Research On The Cleaness And Properties Of Bearing Steel G20CrNi2Mo

Bearing steel G20CrNi2Mo is one of the carborizing bearing steel, which has the advantages of good machinability and processability at the low temperature, impact resistance, abrasion resistant and high contact fatigue life after carburizing. The bearing steel has been widely used in the bearing under lager impact load. Besides the surface with high hardness, abrasion resistant, high fatigue strength and good dimensional stability, it also has the interior with the high toughness. With the acceleration of the railway and the large-scale of the vehicle, the demand for the properties of bearing steel is becoming higher and higher. Electroslag remelting can effectively improve the purity of the metals and density of the tissue, so the research on manufacturing bearing steel G20CrNi2Mo through vacuum induction treatment (VIM)+Electroslag remelting (ESR)+rolling or forging has important practical significance.In this paper, we prepared bearing steel G20CrNi2Mo by using the 50 kg vacuum induction furnace and electroslag remelting under laboratory conditions. We studied its cleanliness, the number and size of inclusions in steel by using optical microscopy (OM) and Image-Pro Plus6.0, the morphology and species of the inclusions by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), The tensile test and impact test was conducted, the fracture morphology was observed by SEM to study the fracture mechanism. Its hardenability was studied with the test of the end hardenability test.(1) Component of the ignot via vacuum induction melting has a high yield, the mass fraction of the phosphorus, sulfur, oxygen in the steel is in line with expectations, except a higher nitrogen content. After the process of electroslag remelting, the burning rate of the silicon and manganese in the steel is relatively high under the non-protective atmosphere condition, which can be suppressed under the protective atmosphere or by adding the strong reducing agent of aluminum; The burn spoilage rate of other alloy elements such as Cr, V, Mo, Ni, Nb is low no matter what the atmosphere condition is.(2) The protective atmosphere can keep the low oxygen potential of the slag, so that the ESR ingot has low oxygen content; The adding of the aluminum can effectively reduce the oxygen potential of the slag.(3) The average diameter of the inclusions in the the ignot via vacuum induction melting is about 1.5μm, the number of inclusions per square millimeter is about 100.(4) The main types of inclusions are the aluminosilicate inclusion of Al2O3-SiO2-MnO, followed by sulfides inclusions that MnS accounts the main part. It also contains a small amount of multiphase composite inclusions. After electroslag remelting, the aluminosilicate inclusion of Al2O3-SiO2-MnO is removed, the main components of the inclusions are Al2O3 and Al2O3-MnS.(5) The cooling intensity is high during the electroslag remelting, and its strength is higher after the heat treatment. It has good mechanical properties. The end hardenability of the ESR ingot samples are within the specified range, this new ingredient bearing steel 20CrNi2Mo has good hardenability.(6) The mass fraction of the impurities phosphorus, sulfur, oxygen, nitrogen is very low, which has made an obvious improvement compared to the ignot via vacuum induction melting under laboratory conditions; The content of alloying element silicon has decreased slightly after the electroslag remelting, compared with the ignot via electroslag remelting under laboratory conditions, the burn spoilage rate is lower. The the burn spoilage of manganese is similar with the result of electroslag remelting under laboratory conditions, the burning of other alloying elements is negligible.(7) After electroslag remelting, w[P]=0.0040%, w[S]=0.0020%, w[O]=0.0007% and w[N]=0.0005%,the refining effect is better compared with laboratory conditions.(8) The sample of the ESR ingots Rm=1360 MPa, RpO.2=1167 MPa, A=14%, Z=70% tensile strength and required ratio elongation strength are better than the tensile properties of electroslag remelting ingots with protective atmosphere under laboratory conditions; impact energy of the sample of ESR ingot is 197 J. The sample of ESR ingot has good end hardenability.