Effect of Zr–Ti deoxidisation on the hydrogen-induced cracking of X65 pipeline steels

Abstract

The effect of Zr–Ti combined deoxidisation, compared with the traditional Al deoxidisation, on inclusion and microstructure in X65 pipeline steels was investigated by means of analytical characterisation techniques such as non-aqueous solution electrolysis method, optical and electron microscopy in conjunction with energy dispersive X-ray spectroscopy and hydrogen-induced cracking test. Large inclusions as well as elongated MnS particles were observed in the conventional Al-deoxidised steel. However, the type and size of inclusions were efficiently controlled in the Zr–Ti-deoxidised steel, in which MnS particles were spheroidised and evenly dispersed in the matrix. Hydrogen-induced cracking test results showed that centre segregation was the main factor accountable for hydrogen-induced cracking in X65 pipeline steels. The Zr–Ti-deoxidised X65 pipeline steel revealed better HIC-resistance performance.