Toughness of Welded Low Carbon Steels Containing Nitrogen (A Resolved Problem on Recycled Steels)

摘要

Recycled low carbon steels contain many tramp elements. Molten steels absorb nitrogen during refinement of in arc melting furnaces. Nitrogen in ferritic steels makes the steels brittle, but authors have managed to make steels tough by refining microstructures, which were produced during control rolling at temperatures lower than A_1. These fine microstructure steels were arc welded in air. This paper reports the toughness of welds of mother steels containing total nitrogen contents from 58 to 150 mass ppm and having fine microstructures. V-notch Charpy impact values of control rolled mother steel were over 100 J at 273 K, even at nitrogen contents of 58-150. The heat affected zones of these steels had over 150 J V-notch Charpy impact values at 273 K, which were higher than those of mother steels. Rapid cooling after arc welding contributed to the improvement of the steel toughness. In addition, the deposited metals had 150-200 J V-notch Charpy impact values at 273 K, which were higher than those of mother steels.