JP2001323342A - Austenitic stainless steel with excellent precision punching properties - Google Patents

Abstract

(57) [Summary] [Purpose] By adjusting the softening and the austenite stability, the ratio of the shear surface to the punched fracture surface is high,
To provide an austenitic stainless steel capable of extending a mold life. [Structure] This austenitic stainless steel is made of (C
+ 1 / 2N): 0.060% or less, Si: 1.0% or less, Mn: 5% or less, S: 0.006% or less, Cr: 1
5 to 20%, Ni: 5 to 12%, Cu: 5% or less, M
o: 0 to 3.0%, the balance substantially having a composition of Fe,
Are components adjusted so as indicator Md ₃₀ of strain-induced martensite quantity defined by the following equation is the -60 to-10. The rate of increase in Vickers hardness after cold rolling is preferably 20% or more. Also, in the state after finish annealing,
The grain size number specified in JIS G0551 is 8 to 1
It is preferably in the range of 1. Md ₃₀ = 551-462 (C + N) -9.2Si-29 (Ni + Cu) -8.1Mn-1
3.7Cr-18.5Mo

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an austenitic stainless steel having excellent punching properties, especially excellent precision punching properties.

[0002]

2. Description of the Related Art Shearing by pressing, particularly punching, can be performed extremely efficiently, and is therefore used for processing a wide range of metal materials from non-ferrous metals to stainless steel as well as ordinary steel. However, the shear fracture surface formed by the punching process has large irregularities, and has a fracture surface with low dimensional accuracy. Also, sagging is likely to occur on the wide surface side of the metal plate, and the plate thickness decreases near the punched fracture surface. When punching is applied to applications that require dimensional accuracy, post-processing has been adopted to remove the punched fracture surface by barrel polishing, but this requires an extra step, which causes a decrease in productivity. . Therefore, a precision punching process has been adopted in which the clearance at the time of punching is made extremely small to suppress the generation of a fractured surface, and the flow of material is suppressed to reduce the generation of sag. On the other hand, in applications requiring corrosion resistance and heat resistance, stainless steel has been conventionally used, and among them, SUS304 austenitic stainless steel is frequently used.

[0003]

When precision stamping is performed using SUS304 austenitic stainless steel as a material, the mold life is short due to its hardness. In addition, a large amount of fracture surface that deteriorates the shear fracture surface properties is generated, and a large amount of dripping is generated. Even if the dimensional accuracy of the shear fracture surface can be improved by precision punching, the die life is shorter than that of ordinary steel, so the processing cost increases. Therefore, in applications where dimensional accuracy of the shear fracture surface is required, a polishing process has been performed after a normal punching process.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been devised to solve such a problem. The present invention provides a shearing surface occupying a shear fracture surface by adjusting softening and stability of an austenite phase. It is an object of the present invention to provide an austenitic stainless steel which has a large amount of steel and is suitable for precision punching.

[0005] The austenitic stainless steel of the present invention has a (C + 1 / 2N): 0.
060% by mass or less, Si: 1.0% by mass or less, Mn: 5
% By mass, S: 0.006% by mass or less, Cr: 15 to 15%
20% by mass, Ni: 5 to 12% by mass, Cu: 5% by mass or less, Mo: 0 to 3.0% by mass, the remainder substantially having a Fe composition, and the work-induced martensite defined by the following formula the amount of the index Md ₃₀ is characterized in that it is component adjusted to be -60-10. Md ₃₀ = 551-462 (C + N) -9.2Si-29 (Ni + Cu) -8.1Mn-1
3.7Cr-18.5Mo

[0006] This austenitic stainless steel is manufactured through the steps of hot rolling, annealing pickling, cold rolling and finish annealing according to a conventional method, but the rate of increase in Vickers hardness after cold rolling is 20% or more. Preferably, there is. Further, in the state after the finish annealing, it is preferable that the crystal grain size number specified in JIS G0551 is in the range of 8 to 11.

[0007]

The present inventors have conducted various investigations and examinations on the relationship between the state of the punched fracture surface and the material of the precision stamped austenitic stainless steel. As a result, it has been found that the ratio of the shear surface to the punched fracture surface is greatly affected by the amount of work-induced martensite (α ′ phase) generated. The process-induced martensite (α 'phase) is austenite (γ
Phase) and low ductility. Therefore, when the work-induced martensite (α 'phase) is excessively generated, the ductility is greatly reduced, and the fracture at the punched fracture surface occurs early,
The percentage of shear surface decreases. However, if the amount of work-induced martensite (α ′ phase) is too small, the effect of improving ductility due to work-induced transformation plasticity will not be exhibited, and punching will proceed with the γ phase having low ductility. As a result, also in this case, the fracture at the punched fracture surface occurs early, and the ratio of the shear surface decreases. In addition, by appropriately balancing the effect of the work-induced martensite (α 'phase) on the fracture surface properties and the softness, the amount of sag is suppressed, resulting in a punched fracture surface with excellent dimensional accuracy and a long mold life. Clarified that it will become.

Hereinafter, the alloy components, contents, and the like specified in the present invention will be described. (C + ／ N): 0.060% by mass or less C and N are both effective alloy components for adjusting the stability of the austenite phase, but when contained in a large amount, the austenite phase is hardened by solid solution strengthening. In addition, the work-induced martensite phase hardens. Therefore, C and N are restricted to (C + ／ N): 0.060 mass% or less, because it causes an increase in the punching load and a reduction in the mold life. Si: 1.0% by mass or less An alloy component added as a deoxidizing agent at the time of melting, but excessive Si content hardens the austenite phase by solid solution strengthening and lowers the punching property. The upper limit of the amount was set to 1.0% by mass.

Mn: 5% by mass or less Mn is an alloy component that stabilizes the austenite phase and is effective for improving the punching property. The effect of Mn becomes remarkable as the content increases. However, when an excessive amount of Mn exceeding 5% by mass is included, inclusions increase and adversely affect corrosion resistance and workability. S: 0.006% by mass or less The ratio of the shear surface to the punched fracture surface decreases as the S content increases. Since S is a component that adversely affects the corrosion resistance most required for stainless steel, the upper limit is set to 0.
006% by mass. In particular, in applications where punching fracture surface properties are problematic, it is preferable to regulate the S content to 0.003% by mass or less in order to increase the proportion of the shear surface.

[0010] From the viewpoint of ensuring the corrosion resistance required for 15 to 20 mass% stainless steel,
A Cr content of 5% by weight is required. However, when an excessive amount of Cr exceeding 20% by mass is included, the austenitic stainless steel is excessively hardened, and the mold life is shortened. Ni: 5 to 12% by mass An alloy component for stabilizing the austenite phase, and a Ni content of 5% by mass or more is required. In addition, the punching property is improved with an increase in the amount of Ni. However, the upper limit of the Ni content is set to 12% by mass because it is an expensive element that increases the cost of steel.

Cu: 5% by mass or less Cu is an alloy component effective for improving the punchability and stabilizing the austenite phase. However, an excess amount of C exceeding 5% by mass
When u is contained, adverse effects are exerted on hot workability. Mo: 0 to 3.0% by mass It is an alloy component effective for improving the corrosion resistance. However, if an excessive amount of Mo exceeding 3.0% by mass is contained, the alloy is excessively hardened and the precision punching property is reduced.

Index Md of the amount of work-induced martensite formation
₃₀ : -60 to -10 The effect of the amount of work-induced martensite (α 'phase) on the ratio of the shear surface occupying the punched fracture surface was clarified from numerous experimental results by the present inventors. . The amount of the process-induced martensite (α ′ phase) can be calculated from the component and content of the austenitic stainless steel. When the component is adjusted so that the index Md ₃₀ is maintained in the range of −60 to −10, it will be described later. As can be seen from the embodiment, the ratio of the shear surface is high, and the punching fracture surface accuracy is improved.

Increase in hardness of austenitic stainless steel sheet
Addition rate: 20% or more in Vickers hardness The austenitic stainless steel sheet is hardened as compared with an annealed material having few dislocations by introducing many dislocations by cold rolling. When the degree of quality improvement by cold rolling is adjusted to a hardness increase rate of 20% or more by Vickers hardness, the flow of material from the punch slab to the punch downward during punching is reduced, resulting in dripping. The amount of generation is reduced. In the present specification, [[Vickers hardness after cold rolling] −
(Vickers hardness of as-annealed material)] / (Vickers hardness of as-annealed material) × 100% to indicate the rate of increase in hardness. In order to reduce the amount of sag generated by punching to less than half of the case where a material is punched as annealed, a hardness increase rate of 20% or more is required. However, if the material is excessively hard, the shear resistance at the time of punching increases, and the wear of the mold is accelerated. Therefore, it is preferable to set the upper limit of the hardness increase rate to 150% in consideration of the sag reduction effect and the reduction of the mold life.

Grain size number: No. 8 to No. 11 When the crystal grains are coarsened, the material becomes soft and the proportion of the shearing surface occupying the punched fracture surface increases, but the amount of dripping increases, so that In addition, it is not suitable for products that require the precision of the steel plate surface. On the other hand, in the austenitic stainless steel according to the present invention, the usual grain size of 6 to 8 is used.
Grain size number of 8 after finish annealing
In other words, the crystal grain size is finer. Refinement of the crystal grain size is controlled by reducing the heat input by lowering the annealing temperature and shortening the furnace time. By adjusting the grain size number in this way, the ratio of the shear surface is maintained at the same level, and the amount of dripping is reduced.

[0015]

Example 1 Various stainless steels having the compositions shown in Table 1 were melted and hot-rolled at an extraction temperature of 1230 ° C. to produce a hot-rolled sheet having a thickness of 10 mm. The hot rolled sheet was annealed at 1150 ° C. × soaking for 1 minute, pickled, cold rolled to a thickness of 5 mm, and annealed at 1050 ° C. × soaking for 1 minute and pickled.

[0016]

For each cold rolled annealed sheet, JIS Z224
The Vickers hardness of the steel sheet surface was measured as the Rockwell B hardness specified as 0, and the shearing resistance, the ratio of the shear surface to the punched fracture surface, and the amount of sag were investigated in the next punching test. 50 mm outside diameter punch and 50 mm inside diameter.
Using a 2 mm and 50.5 mm dice, the clearance was set to 0.1 mm and 0.25 mm, and the test pieces were set under the conditions of a clearance ratio (clearance / test material thickness) of 2% and 5% and a punching speed of 600 mm / min. Was punched.

The sagging amount Z of the test piece punched in a disk shape
Was measured by a laser non-contact displacement meter at a total of eight measurement points at two points in each of a rolling direction, a direction perpendicular to the rolling direction, and a direction at 45 degrees to the rolling direction (FIG. 1). The measured values were averaged, and the ratio to the plate thickness was determined as the sag rate. In addition, the punched test specimens had a rolling direction, a direction perpendicular to the rolling direction, and a rolling direction of 4 mm.
The thickness of the shear surface S was measured at eight measurement points at two points in each of the 5 ° directions. The measured values were averaged, and the ratio to the plate thickness was determined as a shear surface ratio.

The relationship between the Md ₃₀ value and the shear rate of each test piece when punched at a clearance ratio of 2% was investigated. FIG.
As shown in the survey results, the Md ₃₀ value was −60 to −1.
When it was in the range of 0, good fracture surface properties with a shear surface ratio of 100% were obtained. However, test numbers 4, 15, and 16 are Md
_{Although the 30} value was in the range of -60 to -10, the shear surface percentages were exceptionally 85%, 95% and 71%, and the fracture surface properties were poor. Test number 1 with Md ₃₀ value of -60 to -10
About ~ 4,12, the relationship between the (C + 1 / 2N) amount and the shear ratio was investigated. As can be seen from the survey results in FIG.
Test number 1 with (C + 1 / 2N) amount of 0.06% by mass or less
In the cases of ３，3 and 12, a shear surface ratio of 100% was obtained. On the other hand, in Test No. 4 in which the (C + 1 / 2N) amount exceeded 0.06% by mass, the shear surface ratio was 85%.

Further, Test Nos. 1 to 3 having an Md ₃₀ value of -60 to -10 and (C + 1 / 2N) ≦ 0.06% by mass,
13 to 16 test pieces are punched at a clearance ratio of 2%,
The relationship between the shear ratio and the S content was investigated. As can be seen from the investigation results in FIG. 5, in test numbers 1 to 3, 13, and 14 in which the S content was 0.006% by mass or less, a shear surface ratio of 100% was obtained. On the other hand, in Test Nos. 15 and 16 containing S exceeding 0.006% by mass,
%, 71%.

The relationship between the S content and the shear rate varies depending on the clearance ratio even when the same material is used. That is, when the test pieces of Test Nos. 13 and 14 are punched with a clearance of 2%, a fracture surface property with a shear surface ratio of 100% is obtained. However, when the clearance ratio is 5%, as shown in FIG. It drops to 88%. From this,
It can be seen that it is effective to regulate the S content to 0.003% by mass or less when performing punching with a large clearance ratio at which the shear ratio is easily reduced.

[0022]

Example 2 Steels A and B shown in Table 2 were melted and extracted at an extraction temperature of 123.
Hot rolling was performed at 0 ° C. to obtain a hot-rolled sheet having a thickness of 10 mm.
After annealing the hot rolled sheet at 1150 ° C x soak for 1 minute, pickling
Cold rolled to an intermediate plate thickness of 5 to 8 mm, 1050 ° C x soak 1
Anneal and pickling. A steel sheet having a thickness of 5 mm is used as an annealed material (A1, B1), and the remaining annealed material having an intermediate thickness is further cold-rolled to a temper rolled material having a thickness of 5 mm (A2 to A6, B).
2, B3).

[0023]

A test piece was cut out from the annealed material and the temper rolled material, and was punched under the same conditions as in Example 1 in which the clearance was set to 2%. As can be seen from FIG. 7 showing the relationship between the Vickers hardness of each test piece and the shear surface area, the test steel types A1 to A6 according to the present invention had a shear surface area of 100% for both the annealed material and the temper rolled material. Was. On the other hand, B1 to B3 corresponding to SUS304 all had a low shear surface ratio of about 45%.

Further, the ratio of the sag rate of the tempered material to the sag rate of the annealed material was calculated as the sag ratio, and the relationship with the hardness increase rate by temper rolling was investigated. As can be seen from the survey results in FIG. 8, the heat treatment materials A3 to A6 whose hardness increase rate exceeds 20%
In each case, the sag ratio was 50% or less, and the sag was reduced to half or less of the annealing material A1. On the other hand, in the tempered material A2 whose hardness increase rate is less than 20%, the ratio of the annealed material A1 to the sag is only about 70%, and the sag is not sufficiently reduced.

Each test piece was continuously punched to determine the number of punches until the die was replaced, and the effect on die life was investigated. As can be seen from the survey results in Table 3, steel type A
It can be seen that, compared to steel type B, the number of times of punching until the die was replaced was larger in each case, and the die life was extended. In comparison with steel type A, in A6 in which the rate of increase in hardness exceeds 150%, the number of times of punching until mold replacement is reduced, indicating that excessive hardening reduces the life of the mold.

[0027]

[0028]

Example 3 Steels C and D shown in Table 4 were melted and extracted at an extraction temperature of 123.
Hot rolling was performed at 0 ° C. to a thickness of 10 mm. The obtained hot-rolled sheet was annealed at 1150 ° C. × soaking for 1 minute, pickled, and had a thickness of 5 m.
m, cold-rolled to 850 to 1100 ° C and soaked for 1 minute, followed by pickling.

[0029]

A test piece was cut out from the annealed pickling material and punched under the same conditions as in Example 1 in which the clearance ratio was set to 2%. The shear ratio of the punched test piece was measured, and the relationship with the grain size number was investigated. As can be seen from the investigation results in FIG. 8, the steel type C according to the present invention exhibited a shear surface ratio of 100% regardless of the grain size. On the other hand, SUS304
All of the steel types D corresponding to the above had a low shear surface ratio of about 45%. FIG. 9 shows the relationship between the sag ratio and the grain size number. That is, when the crystal grain size number increases (fine-grained), the sag ratio tends to decrease regardless of the type of steel. Regarding the steel type C according to the present invention, in C3 to C6 having a grain size number of 8 or more,
1 and C2, the sag is reduced to half or less.

Each test piece was continuously punched, and the number of punches until the die was replaced was examined. As can be seen from the inspection results in Table 5, it is understood that the steel types C and D both have a large number of punching times until the die is replaced, and the die life is extended. However, in the case of C6 having a grain size number of more than 11, the number of times of punching is reduced, and it is shown that excessive grain refinement reduces the life of the mold.

[0032]

[0033]

As described above, in the austenitic stainless steel of the present invention, the ratio of the shear surface to the fractured surface formed by punching, particularly, precision punching, is high, and sag is reduced. Therefore, it is processed into a punched product with high dimensional accuracy. In addition, the mold life is longer than that of austenitic stainless steel such as SUS304 which has been conventionally applied. Therefore, by using the austenitic stainless steel of the present invention, a punched product having good dimensional accuracy can be obtained without increasing the manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a view for explaining sagging generated in a punched product and its measuring position.

FIG. 2 is a view for explaining a shear surface generated on a fracture surface of a punched product and a measurement position thereof.

FIG. 3 is a graph showing the relationship between the component index Md ₃₀ value and the shear ratio according to the present invention.

FIG. 4 is a graph showing the relationship between (C + ／ N) amount and shear rate.

FIG. 5 is a graph showing the relationship between the S content and the shear ratio at a clearance ratio of 2%.

FIG. 6 is a graph showing the relationship between the S content and the shear ratio at a clearance ratio of 5%.

FIG. 7 is a graph showing the relationship between Vickers hardness and shear ratio.

FIG. 8 is a graph showing the relationship between the rate of increase in hardness due to temper rolling and the sag ratio.

FIG. 9 is a graph showing the relationship between the grain size and the shear ratio.

FIG. 10 is a graph showing the relationship between the crystal grain size and the sag ratio.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hiroshi Fujimoto 4976 Nomuraminamicho, Shinnanyo-shi, Yamaguchi Prefecture Inside Nisshin Steel Corporation Stainless Steel Business Headquarters (72) Inventor Naoto Hiramatsu 4976 Nomuraminamicho, Shinnanyo-shi, Yamaguchi Prefecture Sun New Steel Co., Ltd. Stainless Business Division

Claims (4)

[Claims] 1. (C + 1 / 2N): 0.060% by mass or less, Si: 1.0% by mass or less, Mn: 5% by mass or less,
S: 0.006% by mass or less, Cr: 15 to 20% by mass,
Ni: 5 to 12% by mass, Cu: 5% by mass or less, the balance substantially has a Fe composition, and the index Md _{30 of the} amount of work-induced martensite defined by the formula (1) is −60 to −10.
Austenitic stainless steel with excellent precision punching characteristics, the components of which are adjusted so that Md ₃₀ = 551-462 (C + N) -9.2Si-29 (Ni + Cu) -8.1Mn-1
3.7Cr 2. A further Mo: includes 3.0 mass% or less, are components adjusted so as indicator Md ₃₀ of strain-induced martensite amount defined by Equation (2) is -60 to-10 The austenitic stainless steel according to claim 1. Md ₃₀ = 551-462 (C + N) -9.2Si-29 (Ni + Cu) -8.1Mn-1
3.7Cr-18.5Mo 3. The steel sheet is hardened to a Vickers hardness increase rate of 20% or more by cold rolling after annealing and pickling.
Or the austenitic stainless steel according to 2. 4. The austenitic stainless steel according to claim 1, wherein the austenitic stainless steel is refined to have a grain size of 8 to 11.