Method for reducing edge crack defect rate of 12CrNi series stainless steel and 12CrNi series stainless steel hot-rolled plate

Abstract

The invention belongs to the technical field of stainless steel production, and discloses a method for reducing the edge crack defect rate of 12CrNi series stainless steel and a 12CrNi series stainless steel hot rolled plate. The method sequentially comprises the steps that (1) steelmaking components are optimized, and a ferrite influence factor FFlt is controlled; fF = (Cr + 6Si + 8Ti + 4Mo + 2Al)-[40 (C + N) + 2Mn + 4Ni], and the elements in the formula are mass percent; (2) the circulation temperature of the plate blank is controlled, the continuous casting plate blank is fed into a furnace with the temperature, and the temperature is controlled to be 100-400 DEG C; (3) heating furnace heat preservation process control is conducted, the heat preservation temperature ranges from (A4-20) DEG C to A4 DEG C, the heat preservation time ranges from 0.9 D min to 1.2 D min, A4 is the gamma-delta phase change starting temperature, and D is the slab thickness (mm); and (4) the rolling process of hot continuous rolling is controlled, the rough rolling and finish rolling temperature ranges from 950 DEG C to 1050 DEG C, an edge heater is started after rough rolling, and the power ranges from 1200 kW to 2000 kW. According to the method, the edge crack defect occurrence rate in the hot rolling process can be remarkably reduced.

Description

Technical Field

[0001] This invention relates to the field of stainless steel production technology, specifically to a method for reducing the edge crack defect rate of 12CrNi stainless steel and a hot-rolled 12CrNi stainless steel plate. Background Technology

[0002] 12CrNi series stainless steel is widely used in building panels, rail transportation, and home appliances and bathroom products due to its excellent corrosion resistance, oxidation resistance, high strength, good processing and welding properties, and relatively low alloy content, resulting in significant cost-effectiveness. However, because of the relatively low Cr content in this type of stainless steel, the ferrite potential is insufficient, leading to complex phase transformation curves during heat treatment, often exhibiting a multiphase coexistence of austenite and ferrite. Taking the European standard material 1.4003 as an example, during the temperature change from high to low, there are successively existing γ-austenite single-phase regions, γ-austenite + α-ferrite two-phase regions, and α-ferrite single-phase regions.

[0003] During hot rolling, due to uneven phase transformation and stress concentration, 12CrNi stainless steel is highly susceptible to edge cracks, known as "edge crack defects," in slabs. These defects reduce the effective width of the product, decrease yield, and in severe cases, even lead to the scrapping of the entire coil, causing significant economic losses to the company. Despite existing production processes involving temperature control and rolling optimization, the incidence of edge cracks remains high, generally exceeding 10%, failing to meet the requirements of high-end users for consistent product width and surface quality.

[0004] Therefore, how to systematically regulate the microstructure and stress state of 12CrNi stainless steel throughout the entire process of steelmaking, continuous casting, heating, and rolling, and fundamentally suppress the generation of edge crack defects, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The present invention aims to provide a method for reducing the edge crack defect rate of 12CrNi stainless steel and a hot-rolled 12CrNi stainless steel plate that can significantly reduce the occurrence rate of edge crack defects during hot rolling.

[0006] The method for reducing the edge crack defect rate of 12CrNi stainless steel according to the present invention includes the following steps: Step 1: Steelmaking Composition Optimization: Control the composition of molten steel to ensure that the ferrite influence factor (FF) value of the final cast billet is less than 7.5. The FF value is calculated using the following formula: FF = (Cr + 6Si + 8Ti + 4Mo + 2Al) [40(C+N)+2Mn+4Ni] In the formula, the symbols of each element represent its mass percentage content in the steel; Step 2: Slab flow temperature control: The slab produced by continuous casting is directly transported to the hot continuous rolling furnace while still warm, and the furnace entry temperature of the slab is controlled between 100℃ and 400℃. Step 3: Hot continuous rolling furnace holding process control: The slab is heated in the hot continuous rolling furnace, and the holding temperature is controlled from (A4-20)℃ to A4℃, where A4 is the starting temperature of the transformation of the austenite γ phase to the high-temperature ferrite δ phase in stainless steel; the holding time is controlled from (0.9D) minutes to (1.2D) minutes, where D is the slab thickness in mm; Step 4: Hot continuous rolling process control: The heated slab is subjected to hot continuous rolling, and the final rolling temperature of the roughing rolling is controlled at 950℃~1050℃; and the edge heater is turned on after the roughing rolling is completed, and the power of the edge heater is controlled at 1200 kW~2000kW.

[0007] Furthermore, the FF value ranges from 6.0 to 7.4.

[0008] Furthermore, in step two, the furnace temperature of the slab is controlled between 100℃ and 300℃.

[0009] Furthermore, in step three, the insulation temperature is (A4-15)℃ to A4℃.

[0010] Furthermore, in step three, the heat preservation time is (0.95D) minutes to (1.1D) minutes.

[0011] Furthermore, in step four, the roughing and finishing rolling temperature is controlled between 980℃ and 1030℃.

[0012] Furthermore, in step four, the power of the side heater is controlled between 1400 kW and 1800 kW.

[0013] Furthermore, in 12CrNi series stainless steel, by mass percentage, the C content is ≤0.03%, the Si content is ≤0.5%, the Mn content is ≤1.5%, the Cr content is 10.5%~12.5%, the Ni content is 0.5%~1.5%, the N content is ≤0.025%, and the Ti content is ≤0.3%.

[0014] Furthermore, 12CrNi series stainless steel meets the composition requirements of grade 1.4003 in European standard EN10088-2.

[0015] The 12CrNi series stainless steel hot-rolled plate produced according to the present invention using the above-mentioned method for reducing the edge crack defect rate of 12CrNi series stainless steel has an edge crack defect rate of less than 5%, a tensile strength of ≥550MPa, and an elongation after fracture of ≥25%.

[0016] Compared to existing technologies that only make localized adjustments to single stages such as rolling or heating, lacking systemic coordination and still resulting in an edge crack rate exceeding 10%, the method for reducing the edge crack defect rate of 12CrNi stainless steel in this invention proposes a coordinated control system covering the entire process of "composition-conveying-heating-rolling," with the following advantages: 1) Introduce the FF value as a quantitative indicator for composition design to optimize the phase transition properties of materials from the source; 2) A personalized heating regime based on the A4 phase transition point enables precision in the heating process; 3) The active temperature control of the edge heater is integrated after rough rolling, which effectively makes up for the shortcoming of excessively rapid temperature drop at the edge in the traditional process.

[0017] The method of reducing the edge crack defect rate of 12CrNi stainless steel of the present invention forms a complete process closed loop by coupling the above-mentioned technical means, and successfully controls the edge crack rate of hot-rolled 12CrNi stainless steel to below 5%, which significantly improves the product yield, width consistency and economic benefits, and solves the long-standing quality bottleneck problem of this steel in large-scale production. Attached Figure Description

[0018] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the embodiments of the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 A flowchart of a method for reducing the edge crack defect rate of 12CrNi stainless steel according to an embodiment of the present invention is shown. Detailed Implementation

[0019] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0020] Figure 1 A flowchart illustrating a method for reducing the edge crack defect rate of 12CrNi-based stainless steel according to an embodiment of the present invention is shown. Figure 1 As shown, the method for reducing the edge crack defect rate of 12CrNi stainless steel may include the following steps: Step 1 S1: Steelmaking composition optimization: Control the composition of molten steel so that the ferrite influence factor FF value of the final cast billet is less than 7.5. The FF value is calculated according to the following formula: FF = (Cr + 6Si + 8Ti + 4Mo + 2Al) [40(C+N)+2Mn+4Ni] In the formula, the symbols of each element represent its mass percentage content in the steel; Step 2 S2: Slab flow temperature control: The slab produced by continuous casting is directly transported to the hot continuous rolling furnace while still warm, and the furnace entry temperature of the slab is controlled between 100℃ and 400℃. Step 3 S3: Hot Continuous Rolling Heating Furnace Holding Process Control: The slab is heated in the hot continuous rolling heating furnace, and the holding temperature is controlled from (A4-20)℃ to A4℃, where A4 is the starting temperature of the transformation of the austenite γ phase to the high-temperature ferrite δ phase in stainless steel; the holding time is controlled from (0.9D) minutes to (1.2D) minutes, where D is the slab thickness in mm; Step 4 S4: Hot continuous rolling process control: The heated slab is subjected to hot continuous rolling, and the final rolling temperature of roughing is controlled at 950℃~1050℃; and the edge heater is turned on after roughing is completed, and the power of the edge heater is controlled at 1200 kW~2000 kW.

[0021] The method for reducing the edge crack defect rate of 12CrNi stainless steel according to this invention first optimizes the steelmaking composition by designing the molten steel composition based on the formula FF < 7.5, thereby controlling the phase transformation behavior of the material from a metallurgical perspective and suppressing the formation of brittle phases. Subsequently, during the slab flow stage, the slab's furnace entry temperature is maintained at 100℃~400℃ to avoid internal stress and microcracks caused by excessively rapid cooling or room temperature storage. After entering the hot continuous rolling furnace, the slab is held at the austenite γ→δ ferrite phase transformation initiation temperature A4, within the range of (A4-20)℃~A4℃ for (0.9D~1.2D) minutes to achieve uniform austenitization and suppress the precipitation of harmful δ ferrite. Finally, in the rolling stage, the roughing and finishing rolling temperature is controlled at 950℃~1050℃, and an edge heater of 1200~2000 kW is immediately activated after roughing to compensate for the edge temperature drop, ensuring uniform temperature across the slab cross-section and preventing edge cracking due to low-temperature brittleness.

[0022] The method for reducing the edge crack defect rate of 12CrNi stainless steel in this invention follows a process logic of "composition pre-setting—temperature control connection—heating homogenization—rolling compensation". Its starting point is composition design based on the FF value, pre-optimizing the phase transformation path of the material by adjusting the proportions of elements such as C, N, Cr, and Ni. The slab immediately enters the heat preservation and conveying process after continuous casting, maintaining its furnace entry temperature at 100–400°C to prevent the initiation of cold cracks. In the heating furnace, heat preservation is performed using point A4 as the temperature reference to ensure the slab reaches a uniform austenitic state while suppressing the formation of high-temperature δ-ferrite. During rolling, rough rolling is completed in the high-temperature plastic range, and the edge heaters are simultaneously activated to provide real-time heat compensation for the fast-dissipating edges, achieving temperature balance and deformation coordination across the entire slab. The method for reducing the edge crack defect rate of 12CrNi stainless steel in this invention embodiment controls the entire process from source to end, rather than local repair. It achieves the core goal of significantly reducing the occurrence rate of edge cracks by systematically coordinating four steps: steelmaking composition optimization, slab flow temperature control, heating furnace heat preservation process control, and rolling process control. From material design and process temperature control to deformation compensation, it suppresses the causes of edge cracks throughout the entire process.

[0023] In a preferred embodiment, the FF value can be in the range of 6.0 to 7.4. By further limiting the FF value to between 6.0 and 7.4, the phase transformation control window is optimized, which avoids excessive ferrite affecting plasticity due to an excessively low FF value, and also prevents austenite instability due to an excessively high FF value, thereby improving the precision of microstructure control.

[0024] In a preferred embodiment, in step S2, the furnace temperature of the slab can be controlled between 100°C and 300°C. By reducing the upper limit of the furnace temperature from 400°C to 300°C, the dwell time of the slab in the high-temperature section is reduced, thereby lowering the risk of surface oxidation and grain coarsening, while still effectively avoiding cold stress cracking.

[0025] Furthermore, in step S3, the holding temperature can be from (A4-15)℃ to A4℃. By narrowing the holding temperature range to (A4-15)℃~A4℃, the austenitization process becomes more uniform and stable, which is beneficial to suppressing the precipitation of δ-ferrite and further improving the homogeneity of the pre-rolling microstructure.

[0026] Furthermore, in step S3, the heat preservation time can be from (0.95D) minutes to (1.1D) minutes. By optimizing the heat preservation time to (0.95D) to (1.1D) minutes, the ineffective heat preservation time is shortened while ensuring heat penetration, thereby improving production line efficiency and reducing energy consumption.

[0027] Furthermore, in step S4, the final rolling temperature of the roughing roll can be controlled between 980℃ and 1030℃. By narrowing the final rolling temperature range of the roughing roll to 980℃ to 1030℃, the rolling process is made to be more stably located within the optimal thermoplastic range of the material, further reducing edge cracking caused by temperature fluctuations.

[0028] Furthermore, in step S4, the power of the edge heater can be controlled between 1400 kW and 1800 kW. By limiting the power of the edge heater to between 1400 kW and 1800 kW, more balanced edge heat compensation is provided, effectively suppressing edge temperature drop, improving cross-sectional temperature uniformity, and reducing the risk of edge cracking.

[0029] According to a preferred embodiment of the present invention, in the 12CrNi-based stainless steel, by mass percentage, the C content is ≤0.03%, the Si content is ≤0.5%, the Mn content is ≤1.5%, the Cr content is 10.5%–12.5%, the Ni content is 0.5%–1.5%, the N content is ≤0.025%, and the Ti content is ≤0.3%. This embodiment clarifies the specific composition range of the 12CrNi-based stainless steel, providing a clear composition control standard for the steelmaking process and ensuring the effective implementation of FF value calculation and subsequent process parameters.

[0030] According to the present invention, 12CrNi series stainless steel meets the composition requirements of grade 1.4003 in European standard EN10088-2. The method of the present invention is specifically applicable to grade 1.4003 conforming to EN 10088-2, enhancing the practicality and relevance of the method and facilitating its widespread application in typical stainless steel grades.

[0031] The 12CrNi series stainless steel hot-rolled plate produced by the above-mentioned method for reducing the edge crack defect rate of 12CrNi series stainless steel according to the present invention has an edge crack defect rate of less than 5%, a tensile strength of ≥550MPa, and an elongation after fracture of ≥25%. The 12CrNi series stainless steel hot-rolled plate has excellent comprehensive performance.

[0032] The following are specific embodiments of hot-rolled 12CrNi stainless steel plates produced using the method for reducing the edge crack defect rate of 12CrNi stainless steel according to the present invention.

[0033] Example 1: The steel composition is shown in Table 1. The calculated FF value of the material is 7.0, which meets the requirement of being less than 7.5. A total of 9 billets were produced in this heat, all of which were transferred to the hot continuous rolling furnace on the same day as the continuous casting output. The minimum furnace entry temperature was 120℃, which meets the requirement of being greater than 100℃. Based on the phase diagram, the A4 temperature of this material is 1150℃. The calculated holding temperature control range for the hot continuous rolling furnace is 1130℃~1150℃. With a billet thickness of 200mm, the calculated holding time control range is 180min~240min. The actual holding temperature was 1140℃, and the holding time was 200min. The final rolling temperature of the hot continuous rolling roughing was 1010℃, which meets the requirement of being within the range of 950℃~1050℃. The edge heater was turned on with a power of 1500KW, which meets the requirement of 1200~2000KW.

[0034] This embodiment produced a total of 9 hot-rolled stainless steel coils without any edge cracking defects.

[0035] Table 1. Specific components (wt%) of Example 1

[0036] Example 2: The steel composition is shown in Table 2. The calculated FF value of the material is 6.9, which meets the requirement of being less than 7.5. A total of 7 billets were produced in this heat, all of which were transferred to the hot continuous rolling furnace on the same day as the continuous casting output. The minimum furnace entry temperature was 140℃, which meets the requirement of being greater than 100℃. Based on the phase diagram, the A4 temperature of this material is 1165℃. The calculated holding temperature control range for the hot continuous rolling furnace is 1145℃~1165℃. With a billet thickness of 200mm, the calculated holding time control range is 180min~240min. The actual holding temperature was 1160℃, and the holding time was 210min. The final rolling temperature of the hot continuous rolling roughing was 1023℃, which meets the requirement of being within the range of 950℃~1050℃. The edge heater was turned on with a power of 1500KW, which meets the requirement of 1200~2000KW.

[0037] In this second embodiment, a total of 7 hot-rolled stainless steel coils were produced without any edge cracking defects.

[0038] Table 2. Specific components (wt%) of Example 2

[0039] Example 3: The steel composition is shown in Table 3. The calculated FF value of the material is 6.4, which meets the requirement of being less than 7.5. A total of 9 billets were produced in this heat. All billets produced by continuous casting were transferred to the hot continuous rolling furnace the following morning, with a minimum furnace entry temperature of 105℃, which meets the requirement of being greater than 100℃. The phase diagram shows that the A4 temperature of this material is 1155℃. The calculated holding temperature control range for the hot continuous rolling furnace is 1135℃~1155℃. With a billet thickness of 200mm, the calculated holding time control range is 180min~240min. The actual holding temperature was 1150℃, and the holding time was 190min. The final rolling temperature of the hot continuous rolling roughing was 1014℃, which meets the requirement of being within the range of 950℃~1050℃. The edge heaters were turned on with a power of 1500KW, which meets the requirement of 1200~2000KW.

[0040] In this third embodiment, a total of 9 hot-rolled stainless steel coils were produced without any edge cracking defects.

[0041] Table 3. Specific components (wt%) of Example 3

[0042] The results of the above embodiments show that, under different compositional combinations and corresponding personalized process parameters, none of the 25 hot-rolled plates produced exhibited any edge crack defects, successfully achieving an excellent result of zero edge crack incidence. This fully verifies the strong applicability, high stability, and excellent reproducibility of the method for reducing the edge crack defect rate of 12CrNi stainless steel in the embodiments of the present invention under different compositional fluctuations. It conclusively proves that by systematically controlling key aspects such as composition (FF<7.5), slab temperature feeding (furnace temperature 100-400℃), A4 reference heating, and rolling edge heating, the edge crack defect rate of 12CrNi stainless steel can be stably and reliably reduced to a level far below 5%, fully achieving the intended purpose of the present invention.

[0043] 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 or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for reducing the edge crack defect rate of 12CrNi stainless steel, characterized in that, Includes the following steps: Step 1: Steelmaking Composition Optimization: Control the composition of molten steel to ensure that the ferrite influence factor (FF) value of the final cast billet is less than 7.

5. The FF value is calculated according to the following formula: FF=(Cr+6Si+8Ti+4Mo+2Al) [40(C+N)+2Mn+4Ni] In the formula, the symbols of each element represent its mass percentage content in the steel; Step 2: Slab flow temperature control: The slab produced by continuous casting is directly transported to the hot continuous rolling furnace while still warm, and the furnace entry temperature of the slab is controlled between 100℃ and 400℃. Step 3: Hot continuous rolling furnace holding process control: The slab is heated in the hot continuous rolling furnace, and the holding temperature is controlled from (A4-20)℃ to A4℃, where A4 is the starting temperature of the transformation of the austenite γ phase to the high-temperature ferrite δ phase in stainless steel; the holding time is controlled from (0.9D) minutes to (1.2D) minutes, where D is the slab thickness in mm; Step 4: Hot continuous rolling process control: The heated slab is subjected to hot continuous rolling, and the final rolling temperature of the roughing rolling is controlled at 950℃~1050℃; and the edge heater is turned on after the roughing rolling is completed, and the power of the edge heater is controlled at 1200 kW~2000 kW.

2. The method for reducing the edge crack defect rate of 12CrNi stainless steel according to claim 1, characterized in that, The value of FF ranges from 6.0 to 7.

4.

3. The method for reducing the edge crack defect rate of 12CrNi stainless steel according to claim 1, characterized in that, In step two, the furnace temperature of the slab is controlled between 100℃ and 300℃.

4. The method for reducing the edge crack defect rate of 12CrNi stainless steel according to claim 1, characterized in that, In step three, the heat preservation temperature is (A4-15)℃ to A4℃.

5. The method for reducing the edge crack defect rate of 12CrNi stainless steel according to claim 1, characterized in that, In step three, the heat preservation time is (0.95D) minutes to (1.1D) minutes.

6. The method for reducing the edge crack defect rate of 12CrNi stainless steel according to claim 1, characterized in that, In step four, the final rolling temperature of the roughing and rolling is controlled between 980℃ and 1030℃.

7. The method for reducing the edge crack defect rate of 12CrNi stainless steel according to claim 1, characterized in that, In step four, the power of the edge heater is controlled between 1400 kW and 1800 kW.

8. The method for reducing the edge crack defect rate of 12CrNi stainless steel according to any one of claims 1 to 7, characterized in that, In the 12CrNi series stainless steel, by mass percentage, the C content is ≤0.03%, the Si content is ≤0.5%, the Mn content is ≤1.5%, the Cr content is 10.5%~12.5%, the Ni content is 0.5%~1.5%, the N content is ≤0.025%, and the Ti content is ≤0.3%.

9. The method for reducing the edge crack defect rate of 12CrNi stainless steel according to claim 8, characterized in that, The 12CrNi series stainless steel meets the composition requirements of grade 1.4003 in European standard EN10088-2.

10. A hot-rolled 12CrNi stainless steel sheet produced using the method for reducing the edge crack defect rate of 12CrNi stainless steel as described in any one of claims 1-9, characterized in that, Its edge crack defect rate is less than 5%, tensile strength is ≥550MPa, and elongation after fracture is ≥25%.

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