The Role of Zirconium in Microalloyed Steels T N Baker Department of Mechanical and Aerospace Engineering The University of Strathclyde, Glasgow G1 1XJ, UK. E-mail:
[email protected]. Abstract Recently there has been a renewed interest in the addition of zirconium to microalloyed steels. It has been used since the early 1920’s, but has never been universally employed, as have niobium, titanium or vanadium. The functions of zirconium in steelmaking are associated with a strong chemical affinity, in decreasing order, for oxygen, nitrogen, sulphur and carbon. Historically, the main use of additions of zirconium to steel was for combination preferentially with sulphur and so avoid the formation of manganese sulphide, known to have a deleterious influence of the impact toughness of wrought and welded steel. Modern steelmaking techniques have also raised the possibility that zirconium additions can reduce the austenite grain size and increase dispersion strengthening, due to precipitation of zirconium carbonitrides, or in high nitrogen vanadium-zirconium steels, vanadium nitride. This review gathers information on the compounds of zirconium identified in steels together with crystallographic data and solubility equations. Also brief accounts of the role of sulphides and particles in general on austenite grain size control and toughness are included. Keywords: Zirconium compounds, mechanical properties, impact, microstructure 1 1 Introduction The term microalloying, as applied to steels, is generally accepted as emanating from the paper by Beiser1 published in 1959, which reported the results of small additions of niobium to commercial heats of a carbon steel. However, it has not been recognized that microalloying as such, first occurred some 35 years earlier, when small additions of zirconium were added to plain carbon steels, and the effects reported by Feild2 and by Beckett3.