Hot rolling cooling process of 20CrMnTi round steel

Abstract

The invention discloses a hot rolling cooling process of 20CrMnTi round steel, and belongs to the technical field of 20CrMnTi round steel. Comprising the following steps: smelting in a converter, preparing pre-alloyed molten steel, carrying out secondary alloying, preparing final molten steel, continuously casting, preparing a heated steel billet, and carrying out two-stage rolling to obtain the 20CrMnTi round steel. According to the method, collaborative optimization of links such as smelting, refining, rolling and cooling is achieved, all the process steps are mutually matched and supported, a complete quality guarantee is provided, high-performance products are stably produced, and the requirement of high-precision parts for steel quality stability is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of 20CrMnTi round steel, and particularly relates to a hot rolling and cooling process of 20CrMnTi round steel. BACKGROUND

[0002] As a commonly used low-carbon alloy structural steel, 20CrMnTi steel is widely used in the fields of mechanical manufacturing and automobile transmission system due to its good mechanical properties and processing performance, and is particularly suitable for manufacturing parts with high requirements for strength, toughness and microstructure stability.

[0003] The prior art has defects in controlling the ferrite-pearlite banded structure, and the research of Wang Zhen, Li Bopeng, Tang Zhigang, et al. Control of ferrite-pearlite banded structure of 20CrMnTi steel hot-rolled bar [J]. Metal processing (hot working), 2025, (07): 94-100 shows that the formation of banded structure is closely related to temperature control and cooling speed in the rolling process, and annealing treatment will further aggravate the banded structure, resulting in uneven mechanical properties of the steel along the rolling direction, such as strength fluctuation, which is difficult to meet the requirements of high-precision parts for performance consistency. However, most of the existing processes fail to effectively combine the regulation of finish rolling temperature and cooling speed after rolling with the quality control of the early smelting and continuous casting link, solve the cleanliness problem but fail to inhibit the generation of banded structure, resulting in that the comprehensive performance of the product is difficult to meet the standard.

[0004] Based on this, the present application designs a hot rolling and cooling process of 20CrMnTi round steel to solve the above problems. SUMMARY

[0005] In view of the above-mentioned defects of the prior art, the present application provides a hot rolling and cooling process of 20CrMnTi round steel.

[0006] To achieve the above purpose, the present application is realized by the following technical scheme: A hot rolling and cooling process of 20CrMnTi round steel, comprising the following steps: S1: adopting oxidation method for converter smelting, temperature 1550-1600℃, tapping temperature 1640-1660℃, converter opening water gap, adding carbon powder for pre-deoxidation, obtaining 20CrMnTi primary molten steel; S2: adding low-carbon chromium iron and high-carbon chromium iron, synchronously adding carbon powder, and simultaneously adding synthetic refining slag and lime, obtaining pre-alloyed molten steel; S3: transferring the pre-alloyed molten steel into a ladle refining furnace, adding a modifier, and spreading white slag, adding silicon-manganese alloy, titanium-iron and niobium-iron for secondary alloying; S4: After secondary alloying, calcium wire is fed in, rare earth oxides are added, and soft argon blowing is performed. The final steel liquid composition is: carbon 0.17%-0.23%, silicon 0.17%-0.37%, manganese 0.50%-0.80%, chromium 1.00%-1.30%, titanium 0.04%-0.10%, niobium 0.020%-0.060%, total rare earth 0.0020%-0.0035%, phosphorus ≤0.035%, sulfur ≤0.035%, H ≤2.0ppm, to obtain the final molten steel. S5: The final molten steel is continuously cast at 1530-1570℃. After continuous casting, the billet is slowly cooled to 600-650℃ within 12-18 hours to obtain the continuously cast billet. S6: The continuously cast billet is fed into the heating furnace and passes through the preheating section at 800-900℃, the heating section at 1170-1270℃, and the soaking section at 1150-1200℃ in sequence. The total heating time is 2.5-4.0h to obtain the heated steel billet. S7: The heated steel billet is rolled in two stages. The first stage is rolled at 900-1000℃. After rolling, it is cooled to 850-880℃ by a water cooling device at a rate of 5-10℃ / s. The second stage is rolled at 820-880℃. The final rolling temperature is 915-945℃. The billet is rolled into 20CrMnTi round steel. S8: Feed the final rolled 20CrMnTi round steel into the uniform temperature roller table and keep it at 900-920℃ for 2-5 minutes; S9: Cool the 20CrMnTi round steel after S8 homogenization at a rate of 1.5-3.0℃ / s to 800-830℃. Then, cool the 20CrMnTi round steel to 550-600℃ at a rate of 0.8-1.2℃ / s. Continue to control the cooling rate to ≤0.5℃ / s and cool to 300-350℃. Hold the steel at 300-350℃ for 10-20 minutes and then air cool it to below 200℃.

[0007] Furthermore, S1 specifically involves: using an oxidation method for converter smelting at a temperature of 1550-1600℃, maintaining net boiling for 10-20 minutes, tapping at a temperature of 1640-1660℃, and tapping for 3-4 minutes. The converter's taphole is opened, and molten steel is poured into a pre-prepared empty ladle. When the amount of steel tapped reaches 1 / 4 of the total capacity, 0.70-0.95 kg of carbon powder is added per ton of steel for pre-deoxidation to obtain 20CrMnTi primary smelted steel.

[0008] Furthermore, S2 specifically refers to the following steps: when the steel output reaches 1 / 2 of the total capacity, add 10-12 kg of low-carbon ferrochrome and 4-5 kg ​​of high-carbon ferrochrome per ton of steel, simultaneously add 0.3-0.5 kg of carbon powder per ton of steel, and add 5-6 kg of synthetic refining slag and 2-3 kg of lime per ton of steel to obtain pre-alloyed molten steel.

[0009] Furthermore, the synthetic refining slag contains 40-50 wt% calcium oxide and 30-45 wt% aluminum oxide.

[0010] Furthermore, S3 specifically involves: transferring pre-alloyed molten steel into a ladle refining furnace, adding 1.55-2.05 kg of modifier per ton of steel, and spreading 0.23-0.35 kg of white slag per ton of steel. 5-10 minutes before tapping, adding 0.30-0.60 kg of silicon-manganese alloy, 0.13-1.06 kg of ferrotitanium, and 0.028-0.154 kg of ferroniobium per ton of steel for secondary alloying.

[0011] Furthermore, in S4, after secondary alloying, calcium wire is fed in at a rate of 0.35-0.60m per ton of steel, rare earth oxides are added, and soft argon blowing is performed for 10-15 minutes.

[0012] Furthermore, S9 specifically involves: using a laminar flow cooling device to cool the 20CrMnTi round steel after S8 homogenization, controlling the cooling rate at 1.5-3.0℃ / s, cooling it to 800-830℃, then switching to a mist cooling device, cooling the 20CrMnTi round steel to 550-600℃ at a cooling rate of 0.8-1.2℃ / s, then transferring the cooled 20CrMnTi round steel to a cooling bed for air cooling, controlling the cooling rate at ≤0.5℃ / s, cooling it to 300-350℃, then starting the built-in heat preservation device of the cooling bed for online pre-tempering, holding the temperature at 300-350℃ for 10-20 minutes, and then air cooling it to below 200℃.

[0013] Furthermore, the preparation of the modifier includes: A1: Calcium carbide, industrial silicon carbide, rare earth oxides, sodium borate, nano alumina powder, and sodium citrate dispersant are all fed into a hot air drying kiln and dried at 120-150℃ for 2-4 hours. The dried calcium carbide, rare earth oxides and sodium borate are coarsely crushed to 5-10 mm and then finely crushed, with the calcium carbide crushed to 1-3 mm and the rare earth oxides and sodium borate crushed to 100-200 mesh. A2: Weigh 80-100 parts of dried silicon carbide, 0.5-2 parts of rare earth oxides, and 1-5 parts of polysulfonate dispersant by weight, ball mill for 1-2 hours at a ball-to-material ratio of 4-6:1 and a rotation speed of 200-300 r / min to obtain modified silicon carbide particles. A3: Weigh 25-35 parts of modified silicon carbide particles and 35-45 parts of calcium carbide by weight, stir at 50-80℃ and 60-100r / min for 5-10min, then feed them into a disc granulator, use polyvinyl alcohol aqueous solution as binder to obtain particles with a particle size of 2-4mm, and feed them into a hot air dryer to dry at 80-100℃ for 1-2h. A4: Weigh out 0.8-1.5 parts by weight of rare earth oxides, 5-12 parts by weight of sodium borate, 3-8 parts by weight of nano alumina powder, and 0.5-2 parts by weight of sodium citrate dispersant. Stir at room temperature for 3-5 minutes at a speed of 800-1200 r / min to obtain a mixture. The dried granules from step A3 are fed into a fluidized bed coating machine and heated to 60-90℃. First, a polyvinyl alcohol aqueous solution accounting for 3-6 wt% of the mixture is sprayed in, and then the mixture is added in 3-4 batches. The coating time is 5-10 minutes to obtain composite granules. The coated composite particles are then subjected to low-temperature curing at a heating rate of 5-10℃ / min and a curing temperature of 200-280℃ for 1-2 hours to obtain the modifier.

[0014] Compared with the prior art, the beneficial effects of this invention are as follows: 1. This invention achieves synergistic optimization of smelting, refining, rolling, and cooling processes. Each process step is mutually compatible and supportive, providing complete quality assurance, stable production of high-performance products, reducing performance fluctuations caused by deviations in a single process, significantly improving the consistency of product performance and mechanical properties in mass production, and meeting the requirements of high-precision parts for the stability of steel quality.

[0015] 2. Compared with commercially available modifiers, the modifier prepared by this invention is better suited to the smelting and refining process of 20CrMnTi steel. At the same time, the segmented temperature-controlled rolling and cooling method solves the problem of improper control of banded structure in the existing process, thereby ensuring that the core indicators such as strength and hardness of the round steel meet the standards. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0017] Figure 1 This is a process flow diagram of a hot rolling and cooling process for 20CrMnTi round steel according to the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] Example 1: This example discloses a hot rolling and cooling process for 20CrMnTi round steel, including the following steps: S1: The converter is smelted using the oxidation method at a temperature of 1550℃, maintaining net boiling for 10 minutes, with a tapping temperature of 1640℃ and a tapping time of 3 minutes. The converter is opened and molten steel is poured into a pre-prepared empty ladle. When the amount of steel tapped reaches 1 / 4 of the total capacity, 0.70 kg of carbon powder is added per ton of steel for pre-deoxidation to obtain 20CrMnTi primary molten steel. S2: When the steel output reaches 1 / 2 of the total capacity, add 10 kg of low-carbon ferrochrome and 4 kg of high-carbon ferrochrome per ton of steel, add 0.3 kg of carbon powder per ton of steel, and add 5 kg of synthetic refining slag and 2 kg of lime per ton of steel to obtain pre-alloyed molten steel. The synthetic refining slag contains 40-50 wt% calcium oxide and 30-45 wt% aluminum oxide; S3: The pre-alloyed molten steel is transferred to the ladle refining furnace. 1.55 kg of modifier is added per ton of steel, and 0.23 kg of white slag is spread per ton of steel. 5 minutes before tapping, 0.30 kg of silicon-manganese alloy (silicon-manganese molar ratio of 10:60), 0.13 kg of ferrotitanium (20-30 wt% Ti), and 0.028 kg of ferroniobium (39-45 wt% Nb) are added per ton of steel for secondary alloying. The preparation of the modifier includes: A1: Calcium carbide (CaC2 purity ≥ 85wt%), industrial silicon carbide (SiC purity ≥ 88wt%), rare earth oxides (CeC2 and La2O3 composite with a molar ratio of 2:1), sodium borate, nano alumina powder (produced by Jiangsu Tianxing New Materials Co., Ltd., particle size 40-80nm), and sodium citrate dispersant are all fed into a hot air drying kiln and dried at 120℃ for 2 hours. The dried calcium carbide, rare earth oxides and sodium borate are coarsely crushed to 5-10mm by a jaw crusher, and then finely crushed by an impact crusher, with the calcium carbide crushed to 1-3mm and the rare earth oxides and sodium borate crushed to 100-200 mesh. A2: Weigh 80 parts of dried silicon carbide, 0.5 parts of rare earth oxide, and 1 part of polysulfonate dispersant by weight, add them to a planetary ball mill, and ball mill for 1 hour at a ball-to-material ratio of 4:1 and a rotation speed of 200 r / min to obtain modified silicon carbide particles. A3: Weigh 25 parts of modified silicon carbide particles and 35 parts of calcium carbide by weight, add them to a twin-screw mixer, stir at 50°C and 60 r / min for 5 min, then send them to a disc granulator, use polyvinyl alcohol aqueous solution as binder (addition amount accounts for 3wt% of the total mass of modified silicon carbide particles and calcium carbide, concentration 5wt%), to obtain particles with a particle size of 2-4 mm, and send them to a hot air dryer to dry at 80°C for 1 h; A4: Weigh out 0.8 parts rare earth oxide, 5 parts sodium borate, 3 parts nano alumina powder, and 0.5 parts sodium citrate dispersant by weight, add them to a high-speed mixer, and stir at 800 r / min for 3 min at room temperature to obtain a mixture; The dried granules from step A3 are fed into a fluidized bed coating machine and heated to 60°C. First, a polyvinyl alcohol aqueous solution (concentration 5wt%) accounting for 3wt% of the mass of the mixture is sprayed in, and then the mixture is added in 3 portions. The coating time is 5 minutes to obtain composite granules. The coated composite particles were fed into a tunnel curing oven for low-temperature curing at a heating rate of 5℃ / min and a curing temperature of 200℃ for 1 hour to obtain the modifier. S4: After secondary alloying, calcium wire is fed in at a rate of 0.35m per ton of steel, and rare earth oxides (a CeC2 and La2O3 composite with a molar ratio of 2:1) are added. Soft argon blowing is performed for 10 minutes. The final steel liquid composition (wt%) is: carbon 0.17%-0.23%, silicon 0.17%-0.37%, manganese 0.50%-0.80%, chromium 1.00%-1.30%, titanium 0.04%-0.10%, niobium 0.020%-0.060%, total rare earth 0.0020%-0.0035%, phosphorus ≤0.035%, sulfur ≤0.035%, and H ≤2.0ppm, yielding the final molten steel. S5: The final molten steel is continuously cast at 1530℃. After continuous casting is completed, the billet is slowly cooled to 600℃ within 12 hours to obtain the continuously cast billet. S6: The continuously cast billet is fed into the heating furnace and passes through the 800℃ preheating section, the 1170℃ heating section, and the 1150℃ soaking section in sequence. The total heating time is 2.5 hours, and the heated steel billet is obtained. S7: The heated steel billet is rolled in two stages. The first stage is rolled at 900℃, and after rolling, it is cooled to 850℃ at a rate of 5℃ / s by a water cooling device. The second stage is rolled at 820℃, and the final rolling temperature is 915℃, which yields 20CrMnTi round steel (φ5.5-50mm). S8: Feed the final rolled 20CrMnTi round steel into the uniform temperature roller table and keep it at 900℃ for 2 minutes; S9: The 20CrMnTi round steel after S8 homogenization is cooled using a laminar flow cooling device at a controlled cooling rate of 1.5℃ / s. When the temperature reaches 800℃, the device is switched to a mist cooling device at a cooling rate of 0.8℃ / s to cool the 20CrMnTi round steel to 550℃. The cooled 20CrMnTi round steel is then transferred to a cooling bed for air cooling at a controlled cooling rate of ≤0.5℃ / s. When the temperature reaches 300℃, the built-in heat preservation device of the cooling bed is activated for online pre-tempering at a heat preservation temperature of 300℃ for 10 minutes. Subsequently, the temperature is air-cooled to below 200℃.

[0020] Example 2: This example discloses a hot rolling and cooling process for 20CrMnTi round steel, including the following steps: S1: The converter is smelted by oxidation at a temperature of 1600℃ and kept in net boiling for 20 minutes. The tapping temperature is 1660℃ and the tapping time is 4 minutes. The converter tapping nozzle is opened and molten steel is poured into a pre-prepared empty ladle. When the amount of steel tapped reaches 1 / 4 of the total capacity, 0.95 kg of carbon powder is added per ton of steel for pre-deoxidation to obtain 20CrMnTi primary molten steel. S2: When the steel output reaches 1 / 2 of the total capacity, add 12 kg of low-carbon ferrochrome and 5 kg of high-carbon ferrochrome per ton of steel, add 0.5 kg of carbon powder per ton of steel, and add 6 kg of synthetic refining slag and 3 kg of lime per ton of steel to obtain pre-alloyed molten steel. The synthetic refining slag contains 40-50 wt% calcium oxide and 30-45 wt% aluminum oxide; S3: Pre-alloyed molten steel is transferred to the ladle refining furnace. 2.05 kg of modifier is added per ton of steel, and 0.35 kg of white slag is spread per ton of steel. 10 minutes before tapping, 0.60 kg of silicon-manganese alloy (silicon-manganese molar ratio of 25:70), 1.06 kg of ferrotitanium and 0.154 kg of ferroniobium are added per ton of steel for secondary alloying. The preparation of the modifier includes: A1: Calcium carbide (CaC2 purity ≥ 85wt%), industrial silicon carbide (SiC purity ≥ 88wt%), rare earth oxides (CeC2 and La2O3 composite with a molar ratio of 2:1), sodium borate, nano alumina powder (produced by Jiangsu Tianxing New Materials Co., Ltd., particle size 40-80nm), and sodium citrate dispersant are all fed into a hot air drying kiln and dried at 150℃ for 4 hours. The dried calcium carbide, rare earth oxides and sodium borate are coarsely crushed to 5-10mm by a jaw crusher, and then finely crushed by an impact crusher, with the calcium carbide crushed to 1-3mm and the rare earth oxides and sodium borate crushed to 100-200 mesh. A2: Weigh 100 parts of dried silicon carbide, 2 parts of rare earth oxides, and 5 parts of polysulfonate dispersant by weight, add them to a planetary ball mill, and ball mill for 2 hours at a ball-to-material ratio of 6:1 and a rotation speed of 300 r / min to obtain modified silicon carbide particles. A3: Weigh 35 parts of modified silicon carbide particles and 45 parts of calcium carbide by weight, add them to a twin-screw mixer, stir at 100 r / min for 10 min at 80℃, then send them to a disc granulator, use polyvinyl alcohol aqueous solution as binder (addition amount accounts for 5 wt% of the total mass of modified silicon carbide particles and calcium carbide, concentration 10 wt%), to obtain particles with a particle size of 2-4 mm, and send them to a hot air dryer to dry at 100℃ for 2 h; A4: Weigh out 1.5 parts rare earth oxide, 12 parts sodium borate, 8 parts nano alumina powder, and 2 parts sodium citrate dispersant by weight, add them to a high-speed mixer, and stir at 1200 r / min for 5 min at room temperature to obtain a mixture; The dried granules from step A3 are fed into a fluidized bed coating machine and heated to 90°C. First, a polyvinyl alcohol aqueous solution (concentration 10wt%) accounting for 6wt% of the mass of the mixture is sprayed in, and then the mixture is added in 4 portions. The coating time is 10 minutes to obtain composite granules. The coated composite particles were fed into a tunnel curing oven for low-temperature curing at a heating rate of 10℃ / min and a curing temperature of 280℃ for 2 hours to obtain the modifier. S4: After secondary alloying, calcium wire is fed in at a rate of 0.60m per ton of steel, and rare earth oxides (a CeC2 and La2O3 composite with a molar ratio of 2:1) are added. Soft argon blowing is performed for 15 minutes. The final steel liquid composition (wt%) is: carbon 0.17%-0.23%, silicon 0.17%-0.37%, manganese 0.50%-0.80%, chromium 1.00%-1.30%, titanium 0.04%-0.10%, niobium 0.020%-0.060%, total rare earth 0.0020%-0.0035%, phosphorus ≤0.035%, sulfur ≤0.035%, and H ≤2.0ppm, yielding the final molten steel. S5: The final molten steel is continuously cast at 1570℃. After continuous casting is completed, the billet is slowly cooled to 650℃ within 18 hours to obtain the continuously cast billet. S6: The continuously cast billet is fed into the heating furnace and passes through the 900℃ preheating section, the 1270℃ heating section, and the 1200℃ soaking section in sequence. The total heating time is 4.0h to obtain the heated steel billet. S7: The heated steel billet is rolled in two stages. The first stage is rolled at 1000℃. After rolling, it is cooled to 880℃ at a rate of 10℃ / s by a water cooling device. The second stage is rolled at 880℃. The final rolling temperature is 945℃, and the billet is rolled into 20CrMnTi round steel (φ5.5-50mm). S8: Feed the final rolled 20CrMnTi round steel into the uniform temperature roller table and keep it at 920℃ for 5 minutes; S9: The 20CrMnTi round steel after S8 homogenization is cooled using a laminar flow cooling device at a controlled cooling rate of 3.0℃ / s. When the temperature reaches 830℃, the device is switched to a mist cooling device at a cooling rate of 1.2℃ / s to cool the 20CrMnTi round steel to 600℃. The cooled 20CrMnTi round steel is then transferred to a cooling bed for air cooling at a controlled cooling rate of ≤0.5℃ / s. When the temperature reaches 350℃, the built-in insulation device of the cooling bed is activated for online pre-tempering at a holding temperature of 350℃ for 20 minutes. Subsequently, the steel is air-cooled to below 200℃.

[0021] Example 3: This example discloses a hot rolling and cooling process for 20CrMnTi round steel, including the following steps: S1: The converter is smelted using the oxidation method at a temperature of 1580℃, maintaining net boiling for 16 minutes, with a tapping temperature of 1650℃ and a tapping time of 3 minutes. The converter is opened and molten steel is poured into a pre-prepared empty ladle. When the amount of steel tapped reaches 1 / 4 of the total capacity, 0.85 kg of carbon powder is added per ton of steel for pre-deoxidation to obtain 20CrMnTi primary molten steel. S2: When the steel output reaches 1 / 2 of the total capacity, add 11 kg of low-carbon ferrochrome and 5 kg of high-carbon ferrochrome per ton of steel, add 0.4 kg of carbon powder per ton of steel, and add 6 kg of synthetic refining slag and 2 kg of lime per ton of steel to obtain pre-alloyed molten steel. The synthetic refining slag contains 40-50 wt% calcium oxide and 30-45 wt% aluminum oxide; S3: The pre-alloyed molten steel is transferred to the ladle refining furnace. 1.85 kg of modifier is added per ton of steel, and 0.28 kg of white slag is spread per ton of steel. 8 minutes before tapping, 0.52 kg of silicon-manganese alloy (silicon-manganese molar ratio of 20:65), 0.95 kg of ferrotitanium and 0.154 kg of ferroniobium are added per ton of steel for secondary alloying. The preparation of the modifier includes: A1: Calcium carbide (CaC2 purity ≥ 85wt%), industrial silicon carbide (SiC purity ≥ 88wt%), rare earth oxides (CeC2 and La2O3 composite with a molar ratio of 2:1), sodium borate, nano alumina powder (produced by Jiangsu Tianxing New Materials Co., Ltd., particle size 40-80nm), and sodium citrate dispersant are all fed into a hot air drying kiln and dried at 135℃ for 3 hours. The dried calcium carbide, rare earth oxides and sodium borate are coarsely crushed to 5-10mm by a jaw crusher, and then finely crushed by an impact crusher, with the calcium carbide crushed to 1-3mm and the rare earth oxides and sodium borate crushed to 100-200 mesh. A2: Weigh 95 parts of dried silicon carbide, 1 part of rare earth oxide, and 3 parts of polysulfonate dispersant by weight, add them to a planetary ball mill, and ball mill for 2 hours at a ball-to-material ratio of 5:1 and a rotation speed of 260 r / min to obtain modified silicon carbide particles. A3: Weigh 30 parts of modified silicon carbide particles and 40 parts of calcium carbide by weight, add them to a twin-screw mixer, stir at 80 r / min for 8 min at 75℃, then send them to a disc granulator, use polyvinyl alcohol aqueous solution as binder (addition amount accounts for 4 wt% of the total mass of modified silicon carbide particles and calcium carbide, concentration 8 wt%), to obtain particles with a particle size of 2-4 mm, and send them to a hot air dryer to dry at 90℃ for 2 h; A4: Weigh out 1.5 parts rare earth oxide, 10 parts sodium borate, 5 parts nano alumina powder, and 0.8 parts sodium citrate dispersant by weight, add them to a high-speed mixer, and stir at 1000 r / min for 5 min at room temperature to obtain a mixture; The dried granules from step A3 are fed into a fluidized bed coating machine and heated to 78°C. First, a polyvinyl alcohol aqueous solution (7wt% concentration) accounting for 4wt% of the mass of the mixture is sprayed in, and then the mixture is added in 3 portions. The coating time is 7 minutes to obtain composite granules. The coated composite particles were fed into a tunnel curing oven for low-temperature curing at a heating rate of 8℃ / min and a curing temperature of 240℃ for 2 hours to obtain the modifier. S4: After secondary alloying, calcium wire is fed in at a rate of 0.55m per ton of steel, and rare earth oxides (a CeC2 and La2O3 composite with a molar ratio of 2:1) are added. Soft argon blowing is performed for 12 minutes. The final steel liquid composition (wt%) is: carbon 0.17%-0.23%, silicon 0.17%-0.37%, manganese 0.50%-0.80%, chromium 1.00%-1.30%, titanium 0.04%-0.10%, niobium 0.020%-0.060%, total rare earth 0.0020%-0.0035%, phosphorus ≤0.035%, sulfur ≤0.035%, H ≤2.0ppm, yielding the final molten steel. S5: The final molten steel is continuously cast at 1550℃. After continuous casting is completed, the billet is slowly cooled to 620℃ within 14 hours to obtain the continuously cast billet. S6: The continuously cast billet is fed into the heating furnace and passes through the 850℃ preheating section, the 1270℃ heating section and the 1180℃ soaking section in sequence. The total heating time is 3 hours to obtain the heated steel billet. S7: The heated steel billet is rolled in two stages. The first stage is rolled at 1000℃. After rolling, it is cooled to 850-880℃ by a water cooling device at a rate of 8℃ / s. The second stage is rolled at 850℃. The final rolling temperature is 930℃, and the billet is rolled into 20CrMnTi round steel (φ5.5-50mm). S8: Feed the final rolled 20CrMnTi round steel into the uniform temperature roller table and keep it at 920℃ for 5 minutes; S9: The 20CrMnTi round steel after S8 homogenization is cooled using a laminar flow cooling device at a controlled cooling rate of 2℃ / s. When the temperature reaches 830℃, the device is switched to a mist cooling device at a cooling rate of 1℃ / s to cool the 20CrMnTi round steel to 580℃. The cooled 20CrMnTi round steel is then transferred to a cooling bed for air cooling at a controlled cooling rate of ≤0.5℃ / s. When the temperature reaches 320℃, the built-in heat preservation device of the cooling bed is activated for online pre-tempering at a heat preservation temperature of 320℃ for 15 minutes. Subsequently, the steel is air-cooled to below 200℃.

[0022] Comparative Example 1: The difference between this comparative example and Example 3 is that the modifier is replaced with an existing commercially available product (Hebei Kunshengda New Material Co., Ltd., model ksd3498).

[0023] Comparative Example 2: The difference between this comparative example and Example 3 is that in S9, the temperature was cooled from 920°C to 320°C at a rate of 1°C / s; and in S7, the final rolling temperature was 900°C.

[0024] Comparative Example 3: The difference between this comparative example and Example 3 is that the modifier was replaced with an existing commercially available product, and in S9 the temperature was cooled from 920°C to 320°C at a rate of 1°C / s; and in S7 the final rolling temperature was 900°C.

[0025] Experimental Example 1: Tensile strength and yield strength (MPa) were tested according to GB / T 228.1-2021. Experimental Example 2: Brinell hardness (HB) was tested according to GB / T 231.1-2018.

[0026] The results are shown in the table below:

[0027] As shown in the table above, the 20CrMnTi round steel prepared by this invention has a high and stable level in terms of tensile strength, yield strength and Brinell hardness, with no obvious performance fluctuations.

[0028] The modifier prepared by this invention can be adapted to the smelting and refining process of 20CrMnTi steel through a specific formula, while the components of commercially available modifiers cannot play the same refining and modification role, thus affecting the mechanical properties. When the final rolling temperature is >915℃ and the cooling rate is controlled at 1.50℃ / s, the strip thickness of 20CrMnTi hot-rolled bars can be controlled to <2.0 grade, ultimately improving strength and hardness.

[0029] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. 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 of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hot rolling and cooling process for 20CrMnTi round steel, characterized in that, Includes the following steps: S1: The converter smelting is carried out by oxidation method at a temperature of 1550-1600℃ and a tapping temperature of 1640-1660℃. The converter tap is opened and carbon powder is added for pre-deoxidation to obtain 20CrMnTi primary molten steel. S2: Add low-carbon ferrochrome and high-carbon ferrochrome, simultaneously add carbon powder, and add synthetic refining slag and lime to obtain pre-alloyed molten steel; S3: The pre-alloyed molten steel is transferred to the ladle refining furnace, where modifiers are added, white slag is spread out, and silicon-manganese alloy, ferrotitanium and ferroniobium are added for secondary alloying. S4: After secondary alloying, calcium wire is fed in, rare earth oxides are added, and soft argon blowing is performed. The final steel liquid composition is: carbon 0.17%-0.23%, silicon 0.17%-0.37%, manganese 0.50%-0.80%, chromium 1.00%-1.30%, titanium 0.04%-0.10%, niobium 0.020%-0.060%, total rare earth 0.0020%-0.0035%, phosphorus ≤0.035%, sulfur ≤0.035%, H ≤2.0ppm, to obtain the final molten steel. S5: The final molten steel is continuously cast at 1530-1570℃. After continuous casting, the billet is slowly cooled to 600-650℃ within 12-18 hours to obtain the continuously cast billet. S6: The continuously cast billet is fed into the heating furnace and passes through the preheating section at 800-900℃, the heating section at 1170-1270℃, and the soaking section at 1150-1200℃ in sequence. The total heating time is 2.5-4.0h to obtain the heated steel billet. S7: The heated steel billet is rolled in two stages. The first stage is rolled at 900-1000℃. After rolling, it is cooled to 850-880℃ by a water cooling device at a rate of 5-10℃ / s. The second stage is rolled at 820-880℃. The final rolling temperature is 915-945℃. The billet is rolled into 20CrMnTi round steel. S8: Feed the final rolled 20CrMnTi round steel into the uniform temperature roller table and keep it at 900-920℃ for 2-5 minutes; S9: Cool the 20CrMnTi round steel after S8 homogenization at a rate of 1.5-3.0℃ / s to 800-830℃. Then, cool the 20CrMnTi round steel to 550-600℃ at a rate of 0.8-1.2℃ / s. Continue to control the cooling rate to ≤0.5℃ / s and cool to 300-350℃. Hold the steel at 300-350℃ for 10-20 minutes and then air cool it to below 200℃.

2. The hot rolling and cooling process for 20CrMnTi round steel according to claim 1, characterized in that, S1 specifically involves: using the oxidation method for converter smelting at a temperature of 1550-1600℃, maintaining net boiling for 10-20 minutes, tapping at a temperature of 1640-1660℃, and tapping for 3-4 minutes. The converter nozzle is opened, and molten steel is poured into a pre-prepared empty ladle. When the amount of steel tapped reaches 1 / 4 of the total capacity, 0.70-0.95 kg of carbon powder is added per ton of steel for pre-deoxidation to obtain 20CrMnTi primary smelted steel.

3. The hot rolling and cooling process for 20CrMnTi round steel according to claim 1, characterized in that, S2 specifically involves adding 10-12 kg of low-carbon ferrochrome and 4-5 kg ​​of high-carbon ferrochrome per ton of steel, along with 0.3-0.5 kg of carbon powder per ton of steel, and simultaneously adding 5-6 kg of synthetic refining slag and 2-3 kg of lime per ton of steel to obtain pre-alloyed molten steel.

4. The hot rolling and cooling process for 20CrMnTi round steel according to claim 1, characterized in that, The synthetic refining slag contains 40-50 wt% calcium oxide and 30-45 wt% aluminum oxide.

5. The hot rolling and cooling process for 20CrMnTi round steel according to claim 1, characterized in that, S3 specifically involves: transferring pre-alloyed molten steel into a ladle refining furnace, adding 1.55-2.05 kg of modifier per ton of steel, and spreading 0.23-0.35 kg of white slag per ton of steel. 5-10 minutes before tapping, adding 0.30-0.60 kg of silicon-manganese alloy, 0.13-1.06 kg of ferrotitanium, and 0.028-0.154 kg of ferroniobium per ton of steel for secondary alloying.

6. The hot rolling and cooling process for 20CrMnTi round steel according to claim 1, characterized in that, In S4, after secondary alloying, calcium wire is fed in at a rate of 0.35-0.60m per ton of steel, rare earth oxides are added, and soft argon blowing is performed for 10-15 minutes.

7. The hot rolling and cooling process for 20CrMnTi round steel according to claim 1, characterized in that, Specifically, S9 involves using a laminar flow cooling device to cool the 20CrMnTi round steel after S8 homogenization, controlling the cooling rate at 1.5-3.0℃ / s, cooling it to 800-830℃, then switching to a mist cooling device, cooling the 20CrMnTi round steel to 550-600℃ at a cooling rate of 0.8-1.2℃ / s, then transferring the cooled 20CrMnTi round steel to a cooling bed for air cooling, controlling the cooling rate at ≤0.5℃ / s, cooling it to 300-350℃, then starting the built-in heat preservation device of the cooling bed for online pre-tempering, holding the temperature at 300-350℃ for 10-20 minutes, and then air cooling it to below 200℃.

8. The hot rolling and cooling process for 20CrMnTi round steel according to claim 1, characterized in that, The preparation method of the modifier includes the following steps: A1: Calcium carbide, industrial silicon carbide, rare earth oxides, sodium borate, nano alumina powder, and sodium citrate dispersant are all fed into a hot air drying kiln and dried at 120-150℃ for 2-4 hours. The dried calcium carbide, rare earth oxides and sodium borate are coarsely crushed to 5-10 mm and then finely crushed, with the calcium carbide crushed to 1-3 mm and the rare earth oxides and sodium borate crushed to 100-200 mesh. A2: Weigh 80-100 parts of dried silicon carbide, 0.5-2 parts of rare earth oxides, and 1-5 parts of polysulfonate dispersant by weight, ball mill for 1-2 hours at a ball-to-material ratio of 4-6:1 and a rotation speed of 200-300 r / min to obtain modified silicon carbide particles. A3: Weigh 25-35 parts of modified silicon carbide particles and 35-45 parts of calcium carbide by weight, stir at 50-80℃ and 60-100r / min for 5-10min, then feed them into a disc granulator, use polyvinyl alcohol aqueous solution as binder to obtain particles with a particle size of 2-4mm, and feed them into a hot air dryer to dry at 80-100℃ for 1-2h. A4: Weigh out 0.8-1.5 parts by weight of rare earth oxides, 5-12 parts by weight of sodium borate, 3-8 parts by weight of nano alumina powder, and 0.5-2 parts by weight of sodium citrate dispersant. Stir at room temperature for 3-5 minutes at a speed of 800-1200 r / min to obtain a mixture. The dried granules from step A3 are fed into a fluidized bed coating machine and heated to 60-90℃. First, a polyvinyl alcohol aqueous solution accounting for 3-6 wt% of the mixture is sprayed in, and then the mixture is added in 3-4 batches. The coating time is 5-10 minutes to obtain composite granules. The coated composite particles are then subjected to low-temperature curing at a heating rate of 5-10℃ / min and a curing temperature of 200-280℃ for 1-2 hours to obtain the modifier.

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