高温形变热处理对20CrMnTiH钢锻件组织及性能的影响

Effect of high temperature thermomechanical treatment on microstructure and properties of 20CrMnTiH steel forgings

为探究锻件在锻后空冷+正火+淬火+回火后性能合格率低的原因,以及采用高温形变热处理对其进行工艺改进后的具体影响,通过显微组织观察和力学性能检测等方法,研究了20CrMnTiH钢锻件在原工艺和高温形变热处理后的组织转变特性和力学性能。结果表明,原工艺的冷速不足导致其淬火组织中出现粒状贝氏体,粒状贝氏体回火产生的碎片状铁素体导致其硬度不足且分布离散,晶粒不够细化则导致冲击性能不足。改进后的工艺保证了充足的冷速,最终得到大量回火托氏体+少量贝氏体的均匀混合组织,而锻热淬火保留的大量塑性变形位错则在回火过程中形成亚晶块,极大地细化了晶粒,同时α相上大量弥散分布的θ-Fe_(3)C质点对拉伸变形时的位错起到了钉扎作用,最终使锻件性能得到显著提升。

To investigate the reasons for the low acceptance rate of forgings after air cooling+normalizing+quenching+tempering,the influence of high temperature thermomechanical treatment on the process improvement,the microstructure transformation characteristics and mechanical properties of 20CrMnTiH forgings under two different processes were studied by means of metallographic observation and mechanical properties test.The results show that the insufficient cooling speed of the original process leads to the appearance of granular bainite,the tempered fragments ferrite resulting in insufficient hardness and discrete distribution,and insufficient refinement of grains resulting in low impact property.The improved process ensures sufficient cooling rate and finally obtains a large number of tempered troostite and a small amount of bainite.While a large number of plastic deformation dislocations retained by forging-quenching form sub-crystals during tempering,which greatly refines the grains.In addition,a large number of dispersed θ-Fe_(3)C particles inαphase pin the dislocations during tensile deformation,properties of the forgings is improved significantly.