• Korean Journal of Metals and Materials
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• v.46 no.10
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• pp.609-616
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• 2008

Conventional bake-hardenable(BH) steels should be annealed at higher temperatures because of the addition of Ti or/and Nb which forms carbides and raises recrystallization start temperature. In this study, the development of new BH steels without Ti or Nb addition has been reviewed. The new BH steels have nearly same mechanical properties as the conventional BH steels even though it is annealed at lower temperature. The steels also show smaller deviation of the mechanical properties than that of the conventional BH steels because of the conarol of solute carbon content during steel making processes. The deviation of mechanical properties in conventional BH steels is directly dependent on the deviation of solute carbon which is greatly influenced by the amount of the carbide formers in conventional BH steels. Less alloy addition in the newly developed BH steels gives economical benefits. By taking the advantage of sulfur and/or nitrogen which scarenge in Interstitial-Free or conventional BH steels, fine manganese sulfides or nano size copper sulfides were designed to precipitate, and result in refined ferrite grains. Aluminum nitrides used as a precipitation hardening element in the developed steels were also and resull in fine and well dispersed. As a result, the developed steels with less production cost and reduced deviation of mechanical properties are under commercial production. Note that the developed BH steels are registered as a brand name of MAFE(R) and/or MAF-E(R).

• Journal of Powder Materials
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• v.12 no.3
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• pp.214-219
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• 2005

In order to investigate the formation of AlN, mechanical alloying was carried out in $N_2$ and $NH_3$ atmosphere. Differential thermal analysis (DTA), x-ray diffraction (XRD) and chemical analysis were carried out to examine the formation behavior of aluminum nitrides. No diffraction pattern of AlN was observed in XRD analysis of the as-milled powders in $NH_3\;or\;N_2$ atmosphere. However, DTA and chemical analysis indicated that the precursors for AlN were formed in the Al powders milled in $NH_3$ atmosphere. The AlN precursors transformed to AlN after heat treatment at and above $600^{\circ}C$. It was considered that the reaction between Al and $NH_3$ was possible by the formation of fresh Al surface during mechanical alloying of Al powders.