The behaviour of AISI 4340 steel coatings on low carbon steel substrate produced by friction surfacing

Abstract

In the present work, AISI 4340 alloy steel coatings were deposited on ASTM A36 low carbon steel substrates by friction stir surfacing with varying processing parameters. Temperature evolution during deposition was monitored by using an infrared camera. The coatings obtained were subsequently analysed in terms of their microstructure, mechanical properties and residual stresses. Prior austenite grain boundary analysis revealed that with increasing rotation and translational speeds, larger strain rates and a finer austenite grain size were obtained, which influenced the coating microstructure after cooling. The coatings with smaller austenite grain sizes exhibited average hardness values of 510 ± 60 HV0.025 and compressive residual stresses (between approximately −75 and 200 MPa). On the other hand, coatings produced with lower rotation and translational speeds developed relatively larger austenite grain sizes and exhibited mostly martensitic microstructures with average hardness values of 610 ± 60 HV0.025 and evolved tensile residual stresses (between approximately 10 and 90 MPa). Finally, it was possible to notice that the harder predominantly martensitic coatings with tensile residual stresses exhibited less adhesion with the substrate in comparison with the lower hardness coatings with compressive residual stresses.