Influence of Heat Treatment on the Microstructure and Low-Temperature Performance of Low-Carbon Steel

Resumo

In the present work, 20L and 20GL steels are investigated with a view to increase in their impact strength at negative temperatures, by adjusting the structural state in final heat treatment of valve and pipeline components. Stable impact strength KCV may be established in 20L steel at –40°C and in 20GL steel at ‒60°C by three-stage heat treatment: double quenching in water and subsequent high tempering. The other three heat treatments considered proved ineffective. The greater strength of 20GL steel components in comparison with 20L steel components may be attributed to its finer structure and greater bulk content of acicular α phase, on account of the higher content of manganese, which deters the ferrite transformation of austenite.