Ultrafining Heat-treatment Technics Of 10Ni5CrMoV Steel

10Ni5CrMoV is a sort of high strength low alloy steel developed by our nation with strength more than 785MPa. It is also one of sheep plates with highest strength. In order to further tap the property potential of the steel, this paper focuses on promote the combination mechanic properties by ultra-fining treatment.The mechanism of grain growth is determined by austenitizing treatment at various temperatures. The mechanisms of structure inheritance and recrystallization are investigated by secondary quenching at various heating temperatures and heat preservation times. The exploratory research on the processing of circle heating-quenching was carried out. The size of initial austenitizing grain after circle heating-quenching was measured according to "Metel-methods for estimating the average grain size", and the effect of parameters on the degrees of fining was evaluated.The results indicated, grain grown significantly at austenitizing temperature above 1200℃; structure inheritance present at the heating temperature between Ac₃～925℃, gently decayed with increase of heating temperature and heat preservation time; while at the temperature range of 940-960℃, the 10Ni5CrMoV steel recrystallize completed and structure inheritance totally disappeare; and the fined grain began to grow from 970℃, raising the quenching temperature led to the growth of fined grain and lowered the fining effect.The size of grain could be fined to ASTM 12 degree based on circle heating-quenching by triple short-time circle heating-quenching (about100s). It was concluded that triple 100s-heating circle at 950℃is the optimal circle heating-quenching of 10Ni5CrMoV steel, the grain size can not be refined when the degree of circle heating was increased. With this ultrafining heat-treatment, the strength of 10Ni5CrMoV steel is improved, but the plasticity and ductility is decreased.