A study on micro-Structure and wear behavior of AISI M4 and CPM15V deposited by laser melting

Abstract

AISI M4 and CPM15V are used as tool steels since they have high hardness and wear resistance. This study is concerned with die and mold hardfacing using laser melting deposition with M4 and CPM15V powders. For this purpose, the two types of metal powders were deposited on SKD11 base metal, and the microstructures, hardness and wear resistance of the deposited materials were compared. During processing, substrate preheating was used to reduce the degree of thermal deformation and prevent crack formation. Based on the preliminary experiments, the process conditions were established. As a result of observing of the microstructure, columnar and cellular dendrites were observed in the M4 deposited layer. Using EDS analysis, the carbides precipitated along grain boundaries were identified to be M6C/M23C6 carbides with a high content of molybdenum and tungsten. On the other hand, no dendritic microstructures were observed in the CPM15V deposited layer, and metastable austenite, martensite, and M8C7 carbides were formed. A large amount of fine carbide was found to have a high content of vanadium and chromium. The M4 and CPM 15V deposited regions had average hardnesses of 815 and 897 HV, respectively. The ball-on-disc test results showed that the deposited CPM15V had better wear resistance than that of the M4 deposited. These results are attributed to high martensite fraction, and the types and sizes of carbides of the deposited CPM15V.