Effect of Tempering Temperature on Microstructure Evolution and Mechanical Properties of 5% Cr Steel via Electro‐Slag Casting

Abstract

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 8C. 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 8C tempering was not stable and transformed to M 7 C 3 during tempering above 600 8C. After tempered at the temperature higher than 600 8C, 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 8C tempering.

Correlations of Ni Contents, Formation of Reversed Austenite and Toughness for Ni-Containing Cryogenic Steels

“…This can be attributed to the decrease in the amount of the cementite. The cementite could inhibit the dislocation motion, thus increased the strength of matrix [20]. And the effect of precipitation strengthening increased with the increase in volume fraction of the cementite.…”

“…10d. The plastic deformation zones hindered crack propagation, which enhanced the crack propagation energy [18][19][20]. It should been pointed out that the reversed austenite is mechanically unstable and will transform to hard martensite due to stress concentration during the impact process; this is known as the ''TRIP effect.''…”

Study of Phase Transformations in Steel X38CrMoV5-1 Using Dilatometry and Differential Thermal Analysis

“…Nowadays, in the industry, there is a new manufacturing method called electro‐slag melting that provides a lower degree of segregation, microporosity, and less impurities, but the parts produced for this application are manufactured by high pressure die casting with the presence of dendritic porosity created by the casting process itself during the solidification. Porosity is one of the main fracture causes when the parts work in tension and microstructural defects can lead to early fractures in parts due to the casting process …”