Influence of carbide morphology and matrix hardness on the sliding wear behaviour of tool steels

ABSTRACT When using tool steels with martensitic microstructure, the hardness is regarded as one of the main criteria defining its wear properties. The premise is that the harder the material, the greater the sliding wear resistance. This is especially common when using tool steels, as the highest possible hardness is pursued, but the influence of the microstructure is often neglected. Presence of different carbides in terms of fraction, type and size (morphology) in martensitic matrix has different effects on wear, especially if matrix hardness changes. The objective of this study was to establish a correlation between the fraction and morphology of V and Cr-rich carbides in tool steel with its microstructure, fracture toughness, and overall influence on material sliding wear resistance. To achieve this, commercially available tool steels (Mat. No. 1.2379 cold work tool steel and modified Mat. No. 1.2367 hot work tool steel) were selected, exhibiting notably diverse microstructures, particularly in terms of carbide fraction and morphology. To enable a direct comparison, both steels underwent heat treatment to attain three distinct hardness levels: 45 +/-1 HRC, 49 +/-1 HRC, and 54 +/-1 HRC. Sliding wear resistance and behavior under various contact conditions were correlated with microstructure, specifically focusing on hard carbides. Additionally, the study examined the effect of wear particles being trapped within or removed from the tribological contact. It was observed that the sliding wear behavior is significantly influenced when the microstructure comprises a martensitic matrix with a higher fraction of carbides, particularly coarse eutectic M 7 C 3 carbides, especially if the matrix hardness is insufficient. Matrix hardness plays a crucial role in preventing carbide detachment from the matrix. Plastic deformation of the tempered martensite matrix, along with carbide cracking and detachment from the matrix, was identified as contributing factors intensifying wear during the wear process.