JPH08199310A - Production of high strength martensitic stainless steel member - Google Patents

Abstract

PURPOSE: To produce a high strength martensitic stainless steel member by subjecting a slab having a specified compsn. to hot rolling and cooling under specified conditions, working the same to a prescribed shape and executing quenching heat treatment to form its structure into a one essentially consisting of martensite. CONSTITUTION: A slab having a compsn. contg., by weight, 0.01 to 1.0% Si, 0.02 to 3.0% Mn, 7.5 to 14.0% Cr, 1.5 to 4.5% Cu, 0.2 to 1.0% Ni and 0.005 to 0.5% Al, in which the contents of C is reduced to <=0.05%, N to <=0.03%, P to 0.03% and S to <=0.01%, and the balance Fe with inevitable impurities is heated to 1050 to 1300 deg.C. Next, it is subjected to hot rolling so as to regulate the cumulative draft at <=1050 deg.C to >=65% and the rolling finishing temp. to >=800 deg.C and is cooled at a cooling rate of <=0.05 deg.C/sec till at least 500 deg.C to form into a steel having a metallic structure in which the ferrite fractional rate is regulated to >=50%. Moreover, it is subjected to cold or warm working into the shape of a prescribed shape and is subjected to quenching heat treatment or quenching and tempering heat treatment, by which the stainless steel member having a metallic structure essentially consisting of martensite can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-strength martensitic stainless steel member, and more specifically, it contains, for example, 7.5% or more of Cr and is cold or warm during the processing stage of the member. The martensitic stainless steel member, which has good workability and high strength in the final product,
A low cost and easy manufacturing method.

[0002]

2. Description of the Related Art Martensitic stainless steel is already widely used as a material that can satisfy corrosion resistance and high strength. Typical examples are SUS403 and SU defined in JIS G4304 or G4305.
S410, SUS420J1, SUS420J2, SU
Examples include S429J1 and SUS440A. However, all of these steels have a C content in order to obtain a martensitic structure.
However, it has a drawback that it is poor in corrosion resistance and toughness.

Further, since all of these steels have a high C content, the strength is very high even in the as-hot-rolled state (while hot-rolled and then left to cool), and the workability and machinability in cold or warm are poor. There was a difficulty. Therefore, if workability is required, heat treatment such as tempering and quenching and tempering is performed to reduce the strength. However, such heat treatment does not sufficiently reduce the strength. Cold workability is not sufficient. Therefore, when manufacturing a member having a complicated shape using such steel, cutting is unavoidable instead of plastic working, which requires a great deal of time and cost.

On the other hand, as a martensitic stainless steel containing a substitutional austenite forming element in place of C in which the amount of C in high Cr steel is reduced, JP-A-62-54063 is used.
Japanese Patent Laid-Open No. 2-243739, Japanese Patent Laid-Open No. 2-2
For example, Japanese Patent No. 43740 has been proposed. However, in each of these steels, a large amount of Ni is contained, and since only strength adjustment by ordinary quenching and tempering heat treatment is considered, high-strength materials are easy to manufacture, while tempering temperature is high. Since it is difficult to lower the strength because the softening behavior is limited, the manufacturing of a member having a complicated shape requires a great deal of time and cost.

Japanese Unexamined Patent Publication (Kokai) No. 5-255736 proposes a method for producing martensitic stainless steel by adding a workability of 65% or more in a temperature range of 1100 ° C. or less to a steel whose components are limited. However, in this method, the main purpose is to soften the pipe or bloom to the extent necessary for sawing the pipe or sawing the bloom, and consider the cold workability of martensitic stainless steel. Nor is it intended to simultaneously obtain important properties such as strength, corrosion resistance and weldability. Furthermore, it is not suitable for manufacturing stainless steel members.

Japanese Unexamined Patent Publication (Kokai) No. 6-136490 discloses a steel with limited components at a temperature of 750 ° C. or higher and 1100 ° C. or lower.
Add a workability with a total reduction of 65% or more and cooling rate ≤
A method for producing martensitic stainless steel has been proposed in which, after cooling at 0.1 ° C./s, normalizing treatment is performed again at the austenitizing temperature, and then tempering treatment is performed immediately below the Ac ₁ point. However, in this method, only softening to the extent necessary for sawing an intermediate product is obtained, and it is difficult to obtain sufficient cold workability and required properties as a product.

On the other hand, the content of C is 0.2% or more, and the content of Cr is 1
It is well known that in high carbon martensitic stainless steel containing 2 to 14%, coarse Cr carbides can be precipitated and softened in-line by controlling hot rolling conditions and subsequent cooling conditions. There is. However, such a technique has not been established for low C materials.
In addition, high carbon martensite is inferior in impact toughness and corrosion resistance, and has a drawback that weldability is very poor.

[0008]

In view of the above situation, the present invention is a martensite that can be easily cold-worked or warm-worked into the shape of a member, and can obtain high strength, high toughness, and corrosion resistance in the final shape. An object of the present invention is to provide a method for easily producing a low-cost stainless steel member at low cost.

[0009]

The gist of the present invention resides in the following (1) to (8). (1) Weight%, Si: 0.01 to 1.0%, M
n: 0.02 to 3.0%, Cr: 7.5 to 1
4.0%, Cu: 1.5 to 4.5%, Ni: 0.
2 to 1.0%, Al: 0.005 to 0.5%,
, C is 0.05% or less, N is 0.03% or less,
P is reduced to 0.03% or less and S is reduced to 0.01% or less,
The balance is a steel slab consisting of Fe and unavoidable impurities.
After heating to a temperature of 0 to 1300 ° C., the cumulative reduction amount at a temperature of 1050 ° C. or less is 65% or more, and the rolling end temperature is 800 ° C. or more, the hot rolling is finished, and at least 500 ° C. After cooling at a cooling rate of less than ° C / sec to form a steel having a metal structure of a ferrite fraction of 50% or more, the steel is processed into a predetermined member shape in a cold or warm state, and then a quenching heat treatment. Alternatively, a method for producing a high-strength martensitic stainless steel member is characterized by performing quenching and tempering heat treatment to form a metal structure mainly containing martensite.

(2) The steel after hot rolling is reheated to a temperature of 600 ° C. or more and Ac ₁ transformation point or less after cooling the steel to 300 ° C. or less and before processing into a member shape. The method for producing a high-strength martensitic stainless steel member according to (1) above. (3) The method for producing a high-strength martensitic stainless steel member according to (2), wherein the reheating conditions satisfy the following conditions. T × (log t + 21) ≧ 21000 where T is the reheating temperature (K) and t is the reheating holding time (min).

(4) The quenching condition of the member is such that the member is reheated to a temperature of 850 ° C. or more and 1050 ° C. or less, held for 5 minutes or more, and then cooled to 300 ° C. or less. _The method for producing a high-strength martensitic stainless steel member according to (1), (2), or (3), which comprises reheating to a temperature not higher than _one transformation point, holding for 5 minutes or more, and then cooling. (5) Steel slab is added as an additional component in a weight% of M
O: 3.0% or less, W: 3.0% or less, one or more of them are contained, and the total content represented by Mo + 0.5W is 3.0% or less (1), ( 2),
(3) or the method for producing a high-strength martensitic stainless steel member according to (4).

(6) The steel slab further contains, as an additional component, 1.0% or less by weight% of the total content of one or more of Nb, V, Ti, Zr, and Ta. ), (2), (3), (4) or (5), the method for producing a high-strength martensitic stainless steel member. (7) The content of C and N in the steel slab is% by weight, and the content of C is 0.
015% or less, N is reduced to 0.015% or less, and the total content of C + N is 0.02% or less, (1), (2), (3), (4), (5) ) Or (6)
For manufacturing a high-strength martensitic stainless steel member.

(8) The composition of the steel slab is such that the MC value ([% X] is the content of the element X expressed in% by weight) given by the following formula is 0 or more, (1), (2) ), (3),
(4), (5), (6) or (7) high-strength martensitic stainless steel member manufacturing method. MC value = 80 + 420 [% C] +440 [% N] +30 ([% Ni] + [% Cu] + [% Co]) + 15 [% Mn] -12 ([% Si] + [% Cr] + [% Mo])-24 [% Nb] -48 ([% V] + [% Ti] + [% Al])-6 [% W]

[0014]

The reason why the range of each component is limited in the present invention will be described below. In the present invention,% means% by weight unless otherwise specified. Si: Si is effective to be added as a deoxidizing agent and a strengthening element to steel containing 7.5% to 14.0% of Cr, but if the content is less than 0.01%, the deoxidizing effect is high. It is not sufficient, and even if the content exceeds 1.0%, not only the effect is saturated but also the workability and impact toughness are reduced,
The Si content range is limited to 0.01 to 1.0%.

Mn: Mn is Cr in the range of 7.5 to 14.0.
% Is necessary as a deoxidizing agent and strengthening element for steel,
It is necessary to contain 0.02% or more. Further, Mn is an element that is also useful in stabilizing the austenite structure at high temperatures. However, even if the content exceeds 3.0%, the effect is not only saturated, but also excessive M
Since the inclusion of n causes difficulty in steelmaking, the upper limit content is 3.0%.

Cr: Cr is 7.5% in order to secure the desired corrosion resistance of martensitic stainless steel.
Although it is necessary to contain the above, if the content exceeds 14.0%, not only the cost is unnecessarily increased, but also it becomes difficult to secure the austenite phase at high temperature. Therefore, the Cr content is 7.5 to 14.0.
%.

Cu: Cu is a high Cr with reduced C and N.
It is a necessary and useful element for addition to the contained steel so that the metal structure at high temperature becomes an austenite single phase.
When the content of Cu is less than 1.5%, austenite is not stable at high temperature and ferrite is easily generated. If ferrite is already formed during hot working and is mixed in austenite, the hot workability is deteriorated and the impact toughness after cooling is significantly decreased. Cu must be added in an amount of 1.5% or more in order to make the metal structure at a high temperature a single phase of austenite. On the other hand, if Cu is added in an amount of more than 4.5%, it becomes difficult to transform into ferrite even if the cooling rate is controlled after hot working to cool it. Therefore, the upper limit content of Cu is 4.5%. To do.

Ni: Ni is added in an amount of 0.2% or more for the purpose of ensuring strength and toughness. When Ni is less than 0.2%,
Even if a quenching heat treatment or a quenching and tempering heat treatment is performed at the stage of the member, the strength as martensitic stainless steel is not sufficient. On the other hand, if Ni is added in an amount of more than 1.0%, it is difficult to transform into ferrite regardless of how the hot rolling conditions and the cooling rate after hot working are controlled. The upper limit content of Ni is 1.0%. Even when the Ni content is less than 0.2%, softening is possible by controlling the hot rolling conditions. However, in this case, it is difficult to obtain high strength even if the heat treatment for quenching or the heat treatment for quenching is performed after processing into the shape of the member. In such a case, there is not much advantage as compared with the conventional ferritic stainless steel.

Al: Al is 0.005 as a deoxidizing agent.
% Or more must be added. However, if added in excess of 0.5%, coarse oxide inclusions are formed and corrosion resistance is reduced, so the upper limit content is made 0.5%. C: C forms a carbide with Cr to reduce toughness and corrosion resistance and also reduces weldability, so the C content is limited to 0.05% or less. When the toughness after hot working, the impact toughness of the weld heat affected zone, the low hardness and the like are required, C is more preferably 0.03% or less.

N: N also binds to Cr and deteriorates corrosion resistance, so the N content is limited to 0.03% or less.
When toughness after hot working, impact toughness of weld heat affected zone, low hardness, etc. are required, N is more preferably 0.02% or less. Further, when the member is a welded structure and it is particularly necessary to reduce the hardness of the weld heat affected zone and improve the weldability, the C content is 0.015% or less,
More preferably, the N content is 0.015% or less, and the total C + N content is 0.02% or less.

P: When P is present in a large amount, it lowers the toughness and weldability. Therefore, it is preferable that the amount is small, and it is necessary to reduce it to 0.03% or less.
More preferably, it is 0.018% or less. S: If a large amount of S is present, hot workability, ductility and corrosion resistance are deteriorated.
It is necessary to reduce it to 1% or less, and more preferably 0.005% or less.

The above is the basic composition of the steel targeted by the present invention. However, in the present invention, the following elements are further added, if necessary, to further improve the properties. . Mo, W: Mo and W have an effect of improving corrosion resistance by adding Cr to steel containing 7.5 to 14.0%,
In any case, even if added over 3.0%, the effect is no longer saturated. If the content of both elements alone exceeds 3.0%, or if the total content represented by Mo + 0.5W exceeds 3.0%, in order to secure hot workability and structural stability at high temperature, The alloying elements such as Ni and Mn must be contained in a larger amount in excess of the above upper limit amount, and the amount of ferrite in the steel, and thus the cold workability, can be controlled by controlling the hot rolling conditions and the subsequent cooling conditions. It becomes difficult to secure. Therefore, the upper limit content of Mo and W is 3.0.
%, And the total content represented by Mo + 0.5W is also 3.0% or less.

Nb, V, Ti, Zr, Ta: Nb,
V, Ti, Zr, and Ta are effective in improving workability and corrosion resistance when added to steel containing Cr in an amount of 7.5 to 14.0%. However, even if added excessively, these effects saturate, but since the toughness of the base material is lowered, the total content of one or more of Nb, V, Ti, Zr, and Ta is 1 or less. It shall not exceed 0.0%.

When particularly excellent base material toughness is required, the total content of one or more of Nb, V, Ti, Zr and Ta is preferably not more than 0.5%. On the other hand, in order to sufficiently reduce the hardness of the welding heat affected zone or to further improve the workability, Nb, V, T
The total content of one or more of i, Zr, and Ta is
It is preferably 0.1% or more.

Further, in the present invention, as a combination of the contents of the respective elements, it is more preferable that the MC value defined by the following formula is 0 or more. MC value = 80 + 420 [% C] +440 [% N] +30 ([% Ni] + [% Cu] + [% Co]) + 15 [% Mn] -12 ([% Si] + [% Cr] + [% Mo])-24 [% Nb] -48 ([% V] + [% Ti] + [% Al])-6 [% W] Here, [% X] is the element X in the case of being expressed by weight%. The content of is shown.

The MC value is detailed with respect to the optimum composition and combination of components required by the present inventors to obtain the properties as martensitic stainless steel, particularly the strength of the base metal, the impact toughness of the base metal and the weld heat affected zone. It is a finding based on the results of the study described above, and if the MC value is less than 0, δ ferrite may be generated at a high temperature. Δ in hot rolling zone
The presence of a large amount of ferrite reduces the impact toughness and strength of steel. In order to avoid this, if the MC value is set to 0 or more, δ ferrite will not be generated at a high temperature, and a structure consisting essentially of austenite will be obtained in the hot working temperature range.

By subjecting this austenite structure to ferrite transformation by controlled hot addition, workability at room temperature can be ensured. When the MC value is set to 0 or more, high strength, high toughness, and high corrosion resistance can be achieved as a member at the same time by performing quenching and tempering heat treatment after processing into a member shape. When the MC value is less than 0, the strength or the toughness may be insufficient even if the member shape is subjected to quenching heat treatment or quenching and tempering heat treatment.

In the steel targeted by the present invention, in addition to the above components, Co, B, and B are added as impurities mixed from scraps or the like, or for the purpose of adjusting toughness and workability.
Hf and the like can be contained. Alternatively, it is also possible to contain a rare earth element (REM), Ca, Mg or the like for the purpose of improving hot workability and corrosion resistance. The addition of these elements does not depart from the scope of the method of the invention. Here, the rare earth elements refer to elements having atomic numbers 57 to 71 and 89 to 103 and Y.

Further, although the oxygen content is not particularly limited in the present invention, it is natural that the smaller the oxygen content, the better since it is an impurity which is a root source for forming oxide-based non-metallic inclusions. It is more preferably 0.004% or less.

Next, the process of the present invention and the reason for limiting the process will be described. In the present invention, the composition of steel and hot rolling conditions, cooling conditions, heat treatment conditions, etc. are precisely selected and controlled to form a structure mainly composed of austenite during hot working at high temperature, and a large amount of ferrite is added after cooling. Steel with excellent workability, and then cold or warm processed into the final shape as a member, and heat-treated in the final shape to obtain a martensite-based structure, resulting in high strength and high toughness. To manufacture the member.

Steel billet heating temperature: It is necessary to uniformly heat the billet to its central portion to ensure hot workability in hot rolling. However, heating above 1300 ° C. is not preferable because the material loss due to the formation of oxide scale becomes remarkable and the production yield decreases. On the other hand, the heating temperature is 10
If it is less than 50 ° C, the deformation resistance in hot rolling becomes too large, which is not preferable. Therefore, the billet heating temperature is 1
It is set to 050 to 1300 ° C.

Hot rolling: The hot rolling can be carried out by a conventional thick plate rolling process, hot coil rolling process, or bar / wire rolling process. In the case of a hot coil, the plate thickness is 2.0 mm or more and 25.4 mm or less in view of the rollable size and suitability as a strength member.

Hot rolling conditions: In cooling after the hot rolling, in order to make the metal structure be steel substantially composed of ferrite, hot rolling is performed in a temperature range in which the metal structure is substantially an austenite single phase. When the temperature is completed and the temperature is 1050 ° C. or lower, the cumulative reduction amount must be 65% or more. The reduction at a high temperature exceeding 1050 ° C. does not have the effect of promoting the ferrite transformation during the subsequent cooling. This is because the cumulative reduction amount at a low temperature, that is, at a temperature of 1050 ° C. or lower must be 65% or more in order to sufficiently transform the steel that has been hot rolled in the austenite region into ferrite transformation. When the cumulative reduction amount at 1050 ° C. or less is less than 65%, the effect of promoting ferrite transformation by hot working is not sufficient, and most of austenite is transformed into martensite, resulting in insufficient workability at room temperature. .

On the other hand, if the hot rolling temperature is too low, ferrite transformation starts during hot rolling and the ferrite is hot worked to lower the toughness, or the temperature of the steel becomes lower than the temperature at which ferrite transformation is possible. Therefore, the ferrite transformation does not proceed effectively. Therefore, hot rolling must be completed at 800 ° C or higher. further,
In order to obtain a ferrite structure more stably after hot rolling, it is more preferable to set the cumulative reduction amount at 1050 ° C. or less to 75% or more, or the cumulative reduction amount at 1000 ° C. or less to 65% or more.

Cooling condition: When cooling the steel after hot rolling or the hot coil wound after hot rolling, cooling to at least 500 ° C. at a cooling rate of less than 0.05 ° C./sec. I won't. This is to sufficiently transform the hot worked austenite into ferrite. When the cooling rate is 0.05 ° C./second or more, even after the hot working austenite, the structure after transformation is mainly martensite, and the workability at room temperature deteriorates.

On the other hand, in the steel targeted by the method of the present invention, the ferrite transformation from hot-worked austenite is 5
Since it is completed up to 00 ° C, any cooling rate may be used if it is less than 500 ° C. Considering equipment, productivity, etc., it may be gradually cooled, or may be rapidly cooled at less than 500 ° C.

When the steel sheets are gradually cooled, they may be heat-retained one by one and gradually cooled. However, if two or more steel sheets are stacked and then gradually cooled by covering with a slow cooling cover or the like, the efficiency is improved. Target. In the case of hot coils, each hot coil may be covered with a heat-retaining cover or the like to be gradually cooled, or a plurality of hot coils may be stacked or arranged side by side to gradually cool multiple coils with one heat-retaining cover. Cooling is efficient. In order to obtain sufficient workability in cold working or warm working, the ferrite fraction in the metal structure after cooling is 5
It is preferably 0% or more.

Reheating: Reheating is effective for further reducing the strength of ferrite transformed from hot-worked austenite to improve workability. For reheating, the steel after hot working is once cooled to 300 ° C or lower,
It must be performed after sufficient ferrite transformation and after the residual austenite has undergone martensite transformation. If reheated before being cooled below 300 ° C,
The effect is insufficient. On the other hand, if the temperature of the steel or hot coil becomes 300 ° C. or lower, it may be reheated before being cooled to room temperature, or may be cooled to room temperature and then reheated. .

The purpose of this step is to reheat the steel after hot working to a high temperature to hold Cu in the overaged region to cause precipitation and to temper the martensite partially formed after hot working, It further enhances workability at room temperature. If the reheating temperature is lower than 600 ° C, the workability is not sufficiently improved at room temperature, and especially if the reheating temperature is lower than 570 ° C,
On the contrary, Cu may be finely precipitated to increase the strength and thus reduce the workability at room temperature. On the other hand, if the reheating temperature exceeds the Ac ₁ transformation point, fresh cooling will occur during subsequent cooling.
Martensite is formed and the workability at room temperature is lowered, and the toughness and stress corrosion cracking resistance of the base material are lowered.

Upon reheating, the reheating temperature T (K) and the holding time t (min) are T × (log t +21) ≧ 21.
If reheating conditions are set so as to satisfy 000, the strength of ferrite and martensite transformed from hot-worked austenite is sufficiently reduced, and cold workability is further improved. It is valid.

The atmosphere for reheating may be the atmosphere,
Reduces the oxide scale on the steel surface, does not reduce corrosion resistance,
In order to improve the production yield of the steel pipe, the reheating atmosphere is more preferably a weakly oxidizing atmosphere, a non-oxidizing atmosphere or a reducing atmosphere. For example, it is effective to use a mixed gas containing 5 to 15% of hydrogen and the balance of nitrogen or argon gas.

Processing into member shape: By the composition and processing described above, martensitic stainless steel having improved workability in cold or warm can be obtained. This steel is cold or warm worked into a predetermined shape. As a working method, plastic working, cutting or the like can be applied. In the present invention, cold working means working at room temperature, and warm working means working at a temperature lower than the recrystallization temperature and the Ac ₁ transformation temperature.

Heat treatment: After processing into the final member shape,
High strength can be obtained by heat treatment to make the metal structure mainly composed of martensite. In other words, a member that has high strength at the stage of final use and is excellent in corrosion resistance and impact toughness is given excellent workability at the stage of cold or warm processing, resulting in low cost. Can be easily manufactured. The steel targeted by the present invention has relatively good toughness even after being quenched, so that the final heat treatment is left as quenched, particularly when high strength is prioritized. Alternatively, for the purpose of adjusting the strength to a predetermined value, particularly for obtaining excellent impact toughness, the final heat treatment is a quenching and tempering heat treatment.

In the present invention, the metal structure mainly composed of martensite means a martensite single phase structure or a structure containing a small amount of ferrite and / or retained austenite in martensite. Since the strength and toughness decrease when a large amount of ferrite is present, the amount of ferrite is preferably 5% or less, more preferably 3% or less. Retained austenite does not lower the toughness but slightly lowers the strength, so it is preferably made 5% or less.

The final heat treatment conditions are as follows. Quenching: The heating temperature must be 850 ° C. or higher in order to fully austenize and increase the strength after quenching.
If the heating temperature exceeds 1050 ° C, the austenite crystal grains become coarse and the impact toughness decreases. When particularly excellent impact toughness is required, the heating temperature is preferably 980 ° C or lower. The holding time is preferably 5 minutes or more in order to secure uniform strength as a member.
It is more preferable to hold for 15 minutes or more for a large member. In the subsequent cooling, when the tempering treatment is subsequently performed, the austenite remains unless the temperature is cooled to 300 ° C. or less, and the tempering effect is not sufficient.

The steel to which the present invention is applied has a very high hardenability, and ferrite is not formed unless it is hard worked by hot working. In the final heat treatment, no hot working is applied, so that there is no particular restriction on the cooling rate. That is, any of water cooling, oil cooling, air cooling, furnace cooling and the like can be applied. Since high Cr steel undergoes martensitic transformation in air cooling, quenching is often referred to as normalization, but both are synonymous in terms of metallurgy. Also,
The steel targeted by the present invention is very unlikely to cause quench cracks even when water-cooled, so water-cooling can also be applied. In short, cooling takes into consideration equipment, productivity, etc.
Choose the most appropriate one.

Tempering: For the purpose of enhancing impact toughness, the tempering temperature must be 600 ° C or higher. If the tempering temperature is lower than 600 ° C., Cu may precipitate and the impact toughness may be decreased. On the other hand, when the tempering temperature exceeds the Ac ₁ transformation point, fresh martensite is generated in the subsequent cooling, and the impact toughness of the base material decreases. When adjusting the strength while maintaining a relatively high strength, the tempering temperature may be 200 to 450 ° C. In this case, if the tempering temperature exceeds 450 ° C., Cu is finely precipitated to reduce the impact toughness, so care must be taken. To evenly temper the entire member,
The holding time for tempering is preferably 5 minutes or more, and more preferably 15 minutes or more for a large member.

[0048]

Example: A steel having the components shown in Table 1 was melted to a thickness of 240 mm.
Then, a hot-rolled steel sheet having a plate thickness of 2.6 mm was manufactured under the conditions shown in Table 2 by a normal hot rolling process. The billet heating temperature in the hot rolling was 1240 ° C. In Table 1, Comparative Example 17 is an AISI 420 equivalent steel. After each steel plate was used as a material for cold-pressing into wheel discs that are automobile parts, Table 2
The final heat treatment was applied under the conditions shown in. A test piece was taken from each member, and the Vickers hardness (load 10 kg) at room temperature was measured on the cross section.

[0049]

[Table 1]

[0050]

[Table 2]

The test results are also shown in Table 2. As is apparent from Table 2, the present invention example No. 1 according to the present invention. 1 to N
o. No. 12 is the final member and has high hardness. On the other hand, Comparative Example No. 1 in which the hot rolling conditions or the components were not appropriate. 13-No. In No. 17, since cold workability was insufficient, cracking occurred in cold press working, and it was impossible to work into the shape of the wheel disk.
Comparative Example No. Although 18 was able to be processed into a wheel / disk shape, the hardness after the final heat treatment was low.

[0052]

INDUSTRIAL APPLICABILITY The present invention makes it possible to manufacture a high-strength martensitic stainless steel member at low cost and with high productivity, and it greatly contributes to industrial development.

Claims (8)

[Claims] 1. By weight%, Si: 0.01 to 1.0%, Mn: 0.02 to 3.0%, Cr: 7.5 to 14.0%, Cu: 1.5 to 4. 5%, Ni: 0.2-1.0%, Al: 0.005-0.5% are contained, C is 0.05% or less, N is 0.03% or less, P is 0.03. % Or less, S is reduced to 0.01% or less, and the balance is Fe and unavoidable impurities. After heating a steel slab to a temperature of 1050 to 1300 ° C., the cumulative reduction amount at a temperature of 1050 ° C. or less is 65%. Above, and when the rolling end temperature is 800 ° C or higher, the hot rolling is finished, and at least 500 ° C up to 0.0
After cooling at a cooling rate of less than 5 ° C./sec to obtain a steel having a metal structure of a ferrite fraction of 50% or more, the steel is processed into a predetermined member shape in a cold or warm state, and then quenched. A method for producing a high-strength martensitic stainless steel member, which comprises heat-treating or quenching-tempering heat treatment to form a metal structure mainly composed of martensite. 2. A step after the steel after hot rolling is cooled to 300 ° C. or lower and before being processed into a member shape,
The method for producing a high-strength martensitic stainless steel member according to claim 1, further comprising reheating to a temperature of 600 ° C. or higher and an Ac ₁ transformation point or lower. 3. The method for producing a high-strength martensitic stainless steel member according to claim 2, wherein the reheating conditions satisfy the following conditions. T × (log t + 21) ≧ 21000 where T is the reheating temperature (K) and t is the reheating holding time (min). 4. The hardening condition of the member is 850 ° C. or higher 105
After reheating to a temperature of 0 ° C or less and holding for 5 min or more, 3
It is cooled to below 00 ° C, and the tempering condition is 60
The method for producing a high-strength martensitic stainless steel member according to claim 1, 2 or 3, which is reheated to a temperature of 0 ° C or more and Ac ₁ transformation point or less, held for 5 minutes or more, and then cooled. 5. A steel slab is further added as an additional component in a weight percentage.
, Mo: 3.0% or less, W: 3.0% or less, and one or more of them are contained, and the total content represented by Mo + 0.5W is 3.0%.
The method for producing a steel pipe excellent in corrosion resistance and weldability according to claim 1, 2, 3 or 4 below. 6. A steel slab is further added as an additional component in a weight percentage.
And containing 1.0% or less of the total content of one or more of Nb, V, Ti, Zr, and Ta.
4. The method for producing the high-strength martensitic stainless steel member according to 4 or 5. 7. The content of C and N in the steel slab is reduced to 0.015% or less of C and 0.015% or less of N by weight%, and the total content of C + N is 0.02. % Or less, Claims 1, 2, 3, 4,
5. The method for producing a high-strength martensitic stainless steel member according to 5 or 6. 8. The composition of the steel slab is M given by the following formula:
The C value ([% X] is the content of the element X expressed in% by weight) is 0 or more, 1, 2, 3, 4, 5, 6 or 7.
The method for producing a high-strength martensitic stainless steel member according to 1. MC value = 80 + 420 [% C] +440 [% N] +30 ([% Ni] + [% Cu] + [% Co]) + 15 [% Mn] -12 ([% Si] + [% Cr] + [% Mo])-24 [% Nb] -48 ([% V] + [% Ti] + [% Al])-6 [% W]