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A study of the dissolution and precipitation of microalloy elements in HLSA steels

ABSTRACT: Conventional methods used to determine bulk steel compositions do not necessarily detect trace levels of microalloy elements (~0.001wt.%), which can influence the dissolution behaviour and precipitation kinetics of intentional alloy additions. In this work, energy filtered TEM has been used to study the influence of titanium on the dissolution of niobium in austenite during reheating prior to hot deformation. Plane strain compression testing has been used to assess the consequential variation in strain-induced precipitation kinetics. Measurements show that the level of precipitation is reduced, due to titanium stabilising niobium during the reheating process. 1

1. INTRODUCTION

Microalloy additions are combined with the thermomechanical processing of low carbon steels to improve strength and toughness properties in the final product. Elements including titanium, vanadium and niobium are used, either alone or in combination, at varying levels depending on the particular hot deformation schedule. The improvement in mechanical properties is due to a refined microstructure on transformation. This is achieved by controlling the recrystallisation of austenite during the deformation schedule, via the strain-induced precipitation of microalloy carbides/nitrides.