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A new 13% Cr martensitic stainless steel (0.025% C-13% Cr-Ni-Mo) with excellent resistance to carbon dioxide (CO 2 ) corrosion and good resistance to sulfide stress cracking (SSC) was developed, and its application limits in oil and gas environments were clarified. The CO 2 corrosion rate of the 13% Cr steels with Ni and Mo was < 0.3 mm/y at 180°C (356°F) in 20% sodium chloride (NaCl). It was less than that of the conventional 13% Cr steel (0.2% C-13% Cr). The corrosion rate of the steel slightly decreased with the increase in Mo and Ni content. The SSC resistance improved with the increase in Mo content. The critical partial pressure of hydrogen sulfide (H 2 S) for the 2% Mo steel was > 0.005 MPa at pH 3.5. Effects of Ni and Cu on SSC were not distinctive for this kind of steel. These results depended upon hydrogen permeability. The critical H 2 S partial pressure for the 110grade steel was the same as that of the 95-grade steel at pH 4.5 and pH 3.0 and was slightly lower at pH values between 3.0 and 4.5. The new 13% Cr steel proved to have excellent properties in the sweet and slightly sour environments.

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Synopsis :The influence of alloying elements on microstructure and wear resistance of High Speed tool Steel roll (HSS roll) was studied in order to improve wear resistance and surface deterioration resistance of HSS roll. Although the volume of eutectic M7C3 carbide increased with the increase in C and Cr contents, wear resistance was not improved. The increase in Cr and Mo contents in good balance improved the wear resistance of HSS Roll remarkably, as eutectic carbide of M7C3 type became tough and the damage on the worn surface was prevented.The destructive prevention mechanism of carbide was discussed from change of the alloy concentration and the lattice constant of carbide by increasing in Cr and Mo contents.