JPH1150143A - Production of two phase stainless steel excellent in workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a stainless steel excellent in the workability showing good elongation by air-cooling or forcedly cooling to the temp. range depositing austenitic phase after heating the steel to the temp. becoming ferritic single phase range and hot-working in this temp. range. SOLUTION: In a process for hot-rolling or hot-forging the steel, when T1 is the temp. becoming the ferritic single phase in the steel, the steel is heated to a temp. T represented by T1 <=T<=T1 +100 deg.C, preperably to about 1200-1300 deg.C. When T2 is the temp. range depositing the austenitic phase in this steel, the steel is air-cooled or forcedly cooled to the temp. range of T1 -150<=T2 <=T1 deg.C, preferably to about 1150-1200 deg.C and the hot-working is started in two phase range of the ferite-austenite in the steel structure. By this method, two phase stainless steel sheet to which a complicate working can be executed and the breakage of whose pressed product developed at the time of forming can be effectively prevented, is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing a polymer having excellent workability.
With regard to a method for producing a duplex stainless steel, a method for producing a duplex stainless steel strip / plate showing particularly good elongation is proposed.

[0002]

2. Description of the Related Art A duplex stainless steel sheet has excellent corrosion resistance and high strength, and is therefore used as a device and equipment for various chemical industries. However, such a duplex stainless steel has a problem that elongation is lower than that of austenitic stainless steel represented by SUS-304, so that press working is restricted.

In this regard, in order to improve the workability of the duplex stainless steel, Japanese Patent Publication No. 60-59017 discloses an annealing temperature (T-100) ° C. or higher (T: temperature at which a ferrite single phase is formed). Annealed hot rolled sheet at, cold rolled, annealing temperature 10
A method for producing a duplex stainless steel having excellent workability by performing cold-rolled sheet annealing in the range of 00 to (T-150) ° C has been proposed.

In Japanese Patent Publication No. 8-41594,
Excellent workability by defining the rolling start temperature, end temperature, inter-pass time, number of passes and rolling reduction in hot rolling, and further defining the hot-rolled sheet annealing temperature and cold-rolled sheet annealing temperature 2
A method for producing duplex stainless steel is proposed.

[0005]

However, with respect to these conventional manufacturing methods, in the former case, the hot-rolled sheet annealing is performed by (T-
Since it is performed at a high temperature of 100) ° C. or higher (T: temperature at which a single phase of ferrite is formed), there is a problem that the hot-rolled sheet is softened in a heating furnace, breaks, and the operation is stopped. On the other hand, in the latter case, no mention is made of the ferrite and austenite phase ratios at the time of heating and at the start of hot rolling, and 2
The cause of the elongation characteristics of the duplex stainless steel sheet is not clear, but there is a problem that the variation is large.

An object of the present invention is to propose a technique for inexpensively producing a duplex stainless steel exhibiting good elongation and excellent workability. Another object of the present invention is to propose an advantageous production method for obtaining a duplex stainless steel excellent in workability, which does not have press breaks often observed in press forming and enables more complex press. is there.

[0007]

Means for Solving the Problems Conventional techniques for improving the workability of a duplex stainless steel are techniques focusing on hot rolling conditions and subsequent annealing conditions. As a result of intensive research on this matter, the inventors have been able to produce a duplex stainless steel having excellent workability (elongation at room temperature) by controlling the structure of the steel slab before hot rolling or forging. , And the present invention has been developed.

That is, according to the present invention, in producing a duplex stainless steel strip or plate comprising austenite and ferrite, the steel is heated to a temperature in a ferrite single phase region in a hot rolling or hot forging step. This is a method for producing a duplex stainless steel excellent in workability, characterized in that cooling or forced cooling is performed to a temperature range in which an austenite phase is precipitated, and hot working is started in that temperature range.

Further, in the present invention, in the production of a duplex stainless steel strip or plate comprising austenite and ferrite, the temperature T _{1 at} which ferrite becomes a single phase and the hot deformation are reduced in a hot rolling or hot forging step. T ₂ to start temperature
To time, followed by heating the steel to a temperature in the range of _{T 1 ≦ T 1 +100 ℃,} T 1 and - 150 to initiate hot working in Kitaichi has a temperature in the range of ≦ T ₂ ≦ T ₁ ℃ This is a method for producing a duplex stainless steel having excellent workability. Further, in the present invention, in the production of a duplex stainless steel strip or plate comprising austenite and ferrite, in a hot rolling or hot forging step, the steel is heated to a temperature in a ferrite single phase region, and then the austenite phase is heated. It is allowed to cool or forcibly cool to the temperature range in which is deposited, start hot working in that temperature range, then annealed the obtained hot rolled sheet, and then perform cold rolling and cold rolled sheet annealing. This is a method for producing a duplex stainless steel excellent in characteristic workability.

[0010] Further, the present invention relates to a method for producing a duplex stainless steel strip or plate comprising austenite and ferrite, in a hot rolling or hot forging step, a temperature T _{1 at} which a ferrite single phase is formed, and a hot deformation. T ₂ to start temperature
When the, then heating the steel to a temperature in the range of _{T 1 ≦ T 1 +100 ℃,} T 1 - hot working and start Kitaichi has a temperature of 0.99 ≦ T in the range of ₂ ≦ T ₁ ° C., Next, a method for producing a duplex stainless steel excellent in workability, characterized by annealing the obtained hot-rolled sheet and thereafter performing cold rolling and cold-rolled sheet annealing, is proposed.

Further, in the present invention, in producing a duplex stainless steel strip or plate comprising austenite and ferrite, C: 0.03 wt% or less, Si: 2.0 wt% or less, Mn: 3.0 wt%.
Below, P: 0.045wt% or less, S: 0.005wt% or less, Cr: 20.0
~ 35.0wt%, Ni: 3.0 ~ 10.0wt%, Mo: 0.5 ~ 6.0wt%, C
u: 2.0 wt% or less, B: 0.01 wt% or less, N: 0.08 to 0.3 wt%,
And a steel slab containing at least one of W: 0.03 to 2.0 wt% and V: 0.03 to 2.0 wt%, with the balance being Fe and unavoidable impurities, heated to a temperature of 1200 to 1300 ° C. After the structure to ferrite single phase, 1150 ~ 1200 ℃
After cooling or forced cooling to a temperature to precipitate an austenitic phase, hot rolling is performed, the obtained hot rolled sheet is annealed, and then cold rolling and cold rolled sheet annealing are performed. We propose a method for producing duplex stainless steel with excellent workability.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a duplex stainless steel according to the present invention is characterized in that elongation characteristics at room temperature are improved by devising the processing conditions in the hot rolling or hot forging process. There is a feature in the configuration.

In order to obtain the desired effect of the present invention, the structure of the steel slab before starting the hot working needs to be once a ferrite single phase. Therefore, the heating temperature of the steel slab at this stage is a temperature at which the ferrite becomes a single phase. However, in practice, if the temperature is raised excessively, the strength of the steel slab will decrease, and it will buckle in the heating furnace, making hot rolling or forging impossible. Therefore, in the present invention, the heating temperature of the steel slab is set to T ₁ ≦ T ≦ T ₁ + 100 ° C. (however, the temperature at which the T ₁ ferrite single phase is formed). In addition, in a component system such as the steel slab described above, the heating temperature is preferably in a range of 1200 to 1300 ° C.

Further, in the present invention, it is necessary to control the temperature at which hot working is started. That is, the start of hot rolling or forging starts when the steel structure starts in the ferrite-austenite two-phase region. For example, if hot rolling or forging is started in the single phase region of ferrite, good elongation cannot be obtained. On the other hand, when the hot working start temperature is too low, the σ phase is precipitated, and the elongation of the material also tends to decrease. Preferred hot working starting temperature (T ₂ )
Is T ₁ −150 ≦ T ₂ ≦ T ₁ ° C. (T ₁ : temperature at which a ferrite single phase is formed).

As described above, in the present invention, the temperature at which hot working is started is set to a temperature at which the ferrite-austenite two-phase region is reached. In addition, in the component system such as the steel slab described above,
The hot working start temperature is preferably in a temperature range of 1150 to 1200 ° C. The steel slab used in the present invention is basically J
Duplex stainless steel or the like specified in IS-G4304 and JIS-G4305 is advantageously used. In particular, it is preferable to use a duplex stainless steel having the above component composition. Hereinafter, the component composition of the duplex stainless steel preferred in the present invention will be described in detail.

C: not more than 0.03 wt% C is not only an element that lowers the corrosion resistance of stainless steel, but also causes hardening during cold rolling, making subsequent processing difficult. Therefore, C is set to 0.03 wt% or less, preferably 0.02 wt% or less.

Si: 2.0 wt% or less Si is known as a very effective element for improving corrosion resistance, but promotes precipitation of the σ phase and causes embrittlement. Therefore, Si is 2.0 wt% or less, preferably 0.5 to
Within 1.0 wt%.

Mn: 3.0 wt% or less Mn acts as a deoxidizing element at the time of melting and refining, but if contained in an excessively large amount, the corrosion resistance is deteriorated.
3.0 wt% or less, preferably 0.5 to 2.0 wt%.

P: 0.045 wt% or less P is an element harmful to corrosion resistance, so the smaller the better, the better.
However, excessive reduction of the content requires special smelting technology and leads to an increase in production cost.
% Needs to be controlled.

S: 0.005 wt% or less S is an element that precipitates at the grain boundary of ferrite-austenite to deteriorate hot workability and also has an adverse effect on corrosion resistance. In particular, this S amount
If the content exceeds 0.005 wt%, the effect becomes remarkable.
Shall be 0.005 wt% or less.

Cr: 20.0-35 wt% Cr is one of the ferrite forming elements contributing to the improvement of corrosion resistance, and is also a sigma phase constituent element. Cr content is 20.0wt
%, The corrosion resistance and oxidation resistance are insufficient, while the Cr content exceeding 35.0 wt% deteriorates the toughness. Therefore,
Cr is 20.0 to 35.0 wt%, preferably 23.0 to 27.0 wt%.

Ni: 3.0 to 10.0 wt% Ni is an austenite-forming element. If the content of Ni is less than 3.0 wt%, the ratio of the γ phase is too small even when adjusted by other ferrite-forming elements or austenite-forming elements.
If it exceeds 10.0 wt%, not only will the ratio of the γ phase become unnecessarily high, but also the cost will increase. Therefore, Ni is 3.0
To 10.0 wt%, preferably 5.0 to 8.5 wt%.

Mo: 0.5 to 6.0 wt% Mo is used to improve corrosion resistance such as pitting corrosion resistance and crevice corrosion resistance.
It is also an element that contributes to solid solution strengthening. This Mo content
If it is less than 0.5 wt%, the effect of the addition is ineffective, while 6.0 wt%
If it exceeds, the toughness is deteriorated, and the production cost is increased.
Therefore, Mo is 0.5 to 6.0 wt%, preferably 1.0 to 4.
0 wt%.

Cu: 2.0 wt% or less Cu is an element that contributes to improvement of corrosion resistance.
If added in excess of, the hot workability is significantly degraded. Therefore, the Cu content is 2.0 wt% or less, preferably 1.5 wt% or less.

B: 0.01 wt% or less B is an element which exists at the grain boundary of the alloy when added in a small amount and improves the hot workability. However, at the same time, it is also an element that deteriorates corrosion resistance such as intergranular corrosion. Therefore, the content of B is set to 0.01 wt% or less, preferably 0.005 wt% or less.

N: 0.08 to 0.3 wt% N is an austenite-forming element like C, and therefore, the N content must be determined from the composition under the balance with other ferrite-forming elements. This N is
There is also an effect of improving pitting corrosion resistance, and the content of N must be at least 0.08 wt%. However, if the content exceeds 0.3 wt%, the hot workability deteriorates. Therefore, the content is set to 0.08 to 0.3 wt%, preferably 0.10 to 0.20 wt%.

W: 2.0 wt% or less, V: 2.0 wt% or less Both W and V are ferrite forming elements and are effective elements for improving the local corrosion resistance. However, adding less than 0.03 wt% has no effect, while adding more than 2.0 wt% deteriorates hot workability due to deterioration of toughness and is disadvantageous in terms of manufacturing cost. Therefore, the addition amounts of W and V are both 0.
03 to 2.0 wt%, preferably 0.05 to 0.24 wt%.

[0028]

EXAMPLE A slab of a duplex stainless steel having the composition shown in Table 1 was heated under the conditions shown in Table 2, hot-rolled, then hot-rolled sheet annealing, cold-rolled sheet, and cold-rolled sheet annealing. Thus, a cold-rolled sheet having a thickness of 1.5 mm was obtained. The measured elongation (%)
This is a numerical value obtained by performing a mechanical test in a direction perpendicular to the rolling direction according to No. 13B specified in JIS-Z2201. The results obtained are shown in Table 2. As is clear from the results shown in Table 2, it was found that the duplex stainless steel manufactured according to the present invention had improved elongation as compared with the one manufactured by the conventional manufacturing method. That is, by applying the method of the present invention, it is possible to produce a duplex stainless steel having excellent workability.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

As described above, according to the present invention,
Duplex stainless steel having good workability, particularly good elongation characteristics, can be produced at low cost. In addition, the duplex stainless steel sheet manufactured according to the method of the present invention can be subjected to complicated processing, can effectively prevent breakage of a pressed product at the time of forming, and reduce the cost of the processed product. Can be.

Claims (5)

[Claims] In the production of a duplex stainless steel strip or plate comprising austenite and ferrite, in a hot rolling or hot forging step, after the steel is heated to a temperature in a ferrite single phase region, the austenitic phase is heated. Excellent workability characterized by cooling or forcibly cooling to the temperature range where precipitation occurs, and starting hot working in that temperature range 2
Method of manufacturing duplex stainless steel. 2. A method for producing a duplex stainless steel strip or plate composed of austenite and ferrite, wherein a temperature T _{1 at} which ferrite becomes a single phase and a temperature at which hot deformation is started in a hot rolling or hot forging step. when the T _2, then heating the steel to a temperature in the range of _{T 1 ≦ T 1 +100 ℃,} T 1 -
A method for producing a duplex stainless steel having excellent workability, characterized in that hot working is started by bringing a temperature within a range of 150 ≦ T ₂ ≦ T ₁ ° C. 3. In the production of a duplex stainless steel strip or plate comprising austenite and ferrite, in a hot rolling or hot forging step, after the steel is heated to a temperature in a ferrite single phase region, the austenitic phase is turned into a ferrite single phase region. Allow to cool or forcibly cool to the temperature range where precipitation occurs, start hot working in that temperature range, then annealed the obtained hot rolled sheet,
A method for producing a duplex stainless steel having excellent workability, characterized by subsequently performing cold rolling and cold rolled sheet annealing. 4. When producing a duplex stainless steel strip or plate comprising austenite and ferrite, in the hot rolling or hot forging step, the temperature T _{1 at} which the ferrite becomes a single phase and the temperature at which hot deformation starts are defined. when the T _2, then heating the steel to a temperature in the range of _{T 1 ≦ T 1 +100 ℃,} T 1 -
The hot working is started by bringing the temperature within the range of 150 ≦ T ₂ ≦ T ₁ ° C., then the obtained hot-rolled sheet is annealed, and then cold-rolled and cold-rolled sheet annealing are performed. Method for producing duplex stainless steel with excellent workability. 5. A method for producing a duplex stainless steel strip or plate comprising austenite and ferrite, wherein C: 0.03 wt.
%, Si: 2.0 wt% or less, Mn: 3.0 wt% or less, P: 0.045 wt%
%, S: 0.005wt% or less, Cr: 20.0-35.0wt%, Ni:
3.0 to 10.0 wt%, Mo: 0.5 to 6.0 wt%, Cu: 2.0 wt% or less,
B: 0.01 wt% or less, N: 0.08 to 0.3 wt%, and W: 0.03
~ 2.0wt%, V: 0.03 ~ 2.0wt%
A steel slab containing seeds and the balance consisting of Fe and inevitable impurities was heated to a temperature of 1200 to 1300 ° C to make the structure a ferrite single phase, and then allowed to cool or forcibly cooled to a temperature of 1150 to 1200 ° C. Hot-rolled after precipitating the austenite phase by annealing, annealing the obtained hot-rolled sheet, and then performing cold-rolling and cold-rolled sheet annealing. Steel production method.