HIGH-STRENGTH STEEL FOR MAIN PIPELINES WITH LOW YIELD FACTOR AND HIGH LOW-TEMPERATURE DUCTILITY Russian patent published in 1999 - IPC

FIELD: metallurgy, more specifically, ultrahigh-strength steel for main pipelines with low yield factor and high low- temperature ductility and weldability and ultimate strength of 95P MPa, exceeding X100 API standard. SUBSTANCE: steel is low-carbon high Mn-Mo-Nb-Ti traces steel selectively containing B, Cu,Cr and V, if required. Its microstructure contains martensite/bainite and ferrite soft/hard mixed structure having ferrite fraction from 20 to 90%. Said ferrite includes from 50 to 100% of cold-hardened (treated) ferrite with average ferrite grain size within 5 mcm. Design formulas are offered for determination of steel hardenability value in its hardening varying from 1.9 to 4.0, depending on steel chemical composition. EFFECT: higher reliability of main pipelines manufactured from claimed steel, efficiency of their manufacture and efficiency of conveying of natural gases, raw oils, oils through said pipelines. 8 cl, 6 tbl