Influence of Chromium on Mechanical Properties and CO2/H2S Corrosion Behavior of P110 Grade Tube Steel

 A Four kinds of P110 grade tube steels containing different chromium contents were designed to probe the influence of Cr on the properties of tube steel. The microstructure, mechanical properties and corrosion behavior of the four kinds of P110 grade tube steels were studied deeply and thoroughly. The analysis of the mechanical properties indicated that tensile strength and yield strength of the steel plates were improved, while transverse and longitudinal impact energy and elongation first increased and then decreased when Cr content rose. The impact energy and elongation reached the peak when Cr content was 1%. Cr precipitates were found only in 3% Cr steel, with (Nb,Ti)(C,N) or Nb(C,N) as the core of precipitation and then grew up. The corrosion experiments demonstrated that the scales on the four steels had a two-layer structure under the corrosion of CO2 and H2S. The outer layer was mainly composed of FeS or FeS1-x and the inner layer consisted of FeCO3 and Cr compounds. Cr was rich in the inner layer and the Cr content of the inner layer increased with the Cr content in matrix. The enriched Cr enhanced the compactness of the scales, further hindering the diffusion of ions from liquid to the surface of steel, thus reducing corrosion rate.