2014 Volume 55 Issue 5 Pages 831-837
The residual stresses and dimensional changes related to the lattice parameter of the JIS SKD11 tool steel have been investigated for both conventional and cryogenic treatments. As trapped carbon atoms are released from the martensite, the martensite c/a ratios and dimensions of the specimens treated conventionally decreased at tempering temperatures above 673 K. However, these values increased owing to the increase in the c-axis when tempering was conducted at temperatures higher than 673 K. At higher temperatures, the retained austenite is converted into martensite. The martensite c/a ratios and dimension change ratios in the cryogenically treated specimens decreased significantly with the tempering temperature because the amount of retained austenite is reduced by cryogenic treatment. In the conventionally treated specimens, the compressive residual stress decreased with quenching after tempering because of the release of trapped carbon atoms. However, the retained austenite to martensite transformation and the precipitation of alloy carbides leads to increased martensite lattice parameters and dimensional residual stress changes. The residual stress is also changed to generate compressive residual stresses. The dimension change ratio in cryogenically treated and tempered specimens decreased as the tempering temperature increased through a reduction in the amount of trapped carbon. However, the magnitude of the compressive residual stress was reduced to zero.