Study On The Control Of The Uniformity Of Carbide And Its Mechanism In GCr15SiMn Bearing Steel

Bearing steel is the largest production variety in special steel and its quality requirements are extremely strict. GCr15 has always been the world’s most widely used bearing steel grade for its low price, simple processing and good overall performance. to become. But GCr15 is only suitable for the production of small-sized bearing parts for its low hardenability. In order to meet demand for large-size bearings in equipment manufacturing and other industries, high hardenability steel such as GCr15 Si Mn and GCr15 Si Mo have been developed. Among which, GCr15 Si Mn is the grade second in production only to GCr15 for its relatively low price. Therefore, the research and development of high-quality bearing steel GCr15 Si Mn has important practical significance and broad application prospects.The work in this paper focused on controlling the carbide uniformity in GCr15 Si Mn steel during processing.The control of the uniformity of carbide is mainly reflected in two aspects: carbide liquid-extractions,carbide bands and carbide networks in the original structure(before spheroidizing annealing);the size, spacing and morphology of carbide after spheroidizing annealing. A series of experimental studies have been carried out against the formation characteristics of various carbide inhomogeneities: the distribution of carbon element in the cross-section of the billet was analyzed by the method of drilling sampling. The fine structure of as-cast eutectic carbides was characterized by optical and scanning microscopy and a preliminary study on its elimination method was made; The effects of deformation temperature on themicrostructure evolution of GCr15 Si Mn bearing steel were investigated by uniaxial hot compression simulation experiment;The effects of annealing time on the spheroidizing annealing quality of GCr15 Si Mn were explored, and appropriate isothermal spheroidizing annealing process was proposed; The effects of rapid cycling quenching on the microstructure and properties of GCr15 Si Mn were discussed.The results show that:( 1) The segregation can be reduced by multipule electromagnetic stirring and low superheat casting.Considerable eutectic carbides are formed with the core of non-metallic inclusions such as Al2O3, Mn S and Ti N.The carbide liquid-extraction can be eliminated by sufficient homogenizing annealing.(2)Carbide networks can be effectively removed when the finishing temperature are controlled at 800~850 ℃.This is the result of the joint action of grain refinement and“mechanical disruption”.(3)After holding at 790 ℃ for 1-6h and then at 720 ℃ for1-6h, a desirable spheroidized structure has been achieved.(4)By adopting the rapid cycle phase transformation treatment at 830℃for 2 min,the structure can be uniformed,the grain can be refined by 1~2 level and the impact toughness can be increased by40% to 130%. The hardness of more than twice processing can meet or exceed the level of conventional quenching and tempering treatment.