Abstract: A low-alloy steel containing, by weight percent, C 0.03-0.13%, Mn 0.90-1.80%, Si?0.40%, P?0.020%, S?0.005%, Ni 0.10-1.00%, Cr 0.20-1.20%, Mo 0.15-0.80%, Ca?0.040%, V?0.10%, Nb?0.040%, Ti?0.020% and N?0.011% for making high-strength, weldable steel seamless pipe, characterized in that the microstructure of the alloy steel is a mixture of bainite and martensite and the yield stress is at least 621 MPa (90 Ksi). It is a second object of the present invention to provide a high-strength, weldable steel seamless pipe, comprising an alloy steel containing, by weight percent, C 0.03-0.13%, Mn 0.90-1.80%, Si?0.40%, P?0.020%, S?0.005%, Ni 0.10-1.00%, Cr 0.20-1.20%, Mo 0.15-0.80%, Ca?0.040%, V??0.10%, Nb?0.040%, Ti?0.020% and N?0.011% also characterized in that the microstructure of the alloy steel is predominantly martensite and the yield stress is at least 690 MPa (100 ksi).

Abstract: The present invention pertains to steel with high mechanical resistance at room temperature and up to 130° C., good toughness and good corrosion resistance in the metal base as well as good resistance to cracking in the heat affected zones (HAZ) once the tubing is welded together, and more specifically to heavy gauge seamless steel tubing with high mechanical resistance, good toughness and good corrosion resistance called catenary conduit. The advantages of the present invention with respect to those of an the state of technology reside in providing a chemical composition for steel used to manufacture heavy gauge seamless steel tubing with high mechanical resistance, good toughness, good fissure resistance in the HAZ and good corrosion resistance and a process for manufacturing this product. These advantages are obtained by using a composition made up basically of Fe and a specific chemical composition.

Abstract: A low-alloy steel containing, by weight percent, C 0.03-0.13%, Mn 0.90-1.80%, Si?0.40%, P?0.020%, S?0.005%, Ni 0.10-1.00%, Cr 0.20-1.20%, Mo 0.15-0.80%, Ca?0.040%, V?0.10%, Nb?0.040%, Ti?0.020% and N?0.011% for making high-strength, weldable steel seamless pipe, characterized in that the microstructure of the alloy steel is a mixture of bainite and martensite and the yield stress is at least 621 MPa (90 Ksi). It is a second object of the present invention to provide a high-strength, weldable steel seamless pipe, comprising an alloy steel containing, by weight percent, C 0.03-0.13%, Mn 0.90-1.80%, Si?0.40%, P?0.020%, S?0.005%, Ni 0.10-1.00%, Cr 0.20-1.20%, Mo 0.15-0.80%, Ca?0.040%, V??0.10%, Nb?0.040%, Ti?0.020% and N?0.011% also characterized in that the microstructure of the alloy steel is predominantly martensite and the yield stress is at least 690 MPa (100 ksi).