JPH07258789A - Steel excellent in high temperature strength and its production - Google Patents

Abstract

PURPOSE:To obtain a steel capable of reducing the content of rare metals and dealing with various needs by introducing a new heat treating method into a steel having a specified compsn. contg. Nb and Mo and allowing specified amounts of Nb and Mo to exist in a solid solution state. CONSTITUTION:A slab having a compsn. contg., by weight, 0.04 to 0.25% C, 0.03 to 0.60% Si, 0.30 to 2.0% Mn, <=0.025% P, <=0.015% S and 0.001 to 0.10% Al and contg. one or more kinds among 0.01 to 0.10% Nb and 0.30 to 1.01% Mo is used. The steel is produced while the slab is heated to 1100 to 1350 deg.C, and immediately quenched after the completion of rolling at 1000 deg.C to the Ar3 point or above, or acceleratedly cooled. Then, the steel excellent in high temp. strength in which one or more kinds of 0.007 to 0.07% Nb and 0.15 to 0.50% solid solution Mo are present in a solid solution state can be obtd. Moreover, the steel may be incorporated with one or more kinds of 0.05 to 1.0% Cu and 0.05 to 1/.5% Ni and/or <=10.0% Cr and/or 0.005 to 0.10% V and/or 0.005 to 0.03% Ti and/or 0.0003 to 0.002% B.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to high-temperature strength or creep strength of various structures in the fields of steel, boilers, pressure vessels, etc., which are excellent in fire resistance of various structures in the fields of construction, civil engineering, marine structures, etc. The present invention relates to an excellent steel material manufacturing method. Incidentally, as the steel material, JIS G3103, JI
S G3109, JIS G3120, JIS G410
9, steel materials such as JIS G4110 and Nippon Steel Technique No. Three
48, p55 (1993) is a newly developed refractory steel material for construction that will be standardized in the future.

[0002]

2. Description of the Related Art As is well known, the above-mentioned steel material is manufactured as it is by rolling or by heat treatment (normalization, quenching) and subsequent tempering. Further, with the recent progress of TMCP technology, a part of heat treatment may be replaced with TMCP. Therefore, the chemical composition required for the steel material is determined by the plate thickness and the heat treatment method, and cannot be largely changed.
On the other hand, by adopting TMCP, we have achieved the target in terms of process saving such as omission of normalization and direct quenching of quenching, but from the viewpoint of resource saving, even in that case, a small amount of a small amount effective for improving weldability etc. However, the reality was that the chemical components could not be reduced. Therefore, it is not possible to meet the further resource saving needs centered on the significant reduction of rare metals caused by the manifestation of global environmental problems (requirement of ecological).

For example, Japanese Examined Patent Publication No. 4-50362 relates to a method of manufacturing a low yield ratio steel material for construction having excellent fire resistance, but in the step of manufacturing a steel sheet, a precipitate is formed to make maximum use of precipitation strengthening. That is the basic idea. On the other hand, in the present invention, the basic idea is that precipitates are not formed as much as possible in the steel sheet manufacturing stage, and are present in the steel in the form of solid solution Nb or solid solution Mo in the solid solution state. The formation of precipitates of solid solution Nb or solid solution Mo for the first time when exposed to
Alternatively, Mo is used to improve the high temperature strength extremely effectively.

Further, Japanese Patent Application Laid-Open No. 2-163341 relates to a structural steel material having excellent fire resistance and a method for manufacturing the structural steel material. The addition of V or the combined addition of Mo and V started the movement at the time of deformation at high temperature. The basic idea is to precipitate these carbides at dislocations. Therefore, there is no idea to use mainly solid solution Nb or solid solution Mo to improve the high temperature strength, mainly for V, where solid solution and precipitation are extremely easily performed. Therefore, in the manufacturing method, the effect on the high temperature strength does not change by air cooling, accelerated cooling, and normalizing after the completion of rolling, and the idea of increasing solid solution Nb or solid solution Mo is not recognized. Further, as is apparent from the reason why Nb is limited, stable carbonitrides are formed at the stage of manufacturing a steel sheet to improve the fire resistance strength of the steel.

On the other hand, the basic idea of the present invention is to increase the high temperature strength by not forming precipitates in the steel sheet manufacturing stage as much as possible and allowing solid solution Nb or solid solution Mo to exist in the steel in a solid solution state. Therefore, the production method is limited to producing steel with direct quenching or with accelerated cooling to secure the solid solution amount of these rare metals, and precipitates are not formed until the steel is exposed to high temperature. By producing a small amount of a rare metal, that is, Nb or Mo, the high temperature strength is effectively improved.

Further, JP-A-58-217661 relates to heat-resistant steel. Mo or Nb forms carbonitrides to improve high temperature strength and temper softening characteristics.
The basic idea is to improve temper brittleness. Therefore, there is no idea to control the solid solution Nb or the solid solution Mo,
As for the heat treatment, tempering is performed after general quenching.
On the other hand, the present invention effectively improves the high temperature strength by allowing solid solution Nb or solid solution Mo to exist in the steel in a solid solution state. Therefore, the heat treatment after the rolling is directly quenched or accelerated cooling. The basic idea is to limit it as it is.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a steel material excellent in high temperature strength, which can greatly reduce the use of rare metals by introducing a new heat treatment method by changing the way of thinking for heat treatment and which can meet the resource saving needs. It is to provide the manufacturing method.

[0008]

The present invention makes it possible to significantly reduce the use of rare metals by producing steel while quenching or accelerating cooling immediately after completion of hot rolling or by performing low temperature tempering as necessary. A steel material excellent in high-temperature strength and a manufacturing method thereof. That is, the gist of the present invention is as follows. (1) By weight ratio, C: 0.04 to 0.25%, Si:
0.03-0.60%, Mn: 0.30-2.0%, P
≦ 0.025%, S ≦ 0.015%, Al: 0.001
.About.0.10%, Nb: 0.01 to 0.10%,
Mo: 0.30 to 1.10% in steel containing one or two kinds of solid solution Nb: 0.007 to 0.07%, solid solution M
o: A steel material having excellent high-temperature strength, characterized in that 0.15 to 0.50% of one or two kinds are present in the steel in a solid solution state. (2) By weight ratio, Cu: 0.05 to 1.0%, Ni:
0.05 to 1.5% of one or two and / or Cr ≦ 1
0.0% and / or V: 0.005 to 0.10% and / or
Or Ti: 0.005 to 0.03% and / or B: 0.
A steel material excellent in high temperature strength as described in (1) above, which contains 0003 to 0.002%.

(3) By weight ratio, C: 0.04 to 0.25
%, Si: 0.03 to 0.60%, Mn: 0.30
2.0%, P ≦ 0.025%, S ≦ 0.015%, A
1: 0.001 to 0.10%, Nb: 0.01
~ 0.10%, Mo: 0.30 to 1.10%, after heating a steel slab containing one or two kinds to 1100 to 1350 ° C,
A method for producing a steel material having excellent high-temperature strength, which comprises producing steel immediately after quenching at 1000 ° C. to Ar ₃ points or higher and immediately after quenching or with accelerated cooling. (4) Cu: 0.05-1.0% and Ni: 0.
05 to 1.5% of one or two and / or Cr ≦ 10.
0% and / or V: 0.005 to 0.10% and / or Ti: 0.005 to 0.03% and / or B: 0.00
03-0.002% is contained, The manufacturing method of the steel material excellent in high temperature strength of said (3) characterized by the above-mentioned. (5) The method for producing a steel material excellent in high temperature strength according to the above (3) or (4), characterized by performing tempering in a temperature range of 150 to 450 ° C.

[0010]

The present inventor has made a detailed investigation on the influence of the heat treatment method and the chemical composition on the high temperature strength of the steel material. As a result, depending on the type of the chemical composition, the existence state in the steel and the high temperature strength and hence the creep strength are closely related. I found a relationship. That is, if a rare metal that forms a strong nitride such as Nb or Mo is solidly supersaturated in the steel material before being subjected to high temperature, it will be supersaturated when the steel material is exposed to a high temperature condition such as a fire or an operation at a high temperature. Nb and Mo which are solid-solved in the solution form precipitates, and this high temperature precipitation strengthening causes high temperature strength (creep strength).
Have been found to significantly improve.

As a result, the steel is heated to a temperature above the temperature at which these rare metals form a solid solution, and after hot rolling is completed, the steel is immediately quenched or accelerated cooled to produce the steel, thereby supersaturating the rare metals in the steel. By making a solid solution in
The inventors have invented a steel material excellent in high-temperature strength in which the amount of rare metals used is greatly reduced, and a manufacturing method thereof. Furthermore, from the viewpoints of shape correction and residual stress relaxation, it is of course possible to obtain the same effect as long as the amount of the rare metal dissolved in supersaturated solid solution in the steel does not change even if low-temperature tempering is performed if necessary. While turned out.

The present invention will be described in detail below. C is
If it is less than 0.04%, the strength is not satisfied, and if it exceeds 0.25%, low temperature toughness and weldability are impaired, so 0.04 to 0.25%.
Limited. Si must be 0.03% or more on deoxidation,
If it exceeds 0.60%, the low temperature toughness and the weldability are impaired, so that
It was limited to 03 to 0.60%. When temper brittleness is a problem, Si is preferably 0.03 to 0.10%. Mn needs to be 0.30% or more in terms of strength, and is 2.0
%, If it exceeds 0.3%, the low temperature toughness and weldability are impaired.
Limited to 2.0%. When temper brittleness is a problem, Mn is preferably 0.30 to 0.60%.

The lower the impurities such as P and S, the more preferable. P is limited to 0.025% or less and S is limited to 0.015% or less. Furthermore, when the lamellar tear resistance is required due to the shape of the structure, S is controlled to 0.003% or less, and morphology control of MnS using Ca or REM is also necessary. Al is an important element for deoxidation, but Si or Ti
Deoxidation is also carried out, the lower limit is 0.001
% Or more, and if it exceeds 0.10%, the weldability and the cleanliness due to inclusions are impaired, so 0.001 to 0.10% is restricted.

Nb is set to 0.01% or more in order to secure a solid solution Nb amount of 0.007% or more immediately after hot rolling or with accelerated cooling, and if it exceeds 0.10%, low temperature toughness is obtained. , 0.01 to 0.10 to impair the weldability
Limited to%. Mo is set to 0.30% or more in order to secure a solid solution Mo amount of 0.15% or more immediately after the hot rolling is finished, while being quenched or accelerated cooled. If it exceeds 1.10%, low temperature toughness and weldability are obtained. 0.30 to 1.10 to damage
Limited to%.

If the solid solution Nb exceeds 0.07%, the low temperature toughness and weldability are impaired, and if it is less than 0.007%, the required improvement in high temperature strength cannot be obtained, so 0.007 to 0.07.
Limited to%. If the solid solution Mo exceeds 0.50%, the low-temperature toughness and weldability are impaired, and if it is less than 0.15%, the required high-temperature strength cannot be obtained, so the content is limited to 0.15 to 0.50%. Cu is added in an amount of 0.05% or more in order to improve low temperature toughness and ensure strength, and if it exceeds 1.0%, it is limited to 0.05 to 1.0% to promote hot embrittlement.

Ni is added in an amount of 0.05% or more in order to improve the low temperature toughness and secure the strength. If it exceeds 1.5%, the effect is saturated, so Ni is limited to 0.05 to 1.5%. Cr is
It is an important element for high temperature strength. 1.
25%, 2.25%, 3%, 9% were added as targets, and 1
It was limited to 0.0% or less. Generally, 0.05% or more is added to the refractory steel or the like in terms of strength, and if it exceeds 1.0%, the weldability is impaired, so the content is preferably 0.05 to 1.0%. V is added in an amount of 0.005% or more for improving the strength, and if it exceeds 0.10%, it is limited to 0.005 to 0.10% to impair the weldability and the low temperature toughness.

Ti is added in an amount of 0.005% or more to prevent cracking during casting and to improve joint toughness. If it exceeds 0.03%, it deteriorates weldability and low temperature toughness, and 0.005 to 0.03 is added.
Limited to%. B is added in an amount of 0.0003% or more in terms of strength, and the addition of more than 0.002% impairs weldability and low-temperature toughness, and is therefore limited to 0.0003 to 0.002%. In the case of adding Ca or REM from the viewpoint of lamella tear resistance, etc., C
a: 0.001 to 0.008%, REM: 0.001 to
0.005% is preferable.

The heating temperature is set to 1100 ° C. or higher in order to form a solid solution of Nb and Mo added to steel, and if it exceeds 1350 ° C., various problems such as scale may occur in operation, and therefore 1100 to 100 ° C.
Limited to 1350 ° C. End temperature of hot rolling is 1000 ℃
If it exceeds the above value, the crystal grains become coarse and the low temperature toughness is impaired. If it is less than the Ar ₃ point, carbonitrides of Nb and Mo are precipitated during rolling, and necessary solid solution Nb or solid solution Mo cannot be secured.
It was limited to 0 ° C to Ar ₃ points. Note that, when controlled rolling is performed, work-induced precipitation occurs, so a rolling end temperature of 1000 to 850 ° C. is preferable in order to prevent a decrease in solid solution Nb or solid solution Mo, particularly solid solution Nb.

Quenching is limited to direct quenching performed immediately after the completion of rolling to secure solid solution Nb and solid solution Mo, or accelerated cooling by the recently developed TMCP technique. Accelerated cooling is performed immediately after rolling at a cooling rate of 30 to 1 ° C / sec.
It is desirable to keep cooling to any temperature below ℃. Although it depends on the plate thickness, the cooling rate does not change from the cooling rate of direct quenching at 30 ° C / sec or more and does not change from the cooling rate of air cooling at less than 1 ° C / sec. Therefore, the cooling rate is 30 to 1 ° C / sec. Constrained. Further, if the temperature exceeds 450 ° C., precipitates are likely to be generated, so it was decided to accelerate cooling to 450 ° C. or less.

It is desirable not to carry out tempering in principle, but if it is absolutely necessary from the viewpoint of shape correction and residual stress relaxation, solid solution N in the temperature rising process is required.
150 to 450 with little precipitation of carbonitrides of b and solid solution Mo
Limited to low temperature tempering at ℃. The shorter the tempering time is, the more preferable it is for 2 hours or more.

[0021]

[Examples] The chemical components are shown in Table 1 and the results are shown in Table 2. The steels A to E of the invention examples and the steel F of the comparative examples were heated at 1250 ° C., and then hot rolling was terminated at 850 ° C. or 800 ° C. Steel F of the invention examples of Steel A to Steel E and Comparative Example was immediately quenched (DQ or TMCP) after completion of rolling. Steel C of the invention example was tempered at a low temperature of 450 ° C. to relax the residual stress after press straightening. On the other hand, in Comparative Examples of Steel A, Steel C, and Steel E, quenching or normalization was performed after air cooling after the completion of rolling.

[0022]

[Table 1]

[0023]

[Table 2]

The solid solution Mo or solid solution Nb of steels A to E as the invention examples in which the heat treatment of the present invention is carried out is within the scope of the present invention. On the other hand, solid solution Mo or solid solution Nb of steel A, steel C, and steel E as comparative examples not subjected to the heat treatment of the present invention
Is outside the scope of the present invention. Although the heat treatment of the present invention is carried out, the chemical composition is outside the scope of the present invention.
The solid solution Mo or solid solution Nb is outside the scope of the present invention. From Table 2, the high temperature strength at 600 ° C. is clearly higher in the invention examples in which the solid solution Mo or the solid solution Nb is within the scope of the present invention as compared with the comparative example. Therefore, according to the present invention, not only the process saving but also the high temperature strength can be improved, and if the same high temperature strength is targeted, it is possible to significantly reduce the rare metals.

[0025]

INDUSTRIAL APPLICABILITY The present invention uses a new heat treatment method, that is, by heating a steel material to a temperature at which a rare metal is solid-solved or above and finishing hot rolling, immediately producing a steel material with quenching or accelerated cooling. By providing a supersaturated solid solution of a metal in steel, the present invention provides a method for manufacturing a steel material excellent in high temperature strength in which the amount of a rare metal used is greatly reduced, and at the same time, a method capable of saving a process. This enables a rational manufacturing method of steel materials excellent in high temperature strength at the same time as resource saving needs for global environmental problems, and it is thought that there are enormous benefits not only to industry but also to humanity as a whole.

Claims (5)

[Claims] 1. C: 0.04 to 0.25% by weight, Si: 0.03 to 0.60%, Mn: 0.30 to 2.0%, P ≤ 0.025%, S ≤ 0.015%, Al: 0.001 to 0.10% contained, Nb: 0.01 to 0.10%, Mo: 0.30 to 1.10% in steel containing one or two kinds. Solid solution Nb: 0.007 to 0.07%, solid solution Mo: 0.15 to 0.50% of one or two kinds are present in the steel in a solid solution state, which is excellent in high temperature strength. Steel material. 2. A weight ratio of Cu: 0.05 to 1.0%, N
i: 0.05 to 1.5% of one or two and / or Cr
≦ 10.0% and / or V: 0.005 to 0.10% and / or Ti: 0.005 to 0.03% and / or B:
The steel material excellent in high-temperature strength according to claim 1, wherein the steel material contains 0.0003 to 0.002%. 3. By weight ratio, C: 0.04 to 0.25%, Si: 0.03 to 0.60%, Mn: 0.30 to 2.0%, P ≤ 0.025%, S ≤ Steel slab containing 0.015%, Al: 0.001 to 0.10%, Nb: 0.01 to 0.10%, Mo: 0.30 to 1.10%. After heating to 1100 to 1350 ° C, 1000 ° C to A
A method for producing a steel material excellent in high-temperature strength, which comprises producing steel immediately after quenching or accelerated cooling after completion of rolling at r ₃ points or more. 4. Cu: 0.05-1.0% by weight ratio, N
i: 0.05 to 1.5% of one or two and / or Cr
≦ 10.0% and / or V: 0.005 to 0.10% and / or Ti: 0.005 to 0.03% and / or B:
The method for producing a steel material excellent in high-temperature strength according to claim 3, wherein the steel material contains 0.0003 to 0.002%. 5. The method for producing a steel material excellent in high temperature strength according to claim 3 or 4, wherein tempering is performed in a temperature range of 150 to 450 ° C.