Research on Hardenability in High-purity Steels

点击翻译按钮获取中文摘要

The present study has been undertaken to make clear the effect of impurity elements such as P and S on hardenabilty and isothermal transformation behavior in high-purity carbon steels without other alloying elements excepted for carbon. Four 0.35% carbon steels with different level of P and S contents (i,e., 10 ppmP + 10 ppmS, 70 ppmP + 10 ppmS, 410 ppmP + 10 ppmS, and 10 ppmP + 100 ppmS) were vacuum-melted and used for the Jominy tests, the continuous transformation tests, and the isothermal transformation tests. The main results obtained are as follows.(1) The Jominy distance increased with increase in the P content of specimen. The tendency of increase in the Jominy distance against the P content was parabolic, namely, the slope of the Jominy distance-the P content curve decreased with increase in the P content.(2) The diffusional transformation which competes with martensite transformation and controlls the hardenabilty in the present steels was the pearlite transformation at around 820 K.(3) The isothermal transformation kinetics from austenite to pearlite was markedly retarded by adding the impurity element of P as well as S.(4) The addition of the impurity elements of P and S strongly reduced the growth rate of the pearlite colony at 823 K but scarcely affected the nucleation rate.It can be concluded from these results that the hardenabilty increases by adding the impurity elements of P and S to high-purity 0.35% carbon steel and this increase in the hardenability is contributed to the decrease in the growth rate of the pearlite transformation which competes with the martensite transformation.