Comparative study on the effect of Y content on grain refinement in the simulated coarse-grained heat-affected zone of X70 pipeline steels

Effect of Yttrium-Based Rare Earth on Inclusions and Cryogenic Temperature Impact Properties of Offshore Engineering Steel

EH36 offshore engineering steels with varied yttrium-based rare earth content were prepared by trials in industrial production. The effects of yttrium-based rare earth on the inclusions and cryogenic temperature impact properties of EH36 offshore engineering steel were investigated by scanning electron microscopy, automatic statistics of inclusions, thermodynamic analysis and fracture morphology analysis. Yttrium-based rare earth could refine the inclusions and modify irregular Al2O3 and MnS inclusions into small, spherical, regular rare earth inclusions. The optimal impact properties were found in EH36 steel with 0.020 wt.% yttrium-based rare earth. Compared with 0RE steel, the RE-inclusions were within 3 μm (91.95% of total inclusions) in diameter and were spherical or quasi-spherical when dispersed in 200RE steel. Meanwhile, the cryogenic temperature impact properties significantly increased: 200RE steel impact properties were increased by 245.1% at −80 °C.

Mechanism of Yttrium composite inclusions on the localized corrosion of pipeline steels in NaCl solution

In order to solve the problem of where, why, and how to start pitting, it is necessary to study the influence of different dissolution activity of the internal heterogeneous structures of the complex inclusions. In this paper, mechanism of internal activity difference of two typical Yttrium composite inclusions on pitting corrosion is revealed from atomic scale by using immersion test, FE-SEM/EDS analysis and first-principles calculations. The results show that, for Mg-Y-S composite inclusions, pitting potential is lower than that of the matrix, therefore, The matrix around the composite inclusions dissolves preferentially; for Y-S-O composite inclusions with core-shell structure, Y-O inclusions in the shell are deformed and cracked due to the internal stress of the matrix and Y-S during the immersion process, resulting in the simultaneous dissolution of inclusions and steel matrix.