Stress-affected transformation to lower bainite

L. C. Chang and H. K. D. H. Bhadeshia

Abstract

Experiments have been conducted on the formation of lower bainite under the influence of an externally applied stress. It was found that both the ferritic and cementite components of the microstructure respond to the stress. The ferrite plates that grow appear to comply best with the applied stress, leading to an aligned microstructure. Within any given ferrite plate, the stress was found to favour the formation of a single variant of cementite. The results are consistent with a displacive mechanism of transformation, and provide an explanation for the frequent observation that cementite precipitates in a single orientation within any given plate of lower bainite ferrite.

JOURNAL OF MATERIALS SCIENCE, 1996, Vol.31, No.8, pp. 2145-2148.

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Lower bainite: Fe-0.46C-2.1Si-2.15Mn wt%. Austenitised at 1000°C for 10 min, isothermally transformed at 270°C for 2500 s. Zero stress.	Lower bainite: Fe-0.46C-2.1Si-2.15Mn wt%. Austenitised at 1000°C for 10 min, isothermally transformed at 270°C for 2500 s. Transformed under the influence of 700 MPa compressive stress.
Lower bainite: Fe-0.46C-2.1Si-2.15Mn wt%. Austenitised at 1000°C for 10 min, isothermally transformed at 295°C for 2500 s.	Lower bainite: Fe-0.46C-2.1Si-2.15Mn wt%. Austenitised at 1000°C for 10 min, isothermally transformed at 270°C for 2500 s. Transformed under the influence of 700 MPa compressive stress.
Lower bainite: Fe-0.46C-2.1Si-2.15Mn wt%. Austenitised at 1000°C for 10 min, isothermally transformed at 270°C for 2500 s.	Lower bainite: Fe-0.46C-2.1Si-2.15Mn wt%. Austenitised at 1000°C for 10 min, isothermally transformed at 270°C for 2500 s. Transformed under the influence of 700 MPa compressive stress.