Thermodynamic basis of twin-related variant pair in high strength low alloy steel

We elucidated here the mechanism of formation of twin-related V1/V2 variant pair from the perspective of thermodynamics. It was observed that the low cooling rate and phase transformation near Ms temperature contribute to produce more V1/V2 variant pairs. The reason why the content of V1/V2 variant pairs in the lath bainite is higher than that of martensite is the diffusion of carbon, which the local carbon enrichment promotes the increase of the content of V1/V2 variant pairs. The microstructure of high-hardenability steel at low cooling rates is mainly lath bainite with a higher content of V1/V2 variant pairs.