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Effect of Tempering Temperature on Microstructure Evolution and Mechanical Properties of 5% Cr Steel via Electro‐Slag Casting
Author(s) -
Liu Jian,
Yu Hao,
Wang Juan,
Zhou Tao,
Song Chenghao
Publication year - 2015
Publication title -
steel research international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.603
H-Index - 49
eISSN - 1869-344X
pISSN - 1611-3683
DOI - 10.1002/srin.201400358
Subject(s) - tempering , materials science , microstructure , metallurgy , carbide , martensite , quenching (fluorescence) , toughness , ultimate tensile strength , composite material , physics , quantum mechanics , fluorescence
The newly designed 5% Cr steel processed by electro‐slag casting can be a candidate material as components in blast furnace top gas recovery turbine unit (TRT). The present study focuses on the evolution of the microstructure, strength and toughness with increasing tempering temperature from 550 to 700 °C. Typical tempered martensitic structure was achieved after quenching and tempering for the 5% Cr steel. The microstructure characterization shows that M 3 C in the matrix after 550 °C tempering was not stable and transformed to M 7 C 3 during tempering above 600 °C. After tempered at the temperature higher than 600 °C, only M 7 C 3 existed in the specimens. The M 7 C 3 carbides along the boundaries were significantly larger than those in the matrix due to the effect of direct nucleation as well as the greater mobility of alloy elements. The size and Cr content of M 7 C 3 increased considerably with increasing tempering temperature. With the increase of tempering temperature, both tensile and yield strength decreased, which can be attributed to the recovery of martensitic laths and the decrease of the quantity of interstitial carbon atoms in the matrix as well as the coarsening of carbides. The softening of matrix and increase of the length of high angle grain boundaries were responsible for the increase of impact toughness. The integrated effects of the softening of matrix and coarsening of carbides resulted in the slight decrease of the impact absorbed energy after 700 °C tempering.