JPH08269639A - High strength non-magnetic stainless steel sheet for fastener and its production - Google Patents

Abstract

PURPOSE: To produce a material free from cracking at the time of forming, having a strength equal to or higher than that of conventional steel SUS 301, keeping non-magnetism, and suitable for use in a lock pin for slide fastener. CONSTITUTION: This material has a composition which consists of, by weight, 0.3-6.0% Si, 2.0-7.0% Mn, 10.5-15.0% Ni, 16.0-20.0% Cr, 0.06-0.40% N, <=0.15% C, <=0.0040% S, <=0.0060% O, and the balance Fe with impurities and in which the value of Ni equivalent represented by equation (Ni equivalent)=Ni+0.6Mn+9.69(C+N)+0.18Cr-0.11Si<2> is regulated to 17.0-21.5. Further, this material has <=1.01 magnetic permeability (μ) and >=700N/mm<2> spring limit value. By this method, the high strength non-magnetic stainless steel sheet for fastener, excellent in formability and durability, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to stainless steel for fasteners having high strength and exhibiting non-magnetism, and a method for producing the same.

[0002]

2. Description of the Related Art A fastener consists of a slider and a tooth, and the slider consists of the body itself and a puller for moving the slider. There is an auto fastener that has a lock pin so that it does not open naturally. Among the constituent parts of these components, brass has been mainly used in the past as the slider body and coupling element. on the other hand,
The lock pin is required to have a certain level of strength and spring characteristics for its function. In particular, when the opening force during use is large, such as sportswear, a large force is required to fix the slider, and high strength and spring characteristics are required. For such applications, work-hardening austenitic stainless steel SUS301, which can obtain strength and spring characteristics by appropriate cold working, is used.

[0003]

In recent years, a needle detector utilizing magnetism has come to be used as a method for checking the mixture of sewing needles used at the time of sewing. Therefore, it has become necessary to add the characteristic of non-magnetism to the required characteristics of the lock pin in addition to the conventional characteristics. However, the SUS3
Since the 01 series steel is intended to have high strength by utilizing the work-induced martensite phase generated by cold working, it cannot satisfy the property of non-magnetism. Examples of existing non-magnetic steels include SUS316, but since this steel has a small work hardening, it is necessary to perform strong cold working in order to obtain the same properties as SUS301.
In the case of a lock pin that requires molding, there is a problem that microcracks are generated in the R portion on the outside of the bending during the molding, and the fatigue strength is lowered, so that it cannot be used. For this reason,
It is inevitable that the forming process R is increased, or the cold process is reduced to secure the forming processability, and the decrease in the strength level is compensated for by the plate thickness. It couldn't fit into the size of the zipper, and the size of the zipper was larger than necessary.
Recently, there are many fields where SUS301 lacks strength. The present invention is intended to develop a material suitable for use as a lock pin of a slide fastener that has strength higher than that of conventional steel SUS301, and that is non-magnetic, without generating cracks during molding. .

[0004]

According to the present invention, the weight percent is
And C: 0.15% or less, Si: 0.3 to 6.0%, Mn: 2.0
~ 7.0%, Ni: 10.5 ~ 15.0%, Cr: 16.0 ~ 20.0%,
N: 0.06 to 0.40%, the balance consisting of Fe and impurities, and S and O of the impurities S: 0.
0040% or less, O: 0.0060% or less, and Ni equivalent = Ni + 0.6Mn + 9.69 (C + N) + 0.18Cr
The value of Ni equivalent according to the formula of −0.11Si ² satisfies the range of 17.0 to 21.5,
Permeability μ = 1.01 or less and spring limit value is 700 N / mm ²
The high-strength non-magnetic stainless steel sheet for fasteners having excellent moldability and durability as described above is provided.

Further, according to the present invention, in particular, N: 0.1-
0.2%, and S and O as impurities, S: 0.0
Provided is a high-strength nonmagnetic stainless steel sheet for fasteners, which is excellent in formability and durability and is limited to 020% or less and O: 0.0045% or less. Further, according to the present invention, after hot-rolling and cold-rolling steel sheets are annealed to substantially austenite phase structure, Ni equivalent = Ni + 0.6Mn + 9.69 (C + N) + 0.18Cr
Depending on the value of Ni equivalent according to the formula of −0.11Si ² , a, b, c,
Provided is a method for producing a high-strength non-magnetic stainless steel sheet for a fastener, which is excellent in formability and durability and is finished by temper rolling at a cold rolling rate in the range surrounded by d. Further, according to the present invention, in the manufacturing method, the total cold rolling reduction rate (%) = {1- (finished thickness after temper rolling / thickness at the start of cold rolling after hot rolling) A method for manufacturing a high-strength non-magnetic stainless steel sheet for fasteners, which is excellent in formability and durability and is finished according to the formula} × 100 so that the total cold rolling rate is 85% or more.

[0006]

As a result of various tests conducted by the present inventors, the formability and fatigue properties of the fastener member are determined by the total rolling rate and temper rolling rate from the hot-rolled sheet to the product, and the non-metallic intervening rolling rate. Depends on the form of the object,
It was found that the spring characteristics are not governed only by the strength level. That is, in order to enhance the formability after cold working as much as possible, consider the components so as to obtain as high strength as possible in low cold working, and to obtain as high strength and high spring limit value as possible after aging treatment, Further, the total cold rolling reduction rate is increased so as to refine the non-metallic inclusions existing in the steel, and MnS extending in the rolling direction is extended.
The amount of non-metallic inclusions in the system was reduced as much as possible, and the amounts of S and O were controlled so that the distribution was small. Further, N was effectively utilized so that high strength and high spring limit value could be obtained after aging treatment, and higher strength could be exhibited by adding Si. The decrease in the solid solubility limit of N due to the addition of Si is due to Mn.
Was added to compensate for this. First, the reasons for limiting the composition range of the steel of the present invention will be described below.

C is an austenite forming element and is extremely effective for suppressing δ ferrite generated at high temperature and for work hardening in cold working. However, in order to obtain excellent formability after temper rolling, it is desirable that the material does not significantly harden by cold working. Further, if C is excessively increased, carbide may be precipitated depending on annealing before tempering or aging treatment conditions. Therefore, C is set to 0.15% or less.
It is more preferably 0.03 to 0.10%.

Si is effective as a deoxidizing agent, but it further enhances solid solution hardening to enhance the strength in the cold-rolled state and has a slight effect on the increase in the strength after the aging treatment. In order to exert these effects, it is preferable to contain 0.30% or more. However, as its content increases, the magnetic permeability after cold working rapidly increases and promotes the formation of δ ferrite, and it is necessary to add a large amount of austenite-forming elements Mn and Ni. Will occur. Therefore, the upper limit is 6.0%. More preferably
0.6% or more and 5.0% or less.

Mn works effectively as a deoxidizer, but it is an element that controls the stability of the austenite phase, and its utilization is considered in balance with other elements. In the present invention steel, M
n plays the role of suppressing the increase in magnetic permeability due to cold working and increasing the solid solubility of N. At least 2.0% is required to fully exhibit this effect. Also, in order to maintain the non-magnetic property after cold working, it is necessary to adjust the amount together with the content of austenite forming elements such as Ni, but if the addition exceeds 7.0%, the effect is improved. In addition, when Si is high, the hot workability is deteriorated, so the upper limit was made 7.0%. It is preferably 2.0% to 5.0%.

Ni is an essential component for stabilizing the austenite phase at high temperature and room temperature, but in the present invention, it is a balance with other alloy components in order to ensure non-magnetism after cold working. However, about 10.5% or more is required. The upper limit is not particularly limited in terms of ensuring non-magnetism after cold working, but when Si is high, a large amount of Ni deteriorates hot workability, so the upper limit was made 15.0%. It is preferably 11.0% to 13.5%.

Cr is an essential component for corrosion resistance, and 16.0% or more is required to impart excellent corrosion resistance. However, since Cr is a ferrite-forming element, if it is made too high, a large amount of δ-ferrite is formed at high temperatures, and the δ-ferrite phase remains even after annealing and tempering, making it impossible to secure non-magnetism. In order to suppress δ ferrite,
It is necessary to add a large amount of austenite forming elements (C, N, Ni, Mn, etc.), which is unnecessarily expensive. Therefore, the upper limit of Cr is set to 20.0%. It is more preferably 17.0 to 19.0%.

N is an element that plays an important role in achieving the object of the present invention. It promotes work hardening by cold working, and increases strength by aging treatment, especially strengthening of yield strength and high spring limit value. Contribute to that. In order to exhibit these characteristics, it is necessary to add at least 0.06%. However, if added in a large amount, it may cause blowholes, so the content was made 0.30% or less. More preferably 1.0-
It is 0.20%.

S coexists with Mn to form MnS, which causes deterioration of ductility and workability such as bending.
In particular, the spring of the auto fastener is a small part and is subjected to bending, so if inclusions extending in the rolling direction are present, cracks will occur during processing and fatigue strength will be reduced, resulting in reduced durability. Connect Therefore, 0.004
% Or less. It is more preferably 0.0020% or less.

O is an element that easily forms a non-metallic inclusion that becomes a starting point of fatigue fracture, and is particularly prominent when an element having a large affinity with O such as Al is contained. Moreover, when O was high, it was observed that the morphology of other non-metallic inclusions, for example, MnS, was largely aggregated. Therefore, the O content is preferably low, but if 0.0060% or less, the durability as the lock pin of the auto fastener can be secured and the object can be achieved, so the content was made 0.0060% or less. It is preferably 0.0045% or less. In addition to the above, the steel of the present invention has Ca (REM) added as a deoxidizing agent and B (0.01%) which is effective in improving hot workability.
In addition to the following), impurities that are inevitably mixed can be contained.

Regarding Ni equivalent value and temper rolling ratio, Ni equivalent = Ni + 0.6 Mn + 9.69 (C + N) + 0.18Cr
-0.11Si ² The Ni equivalent represented by this formula is an index of the austenite stability confirmed in the laboratory, and as shown in FIG. 1, the magnetic permeability in relation to the cold rolling rate. Will be an indicator of. At the time of sewing, it is necessary to keep the permeability of fastener parts low because it is magnetically discriminated with a needle detector whether sewing needles are mixed or not. Must be: In order to obtain a strength level that can be used as a part (lock pin) of an auto fastener, the steel of the present invention has a strength of 20%.
The above temper rolling is required. At this time, the Ni equivalent value needs to be 16.5 or more in order to secure the magnetic permeability of 1.01 or less, but the lower limit value is set to 17.0 in consideration of the increase of the magnetic permeability when processed into parts.

On the other hand, if the temper rolling ratio is too high, the workability deteriorates, and if it exceeds 55%, microcracks are generated during the molding process. Therefore, the upper limit of the temper rolling rate is limited to 55%. The upper limit of the Ni equivalent value is not particularly limited in terms of magnetic permeability, but if it is too high, it becomes expensive, so the upper limit is set to 21.5,
The range is a, b, c, d shown in FIG.

The inventors of the present invention have focused on the distribution of non-metallic inclusions existing in the material (tempered rolled material) before the forming process in order to prevent the generation of microcracks during the forming process.
As a result of various investigations, it was found that when the oxide-based nonmetallic inclusions are reduced and the extended MnS-based nonmetallic inclusions are small and randomly distributed, no microcracks are generated. To obtain such a metal structure,
First, as described above, it is effective to reduce S and O as much as possible and suppress the generation of nonmetallic inclusions in the steelmaking process. Furthermore, as another finding, it was found that it is effective to randomize the distribution of nonmetallic inclusions by cold rolling. For this purpose, the total rolling rate of cold rolling including temper rolling may be increased.

Specifically, the total cold rolling rate (%) =
{1- (finished thickness after temper rolling / thickness at the start of cold rolling after hot rolling)} × 100 The tempering is performed so that the total cold rolling reduction rate is 85% or more. Finish rolling and finish. Even if annealing is performed during cold rolling, the distribution of non-metallic inclusions is not affected.
That is, by increasing the total rolling rate of cold rolling performed after hot rolling, nonmetallic inclusions are finely divided, and as a result, the formability is improved and the durability is improved.

In order to obtain the strength characteristics as an auto fastener component, after the component is molded and processed,
It is desirable to perform the aging treatment in the temperature range of 700 ° C or lower. Below 300 ° C, it takes a long time to reach the target strength level, which is uneconomical. If it exceeds 700 ° C., a recovery phenomenon may occur and the target strength may not be obtained. Regarding the aging treatment time, the effect appears when it is 10 seconds or more, but about 30 minutes is preferable in order to stably obtain the target strength. In addition, since the composition of the steel of the present invention is adjusted so as to exhibit an austenite structure in the solution treatment state as described above, hot rolling and cold working steps before temper rolling should be manufactured in the same manner as conventional steps. You can

[0020]

EXAMPLES Steels of the present invention (N1 to 8), comparative steels (C1 to 5) and conventional steels (A: SUS301, B: SUS304) having the components shown in Table 1
N, C: SUS316) was melted in a high-frequency vacuum melting furnace of 30 kg, hot-rolled, cold-rolled, annealed and pickled to give a plate thickness of 0.40 mm after final temper rolling. This was taken as a sample as cold rolled. Furthermore, the steel plate is heated at 450 ° C for 20
Aging treatment was performed for a minute, and this was used as a sample after the aging treatment. Furthermore, some of the test materials were melted using a 500 kg high-frequency vacuum melting furnace, and were also subjected to a substantial durability test with fasteners. Details of the total rolling ratio and the temper rolling ratio until commercialization are shown in Table 2 of each. In addition, the Ni equivalents obtained by the limiting formula (1) are also shown in Table 1.

Among the collected samples, the cold rolled sample was subjected to a magnetic permeability measurement and a forming workability test, and the aged sample was subjected to a tensile test and a spring limit value measurement and a fatigue test. went. The results are also shown in Table 2. The molding processing test is the outside R part (inside R = 0. 0) when the test piece is processed into the shape shown in FIG.
3) was observed and evaluated by the absence of microcracks (○), the presence of fine cracks (△), and the presence of cracks (×). In addition, the fatigue test was carried out by applying maximum stress to the test piece formed into the W bead shape.
A one-sided swing fatigue test was conducted under which a stress amplitude of 200 N / mm ² was applied under a load of 500 N / mm ² , and the evaluation was made by the number of repetitions up to fracture × 10 ⁴ . In the durability test, an auto-fastener incorporating a lock pin was produced, and a zipper having a length of 30 cm was mechanically repeatedly opened, opened and closed, and the durability was evaluated by the change in the opening load and the number of breaks. The maximum number of repetitions was 3000.

[0022]

[Table 1]

[0023]

[Table 2]

From the results of Table 2, the following can be seen. Invention steels (N1-8) by the manufacturing method according to the present invention, that is,
The total rolling ratio by the method of the present invention exceeds 85%, and the temper rolling ratio is 20-
When treated so as to have a range of 55%, no microcracks or cracks were formed in any of the steels during forming, and at the same time, it showed high yield strength after aging treatment.
It has a spring limit value of 0 N / mm ² or more. Also, regarding the fatigue rupture life, those with a temper rolling ratio of more than 40% showed a rupture life of 850,000 times or more, and those of 20% showed a rupture life of 450,000 times. On the other hand, the magnetic permeability at that time is μ =
It keeps a low value of 1.01 or less. However, Example No.
The magnetic permeability μ exceeds 1.01 outside the range surrounded by a, b, c, d shown in FIG.

The steels of the present invention (N4, 7) also have comparative examples Nos. 14 and 15.
As shown in, when the total rolling reduction is less than 85%, the fatigue rupture life tends to be shorter than that of the method of the present invention. Further, as shown in Comparative Examples No. 16 and 18, when the temper rolling ratio exceeds the upper limit of the method of the present invention, the moldability is poor, and microcracks are generated on the outer surface of the bending R part and fatigue fracture occurs. The life will be significantly reduced. On the other hand, if the temper rolling ratio is less than the lower limit as in Comparative Example No. 17, the desired spring limit value cannot be obtained and the yield strength is low.

Comparative steel No. 19 is a steel (C1) in which N is lower than the steel of the present invention and deviates from the steel of the present invention within the production range of the method of the present invention. Compared with the steel of the present invention which has been given, the yield strength, the spring limit value is low, the target is not particularly satisfied with regard to the spring characteristics, and the desired force cannot be obtained due to deformation in the durability test with the zipper, and the durability is insufficient and it fails. Met. Comparative steel No. 20 is a steel (C2) in which N is slightly lower than that of the steel of the present invention, and is manufactured within the manufacturing range of the method of the present invention. However, the desired characteristics have not been reached. Also, O
The fatigue property is inferior due to the high value. Comparative steel No. 21 is a steel (C3) in which O is higher than the steel of the present invention and deviates from the steel of the present invention within the manufacturing range of the method of the present invention. And the like satisfy the target, but the O content is high, so that the fatigue property is inferior. Comparative steel No. 22 is an example of a steel (C4) in which 0 is higher than the steel of the present invention and deviates, and in this case, the same level of strength and spring characteristics as the steel of the present invention is exhibited, but O is high. The fatigue life is lower than that of comparative steel No. 21, though. Comparative steel No. 23 is an example of a steel (C5) in which S and O are deviated higher than those of the present invention steel, and in this case, the same level of strength and spring characteristics as those of the present invention steel are shown It also becomes inferior in properties and the fatigue life is significantly lower than that of comparative steel No. 22 in which only O is high.

Conventional steel Nos. 24 and 25 are prepared by comparing the properties of SUS301, which has been used in the field where non-magnetic property is not required, with different tempering rolling rates and different strength levels. As can be seen from the table, if the strength level (proof stress) is the same level, the desired spring characteristics cannot be obtained, and if the temper rolling ratio is increased to increase the strength, austenite stability is low and a large amount of martensite phase is generated. However, the moldability becomes poor and the fatigue life decreases. Even in the durability test, at the same plate thickness, the value was low in terms of opening load. In conventional applications, this insufficient load is used by covering it with a plate thickness. Conventional steel NO.26 is for SUS304N, but 35% is required to obtain the desired yield strength and spring limit value.
The temper rolling rate above is required, in which case the permeability μ is 1.01.
And the object of the present invention cannot be achieved. Conventional steel Nos. 27, 28, and 29 are shown for SUS316, but since the Ni equivalent of this steel is within the range of the steel of the present invention, the magnetic permeability μ is 1.01 or less even after high temper rolling. But N
Is low, the desired strength and spring limit cannot be obtained,
In the durability test, it is difficult to obtain sufficient durability due to settling. If the temper rolling ratio is increased to improve the spring characteristics, the formability is poor and the fatigue life is also low.

FIG. 1 shows the relationship between magnetism, Ni equivalent and rolling rate when cold rolling various steels within the composition range of the present invention and conventional steel B. From this figure, a, b and c are shown. It can be seen that the one surrounded by the range of d has a magnetic permeability μ = 1.01 or less.

FIG. 2 shows the relationship between the N content and the spring limit value after aging treatment when a 20% temper rolling ratio is applied to a material having a Ni equivalent within the range of the steel of the present invention, and the magnetic permeability μ It can be seen that the spring limit value after aging treatment in the nonmagnetic region of 1.01 or less is largely controlled by the N content. On the other hand, FIG. 3 shows the aging of steel N3 of the present invention and conventional steel A (SUS301), which produces a work-induced martensite phase and whose strength level is remarkably increased by working, by various temper rolling and varying the strength level. It shows the relationship between the yield strength after treatment and the spring limit value. A high spring limit value after aging treatment can be obtained even with the same yield strength level by adding N even with a structurally stable material such as the steel of the present invention. Is recognized. The effect of N is promoted by the combined addition of Si. All of the total rolling ratios at the time of production were according to the method of the present invention.

FIG. 4 shows the W having the shape shown in FIG.
After aging the test piece with the bead formed and applied, a swinging fatigue test (a stress amplitude of 200 N / mm ² is applied to the test piece with W bead processing as shown in Fig. 6 at a maximum stress of 500 N / mm ² ) The results of investigation of the effect of O and the effect of manufacturing conditions on the fatigue life are shown. Each of the steels of the present invention manufactured by the method of the present invention has a breaking life of 800,000 cycles or more, and exhibits excellent fatigue properties. Even within the composition range of the steel of the present invention, when the total rolling ratio was outside the production range of the present invention (marked with ●), the fracture life was lower than that of the method of the present invention. Further, among the comparative steels, the one having a high content of both O and S (▲) exhibited a lower fracture life than the one having a high content of O alone (Δ).

[0031]

EFFECTS OF THE INVENTION The steel of the present invention has a large increase in strength and spring characteristics due to aging treatment as compared with the conventional non-magnetic stainless steel, so the strength before aging treatment can be reduced. Therefore, it is more excellent in molding processability. Moreover, after aging treatment, it is possible to provide high-strength non-magnetic stainless steel with excellent fatigue properties in the formed part, and it has excellent durability as a part that has undergone complicated forming such as lock pin of auto fastener. . In addition, since it has high strength and a spring limit value, it is possible to reduce the size of parts. Further, the cost is the same as that of the conventional steel even when it is manufactured, so it is economical. Since the steel of the present invention exhibits an austenite phase in the annealed state and is excellent in workability, other sliders, fastener teeth, pullers, etc. constituting the fastener as well as the lock pin should be used in place of the conventional brass. You can

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a Ni equivalent and a cold rolling rate that affect magnetic permeability.

FIG. 2 is a diagram showing the relationship between the amount of N and the spring limit value after aging treatment when a 20% temper rolling rate is applied to a material having a Ni equivalent in the range of the steel of the present invention.

FIG. 3 is a diagram showing a relationship between a yield strength and a spring limit value after aging treatment of a steel N3 of the present invention which has been subjected to various temper rolling and a conventional steel A.

FIG. 4 is a diagram showing the relationship between the number of repetitions and the amount of O until breakage in a one-sided tensile fatigue test of a W bead forming-applied product of an aging treated material.

FIG. 5 is a schematic cross-sectional view showing a W bead shape evaluated for moldability.

FIG. 6 is a diagram for explaining an outline of a one-sided tensile fatigue test of a W beading imparting material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Takemoto 4976 Nomura-Minamimachi, Shinnanyo-shi, Yamaguchi Nisshin Steel Co., Ltd. Steel Research Laboratory

Claims (4)

[Claims] 1. By weight%, C: 0.15% or less, Si: 0.3
~ 6.0%, Mn: 2.0 ~ 7.0%, Ni: 10.5 ~ 15.0%,
Cr: 16.0 to 20.0%, N: 0.06 to 0.40%,
The balance consists of Fe and impurities, and among the impurities, S
And O are limited to S: 0.0040% or less, O: 0.0060% or less, and Ni equivalent = Ni + 0.6Mn + 9.69 (C + N) + 0.18Cr.
The value of Ni equivalent according to the formula of −0.11Si ² satisfies the range of 17.0 to 21.5,
Permeability μ = 1.01 or less and spring limit value is 700 N / mm ²
The high-strength non-magnetic stainless steel plate for fasteners, which is excellent in moldability and durability as described above. 2. N: 0.1 to 0.2%, S: 0.0020% or less,
O: 0.0045% or less, the moldability according to claim 1,
High strength non-magnetic stainless steel plate for fasteners with excellent durability. 3. A steel sheet that has been hot-rolled and cold-rolled is annealed to have a substantially austenitic phase structure, and then Ni equivalent = Ni + 0.6Mn + 9.69 (C + N) + 0.18Cr.
Depending on the value of Ni equivalent according to the formula of −0.11Si ² , a, b, c,
A high-strength non-magnetic stainless steel sheet for fasteners, which is excellent in formability and durability according to claim 1 or 2, characterized in that it is finished by temper rolling at a cold rolling rate in a range surrounded by d. Manufacturing method. 4. A cold rolling according to the formula: cold rolling total rolling ratio (%) = {1- (finished thickness after temper rolling / thickness at the start of cold rolling after hot rolling)} × 100 The forming workability according to claim 3, wherein the finishing is performed so that the total rolling rate becomes 85% or more.
A method of manufacturing a high-strength non-magnetic stainless steel plate for fasteners having excellent durability.