310S)												0.06	0.5	20	25	-	-	-	-	△	×

(III) film coating method

(a) The method for coating the surface of the alloy in the present embodiment may be a TD salt bath method, and specifically, the following steps are performed.

After a surface carburization treatment is performed in a non-equilibrium supersaturated state in advance, a part preheated to 500 ℃ is immersed in a salt bath of 1000 ℃ or lower composed of borax, chloride, and chromium oxide, thereby forming a chromium carbide coating film.

(b) Inhibition of tissue embrittlement

The tissue embrittlement inhibiting data are shown in table 2 below.

TABLE 2

Test article	Test for resistance to tissue embrittlement
			Anti-sensitization	High temperature wear resistance
	Without covering film	○			×
With a coating film			◎	◎

(IV) stress imparting treatment

(a) Processed content

Before the precipitation heat treatment, the part is subjected to a certain processing as uniformly as possible within an allowable range, and in some cases, a hydrostatic pressure such as a hydraulic pressure is applied to introduce a plastic strain under a stress.

(b) Inhibition of tissue embrittlement

The tissue embrittlement inhibiting data are shown in table 3 below.

TABLE 3

Test article		Resistance to overaging
			A	General parts working	×
B	Uniform part machining	○
			C	B ⊕ hydrostatic pressure treatment	◎

[ embodiment 3]

The alloy of embodiment 3 is produced by a usual method. Specific three embodiments are shown in table 4.

The reason for limiting the respective components of the alloy is as follows.

W is 0.3% or more in order to effectively cause temper secondary hardening at a high temperature.

The reason why V is 1.0% or more is to effectively cause temper secondary hardening at a high temperature.

The reason why Mo is 1.0% or more is to effectively cause temper secondary hardening at a high temperature.

Hf is 0.5% or more in order to enable the occurrence of temper secondary hardening at high temperature efficiently.

(I) Manufacture of exhaust guide assembly

The composition is controlled by converter refining, after the composition is further refined by the external refining, the steel plate blank, the small and medium square billet, the large square billet and the like are manufactured by continuous casting, and then the stainless steel raw material is manufactured by hot rolling and cold rolling. The exhaust guide assembly is manufactured by machining and heat treatment using the material.

(II) durability

Table 4 below shows the data of durability improvement.

TABLE 4

Test article			Ingredient (wt%)						Durability test
										C	Cr	W	V	Mo	Hf	HV (Vickers hardness) after secondary hardening at 800 DEG C
			A	SUS420J2		0.3	13	-	-								-	-	200
B	Steel material according to embodiment 3	①②③								0.50.50.5	131313	0.40.40.4	1.21.2	-1.21.2	--0.7	520560600
			C	B + work strain	①②③	0.50.50.5	131313	0.40.40.4	-1.21.2								-1.21.2	--0.7	600700800

(III) film coating method

(a) As a method for coating the surface of the martensitic stainless steel of the present embodiment, a chromium carbide film formation method by a salt bath method is preferably used, and specifically, the following steps are performed.

Since the solid solution carbon is contained sufficiently, the bath is preheated to 500 ℃ after cleaning, immersed in a salt bath of about 1000 ℃ composed of borax, chloride and chromium oxide, and then taken out and neutralized for cleaning. In this case, it is preferable to perform a short-time treatment at as low a temperature as possible in order to prevent the secondary cured state from deteriorating.

(b) High temperature durability

Table 5 below shows data of the improvement of high temperature durability.

TABLE 5

Test article	High temperature durability
		Without covering film	Delta (high temperature oxidation and sintering)
With a coating film	O (the phenomenon hardly occurs)

[ embodiment 4]

The heat-resistant member (alloy) according to embodiment 4 is produced by a general method. Two specific embodiments are shown in table 6.

The reason for limiting the respective components of the alloy is as follows.

The C content of 0.2 to 0.5% is an appropriate range in which sufficient film formation can be achieved, provided that chromium carbide having sufficient high-temperature durability is obtained.

Mn is 5 to 10% in order to keep the amount of solid solution of carbon within an appropriate range of 0.2 to 0.5%.

Ni is 10 to 20% in order to maintain the amount of carbon dissolved in the carbon in an appropriate range of 0.2 to 0.5%.

The Cr content is 15 to 25% in order to maintain the amount of carbon dissolved in the alloy in an appropriate range of 0.2 to 0.5%.

N is 0.05 to 0.2% in order to keep the amount of carbon dissolved in the carbon in an appropriate range of 0.2 to 0.5%.

One or both of La, Ce and Sm are 0.01 to 0.1% in order to maintain the amount of carbon dissolved in the alloy in an appropriate range of 0.2 to 0.5%, which contributes to the formation of chromium carbide.

(I) Manufacture of exhaust guide assembly

The composition is controlled by converter refining, after the composition is further refined by the external refining, the steel plate is made into plate blanks, small and medium-sized square blanks, large square blanks and the like by continuous casting, and then the heat-resistant material is made by hot rolling and cold rolling. The exhaust guide assembly is manufactured by machining and heat treatment using the material.

(II) high temperature Strength

Table 6 below shows the data for the high temperature strength improvement.

TABLE 6

Test article		Ingredient (wt%)								High temperature strength
											C	Mn	Ni	Cr	N	La	Ce	Sm	Tensile Strength (MPa) at 800 ℃
		A	Steel material of embodiment 4	0.3	5.5	19	24	0.10	0.07	-										-	220
B	0.4										6.0	19	24	0.10	-	0.05	0.02	230
		C		Contrast steel material (SUS310S)	0.06	0.5	20	25	0.02	-									-	-	170

(III) film coating method

(a) The method for coating the surface of the alloy of the present embodiment may be a salt bath method, and specifically, the following steps are performed.

The component parts are cleaned, preheated to 500 deg.C, then immersed in a salt bath containing chloride and chromium oxide in borax at about 1000 deg.C, and then neutralized and cleaned.

(b) Durability

Table 7 below shows the data of durability improvement.

TABLE 7

Test article		Ingredient (wt%)								Durability
											C	Mn	Ni	Cr	N	La	Ce	Sm	Coefficient of friction at 850 DEG C
		A	Steel material of embodiment 4	0.3	5.5	19	24	0.10	0.07	-										-	0.5
B	0.4										6.0	19	24	0.10	-	0.05	0.02	0.4
		C		Contrast steel material (SUS310S)	0.06	0.5	20	25	0.02	-									-	-	1.8

[ embodiment 5]

Embodiment 5 is manufactured by adding carbon to JIS SUS310S, and specifically, the following procedure is performed. Specific embodiments are shown in table 8 below.

The composition of the components is controlled by converter refining, and after the components are refined outside the furnace to further ensure the composition to be accurate, the components are manufactured into slabs by a continuous casting machine. Then, the slab is uniformly heated at 1200 ℃ or higher for 1 hour or more, hot-rolled by a steckel mill or the like under a light pressure, hot-rolled while controlling the lower limit temperature of rolling to 950 ℃ or higher, and finally quenched with a large amount of cooling water. The hot rolled coil thus obtained is cold rolled, and annealing is performed at about 1100 ℃ in a continuous facility in order to prevent carbide from being generated from the matrix iron, thereby producing a finished raw material.

The carbon content is set to 0.15 to 0.35% within a range in which carbon is solid-dissolved by the treatment of the present embodiment and a chromium carbide coating can be formed without carburizing.

(I) Manufacture of exhaust guide assembly components

The composition is controlled by converter refining, and a slab obtained by continuous casting is heated at a high temperature of 1250 ℃ or higher, and then subjected to a rolling/forging quenching process to produce a heat-resistant member.

(II) strengthening

Table 8 below shows the hot hardness data.

TABLE 8

Test article	Carbon content	High temperature hardness HV (800 ℃) HV: vickers hardness	Abrasion (sintering)	Coefficient of friction at 850 DEG C
					Steel material according to embodiment 5	0.32	510	Is free of	0.4
SUS310S	0.05	290	Take place of	1.8

(III) film coating method

(a) The coating on the surface of the alloy of the present embodiment is performed by utilizing most of the dissociated and solid-dissolved carbon in the heat-resistant material, and specifically, is performed in the following steps.

The member is cleaned, preheated at 500 ℃, immersed in a salt bath containing chromium oxide, titanium, tungsten, or the like, and then subjected to neutralization treatment.

(b) High wear resistance

Data relating to high temperature hardness and high temperature wear resistance are shown in table 8 above.

[ embodiment 6]

(I) Manufacture of exhaust guide assembly

Various superalloys having a predetermined composition are subjected to component adjustment and melting by vacuum melting, and the casting superalloy (inconel 713C) is an ingot and used as an intermediate alloy for sand casting or precision casting to manufacture a component. On the other hand, a superalloy for rolling/forging (inconel 800H) is cast or, as the case may be, continuously forged into slab, large billet, medium or small billet, and then rolled/forged into a superalloy material. Thereafter, the assembly member is manufactured by machining (and heat treatment).

(II) high temperature Strength

Table 9 below shows the high temperature strength data.

TABLE 9

Test article	High temperature Strength (tensile Strength, MPa: 800 ℃ C.)
		Inconel nickel chromium stainless steel 800H	500
Inconel 713C	600
		Hasteloy S	550

(III) film coating method

(a) The surface coating of the superalloy of the present embodiment with chromium carbide, titanium carbide, tungsten carbide, vanadium carbide, niobium carbide, or molybdenum carbide is performed after carburizing and nitriding, specifically, by the following steps.

After ion carburizing or ion nitriding, the superalloy raw material is preheated to 500 ℃, dipped in a salt bath containing chromium, titanium, tungsten, vanadium, niobium or molybdenum, and then subjected to neutralization treatment.

(b) Suppression of reduction in high-temperature sliding wear resistance

Table 10 below shows data in which the decrease in abrasion resistance was suppressed.

Watch 10

Test article	Film coating	Suppression of wear deterioration (Friction coefficient at 900 ℃ C.)
			Inconel nickel chromium stainless steel 800H	Is free of	1.5
Inconel nickel chromium stainless steel 800H	Cr-C	0.5
			Inconel nickel chromium stainless steel 800H	Ti-C	0.4
Inconel nickel chromium stainless steel 800H	W-C	0.4
			Inconel nickel chromium stainless steel 800H	Mo-C	0.5
Inconel nickel chromium stainless steel 800H	V-C	0.5
			Inconel nickel chromium stainless steel 800H	Nb-C	0.5

[ embodiment 7]

A molded material of the heat-resistant member (alloy) according to embodiment 7 is basically produced by precision casting or metal injection molding (material quality tables 11 and 12 below).

The composition of the components is controlled by converter refining, and after the components are refined outside the furnace to further refine the composition, the components are manufactured into slabs by a continuous casting machine. Then, the slab is uniformly heated at 1200 ℃ or higher for 1 hour or more, first hot-rolled in a steckel mill or the like under a light pressure, hot-rolled while controlling the lower limit temperature of rolling to 950 ℃ or higher, and finally quenched with a large amount of cooling water. The hot rolled coil thus obtained is cold rolled, and annealing is performed at about 1100 ℃ in a continuous facility in order to prevent carbide from being generated from the matrix iron, thereby producing a finished raw material.

The reason for limiting the respective components of the alloy cast steel is as follows.

The C content is 0.2 to 0.5% for improving the melt fluidity, high-temperature strength and film processability.

The Cr content is 15-30% for improving heat resistance.

The Ni content is 15 to 30% in order to improve the high-temperature strength, the high-temperature oxidation resistance, the thermal fatigue resistance, and the thermal expansion (dimensional change), in particular.

Pb is 0.01-0.1% for facilitating precision casting and mechanical cutting of MIM shape extremely close to the part and for improving sintering property of MIM.

Se is 0.01 to 0.1% for facilitating precision casting and mechanical cutting of MIM shape extremely close to parts and for improving sintering property of MIM.

Te is 0.01 to 0.1% for facilitating precision casting and mechanical cutting of MIM having a shape extremely close to that of a part and for improving sinterability of MIM.

O is 0.02 to 0.1% for good melt fluidity in precision casting.

The reason for S being 0.005-0.05% is to have good melt fluidity during precision casting.

(I) Manufacture of exhaust guide assembly

(a) Precision casting method

1. Manufacture of

The casting is carried out by a lost wax casting method which is a typical precision casting method and has the above composition. This method is a method of manufacturing a product by forming a refractory coating around a wax pattern having the same shape as the product to be cast, and then heating the entire product to melt only the wax pattern, and specifically, in the following steps, measures are taken to improve the degree of closeness of the shape.

The composition of the cast product is adjusted by using Fe-Ni-Cr intermediate alloy in an electric furnace, the melt viscosity is reduced by high-temperature melting, and the cast product is subjected to rapid cooling casting within a range in which thermal stress cracking does not occur in a mold made of the refractory material, so that the dimensional tolerance is extremely small, that is, the dimensional accuracy is improved. Then, after cooling, the mold is disassembled, the runner and the like are cut, and the product is made into a product having a very similar shape by acid washing and washing. And then, the components of the assembly are manufactured through a light cutting process. In the present embodiment, a new idea is made that no load is applied as much as possible in the steps of cutting, polishing, and the like in the subsequent steps.

2. Data relating to manufacture

Table 11 below shows comparative data with the prior art.

TABLE 11 precision casting method

Test article	Ingredient (wt%)								Free flowing property	Dimensional accuracy	Machinability and cutting property
												C	Cr	Ni	Pb	Se	Te	O	S
	Steel material form of embodiment 7	0.40	20	24	0.04	0.03	0.02	0.09												0.020	Good wine	Improvements in or relating to	Cutting once to obtain
Existing materials									0.06	20	24	-	-	-	0.05	0.007	Has difficulty in flowing into or generating pores in the small R part	-	2 to 3 times of cutting

(b) Metal injection molding method

1. Manufacture of

The method comprises forming fine raw material powder by increasing the atomizing spray velocity of air/water, increasing the cooling velocity and controlling the shape and size of a nozzle, removing surface oxide in a reducing atmosphere, sintering at a temperature slightly lower than the melting point (about 20 ℃ lower) to independently bubble, and injection molding to obtain a product with a very similar shape. And then, the components of the assembly are manufactured through a light cutting process.

2. Data relating to an article

Table 12 below shows comparative data with the prior art materials.

Injection molding method for metal of watch 12

Test article	Ingredient (wt%)								Generation of independent bubbles	High temperature bending fatigue	Machinability and cutting property
												C	Cr	Ni	Pb	Se	Te	O	S
	Steel material form of embodiment 7	0.40	20	24	0.04	0.03	0.02	0.09												0.020	Approximately 100%	The fatigue strength limit is improved by 50-100 percent compared with the existing material	Cutting once to obtain
Existing materials									0.06	20	24	-	-	-	0.05	0.007	About 50 percent	-	Requiring 2-3 cuts

(III) durability

In order to form a carbide coating on the above-described lost-wax casting or MIM cutting material, salt bath treatment (carburizing treatment if necessary) is performed to produce a component.

Table 13 below shows the data of durability improvement.

TABLE 13 high-temperature coefficient of friction with and without coating treatment

Test article			Durability (coefficient of friction at 850 ℃ C.)
				Method of manufacture		Presence or absence of a coating film
A	Lost wax modeling method	With film coating treatment					0.4
			B	Treatment without coating film	1.8
C		MIM				With film coating treatment	0.5
	D		Treatment without coating film	1.9

[ embodiment 8]

(I) High-alloy austenitic heat-resistant stainless steel

(a) Example of performing ion carburization and TD salt bath treatment alone

A glow discharge is formed in a rare gas atmosphere of 2 to 3 Torr containing a hydrocarbon gas including methane or propane, and the generated hydrocarbon plasma is caused to act on the surface of the object to be treated to thereby carburize the object. Next, the object to be treated is immersed in a high-temperature TD salt bath in which oxides of Cr, V, Ti, W, etc. and chlorides as auxiliaries are mixed in borax, and a carbide is formed by a high-temperature chemical reaction.

(b) Examples of Using SUS310S or SUH310

Basically the same as the above method, but since there is a difference of SUS310S C < 0.1% and SUH 310C ≈ 0.2%, the ion carburization conditions should be changed accordingly. As a result of the TD salt bath treatment, high-temperature durability, mainly high-temperature wear resistance and high-temperature oxidation resistance, is significantly improved. Further, since the addition of Ti, Ni, B, Hf or the like can refine crystal grains, high-temperature hardness, fatigue strength, creep resistance and the like are improved. And (c) adopting the treatment method (a).

(c) Example Using SCH21

Basically, the method is the same as the above method, but the ion carburizing time is shortened because C is approximately equal to 0.3% and more. The effect and grain refining effect of TD salt bath treatment were the same as those of SUS310S and SUH 310. And (c) adopting the treatment method (a).

(d) Examples of using rolled materials

The material is heated in advance, lightly pressed at the austenite stage to transform the material into ferrite, and then rolled at a high pressure at a time to greatly increase the number of recrystallization nuclei generated, thereby avoiding the transformation from austenite to ferrite during cooling (in general hot rolling, transformation occurs after pressing down to generate ferrite recrystallization from austenite grains), and fine grains can be obtained. Therefore, heat resistance such as high-temperature strength is improved. And (c) adopting the treatment method (a).

(II) example Using iron-based superalloy

Since iron-based superalloys such as SUH660 and inconel 800H contain a large amount of Ni, Ti, Al, and the like, care must be taken to clean and activate the surface during ion carburization. The others are substantially the same as (a).

(III) examples Using Nickel-based superalloys

(a) Example of performing ion carburization and TD salt bath treatment alone

Since the matrix of the Ni-based superalloy, such as inconel 718 and inconel 713C, is Ni, the degree of vacuum must be minimized during ion carburizing, and the glow discharge stress must be increased. In the same manner as in the salt bath treatment, the salt bath is added to balance the chloride (to shift the salt bath balance of the reducing agent and the oxide to the high concentration side with respect to the boric acid medium) in consideration of the diffusion rate of the carbon dissolved in the Ni matrix.

(b) Example of precipitating the γ' phase

In Ni₃Ti and Ni₃When a γ 'precipitation type Ni-based superalloy such as Al (including SUH660) is used for this high-temperature application, it is necessary to disperse the γ' phase as finely and uniformly as possible. Therefore, the introduction of strain is performed before the deposition treatment, and/or the deposition heat treatment adopts a polygonization treatment (secondary heat treatment) process as a countermeasure.

The heat-resistant material constituting the exhaust guide assembly a is manufactured or formed as described above, and a method of manufacturing a molding material having the shape of the variable vane 1, which is also referred to in some cases in embodiment 7, will be described below.

The material for forming the variable vane 1 is a metal material in which the vane portion 11 and the shaft portion 12 are integrated before being manufactured, and the target variable vane 1 is formed by appropriately performing roll forming, grinding, and the like on the material. As a material of the molding material, a heat-resistant metal material such as SUS310S can be used. Here, a molded material is obtained by a precision casting method or a metal injection molding method, and the following description will be made of a precision casting method as embodiment 9 and a metal injection molding method as embodiment 10.

[ embodiment 9]

The precision casting method according to embodiment 9 is a method that can achieve high precision of a cast product (a molding material) in general, and a lost wax pattern casting method is used as an example. The lost-wax pattern casting method is a method in which a wax pattern having the same shape as a product to be cast is generally formed first, a refractory coating layer is formed around the wax pattern, and then the entire body is heated to melt only the wax pattern to form a casting mold (coating layer).

As the precision casting method, in addition to the lost wax pattern casting method described above, there are shore precision casting method and CADIC method, and these methods can be used. Incidentally, the shore precision casting method is a method in which a liquid alkyl silicate binder and a granular refractory material are kneaded and molded into a wet mold, the wet mold is rapidly dried, and cracks generated due to the drying are generated as fine cracks invisible to the eyes, thereby preventing the mold from being subjected to global shrinkage deformation.

In the precision casting method, the shape and size of the formed mold and the target product (here, the variable vane 1) are substantially the same, and a cast product (molding material) extremely faithful to the target product can be reproduced with high precision. However, even this precision casting method has a drawback that it is difficult to finish the molding material into a nearly clean shape without taking measures, and in order to obtain the variable vane 1 having a desired shape and precision, the dimensional precision of the molded material cast is still significantly insufficient and has discreteness. Further, the formed material has a disadvantage that sharp burrs are easily formed at the time of post-processing such as roll forming. Therefore, as the present embodiment, the following technical measures are appropriately taken at the time of casting.

First, in order to improve the fluidity of molten metal cast into a mold, a virgins material mainly composed of a heat-resistant metal is used, and the amounts of C (carbon), Si (silicon), and O (oxygen) contained in the virgins material are adjusted to be appropriate. Specifically, a raw material (virginator material) directly reduced from iron sand, iron ore, or the like is used without passing through the process of washing the waste material by selegil, and the proportions of components such as C, Si, O, and the like are adjusted to 0.05 to 0.5%, 0.5 to 1.5%, and 0.01 to 0.1% (by weight), respectively, to improve the fluidity of the molten metal, the shape and dimensional accuracy of the formed raw material, and the roll formability. Incidentally, when the component ratios of the respective elements are adjusted, the amount of change is adjusted while monitoring it in the electric furnace.

In addition, at the time of casting, one or both of the mold and the molding material are rapidly cooled to shorten the time until the mold is removed, so that the solidified structure of the molding material becomes thin. Specifically, for example, the time required for cooling the mold by spraying water to the mold before and after casting is reduced to 1 hour or less (1 to 4 hours are required for ordinary air cooling). In this case, the cooling before casting is performed only on the mold, and the cooling after casting is performed on both the mold and the molding material. Of course, the quenching should be performed within a range in which thermal stress cracking does not occur in the mold. If it is not necessary to perform cooling in both the period before and after casting, it is possible to perform cooling in either period, and if it is desired to further improve the cooling effect, the shaped material taken out of the mold may be sprayed with cooling water in addition to cooling in both the period before and after casting.

By adopting the above technical measures (rapid cooling), as an example of the solidification structure of the molding material, the solidification structure is thinned to 50 to 100 μm (about 100 to 500 μm in ordinary air cooling), and sharp burrs are not easily generated due to uniform strain during subsequent processing such as roll forming, and the roll forming and the like are facilitated.

Further, one or more of Pb (lead), Se (selenium), and Te (tellurium) are added to the molten metal poured into the mold, and the molten metal contains a large amount of O (oxygen) and S (sulfur) in a range where the presence of non-metallic inclusions does not adversely affect the molten metal. Specifically, Pb, Se, and Te may be 0.01 to 0.1 wt%, O, and S may be 0.02 to 0.1 wt%, and S may be 0.005 to 0.5 wt%, respectively. Pb, Se, Te and the like are added for the purpose of improving the roll formability and machinability (mainly exhibiting machinability) of the shaped material, and O, S and the like are added for the purpose of improving the melt fluidity. Incidentally, the applicant of the present invention confirmed that the melt fluidity is improved by at least 20 to 40% in viscosity fluidity of the stokes flow.

In addition, fig. 3 shows the relationship between the temperature (expressed as the heating state with respect to the melting point) and the viscosity, taking Ni (nickel) -based heat-resistant material and Fe (iron) -based heat-resistant material as examples, in which the molten metal is heated to the melting point or higher and cast into the mold in the state where the viscosity is lower than the melting point temperature at the time of casting. The melt fluidity (standard value) shown in the figure is the fluidity of the melt to be cast, and corresponds to the viscosity. From this figure, it is understood that the viscosity of the molten metal has a high temperature dependency in the vicinity of the melting point, and the viscosity decreases as the temperature of the raw material increases, but it is also understood that the temperature dependency of the viscosity decreases in the vicinity of about 30 ℃ further heated from the melting point, and the viscosity does not decrease by that amount even when the temperature is increased. Therefore, in the present embodiment, in consideration of the effect of viscosity reduction and the heating cost, one example is casting the raw material in a state of being heated to about 30 ℃ higher than the melting point.

[ embodiment 10]

The metal injection molding method according to embodiment 10 is substantially the same as the conventionally known general injection molding of synthetic resins (plastics), and for example, metal powder (material) such as iron or titanium is kneaded with a binder (mainly an additive for binding with the metal powder, and an example thereof is a mixture of polyethylene resin, wax, and phthalate) to impart plasticity thereto. Thereafter, a material having plasticity is injected into a mold, solidified into an appropriate shape, and sintered after removing the binder, thereby obtaining a molding material having a desired shape.

In this way, metal injection molding can also obtain a molded article (molding material) that is substantially faithful to the target product (here, the variable blade 1) as in the precision casting method, but on the other hand, the molded molding material has a higher porosity than a solid material, and particularly a heat-resistant high alloy material has disadvantages such as insufficient bulk density and poor high-temperature bending fatigue strength. The porosity mentioned here is one of cavities (an aggregate of a plurality of point defects which together may even cause formation of fine cracks) in a crystal of a metal material or the like, and if the ratio thereof is too high, it may adversely affect the metal material. As described above, in the present embodiment, the following technical measures are appropriately taken when metal injection molding is performed.

First, sintering is performed for a long time so that independent bubbles (spherical gaps between metal particles) can be generated small and uniformly, and specifically, for example, when SUS310S having a melting point of 1500 ℃ is used, sintering is performed at 1300 ℃ for a long time of about 2 hours.

Although such sintering is performed to reduce the void ratio of the molding material and increase the bulk density, the injection-molded molding material is subjected to a HIP treatment (Hot isostatic pressing) to further increase the bulk density. Specifically, the molding material is heated to, for example, about 1300 ℃ and a pressure of about 100MPa (1000 atmospheres) is applied to the molding material uniformly in each direction.

By the above sintering and HIP treatment, the individual bubbles of about 100 μm degree before sintering become about 10 μm degree after sintering, and the volume density increases by about 5%, which has been confirmed by the present inventors. Further, the increase in the bulk density not only improves the strength of the molding material but also improves the dimensional accuracy, and a molding material having a more nearly clean shape can be obtained.

In addition, when sintering the metal powder, γ' (an intermetallic compound called a gamma prime layer (prime) which represents Ni3(Al, Ti)) is formed by rapidly heating a precipitation-hardening heat-resistant material such as SUH660, and growth thereof is suppressed to make it finer. This is to suppress the over-aging phenomenon in a high-temperature environment, and in this case, an induction heating method in which a heating current is generated by electromagnetic induction is preferably used for rapid heating.

In addition, in this embodiment, the metal powder for injection molding is spherical and fine, and technical measures for improving the high-temperature rotary bending fatigue strength of the molded material are also taken. Here, in order to make the metal powder spherical and fine, for example, a molten metal is ejected from a nozzle, a high-speed fluid such as air or water is applied to the ejected molten metal, the metal is divided into many droplets by the impact force of the high-speed fluid, and then the droplets are cooled and solidified to obtain metal powder, and what is called an air atomization method or a water atomization method is used here. In addition, when such an atomization method is employed, metal powder of a desired size can be obtained by appropriately changing the shape and bore size of a nozzle for ejecting molten metal, the ejection speed of a fluid such as air or water acting on the molten metal, the cooling speed, and the like. Therefore, it was confirmed by the present inventors that when the metal powder of SUS310S was sintered as fine as about 200 μm, the high-temperature rotary bending fatigue strength was improved by about 20%.

In the metal injection molding, the surface of the metal material before sintering is reduced, specifically, a gas such as hydrogen, ammonia, or carbon monoxide having a reducing atmosphere is passed through the surface of the metal particles and brought into contact therewith to reduce the metal particles. Thus, the oxide on the surface of the metal particle is removed, and not only the sinterability is improved, but also the effect of the hydrostatic pressure hot pressing treatment can be increased, which greatly contributes to the reduction of the void ratio.

According to the present invention, the heat resistance of the exhaust guide assembly a, such as high-temperature strength, oxidation resistance, and high-temperature wear resistance, can be improved while reducing the cost. Specifically, the high temperature durability can be improved by reducing the amount of nonmetallic inclusions and miniaturizing the size (see embodiment 1), or by adding rare earth elements (see embodiment 2). Further, for example, W (tungsten), V (vanadium), Mo (molybdenum), Hf (hafnium), etc. may be added to the martensitic stainless steel that is relatively inexpensive such as SUS410 or SUS440 (see embodiment 3). As for a material such as a rolled material of a high-alloy austenitic heat-resistant stainless steel or an iron-based superalloy, rolling under a large pressure is performed at a ferrite stage to refine grains and improve high-temperature strength (see embodiment 8). On the other hand, for example, for a material such as an iron-based superalloy such as inconel 800H or inconel 713C, or a nickel-based superalloy, a coating such as chromium carbide, titanium carbide, tungsten carbide, vanadium carbide, niobium carbide, or molybdenum carbide is formed on the surface thereof to improve the high-temperature strength durability and reduce wear during high-temperature sliding (see embodiment 6).

Further, according to the present invention, it is possible to suppress the performance of the exhaust guide assembly a from being degraded with use in a high-temperature atmosphere. Specifically, the precipitation hardening heat-resistant material such as SUH660 may be subjected to stress application treatment in advance so that the precipitated γ' phase (gamma prime layer) does not grow but is finely and uniformly formed during use in a high-temperature atmosphere (e.g., 700 to 800 ℃), thereby preventing overaging (see embodiment 2). In addition, the carbon content of the raw material is reduced, the crystal grains are refined, and the sensitization phenomenon which is easy to occur at the working temperature of about 600-800 ℃ can be prevented. Further, the generation of sigma embrittlement, which is likely to occur at an operating temperature of about 850 ℃, can be prevented by increasing Si (silicon) and Mn (manganese) while reducing the Cr (chromium) content of the raw material.

Further, according to the present invention, when the solid solubility limit of carbon at high temperature of the raw material to be used is increased (see embodiment 4), or when the raw material is melted and refined, and then the carbide is dissociated by heating a high-temperature slab to obtain high-carbonization (see embodiment 5), a carbide coating can be formed without performing a carburizing treatment.

Further, it is also possible to obtain a molding material having high dimensional accuracy, strength, and the like by adding Se (selenium), Te (tellurium), O (oxygen), S (sulfur), and the like to Cr or Ni — Cr heat-resistant materials to improve melt fluidity during precision casting or to refine individual bubbles during metal injection molding (see embodiments 7, 9, and 10).

Possibility of industrial utilization

As described above, the present invention is suitable for use in applications where it is desired to improve the high-temperature wear resistance, oxidation resistance, and high-temperature hardness of the components that constitute the exhaust guide assembly of a variable geometry turbocharger. The present invention is suitable for use in a case where it is desired to form a molding material (profile) of a variable vane, which is one component of an exhaust guide assembly, into a substantially clean shape.

Claims (4)

1. A method of manufacturing a heat-resistant member applicable to an exhaust guide assembly of a variable geometry turbocharger,

the variable vane device is suitable for being provided with a variable vane (1) for adjusting the flow rate of exhaust gas (G) discharged by an engine to rotate an exhaust turbine (T), a turbine frame (2) for rotatably supporting the variable vane (1) on the outer peripheral part of the exhaust turbine (T), and a variable mechanism (3) for adjusting the flow rate of the exhaust gas (G) by rotating the variable vane (1);

a method for manufacturing a heat-resistant member of an exhaust guide unit (A) in a turbocharger of a variable geometry turbocharger capable of increasing the speed of exhaust gas by throttling the flow rate of exhaust gas with a variable vane (1) and achieving high output even when rotating at a low speed,

a certain material selected from an iron-based superalloy and a nickel-based superalloy is subjected to ion carburization, and then subjected to TD salt bath treatment.

2. The method of manufacturing a heat-resistant member applicable to an exhaust guide assembly of a variable geometry turbocharger according to claim 1, wherein one or more of Ti, Nb, B, Hf, and Zr is contained when the iron-based superalloy is selected as a raw material.

3. The method of manufacturing a heat-resistant member applicable to an exhaust guide assembly of a variable geometry turbocharger as set forth in claim 1, wherein, when a rolled material of an iron-based superalloy is selected as a starting material, the starting material is hot-rolled under a high pressure in a ferrite region to be grain-refined.

4. The method of manufacturing a heat-resistant member applicable to an exhaust guide assembly of a variable geometry turbocharger according to claim 1, wherein, in the case where the nickel-based superalloy is selected as a raw material, a large amount of internal strain is accumulated under high stress within an allowable range, and a fine γ' phase is precipitated as nuclei of the strain.