AISI D2 강의 미세조직 및 내마모 특성에 미치는 이전 냉간가공의 영향

Abstract

The effects of prior cold woriking and austenitnizing conditions(temperature and time) on the microstruture(such as the volume fraction of retained austenite(Rγ) and carbide) and wear resistance were studied by metallography, X-ray diffractometry, image analysis, hardness and wear rate measurement in AISI D2 steel. The results obtained are as follows;

(1) With increasing austenitizing temperature and time, the mean grain size and the volume fraction of carbide dissolved the matrix increased. As a result, the volume fraction of Rγ increased by the stabilization of parent phase due to higher alloying elements i.e., C and Cr etc.,.

(2) With increasing austenitizing temperature and time resulted in the decrease in hardness and wear resistance by the reduction of volume fraction of carbide, grain growth and the increase of volume fraction of Rγ.

(3) With the 10 minutes in austenitizing time, the non-transformed ferrite could be observed in D2 steel. As a result, the steel showed the least hardness and wear resistance. In addition, the volume fraction of martensite show more effect on the mechanical characterization than the volume fraction of carbides and the grain size.

(4) As the amount of cold working increased, the mean grain size and the volume fraction of carbide were decreased, but the volume fraction of Rγ was increased. Even though, the grain size was decreased due to the recrystallization, the hardness and wear resistance were decreased.

(5) It is confirmed that the more amount of Rγ, the lower mechanical properies. Additionally, It is confirmed that prior cold working caused recrystallization in the AISI D2 steel during autenitizing treatment resulting in reduced grain size. However, the increase in the amount of carbide into the matrix and the increase in the volume fraction of Rγ resulted in lower the mechanical properties.