The effect of ultra-fast surface hardening and strengthening on microstructure and mechanical properties of cast (9Cr–3Co–3W) heat-resistant steel

There is a need to investigate a novel non-traditional surface hardening procedure for heat-resistant steel micro-alloyed with boron. In this research, boron powder pack processing was employed. Steel samples were boronized and mechanically investigated using hardness, three-point bending, and wear tests. Scanning electron microscopes and EDX were used to examine the microstructure before and after boronization. Boron was added in the form of a 50/50 combination of borax and boric acid in a crucible inside an induction furnace at 1050 °C for 30 min. The application of borax and boric acid 50/50 increased flexural strength from 614 to 1526 MPa and a further increase to 1700 MPa is achieved when ammonia bicarbonate (25%) with borax and boric acid 50/50 (75%) were used. The combination of ultra-fast boronizing and ammonia causes both surface and bulk hardening, which increases flexural strength. The produced steels are suitable for thermal and neutron shielding.