Influence of Chemical Compositions on Toughness of Steels with the Microstructure of As-quenched Martensite

摘要

Influence of alloying elements (Ni,Mn and Cu) and cooling conditions on toughness of as-thermal cycled martensite simulating the microstructure of coarse-grained weld heat-affected zone (HAZ) of Quenched and tempered high strength steels was investigated. Regardless of the cooling conditions, toughness of as-thermal cycled martensite increases with increasing Ni content and deteriorates with increasing Mn content, whereas toughness is not influenced by Cu content.Toughness change of as-thermal cycled martensite is mainly attributed to change in cleavage facet size and amount of cementite precipitated due to auto tempering in the laths of martensite. Cleavage facet size at the initiation point of brittle fracture tends to be refined with increasing Ni content. The amount of cementite in the laths of martensite precipitated during auto tempering decreases with increasing Mn content and cooling rate. Therefore, soluble C presumably detrimental to the toughness of as-thermal cycled martensite.