JPH02225647A - High strength and high ductility stainless steel material and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the stainless steel material having high strength and high ductility by furthermore incorporating one or more kinds among Nb, Ti, V and Zr into a high Si-contg. Cr-Ni series steel and regulating the range of Ni equivalent to prescribed one. CONSTITUTION:The above stainless steel material contains, by weight, <=0.15% C, 3.0 to 7.0% Si, <=8.0% Mn, 8.0 to 13.0%, 12.0 to 17.0% Cr and 0.10% Si and satisfies 8.0 to 14.0% Ni equivalent defined by the formula. Furthermore, the steel material has an austenitic (gamma) single phase or a mixed structure of a gamma phase and a martensitic (alpha') phase. In the above constitution, gamma stability is reduced to facilitate alpha' phase-transformation treatment by incorporating Si into a Cr-Ni series austenitic stainless steel. Moreover, the stainless steel is subjected to moderate heat treatment after cold-rolled to refine the inverse transformation austenitic grains to be formed, by which the steel material having high strength and high ductility following the solid-soln. strengthening and the impartation of high ductility by Si can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high-strength, high-ductility stainless steel material with excellent corrosion resistance and ductility, and a method for manufacturing the same.

[Prior art and its problems]

Conventionally, high-strength stainless steels for spring materials and structural materials that require corrosion resistance and high strength include (a) work-hardening stainless steels such as 5US301 steel, and (b) 17-4.
Precipitation hardening stainless steel typified by PH, 1,77-7P)I is used.

Work hardening type austenitic stainless steel is 5US30
No. 111.5 US30411: This is a stainless steel having a metastable austenite phase, and high strength is obtained by inducing a hard martensitic (α') phase through cold working. However, in order to obtain high strength, a high cold rolling rate must be applied to generate a large amount of α' phase, resulting in a significant decrease in ductility.

Precipitation hardening stainless steel has A0. High strength is obtained by adding precipitation hardening elements such as Cu and precipitating intermetallic compounds through aging treatment. The structure of 17-JPH steel is martensite, and although high strength can be obtained through aging treatment, it has the drawback of poor ductility.

On the other hand, x7-7pn steel is subjected to cold working to generate the α' phase and then age hardened, and as with the work hardening type stainless steel described above, a decrease in ductility is inevitable.

Therefore, JP-A-62-124218 discloses a method for producing a high-strength TI ductile stainless steel material in which austenite grains are generated from the martensitic phase by subjecting the high-strength stainless steel to appropriate heat treatment separately from the above-mentioned high-strength stainless steel.

The invention has a martensitic m weave in an annealed state, and by subjecting it to appropriate heat treatment, it becomes a single martensite phase or a multi-phase structure of a martensite phase and a fine austenite phase, thereby obtaining high strength and high ductility. It is something. However, the property obtained by this method is a yield strength of 100 kg.
/am', the elongation is at most 20%, which cannot be said to be highly ductile.

"Tetsu-to-Hagane J74 (1988) 6.p, 105111, austenitic stainless steel is given a high cold rolling rate to form the α' phase (referred to as α' phase mutual treatment), and then subjected to appropriate heat treatment. This method discloses an attempt to obtain high strength and high ductility by obtaining fine austenite grains by reversely transforming the phase into an austenite phase.This method uses a highly ductile austenite structure, and is difficult to obtain high ductility. Although it is considered to be an effective method, the α' phase treatment requires an extremely high cold rolling rate of 90% and there is a risk of breakage during rolling.

In addition, it is difficult to obtain good surface texture or shape, making it difficult to manufacture.

[Knowledge about problem solving]

In order to obtain an austenitic structure in the annealed state in Cr-Ni austenitic stainless steel, the Ms point must be lower than room temperature, and it is necessary to contain a large amount of austenite phase stabilizing elements such as Ni and Cr. However, if the content of these elements increases, the formation of the α' phase is suppressed by cold rolling, so it is necessary to apply a high cold rolling rate to carry out the α' phase mutual treatment.

Therefore, the present inventors conducted extensive research on the effects of alloying elements and processing heat treatment methods on the γ stability against α' transformation and mechanical properties in Cr-Ni metastable stainless steel. It has been found that by reducing the α' phase and promoting the formation of the α' phase, the product can be made into an α' phase mutually treated container. Furthermore, by subjecting high Si-containing Cr-Ni austenitic stainless steel to an appropriate heat treatment after α-phase treatment, an austenitic structure consisting of finer grains can be obtained compared to when the Si content is low, and Si is in the γ phase. The present inventors have discovered that Si is effective in solid solution strengthening and also contributes to improving elongation, making it possible to achieve high strength and high ductility.

[Structure of the invention]

In the present invention, C: 0.15% or less Si: 3.0 to 7.0% Mn: 8.0% or less Ni: 8.0 to 13.0% Cr: 12. Q ~17.0% N: 0. IO% or less, and the remainder consists of Fe and unavoidable impurities.

Ni equivalent = Ni (%) + 0.608n (%) + 9.69
(C+N)(%)+0.18Cr(%)-0,115i
(%) Ni equivalent value defined as 8 is 8.0 to 14.0
The present invention provides a high-strength, high-ductility stainless steel material having a single austenite (γ) phase or a mixed structure of a γ phase and a martensite (α') phase.

The present invention also provides c:o, xs% or less in weight% Si: 3.0-7.0% Mn: 8.0% or less Ni: 8.0-13,0% Cr: 12.0-17.0 % N: Contains 0.10% or less, the remainder consists of Fe and unavoidable impurities, and Ni equivalent = Ni (%) + 0.6ONo (%) + 9.69
(C+N)(%)+0. t8Cr(%)-0,11Si
(%) Ni equivalent value defined as 1 is 8.0 to 14.0
After cold-rolling (α' phase treatment) the steel in the range of Provided is a method for producing a high-strength, high-ductility stainless steel material characterized by having a mixed structure of α' phase and α' phase.

The present invention also provides c:o, is% or less Si: 3.0 to 7.0% Mn: 8.0% or less Ni: 8. G~13.0% Cr:12.0~17.0% N:0. Contains fO% or less, and further includes: Nb: 1.0% or less, Ti: 1.0% or less, V: 1.0
% or less, Zr: contains one or more of 1.0% or less, and the remainder consists of Fe and unavoidable impurities,
And Ni equivalent = Ni (%) + 0.6ONo (%) + 9
．． 69(C+N)(%)+0.18Cr(%) -0,
11Si(%)' +0.60(Nb+τi+v+Zr
)(%) The value of Ni equivalent defined as 8.0 to 14.0 and γ
A high-strength, high-ductility stainless steel material characterized by having a single phase or a mixed structure of γ phase and α' phase is provided.

The present invention also includes C: 0.15% or less Si: 3.0-7.0% Mn: 8.0% or less Ni: 8.0-13.0% Cr: 12.0-17.0% N: 0.10% or less Contains and further.

Nb: 1.0% or less, Ti: 1.0% or less, I/: 1.
0%, Zr: 1.0% or less, and the remainder consists of Fe and inevitable impurities.

Ni equivalent = Ni (%) + 0, 6ONo (%) +
9.69(C+N)(%)+0.18Cr(%)-0,
11Si(%)” +0.60(Nb+Ti+V
+ Zr) (%) Defined Ni equivalent value is 8.0
-14.0 After cold rolling (α' phase treatment) until the steel becomes substantially α' single phase, 600 to 9
Provided is a method for producing a high-strength, high-ductility stainless steel material which is heat-treated within a temperature range of 0.000C and has a single γ phase or a mixed structure of γ phase and α' phase.

The present invention also includes C: 0.15% or less Si: 3.0-7.0% Mn: 8.0% or less Ni: 8.0-13.0% Cr: 12.0-17.0% N: 0.10% or less Contains and further.

Nb: 1.0% or less, TL: 1.0% or less, V: 1.
Zr: 0% or less, Zr: 1.0% or less.

Contains one or two of Mo: 3.0% or less, Cu: 3.0% or less, and the remainder consists of Fe and unavoidable impurities, and Ni equivalent = Ni (%) + 0.6ONo (%) +9.69
(C+N)(%)+0.18Cr(%)-0,11Si
(%)” + 0.60 (Nb+Ti+V+Zr)(%
)+0.6ONo(%)+Cu(%)Ni
A high-strength, high-ductility stainless steel material having an equivalent value of 8.0 to 14.0 and having a single γ phase or a mixed structure of γ phase and α' phase is provided.

The present invention also includes C: o, ts% or less Si: 3.0-7.0% n: 8.0% or less Ni: 8.0-13.0% Cr:12.0-17.0% N: 0.10% or less Contains and further.

Nb: 1.0% or less, Ti: 1.0% or less, V: t
, 0% or less, Zr: 1.0% or less, and Mo: 3.0% or less, Cu: 3.0%
Contains one or two of the following, with the remainder consisting of Fe and unavoidable impurities, and.

Ni equivalent = Ni (%) + 0.60 Mn (%) + 9.69
(C+N)(%)+0.18Cr(%)-0.11Si
(%)” +0.60(Nb+TI+V+Z
r) (%)+0. f50 Cold rolling (α' phase treatment) on steel whose Ni equivalent value defined by Mo (%) + Cu (%) is within the range of 8.0 to 14.0 until it becomes substantially α' single phase. Provided is a method for producing a high-strength, high-ductility stainless steel material, which is characterized in that it has a γ single phase or a mixed structure of a γ phase and an α' phase by performing heat treatment within a temperature range of 600 to 900°C. It is.

Next, the reasons for limiting the steel composition in the steel of the present invention will be explained below.

C: C is an austenite (γ) forming element and is extremely effective in suppressing the formation of delta (δ) ferrite phase at high temperatures and strengthening martensite (α') phase induced by cold working. However, in the steel of the present invention, the Si content is high and the solid solubility limit of C is low, so when the C content is increased, Cr carbide precipitates at the grain boundaries, resulting in a decrease in intergranular corrosion resistance and ductility. The content shall be 0.15% or less.

Si: Sl is an essential element for exhibiting the high strength and high ductility characteristic of the steel of the present invention. Si contributes to solid solution strengthening of the γ phase and improves elongation, and Si contributes to solid solution strengthening of the γ phase and improves elongation.
It has the effect of facilitating α' phase processing. 3.0% or more of Si is required to exhibit these characteristics, but
If it is contained in a large amount, hot workability will deteriorate, so the upper limit is set to 7.
0%.

Mn: Like Ni, Mn is an austenite-forming element and is an element necessary to obtain an austenite structure in the annealed material. However, Mn is an element that increases the Ni equivalent, and if it is contained in a large amount, α' phase treatment by cold rolling becomes difficult, so the upper limit is set at 8.0%.

Ni:NL is a basic component of austenitic stainless steel and is a strong austenite phase stabilizing element.

In the steel of the present invention containing a large amount of Si, the Si content must be 8.0% or more in order to suppress the formation of δ ferrite and obtain a stable austenite phase in the annealed state. However, if it is contained in a large amount, the Ni equivalent will increase and the α' phase treatment by cold rolling will become difficult, so the upper limit is set at 13.0%.

Cr: Cr is a basic component of stainless steel and must be contained in an amount of 12.0% or more in order to obtain good corrosion resistance.

However, Cr is a ferrite-forming element, and when it is included in a large amount, a large amount of δ ferrite is generated.

Since hot workability decreases, the upper limit is set at 17.0%.

N: Similar to C, N contributes to solid solution strengthening, but if it exceeds 0.10%, blowholes will occur and a sound steel ingot will not be obtained, so this is the upper limit.

Nb, Ti, V, Zr: Nb4i, V and Zr suppress the grain growth of austenite grains that are generated with appropriate heat treatment after α' phase treatment by cold working, contributing to high strength and high ductility of steel. do. Also, Nb, Ti, V and Z
The addition of r also improves intergranular corrosion resistance. but.

If the amount added increases, δ ferrite is generated and hot workability deteriorates, so the upper limit for each is set at 1.0%.

No: P4o makes crystal grains finer, contributes to higher strength through solid solution strengthening, and is also effective in improving corrosion resistance, but if it is contained in a large amount, a large amount of delta (δ) ferrite is generated, and heat The upper limit is set to 3. since machinability decreases.
0%.

Cu: Like Ni, Cu is an austenite-forming element and contributes to stabilizing the γ phase. Further, like No, Cu contributes to improving corrosion resistance. However, if it is contained in a large amount, hot workability deteriorates, so the upper limit is set at 3.0%.

Next, the Ni equivalent, cold rolling rate, and heat treatment after α' phase treatment will be explained.

Ni equivalent: Ni equivalent is an index of γ stability against α' transformation, and is an empirical formula derived from experimental results. The lower the Ni equivalent, the easier the α' phase treatment by cold rolling becomes, which is preferable in terms of manufacturing. However, if it is too low, a martensitic phase is generated in the annealing state, making it impossible to obtain high ductility, so the lower limit is set at 8.0. On the other hand, as the Ni equivalent increases, α' transformation is suppressed and α' phase conversion becomes difficult, so the upper limit is set to 14.0.

Cold rolling ratio: The steel of the present invention is subjected to α' phase treatment by cold rolling, and the austenite grains produced by subsequent heat treatment are refined to achieve high strength and high ductility.

The cold rolling rate required for α′ phase treatment depends on the Ni equivalent.
The higher the i equivalent, the higher the cold rolling rate to be applied. When the Ni equivalent is in the range of 8.0 to 14.0, the applied cold rolling rate is different, and the smaller the Ni equivalent is.

The cold rolling reduction that should be applied becomes smaller.

Heat treatment: The steel of the present invention obtains high strength and high ductility by subjecting it to appropriate heat treatment after α' phase treatment by cold rolling.

At temperatures below 600°C, transformation from α' phase to γ phase does not occur, so high ductility cannot be obtained; at temperatures above 900°C, although γ phase is easily formed, γ phase grain growth occurs, resulting in a decrease in strength. This will lead to a decline. Therefore, the heat treatment temperature range after the α' phase treatment is set to 600 to 900°C. The holding time depends on the heat treatment temperature; at low temperatures, the time required for transformation to the γ phase increases, so a long heat treatment is required. In a high temperature range, transformation of the γ phase occurs rapidly, and if held for a long time, γ grains grow and the strength decreases, so it is preferable to treat in a short time.

(Specific Disclosure of the Invention) [Example] The characteristics of the steel of the present invention will be clarified through examples by comparing it with comparative steel.

Table 1 Table 1 shows the components of the invention steel and comparative steel.

Sample No. 1 to 12m is the steel of the present invention.

Sample No. 13.14 steel is comparative steel, 5US304 steel and 5US301 steel, respectively, and the Ni equivalent is within the range of the present invention, but the Si content is outside the range of the present invention.

Each steel is melted and forged in a 30 pupil high frequency induction melting furnace,
The material was hot rolled to a thickness of 3wn and 10 (lIIll), and then subjected to solution treatment to form a γ phase. After applying 60% cold rolling to this material and subjecting it to α' phase treatment,
A test piece was prepared by heat treatment at 825°C (0 to 10 minutes) (soaking). Comparative steels 5US304 and 30111 were made into γ phase by solution treatment and then cold rolled, and 60% cold rolled and then 650~b×2
Tensile tests were conducted on these test pieces to measure yield strength, tensile strength, and elongation.

Table 2 shows 30% cold rolled material at each end shown in Table 1.
Sample Nos. 1 to 4 as known from Table 2 showing the proof stress and tensile strength after heat treatment when obtaining % elongation.
As the S1 content increases, the yield strength and tensile strength of steel improve. In steel samples No. 5 to 12, the strength is improved by containing relatively large amounts of solid solution strengthening elements C and N. The strength is also increased by containing Nb, Ti, V, and Zr.

On the other hand, sample No. 1311 (SUS304) is a solution-treated material that has been cold-rolled, and has a yield strength of 60 kg/m and a tensile strength of 83 kg/m when elongating by 30%.
g/-2], and those subjected to heat treatment after 60% cold rolling have inferior strength compared to those subjected only to cold rolling.

Sample No. 14 steel (SUS301) is a solution-treated material that has been cold-rolled, and has a yield strength of 74 (kg/■8) and a tensile strength of 110 [kH/■2] when 30% elongation is obtained.
], and those subjected to heat treatment after 60% cold rolling have inferior strength compared to those subjected only to cold rolling.

〔Effect of the invention〕

The present invention reduces γ stability and improves α' by incorporating Si into Cr-Ni austenitic stainless steel.
A steel material that has high strength and high ductility through easy phase treatment and refines the reversely transformed austenite grains produced by applying appropriate heat treatment after cold rolling, solid solution strengthening of Si, and high ductility, and its production. This method provides an extremely high industrial value.

Claims (1)

[Claims] 1. In weight %: C: 0.15% or less Si: 3.0 to 7.0% Mn: 8.0% or less Ni: 8.0 to 13.0% Cr: 12. 0 to 17.0% N: Contains 0.10% or less, the remainder consists of Fe and unavoidable impurities, and Ni equivalent = Ni (%) + 0.60 Mn (%) + 9.69
(C+N)(%)+0.18Cr(%)-0.11Si
(%) The value of Ni equivalent defined as ^2 is 8.0 to 14.
0, and has a single austenite (γ) phase or a mixed structure of a γ phase and a martensite (α') phase. 2. In weight%, C: 0.15% or less Si: 3.0-7.0% Mn: 8.0% or less Ni: 8.0-13.0% Cr: 12.0-17.0% N: Contains 0.10% or less, the remainder consists of Fe and unavoidable impurities, and Ni equivalent = Ni (%) + 0.60 Mn (%) + 9.69
(C+N)(%)+0.18Cr(%)-0.11Si
(%) The value of Ni equivalent defined as ^2 is 8.0 to 14.
Substantially martensite (α′) in the steel within the range of 0
After cold rolling (α′ phase treatment) until it becomes a single phase,
A method for producing a high-strength, high-ductility stainless steel material, which is heat-treated within a temperature range of 600 to 900°C and has a single γ phase or a mixed structure of γ phase and α' phase. 3. In weight%, C: 0.15% or less Si: 3.0-7.0% Mn: 8.0% or less Ni: 8.0-13.0% Cr: 12.0-17.0% Contains N: 0.10% or less, further Nb: 1.0% or less, Ti: 1.0% or less, V: 1.0
% or less, Zr: 1.0% or less, the remainder consists of Fe and unavoidable impurities, and Ni equivalent = Ni (%) + 0.60 Mn (%) + 9.6
9(C+N)(%)+0.18Cr(%)-0.11S
i(%)^2+0.60(Nb+T1+V+Zr)(%
) is 8.0 to 14.0 and γ
A high-strength, high-ductility stainless steel material characterized by having a single phase or a mixed structure of γ phase and α' phase. 4. In weight%, C: 0.15% or less Si: 3.0-7.0% Mn: 8.0% or less Ni: 8.0-13.0% Cr: 12.0-17.0% Contains N: 0.10% or less, furthermore, Nb: 1.0% or less, Ti: 1.0% or less, V: 1.0
% or less, Zr: 1.0% or less, the remainder consists of Fe and unavoidable impurities, and Ni equivalent = Ni (%) + 0.60 Mn (%) + 9.6
9(C+N)(%)+0.18Cr(%)-0.11S
i(%)^2+0.60(Nb+Ti+V+Zr)(%
) is cold rolled (α'
Production of high-strength, high-ductility stainless steel material characterized by having a γ single phase or a mixed structure of γ' phase and α' phase by performing heat treatment within a temperature range of 600 to 900 ° C. Method. 5. In weight%, C: 0.15% or less Si: 3.0-7.0% Mn: 8.0% or less Ni: 8.0-13.0% Cr: 12.0-17.0% Contains N: 0.10% or less, furthermore, Nb: 1.0% or less, Ti: 1.0% or less, V: 1.0
% or less, Zr: 1.0% or less, and contains one or more of Mo: 3.0% or less, Cu: 3.0% or less, and the balance is Consists of Fe and unavoidable impurities, and Ni equivalent = Ni (%) + 0.60 Mn (%) + 9.69
(C+N)(%)+0.18Cr(%)-0.11Si
(%)^2+0.60(Nb+Ti+V+Zr)(%)
+0.60Mo(%)+Cu(%)The Ni equivalent value is 8.0 to 14.0 and has a γ single phase or a mixed structure of γ single phase and α' phase. High strength and ductility stainless steel material. 6. In weight%, C: 0.15% or less Si: 3.0-7.0% Mn: 8.0% or less Ni: 8.0-13.0% Cr: 12.0-17.0% Contains N: 0.10% or less, further Nb: 1.0% or less, Ti: 1.0% or less, V: 1.0
% or less, Zr: 1.0% or less, and contains one or more of Mo: 3.0% or less, Cu: 3.0% or less, and the balance is Consists of Fe and unavoidable impurities, and Ni equivalent = Ni (%) + 0.60 Mn (%) + 9.69
(C+N)(%)+0.18Cr(%)-0.11Si
(%)^2+0.60(Nb+Ti+V+Zr)(%)
+0.60Mo (%) +Cu (%) Steel having a Ni equivalent value in the range of 8.0 to 14.0 is subjected to cold rolling (α' phase) until it becomes substantially α' single phase. 1. A method for producing a high-strength, high-ductility stainless steel material, which is characterized in that the stainless steel material is subjected to heat treatment within a temperature range of 600 to 900° C. to have a γ single phase or a mixed structure of γ phase and α' phase.