Double-rack steekle mill control process for reducing economic duplex stainless steel hot rolling edge cracks

Abstract

The invention discloses a double-rack steekle mill control process for reducing economic duplex stainless steel hot-rolled edge cracks, which comprises the following steps: casting blank heating process control: the final heating temperature of a casting blank is 1150-1260 DEG C, and the total furnace staying time is 140-280 minutes; the rough rolling process is controlled, 5-7 passes of rolling are adopted, rough rolling descaling is carried out in the first pass, the reduction rate of each pass is 15-25%, the rolling speed is 3-5 m / s, and the rough rolling outlet temperature is 1000-1100 DEG C; the finish rolling process is controlled, double-rack three-rolling-process six-pass rolling is adopted, in the first four passes, the reduction rate is 25-35%, the rolling speed is 6-9 m / s, in the second two passes, the reduction rate is 10-15%, the rolling speed is 2-3 mm, the finish rolling outlet temperature is 900-1000 DEG C, the heating temperature of a coiling furnace is 1000-1100 DEG C, and the coiling temperature is 500-700 DEG C. According to the method, a double-rack steekle mill control process is adopted, and through casting blank heating process control, rough rolling process control and finish rolling process control, the width of the economical dual-phase stainless hot-rolled edge crack is reduced by 70% or above compared with the prior art, and the edge quality of a product is effectively improved.

Description

Technical Field

[0001] The invention belongs to the field of development and application of special stainless steel varieties, and specifically relates to a double-frame furnace coil mill control process for reducing edge cracking of hot rolled economical duplex stainless steel. Background Art

[0002] From the perspective of the long-term development of stainless steel worldwide, high-performance, resource-saving stainless steel represented by duplex stainless steel has become one of the main development trends. Characteristics such as high strength, high toughness and low alloy cost have become an important reference for design and manufacturing.

[0003] Low-Ni economical duplex stainless steel represented by S32101 has an austenite-ferrite ratio close to 1:1. This structure enables this steel to have both the characteristics of austenite and ferrite stainless steels. It has good mechanical properties at room temperature, excellent resistance to stress corrosion, crevice corrosion, comprehensive mechanical properties and welding properties, and is therefore widely used in the chemical industry.

[0004] The conventional production of S32101 economical duplex stainless steel hot coil adopts hot rolling process. Since this steel is composed of austenite and ferrite, the high temperature strength difference between austenite and ferrite is large, the phase boundary deformation is difficult, and cracks are easily generated at the two-phase interface during rolling. Under the technical conditions of the current existing technology, the edge crack of economical duplex stainless steel hot coil is about 40mm, which seriously affects the edge quality of the material. Summary of the invention

[0005] In order to solve the above-mentioned technical problems existing in the prior art, the present invention aims at the edge cracking problem of low-Ni economical duplex stainless steel hot coil represented by S32101, adopts a double-frame furnace coil mill for rolling, reduces the edge cracking width of the economical duplex stainless steel hot coil by controlling the rolling process, and improves the product quality.

[0006] The double-stand Steckel mill control process for reducing edge cracking of economical duplex stainless steel hot coils of the present invention comprises:

[0007] (1) Billet heating process control

[0008] The ingot is heated in the heating furnace according to the process of controlling the heating temperature and the residence time in the heating furnace. The final heating temperature of the ingot is controlled at 1150-1260°C, and the total residence time is controlled at 140-280min.

[0009] (2) Rough rolling process control

[0010] The rough rolling adopts 5 to 7 passes, and the rough rolling is carried out for descaling in the first pass. The rolling reduction rate of each pass is controlled to be 15 to 25%, and the rolling speed is controlled to be 3 to 5 m / s. The rolling speed and rolling reduction rate increase with the number of passes, and the rough rolling outlet temperature is controlled to be 1000 to 1100°C.

[0011] (3) Finishing rolling process control

[0012] The finishing rolling adopts double-stand three-rolling process and six-pass rolling. In the first four passes, the rolling reduction rate is controlled at 25-35%, and the rolling speed is controlled at 6-9m / s. The rolling speed increases with the pass, and the reduction rate decreases with the pass; in the last two passes, the rolling reduction rate is controlled at 10-15%, and the rolling speed is controlled at 2-3mm; the finishing rolling outlet temperature is controlled at 900-1000℃; the heating temperature of the coiling furnace of the double-stand furnace coil mill is controlled at 1000-1100℃; laminar cooling is used during coiling, and the coiling temperature is controlled at 500-700℃.

[0013] Furthermore, in the above-mentioned double-stand Steckel mill control process for reducing the edge cracking of hot rolled economical duplex stainless steel, in the ingot heating process control, in the preheating section of the heating furnace, the heating furnace temperature is controlled to be 500-700°C, and the residence time is controlled to be 50-100min; in the first heating section of the heating furnace, the heating furnace temperature is controlled to be 1000-1050°C, and the residence time is controlled to be 30-60min; in the second heating section of the heating furnace, the heating furnace temperature is controlled to be 1100-1150°C, and the residence time is controlled to be 30-60min; in the third heating section of the heating furnace, the heating furnace temperature is controlled to be 1150-1260°C, and the residence time is controlled to be 30-60min.

[0014] Further, in the above-mentioned double-stand furnace coil mill control process for reducing hot rolled edge cracking of economical duplex stainless steel, the economical duplex stainless steel is a low-Ni economical duplex stainless steel, and its chemical composition includes, by mass percentage: C≤0.040%, Si≤1.00%, Mn: 4.00%~6.00%, P≤0.040%, S≤0.030%, Cr: 21.00%~22.00%, Ni: 1.35%~1.70%, Mo: 0.1%~0.8%, Cu: 0.1%~0.8%, N: 0.20%~0.25%, and the rest is Fe and unavoidable impurities.

[0015] Furthermore, in the above-mentioned double-stand Steckel mill control process for reducing hot-rolled edge cracking of economical duplex stainless steel, the grade of the economical duplex stainless steel is S32101.

[0016] The dual-stand Steckel mill control process for reducing edge cracking of economical duplex stainless steel hot coils of the present invention has the following advantages and beneficial effects:

[0017] Aiming at the serious edge cracking problem of hot-rolled continuous rolling of low-Ni economical duplex stainless steel represented by S32101, the present invention adopts a double-frame furnace coil mill control process, controls the heating process of the ingot, designs the temperature range and the temperature rise curve of the ingot heating process, ensures uniform temperature of the ingot and pure structure; controls the rough rolling process, designs the rolling passes, the pass reduction rate and the rolling speed, ensures uniform structure, uniform force and controllable hot working plastic temperature; controls the finishing rolling process, designs the heating process of the coiling furnace, designs the rolling passes, the pass reduction rate and the rolling speed, designs the coiling process, ensures controllable hot working temperature range and good plate surface quality and precision, and combines the control of the above technical means to reduce the width of the edge crack of the economical duplex stainless hot coil by more than 70% compared with the prior art, and effectively improves the edge quality of the product. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0019] The dual-frame furnace coil mill control process for reducing the edge cracking of hot rolled economic duplex stainless steel of the present invention effectively reduces the edge cracking of hot rolled economic duplex stainless steel and improves the edge quality of the product through technical means such as the heating process control of the ingot casting, the rough rolling process control, and the finishing rolling process control. Specifically, the dual-frame furnace coil mill control process for reducing the edge cracking of hot rolled economic duplex stainless steel of the present invention includes:

[0020] (1) Billet heating process control

[0021] The ingot is heated in the heating furnace according to the process of controlling the heating temperature and the dwelling time in the zone. The final heating temperature of the ingot is controlled at 1150-1260°C, and the total dwelling time is controlled at 140-280min. Among them, in the preheating section of the heating furnace, the heating furnace temperature is controlled at 500-700°C, and the dwelling time is controlled at 50-100min; in the first heating section of the heating furnace, the heating furnace temperature is controlled at 1000-1050°C, and the dwelling time is controlled at 30-60min; in the second heating section of the heating furnace, the heating furnace temperature is controlled at 1100-1150°C, and the dwelling time is controlled at 30-60min; in the third heating section of the heating furnace, the heating furnace temperature is controlled at 1150-1260°C, and the dwelling time is controlled at 30-60min.

[0022] In the above-mentioned ingot heating process control, the design and control of the ingot heating temperature and the furnace dwelling time mainly consider the high-temperature thermoplasticity of the material, and it is necessary to ensure that the material has good high-temperature plasticity at this temperature. According to research, the high-temperature plasticity of economical duplex stainless steel materials increases with increasing temperature within a certain range, which is conducive to hot processing of the material. However, after the temperature exceeds 1260°C, the thermoplasticity of the material decreases due to changes in the phase boundary and grain boundary properties of the material. Therefore, the final heating temperature of the economical duplex stainless steel ingot is controlled to be the temperature range of 1150-1260°C for the best thermoplasticity.

[0023] In the above-mentioned ingot heating process control, the uniformity of material heating is ensured by heating the material in the preheating section of the heating furnace at a heating temperature of 500-700°C and a residence time of 50-100 minutes. Then, the temperature is quickly raised to above 1000°C in the heating section of the heating furnace to avoid the generation of the second phase such as Cr2N phase of the economical duplex stainless steel and affect the thermoplasticity. Subsequently, the temperature gradient is further accurately controlled in the second and third heating sections of the heating furnace to finally ensure that the temperature is uniformly raised to the temperature range of 1150-1260°C with the best thermoplasticity under the condition of high organizational purity.

[0024] (2) Rough rolling process control

[0025] The rough rolling adopts 5 to 7 passes, and the rough rolling is carried out for descaling in the first pass. The rolling reduction rate of each pass is controlled at 15 to 25%, and the rolling speed is controlled at 3 to 5 m / s. The rolling speed and rolling reduction rate increase with the number of passes. The rough rolling outlet temperature is controlled at 1000 to 1100°C.

[0026] In the above-mentioned rough rolling process control, by designing a first-pass descaling process rather than a multi-pass descaling process, the surface oxide scale generated by long-term heating on the material surface can be removed, avoiding the influence of surface oxides on the rolling surface, and the temperature reduction caused by multi-pass descaling can be avoided, preventing the impact on processing thermoplasticity and even causing edge cracking.

[0027] In the above-mentioned rough rolling process control, the pass reduction rate is designed to ensure that the material pass deformation rate exceeds the critical recrystallization deformation rate of the material, thereby avoiding edge cracking caused by uneven structure due to non-recrystallization softening caused by a deformation rate lower than the critical recrystallization deformation rate.

[0028] In the above rough rolling process control, the high temperature resistance and deformation temperature of the material are guaranteed to be stable by designing the rolling passes, rolling reduction rate and rolling speed. The normal hot rolling process of the material is a cooling process. By designing the rolling reduction rate and rolling speed to increase with the pass, the work hardening and dynamic recovery and recrystallization softening processes in the material process are matched, and the natural temperature drop of the material and the temperature rise of the accumulated deformation energy are matched, so as to control the deformation resistance and processing temperature in the rolling process to be stable and ensure that the rolling force remains stable. This design is conducive to ensuring that the overall material is uniformly stressed under the condition of ensuring the thermoplasticity of the material, thereby ensuring the material plate shape and good edge quality. Moreover, by designing the rolling passes, rolling reduction rate and rolling speed, the natural temperature drop of the material and the temperature rise of the accumulated deformation energy are matched, so as to ensure that the final temperature range of the rough rolling is controlled at 1000-1100℃.

[0029] (3) Finishing rolling process control

[0030] The finishing rolling adopts double-stand three-rolling process and six-pass rolling. In the first four passes, the rolling reduction rate is controlled at 25-35%, and the rolling speed is controlled at 6-9m / s. The rolling speed increases with the pass, and the reduction rate decreases with the pass; in the last two passes, the rolling reduction rate is controlled at 10-15%, and the rolling speed is controlled at 2-3mm; the finishing rolling outlet temperature is controlled at 900-1000℃; the heating temperature of the coiling furnace of the double-stand furnace coil mill is controlled at 1000-1100℃; laminar cooling is used during coiling, and the coiling temperature is controlled at 500-700℃.

[0031] In the above-mentioned finishing rolling process control, the coiling furnace of the double-stand Steckel mill is set at a temperature of 1000-1100°C. The two coiling furnaces arranged at the entrance and exit of the rolling mill ensure the stability of the hot processing temperature of the material, especially the edge temperature, to reduce the processing cracking caused by the difference in high-temperature strength of the two phases due to the temperature drop at the edge. The material temperature is evenly distributed on the entire plate surface, thereby ensuring uniform rolling force and controlling the flatness of the plate shape, which is beneficial to the rolling and coiling of the Steckel mill and ensures good edge quality.

[0032] In the above-mentioned finishing rolling process control, double-stand three-rolling process and six-pass rolling are adopted. The first four passes are designed with a higher reduction rate and rolling speed to match the natural temperature drop of the material and the accumulated temperature rise of the deformation energy, thereby ensuring the stability of the hot processing temperature and rolling force. The last two passes are designed with a low reduction rate and rolling speed, which is conducive to controlling the precise size and ensuring the surface and edge quality.

[0033] In the above-mentioned finishing rolling process control, laminar cooling is adopted during coiling, and the cooling rate is controlled to ensure uniform temperature drop, reduce thermal stress, and avoid stress cracking caused by cooling rate mismatch. The coiling temperature is controlled at 500-700°C. Cooling in this temperature range can ensure that the material has a certain thermoplasticity to meet the coiling requirements, and avoid the precipitation of the second phase caused by coiling at a higher temperature, which affects the material performance and edge quality.

[0034] As a specific implementation, in the above-mentioned double-stand Steckel mill control process for reducing hot rolled edge cracking of economical duplex stainless steel, the economical duplex stainless steel is a low-Ni economical duplex stainless steel, and its chemical composition includes, by mass percentage: C≤0.040%, Si≤1.00%, Mn: 4.00%~6.00%, P≤0.040%, S≤0.030%, Cr: 21.00%~22.00%, Ni: 1.35%~1.70%, Mo: 0.1%~0.8%, Cu: 0.1%~0.8%, N: 0.20%~0.25%, and the rest is Fe and unavoidable impurities.

[0035] As a specific implementation, in the above-mentioned double-stand Steckel mill control process for reducing hot-rolled edge cracking of economical duplex stainless steel, the grade of the economical duplex stainless steel is S32101.

[0036] The following describes the control process of a dual-stand Steckel mill for reducing edge cracking of hot coils of economical duplex stainless steel according to the present invention in conjunction with specific embodiments.

[0037] Example 1

[0038] In Example 1 of the present invention, the economical duplex stainless steel is S32101 economical duplex stainless steel, and its chemical composition by mass percentage is: C: 0.019%, Si: 0.63%, Mn: 5.12%, P: 0.021%, S: 0.001%, Cr: 21.52%, Ni: 1.53%, Mo: 0.13%, N: 0.20%, and the rest is Fe and unavoidable impurities.

[0039] The specific implementation process of the double-stand Steckel mill control process for reducing edge cracking of hot-rolled economical duplex stainless steel in Example 1 is as follows:

[0040] (1) Billet heating process control

[0041] The final heating temperature of the ingot is controlled at 1150-1260°C, and the total residence time is controlled at 140-280 minutes. The heating temperature and residence time are controlled by section according to the process parameters shown in the following table:

[0042] Heating furnace section Preheating section One section Second paragraph Three sections Time (min) 50～100 30～60 30～60 30～60 Heating furnace temperature (℃) 500～700 1000～1050 1100～1150 1150～1260

[0043] (2) Rough rolling process control

[0044] The rough rolling adopts 7 passes, and the rough rolling is used for descaling in the first pass. The rolling reduction rate of each pass is 15-25%, and the rolling speed is 3-5m / s. The rolling speed and rolling reduction rate increase with the pass. The rough rolling outlet temperature is controlled at 1076℃.

[0045] (3) Finishing rolling process control

[0046] The finishing rolling adopts double-stand three-rolling process and six-pass rolling. In the first four passes, the rolling reduction rate is 25-35% and the rolling speed is 6-9m / s. The rolling speed increases with the pass, and the reduction rate decreases with the pass; in the last two passes, the rolling reduction rate is 10-15% and the rolling speed is 2-3mm; the finishing rolling outlet temperature is controlled at 960℃; the heating temperature of the coiling furnace of the double-stand furnace coil mill is 1000-1100℃; laminar cooling is used during coiling, and the coiling temperature is controlled at 500-700℃.

[0047] The finished product specification of the S32101 economical duplex stainless steel hot coil manufactured in Example 1 is 5×1280×L mm. After testing, the width of the hot coil edge crack is 5-10 mm.

[0048] Example 2

[0049] In Example 2 of the present invention, the economical duplex stainless steel is S32101 economical duplex stainless steel, and its chemical composition by mass percentage is: C: 0.019%, Si: 0.63%, Mn: 5.12%, P: 0.021%, S: 0.001%, Cr: 21.52%, Ni: 1.53%, Mo: 0.13%, N: 0.20%, and the rest is Fe and unavoidable impurities.

[0050] The specific implementation process of the double-stand Steckel mill control process for reducing edge cracking of hot-rolled economical duplex stainless steel in Example 2 is as follows:

[0051] (1) Billet heating process control

[0052] The final heating temperature of the ingot is controlled at 1150-1260°C, and the total residence time is controlled at 140-280 minutes. The heating temperature and residence time are controlled by section according to the process parameters shown in the following table:

[0053] Heating furnace section Preheating section One section Second paragraph Three sections Time (min) 50～100 30～60 30～60 30～60 Heating furnace temperature (℃) 500～700 1000～1050 1100～1150 1150～1260

[0054] (2) Rough rolling process control

[0055] The rough rolling is carried out in 5 passes, with descaling in the first pass. The rolling reduction rate of each pass is 15-25%, the rolling speed is 3-5m / s, and the rolling speed and rolling reduction rate increase with the pass. The rough rolling outlet temperature is controlled at 1050℃.

[0056] (3) Finishing rolling process control

[0057] The finishing rolling adopts double-stand three-rolling process and six-pass rolling. In the first four passes, the rolling reduction rate is 25-35% and the rolling speed is 6-9m / s. The rolling speed increases with the pass, and the reduction rate decreases with the pass; in the last two passes, the rolling reduction rate is 10-15% and the rolling speed is 2-3mm; the finishing rolling outlet temperature is controlled at 935℃; the heating temperature of the coiling furnace of the double-stand furnace coil mill is 1000-1100℃; laminar cooling is used during coiling, and the coiling temperature is controlled at 500-700℃.

[0058] The finished product specifications of the S32101 economical duplex stainless steel hot coil manufactured in Example 2 are 6×1280×L mm. After testing, the width of the hot coil edge crack is 5 to 10 mm.

[0059] In summary, compared with the prior art, the dual-stand Steckel mill control process for reducing edge cracking of hot rolled economical duplex stainless steel of the present invention has the following advantages and beneficial effects:

[0060] Aiming at the serious edge cracking problem of hot-rolled continuous rolling of low-Ni economical duplex stainless steel represented by S32101, the present invention adopts a double-frame furnace coil mill control process, controls the heating process of the ingot, designs the temperature range and the temperature rise curve of the ingot heating process, ensures uniform temperature of the ingot and pure structure; controls the rough rolling process, designs the rolling passes, the pass reduction rate and the rolling speed, ensures uniform structure, uniform force and controllable hot working plastic temperature; controls the finishing rolling process, designs the heating process of the coiling furnace, designs the rolling passes, the pass reduction rate and the rolling speed, designs the coiling process, ensures controllable hot working temperature range and good plate surface quality and precision, and combines the control of the above technical means to reduce the width of the edge crack of the economical duplex stainless hot coil by more than 70% compared with the prior art, and effectively improves the edge quality of the product.

[0061] It should be noted that, in this article, the term "comprise" or any other variation thereof is intended to cover non-exclusive inclusion, so that an article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such article or device.

[0062] It should also be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A double-stand Steckel mill control process for reducing edge cracking of hot rolled economic duplex stainless steel, characterized in that: include: (1) Billet heating process control The ingot is heated in the heating furnace according to the process of controlling the heating temperature and the residence time in the heating furnace. The final heating temperature of the ingot is controlled at 1150-1260°C, and the total residence time is controlled at 140-280min. (2) Rough rolling process control The rough rolling adopts 5 to 7 passes, and the rough rolling is carried out for descaling in the first pass. The rolling reduction rate of each pass is controlled to be 15 to 25%, and the rolling speed is controlled to be 3 to 5 m / s. The rolling speed and rolling reduction rate increase with the number of passes, and the rough rolling outlet temperature is controlled to be 1000 to 1100°C. (3) Finishing rolling process control The finishing rolling adopts double-stand three-rolling process and six-pass rolling. In the first four passes, the rolling reduction rate is controlled at 25-35%, and the rolling speed is controlled at 6-9m / s. The rolling speed increases with the pass, and the reduction rate decreases with the pass; in the last two passes, the rolling reduction rate is controlled at 10-15%, and the rolling speed is controlled at 2-3mm; the finishing rolling outlet temperature is controlled at 900-1000℃; the heating temperature of the coiling furnace of the double-stand furnace coil mill is controlled at 1000-1100℃; laminar cooling is used during coiling, and the coiling temperature is controlled at 500-700℃.

2. The double-stand Steckel mill control process for reducing edge cracking of hot rolled economic duplex stainless steel according to claim 1, characterized in that: In the ingot heating process control, in the preheating section of the heating furnace, the heating furnace temperature is controlled at 500-700°C, and the furnace dwelling time is controlled at 50-100min; in the first heating section of the heating furnace, the heating furnace temperature is controlled at 1000-1050°C, and the furnace dwelling time is controlled at 30-60min; in the second heating section of the heating furnace, the heating furnace temperature is controlled at 1100-1150°C, and the furnace dwelling time is controlled at 30-60min; in the third heating section of the heating furnace, the heating furnace temperature is controlled at 1150-1260°C, and the furnace dwelling time is controlled at 30-60min.

3. The double-stand Steckel mill control process for reducing edge cracking of hot rolled economical duplex stainless steel according to claim 1, characterized in that: The economical duplex stainless steel is a low-Ni economical duplex stainless steel, and its chemical composition, by mass percentage, includes: C≤0.040%, Si≤1.00%, Mn: 4.00%-6.00%, P≤0.040%, S≤0.030%, Cr: 21.00%-22.00%, Ni: 1.35%-1.70%, Mo: 0.1%-0.8%, Cu: 0.1%-0.8%, N: 0.20%-0.25%, and the rest is Fe and unavoidable impurities.

4. The double-stand Steckel mill control process for reducing edge cracking of hot rolled economic duplex stainless steel according to claim 1, characterized in that: The grade of the economical duplex stainless steel is S32101.