Manufacturing method of martensitic stainless steel

Abstract

The invention provides a manufacturing method of martensitic stainless steel. The manufacturing method comprises the following steps: controlling the following chemical components of the martensitic stainless steel in percentage by weight: 0.19-0.21 wt% of C, less than or equal to 0.50 wt% of Si, less than or equal to 0.50 wt% of Mn, less than or equal to 0.030 wt% of P, less than or equal to 0.005 wt% of S, 12.00-12.50 wt% of Cr, less than or equal to 0.050 wt% of N and less than or equal to 0.20 wt% of Ni; the process route comprises the steps of first-grade 410 waste stainless steel, alloy melting furnace smelting, LF refining, slab continuous casting, steel billet hot delivery, hot continuous rolling, annealing, inspection, packaging and warehousing. A four-rack hot continuous rolling mill is adopted for rough rolling, a nine-rack hot continuous rolling mill is adopted for finish rolling, the initial rolling temperature is 1190-1220 DEG C, the final rolling temperature is controlled to be 1020-1070 DEG C, and the coiling temperature is 870-970 DEG C; the martensitic stainless steel hot-rolled coil is placed in a box-type annealing furnace, the temperature is increased to 640 DEG C firstly, then increased to 800 DEG C and kept for 2 hours, the temperature is increased to 840 DEG C at the speed of 0.22 DEG C / min and kept for 30 hours, and the martensitic stainless steel hot-rolled coil is cooled to the room temperature along with the furnace after heat preservation is finished.

Description

Technical Field

[0001] This invention relates to the field of stainless steel production and manufacturing, and specifically to a method for manufacturing martensitic stainless steel. Background Technology

[0002] Martensitic stainless steel is a type of stainless steel whose properties can be adjusted through heat treatment (quenching and tempering). It is a type of hardenable stainless steel, with typical grades including 1Cr13, 2Cr13, 3Cr13, and 4Cr13. Under hardening conditions, martensitic stainless steel exhibits good resistance to the atmosphere, certain wear resistance and corrosion resistance, and high hardness, making it suitable for the processing and manufacturing of cutting tools, medical devices, shearing blades, and various precision machinery.

[0003] Currently, there are two types of production processes for martensitic stainless steel: short-process and long-process. Chinese invention patent CN202210635608.6 discloses a highly efficient long-process method for producing martensitic stainless steel, employing hot metal pretreatment, induction furnace melting of scrap steel and ferrochrome, blending, and AOD converter blowing. This method uses a medium-frequency furnace to melt ferrochrome and scrap steel, increasing the AOD furnace inlet temperature, reducing the amount of ferrochrome added during AOD smelting, lowering ferrosilicon consumption, and reducing slag volume during AOD smelting. Chinese invention patent CN200810236260.3 discloses a short-process method for smelting high-carbon, high-chromium martensitic stainless steel, using a medium-frequency induction furnace to heat the raw materials, melting them into a liquid state. The resulting liquid raw material is transferred to a refining furnace where it is electrically heated to create slag, argon-blown, and stirred to remove inclusions.

[0004] The short-process method in the aforementioned invention patent, which uses an electric furnace (medium-frequency furnace), has the main problems of high requirements for raw material composition, limited raw material applicability, large slag output, and the need for refining in an AOD furnace. The long-process method, which uses all molten iron, suffers from a long AOD smelting cycle, and only adds 400 series scrap steel in the induction furnace and AOD converter sections, resulting in low scrap steel utilization.

[0005] In summary, the existing technology has the following problems: the short-process production of martensitic stainless steel produces a large amount of slag, which is difficult to remove and requires refining in an AOD furnace. Summary of the Invention

[0006] This invention provides a method for manufacturing martensitic stainless steel to solve the problems of large slag output, difficulty in slag removal, and the need for refining in an AOD furnace in short-process production of martensitic stainless steel.

[0007] Therefore, the present invention proposes a method for manufacturing martensitic stainless steel, the method comprising:

[0008] The chemical composition of martensitic stainless steel is controlled as follows by weight percentage: C: 0.19-0.21 wt%, Si ≤ 0.50 wt%, Mn ≤ 0.50 wt%, P ≤ 0.030 wt%, S ≤ 0.005 wt%, Cr: 12.00-12.50 wt%, N ≤ 0.050 wt%, Ni ≤ 0.20 wt%, and the total amount of one or more of Cu and Al ≤ 0.1%, with the balance being Fe and unavoidable trace elements;

[0009] The manufacturing process of martensitic stainless steel is as follows: Grade 1 410 scrap stainless steel, alloy melting furnace smelting, LF refining, slab continuous casting, hot billet delivery, hot continuous rolling, annealing, inspection, packaging and warehousing.

[0010] In hot continuous rolling: the roughing mill adopts a four-stand hot continuous rolling mill, the finishing mill adopts a nine-stand hot continuous rolling mill, the initial rolling temperature is 1190~1220℃, the final rolling temperature is controlled at 1020~1070℃, and the coiling temperature is 870~970℃.

[0011] During annealing: hot-rolled martensitic stainless steel coils are placed in a box-type annealing furnace and first heated to 640℃, then heated to 800℃ and held for 2 hours. The temperature is then increased to 840℃ at a rate of 0.22℃ / min and held for 30 hours. After the holding period, the furnace is cooled to room temperature.

[0012] This invention also provides a hot-rolled martensitic stainless steel strip. The chemical composition of the martensitic stainless steel, by weight percentage, is: C: 0.19–0.21 wt%, Si ≤ 0.50 wt%, Mn ≤ 0.50 wt%, P ≤ 0.030 wt%, S ≤ 0.005 wt%, Cr: 12.00–12.50 wt%, N ≤ 0.050 wt%, Ni ≤ 0.20 wt%, and one or more of Cu and Al in total ≤ 0.1%, with the balance being Fe and unavoidable trace elements. The hot-rolled martensitic stainless steel strip is manufactured using the aforementioned method for manufacturing martensitic stainless steel.

[0013] Furthermore, the hot-rolled thickness of martensitic stainless steel hot-rolled strip is 2-5 mm.

[0014] Furthermore, the hot-rolled thickness of the martensitic stainless steel hot-rolled strip is 3-4 mm.

[0015] Furthermore, the hot-rolled thickness of the martensitic stainless steel hot-rolled strip is 3 mm, and the chemical composition of the martensitic stainless steel hot-rolled strip by weight percentage is: C: 0.207, Si: 0.39, Mn: 0.50, P: 0.029, S: 0.002, Ni: 0.13, Cr: 12.30, Al: 0.002, N: 0.036;

[0016] Furthermore, the hot-rolled thickness of the martensitic stainless steel hot-rolled strip is 3 mm, and the chemical composition of the martensitic stainless steel hot-rolled strip by weight percentage is: C: 0.209, Si: 0.48, Mn: 0.47, P: 0.031, S: 0.003, Ni: 0.12, Cr: 12.30, Al: 0.004, N: 0.037;

[0017] Furthermore, the hot-rolled thickness of the martensitic stainless steel hot-rolled strip is 4 mm, and the chemical composition of the martensitic stainless steel hot-rolled strip by weight percentage is: C: 0.214, Si: 0.45, Mn: 0.41, P: 0.028, S: 0.003, Ni: 0.12, Cr: 12.33, Al: 0.002, N: 0.034;

[0018] Furthermore, the hot-rolled thickness of the martensitic stainless steel hot-rolled strip is 4 mm, and the chemical composition of the martensitic stainless steel hot-rolled strip by weight percentage is: C: 0.206, Si: 0.40, Mn: 0.42, P: 0.027, S: 0.002, Ni: 0.11, Cr: 12.29, Al: 0.002, N: 0.032.

[0019] This invention employs a short-process technology, selects widely applicable scrap steel raw materials, and utilizes a suitable alloy melting furnace process, continuous casting, rolling, and annealing processes to obtain martensitic stainless steel with stable mechanical properties and good pitting corrosion resistance. By selecting first-grade scrap stainless steel raw materials and quantitatively adding ferrosilicon powder for slag formation before tapping from the alloy melting furnace, the composition of the slag is controlled, the tapping temperature of the alloy melting furnace is increased, and the LF refining time is guaranteed. This solves the problems of long AOD smelting cycles and low scrap steel utilization rates in long-process technologies, achieving green, efficient, and stable production. The martensitic stainless steel obtained by this invention has a yield strength Rp0.2 ≥ 225 MPa, a tensile strength Rm ≥ 520 MPa, and an elongation A... 50mm ≥18%, Rockwell hardness ≤97, metallographic structure is ferrite and carbide, grain size is grade 10. Attached Figure Description

[0020] Figure 1 This is a metallographic image of Embodiment 1 of the present invention, magnified 500 times. Detailed Implementation

[0021] To provide a clearer understanding of the technical features, objectives, and effects of this invention, the invention is now described.

[0022] This invention provides a method for manufacturing martensitic stainless steel, the process route of which is: Grade 1 410 scrap stainless steel → alloy melting furnace → LF refining → slab continuous casting → hot billet delivery → hot continuous rolling → annealing → inspection, packaging and warehousing.

[0023] Alloy melting furnace smelting: Scrap steel is poured into the alloy melting furnace and heated by electricity. Under normal furnace cycles, a steel retention operation is adopted, with 60 tons of molten steel discharged into the ladle and 10 tons retained to provide heat for the next furnace. In the later stage of melting (when about 50 tons have melted), 60 kg of ferrosilicon powder is added to each furnace to deoxidize and reduce the top slag of the alloy melting furnace, thereby reducing chromium oxides in the slag and improving its fluidity. After the scrap steel is melted clean, samples are taken to test the composition. Carbon raisers and ferrochrome are added according to the composition. After the composition meets the requirements, the steel is tapped at a tapping temperature of 1630℃, and slag is not skimmed off during tapping. The composition of the tapped steel from the alloy melting furnace is shown in Table 1.

[0024] Table 1. Steel composition (%) from alloy melting furnace

[0025] C Si Mn P S Cr N Ni Mo Co Cu Ca Al 0.198 0.29 0.43 0.028 0.004 12.34 0.036 0.14 0.016 0.02 0.06 0.0004 0.001

[0026] LF refining: The LF inlet temperature is 1550℃. The molten steel is heated in the LF furnace by electricity. Lime, fluorite balls and other slag-forming materials are added according to the top slag condition. The slag basicity is controlled at 2.0-2.5 to ensure the desulfurization effect. Argon gas is used to stir and remove impurities.

[0027] Slab continuous casting: The process adopts full-process protective casting process, the tundish casting temperature is 1530~1550℃, the tundish uses alkaline covering agent, the liquid level fluctuation in the crystallizer is controlled within ±3mm, special protective slag for martensitic stainless steel is used, and the billet casting speed is 0.7~0.9m / min.

[0028] High-precision continuous casting control process: adopt the casting process of "weak cooling (specific water volume 0.50L / kg) + low casting speed (0.7~0.9m / min) + high straightening temperature (950℃ and above)" to reduce the generation of surface cracks on slabs.

[0029] Hot continuous rolling: The billet is hot-sent, with an entry temperature >400℃ to prevent cold cracking. The homogenization temperature is controlled at 1200-1250℃, and the time in the furnace is about 190-230 minutes. The roughing rolling adopts a four-stand hot continuous rolling mill, and the finishing rolling adopts a nine-stand hot continuous rolling mill. The initial rolling temperature is 1190-1220℃, the final rolling temperature is controlled at 1020-1070℃, and the coiling temperature is 870-970℃. During the rolling process, the amount of cooling water in the roller table and the roll cooling water is controlled. Laminar flow cooling and side spray are not used to avoid cooling water splashing onto the surface of the steel strip. The steel strip is piled up to cool after leaving the line to prevent cold cracking.

[0030] Annealing: The hot-rolled martensitic stainless steel coil is placed in a box-type annealing furnace and heated to 640℃, then heated to 800℃ and held for 2 hours. The temperature is then increased to 840℃ at a rate of 0.22℃ / min and held for 30 hours. After the holding period, the coil is cooled to room temperature with the furnace.

[0031] The product (martensitic stainless steel hot-rolled strip in annealed state) has a yield strength Rp0.2≥225MPa, tensile strength Rm≥520MPa, elongation A50mm≥18%, and Rockwell hardness≤97.

[0032] Specific examples:

[0033] Martensitic stainless steel and its production method employ the following component ratios and specific processes. Table 2 shows the composition (by weight percentage) of the steels in each embodiment. Table 3 shows the process parameters corresponding to the steels described in Table 2. Table 4 shows the mechanical properties corresponding to the steels with the compositions described in the embodiments of Table 2.

[0034] Table 2: Chemical Composition of Products (by Weight Percentage) and Indicators

[0035]

[0036] Table 3: Key process parameters for each embodiment

[0037]

[0038] Table 4: Mechanical properties of austenitic stainless steel obtained in each embodiment

[0039] Example <![CDATA[R p0.2 / MPa]]> <![CDATA[R m / MPa]]> <![CDATA[A 50mm / %]]> Rockwell hardness HRB Example 1 352 609 22.0 86 Example 2 350 580 22.0 84 Example 3 345 595 22.0 85 Example 4 349 584 22.0 85

[0040] Figure 1 The metallographic structure of Example 1 is: ferrite and carbides, with a grain size of grade 10.

[0041] The martensitic stainless steel of this invention has a yield strength of 340 MPa ≤ Rp0.2 ≤ 370 MPa, a tensile strength of 570 MPa ≤ Rm ≤ 620 MPa, and an elongation A. 50mm ≥18%, can reach 22%, Rockwell hardness ≤97, can reach below 87, for example 84-86.

[0042] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the invention. The various components of the present invention can be combined with each other without conflict. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for manufacturing martensitic stainless steel, characterized in that, The method for manufacturing the martensitic stainless steel includes: The chemical composition of martensitic stainless steel is controlled as follows by weight percentage: C: 0.19-0.21 wt%, Si ≤ 0.50 wt%, Mn ≤ 0.50 wt%, P ≤ 0.030 wt%, S ≤ 0.005 wt%, Cr: 12.00-12.50 wt%, N ≤ 0.050 wt%, Ni ≤ 0.20 wt%, and the total amount of one or more of Cu and Al ≤ 0.1%, with the balance being Fe and unavoidable trace elements; The manufacturing process of martensitic stainless steel is as follows: Grade 1 410 scrap stainless steel, alloy melting furnace smelting, LF refining, slab continuous casting, hot billet delivery, hot continuous rolling, annealing, inspection, packaging and warehousing. In hot continuous rolling: the roughing mill adopts a four-stand hot continuous rolling mill, the finishing mill adopts a nine-stand hot continuous rolling mill, the initial rolling temperature is 1190~1220℃, the final rolling temperature is controlled at 1020~1070℃, and the coiling temperature is 870~970℃. During annealing: hot-rolled martensitic stainless steel coils are placed in a box-type annealing furnace and first heated to 640℃, then heated to 800℃ and held for 2 hours. The temperature is then increased to 840℃ at a rate of 0.22℃ / min and held for 30 hours. After the holding period, the furnace is cooled to room temperature.

2. The method for manufacturing martensitic stainless steel as described in claim 1, characterized in that, In the alloy melting furnace smelting process: scrap steel is poured into the alloy melting furnace and heated by electricity. A steel retention operation is adopted, with 60 tons of molten steel being poured into the ladle furnace and 10 tons retained to provide heat for the next furnace. In the later stage of melting, 60 kg of ferrosilicon powder is added to each furnace to deoxidize and reduce the top slag of the alloy melting furnace, thereby reducing chromium oxides in the slag and improving its fluidity. After the scrap steel is melted and cleaned, samples are taken to test the composition. Carbon raisers and ferrochrome are added according to the composition. After the composition meets the requirements, the steel is tapped at a tapping temperature of 1630℃. Slag is not removed during tapping.

3. The method for manufacturing martensitic stainless steel as described in claim 1, characterized in that, During LF refining: The LF inlet temperature is 1550℃. The molten steel is heated in the LF furnace by electricity. Depending on the top slag condition, lime, fluorite balls and other slag-forming materials are added to control the slag basicity at 2.0-2.5 to ensure desulfurization effect. Argon gas is used to stir and remove impurities.

4. The method for manufacturing martensitic stainless steel as described in claim 1, characterized in that, In slab continuous casting: a full-process protective casting process is adopted, the tundish casting temperature is 1530~1550℃, an alkaline covering agent is used in the tundish, the liquid level fluctuation in the crystallizer is controlled within ±3mm, a special protective slag for martensitic stainless steel is used, and the billet casting speed is 0.7~0.9m / min.

5. The method for manufacturing martensitic stainless steel as described in claim 1, characterized in that, In hot continuous rolling: control the amount of cooling water for the roller table and the rolls during the rolling process. Laminar flow cooling and side spraying are not used to avoid cooling water splashing onto the surface of the steel strip. After the steel strip leaves the line, it is piled up to cool to prevent cold cracks.

6. The method for manufacturing martensitic stainless steel as described in claim 1, characterized in that, In hot continuous rolling: the hot delivery temperature of the billet is >400℃, the soaking temperature is 1200~1250℃, and the furnace time is 180~230min.

7. The method for manufacturing martensitic stainless steel as described in claim 1, characterized in that, The hot-rolled thickness of the martensitic stainless steel is 3.0 mm, the soaking temperature is 1210℃, the furnace time is 220 min, the final rolling temperature is 1023℃, the coiling temperature is 915℃, the annealing temperature is 850℃, and the annealing holding time is 30 h.

8. The method for manufacturing martensitic stainless steel as described in claim 1, characterized in that, The hot-rolled thickness of the martensitic stainless steel is 3.0 mm, the soaking temperature is 1200℃, the furnace time is 226 min, the final rolling temperature is 1030℃, the coiling temperature is 918℃, the annealing temperature is 850℃, and the annealing holding time is 30 h.

9. The method for manufacturing martensitic stainless steel as described in claim 1, characterized in that, The hot-rolled thickness of the martensitic stainless steel is 4.0 mm, the soaking temperature is 1200℃, the furnace time is 223 min, the final rolling temperature is 1050℃, the coiling temperature is 927℃, the annealing temperature is 850℃, and the annealing holding time is 30 h.

10. The method for manufacturing martensitic stainless steel as described in claim 1, characterized in that, The hot-rolled thickness of the martensitic stainless steel is 4.0 mm, the soaking temperature is 1205℃, the furnace time is 198 min, the final rolling temperature is 1048℃, the coiling temperature is 946℃, the annealing temperature is 850℃, and the annealing holding time is 30 h.

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