Rolling process of 40CrNiMo steel

Abstract

The invention relates to the technical field of steelmaking, and discloses a rolling process of 40CrNiMo steel, which comprises the following steps: S1, casting blank preparation, S2, casting blank stacking and slow cooling in an enclosing wall, S3, rolling process and S4, rolling process optimization. And the S3 rolling process comprises the steps of S301 bar second-line rolling 90 mm specification rolling, S302 bar second-line rolling 80 mm specification rolling, S303 bar first-line rolling 38 mm specification trial rolling, S304 bar first-line rolling 40 mm specification rolling and S305 bar first-line rolling 45 mm specification rolling. According to the technology, quality improvement is achieved, through strict steelmaking technology control, the casting blank crack risk is greatly reduced, and the production efficiency is improved. The casting blank quality is guaranteed through precise chemical component control and a reasonable cooling system, high-quality blanks are provided for follow-up rolling, the product quality problem caused by blank defects is reduced, technological parameters are optimized during rolling, a descaling mode is innovated, the product surface quality is effectively improved, the defects such as scale, pitted surfaces and microcracks are reduced, and the product quality is improved. For example, the quality of pickling samples after first-line and second-line multi-specification rolling is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of steelmaking, and specifically to a rolling process for 40CrNiMo steel. Background Art

[0002] As a high-Ni alloy structural steel bar, 40CrNiMo steel is widely used in the industrial field, but its production faces many challenges. Due to the characteristics of the Ni element, internal stress cracks and hydrogen-induced cracks are likely to occur during the cooling and heating of the continuous casting billet. During steelmaking, it is necessary to accurately control the composition of the molten steel, such as precisely adjusting the Ni content, strictly controlling the H content, and optimizing the continuous casting billet cooling process to reduce the risk of cracks. In the rolling process, its rolling process is complex and demanding. Different specifications of products have different requirements for parameters such as rolling temperature, time, descaling method, and speed. For example, the 90mm specification has specific requirements for preheating temperature, soaking temperature, and residence time in the furnace, and the descaling effect also affects the surface quality; small-specification products such as 38mm also need to adapt the process to ensure quality. Although the industry has explored before, a comprehensive, accurate, and stable production process system has not been formed, making it difficult to efficiently produce high-quality 40CrNiMo steel products, resulting in limitations in meeting market demands, improving product performance, and quality stability. Summary of the Invention

[0003] (I) Technical Problems to be Solved In view of the deficiencies of the prior art, the present invention provides a rolling process for 40CrNiMo steel, which has the advantages of effectively improving the surface quality of the product, reducing scale, pitted surface, micro-cracks, etc., and solves the problem of poor quality stability.

[0004] (II) Technical Solutions To achieve the above object, the present invention provides the following technical solutions: A rolling process for 40CrNiMo steel, including S1 continuous casting billet preparation, S2 continuous casting billet stacking and slow cooling inside the enclosure wall, S3 rolling process, and S4 rolling process optimization. The S3 rolling process includes S301 rolling of 90mm specification on the second bar line, S302 rolling of 80mm specification on the second bar line, S303 trial rolling of 38mm specification on the first bar line, S304 rolling of 40mm specification on the first bar line, and S305 rolling of 45mm specification on the first bar line.

[0005] Preferably, for the S1 continuous casting billet preparation: During the steelmaking process, strictly control the composition of the molten steel. For example, when using a converter to charge iron, add Ni iron and add Ni plates in the ladle furnace to accurately control the Ni content. After vacuum degassing treatment in the VD furnace, the H content is less than 2.0ppm, and ensure that the chemical composition of the continuous casting billet meets the internal control standards (such as accurate control of elements such as C%, Si%, Mn%, P%, S%, Cr%, Ni, Al%, Mo%, etc.).

[0006] Preferably, the S2 billets are stacked in the enclosure wall for slow cooling. The bottom and top layers are preheated and insulated with hot billets of other steel grades at ≥200 °C. After stacking, the surface temperature of the billets is ≥600 °C, and the stacking cooling time is not less than 24 hours to ensure the quality of the billets and prevent cooling internal stress cracks and hydrogen-induced cracks.

[0007] Preferably, for the S301 bar second-line rolling of 90 mm specification: Check the surface of the billets before charging, treat a small amount of oscillation marks and end cutting residues. The preheating section is about 610 °C, the soaking section is about 1220 °C, and it stays in the furnace for about 320 minutes. Switch to the special descaling box for 240-square billets before rolling, descale at a pressure of about 12 MPa, the 800 rolling mill turns the steel multiple times and uses 2 passes of small reduction to remove the scale. Some online pickling samples have scale pressed into the pitted surface, and the offline pickling samples show micro-cracks. Then, quickly collect them into the pit (the temperature when entering the pit is about 670 - 730 °C) to ensure the temperature when entering the pit.

[0008] Preferably, for the S302 bar second-line rolling of 80 mm specification: The preheating section is about 610 °C, the soaking section is about 1200 °C, and it stays in the furnace for about 340 minutes. The descaling effect of the first 2 passes of small reduction in front of the 800 rolling mill is good, and there are no defects in the online and offline pickling samples. Adopt the process of quickly getting off the cooling bed and into the pit for slow cooling.

[0009] Preferably, for the S303 bar first-line trial rolling of 38 mm specification: 3 trial rolls are successful. The soaking section is about 1140 °C, the water descaling is not good, the scale is removed by rolling on the 1st and 2nd rolling mills. There are no defects such as pitted surface in the pickled finished product samples, and there are also no defects in the offline pickling.

[0010] Preferably, for the S304 bar first-line rolling of 40 mm specification: The soaking section is about 1120 °C, and it stays in the furnace for about 90 minutes. The high-pressure water descaling is poor, and the scale falls off during rolling on the 1st and 2nd stands. There are no defects in the off-line and on-line pickling samples.

[0011] Preferably, for the S305 bar first-line rolling of 45 mm specification: The soaking section is about 1120 °C, and it stays in the furnace for about 90 minutes. There are no defects in the off-line and on-line pickling samples.

[0012] Preferably, for the optimization of the S4 rolling process: When the bar mill is rolling, the 800 rolling mill adopts the small reduction descaling process, and for some specifications of rolling, two passes of turning the steel for descaling are used to improve the descaling effect; according to the characteristics and quality requirements of different specifications of products, accurately control parameters such as preheating, soaking temperature and furnace time to ensure the stability of product performance and quality; reasonably adjust the rolling rhythm and speed to ensure uniform and stable rolling deformation in each pass and improve the dimensional accuracy and surface quality of the products; optimize the process according to the actual production situation.

[0013] (III) Beneficial effects Compared with the prior art, the present invention provides a rolling process for 40CrNiMo steel, which has the following beneficial effects: 1. In the rolling process of 40CrNiMo steel, the quality is improved: Through strict steelmaking process control, the risk of slab cracks is significantly reduced. Precise chemical composition control and reasonable cooling system ensure the quality of the slab, providing high-quality billets for subsequent rolling, reducing product quality problems caused by billet defects. During rolling, the process parameters are optimized and the descaling method is innovated, effectively improving the surface quality of the product, reducing defects such as scale, pitted surface, and microcracks. For example, the quality of pickled samples after multi-specification rolling on Bar Line 1 and Bar Line 2 is improved, and the dimensional accuracy is more precise and stable due to process optimization, meeting the requirements of high-end manufacturing for high-precision steel for components, and improving the product qualification rate and market competitiveness.

[0014] 2. In the rolling process of 40CrNiMo steel, the performance is optimized: Precise processes ensure that the mechanical properties of the product are stably up to standard. The optimized rolling process helps to refine grains and improve the tissue uniformity, enhancing the comprehensive performance of the steel and meeting the mechanical property requirements under different working conditions. After multiple trial productions and tests, the product's tensile strength, yield strength, elongation, reduction of area, and impact toughness and other indicators are good and stable, providing reliable material guarantee for the manufacture of key components, expanding the application range, and highlighting the advantages in the manufacture of key components in fields such as automobiles and aerospace, improving the service life and reliability of components.

[0015] 3. In the rolling process of 40CrNiMo steel, the balance between production efficiency and cost is achieved: Stable processes reduce the rejection rate and rework rate, improve production efficiency, and save costs. Reasonable processes reduce rolling failures and equipment wear, extend the equipment life, and reduce maintenance costs; Optimize steelmaking composition control and rolling parameters, shorten the production cycle, and increase production capacity, occupying an advantage in market competition with high efficiency and low cost, achieving double improvements in economic benefits and production efficiency, and promoting the sustainable development of the industry. Specific embodiments

[0016] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0017] This solution provides a technical solution, specifically, a rolling process for 40CrNiMo steel, including the following specific process steps: S1 billet preparation, S2 billet enclosing wall stacking and slow cooling, S3 rolling process, and S4 rolling process optimization; The S3 rolling process includes S301 bar second line rolling 90mm specification rolling, S302 bar second line rolling 80mm specification rolling, S303 bar first line rolling 38mm specification trial rolling, S304 bar first line rolling 40mm specification rolling and S305 bar first line rolling 45mm specification rolling.

[0018] S1 Billet preparation: The composition of molten steel is strictly controlled during the steelmaking process, such as adding Ni iron when mixing iron in the converter and adding Ni plates in the ladle furnace to accurately control the Ni content. The H content is reduced to less than 2.0ppm by vacuum degassing in the VD furnace, and the chemical composition of the billet is ensured to meet the internal control standards (such as precise control of C%, Si%, Mn%, P%, S%, Cr%, Ni, Al%, Mo% and other elements); S2 ingots are stacked in the enclosure for slow cooling. The bottom and top layers are preheated and insulated with hot ingots of other steel grades at ≥200 degrees. The surface temperature of the ingots after stacking is ≥600 degrees. The stack cooling time is not less than 24 hours to ensure the quality of the ingots and prevent internal stress cracks and hydrogen cracks during cooling. S3 rolling process: S301 rod second-line rolling 90mm specification rolling: check the surface of the ingot before loading, deal with a small amount of vibration marks and end cutting residues, preheating section about 610℃, soaking section about 1220℃, in the furnace for about 320 minutes, start rolling and change 240 square billet special descaling box, descaling at a pressure of about 12MPa, 800 rolling mill unit repeatedly turned steel and used 2 passes of small pressure to remove iron oxide scale, some online pickling samples had iron oxide scale pressed into the pitted surface, and offline pickling samples had micro cracks, and then quickly collected and put into the pit (pit temperature is about 670-730℃) to ensure the pit temperature; S302 rod second-line rolling 80mm specification rolling: preheating section about 610℃, soaking section about 1200℃, about 340 minutes in the furnace, 800 rolling mill group first 2 passes of small pressure reduction descaling effect is good, online and offline pickling samples have no defects, and the rapid cooling bed into the pit slow cooling process is adopted; S303 bar first line rolling 38mm specification trial rolling: 3 bars were tested smoothly, the soaking section was about 1140℃, water descaling was not good, 1 and 2 rolling mills were used to remove iron oxide scale, the pickled finished product had no defects such as pitting, and there were no defects in offline pickling; S304 bar rolling 40mm specification rolling: soaking section about 1120℃, in the furnace for about 90 minutes, high pressure water descaling is poor, the iron oxide scale falls off in the 1st and 2nd stands, and there are no defects in the off-line and online pickling samples; S305 rods are rolled in the first line with a specification of 45 mm: the soaking section is about 1120°C, and the furnace is in the furnace for about 90 minutes. There are no defects in the off-line and online pickling samples; Optimization of the S4 rolling process: During the rolling process in the bar mill, the 800 rolling mill adopts the small reduction descaling process, and for some specifications, double turning descaling is used during rolling to improve the descaling effect; according to the product characteristics and quality requirements of different specifications, parameters such as preheating temperature, soaking temperature, and residence time in the furnace are precisely controlled to ensure the stability of product performance and quality; the rolling rhythm and speed are reasonably adjusted to ensure uniform and stable rolling deformation in each pass, improving the dimensional accuracy and surface quality of the product; the process is optimized according to the actual production situation.

[0019] Furthermore, this process has achieved quality improvement: Through strict control of the steelmaking process, the risk of billet cracks has been significantly reduced. Precise chemical composition control and a reasonable cooling system ensure the quality of the billet, providing high-quality billets for subsequent rolling, reducing product quality problems caused by billet defects. During rolling, process parameters are optimized and descaling methods are innovated, effectively improving the surface quality of the product, reducing defects such as scale, pitted surface, and microcracks. For example, the quality of pickling samples after multi-specification rolling on Line 1 and Line 2 of the bar has been improved, and the dimensional accuracy has also become more precise and stable due to process optimization, meeting the requirements of high-end manufacturing for high-precision component steel, improving the product qualification rate and market competitiveness. Furthermore, this process has achieved performance optimization: The precise process ensures that the mechanical properties of the product are stably up to standard. The optimized rolling process helps to refine grains and improve the uniformity of the structure, enhancing the comprehensive performance of the steel and meeting the mechanical property requirements under different working conditions. After multiple trial productions and tests, the product's tensile strength, yield strength, elongation, reduction of area, and impact toughness and other indicators are good and stable, providing reliable material support for the manufacture of key components, expanding the application scope. For example, it shows obvious advantages in the manufacture of key components in the fields of automotive and aerospace, improving the service life and reliability of components. Furthermore, this process has achieved a balance between production efficiency and cost: The stable process reduces the scrap rate and rework rate, improves production efficiency, and saves costs. The reasonable process reduces rolling failures and equipment losses, extends the equipment life, and reduces maintenance costs; optimizing steelmaking composition control and rolling parameters shortens the production cycle and increases production capacity, occupying an advantage in the market competition with high efficiency and low cost, achieving a double improvement in economic benefits and production efficiency, and promoting the sustainable development of the industry.

[0020] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A rolling process for 40CrNiMo steel, comprising S1 billet preparation, S2 billet entering the enclosure stack for slow cooling, S3 rolling process, and S4 rolling process optimization, characterized in that: The S3 rolling process includes S301 rod second-line rolling of 90 mm specification, S302 rod second-line rolling of 80 mm specification, S303 rod first-line rolling of 38 mm specification trial rolling, S304 rod first-line rolling of 40 mm specification rolling, and S305 rod first-line rolling of 45 mm specification rolling.

2. The rolling process of a 40CrNiMo steel according to claim 1, characterized in that: The S1 slab preparation: During the steelmaking process, the chemical composition of the molten steel is strictly controlled. For example, when using a converter to charge iron and add Ni iron, and adding Ni plates in the ladle furnace to accurately control the Ni content. After vacuum degassing treatment in the VD furnace, the H content is less than 2.0 ppm, and the chemical composition of the slab is ensured to meet the internal control standards (such as accurate control of elements such as C%, Si%, Mn%, P%, S%, Cr%, Ni, Al%, Mo%, etc.).

3. The rolling process of a 40CrNiMo steel according to claim 1, characterized in that: The S2 slabs are stacked in the enclosure wall for slow cooling. The bottom and top layers are preheated and insulated with hot slabs of other steel grades at ≥200 degrees. After stacking, the surface temperature of the slabs is ≥600 degrees, and the stacking cooling time is not less than 24 hours to ensure the quality of the slabs and prevent cooling internal stress cracks and hydrogen-induced cracks.

4. The rolling process of a 40CrNiMo steel according to claim 1, characterized in that: The S301 rod second-line rolling of 90 mm specification rolling: Before charging, check the surface of the slab, process a small amount of vibration marks and end cutting residues. The preheating section is about 610 °C, the soaking section is about 1220 °C, and it is in the furnace for about 320 minutes. When starting rolling, change to the special descaling box for 240-square billets, descale with a pressure of about 12 MPa. The 800 rolling mill flips the steel multiple times and uses 2 passes of small reduction to remove the scale. Some on-line pickling samples have scale pressed into the pitted surface, and the off-line pickling samples show micro-cracks. Then, quickly collect and put them into the pit (the temperature when entering the pit is about 670 - 730 °C) to ensure the temperature when entering the pit.

5. A rolling process for 40CrNiMo steel according to claim 1, characterized in that: The S302 rod second-line rolling of 80 mm specification rolling: The preheating section is about 610 °C, the soaking section is about 1200 °C, and it is in the furnace for about 340 minutes. The descaling effect of the first 2 passes of small reduction in front of the 800 rolling mill is good. There are no defects in the on-line and off-line pickling samples, and the rapid cooling bed and pit slow cooling process is adopted.

6. The rolling process of a 40CrNiMo steel according to claim 1, characterized in that: The S303 rod first-line rolling of 38 mm specification trial rolling: 3 trial rolls are successful. The soaking section is about 1140 °C, and the water descaling is not good. The scale is removed by the 1st and 2nd rolling mills. There are no defects such as pitted surface in the pickled finished product samples, and there are also no defects in the off-line pickling.

7. A rolling process for 40CrNiMo steel according to claim 1, characterized in that: The S304 rod first-line rolling of 40 mm specification rolling: The soaking section is about 1120 °C, and it is in the furnace for about 90 minutes. The high-pressure water descaling is poor, and the scale falls off during the 1st and 2nd rolling. There are no defects in the off-line and on-line pickling samples.

8. A rolling process for 40CrNiMo steel according to claim 1, characterized in that: The S305 rod first-line rolling of 45 mm specification rolling: The soaking section is about 1120 °C, and it is in the furnace for about 90 minutes. There are no defects in the off-line and on-line pickling samples.

9. A rolling process for 40CrNiMo steel according to claim 1, characterized in that: The S4 rolling process optimization: When the bar mill is rolling, the 800 rolling mill adopts the small reduction descaling process, and for some specifications of rolling, two passes of steel flipping are used for descaling to improve the descaling effect; according to the product characteristics and quality requirements of different specifications, accurately control parameters such as preheating, soaking temperature, and furnace time to ensure the stability of product performance and quality; reasonably adjust the rolling rhythm and speed to ensure uniform and stable rolling deformation in each pass, and improve the dimensional accuracy and surface quality of the product; optimize the process according to the actual production situation.