MnS 및 V-탄질화물의 석출이 0.26C-1.5Mn강의 페라이트 입내 핵생성에 미치는 영향

Abstract

The effects of manganese sulfide and vanadium carbonitrides on the intragranular ferrite nucleation have been studied by calculating the equilibrium relationship between vanadium carbonitrides and manganese sulfide and by applying controlled cooling rate experiment in 0.26C-1.5Mn steels. Equilibrium calculation shows that there is little interaction between vanadium carbonitrides and MnS. The vanadium nitride forms as a vanadium carbonitride(VC_yN_(1-y)) below about 1100℃ and the carbon composition(y) rises with decreasing temperature. The manganese sulfide is expected to form at above 1500℃, i.e. from liquid phase. Controlled cooling rate experiments showed that MnS particles consist of bimodal size distribution. The relatively fine particles(<5㎛) continuously grow during solid-state cooling and their distribution is influenced by the cooling rate, faster cooling rate favoring ferrite distribution. MnS acts as an important intragranular ferrite nucleation site. Intermediate holding experiments during continuous cooling experiment suggests that Mn depletion around MnS particles is mainly responsible for intragranular ferrite nucleation. In the case of after-heat treatments, MnS particles were believed to act as nucleation site for vanadium carbonitrides, which largely promotes the intragranular ferrite nucleation.