Ageing behavior of a Cu-bearing ultrahigh strength steel

摘要

On ageing at different temperatures a various combination of properties has been obtained for this Cu-bearing ultrahigh strength steel. A substantial increase in strength has been obtained at 450 ℃, accompanied by a drop in percentage elongation, percentage reduction in area and toughness. At 550 ℃ temperature extensive e-Cu precipitates have been observed. The increased strength value retained in the temperature range of 450-600 ℃ and a secondary hardening peak obtained at 600 ℃ is probably due to the formation of fine Mo carbide precipitates. The decrease in strength at 650 ℃ along with an increase in percentage elongation, percentage reduction in area and toughness is due to the coarsening of Cu particles and a partial recovery of matrix. At 700 ℃ most of the Cu precipitates become rod shaped and formation of fresh martensite with a dark contrast is observed at the lath boundaries.