Method for producing and preparing steel bar for automotive bushings by means of ecological and economical arc furnace

Abstract

A method for producing and preparing a steel bar for automotive bushings by means of an ecological and economical arc furnace is provided. The steer bar contains, in percentage by mass: 0.18-0.23% of C, 0.20-0.35% of Si, 0.42-0.60% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.82-1.00% of Cr, less than or equal to 0.25% of Ni, 0.41-0.53% of Mo, less than or equal to 0.15% of Cu, and the balance of Fe and inevitable impurities. By means of smelting in an ecological and economical arc furnace, LF refining, RH refining, continuous casting, a heating process and a rolling process, the method enables batch production of the steel bar for an automobile shaft sleeve by means of a continuous casting procedure using the ecological and economical arc furnace.

1 . A steel bar for automotive bushings, comprising following components in percentage by mass: 0.18-0.23% of C, 0.20-0.35% of Si, 0.42-0.60% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.82-1.00% of Cr, less than or equal to 0.25% of Ni, 0.41-0.53% of Mo, less than or equal to 0.15% of Cu, and the balance of Fe and inevitable impurities. 
     
     
         2 . A method for producing the steel bar for automotive bushings according to  claim 1  by means of ecological and economical arc furnace, comprising processes of ecological and economical arc furnace smelting, LF refining, RH refining, continuous casting, heating furnace heating, and rolling;
 wherein, the ecological and economical arc furnace smelting uses scrap steel for smelting with a scrap steel loading amount of 116-122 t and a tapping temperature of 1655-1665° C., wherein a C content of a liquid steel at tapping is 0.08-0.10% and a P content is less than or equal to 0.010%, auxiliary materials and alloys are added into the liquid steel between one forth and one third of the tapping, a tap weight of liquid steel is 107-112 t, and a smelting cycle lasts 45-55 min, wherein alloy addition per ton of steel is as follows: 4.3-4.4 kg/t of silicomanganese, 11-11.5 kg/t of low-carbon ferrochrome, 17-17.2 kg/t of coke particles, 2-2.2 kg/t of ferroaluminum, and 930-940 kg/t of heavy melting steel, and auxiliary material addition per ton of steel is as follows: 20-21 kg/t of dolomite, 43-44 kg/t of active lime, and 6-6.2 kg/t of ladle ash. 
 
     
     
         3 . The method according to  claim 2 , wherein the LF refining adopts a high current of 20000-25000 A to heat for slag smelting, when a slag surface in the LF fluctuates while the liquid steel and electric arc remain covered, active lime is supplemented into the liquid steel; after 5 min from addition of active lime, a first sample is taken for analyzing chemical composition of the liquid steel, and alloys and silicon carbide are then supplemented into the liquid steel according to the target values of the chemical composition; when a temperature of the liquid steel reaches 1590-1600° C., 2-3 kg of diffusion deoxidizer is added to per ton of steel for diffusion deoxygenation, and the door of the LF is closed for 10-12 min; when the temperature of liquid steel reaches 1620-1630° C., a second sample is taken for analyzing chemical composition of the liquid steel to determine a deviation of each chemical element's content from the target value; after the second sample is taken away, a refining cycle lasts 45-55 min; wherein supplemented alloy addition per ton of liquid steel is as follows: 3.4-3.5 kg/t of ferrosilicon, 1.9-2.0 kg/t of high-carbon ferromanganese, 0.5-0.55 kg/t of high-carbon ferrochrome, 1.8-1.9 kg/t of alumina balls, 0.35-0.36 kg/t of coke particles, 6.6-6.7 kg/t of ferromolybdenum, and 1-1.1 m/t of aluminum wire; and auxiliary material addition per ton of liquid steel is as follows: 6-6.2 kg/t of active lime, and 1-1.1 kg/t of silicon carbide; and
 for the RH refining, a ladle arrival temperature is 1675-1685° C., an processing time lasts 28-32 min, an argon pressure in the ladle before a vacuum pump startup is controlled to be 0.1-0.3 MPa, and ensure that the slag surface slightly fluctuates while the liquid steel remains covered; when a vacuum degree of a vacuum chamber reaches 100-110 Pa, timing begins for 10-15 min, while the argon pressure is adjusted to 0.3-0.5 MPa for calm argon blowing, 2-2.1 m of silicon-calcium alloy cored wire and 0.6-0.7 kg of covering agent per ton of steel are added into the liquid steel after calm argon blowing, and a ladle departure temperature is 1625-1635° C. 
 
     
     
         4 . The method according to  claim 2 , wherein, for the continuous casting, a ladle arrival temperature is 1620-1630° C. with an amount of the liquid steel of 95-103 t, a hydrogen content in a tundish is controlled to be less than or equal to 2 ppm, protected casting is maintained throughout the continuous casting, and a medium-carbon steel mold flux is used in mold. 
     
     
         5 . The method according to  claim 2 , wherein, for the heating furnace heating process, the temperature of a continuous casting billet entering the heating furnace is 350-550° C., a temperature of a preheating section of the heating furnace is 650-700° C. with a heating time of 1.3-1.5 h, a temperature of a heating section 2 is 840-860° C. with a heating time of 1.3-1.5 h, a temperature of a heating section 1 is 1190-1220° C. with a heating time of 1.3-1.5 h, a temperature of a soaking section is 1180-1210° C. with a holding time of 1.3-1.5 h, and a tapping temperature is 1180-1190° C. 
     
     
         6 . The method according to  claim 2 , wherein the rolling process comprises:
 a breakdown blooming process, involving 9 passes of rolling on the continuous casting billet after heating, comprising steps of turning over the casting billet, then performing a first pass rolling on the casting billet with a reduction amount of 65-65.1 mm and a second pass rolling with a reduction amount of 70-70.1 mm, then turning over the casting billet and performing a third pass rolling on the casting billet with a reduction amount of 64-64.1 mm and a forth pass rolling with a reduction amount of 90-90.1 mm, and then turning over the casting billet and performing a fifth pass rolling on the casting billet with a reduction amount of 42-42.1 mm, a sixth pass rolling with a reduction amount of 40-40.1 mm, a seventh pass rolling with a reduction amount of 35-35.1 mm, and an eighth pass rolling with a reduction amount of 34-34.1 mm, and then turning over the casting billet and performing a ninth pass rolling on the casting billet with a reduction amount of 82-82.1 mm, followed by making the casting billet pass through three stands of 850 mm rolling mills, one stand of 735 mm rolling mill, and a 8-stand continuous rolling mill unit for further rolling; and   a finished product rolling process, involving 6 passes of rolling on a steel billet after breakdown blooming, comprising a first pass rolling in obtaining a steel billet with a height of 229-229.1 mm and a width of 245-245.1 mm, a second pass rolling in obtaining a steel billet with a height of 192-192.1 mm and a width of 235-235.1 mm, a third pass rolling in obtaining a steel billet with a height of 200-200.1 mm and a width of 195-195.1 mm, a fourth pass rolling in obtaining a steel billet with a height of 173-173.1 mm and a width of 205-205.1 mm, a fifth pass rolling in obtaining a steel billet with a height of 182.4-182.5 mm and a width of 182.4-182.5 mm, and a sixth pass rolling in obtaining a steel billet with a height of 182.4-182.5 mm and a width of 182.4-182.5 mm, which is the finished product steel.   
     
     
         7 . The method according to  claim 6 , wherein an initial rolling temperature of the rolling process is 1100-1130° C., and a final rolling temperature is 850-950° C. 
     
     
         8 . The method according to  claim 2 , wherein a steel after rolling is subjected to heat preservation under conditions of a pit-entry temperature of the steel of greater than or equal to 600° C., a holding time of 48-55 h, and a pit-exit temperature of the steel of less than or equal to 150° C. 
     
     
         9 . The method according to  claim 3 , wherein a diameter of the coke particles is 20-60 mm, a diameter of the ferro-aluminum is 40-70 mm, a size of the heavy melting scrap is greater than or equal to 800 mm*600 mm, a diameter of the dolomite is 20-70 mm, a diameter of the active lime is 10-70 mm, a diameter of the alumina balls is 10-15 mm, the ferromolybdenum is FeMo60-B, a diameter of the aluminum wire is 10-12 mm, a diameter of the silicon carbide is 2-5 mm, and a diameter of the silicon-calcium alloy cored wire is 12-14 mm. 
     
     
         10 . The method according to  claim 8 , wherein the steel after heat preservation is subjected to heat treatment, comprising the following steps of:
 1) quenching the steel at a temperature of 870-890° C. for 0.8-1.2 h, followed by oil cooling the steel; and   2) tempering the quenched steel at a temperature of 490-510° C. for 1.6-2.0 h, followed by water cooling the steel.