Influence of Thermal Treatment on Microstructure and Hardness of Niobium Alloyed PM‐Tool Steel

Abstract

This work describes carbides present in the tool steel containing 2.5% C, 3.3% Si, 6.2% Cr, 2.2% Mo, 2.6% V, 2.6% Nb, 1.0% W, prepared by the powder metallurgy (PM) process. The influence of thermal treatment conditions on carbide behavior is investigated. During austenitization, some dissolution of M₇C₃ occurs, while MC carbides are thermally stable. So, the quenched steel is composed of two types of carbides: chromium rich M₇C₃ and niobium rich MC, besides martensite and retained austenite. During tempering of the hardened steel at the temperatures above 480°C, the precipitation of very fine carbides and martensite recovery occur, which results in secondary hardening. Precipitated particles are predominantly vanadium and molybdenum rich MC, M₂C, and M₆C carbides.

Keywords:

• Carbides
• Powder metallurgy process
• Tool steel
• Thermal treatment

Acknowledgment

This research was supported by the research projects of Ministry of Education, Youth and Sports of the Czech Republic—E! 2728 UPLETOOLS and MSM223100002.