Fan Zhao

Effect of Niobium Additions on Austenite Grain Coarsening Behavior of GCr15 Bearing Steel

The effect of 0.018% niobium additions on austenite grain coarsening behavior of GCr15 bearing steel was studied. Results indicate that the coarsening temperatures of No.1 and the No.2 experimental steel were 950°C and 1100°C. The austenite grain coarsening temperature was increased by 150°C by the addition of 0.018% Nb in bearing steel. The grain growth equations of two experimental steels at different soaking temperatures from 850°C to 1250°C with the soaking time of 30 min are as follows: the equation of No.1 steel is D1=1.85×105·exp (-6.57×104/RT); the equations of No.2 steel below and above 1100°C is D2=5.08×102·exp (-2.49×104/RT) and D2=1.06×108·exp (-1.31×105/RT), respectively. The grain growth equations of two experimental steels at different soaking time from 15 to 120 min with the soaking temperature of 840°C are as follows: the equation of No.1 steel is D1=4.83×10-2·t0.72 while that of No.2 steel is D2=1.25·t0.18.

Surface Decarburization Behavior of Spring Steel 60Si2MnA under AC1 Temperature and in Temperature Range AC3-G

Surface decarburization of spring steel 60Si2MnA heated under AC1 temperature and in temperature range of AC3-G was investigated. The results show that under the AC1 temperature, pearlite spheroidization and surface decarburization were carried out simultaneously and had a mutual promotion relationship. In the temperature range of AC3-G, decarburized layer consisted of complete and partial decarburization, and the complete decarburized depth increased but the partial decarburized depth just a small change with the increase of heating time. Besides, when heating temperature was 790 °C, functional relation between the total decarburized depth, the complete decarburized depth and the heating time follows the formula of and , respectively.

Hot Ductility of 20Cr13 Steel at High Temperature

Hot ductility of 20Cr13 steel at high temperature was investigated through tensile test. The main phases of the steel in temperature range of 600-1400 °C were calculated with thermodynamic software. The fracture morphologies and microstructure were observed by scanning electron microscopy. The steel showed good hot ductility in temperature range of 1000-1200 °C, and the area reduction was 82 % or more. In temperature range of 800-950 °C, the M23C6 precipitated at the grain boundary of austenite, and it fractured in the tensile process. Thus the micro-crack or micro-hole formed at the grain boundary of austenite, and the area reduction was 52-68 %. The ferrite precipitated at 800 or 1250 °C, and the micro-voids formed at interface of ferrite and austenite because of the discordant deformation of two phases, which was harmful to hot ductility. Moreover, quasi-cleavage fracture happened at 800 °C because of the ferrite cleavage, which further decreased hot ductility of the steel.