4Cr13模具钢的等温相变规律与预处理工艺优化

Isothermal Phase Transformation Characteristics and Pretreatment Process Optimization of 4Cr13 Mold Steel

测试了4Cr13塑料模具钢的过冷奥氏体等温转变曲线,研究了该钢的等温相变规律,分析了经过不同工艺固溶(1 010~1 090℃保温2,3 h)和球化退火(905℃×2 h奥氏体化和700~770℃保温5,8 h等温球化)预处理后的显微组织和硬度,并获得最优工艺。结果表明:在725℃下试验钢的珠光体形核孕育期最短;经1 010℃固溶处理后,组织中存在大量球状碳化物,当固溶温度为1 070~1 090℃时,碳化物基本溶解,马氏体板条束明显粗化,最优固溶工艺为1 050℃×3 h,此时碳化物占比较低且弥散分布;随着等温球化温度升高,链状碳化物数量先减少后增多,并且保温8 h后球状碳化物的分布更均匀;1 050℃固溶3 h+905℃×2 h+750℃×8 h球化退火后试验钢的球化效果最好,直径小于0.5μm的碳化物占比约为78.92%,硬度最低,约为192 HBW。

The isothermal transformation curve of undercooling austenite of 4Cr13 plastic mold steel was tested,and the isothermal phase transformation characteristics of the steel were studied.The microstructure and hardness after pretreatment by different solution(holding at 1 010-1 090 ℃ for 2,3 h) and spheroidization annealing(austenitization at 905 ℃ for 2 h and isothermal spheroidization at 700-770 ℃ for 5 h and 8 h) were analyzed,and the optimal process was obtained.The results show that the at 725 ℃ the test steel had the shortest nucleation and incubation period.After solution at 1 010 ℃,there were a lot of spherical carbides in the structure.After soluted at 1 070-1 090 ℃,the carbides were basically dissolved,and the martensite lath bundles were significantly coarsened.The optimal solution process was 1 050 ℃ ×3 h,and the carbides was dispersely distributed with relatively low proportion.As the isothermal spheroidization temperature increased,the number of chain shaped carbides decreased first and then increased,and the distribution of spherical carbides was more uniform after holding for 8 h.After solution at 1 050 ℃ for 3 h and spheroidization annealing by 905 ℃×2 h+750 ℃×8 h,the spheroidization effect of the test steel was the best;the proportion of carbides with a diameter less than 0.5 μm was about 78.92 %,and the hardness was the lowest of about 192 HBW.