2.47 GPa grade ultra-strong 15Co-12Ni secondary hardening steel with superior ductility and fracture toughness  

作　　者：Young-Kyun Kim Kyu-Sik Kim Young-Beum Song Jung Hyo Park Kee-Ahn Lee 

机构地区：[1]Department of Materials Science and Engineering,Inha University,Incheon,22212,Republic of Korea [2]Agency for Defense Development(ADD),Yuseong-gu,Daegeon,34186,Republic of Korea

出　　处：《Journal of Materials Science & Technology》2021年第7期36-45,共10页材料科学技术（英文版）

基　　金：the financial support provided by Agency for Defense Development (ADD), Republic of Korea (Project No. UE181033GD)。

摘　　要：This study investigated the effect of multi-step heat treatment on the microstructure, mechanical properties and fracture behavior of thick 15 Co-12 Ni secondary hardening steel. As-quenched sample was found to have elongated prior austenite grain(PAG) and coarse lenticular martensitic structure. On the other hand, heat-treated sample was observed to have fine lenticular martensitic structure due to fine PAG size and a lot of nano-sized carbides. Also, after heat treatment, nano-scale reverted austenite film was formed at the martensite interfaces. The heat-treated sample showed 2.47 GPa superior tensile strength and superior elongation of about 12 %. The high strength was mainly due to fine block size and high number density of nano-sized carbides. The average value of plane strain fracture toughness(KIC) was 29.3 MPa m1/2, which indicated a good fracture toughness even with the high tensile strength. The tensile fracture surface was observed to have ductile fracture mode(cup-and-cone) and the formation of about ~1 μm ultra-fine dimples. In addition to this, nano-sized carbides were observed within the dimples.The findings suggested that the nano-sized carbide had a positive effect not only on the strength but also on the ductility of the alloy. The fractured surface after toughness test, also showed ductile fracture mode with a lot of dimples. Based on the above results, correlation among microstructural evolution,deformation and fracture mechanisms along the heat-treatment was also discussed.

关 键 词：Ultra-high strength High Co-Ni secondary hardening steel Microstructure Tensile properties Fracture toughness Reverted austenite 

分 类 号：TG142.1[一般工业技术—材料科学与工程]