Heat Treatment of Precipitation-Hardening Stainless Steels Alloyed with Niobium

Precipitation-hardening stainless steels are iron-nickel-chromium alloys containing precipitation hardening elements such as aluminum, titanium, niobium and copper. In this work, heat treatment is performed in a novel precipitation hardening stainless steel using niobium as a formative element for the hardening precipitates seeking to enhance its surface hardness and wear resistance. The steel composition was 0.08C-0.12Mn - 0.38Si - 11.87Cr - 6.00Ni - 2.60Mo - 1.95Nb (in w%). The samples were solubilized at 1100 ⁰C for 2 hours. The cooling was done in oil and subsequently aged at 500 ⁰C, 550 ⁰C and 600 ⁰C. The solubilized samples showed average hardness of 30 HRc and after aging treatments reached hardness up to 46 HRc. Hardness increase during the aging treatments was very fast. A 5 minutes treatment achieved hardness levels that were close to the maximum obtained. Niobium produced efficient precipitated hardeners, constituted the Laves phase type Fe₂Nb.