HK1044309B - A ni-base brazing alloy - Google Patents

Description

Nickel-based brazing alloy

Technical Field

The present invention relates to a brazing alloy, and more particularly, to a nickel-based brazing alloy having good wettability and fluidity (referred to as wettability), excellent corrosion resistance, and high strength. The alloy is used in the welding process of two pieces of metal, such as stainless steel.

Background

Nickel-based brazing filler metals, defined as JIS standard (japanese industrial standard) of JIS Z3265 and AWS (american society for electrical welding) standard of ANSI/AWS a5.8, are commonly used in the process of brazing stainless steel to produce various products such as heat exchangers and gas turbines.

Recently, there has been a greatly increasing demand for providing a brazing alloy which has corrosion resistance in a strong acid such as sulfuric acid and can be brazed at as low a temperature as possible to form a high-strength brazed joint, however, the nickel-based brazing filler metal, which is a prior art, has several objects as follows.

As a nickel-based brazing filler metal defined in JIS and AWS standards, an alloy BNi-5 having a Ni-Cr-Si composition and having good corrosion resistance is known. However, it has a high liquidus at 1150 ℃ and thus requires heating to 1200 ℃ for brazing, during which the properties of the stainless steel are reduced.

It is also known that some alloys BNi-1, 1A and 2 have a Ni-Cr-Fe-Si-B composition and alloys BNi-3 and 4 have a Ni-Si-B composition, which provide high strength properties of brazed joints but reduce the corrosion resistance of stainless steel due to boron diffusion when brazed.

It is also known that alloys BNi-6 and 7 have a Ni- (Cr) -P composition, which can be brazed at a relatively low temperature of about 1000 ℃. These alloys have good wettability but are brittle and have low braze joint strength.

On the other hand, the present inventors have disclosed a nickel-based brazing alloy having heat resistance, see Japanese laid-open patent application No.9-225679, 1997. The alloys disclosed in the above applications can be brazed at temperatures as low as the welding temperature of BNi-2. However, it has been found that some of the alloy compositions defined in this application form slag when subjected to brazing, resulting in a brazed joint having low strength.

Thus, there is a need to provide a nickel based brazing alloy for use in the welding process of two metals, such as stainless steel, and which enables the alloy to be brazed at as low a temperature as possible, such as about 1100 ℃, to prevent degradation of the properties of the stainless steel. The alloy is accompanied by the characteristic of no slag formation when subjected to brazing, and has good wettability, high strength of brazed joints, and excellent corrosion resistance in sulfuric acid, etc.

Disclosure of Invention

In order to provide an alloy having the above-mentioned required characteristics, the present inventors have reviewed previous alloys having Ni-Cr-P-Si compositions disclosed in Japanese laid-open patent application No.9-225679 of 1997, and found that the alloy of the present invention has a valuable composition with further additives.

According to the invention, the alloy of the invention has a valuable composition with respect to the same applications as described above. Thus, the alloy of the present invention contains an increased amount of Cr to increase strength, which can maintain a preferred melting point and corrosion resistance. Also, the alloy of the present invention contains Cr, P and Si, each of which is used in an amount and the total amount of P and Si such that the alloy has a hypo-eutectic structure. The alloys of the present invention also contain small amounts of Al, Ca, Y and/or rare earth metal mixtures so that the designed alloys can prevent slag formation and improve wettability during or after brazing. The alloy of the invention also contains Fe, Co, Mo and/or V in amounts corresponding to their melting points, their wettability and their corrosion resistance not being adversely affected, which leads to an improved alloy with high strength, especially in the case of brazed joints.

The present invention provides a nickel-based brazing alloy containing Cr in an amount of 25 to 35% by weight, P in an amount of 4 to 8% by weight, and Si in an amount of 3 to 6% by weight, with the total amount of P and Si being 9 to 11.5% by weight, at least one element selected from the group consisting of Al, Ca, Y and a rare earth metal mixture in an amount of 0.01 to 0.10% by weight, and the balance being Ni and unavoidable impurities.

If desired, the alloy may further contain at least one element selected from the group consisting of: fe, used in an amount of 20 wt% or less; co is used in an amount of 20 wt% or less; mo, the dosage is less than 10 weight percent; and V in an amount of 5% by weight or less; the total amount of Fe, Co, Mo and V is 20 wt% or less.

Additional advantages and features of the present invention will become apparent to those skilled in the art upon examination of the following detailed description when taken in conjunction with the accompanying drawings.

Brief Description of Drawings

Figure 1 schematically shows the steps of an alloy brazing test procedure.

Detailed Description

According to the present invention, the amount of each element contained in the alloy is defined as follows, and in the present specification, the content of each element in the alloy is a weight percentage.

According to the invention, the nickel-based brazing alloy has the basic elements Ni, Cr, P and Si. The content of each element in the base composition is particularly important in determining some of the main properties of the resulting alloy.

According to the invention, the alloy contains Cr in an amount of 25 to 35% by weight. It is preferred to contain as much Cr as possible, since Cr can dissolve in Ni to form a solid solution of Ni — Cr, making the resulting alloy resistant to oxidation, heat, corrosion and increased strength. On the other hand, an increase in the Cr content causes a favorable exchange of melting point and wettability. In the case of an alloy containing a deficiency of less than 25 wt% of Cr, it is difficult to improve the strength of the brazing point, the corrosion resistance in sulfuric acid, and the like. In the case of an alloy containing Cr in an amount exceeding 35 wt%, the melting point may be increased to adversely affect the wettability of the stainless steel. Therefore, according to the present invention, the Cr content in the alloy should be limited to the above range.

According to the invention, the weight of P and Si is limited to 9-11.5 wt.%. Each of the P and Si elements significantly affects the melting point of the resulting alloy due to its reaction with the eutectic (eutetic) of the Ni-Cr solid solution, and also affects the properties of the braze joint, corrosion resistance and strength of the alloy. The brazing alloy of the present invention needs to be designed to have a sub-eutectic structure in order to improve strength. The total content of the elements P and Si can seriously affect the melting point and strength of the resulting alloy. Thus, in the case where the alloy has a shortage of less than 9% by weight of the total content of P and Si, the resulting alloy tends to become a sub-eutectic to increase the liquidus temperature, and thus brazing at a predetermined temperature is difficult. On the other hand, in the case where the alloy has an excess amount of the total content of P and Si higher than 11.5 wt%, the resulting alloy becomes a super-eutectic (hyper-eutectic), and thus the alloy becomes brittle to lower the strength.

Also, the content of each of P and Si is defined in accordance with the action and reaction thereof in all the compositions containing Cr. Therefore, if the P content is insufficient and less than 4 wt% and the Si content is excessive and more than 6 wt%, the alloy has an increased melting point.

Further, if the Si content is insufficient by less than 3% by weight and P is excessive by more than 8% by weight, the alloy may decrease the corrosion resistance and decrease the strength.

Therefore, the alloy needs to contain P in an amount of 4 to 8 wt%, and Si in an amount of 3 to 6 wt%, the total content of P and Si being 9 to 11.5 wt%.

The brazing alloy of the present invention having the essential components of Ni, Cr, P and Si as described above, further contains at least one element selected from the group consisting of Al, Ca, Y and a rare earth metal mixture, and is designed to have a low oxygen content to prevent slag formation during or after brazing. And an alloy containing such one or more elements can improve wettability with stainless steel. However, if the alloy contains less than 0.01 wt.% of the total of at least one of the elements Al, Ca, Y and the rare earth metal mixture, no significant improvement in the properties of the alloy is provided. On the other hand, if the total amount of one or more elements contained is more than 0.1% by weight and excessive, the resulting compound may adversely affect the wettability or strength of the alloy. Thus, the alloy desirably contains at least one of the elements Al, Ca, Y and the rare earth metal in a total amount of 0.01 to 0.10 weight percent.

While the nickel-based brazing alloy of the invention has superior properties compared to prior art alloys, the alloy of the invention may also contain Fe, Co, Mo and/or V and have a higher strength. It should be noted that even if these elements are included, an excess of these elements will increase the melting point of the alloy, thereby making it difficult to braze the alloy at the desired temperature (about 1100 ℃). It should also be noted that an excess of these elements can compromise the improved strength of the alloy and adversely affect the corrosion resistance of the alloy. Thus, the alloy needs to contain appropriate amounts of these elements, i.e., the appropriate amounts studied according to the present invention. Accordingly, the alloy of the present invention may contain iron in an amount of 20 wt% or less, Co in an amount of 20 wt% or less, Mo in an amount of 10 wt% or less and V in an amount of 5 wt% or less. If the alloy contains a combination of selected elements, the total content of selected elements should be below 20 wt.%.

Therefore, according to the present invention, the content of Fe is defined as 20 wt% or less, the content of Co is defined as 20 wt% or less, the content of Mo is defined as 10 wt% or less, and the content of V is defined as 5 wt% or less. Further, the total content of Fe, Co, Mo and V is limited to 20% by weight or less.

The nickel-based brazing alloys of the present invention may be formed into powders, generally prepared by atomization, and may be formed into sheets or rods.

Examples and controls:

representative examples with compositions of the present invention and non-inventive comparative examples will now be described below.

The composition of each of some alloys prepared as examples and the composition of comparative examples are listed in tables 1 and 2. Tables 1 and 2 also accompany melting points and results of braze tests at 1100 ℃, transverse rupture tests and corrosion tests in 5% sulfuric acid.

The method for testing various properties is as follows,

(1) measurement of melting Point (liquidus and solidus)

The alloys of examples and comparative examples were melted in an electric furnace filled with argon gas and the melting points were measured by a thermal analysis method. According to the method, a thermocouple is placed in the center of the molten alloy, the thermocouple is connected to a recorder for plotting a thermal analysis curve by which the temperature of the liquidus and solidus can be read.

(2) Brazing test

The alloys of examples and comparative examples were melted in an electric furnace filled with argon gas and the molten alloys were poured into graphite molds to obtain rods having a diameter of 5 mm. The alloy rod was then cut into small pieces, each approximately 5mm long. The obtained sample was further placed in a base material 1 of SUS304 stainless steel as shown in FIG. 1(a), and the sample was subjected to vacuum atmosphere of 10^-3Brazing was carried out by heating at 1100 ℃ for 30 minutes. After brazing, the extension of the melted sample 3 into the furnace is measuredThe area S of (A) is as shown in FIG. 1 (b). The measured area S was divided by the cross-sectional area S in the brazing sample 2_oTo obtain the expansion coefficient W of the molten alloy during brazing, i.e., S/S_oIt can be used to estimate the wettability to the SUS304 stainless steel base material. Further, the appearance after the brazing test was also examined to check whether slag was formed.

(3) Transverse rupture test

The alloys of examples and comparative examples were melted in an electric furnace filled with argon gas and the alloy thus melted was taken in a quartz tube having an inner diameter of 5mm, solidified, and then cut into sample pieces each having a length of 35 mm.

The resulting sample piece was placed on a transverse tester (transverse length 25.4mm) and weighed with a multi-purpose tester to measure the weight at failure. The measured weight was calculated to obtain the transverse rupture strength (kgf/mm)²) This may provide a useful estimate of the intensity.

(4) Corrosion testing in 5% sulfuric acid

The alloys of examples and comparative examples were melted in an electric furnace filled with argon gas and the melted alloys were poured into a housing mold to obtain square prism bars each having a length of 10mm on each side. The bar was cut into 20mm lengths of 10mm by 20mm, and then the surface of the cut bar was low-ground with #240 sand to give sample bar segments. The obtained sample rod piece was placed in a beaker having an internal volume of 300CC and containing a 5% sulfuric acid solution, and the corrosion test was carried out by immersing the sample rod piece in the beaker. The test was carried out at 60 ℃ over a period of 24 hours. The weight and surface area before and after immersion in the sulfuric acid solution were measured, and then the weight loss (mg/m) was calculated²S) which allows an efficient estimation of the corrosion resistance of the sample in a sulfuric acid solution. The results for the alloys of the present invention are shown in Table 1, and it can be seen that all of the alloys of the present invention have a liquidus below 1100 ℃ and none of the alloys of the present invention are accompanied by the formation of slag during the braze test at 1100 ℃, and it can also be seen that the wet spread coefficient indications for all of the alloys of the present inventionAbove 40, this indicates that the alloy of the present invention has excellent wettability to SUS304 stainless steel.

TABLE 1

	Numbering	Composition of alloy (% by weight)									Melting Point (. degree.C.)		Soldering at 1100 deg.C		Transverse rupture (kgf/mm)2)	Weight loss in 5% sulfuric acid solution (mg/m)2s)
																			Ni	Cr	P	Si	Al	Ca	Y	M.M	Others	Solidus line	Liquidus line	Coefficient of performance	Slag of molten slag
Some alloys of the invention	(1)	bal.	25.0	6.0	4.0	0.01	-	-	-	-	980	1055	50	Is free of																		84	0.008
															(2)	bal.	29.0	6.2	3.8	-	0.01	-	-	-	985	1040	50	Is free of	94	0.001
	(3)	bal.	29.7	6.1	4.1	0.04	-	-	0.01	-	980	1025	50	Is free of																	90	0.000
															(4)	bal.	30.1	6.0	4.0	-	0.03	0.03	-	-	980	1030	50	Is free of	91	0.000
	(5)	bal.	35.0	5.8	4.2	-	-	0.01	-	-	980	1035	50	Is free of																	86	0.001
															(6)	bal.	31.5	6.4	4.0	-	-	-	0.01	-	980	1010	50	Is free of	91	0.001
	(7)	bal.	27.9	5.6	3.9	0.02	-	-	0.06	-	980	1060	50	Is free of																	84	0.000
															(8)	bal.	27.0	4.0	6.0	0.10	-	-	-	-	980	1050	40	Is free of	89	0.003
	(9)	bal.	30.0	8.0	3.0	0.05	0.01	0.01	0.03	-	980	1010	40	Is free of																	80	0.002
															(10)	bal.	29.0	6.8	4.7	0.01	0.05	-	-	-	980	990	50	Is free of	90	0.001
	(11)	bal.	28.0	5.0	4.0	0.02	-	0.02	-	-	980	1070	40	Is free of																	95	0.005
															(12)	bal.	29.0	6.0	4.0	0.02	-	-	-	Mo：5.0	980	1000	50	Is free of	124	0.000
	(13)	bal.	28.5	6.0	4.2	0.02	0.03	-	-	Mo：10.0	985	1090	40	Is free of																	101	0.002
															(14)	bal.	30.0	6.0	4.0	0.03	-	-	-	Mo：2.0	980	1010	50	Is free of	120	0.000
	(15)	bal.	30.0	6.0	4.0	0.02	0.01	-	0.01	V：5.0Fe：5.0	1010	1045	40	Is free of																	118	0.002
															(16)	bal.	28.8	5.6	3.6	-	0.03	0.02	-	Fe：10.0	1000	1070	40	Is free of	123	0.005
	(17)	bal.	29.0	6.0	4.0	0.03	-	-	-	Fe：20.0	1030	1075	40	Is free of																	102	0.008
															(18)	bal.	29.4	5.9	3.8	-	0.03	-	-	Fe：5.0	990	1045	50	Is free of	116	0.002
	(19)	bal.	28.8	6.0	4.0	0.05	-	-	-	Mo：5.0Fe：15.0	1000	1080	40	Is free of																	120	0.005
															(20)	bal.	29.0	5.9	4.2	-	0.05	-	-	Co：10.0	1010	1075	40	Is free of	105	0.003
	(21)	bal.	29.2	6.0	4.2	-	0.05	-	-	Co：20.0	1020	1090	40	Is free of																	100	0.003

bal: balance of

M.M.: mixing of rare earth metals

TABLE 2

	Numbering	Composition of alloy (% by weight)									Melting Point (. degree.C.)		Soldering at 1100 deg.C		Transverse rupture (kgf/mm)2)	Weight loss in 5% sulfuric acid solution (mg/m)2s)
																			Ni	Cr	P	Si	Al	Ca	Y	M.M	Others	Solidus line	Liquidus line	Coefficient of performance	Slag of molten slag
Control alloys according to the prior art	(a)	bal.	24.6	8.3	2.8	-	-	-	-	-	970	1030	50	Is provided with																		55
															(b)	bal.	29.0	7.0	4.7	-	-	-	-	-	985	995	50	Is provided with	43
	(c)	bal.	28.5	6.0	4.0	0.13	-	-	-	-	980	1020	5	Is free of																60
															(d)	bal.	37.0	3.8	6.2	-	-	-	-	-	980	1090	15	Is provided with	57
	(e)	bal.	29.0	5.0	3.8	-	-	-	-	-	980	1130	-	-																68
															(f)	bal.	29.0	5.5	4.0	-	-	-	-	Fe：22.0	1040	1130	-	-	85
	(g)	bal.	29.0	6.0	4.2	-	-	-	-	Mo：15.0	990	1180	-	-																65
															(h)	bal.	29.0	5.8	4.0	-	-	-	-	V：7.0Fe：15.0	1030	1100	-	-	87
	(i)	bal.	29.0	6.2	3.8	-	-	-	-	Co：22.0	1020	1110	-	-																85
															BNi-2	bal.	7.0	-	4.5	-	-	-	-	B：3.0Fe：3.0	970	1010	10	Is free of	90		2.290
	BNi-5	bal.	19.0	-	10.2	-	-	-	-	-	1080	1140	101)	Is free of																90		0.009
															BNi-7	bal.	13.0	10.0	-	-	-	-	-	-	885	930	502)	Is free of	40		0.122

bal: balance 1): soldering at 1200 deg.C

M.M.: rare earth metal mixed 2): soldering at 1000 deg.C

According to the results of transverse rupture tests, all the alloys of the invention have a transverse rupture strength greater than 80kgf/mm². In particular, samples (12) to (21) had a strength of greater than 100kgf/mm². Thus, it is confirmed that the strength of the alloy of the present invention is as excellent as or more excellent than that of the comparative alloys BNi-2 and BNi-5, and the alloy of the present invention has a strength 2 to 3 times that of the BNi-7 alloy.

Furthermore, the weight loss of all samples was between 0.000 and 0.008mg/mm according to the corrosion test in 5% sulfuric acid solution²S range. Thus, the alloys of the present invention have excellent corrosion resistance, which is also lower than the BNi-5 alloys that claim excellent corrosion resistance.

On the other hand, Table 2 is about alloys (a) to (i) as comparative samples, each of which has a composition range not defined by the present invention.

Unlike the case of the present invention, the control sample alloy (a) had an excess of P, a deficiency of Si, and contained no Al, Ca, Y and rare earth metal mixtures. Also, alloy (b) has an excessive total amount of P and Si, and does not contain Al, Ca, Y and a rare metal mixture. While alloy (d) has an excess of Cr, an insufficient amount of P, an excess of Si, and no Al, Ca, Y and rare earth metal mixture. Alloys (a), (b) or (d) can be brazed at 1100 c but form slag which reduces the strength of the brazed joint.

Since the alloy (c) has an excessive amount of Al, the alloy (c) has a low wet spread coefficient and a low brazing strength of the molten alloy. Alloy (e) has a non-total amount of P and Si, and thus alloy (e) has an increased liquidus line making it difficult to solder at 1100 c while having a low brazing strength.

The alloy (f), (g), (h) or (i) has an excess of Fe, Mo, V or Co, and thus the alloy has an increased liquidus line, making the alloy incapable of being brazed at 1100 ℃ and incapable of improving strength.

Further, in each of the control samples, the alloys BNi-2, BNi-5, or BNi-7 had a nickel-based brazing filler metal composition as defined in JIS and AWS. BNi-2 alloys can be brazed at 1100 ℃, but have greatly reduced corrosion resistance in sulfuric acid. On the other hand, the BNi-5 alloy has good corrosion resistance in sulfuric acid, but its liquidus is as high as 1140 ℃, which requires heating to 1200 ℃ for brazing. Moreover, the BNi-7 alloy has a low melting point, but the strength of the brazed joint is insufficient.

According to the present invention, each alloy has excellent wettability not only to austenitic (austenite) stainless steel base materials such as SUS304 and 316 but also to pure iron and martensitic (martenite) stainless steel base materials such as SUS 410 and 430.

The alloy of the present invention can be suitably brazed not only in a vacuum atmosphere but also in a hydrogen reducing atmosphere or in an argon inert gas.

Also, the alloys of the present invention have excellent corrosion resistance, not only in sulfuric acid solutions, but also in ammonia solutions, in brine and in various acidic solutions such as nitric acid. The alloy of the present invention also has high strength for brazing.

Claims (2)

1. A nickel-based brazing alloy comprising:

cr in an amount of 25-35 wt%;

p in an amount of 4-8% by weight;

si in an amount of 3-6 wt%, wherein the total amount of P and Si is 9-11.5 wt%;

at least one member selected from the group consisting of Al, Ca, Y and rare earth metal mixtures in an amount of 0.01 to 0.10% by weight, and

the balance nickel and inevitable impurities.

2. The nickel-base brazing alloy according to claim 1, further comprising at least one element selected from the group consisting of: fe in an amount of 20 wt% or less, Co in an amount of 20 wt% or less, Mo in an amount of 10 wt% or less, and V in an amount of 5 wt% or less, wherein the total amount of Fe, Co, Mo and V is 20 wt% or less.