Evolution of MnS inclusions in Ti-bearing X80 pipeline steel

Studies show that manganese sulfide (MnS) inclusions in pipeline steel affect the lateral performance of steel in its rolling deformation, as well as the hydrogen-induced cracking and sulfide stress corrosion cracking resistance performance. To inhibit the precipitation of MnS and its effect on pipeline steel, a quenching experiment and a diffusion couple experiment, which investigated the evolution of MnS inclusions in Ti-bearing X80 pipeline steel, were conducted. The experimental results show that the transformation of the MnS inclusions during solidification is as follows: MnS→ titanium sulfide (TiS) → Ti₄C₂S₂. The transition temperatures of MnS to TiS and TiS to Ti₄C₂S₂ are 1673 and 1273 K, respectively, and the overall size of the sulfide decreased as well. Thermodynamic calculation results confirm that the transition temperatures of MnS to TiS and TiS to Ti₄C₂S₂ are 1623 and 1203 K, respectively. When the sulfur content in the X80 pipeline steel is 0.0015%, all the sulfur in the steel can be converted into Ti₄C₂S₂ with a titanium content of more than 0.02%.