JP2944865B2 - Stainless steel for high strength cold working - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for manufacturing various mechanical parts, fastening parts for construction, etc., and coupling materials with magnetic materials, and particularly for manufacturing members used in fields requiring non-magnetic and high strength. The present invention relates to a high-strength non-magnetic nitrogen-containing austenitic stainless steel excellent in cold workability for a rod, a wire, and a steel pipe used for forming the same.

[0002]

2. Description of the Related Art Generally, austenitic stainless steels are used in various fields because of their excellent corrosion resistance and heat resistance. For example, home appliances, office equipment,
It is used for parts of industrial machines, fasteners such as screws, bolts, nuts and pins, and construction parts and fasteners for structures such as houses, buildings and railways. Most of these parts and fasteners are manufactured by forming a material by cold forging or cold drawing. These methods of forming and manufacturing by cold forging or cold drawing have advantages of high working efficiency and high yield.

However, general austenitic stainless steels have higher deformation resistance and higher cold work hardening properties than ordinary steels and ferritic stainless steels, and thus are subjected to the above-mentioned cold forging or cold drawing. It was difficult to manufacture such parts. In addition, since a martensite phase is generated during cold working, the material is non-magnetic (permeability is 1.02 or less).
For this reason, there is a case where a problem arises when using it for coupling (connection part) with a magnetic material.

[0004] As a material which solves these problems, ie, a material which is excellent in cold workability and corrosion resistance and is non-magnetic, SUSX is used.
M7 and SUS305 are stipulated in JIS, but the strength of such parts often becomes insufficient even after cold working.

[0005]

Recently, various types of mechanical parts and construction parts have been required to have high strength in order to reduce weight and improve reliability. In addition, many of these parts are used for coupling with a magnetic material, and therefore, a demand for a high-strength non-magnetic austenitic stainless steel excellent in cold workability is increasing.

As a high-strength and non-magnetic material for this purpose, a high-Mn nitrogen-containing austenitic stainless steel, for example, 0.1C-15Mn-18Cr-0.4N steel has been developed. Has a very high hardness before cold working,
Due to poor ductility, cracks occur frequently during cold working, and the yield is poor, which is a problem.

The problem to be solved by the present invention is a nitrogen-containing austenitic system which has not been obtained so far and which is excellent in cold workability and has high strength and non-magnetic properties in cold worked parts and fasteners. Is to provide stainless steel.

[0008]

In order to solve the problems] order to solve the above problems
It is the means, 1. Chemical components in weight%, C: 0.12% or less, Si: 0.05-1.00%, Mn: 5.0-8.
5%, P: 0.045% or less, S: 0.015% or less,
Ni: 4.0 to 9.0%, Cr: 16.0 to 21.0
%, Cu: more than 1.0% to 4.0%, N: 0.15 to 0.1%.
30%, O: 0.0040% or less, B: 0.0015 to
0.0040%, and C + N: 0.20
0.35%, the balance being Fe and unavoidable impurities, and conditional expression: 530-410C-350N-10Mn-15Cr-
It is an austenitic stainless steel satisfying 30 (Ni + Cu) -10Mo ≦ -80.

[0009] 2. Further, in addition to the above chemical components, Nb: 0.05 to 0.20% or V: 0.05 to
Contains 0.50% of one or two kinds, and conditional expression: 530-410C-350N-10Mn-15Cr-30 (Ni + Cu) -10Mo ≦ -8
This is an austenitic stainless steel satisfying 0.

[0010]

Next, the reasons for limiting the chemical components of the steel of the present invention will be described.

C increases the strength of austenitic stainless steel. However, in the present invention, the strength point is not necessarily required because it can be replaced by N. If it is present excessively, the corrosion resistance is degraded due to grain boundary precipitation of Cr carbide. Therefore, the upper limit is set to 0.12%.

Although Si is a useful element as a deoxidizing agent, its upper limit is set to 1.00% because it is a strong ferrite-forming element and increases the magnetic permeability. Further, since the effect of the deoxidizing agent cannot be obtained at less than 0.05%, the lower limit is set to 0.0%.
5%.

Mn is a very effective element as a deoxidizing agent and an austenite-forming element, and is an element that can substitute for expensive Ni that suppresses the formation of a martensite phase during cold working. In addition, it increases the solubility of N in the austenite phase, thereby hindering the formation of Cr nitride, which inhibits corrosion resistance. At less than 5.0%, these effects are small,
The lower limit was 5.0%. On the other hand, if the content exceeds 8.5%, deterioration of corrosion resistance and deterioration of cold workability and hot workability due to solid solution Mn are caused. Therefore, the upper limit is set to 8.5%.

When P is present in excess of 0.045%,
Since the hot workability and corrosion resistance deteriorate, the upper limit is set to 0.0
45%.

S combines with Mn to form MnS,
When the content exceeds 0.015%, crack generation during cold working is promoted, so the upper limit is made 0.015%.

Ni is a basic element in austenitic stainless steel, is a strong austenite-forming element, and is an element that improves weather resistance and suppresses the generation of martensite after cold working. However, since Ni is expensive, Mn, Cu, N
It is desirable to substitute as much as possible and reduce as much as possible. If it is less than 4%, it is difficult to ensure the performance, and if it exceeds 9.0%, there is almost no effect of improving the weather resistance, which is regarded as important in the use of the part, so that it is 4.0 to 9.0%. And

Cr, together with Ni, is a basic element in austenitic stainless steel and provides corrosion resistance. 1
Sufficient corrosion resistance is obtained at 6.0% or more, but 21.0%
If it exceeds 1, a ferrite phase is likely to be generated.
0 to 21.0%.

Cu is an austenite forming element,
Stabilizes the austenitic phase. Further, similarly to Ni, the formation of a martensite phase due to processing is suppressed. Especially C
Since u can lower the work hardening index of the matrix and maintain the ductility during cold working, it has the effect of suppressing the occurrence of cracks. To achieve the effect,
Since it is necessary to contain more than 0%, the lower limit is 1.0%
It was super . However, if the content exceeds 4.0%, the hot workability is significantly deteriorated, so the upper limit is set to 4.0%.

N is a strong austenite-forming element like C, and increasing its amount contributes to saving Ni. It also increases the strength of the matrix. In the steel of the present invention, since the effect is remarkably exhibited at 0.15% or more, the lower limit is set to 0.15%. Also, 0.30
%, The cold work deformation resistance value sharply increases and the cold workability is impaired.
%.

O in steel exists as an oxide, and when this amount is large, it becomes a starting point of cracking during cold working. In the present invention, when the O content exceeds 0.0040%, the cold workability is significantly reduced. Therefore, the upper limit is set to 0.0040%.

B is an element that improves hot workability, but its effect is small if it is less than 0.0015%, so the lower limit is made 0.0015%. On the other hand, if the content exceeds 0.0040%, a B compound is generated, and conversely, the hot workability deteriorates. Therefore, the upper limit is made 0.0040%.

When Nb is contained and subjected to a precipitation hardening heat treatment, carbonitrides are formed, crystal grains are refined, and ductility after cold working is increased. In the present invention, particularly when ductility after cold working is required, it is added. In this case, the effect cannot be obtained if the content is less than 0.05%, so the lower limit is set to 0.05%. Further, if the content exceeds 0.20%, the cold workability is impaired, so the upper limit was made 0.20%.

V, like Nb, contains a carbonitride when subjected to a precipitation hardening heat treatment when containing Vb, and has the same effect. Since the effect cannot be obtained if the content is less than 0.05%, the lower limit is set to 0.05%. Further, if the content exceeds 0.50%, the cold workability is deteriorated, so the upper limit is set to 0.50%.

Regarding C + N: Both C and N are necessary to obtain high strength as a solid solution strengthening element, but if the total amount is less than 0.20%, various mechanical parts, fastening parts for construction or the like, or In many cases, the strength is insufficient when used for the parts such as a coupling material with a magnetic material, so the lower limit is set to 0.20%. However, if it exceeds 0.35%, corrosion resistance and cold workability are impaired, so the upper limit was made 0.35%.

Conditional expression: 530-410C-350N-10Mn-15Cr-30 (Ni +
Cu) -10Mo is related to the temperature at which martensite is formed, and FIG. 1 shows the relationship between the value of the conditional expression and the magnetic permeability after 50% cold working. It can be seen that the magnetic permeability can be predicted. Parts such as various mechanical parts, fastening parts for construction, and coupling materials with magnetic materials are usually added with a cold working rate of 40% or more. It is necessary to set a proper component balance. Conditional expression value is -8
If it exceeds 0, the magnetic permeability exceeds 1.02 and non-magnetic properties cannot be maintained, so the upper limit was set to -80.

[0026]

EXAMPLES Steel having the chemical components and the values of the conditional expressions shown in Table 1 and the balance being Fe and inevitable impurities was produced. Table 2 shows hot workability and cold workability of these steels, and mechanical properties and magnetic permeability after cold work. N
o. 1 to No. No. 7 is an embodiment of the present invention. 8 to No.
17 is a comparative example. No. Reference numerals 18 to 21 are conventional examples. No. 1 to No. 7, all of the steels of the present invention have good hot workability and a critical compression ratio of 80% or more and 50% or more.
The hardness (HV) after compression is 420 or more, and the magnetic permeability (μ) after 50% compression is nonmagnetic at a low value of 1.009 or less, which is significantly lower than the nonmagnetic index of 1.02 or less. The deformation resistance value (MPa) during compression is 1200 to 1310, which indicates that all of the steels of the present invention have excellent hot workability and cold workability and are non-magnetic.

By the way, in Table 1, no.
No. 8 has a C content higher than the specified value of the present invention, and
o. No. 9 is a case where the N content is higher than the specified value of the present invention, and therefore, both are cases where the value of C + N is higher than the specified value of the present invention. From Table 2, these lower the magnetic permeability after cold working, It can be seen that the maximum compression ratio was lowered and the limit compression ratio was lowered.

No. of Comparative Example No. 13 indicates that the O content was higher than the specified value of the present invention, and it can be seen that the critical compression ratio was significantly reduced.

In the embodiment of the present invention, No. No. 5 contains an appropriate amount of Nb within the specified value of the present invention, and No. 5 is an example of the present invention. No. 6 contained an appropriate amount of V within the specified value of the present invention, so that the strength after cold working increased without lowering the critical compressibility, but the comparative steel No. 6 did not. N like 17
It can be seen that when the b content exceeds the specified value of the present invention, the critical compression ratio decreases.

[0030]

[Table 1]

[0031]

[Table 2]

Also, from Table 1, No. 1 of the conventional example is shown. 18 (SU
SXM7) and No. 19 (SUS305 equivalent) has a (C + N) content lower than the specified value of the present invention. From Table 2, it can be seen that the hardness after cold working is lower than that of the present invention. No. of the conventional example. 20 (SUS304J3 equivalent)
Table 2 shows that when the Mn content is lower than the specified value of the present invention, the magnetic permeability after cold working is higher than that of the present invention. No. of the conventional example. 21 (corresponding to SUS304) has a lower Cu content than that of the present invention. From Table 2, it can be seen that the critical compression ratio is lower than that of the present invention, and the magnetic permeability and the deformation resistance value are higher.

[0033]

As described above, the austenitic stainless steel of the present invention has an extremely high critical compression ratio of 80% or more, is high in strength, and therefore has cracks in cold working, as compared with the conventional austenitic stainless steel. Rate is low,
It also has low cold work hardening properties and low deformation resistance during compression, so it can be applied to cold forging and cold drawing methods with high working efficiency and yield, and fastening parts such as screws, bolts, nuts and pins And various machine parts and construction parts can be manufactured efficiently. Further, the steel of the present invention has a very low magnetic permeability after cold working even if a cold working rate of 40% or more is added, and is therefore non-magnetic, so that it can be used as a coupling material with a magnetic material. This is an extremely excellent austenitic stainless steel that does not cause the problem described above.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a calculated value of a conditional expression of the present invention and a magnetic permeability after 50% cold working.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Gentaka Abe 3007, Nakajima character, Shima, Himeji City, Hyogo Prefecture Inside Sanyo Special Steel Co., Ltd. (56) References JP-A-63-169362 (JP, A) JP-A-59-35362 (JP, A) JP-A-4-272158 (JP, A) JP-B-2-50980 (JP, B2) JP-B-59-29106 (JP, B2) JP-B-60-427 (JP, B2) JP, B2) (58) Field surveyed (Int. Cl. ⁶ , DB name) C22C 38/00-38/60

Claims (2)

(57) [Claims] 1. A chemical component in weight%, C: 0.12% or less, Si: 0.05 to 1.00%, Mn: 5.0 to 8.0.
5%, P: 0.045% or less, S: 0.015% or less,
Ni: 4.0 to 9.0%, Cr: 16.0 to 21.0
%, Cu: more than 1.0 to 4.0%, N: 0.15 to 0.
30%, O: 0.0040% or less, B: 0.0015 to 0.0040%, and C
+ N: 0.20 to 0.35%, with the balance being Fe
And unavoidable impurities, and conditional expression: 530-410C
Austenitic stainless steel that satisfies -350N-10Mn-15Cr-30 (Ni + Cu) -10Mo ≦ -80. 2. The composition of claim 1, further comprising:
Nb: 0.05 to 0.20% or V: 0.05 to
0.50% of one or two kinds, and the conditional expression: 53
Austenitic stainless steel satisfying 0-410C-350N-10Mn-15Cr-30 (Ni + Cu) -10Mo ≦ -80.