A method for producing a ferritic stainless steel for mining equipment

Abstract

The application discloses a production method of ferrite stainless steel for mine equipment, which comprises the following steps: S1, feeding ferrite stainless steel slab after continuous casting into a holding pit for heat preservation treatment, and performing hot dressing when the surface temperature of the ferrite stainless steel slab in the holding pit is reduced to 400-450 DEG C; S2, feeding the ferrite stainless steel slab after the hot dressing into a hot rolling heating furnace for heating, controlling the furnace temperature of the hot rolling heating furnace at 1180-1210 DEG C, and controlling the furnace time at 180-220 min; S3, coarsely rolling the ferrite stainless steel slab discharged from the furnace to 28-35 mm by a furnace and roll mill, and then finely rolling to 3.0-6 mm; S4, coiling the rolled material by a coiling machine, and controlling the final coiling temperature at 650-700 DEG C; S5, performing full-hydrogen bell furnace annealing treatment on the hot-rolled black coil; S6, performing homogenizing heat treatment on the steel coil after the annealing treatment; and S7, shearing and packaging.

Description

Technical Field

[0001] This invention relates to the technical field of stainless steel production methods, and in particular to a method for producing ferritic stainless steel for mining equipment. Background Technology

[0002] Ferritic stainless steel, due to its lack of nickel or presence of trace amounts, often incorporates small amounts of stabilizing elements such as Nb, Ti, or V to improve strength or corrosion resistance, while simultaneously reducing the content of elements like C and N. This results in a lower overall cost compared to austenitic stainless steel. Ferritic stainless steel also exhibits a low coefficient of linear expansion, offering significant advantages in regions with substantial temperature variations.

[0003] Railway mining equipment operates under harsh conditions, with materials experiencing severe wear, impact loads, moisture corrosion, corrosive media from ores or coal, and high stress during service. Currently used components mainly include freight cars, hopper car unloading systems, tank cars, excavating and loading equipment, and conveying systems. To meet the demands of these applications while maintaining economic efficiency, stainless steel materials must possess good wear resistance, corrosion resistance, high strength, and good toughness. Considering all factors, ferritic stainless steel with a specific composition is suitable for railway mining equipment, meeting current operating conditions while offering excellent economic benefits. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for producing ferritic stainless steel for mining equipment.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A method for producing ferritic stainless steel for mining equipment includes the following steps: S1. The ferritic stainless steel slab after continuous casting is sent into a heat preservation pit for heat preservation treatment. When the surface temperature of the ferritic stainless steel slab in the heat preservation pit drops to 400℃~450℃, hot grinding is performed. The composition of the ferritic stainless steel slab is C 0~0.015%, N 0~0.015%, Mn 1.4~2.0%, P 0~0.025%, S 0~0.002%, Cr 11~12%, Nb+V 0~0.16%, Ti 0~0.12%, Mo 0~0.2%, Fe balance and other trace elements attached to the raw materials. S2. The hot-rolled slab after hot grinding is sent into the hot rolling furnace for heating. The furnace temperature is controlled at 1180℃~1210℃, the furnace time is controlled at 180~220min, and the furnace exit temperature is controlled at 1180℃~1200℃. S3. The slabs exiting the furnace are rough rolled to 28mm-35mm using a hot rolling mill, and then finish rolled to 3.0-6mm. S4. The rolled coil is wound up by a coiler, and the final winding temperature is controlled at 650℃~700℃ to obtain hot-rolled black coil. S5. Hot-rolled black coils are annealed in a full-hydrogen bell-type furnace. S6. The annealed steel coil is subjected to homogenization heat treatment; S7. Cut and package.

[0006] In step S1, the hot grinding involves grinding the head and tail blanks to a depth of 3.5-4.0 mm on one side and the intermediate blanks to a depth of 3.0-3.5 mm on one side. The grinding is performed twice, with the final grinding using a 20-grit grinding wheel.

[0007] In step S3, the slab exiting the furnace is rough rolled 7 times and finish rolled 5 times by a furnace coil mill, with the finish rolling temperature being 970℃~1000℃.

[0008] In step S4, the strip blowing is not used during winding, but laminar flow cooling is used.

[0009] In step S5, the holding temperature of the bell-type furnace is selected between 780 and 830°C in the two-phase region of the phase diagram, the heating and holding time of the bell-type furnace is controlled between 28 and 30 hours, and the hydrogen purging flow rate is controlled between 10 and 20 m³ / h. 3 / h, after the heat preservation is completed, cool to 580℃ with the heating cover on, then replace with a cooling cover for strong cooling treatment. Once the temperature has cooled to 200℃ or below, it can be taken out of the furnace.

[0010] In step S6, the homogenization heat treatment temperature is selected in the single-phase ferrite region of the phase diagram, and the temperature of the entire region is controlled at 650℃~700℃. The homogenization heat treatment adopts the whole-zone furnace temperature control mode, and the process speed is controlled at 10~15m / min. The scale breaking machine adopts the extension mode, and the elongation rate is controlled at 0~0.5%. Cast shot is used for shot blasting and descaling, and the blasting speed is controlled at 68~72m / s, and the flow rate is controlled at 8~12kg / m2. There are two sets of inlet and outlet for re-brushing and descaling, both of which are put into use and adjusted to level 1~3 respectively. Sulfuric acid pre-acid washing is not used. The nitric acid concentration of mixed acid washing is controlled at 50~60g / L, the hydrofluoric acid concentration is controlled at 8~10g / L, the acid temperature is controlled at 40~45℃, and the metal ion concentration is ≤40g / L.

[0011] In step S7, the strip steel after homogenization heat treatment is in NO.1 or 1D surface condition. It is then cut to a fixed width by a steel coil shearing unit and spun into coils according to the actual needs of the customer. After spun into coils, they are weighed and packaged for storage.

[0012] The beneficial effects of this invention are: 1. By adding trace amounts of Mo to conventional ferritic stainless steel, the strength of the material is improved and the pitting corrosion resistance of ferritic stainless steel is enhanced. 2. The hot rolling production of this invention uses a furnace coil mill for rolling, and the strip rolling temperature is relatively stable, which can ensure that the black coil after the line has a relatively good microstructure, providing a good precursor for subsequent bell annealing; 3. Unlike conventional ferritic stainless steel which uses a single bell-type furnace annealing or a single continuous annealing heat treatment method, this invention uses a bell-type annealing furnace to initially control the microstructure of the black coil, selecting the temperature in the two-phase region. After bell-type annealing, the microstructure is mainly ferrite, with a very small amount of martensite. Subsequently, hot annealing and pickling are used to further homogenize the material microstructure, resulting in a final material microstructure of uniform ferrite and a small amount of martensite, thus improving both the strength and toughness of the material. Attached Figure Description

[0013] Figure 1 This is the stainless steel equilibrium phase diagram of the present invention. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of the invention.

[0015] Example 1 1) Hot Grinding of Slabs: After continuous casting, ferritic stainless steel slabs are placed in an insulated pit for heat preservation treatment, with slow cooling throughout. The slab thickness is 220mm. The composition of the ferritic stainless steel slabs involved is: C 0.012%, N 0.010%, Mn 1.6%, P 0.022%, S 0.002%, Cr 11.3%, Nb+V 0.15%, Ti 0.115%, Mo 0.1%, Fe balance, and other trace elements from the raw materials. Hot grinding is performed when the surface temperature of the ferritic stainless steel slab in the insulated pit drops to 400℃. The grinding depth on one side of the head and tail slabs is 3.6mm, and the grinding depth on one side of the intermediate slabs is 3.2mm. Two grinding passes are used in total, with the final grinding using a 20-grit grinding wheel.

[0016] 2) Slab heating: The furnace temperature of the hot rolling heating furnace is controlled at 1190℃, the furnace time is 220min, and the furnace exit temperature is 1190℃.

[0017] 3) Rolling on a hot-rolled coil mill: The slabs exiting the furnace are rough rolled 7 times to 32mm on a hot-rolled coil mill, and then finished rolled 5 times to 5.5mm. The starting temperature for finishing rolling is 970℃.

[0018] 4) Coiling: The rolled coils are coiled by a coiler. The sheet and strip side blowing is not used, but laminar flow cooling is used. The final coiling temperature is 660℃.

[0019] 5) Bell-type annealing: The hot-rolled black coils from the above production line undergo all-hydrogen bell-type furnace annealing. The holding temperature in the bell-type furnace is selected at 820℃ in the two-phase region of the phase diagram. The furnace temperature is lowered from room temperature to 450℃ using full-speed heating for 80 minutes. Heating from 450℃ to 820℃ uses uniform heating for 12 hours. The holding time at 820℃ is 16 hours. The hydrogen purging flow rate is controlled at 18 m³ / h. After the holding period, the coils are cooled to 580℃ with the heating hood on, then replaced with a cooling hood for forced cooling. The coils are then removed from the furnace when the temperature drops to 200℃.

[0020] 6) Hot Annealing and Pickling Homogenization Treatment: The steel coils treated as described above undergo homogenization heat treatment. The homogenization heat treatment temperature is selected in the single-phase ferrite region of the phase diagram, with the entire region temperature controlled at 700℃. The homogenization heat treatment adopts a full-zone furnace temperature control mode, and the process speed is controlled at 13m / min. The scale-breaking machine adopts an elongation mode, with the elongation rate controlled at 0.4%. Cast shot is used for shot blasting and descaling, with the blasting speed controlled at 72m / s and the flow rate controlled at 12kg / m2. There are two sets of inlet and outlet for the re-brushing descaling, both of which are put into use and adjusted to levels 1 and 3 respectively. Sulfuric acid pre-pickling is not used. The mixed acid pickling is controlled with a nitric acid concentration of 60g / L, a hydrofluoric acid concentration of 9g / L, an acid temperature of 43℃, and a metal ion concentration of 32g / L.

[0021] 7) Cutting and Packaging: The strip steel after homogenization treatment is in NO.1 or 1D surface condition. It is cut to width by steel coil shearing unit, and then rolled into coils according to the actual needs of customers. After rolling, the coils are weighed and packaged into warehouse.

[0022] The mechanical properties of the products obtained through Example 1 are shown in Table 1. .

[0023] Example 2 1) Hot Grinding of Slabs: After continuous casting, ferritic stainless steel slabs are placed in an insulated pit for heat preservation treatment, with slow cooling throughout. The slab thickness is 220mm. The composition of the ferritic stainless steel slabs involved is: C 0.014%, N 0.012%, Mn 1.8%, P 0.021%, S 0.002%, Cr 11.6%, Nb+V 0.16%, Ti 0.11%, Mo 0.2%, with Fe as the balance and other trace elements from the raw materials. Hot grinding is performed when the surface temperature of the ferritic stainless steel slab in the insulated pit drops to 450℃. The grinding depth on one side of the head and tail slabs is 3.8mm, and the grinding depth on one side of the intermediate slabs is 3.5mm. Two grinding passes are used in total, with the final grinding using a 20-grit grinding wheel.

[0024] 2) Slab heating: The furnace temperature of the hot rolling heating furnace is controlled at 1210℃, the furnace time is 180min, and the furnace exit temperature is 1200℃.

[0025] 3) Rolling on a hot-rolled coil mill: The slabs exiting the furnace are rough rolled 7 times to 28mm on a hot-rolled coil mill, and then finished rolled 5 times to 4.0mm. The starting temperature for finishing rolling is 1000℃.

[0026] 4) Coiling: The rolled coils are coiled by a coiler. The sheet and strip side blowing is not used, but laminar flow cooling is used. The final coiling temperature is 690℃.

[0027] 5) Bell-type annealing: The hot-rolled black coils from the above production line undergo all-hydrogen bell-type furnace annealing. The holding temperature in the bell-type furnace is selected at 790℃ in the two-phase region of the phase diagram. Full-speed heating is used from room temperature to 450℃ for 60 minutes. Heating from 450℃ to 820℃ is done at a uniform rate for 11 hours. The holding time at 820℃ is 16 hours. The hydrogen purging flow rate is controlled at 16 m³ / h. After the holding period, the coils are cooled to 580℃ with the heating hood on, then the cooling hood is replaced for forced cooling. The coils are then removed from the furnace when the temperature reaches 180℃.

[0028] 6) Hot Annealing and Pickling Homogenization Treatment: The steel coils treated as described above undergo homogenization heat treatment. The homogenization heat treatment temperature is selected in the single-phase ferrite region of the phase diagram, with the entire region temperature controlled at 660℃. The homogenization heat treatment adopts a full-zone furnace temperature control mode, and the process speed is controlled at 10m / min. The scale-breaking machine adopts an elongation mode, with the elongation rate controlled at 0.2%. Cast shot is used for shot blasting and descaling, with the blasting speed controlled at 70m / s and the flow rate controlled at 10kg / m2. There are two sets of inlet and outlet for the re-brushing descaling, both of which are put into use and adjusted to level 2. Sulfuric acid pre-pickling is not used. The mixed acid pickling is controlled with a nitric acid concentration of 52g / L, a hydrofluoric acid concentration of 8g / L, an acid temperature of 42℃, and a metal ion concentration of 35g / L.

[0029] 7) Cutting and Packaging: The strip steel after homogenization treatment is in NO.1 or 1D surface condition. It is cut to width by steel coil shearing unit, and then rolled into coils according to the actual needs of customers. After rolling, the coils are weighed and packaged into warehouse.

[0030] The mechanical properties of the products obtained through Example 2 are shown in Table 2. .

[0031] Example 3 A method for producing ferritic stainless steel for mining equipment includes the following steps: S1. The ferritic stainless steel slab after continuous casting is sent into a heat preservation pit for heat preservation treatment. When the surface temperature of the ferritic stainless steel slab in the heat preservation pit drops to 400℃, hot grinding is performed. The composition of the ferritic stainless steel slab is C 0.015%, N 0.015%, Mn 1.4%, P 0.025%, S 0.002%, Cr 11%, Nb+V 0.16%, Ti 0.12%, Mo 0.2%, Fe balance and other trace elements attached to the raw materials. S2. The hot-rolled slab after hot grinding is sent into the hot rolling furnace for heating. The furnace temperature is controlled at 1180℃, the furnace time is controlled at 180min, and the furnace exit temperature is controlled at 1180℃. S3. The slabs exiting the furnace are rough rolled to 28mm using a hot rolling mill, and then finish rolled to 3.0mm. S4. The rolled coil is wound up by a coiler, and the final winding temperature is controlled at 650℃ to obtain hot-rolled black coil. S5. Hot-rolled black coils are annealed in a full-hydrogen bell-type furnace. S6. The annealed steel coil is subjected to homogenization heat treatment; S7. Cut and package.

[0032] In step S1, the hot grinding involves grinding the head and tail blanks to a depth of 3.5 mm on one side and the middle blank to a depth of 3.0 mm on one side, for a total of two grinding passes, with the final pass using a 20-grit grinding wheel for fine grinding.

[0033] In step S3, the slab exiting the furnace is rough rolled 7 times and finish rolled 5 times by a furnace rolling mill, with the finish rolling temperature at 970°C.

[0034] In step S4, the strip blowing is not used during winding, but laminar flow cooling is used.

[0035] In step S5, the holding temperature of the bell-type furnace is selected to be between 780°C and the two-phase region of the phase diagram, the heating and holding time of the bell-type furnace is controlled at 28 hours, and the hydrogen purging flow rate is controlled at 10 m³ / h. 3 / h, after the heat preservation is completed, cool to 580℃ with the heating cover on, then replace with a cooling cover for strong cooling treatment. Once the temperature has cooled to 200℃ or below, it can be taken out of the furnace.

[0036] In step S6, the homogenization heat treatment temperature is selected in the single-phase ferrite region of the phase diagram, and the temperature of the entire region is controlled at 650℃. The homogenization heat treatment adopts a full-zone furnace temperature control mode, the process speed is controlled at 10m / min, the scale breaking machine adopts an elongation mode, the elongation rate is controlled at 0.5%, and the shot blasting and descaling uses cast shot, the blasting speed is controlled at 68m / s, and the flow rate is controlled at 8kg / m³. 2Two sets of inlet and outlet brushes for phosphorus removal are in use, both set to level 1. Sulfuric acid pre-washing is not in use. The concentration of nitric acid for mixed acid washing is controlled at 50g / L, the concentration of hydrofluoric acid is controlled at 8g / L, the acid temperature is controlled at 40℃, and the concentration of metal ions is ≤40g / L.

[0037] In step S7, the strip steel after homogenization heat treatment is in NO.1 or 1D surface condition. It is then cut to a fixed width by a steel coil shearing unit and spun into coils according to the actual needs of the customer. After spun into coils, they are weighed and packaged for storage.

[0038] Example 4 A method for producing ferritic stainless steel for mining equipment includes the following steps: S1. The ferritic stainless steel slab after continuous casting is sent into a heat preservation pit for heat preservation treatment. When the surface temperature of the ferritic stainless steel slab in the heat preservation pit drops to 450℃, hot grinding is performed. The composition of the ferritic stainless steel slab is C 0.015%, N 0.015%, Mn 2.0%, P 0.025%, S 0.002%, Cr 12%, Nb+V 0.16%, Ti 0.12%, Mo 0.2%, Fe balance and other trace elements attached to the raw materials. S2. The hot-rolled slab after hot grinding is sent into the hot rolling furnace for heating. The furnace temperature is controlled at 1210℃, the furnace time is controlled at 220min, and the furnace exit temperature is controlled at 1200℃. S3. The slabs exiting the furnace are rough rolled to 35mm using a hot rolling mill, and then finish rolled to 6mm. S4. The rolled coil is wound up by a coiler, and the final winding temperature is controlled at 700℃ to obtain hot-rolled black coil. S5. Hot-rolled black coils are annealed in a full-hydrogen bell-type furnace. S6. The annealed steel coil is subjected to homogenization heat treatment; S7. Cut and package.

[0039] In step S1, the hot grinding involves grinding the head and tail blanks to a depth of 4.0 mm on one side and the middle blank to a depth of 3.5 mm on one side, with two grinding passes in total. The final grinding is performed using a 20-grit grinding wheel.

[0040] In step S3, the slab exiting the furnace is rough rolled 7 times and finish rolled 5 times by a furnace coil mill, with the finish rolling temperature at 1000℃.

[0041] In step S4, the strip blowing is not used during winding, but laminar flow cooling is used.

[0042] In step S5, the holding temperature of the bell-type furnace is selected to be between 830°C and the two-phase region of the phase diagram, the heating and holding time of the bell-type furnace is controlled at 30 hours, and the hydrogen purging flow rate is controlled at 20 m³ / h. 3 / h, after the heat preservation is completed, cool to 580℃ with the heating cover on, then replace with a cooling cover for strong cooling treatment. Once the temperature has cooled to 200℃ or below, it can be taken out of the furnace.

[0043] In step S6, the homogenization heat treatment temperature is selected in the single-phase ferrite region of the phase diagram, and the temperature of the entire region is controlled at 700℃. The homogenization heat treatment adopts a full-zone furnace temperature control mode, the process speed is controlled at 15m / min, the scale breaking machine adopts an elongation mode, the elongation rate is controlled at 0.5%, and the shot blasting and descaling uses cast shot, the blasting speed is controlled at 72m / s, and the flow rate is controlled at 12kg / m³. 2 Two sets of inlet and outlet brushes for phosphorus removal are put into use, each set to level 3. Sulfuric acid pre-washing is not used. The concentration of nitric acid for mixed acid washing is controlled at 60g / L, the concentration of hydrofluoric acid is controlled at 10g / L, the acid temperature is controlled at 45℃, and the concentration of metal ions is ≤40g / L.

[0044] In step S7, the strip steel after homogenization heat treatment is in NO.1 or 1D surface condition. It is then cut to a fixed width by a steel coil shearing unit and spun into coils according to the actual needs of the customer. After spun into coils, they are weighed and packaged for storage.

[0045] The equilibrium phase diagrams of ferritic stainless steels in Examples 1-4 are as follows: Figure 1 As shown.

[0046] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for producing ferritic stainless steel for mining equipment, characterized in that, Includes the following steps: S1. The ferritic stainless steel slab after continuous casting is sent into a heat preservation pit for heat preservation treatment. When the surface temperature of the ferritic stainless steel slab in the heat preservation pit drops to 400℃~450℃, hot grinding is performed. The composition of the ferritic stainless steel slab is C 0~0.015%, N 0~0.015%, Mn 1.4~2.0%, P 0~0.025%, S 0~0.002%, Cr 11~12%, Nb+V 0~0.16%, Ti 0~0.12%, Mo 0~0.2%, Fe balance and other trace elements attached to the raw materials. S2. The hot-rolled slab after hot grinding is sent into the hot rolling furnace for heating. The furnace temperature is controlled at 1180℃~1210℃, the furnace time is controlled at 180~220min, and the furnace exit temperature is controlled at 1180℃~1200℃. S3. The slabs exiting the furnace are rough rolled to 28mm-35mm using a hot rolling mill, and then finish rolled to 3.0-6mm. S4. The rolled coil is wound up by a coiler, and the final winding temperature is controlled at 650℃~700℃ to obtain hot-rolled black coil. S5. Hot-rolled black coils are annealed in a full-hydrogen bell-type furnace. S6. The annealed steel coil is subjected to homogenization heat treatment; S7. Cut and package.

2. The method for producing ferritic stainless steel for mining equipment according to claim 1, characterized in that, In step S1, the hot grinding involves grinding the head and tail blanks to a depth of 3.5-4.0 mm on one side and the intermediate blanks to a depth of 3.0-3.5 mm on one side. Two grinding passes are used in total, with the final grinding using a 20-grit grinding wheel.

3. The method for producing ferritic stainless steel for mining equipment according to claim 1, characterized in that, In step S3, the slab exiting the furnace is rough rolled 7 times and finish rolled 5 times by a furnace coil mill, with the finish rolling temperature being 970℃~1000℃.

4. The method for producing ferritic stainless steel for mining equipment according to claim 1, characterized in that, In step S4, the strip blowing is not used during winding, but laminar flow cooling is used.

5. The method for producing ferritic stainless steel for mining equipment according to claim 1, characterized in that, In step S5, the holding temperature of the bell-type furnace is selected between 780 and 830°C in the two-phase region of the phase diagram, the heating and holding time of the bell-type furnace is controlled at 28 to 30 hours, and the hydrogen purging flow rate is controlled at 10 to 20 m³ / h. 3 / h, after the heat preservation is completed, the furnace is cooled to 580℃ with the heating cover on, and then the cooling cover is replaced for strong cooling treatment. The furnace can be taken out when the temperature is cooled to 200℃ or below.

6. The method for producing ferritic stainless steel for mining equipment according to claim 1, characterized in that, In step S6, the homogenization heat treatment temperature is selected in the single-phase ferrite region of the phase diagram, and the temperature of the entire region is controlled at 650℃~700℃. The homogenization heat treatment adopts the whole-zone furnace temperature control mode, and the process speed is controlled at 10~15m / min. The scale breaking machine adopts the extension mode, and the elongation rate is controlled at 0~0.5%. Cast shot is used for shot blasting and descaling, and the blasting speed is controlled at 68~72m / s, and the flow rate is controlled at 8~12kg / m2. There are two sets of inlet and outlet for the re-brushing descaling, both of which are put into use and adjusted to level 1~3 respectively. Sulfuric acid pre-acid washing is not used. The nitric acid concentration of mixed acid washing is controlled at 50~60g / L, the hydrofluoric acid concentration is controlled at 8~10g / L, the acid temperature is controlled at 40~45℃, and the metal ion concentration is ≤40g / L.

7. The method for producing ferritic stainless steel for mining equipment according to claim 1, characterized in that, In step S7, the strip steel after homogenization heat treatment is in NO.1 or 1D surface condition. It is then cut to a fixed width by a steel coil shearing unit and spun into coils according to the customer's actual needs. After spun into coils, the strips are weighed and packaged for storage.

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