Peculiarities of deformation and structure formation in nitrogen-containing steels of various structural kinds

Abstract

The nitrogen influence on strengthening, structure, phase transformation and evolution of the structure of various kinds of steels and alloys during heat and thermomechanical treatment have been investigated using X-ray diffraction analysis, light microscopy and mechanical testing. Investigated materials were microingots of Fe-based and Fe–Cr–based alloys of 1.5 g in mass and ingots of corrosion-resistant steels of 20 kg in mass. HTMT of the steel samples was carried out by using a two-roller mill “300” at a deformation start temperature 1050 °C with strains up to 65% and immediate water cooling. Cold deformation of the alloys and steel samples was carried out by using a two-roller mill “160” at room temperature with strains up to 50%. It is shown that the nitrogen alloying leads to increased heredity and to preserving heterogeneity of cast structure during the following cold or hot deformation. The nitrogen alloying leads to high strengthening and decreasing of the strip broadening at lengthwise cold rolling. The strip broadening also depends on the strength and phase composition of materials. The austenitic–martensitic steels have greater broadening than ferrite–martensitic steels. Prospects for using nitrogen-containing steels and the thermomechanical strengthening methods of them are shown.