Tensile fracture behaviour of microstructurally engineered Cu bearing high strength low alloy steel

Abstract

An attempt has been made to highlight the influence of precipitation and microstructural constituents on tensile fracture behaviour in Cu bearing HSLA 100 steel. Variations in the microconstituents have been incorporated in the steel by engineering the microstructures through thermal treatments consisting of solutionising, water quenching and aging at various temperatures. The microstructure in quenched condition consists of mainly lath martensite, bainite and acicular ferrite besides little amount of retained austenite, carbides and carbonitrides. Aging up to 500 degrees C facilitated fine coherent epsilon-Cu precipitation that lost its coherency at > 550 degrees C. Simultaneously, recovery and recrystallisation of martensite and acicular ferrite occurred at higher temperatures. The formation of new martensite islands occurred on aging at > 650 degrees C. Carbides, carbonitrides and retained austenite remained essentially unchanged. Tensile tests were conducted at a slow strain rate to study the tensile fracture behaviour of the steel. Microstructural and fractographic evidences indicating that coherent Cu precipitate causes the brittleness in the material in initial stages of aging whereas loss of coherency of Cu precipitate in later stages results in the reappearance of ductility in the material.