Production method of hot-rolled and annealed and pickled precipitation hardening martensitic stainless steel sus630

Abstract

The application discloses a production method of hot-rolled annealed pickling of precipitation hardening martensitic stainless steel SUS630. The production method of hot-rolled annealed pickling of precipitation hardening martensitic stainless steel SUS630 comprises the following steps: material preparation; welding; solid solution annealing, the steel strip after welding is preheated and then annealed; tensile straightening and scale breaking process, the annealed steel strip is placed in the tensile straightening and scale breaking area; shot blasting and phosphorus breaking process, the tensile straightened steel strip is placed in the shot blasting area for shot blasting; chemical pickling, the shot blasted steel strip is pickled by mixed acid of sulfuric acid, nitric acid and hydrofluoric acid; and the tension density of each part in the production process is controlled. The application guarantees the hardness, yield strength and tensile strength of the SUS630 steel strip, simultaneously improves the elongation, reduces the pickling difficulty, realizes the assembly line production of the hot-rolled annealed pickling of the precipitation hardening martensitic stainless steel SUS630, and improves the production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of precipitation hardening martensitic stainless steel SUS630 production technology, and particularly relates to a production method of precipitation hardening martensitic stainless steel SUS630 hot rolling annealing pickling. Background Technology

[0002] SUS630, a precipitation-hardening martensitic stainless steel, is a type of martensitic precipitation stainless steel developed by adding elements such as Cu and Nb to Cr17 type stainless steel. Due to its low carbon, high chromium, and copper content, SUS630 exhibits superior corrosion resistance compared to conventional Cr13 type martensitic stainless steel. After age hardening, SUS630 can reach a hardness of HRC50, ensuring high strength, high hardness, and high corrosion resistance while exhibiting no significant thermal expansion or contraction. It is widely used in electronic circuit boards, pressure vessels, turbine blades, and other fields.

[0003] During the production and processing of SUS630 steel strip, the material exists in either a solution-treated or rolled state. It possesses extremely high strength and hardness, but relatively low elongation. For example, its yield strength is 800-1200 MPa, and its hardness is HRC 30-45, but its elongation is only 2-9%, making production extremely difficult. Hot-rolled SUS630 steel strip, due to the presence of iron oxide scale on its surface and its high strength and hardness, cannot be directly cold-rolled and requires annealing and pickling. However, the high strength and poor shape of the raw material necessitate the use of specialized hot-rolling, annealing, and pickling lines. Secondly, during the holding process at 800-950℃, SUS630 experiences brittle phase precipitation, requiring strict adherence to the annealing process. Furthermore, after high-temperature solution annealing, a complex oxide scale composed of elements such as Fe, Cr, Ni, Cu, and Nb forms on the surface, further complicating pickling. Summary of the Invention

[0004] To address some or all of the technical problems existing in the prior art, the present invention provides a production method for precipitation-hardening martensitic stainless steel SUS630 by hot rolling, annealing, and pickling.

[0005] The present invention provides a production method for precipitation-hardening martensitic stainless steel SUS630 through hot rolling, annealing, and pickling, comprising: Step S1: Material preparation. Select hot-rolled SUS630 steel strip and uncoil it using an uncoiler. After uncoiling, cut off the material head. Step S2, welding: trim the tail of the previous steel coil and weld the head and tail of the coil into a steel strip by in-line gas metal arc welding. Step S3, solution annealing: the welded steel strip is preheated and then annealed at a temperature of 1020℃-1060℃. The holding time is 1.1min-2.5min for every 1mm thickness. After the holding time, the strip is rapidly cooled by mist cooling. The temperature of the cooled steel strip is ≤80℃. Step S4, tension straightening and descaling process: The annealed steel strip is placed in the tension straightening and descaling area, where the three sets of descaling rollers have a reduction of 80mm-150mm, 80mm-150mm and 10mm-40mm, a tension of 400KN-1200KN, and a steel strip elongation of 0.5%-1.5%; Step S5, shot blasting process: The stretched and straightened steel strip is placed in the shot blasting area for shot blasting. The shot blasting head current is 80A-95A, the shot blasting speed is 1700 R / min-2100 R / min, the abrasive is S110, and the HRC is 43-48. Step S6, chemical pickling: The shot-blasted steel strip is pickled in a mixed acid solution of sulfuric acid, nitric acid, and hydrofluoric acid. The sulfuric acid concentration is 250g / L-350g / L, the temperature is 70℃-90℃, and the iron ion concentration is ≤60g / L. The mixed acid solution has a nitric acid concentration of 100g / L-180g / L, a hydrofluoric acid concentration of 10g / L-20g / L, a temperature of 40℃-50℃, and an iron ion concentration of ≤40g / L. The reaction time of the steel strip in the sulfuric acid bath is 1.5min-5min, and the reaction time in the mixed acid bath is 4min-13min. After the steel strip exits the acid bath, the surface of the steel strip is rinsed with high-pressure water and brushed and squeezed with rollers.

[0006] Furthermore, in the above-mentioned production method of precipitation-hardening martensitic stainless steel SUS630 hot-rolled, annealed, and pickled, the tension density of the uncoiling portion during the production process is 1.6 KN / mm. 2 -2.0KN / mm 2 The tension density of the inlet loop is 0.8 kN / mm. 2 -1.0KN / mm 2 The tension density of the furnace section is 0.6 kN / mm². 2 -0.8KN / mm 2 The tension density of the pickling section is 1.0 kN / mm². 2 -1.2KN / mm 2 The tension density of the export loop is 0.8 kN / mm. 2 -1.0KN / mm 2 The tension density of the winding section is 1.2 kN / mm. 2 -1.4KN / mm 2 .

[0007] Furthermore, in the above-mentioned production method of precipitation-hardening martensitic stainless steel SUS630 hot-rolled annealed pickled, in step S1, the thickness of the SUS630 steel strip is 5.0mm-14.0mm and the width is 900mm-2100mm.

[0008] Furthermore, in the above-mentioned production method of precipitation hardening martensitic stainless steel SUS630 hot rolling annealing pickling, in step S2, the material head and tail are aligned and pressed together, the distance between the material head and tail is 1mm-6mm, the welding wire is ER309L solid core welding wire, the wire feeding speed is 6m / min-12m / min, the welding speed is 0.4m / min-0.6m / min, the welding voltage is 27V-32V, and the current is 270A-360A.

[0009] Furthermore, in the above-mentioned production method of hot-rolled, annealed, and pickled precipitation-hardening martensitic stainless steel SUS630, in step S3, the preheating temperature is 300℃-600℃, and the preheating time is 0.4min-1min per 1mm thickness. In order to ensure that the temperature range of 800℃-950℃ where brittle phases precipitate is quickly avoided, and that the steel strip quickly reaches the process temperature, the furnace temperature of the first 1 / 6-1 / 5 of the furnace section should be 30-80℃ higher than the process temperature, and the furnace temperature of the remaining part should be the same as the process temperature, with a TV value of 40-80.

[0010] Furthermore, in the above-mentioned production method of precipitation hardening martensitic stainless steel SUS630 hot rolling annealing pickling, in step S4, the stretching and straightening descaling area consists of five sets of descaling rollers with a diameter of 100mm, of which three sets are on top and two sets are on the bottom. When the steel strip passes through, the three sets of descaling rollers on the top press down.

[0011] Furthermore, in the above-mentioned production method of hot-rolled, annealed, and pickled precipitation-hardening martensitic stainless steel SUS630, in step S5, the shot blasting area consists of four shot blasting machines, each with six blasting heads, including three upper blasting heads and three lower blasting heads, each driven by a 90KW variable frequency motor.

[0012] Furthermore, in the above-mentioned production method of hot-rolled annealing and pickling of precipitation-hardening martensitic stainless steel SUS630, in step S6, when the steel strip is pickled in a mixed acid of sulfuric acid, nitric acid and hydrofluoric acid, it first passes through a sulfuric acid tank and then through a mixed acid tank of nitric acid and hydrofluoric acid.

[0013] The production method of precipitation-hardening martensitic stainless steel SUS630 by hot rolling, annealing, and pickling of the present invention has the following advantages and beneficial effects: (1) Solution annealing effectively ensures the strength and hardness of SUS630, improves the elongation, and reduces the occurrence of precipitates during solution annealing; (2) By adopting the stretching and straightening descaling process and the shot blasting descaling process, SUS630 can be pretreated, which can effectively loosen or remove the iron scales on the surface, and at the same time improve the shape of SUS630 steel strip. (3) Chemical pickling can effectively clean the surface of SUS630 steel strip and form an upper production line to meet the needs of mass production. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for further understanding of the embodiments of the present invention and constitute a part of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 The metallographic structure after solution annealing according to the present invention; Figure 2 This is a schematic diagram of the scale-breaking roller distribution in the stretching, straightening, and scale-breaking process of the present invention; Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0016] The present invention provides a production method for precipitation-hardening martensitic stainless steel SUS630 through hot rolling, annealing, and pickling, comprising: Step S1: Material preparation. Select hot-rolled SUS630 steel strip and uncoil it using an uncoiler. After uncoiling, cut off the material head. Step S2, welding: trim the tail of the previous steel coil and weld the head and tail of the coil into a steel strip by in-line gas metal arc welding. Step S3, solution annealing: the welded steel strip is preheated and then annealed at a temperature of 1020℃-1060℃. The holding time is 1.1min-2.5min for every 1mm thickness. After the holding time, the strip is rapidly cooled by mist cooling. The temperature of the cooled steel strip is ≤80℃. Step S4, tension straightening and descaling process: The annealed steel strip is placed in the tension straightening and descaling area, where the three sets of descaling rollers have a reduction of 80mm-150mm, 80mm-150mm and 10mm-40mm, a tension of 400KN-1200KN, and a steel strip elongation of 0.5%-1.5%; Step S5, shot blasting process: The stretched and straightened steel strip is placed in the shot blasting area for shot blasting. The shot blasting head current is 80A-95A, the shot blasting speed is 1700 R / min-2100 R / min, the abrasive is S110, and the HRC is 43-48. Step S6, chemical pickling: The shot-blasted steel strip is pickled in a mixed acid solution of sulfuric acid, nitric acid, and hydrofluoric acid. The sulfuric acid concentration is 250g / L-350g / L, the temperature is 70℃-90℃, and the iron ion concentration is ≤60g / L. The mixed acid solution has a nitric acid concentration of 100g / L-180g / L, a hydrofluoric acid concentration of 10g / L-20g / L, a temperature of 40℃-50℃, and an iron ion concentration of ≤40g / L. The reaction time of the steel strip in the sulfuric acid bath is 1.5min-5min, and the reaction time in the mixed acid bath is 4min-13min. After the steel strip exits the acid bath, the surface of the steel strip is rinsed with high-pressure water and brushed and squeezed with rollers.

[0017] Furthermore, in the production method of precipitation-hardening martensitic stainless steel SUS630 by hot rolling, annealing, and pickling of the present invention, the tension density of the uncoiling portion during the production process is 1.6 KN / mm. 2 -2.0KN / mm 2 The tension density of the inlet loop is 0.8 kN / mm. 2 -1.0KN / mm 2 The tension density of the furnace section is 0.6 kN / mm². 2 -0.8KN / mm 2 The tension density of the pickling section is 1.0 kN / mm². 2 -1.2KN / mm 2 The tension density of the export loop is 0.8 kN / mm. 2 -1.0KN / mm 2 The tension density of the winding section is 1.2 kN / mm. 2 -1.4KN / mm 2 This effectively ensures that the steel strip is not scratched or deviated during operation, and also allows the steel coil to be wound tightly and neatly when it is wound up.

[0018] Furthermore, in the production method of precipitation-hardening martensitic stainless steel SUS630 hot-rolled annealed pickled according to the present invention, in step S1, the thickness of the SUS630 steel strip is 5.0mm-14.0mm and the width is 900mm-2100mm.

[0019] Furthermore, in the production method of precipitation-hardening martensitic stainless steel SUS630 hot-rolled annealed pickled according to the present invention, in step S2, the material head and tail are aligned and pressed together, the distance between the material head and tail is 1mm-6mm, the welding wire is ER309L solid core welding wire, the wire feeding speed is 6m / min-12m / min, the welding speed is 0.4m / min-0.6m / min, the welding voltage is 27V-32V, and the current is 270A-360A.

[0020] Furthermore, in the production method of precipitation-hardening martensitic stainless steel SUS630 by hot rolling, annealing, and pickling according to the present invention, such as Figure 1 As shown, in step S3, the preheating temperature is 300℃-600℃, and the preheating time is 0.4min-1min per 1mm thickness. To ensure rapid avoidance of the brittle phase precipitation temperature range of 800℃-950℃ and to allow the steel strip to quickly reach the process temperature, the furnace temperature of the first 1 / 6-1 / 5 of the furnace section should be 30-80℃ higher than the process temperature, and the furnace temperature of the remaining part should be consistent with the process temperature, with a TV value of 40-80. This effectively ensures that the grains are fully restored after solution annealing, the mechanical properties are qualified, the hardness is still HRC30-HRC33, the yield strength RP0.2 is 800MPa-1100MPa, the tensile strength Rm is 1100 MPa-1300 MPa, and the elongation A50 is 5%-12%.

[0021] Furthermore, in the production method of precipitation-hardening martensitic stainless steel SUS630 by hot rolling, annealing, and pickling according to the present invention, such as Figure 2 As shown, in step S4, the stretching and straightening descaling area consists of five sets of descaling rollers with a diameter of 100mm, three sets on top and two sets on the bottom. When the steel strip passes through, the three sets of descaling rollers on the top press down, thereby causing the iron scales on the surface of the steel strip to crack or even peel off, making the plate shape basically straight.

[0022] Furthermore, in the production method of precipitation-hardening martensitic stainless steel SUS630 hot-rolled annealing and pickling of the present invention, in step S5, the shot blasting area consists of four shot blasting machines, each with six shot blasting heads, including three upper shot blasting heads and three lower shot blasting heads. Each shot blasting head is driven by a 90KW variable frequency motor, thereby ensuring that the upper and lower surfaces of the steel strip are shot blasted simultaneously.

[0023] Furthermore, in the production method of hot-rolled annealed pickling of precipitation-hardening martensitic stainless steel SUS630 of the present invention, in step S6, when the steel strip is pickled in a mixed acid of sulfuric acid, nitric acid and hydrofluoric acid, it first passes through a sulfuric acid tank and then through a mixed acid tank of nitric acid and hydrofluoric acid, thereby effectively removing the surface oxide scale and realizing pickling in an assembly line manner.

[0024] Example 1: Using a coil of SUS630 hot-rolled black steel as raw material, its chemical composition by mass percentage is: C: 0.0337%, Cr: 15.2013%, Ni: 4.2652%, Cu: 3.4975%, Nb: 0.2295%, Si: 0.3666%, Mn: 0.6745%, P: 0.0161%, S: 0.0011%, N: 0.0308%, with the remainder being Fe and other unavoidable impurities. The specifications of this steel coil are: thickness 5.0 mm, width 1507 mm, and weight 23910 kg.

[0025] An embodiment of a production method for precipitation-hardening martensitic stainless steel SUS630 hot-rolled, annealed, and pickled includes the following steps: Step 1: Place the SUS630 steel coil to be produced on the uncoiler of the hot rolling annealing and pickling line for uncoiling. Send the end of the coil to the shearing machine to cut it off, ensuring that the end face of the steel strip is straight after shearing.

[0026] Step 2: Trim the tail of the previous steel coil to align and press the trimmed head and tail together. Use in-line gas metal arc welding (MIG welding) to weld the two steel strips together. The distance (i.e., weld gap) should be 3mm. Use ER309L solid core welding wire, with a wire feed speed of 12m / min, a welding speed of 0.5m / min, a welding voltage of 28V, and a current of 280-300A. The weld joint should have a full front and a complete back weld.

[0027] Step 3: Perform solution annealing on the welded steel strip. Preheating is performed first at 500-550℃ for 3 minutes. The annealing temperature is 1040℃. To ensure the steel strip quickly reaches the process temperature, the temperature of the first 1 / 6 of the furnace is 1080℃, and the remaining furnace temperature is 1040℃, with a TV value of 65, meaning the annealing speed is 13 m / min. After heat treatment, the steel strip is rapidly cooled using mist cooling, resulting in a plate temperature of 65℃.

[0028] Step 4: The solution-annealed steel strip is then introduced into the stretching and straightening descaling area. It is repeatedly bent and stretched between five descaling rollers with a diameter of 100mm, three sets on top and two sets on the bottom. As the strip passes through, the top three sets of rollers press down with reductions of 110mm, 110mm, and 20mm respectively, at a tension of 550KN. The strip undergoes plastic deformation with an elongation of 0.8%. After stretching and straightening with the above parameters, the iron scale on the steel strip surface may crack or even peel off, and the strip shape becomes basically straight.

[0029] Step 5: After the steel strip has been stretched and straightened to break the scale thickness, it enters the shot blasting area. Four shot blasting machines are used, two machines per group, each machine has a total of 6 blasting heads (including 3 upper blasting heads and 3 lower blasting heads), the blasting head current is 85A, the shot blasting wheel speed is 1850r / min, and the abrasive is S110.

[0030] Step 6: After shot blasting, the steel strip undergoes chemical pickling, first passing through a sulfuric acid bath, then through a mixed acid bath of nitric acid and hydrofluoric acid. The sulfuric acid concentration is 338.6 g / L, temperature 81℃, and iron ion concentration is 26 g / L; the mixed acid contains 175 g / L nitric acid, 17.4 g / L hydrofluoric acid, temperature 44℃, and iron ion concentration 33 g / L. Considering the solution annealing time, the reaction time of the steel strip in the sulfuric acid bath is 2 minutes, and the reaction time in the mixed acid bath is 3.2 minutes. After exiting the acid bath, the steel strip surface is rinsed with high-pressure water, and brush rollers and squeeze rollers are used to scrub the surface to ensure uniform pickling and no residual acid.

[0031] To ensure that the steel strip is not scratched, does not deviate, and is wound tightly and evenly during operation, the tension density of each part of the entire production line is shown in the table below:

[0032] In summary, compared with the prior art, the continuous casting method for high-aluminum peritectic steel with an aluminum content ≥0.45% of the present invention has the following advantages and beneficial effects: (1) Solution annealing effectively ensures the strength and hardness of SUS630, improves the elongation, and reduces the occurrence of precipitates during solution annealing; (2) By adopting the stretching and straightening descaling process and the shot blasting descaling process, SUS630 can be pretreated, which can effectively loosen or remove the iron scales on the surface, and at the same time improve the shape of SUS630 steel strip. (3) Chemical pickling can effectively clean the surface of SUS630 steel strip and form an upper production line to meet the needs of mass production.

[0033] It should be noted that, unless otherwise expressly specified and limited, the term "connection" or its synonyms should be interpreted broadly in this document. For example, "connection" can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal communication of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. Furthermore, expressions such as "first" and "second" are merely used to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Meanwhile, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. In addition, the terms "front," "rear," "left," "right," "upper," and "lower" in this document refer to the placement states shown in the accompanying drawings.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing precipitation-hardening martensitic stainless steel SUS630 by hot rolling, annealing, and pickling, characterized in that, The production method of the precipitation-hardening martensitic stainless steel SUS630 hot-rolled annealed pickling includes: Step S1: Material preparation. Select hot-rolled SUS630 steel strip and uncoil it using an uncoiler. After uncoiling, cut off the material head. Step S2, welding: trim the tail of the previous steel coil and weld the head and tail of the coil into a steel strip by in-line gas metal arc welding. Step S3, solution annealing: The welded steel strip is preheated before annealing. The preheating temperature is 300℃-600℃, and the preheating time is 0.4min-1min per 1mm thickness. To ensure rapid avoidance of the brittle phase precipitation temperature range of 800℃-950℃ and to ensure the steel strip quickly reaches the process temperature, the furnace temperature in the first 1 / 6-1 / 5 of the furnace section should be 30-80℃ higher than the process temperature. The temperature of the remaining section should be the same as the process temperature, with a TV value of 40-80. The annealing temperature is 1020℃-1060℃, and the holding time is 1.1min-2.5min per 1mm thickness. After holding, rapid cooling is performed using mist cooling. The temperature of the steel strip after cooling is ≤80℃, effectively ensuring complete grain recovery after solution annealing, qualified mechanical properties, hardness still within HRC30-HRC33, yield strength RP0.2 of 800MPa-1100MPa, and tensile strength Rm of 1100MPa. MPa -1300 MPa, elongation A50 is 5%-12%; Step S4, tension straightening and descaling process: The annealed steel strip is placed in the tension straightening and descaling area, where the three sets of descaling rollers have a reduction of 80mm-150mm, 80mm-150mm and 10mm-40mm, a tension of 400KN-1200KN, and a steel strip elongation of 0.5%-1.5%; Step S5, shot blasting process: The stretched and straightened steel strip is placed in the shot blasting area for shot blasting. The shot blasting head current is 80A-95A, the shot blasting speed is 1700 R / min-2100 R / min, the abrasive is S110, and the HRC is 43-48. Step S6, chemical pickling: The shot-blasted steel strip is pickled in a mixed acid solution of sulfuric acid, nitric acid, and hydrofluoric acid. The sulfuric acid concentration is 250g / L-350g / L, the temperature is 70℃-90℃, and the iron ion concentration is ≤60g / L. The mixed acid solution has a nitric acid concentration of 100g / L-180g / L, a hydrofluoric acid concentration of 10g / L-20g / L, a temperature of 40℃-50℃, and an iron ion concentration of ≤40g / L. The reaction time of the steel strip in the sulfuric acid bath is 1.5min-5min, and the reaction time in the mixed acid bath is 4min-13min. After the steel strip exits the acid bath, the surface of the steel strip is rinsed with high-pressure water and brushed and squeezed with rollers.

2. The production method of precipitation-hardening martensitic stainless steel SUS630 by hot rolling, annealing, and pickling as described in claim 1, characterized in that, The tension density of the unwinding section during production is 1.6 kN / mm. 2 -2.0KN / mm 2 The tension density of the inlet loop is 0.8 kN / mm. 2 -1.0KN / mm 2 The tension density of the furnace section is 0.6 kN / mm². 2 -0.8KN / mm 2 The tension density of the pickling section is 1.0 kN / mm². 2 -1.2KN / mm 2 The tension density of the export loop is 0.8 kN / mm. 2 -1.0KN / mm 2 The tension density of the winding section is 1.2 kN / mm. 2 -1.4KN / mm 2 .

3. The production method of precipitation-hardening martensitic stainless steel SUS630 by hot rolling, annealing, and pickling as described in claim 1, characterized in that, In step S1, the SUS630 steel strip has a thickness of 5.0mm-14.0mm and a width of 900mm-2100mm.

4. The production method of precipitation-hardening martensitic stainless steel SUS630 by hot rolling, annealing, and pickling as described in claim 1, characterized in that, In step S2, the material head and tail are aligned and pressed together, with a distance of 1mm-6mm between them. The welding wire used is ER309L solid core welding wire, the wire feeding speed is 6m / min-12m / min, the welding speed is 0.4m / min-0.6m / min, the welding voltage is 27V-32V, and the current is 270A-360A.

5. The production method of precipitation-hardening martensitic stainless steel SUS630 by hot rolling, annealing, and pickling as described in claim 1, characterized in that, In step S4, the stretching and straightening descaling area consists of five sets of descaling rollers with a diameter of 100mm, three sets on top and two sets on the bottom. When the steel strip passes through, the three sets of descaling rollers on top press down.

6. The production method of precipitation-hardening martensitic stainless steel SUS630 by hot rolling, annealing, and pickling as described in claim 1, characterized in that, In step S5, the shot blasting area consists of four shot blasting machines, each with six blasting heads, including three upper blasting heads and three lower blasting heads, each driven by a 90KW variable frequency motor.

7. The production method of precipitation-hardening martensitic stainless steel SUS630 by hot rolling, annealing, and pickling as described in claim 1, characterized in that, In step S6, when the steel strip is pickled in a mixture of sulfuric acid, nitric acid and hydrofluoric acid, it first passes through a sulfuric acid tank and then through a mixed acid tank of nitric acid and hydrofluoric acid.

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