Surface treatment of ferrous alloys with boron

Boronizing is a thermo-chemical surface hardening treatment in which boron atoms diffused into the metal substrate form the metallic boride layer, providing high hardness, corrosion resistance, and 3-10 times increasing service life. This type of surface treatment is widely used in many applications. The purpose of this work was to investigate the structures and properties of boronized ferrous alloys. Three types of steels, AISI 1018 (plain low carbon steel), AISI 4340 (high strength alloy steel), and AISI 304 (austenitic stainless steel), were used for this study. The boronized AISI 1018 and AISI 4340 demonstrated the saw-tooth structure with average 75-76 μm and 57-5 μm in depth, respectively. On the other hand, the narrow and flatten boride layer with average 10-11 μm was observed in the boronized AISI 304. The microhardness of boride layer in AISI 1018 and AISI 4340 was detected in the range of 1400-2200 HV and 1800-2200 HV, respectively, while that in AISI 304 was about 400-700 HV. Moreover, boronized steels showed the improved corrosion resistance in acid and oxidation resistance at high temperature rather than unboronized steels