Disposition of hot-formed structural steels with 0.4% C to temper brittleness

Abstract

1. Obtaining a polygonized structure in hot forming of austenite in a cycle of HTMT of steels 40Kh, 40KhN, and 40KhN2MA causes an increase of the resistance to brittle failure: after low tempering and embrittling tempering at 500°C (for 200 h) the level of impact toughness increases at normal as well as subzero temperatures; the critical brittle point is lowered; the fraction of crystalline component in the fracture decreases. 2. Hot forming of structural steels with 0.4% C at the steady state of dynamic polygonization (e≌50%) even with partial development of dynamic recrystallization (up to 30% vol. %) is more preferred for reducing disposition to temper brittleness than at the stage of nonsteady dynamic polygonization (e≌25%). Obtaining fully dynamically recrystallized austenite with finer grain than the initial one reduces to a lesser extent the disposition of steels to temper brittleness. 3. The lowering of the critical brittle point T20 as a result of HTMT of steels is directly proportional to the decrease of the fraction of intergranular failure.