Optimization of Mechanical Properties of a Heat-treated Cu-bearing HSLA-80 Steel

Abstract

HSLA-80 steel, a replacement of HY-80 steel, is widely used in Navy vessels, where the requirement is good weldability, high strength and high low-temperature toughness. However, an increase in strength usually causes a decrease in toughness. Hence there is a need for optimization of the properties. The present work attempts to optimize the mechanical properties of an HSLA-80 steel through control of heattreatment variables. The heat treatment region, where the optimum combination of properties is likely to be obtained, is determined by carrying out single factor experiments over a wide range of tempering time-temperature combinations. Subsequently further experiments are done in this zone using statistical design of experiments. The present work involves quantification of properties by (i) classical curve fitting technique with data obtained from single factor experiments, and (ii) forming regression equations from 22 factorial design of experiments. Finally optimum combination of properties of the present steel has been obtained by Grid Search technique with a constraint on yield strength. Transmission Electron Microscopy studies are done, wherever necessary, to understand and correlate the mechanical properties with the microstructures.