The effect of hardening and tempering process on the organization and performance of high-strength and high-toughness non-hardened-and tempered steel of low carbon martensite is researched.

Observations showed that the micro-structure of the steel after forging or high temperature rolling was composed of low-carbon martensite, a little part of bainite and residual austenite.

The formation of the inter-lath austenite in quenched low-carbon steels is described and the existence of the carbon diffusion during the lath martensite formation is emphasized.