JP2006249514A - HOT-ROLLED STEEL PLATE OF Cr-CONTAINING ALLOY HAVING HIGH STRENGTH AND SUPERIOR WORKABILITY, AND MANUFACTURING METHOD THEREFOR - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot-rolled steel plate of a Cr-containing alloy having high strength and superior workability, and to provide a manufacturing method therefor. <P>SOLUTION: The hot-rolled steel plate of the Cr-containing alloy comprises 0.003% to 0.03% C, 0.003% to 0.02% N, more than 1.0% but at most 3.0% Si, more than 1.0% but at most 3.0% Mn, at most 0.05% P, at most 0.01% S, 11% to 18% Cr, more than 1.0% but at most 3.0% Ni, 0.005% or more but less than 0.030% V, at most 0.05% Al, at most 0.0050% O by mass%, and the balance Fe with unavoidable impurities; and has a metallurgic structure comprising, by a volume fraction, a ferritic phase in an amount of 50% or more and a martensitic phase in an amount of less than 50%. The manufacturing method comprises the steps of: hot-rolling the steel having the above composition at a finish-rolling end temperature of 800 to 1,000°C and a winding temperature of 900°C or lower; and annealing the hot-rolled plate at an annealing temperature of 600 to 900°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hot-rolled steel sheet having high strength and excellent workability, and more particularly to a Cr-containing alloy hot-rolled steel sheet having high strength and excellent workability, which is suitable for electrical and electronic equipment parts and automobile parts, and a method for producing the same.

  In recent years, in the automobile industry, from the viewpoint of the preservation of the global environment, it has been strongly demanded to reduce the amount of exhaust gas by reducing the weight of the vehicle body and improving the fuel consumption. As one of the countermeasures, the application of high-strength steel plates to structural members such as undercarriages and body reinforcement parts is being promoted.

  The structural member for automobiles is coated with acrylic, urethane, epoxy resin or the like as a rust prevention treatment after press molding. Painting requires many steps such as degreasing, chemical conversion, painting, washing, drying (baking), and construction of a painting line requires a large amount of funds. For this reason, simplification of the painting process is considered an important issue with the recent expansion of production plants overseas. Furthermore, the rust prevention by painting has a problem that the film thickness at the end of the component tends to be thin, and the corrosion resistance is locally lowered. Moreover, when using for suspension, there exists a problem that a coating film lose | disappears by the bounce of the stone from a road surface, and corrosion resistance falls rapidly, and improving the corrosion resistance of material itself is calculated | required.

  In addition, in parts such as electrical parts and cases of household electrical appliances, it is required to increase the volume by reducing the thickness of the material and cope with higher functionality of the product. Along with higher functionality, the shape of parts is also diversifying, and development of materials that combine high workability and corrosion resistance is underway.

  As described above, Cr-containing steel has begun to be used as a structural member in various industries for the purpose of increasing strength and increasing corrosion resistance. However, in order to apply Cr-containing steel as a structural member having a high workability, it is necessary to have further excellent workability.

As a general high-strength Cr-containing steel, a spring material obtained by hardening austenitic stainless steel such as SUS301 by cold rolling or heat treatment, and martensitic stainless steel such as SUS410 are widely used. Among these, the spring material made of austenitic stainless steel has a problem of high stress corrosion cracking sensitivity when used as a structural material in addition to containing a large amount of expensive Ni. In addition, martensitic stainless steel has the advantage of low price, but if it is intended to have a high strength such that the tensile strength TS exceeds 600MPa, it is heated to _Ac1 point or higher in the final annealing. It is necessary to perform the low temperature treatment (half annealing) from the martensite state. However, the martensitic stainless steel produced by any treatment has a problem that the elongation is low and sufficient workability cannot be obtained.

  In addition, when a high-strength steel plate is applied as various members, a stainless steel plate has been developed for the purpose of adapting to various forming.

For example, Patent Document 1 contains Cr: 6 to 18% by weight, and further adjusts the total of C and N to 0.025% or less, Si: 2% or less, Mn: 1% over 5%, P : 0.05% or less, S: 0.02% or less, Ni: 0.1 to 3%, Al: 0.1% or less, V: 0.03 to 0.3%, and γ _{p =} 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr A technique for obtaining stainless steel excellent in workability and weldability by adjusting γ _p defined by -11.5Si-12Mo-23V-47Nb-49Ti-52Al + 189 to 50 or more and 70 or less is disclosed.

  Patent Document 2 contains Cr: 6 to 15% by weight, C: 0.02% or less, Si: 1% or less, Mn: 1 to 5% or less, P: 0.05% or less, S: 0.02% or less Ni: 1% or less, Al: 0.1% or less, N: 0.02% or less, V: 0.03-0.3%, and F value = Cr + 0.4 × Si + 0.2 × Al + 5 × P-0.4 × Mn The toughness of HAZ is adjusted by substituting the calculated F value to 13.5 or less by substituting the content value of each component into the F value defined by -0.7 × Ni-35 × C-10 × N + 10 × V. A technique for obtaining stainless steel having excellent strength and corrosion resistance is disclosed.

According to Patent Document 3, Cr: more than 8 and less than 15% is contained, and C: 0.01 or more and less than 0.54%, V: 0.01% or more and less than 0.5%, W: 0.001% or more and less than 0.05% At the same time, adjust so that X value defined by X = Cr + Mo + 1.5Si + 0.5Nb + 0.2V + 8Al-Ni-0.6Co-0.5Mn-30C-30N-0.5Cu satisfies 11.0 or less Thus, a technique for obtaining stainless steel excellent in initial rusting property, workability and weldability is disclosed.
JP 2002-167653 A JP 2002-121652 JP JP 2002-53938 A

  However, in the technique described in Patent Document 1, it is necessary to make the V content 0.03% or more, and as a result, the amount of V carbonitride increases, so when applied as a high strength material exceeding 600 MPa. Has a problem that ductility is lowered and workability is deteriorated.

  In the technique described in Patent Document 2, since the Si content is small, it is necessary to contain a large amount of Mn in order to be applied as a high-strength material. Therefore, even when the hot-rolled sheet is subjected to box annealing at about 600 to 900 ° C., there is a problem that ductility is lowered and sufficient workability cannot be obtained.

  In the technique described in Patent Document 3, it is necessary to add Co, V and W in combination, and due to the solid solution strengthening action of these elements, the ductility is lowered and the workability is deteriorated as in References 1 and 2. There is a problem. Moreover, there is a problem that the raw material cost is high.

  The present invention has been made to solve the above problems, and provides a Cr-containing alloy hot-rolled steel sheet having high strength and high ductility and excellent stretch flangeability, which is an important characteristic as a structural member, and a method for producing the same. The purpose is to do.

  In order to solve the above-mentioned problems, the present inventors have intensively studied various factors affecting the strength and workability. As a result, the content of C, N, Si, Mn, P, S, Ni, V, and Al was regulated after containing an appropriate amount of Cr, not steel using a general C strengthening mechanism. By making the steel composition, and further by adjusting the hot rolling conditions and hot rolled sheet annealing conditions at the time of manufacture, the ferrite phase is the base, and the second phase is a structure in which the martensite phase is uniformly dispersed, While maintaining the ductility of the base phase, it was found that the difference in strength from the second phase was relatively small, and the strength and workability were dramatically improved.

  The present invention has been made based on the above findings, and the gist thereof is as follows.

  [1] In mass%, C: 0.003% to 0.03%, N: 0.003% to 0.02%, Si: 1.0% to 3.0%, Mn: 1.0% to 3.0%, P: 0.05% or less, S : 0.01% or less, Cr: 11% to 18%, Ni: 1.0% to 3.0%, V: 0.005% to less than 0.030%, Al: 0.05% or less, O: 0.0050% or less, the balance being Fe It consists of unavoidable impurities, and has a tensile strength of 600 MPa or more, characterized by having a metal structure with a volume fraction of ferrite phase: 50% or more and martensite phase: less than 50%. Cr-containing alloy hot-rolled steel sheet with excellent properties.

  [2] In the above [1], one or two selected in mass% from Ti: 0.05% to 0.3%, Nb: 0.05% to 0.3%, Zr: 0.05% to 0.3% A Cr-containing alloy hot-rolled steel sheet having a high strength and excellent workability with a tensile strength of 600 MPa or more, characterized by containing the above.

  [3] In the above [1] or [2], the Cr-containing alloy having a high tensile strength of 600 MPa or more and excellent workability, further comprising mass% and Cu: 2.0% or less Hot rolled steel sheet.

  [4] When a steel material containing Cr is hot-rolled to form a hot-rolled sheet, the hot-rolled sheet is annealed to produce a Cr-containing alloy hot-rolled steel sheet. To the steel material having the composition according to any one of [3], the hot rolling is performed at a finish rolling finish temperature of 800 to 1000 ° C. and a winding temperature of 900 ° C. or less, and the hot rolled sheet annealing is performed. A method for producing a Cr-containing alloy hot-rolled steel sheet having a tensile strength of 600 MPa or more and excellent workability, characterized in that the annealing temperature is 600 to 900 ° C.

  In addition, in this specification, all% which shows the component of steel is mass%.

  According to the present invention, it is possible to obtain a Cr-containing alloy hot-rolled steel sheet having a tensile strength of 600 MPa or more, an elongation El of 16% or more, a hole expansion ratio λ of 80%, and high strength and excellent workability. it can.

  The Cr-containing alloy hot-rolled steel sheet according to the present invention satisfies all the characteristics of strength, ductility and stretch flangeability required as structural members for automobiles, electrical and electronic equipment, and has remarkable industrial effects. .

  The Cr-containing alloy hot-rolled steel sheet of the present invention is controlled to the following composition, and has a volume fraction of a ferrite phase: 50% or more and a martensite phase: less than 50%. And when these characteristics manufacture the said steel plate, hot rolling is performed by finishing finishing temperature: 800-1000 degreeC, coiling temperature: 900 degrees C or less, and hot-rolled sheet annealing is annealing temperature: 600-900 degreeC In the present invention, the finish rolling conditions and hot-rolled sheet annealing conditions in the hot rolling are the characteristics of the manufacturing method. As described above, a Cr-containing alloy hot-rolled steel sheet having high strength and excellent workability can be obtained by optimizing the composition and the structure.

  Hereinafter, the present invention will be described in detail.

  First, the reasons for limiting the chemical composition (composition) of steel in the present invention are as follows.

C: 0.003% to 0.03%,
C is an element that works extremely effectively in increasing the strength of steel, but excessive inclusion reduces workability and toughness. Therefore, in the present invention, C is made 0.003% to 0.03%. Preferably it is 0.004% or more and 0.025% or less.

N: 0.003% to 0.02%,
N, like C, is an element that effectively acts to increase the strength of steel. However, excessive content not only reduces toughness but also reduces workability. Therefore, in the present invention, N is set to 0.003% or more and 0.02% or less. Preferably it is 0.004% or more and 0.015% or less.

Si: more than 1.0% and less than 3.0%,
Si is a strengthening element of steel, and at the same time, an element that effectively acts to increase oxidation resistance and corrosion resistance. Moreover, it has the effect of stabilizing the ferrite phase and increasing the strength. Furthermore, the composite addition of Mn, which is an austenite phase stabilizing element, stabilizes the austenite phase during hot rolling, so that a large amount of C and N can be dissolved in the austenite phase. In the subsequent cooling process, the austenite phase transforms into a martensite phase, and at this time, it is considered that the precipitation of Cr carbonitride is suppressed. In order to acquire the above effect, Si needs to contain more than 1.0%. On the other hand, if the content exceeds 3.0%, the risk of elongation, toughness deterioration, or processing cracking increases. Therefore, the upper limit is 3.0% or less. That is, in the present invention, Si is more than 1.0% and not more than 3.0%. Preferably they are 1.2% or more and 2.8% or less.

Mn: more than 1.0% and less than 3.0%,
Mn has the effect of stabilizing the austenite phase at high temperatures and generating a martensite phase during subsequent cooling. Therefore, it is effective for increasing the strength of steel and is an important element in the present invention. Such an effect becomes remarkable when the content exceeds 1.0%. On the other hand, if the content exceeds 3.0%, not only the toughness is lowered, but also the corrosion resistance is deteriorated. From the above, in the present invention, Mn is set to more than 1.0% and not more than 3.0%. Preferably they are 1.2% or more and 2.5% or less.

P: 0.05% or less,
P increases the strength of steel, but as the content increases, the elongation and toughness decrease. Therefore, in the present invention, P is set to 0.05% or less. Preferably it is 0.04% or less.

S: 0.01% or less,
Since S is easy to bond with Mn, not only does MnS form and the bending workability of the steel sheet deteriorates, but also the corrosion resistance significantly deteriorates. For this reason, in the present invention, it is desirable to reduce S as much as possible, but if it is contained up to 0.01%, it is acceptable. Therefore, in the present invention, S is set to 0.01% or less. Preferably it is 0.005% or less.

Cr: 11% to 18%,
Cr is an element indispensable for improving corrosion resistance and oxidation resistance. Such an effect becomes remarkable when the content is 11% or more. Cr is also very effective in increasing the strength of the ferrite phase, reducing the difference in strength between the ferrite phase and the second martensite phase, which is a problem with ordinary DP steel sheets that do not contain enough Cr. It also has the effect of preventing cracking due to the strength difference between the phase and the second phase. On the other hand, the content exceeding 18% not only inhibits the formation of the martensite phase important in the present invention, but also causes a decrease in toughness. Therefore, in the present invention, Cr is 11% or more and 18% or less. Preferably they are 11.5% or more and 17.5% or less.

Ni: more than 1.0% and less than 3.0%,
Ni contributes to improvement of toughness and corrosion resistance, and forms a γ phase at a high temperature. The γ phase undergoes martensitic transformation during cooling and contributes effectively to increasing the strength. In order to acquire this effect, it is desirable to contain exceeding 1.0%. On the other hand, Ni is expensive, and the inclusion of a large amount leads to an increase in material cost. Therefore, in the present invention, Ni is set to 3.0% or less. Preferably they are 1.1% or more and 2.8% or less.

V: 0.005% or more and less than 0.030%,
When V contains a large amount of Mn as in the steel of the present invention, it passes through the (α + γ) 2 phase region during hot rolling, and when cooled, most of the ferrite is carbonitride or phosphide. Disperses and precipitates in the phase and stabilizes the ferrite phase. V is weaker in chemical bonding with C and N than other stabilizing elements such as Ti, Nb and Zr, and V carbonitride contains Cr (for example, (Cr, V) ₂ (C, N)). When these V carbonitrides are appropriately dispersed in the ferrite phase, the compatibility with the matrix is good, and when deformation is applied, it is unlikely to become a starting point of fracture at the interface with the matrix. For this reason, it is possible to increase the strength while keeping the ductility of the ferrite phase high. Such a high-strength and excellent ductility ferrite phase is extremely important for improving both strength and workability in the present invention, and such an effect becomes significant when the content is 0.005% or more. . On the other hand, if the content is 0.030% or more, the amount of V carbonitride increases too much, and the solid solution amount of V also increases. Therefore, when aiming for a high strength material exceeding 600 MPa as in the present invention, ductility decreases. However, the workability deteriorates. From the above, in the present invention, V is set to 0.005% or more and less than 0.030%. Preferably it is 0.01% or more and less than 0.025%.

Al: 0.05% or less,
Al is a very strong oxide-forming element. If it contains more than 0.05%, the Al ₂ O ₃ oxide is clustered and surface defects are likely to occur. Therefore, in the present invention, Al is made 0.05% or less. Preferably it is 0.04% or less. In the present invention, the case where Al is not intentionally added as a deoxidizer is included. In that case, Al is allowed to be less than 0.004% as an inevitable impurity.

O: 0.0050% or less,
O is present in the steel in the form of inclusions or in a solid solution state, and generates an oxide during welding. Therefore, it is preferable to reduce it as much as possible in the present invention. Further, if O is contained in an amount exceeding 0.0050%, the amount of oxide increases, not only lowering the workability of the base material itself, but also causing deterioration in corrosion resistance. Therefore, in the present invention, O is made 0.0050% or less. Preferably it is 0.0040% or less.

  The steel sheet of the present invention can achieve the desired characteristics with the above-mentioned essential additive elements, but can contain the following elements depending on the desired characteristics.

Ti: 0.05% to 0.3%, Nb: 0.05% to 0.3%, Zr: 0.05% to 0.3%, one or more,
Ti, Nb, and Zr are elements that are effective in suppressing the sensitization of the heat-affected zone by welding and improving the corrosion resistance, and contain one or more as required. it can. The above-described effects become significant when Ti: 0.05% or more, Nb: 0.05% or more, and Zr: 0.05% or more. On the other hand, the inclusion of Ti: more than 0.3%, Nb: more than 0.3%, and Zr: more than 0.3% lowers the toughness of the base metal and the heat affected zone of the weld zone. Therefore, when contained, Ti: 0.05% to 0.3%, Nb: 0.05% to 0.3%, Zr: 0.05% to 0.3%. Preferably, Ti is 0.08% to 0.25%, Nb is 0.1% to 0.25%, and Zr is 0.08% to 0.25%.

Cu: 2.0% or less,
Cu is an element that improves the corrosion resistance, and can be appropriately contained as required when it is intended to provide higher corrosion resistance. In order to acquire such an effect, it is desirable to contain 0.2% or more. On the other hand, if the content exceeds 2.0%, the surface quality is deteriorated due to a decrease in hot workability, and the toughness of the weld is deteriorated. Therefore, when it contains, Cu shall be 2.0% or less. Preferably they are 0.2% or more and 1.5% or less.

  The balance other than the above components is Fe and inevitable impurities. Inevitable impurities include elements such as Mg, Ca, and B that are expected to be mixed before the steelmaking process, and Mg: 0.0015% or less, Ca: 0.0020% or less, and B: 0.0020% or less are allowed. The

Next, the reason for limiting the steel structure, which is one of the important requirements for the present invention, will be described.
In addition to the composition described above, the Cr-containing alloy hot-rolled steel sheet of the present invention has a structure with a volume fraction of ferrite phase: 50% or more and martensite phase: less than 50%.

  The ferrite phase is a phase that improves workability, and in order to ensure the desired workability, the present invention needs to contain 50% or more by volume fraction. Preferably it is 60% or more.

  The second phase is intended to increase strength and improve stretch flangeability, and the martensite phase should be less than 50% in volume fraction. If the martensite phase that is the second phase exceeds 50%, the strength becomes too high, and at the same time, ductility and workability deteriorate. Preferably it is less than 40%. In addition, as described above, the martensite phase is harder than the ferrite phase, but since the plastic anisotropy is small, it is a phase that promotes uniform deformation and improves stretch flangeability. Therefore, in the present invention, it is desirable to contain the martensite phase in a volume fraction of 3% or more.

  The remaining structure other than the above is not particularly limited. For example, carbonitrides, phosphides, deoxidation products and the like can be included.

  Next, the method for producing a Cr-containing alloy hot-rolled steel sheet having high strength and excellent workability according to the present invention will be described.

  The Cr-containing alloy hot-rolled steel sheet of the present invention is obtained by subjecting a steel material having the above composition to hot rolling to obtain a hot-rolled sheet, and then annealing the hot-rolled sheet. At this time, the hot rolling is performed at a finish rolling finish temperature of 800 to 1000 ° C. and a winding temperature of 900 ° C. or less, and the hot rolled sheet annealing is performed at an annealing temperature of 600 to 900 ° C.

  For example, the steel material having the above composition is subjected to heat treatment, and then hot-rolled by hot rolling including rough rolling and finish rolling (finish rolling finishing temperature: 800 to 1000 ° C., winding temperature: 900 ° C. or less). After making into a plate, it is manufactured by subjecting the hot-rolled plate to annealing (annealing temperature: 600 to 900 ° C.).

  First, the molten steel having the above-described composition is melted by a generally known melting method such as a converter or an electric furnace, and is made into a steel material such as a slab by an ingot-bundling rolling method or a continuous casting method.

  The heating temperature when the heat treatment is performed on the steel material is not particularly limited in the present invention, but is preferably 1050 ° C. or higher. When the heating temperature is less than 1050 ° C., the desired finish rolling end temperature cannot be secured, and the surface quality may be deteriorated due to cracks, roll wrinkles, etc. due to a decrease in the steel strip surface temperature.

  The steel material is preferably heated to a sheet bar having a desired thickness by rough rolling. The sheet bar is preferably subjected to rough rolling or, if necessary, subjected to heating or temperature holding treatment, and then subjected to finish rolling to form a hot-rolled sheet.

  The finish rolling finish temperature (FDT) is set to 800 to 1000 ° C. from the viewpoint of preventing the deterioration of the surface quality and suppressing the formation of a coarse structure. In addition, in order to ensure the above finish rolling finish temperature and improve the workability, the sheet bar is heated before the finish rolling, or the heat treatment of the sheet bar, or a plurality of sheet bars are joined and rolled. It is effective to perform continuous rolling.

  The coiling temperature is 900 ° C or lower. When the coiling temperature is higher than 900 ° C., a band-like structure is formed and the workability of the hot rolled steel sheet is lowered. The temperature is preferably 750 ° C. or lower from the viewpoint of workability.

  After the hot rolling is finished, the hot rolled sheet is annealed. In this case, the heating temperature is 600 to 900 ° C. If it is less than 600 ° C, the workability is lowered, and if it is more than 900 ° C, it becomes soft and the strength is lowered. Further, the annealing in this case may be either continuous annealing or batch annealing.

  Then, after performing shot blasting as necessary, pickling may be performed for scale removal, and smoothing by skin pass rolling may be performed as necessary.

  In addition, there is no problem in use in applying a sacrificial anticorrosive coating composed of various metal powders such as Zn and Al and pigments to the surface of the Cr-containing hot rolled steel sheet of the present invention to further increase the corrosion resistance.

  The above description is only an example of the present invention, and various modifications can be made within the scope of the claims.

  Steel having the chemical composition shown in Table 1 was melted in a converter and used as a steel material (slab) by a continuous casting method. These slabs were subjected to heat treatment at a heating temperature of 1170 ° C., and then subjected to hot rolling consisting of rough rolling and finish rolling shown in Table 2 to obtain 2.5 mm thick hot rolled sheets. Next, the obtained hot-rolled sheet was subjected to hot-rolled sheet annealing that was held for 10 hours at the temperature shown in Table 2 and then gradually cooled. Subsequently, the surface scale was removed by shot blasting and pickling treatment. Then, about 1% skin pass rolling was performed to obtain a 2.5 mm thick hot-rolled annealed sheet.

Various test pieces were collected from the obtained hot-rolled annealed plate and examined for structure observation, tensile characteristics, and stretch flangeability. The test method is as follows.
(1) Microstructure observation Sample specimens for microstructural observation were collected from the obtained hot-rolled annealed plates, and after polishing these specimens, etching was performed using a corrosive solution: Murakami reagent, and the thickness direction center in the rolling direction of the steel sheet. Observed with an optical microscope and scanning electron microscope (100, 400 times), photographed 30 fields of view, and obtained the structure fraction of the ferrite phase for each field of view using an image analyzer. The value was calculated and used as the tissue fraction of each test piece. In addition, when the ferrite phase containing a carbonitride was observed in a grain, the carbonitride in a grain shall be contained in a ferrite phase. In addition, in order to clarify the distinction between the ferrite phase and other phases, measurement was performed by EPMA (electron beam microanalysis). In the EPMA analysis, color mapping of Cr, Si, Mn, Ni (or Cu) was performed at a magnification of 500 and an acceleration voltage of 15 kV at the central portion in the plate thickness direction in the rolling direction of the steel plate. At this time, the structure in which Cr and Si are condensed is defined as a ferrite phase, and the structure in which Mn and Ni (or Cu) is concentrated is defined as a martensite phase.
(2) Tensile properties From the obtained hot-rolled annealed sheet, a No. 13 B test piece based on JIS Z 2201 was taken from the direction perpendicular to the rolling direction, and a tensile test was carried out based on JIS Z 2241. The strength TS and elongation at break El were measured.
(3) stretch flangeability stretch flangeability specimens than hot-rolled annealed sheets (size: 2.5mm × 100mm × 100mm) and punching out the initial hole d ₀ of 10mmΦ 13% clearance in the sample, the apex angle in the hole A 60 ° conical punch was press-fitted from the side opposite to the surface where the burrs appeared, and the hole diameter d was measured when a crack penetrating the plate thickness occurred on the punched end surface. From these values,
λ (%) = (dd ₀ ) / d ₀ × 100
The hole expansion ratio λ defined in (1) was obtained, and the stretch flangeability was evaluated.

  The results obtained are shown in Table 3.

  From Table 3, all of the inventive examples have a high strength with a tensile strength TS of 600 MPa or more, an elongation El of 16% or more, and a hole expansion ratio λ of 80% or more. And it turns out that it is a hot-rolled steel plate excellent in stretch flangeability.

  On the other hand, the comparative example is inferior in any one or more of strength, ductility, and stretch flangeability.

  The Cr-containing alloy hot-rolled steel sheet of the present invention is also suitable for fields requiring high strength and excellent workability other than electrical and electronic equipment parts and automobile parts.

Claims (4)

  In mass%, C: 0.003% to 0.03%, N: 0.003% to 0.02%, Si: 1.0% to 3.0%, Mn: 1.0% to 3.0%, P: 0.05%, S: 0.01% Contains Cr: 11% to 18%, Ni: 1.0% to 3.0%, V: 0.005% to less than 0.030%, Al: 0.05% or less, O: 0.0050% or less, the balance being Fe and inevitable It consists of impurities, and has a metal structure with a volume fraction of ferrite phase: 50% or more and martensite phase: less than 50%. It has a tensile strength of 600 MPa or more and excellent workability. Cr-containing alloy hot-rolled steel sheet.   Furthermore, it is characterized by containing at least one selected from mass: Ti: 0.05% to 0.3%, Nb: 0.05% to 0.3%, Zr: 0.05% to 0.3%. The Cr-containing alloy hot-rolled steel sheet having high tensile strength and excellent workability, having a tensile strength of 600 MPa or more.   The Cr-containing alloy hot-rolled steel sheet having high tensile strength and excellent workability, having a tensile strength of 600 MPa or more, according to claim 1 or 2, further comprising Cu: 2.0% or less in mass%. After hot-rolling a steel material containing Cr to form a hot-rolled sheet, the hot-rolled sheet is annealed to produce a Cr-containing alloy hot-rolled steel sheet. A steel material having the composition of crab,
The hot rolling is performed at a finish rolling end temperature of 800 to 1000 ° C. and a winding temperature of 900 ° C. or less,
A method for producing a Cr-containing alloy hot-rolled steel sheet having a high strength and excellent workability with a tensile strength of 600 MPa or more, wherein the hot-rolled sheet annealing is performed at an annealing temperature of 600 to 900 ° C.