冷却速度对30CrNi3MoV超高强钢组织转变的影响

Effect of cooling rate on microstructure transformation in 30CrNi3MoV ultra-high strength steel

利用线膨胀法,结合金相显微分析和显微硬度测量,研究了冷却速度(1～2000℃/min)对30CrNi3MoV超高强钢过冷奥氏体连续冷却转变的影响,测得了其CCT曲线。结果表明,该试验钢的CCT图中没有珠光体转变区。冷速在1～20℃/min范围,随冷速的增大,组织中依次出现粒状贝氏体、条状上贝氏体和针状下贝氏体;当冷速增大到超过25℃/min以后,组织全部为板条状和针状混合马氏体,一直到2000℃/min,组织形态没有明显变化。

Transformation characteristics of 30CrNi3MoV ultra-high strength steel with different cooling rates from 1 ℃/min to 2 000 ℃/min were investigated using high-resolution dilatometer, along with optical microscope and microhardness meter. Continual cooling transformation （CCT） diagram of under-cooled austenite in the experimental steel was determined. The result shows that there is no pearlitic transformation in 30CrNi3 MoV steel, although with very low cooling rate of 1 ℃/min. In the range from 1℃/min to 20 ℃/min, granular bainite, upper bainite and lower bainite appeared sequentially in the samples with increasing cooling rate. When cooling rate increases beyond 25℃/min, microstructure in the steel consists completely of lath and acicular martensite, and there is no obvious change in the structure character until 2 000℃/min.