钒对高温渗碳SCM420H齿轮钢组织和淬透性的影响

Microstructure and hardenability of vanadium microalloyed high temperature carburized SCM420H gear steel

对高温渗碳SCM420H齿轮钢进行了钒微合金化处理,并对钢中组织及淬透性进行了研究。结果表明:SCM420H齿轮钢中V含量和N含量应控制范围分别在0.03%~0.05%和0.012%~0.018%。MN(M=Ti,V)在966℃时析出并在559℃时向M(C,N)发生转化,常温时的M(C,N)质量百分数约为0.049%。将加热温度控制在1 200℃±20℃,在预热段(室温升至850℃左右)加热时间控制在120 min内,在940~980℃高温渗碳保温6 h后,圆钢的带状组织控制在1.5~2级,奥氏体晶粒稳定在7.5~8级,M(C,N)主要为能起到钉扎晶界、细化奥氏体晶粒的纳米级球状V(C,N)。将连铸结晶器电磁搅拌强度参数调整为150 A,2.5 Hz,铸坯拉速为0.85 m/min,浇铸过热度为15~30℃,碳含量偏差值可控制在0.01%,碳含量的均匀化有利于淬透性的窄带化控制,钒微合金化后,试样的淬透性硬度值(HRC)最高为37,最低为35,淬透性带宽硬度值(HRC)≤3。

The high-temperature carburized SCM420H gear steel was modified with vanadium microalloying, and the structure and hardenability of the steel were studied. The results show that the V and N contents in SCM420H gear steel should be controlled within the range of 0.03%~0.05% and0.012%~0.018%, respectively. MN(M=Ti,V) precipitates at 966 ℃ and transforms into M(C,N) at 559℃. The mass percentage of M(C,N) approximates 0.049%. The heating temperature is controlled at1200 ℃±20 ℃, and the heating time is controlled within 120 minutes in the preheating section(from room temperature to about 850 ℃). After high temperature carburizing and holding at 940~980℃ for 6hours, the banded structure of bar steel is controlled at 1.5 to 2 level, and the austenite grain size is at ASTM 7.5 to 8. M(C,N) is mainly nano-seized spherical V(C,N) which can pin grain boundaries and refine austenite grains. Under the following casting parameters: the electromagnetic stirring intensity parameters of the continuous casting mold are adjusted to 150 A, 2.5 Hz, the casting speed is at 0.85m/min, the casting superheat is 15 to 30 ℃, the deviation value of carbon content can be controlled at0.01% which is beneficial to narrowing control of hardenability. After vanadium microalloying, the maximum hardenability value(HRC) of the sample is 37, the minimum is 35, and the hardenability bandwidth(HRC)is not greater than 3.