Effect Of Rare Earth Ce On Inclusions,Microstructure And Mechanical Properties Of GCr15SiMn Bearing Steel

High carbon chromium bearing steel is one of the most famous bearing steels,which can be used to produce bearings and bearing parts.Among all kinds of high carbon chromium bearing steel,GCr15 has the highest utilization rate and high recognition in the industry,followed by GCr15SiMn.Because of the low hardenability of GCr15,it is usually used in the manufacture of small size bearing parts.However,compared with small-size bearings,large-size bearings are in short supply in the market.In order to meet the needs of the market,developers have successively developed GCr15SiMn,GCr15SiMo and other bearing steels with high hardenability.With the advantage of low cost,GCr15SiMn has become the steel with the utilization rate only lower than GCr15.In order to meet the current demand for oversize bearing materials,the development of GCr15SiMn has made great progress,The research on high quality GCr15SiMn bearing steel has urgent practical prospect and profound practical significance,China has abundant rare earth resources,which have the functions of modifying inclusions,purifying molten steel and microalloying.In this paper,GCr15SiMn bearing steel with different rare earth contents was smelted in a 30 kg vacuum induction furnace.The effect of Ce in a wide range on inclusions,microstructure,mechanical properties and hardenability of high clean GCr15SiMn bearing steel was studied.This paper mainly makes the following research and draws the following conclusions:The effect of rare earth content on the composition and inclusions in steel was studied.The results show that the rare earth can still further deoxidize and desulfurize the bearing steel with very low content of oxygen and sulfur.When the content of rare earth increases,the harmful elements such as P and As in liquid steel begin to combine with rare earth and become rare earth inclusions,which increases the types of rare earth inclusions.In addition,after the addition of excessive rare earth,the inclusions change into large-size inclusions with irregular morphology.The order of inclusions modified by rare earth elements is O、S、As、P and C.In this experiment,the rare earth content is in the range of(0～530×10-6)with the increase of the rare earth content,the number of inclusions increases.When the rare earth content is 160×10-6,the inclusions within 3 μm in the steel reach the highest it accounts for about 89%.When the rare earth content is excessive,the inclusions start to polymerize and grow,thereby increasing the size of the inclusions..The effect of rare earth on as cast carbide,lamellar pearlite distance and secondary dendrite spacing of bearing steel were studied.The results show that rare earth can reduce the size of eutectic carbides and break the network structure of carbides,thus improving the uniformity of carbides.At the same time,Ce can reduce the secondary dendrite spacing of as cast GCr15SiMn bearing steel,specifically,the secondary dendrite spacing further decreases with the increase of RE content.The results show that Ce can obviously reduce the degree of dendrite segregation.With the increase of rare earth content,the pearlite lamellar spacing first decreases and then increases.The effect of rare earths on the structure of the heat-treated bearing steel was studied.It is concluded that the cementite particle size after spheroidizing annealing first decreases and then increases with the increase of the rare earth content.When the rare earth content is 160×10-6,the cementite has the smallest dispersed distribution;the grain size after adding the rare earth appears first the increasing trend after reduction is less than that of bearing steel without rare earth.When the rare earth content is 160×10-6,the grain size is reduced by 20.5%;only when the rare earth content reaches 530×10-6,the tempered structure The carbide size has been significantly reduced.The effect of rare earth content on hardness,strength,toughness and hardenability of bearing steel was studied.The results show that the hardness and strength of bearing steel are improved with the change of rare earth content,and the hardness and strength increase by 3.26%and 22.25%respectively.In addition,it is found that rare earth Ce can significantly affect the impact energy of bearing steel,and the addition of appropriate amount of rare earth elements can produce spherical or ellipsoidal small rare earth inclusions,so as to improve the impact property.Rare earth elements and harmful elements P and As,which segregate at grain boundaries,form compounds to improve grain boundary strength and impact toughness;However,after the addition of excessive rare earth,large and irregular rare earth inclusions are easy to form in the steel.Because of the irregular shape,these large-size inclusions are easy to crack at the grain boundary,and lead to crack propagation in different directions,which seriously worsens the impact properties.The effect of rare earth on the hardenability of bearing steel was studied by end quenching experiment.The results show that the end quenching curve of experimental steel with rare earth is smoother than that without rare earth,and the hardness after quenching is higher than that without rare earth,which indicates that rare earth can improve the hardenability of experimental steel.