Grain refinement and stabilization in spray-formed AISI 1020 steel

An AISI 1020-grade mild steel, with a small amount of aluminum, was spray-f ormed by nitrogen gas-atomization and deposition. The spray-formed 1020 ste el contained 0.05 mass% of nitrogen and 0.06 mass% of aluminum. Rolling the spray deposit at 1123 K for a thickness reduction of 70% and subsequent no rmalizing at low austenitic temperatures produced a fully dense steel havin g a refined ferrite grain size as small as 3 mu m. This grain refinement re sulted from the pinning of prior austenite grain boundaries by fine AIN par ticles which precipitated during the thermomechanical treatments. Room-temp erature tensile properties (YS: 550 MPa, UTS: 630 MPa, elongation: 23%), ex ceeding those of conventional microalloyed high-strength low alloy steels, were achieved in the normalized state. The AlN-pinned fine-grained microstr ucture survived subsequent re-austenizing at temperatures as high as 1273 K . When tensile-tested in the austenite region at 1123 K, the microalloyed 1 020 steel showed a large elongation exceeding 200%. (C) 2000 Elsevier Scien ce S.A. All rights reserved.