锻比对18Ni(250)马氏体时效钢组织及性能的影响

Effect of forging ratio on microstructure and properties of 18Ni(250)maraging steel

采用金相观察、电子背散射衍射(EBSD)技术、力学性能测试研究了不同锻比下C250钢的原始奥氏体晶粒度、马氏体板条块尺寸、大小角度晶界比例等显微组织及力学性能。结果表明:锻造工艺能有效地细化C250钢的晶粒尺寸及马氏体板条块,相同工艺下未变形、晶粒度为0级的C250钢经过大锻比成形后,晶粒度细化至12级;同时,中、高锻比试样的马氏体板条块发生了显著细化,马氏体板条块平均尺寸细化至7μm左右;随着锻比的增加,小于10°的小角度晶界的比例逐渐减少,而50°~60°的大角度晶界比例逐渐增大,小角度晶界逐渐转变为大角度晶界;C250钢的冲击韧度随着晶粒尺寸的减小而不断提高。

Microstructure and mechanical properties including grain size of initial austenite,size of martensite slat block and proportion of small angle and large angle grain boundaries for C250 steel with different forging ratios were studied by means of metallographic microscopy,EBSD technique and mechanical proparty testing.The results show that the sizes of grain and martensite slat block of C250 steel are refined by forging process effectively.The grain size is refined to level 12 for C250 steel with no deformation and grain size of level 0 under the same process by large forging ratio deformation.At the same time,the martensite slat blocks of specimens with medium and large forging ratios are refined significantly,the average grain size of martensite slat block is refined to about 7μm.The proportion of small angle grain boundary which is less than 10°decreases,the proportion of large angle grain boundary which is between 50°to 60°increases gradually,and the small angle grain boundary changes into large angle grain boundary gradually with the increasing of forging ratio.The impact toughness of C250 steel increases with the decreasing of grain sizes.