# Refining the Carbide Size in AISI M50 High-Speed Steel Through Tailored Compositional Modifications

## TL;DR

This study improves the properties of M50 steel by modifying its composition to refine carbides and increase hardness.

## Contribution

A new steel variant with refined carbides and higher hardness was developed through tailored compositional modifications.

## Key findings

- The redesigned steel achieved 66 HRC hardness, 7.57% higher than conventional M50 steel.
- The average primary carbide size was reduced by 27.0% compared to M50 steel.
- V-rich MC carbides were eliminated, and Fe- and Cr-rich M23C6 carbides were detected, enhancing hardness.

## Abstract

The present study focuses on redesigning the composition of the conventional M50 steel grade, which is widely used for high-temperature bearings. Through thermodynamic calculations, a new steel variant was developed in the laboratory with the aim of refining carbides and improving hardness. After undergoing quenching at 1070 °C and triple tempering at 540 °C, the hardness reached 66 HRC, which is 7.57% higher than that of M50 steel (61 HRC). Meanwhile, the hardness at 400 °C reached 60 HRC. In addition to the typical M2C and M6C carbides found in M50 steel, the presence of Fe and Cr-rich M23C6 carbides was detected in the redesigned steel after triple tempering. These carbides play a significant role in enhancing hardness. Furthermore, the heat treatment process effectively eliminated the uneven and coarse carbides. The average size of primary carbides is 4.6 ± 0.6 μm, which represents a 27.0% reduction compared to M50 steel (6.3 ± 0.1 μm). The detrimental V-rich MC carbides commonly found in M50 were eliminated.