Development of Low-Carbon Steel Alloyed with Copper for Pipeline Fittings Prepared by Hot Stamping

Abstract

Results are given for an experimental study of steel manufacturing technology satisfying specifications for strength class not less than K60 for connecting pieces (fittings). Laboratory melts, rolling, and heat treatment by different regimes are performed for low-alloy steels of four composition versions containing 0.05–0.08% carbon. Steels containing about 1% copper, in contrast to steels with a lower content or without addition of copper after normalizing and tempering, demonstrate a level of properties corresponding to strength class K60. Research shows that additional strengthening occurs as a result of precipitation of fine particles enriched in copper after tempering. Steel impact strength KCV–40 and relative elongation of steels alloyed with copper are at a high level due to a low carbon content and addition of nickel, and also prior grain refinement during controlled rolling. During tempering after normalizing, a more balanced set of properties is provided with tempering at 600°C. The steel developed may be used for preparing fittings of strength class K60 by hot stamping without thermal improvement or of strength class K65 after additional quenching and tempering.