A Comparison of the Effects of Cobalt, Silicon, Nickel and Aluminum on the Tempering Response of a Medium Chromium Secondary Hardening Steel

摘要

The effects of additions of 4 wt% cobalt, 8 wt% cobalt, 2 wt% silicon, 2 wt% aluminum and 4 wt% nickel on the tempering response of a base hot work die steel have been compared for four different austenitizing temperatures. After austenitizing at 1 200℃ all alloying additions significantly enhance the peak secondary hardness. The silicon addition is by far the most effective; the aluminium addition was found to be more effective than the addition of 4 wt% cobalt and nearly as effective as the addition of 8 wt% cobalt. The nickel addition was the least effective, but did increase the peak secondary hardness by about 2.5 Rc. The effectiveness of some of these additions in enhancing the peak secondary hardness was found to be sensitive to the choice of austenitizing temperature. Silicon's influence on the peak secondary hardness was more sensitive to the choice of austenitizing temperature than those of the other alloy additions. Apparently this was because of the dissolution of primary carbides in the base + Si steel with increasing austenitizing temperature. The influence of the additions on the hardness after tempering at 600℃ and 650℃ depended again on the addition and the choice of austenitizing temperature. It was found that the silicon additions were more effective than any of the other alloying additions in maintaining hardnesses at 600℃ and 650℃, provided higher austenitizing temperatures were used.