Changes in microstructure of ledeburitic tool steel due to vacuum austenitizing and quenching, sub-zero treatments at −140°C and tempering

• Published in: Vacuum Vol. 170; p. 108977
• Main Authors: Ďurica, Juraj, Ptačinová, Jana, Dománková, Mária, Čaplovič, Lubomír, Čaplovičová, Mária, Hrušovská, Linda, Malovcová, Veronika, Jurči, Peter
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2019
• Subjects: Carbides; Ledeburitic steel; Martensite; Precipitation; Retained austenite; Sub-zero treatment at −140 °C; Ledeburitic steel; Retained austenite; Precipitation; Sub-zero treatment at −140 °C; Martensite; Carbides
• ISSN: 0042-207X; 1879-2715
• DOI: 10.1016/j.vacuum.2019.108977

The microstructure of Vanadis 6 ledeburitic steel subjected to sub-zero treatments at −140 °C for different durations followed by various tempering regimes was investigated. The obtained results infer that: i) retained austenite amount is fivefold reduced by this treatment, and compressive stresses higher than 1500 MPa are generated in this phase, ii) martensite is refined due to SZT, and it contains enhanced number of crystal defects, iii) great number of “extra” cementitic carbides is formed during the sub-zero period; this number is higher than what is achieved by sub-zero treatments at −196 °C, iv) the number of “extra” carbides decreases with tempering, however, it remains higher than after in both the conventionally quenched and sub-zero treated at −196 °C steel, v) sub-zero treatments at −140 °C modify the precipitation behaviour substantially; coherent nano-sized ε-carbides and cementite were found already prior tempering the steel, and besides the cementite also M7C3 phase was detected after tempering treatment. •Retained austenite is fivefold reduced, and high state of compression is generated by sub-zero treatment at −140 °C.•SZT at −140 °C produces refined martensite containing high amount of crystal defects.•Precipitation of transient coherent carbides is enhanced by sub-zero treatments at −140 °C.•SZT at −140 °C generates much more small globular carbides than processing at −196 °C.