Oxide metallurgy enables the development of new grain-size control technology based on the use of inclusions such as MnS, oxides, and nitrides as precipitate nucleation sites. This has made possible the production of high-strength and high-toughness microalloyed steels, and contributed to the expansion of direct heat treatment applications even to highly stressed automotive suspension components.
The negative effects of nonmetallic inclusions were turned into an advantage in new technology to control the composition, size, and distribution of small oxides and MnS during steel solidification and rolling, in order to use them as precipitation nucleation sites for intragranular ferrite. In this way, the finely dispersed inclusions can be used to increase the number of transformation initiation sites within austenite grains, producing a fine distribution of ferrite crystals. Control of solidification and rolling conditions thus plays a key role in strength control. This concept is basically applicable in principle to all types of microalloyed steels and is illustrated in the figure.
For more information, click on the link below (subscription required). Then scroll to Figure 18.
H. Tahira, K. Funatani, Forge and Direct Heat Treatment Processes and Technologies, Heat Treating of Irons and Steels, Vol 4D, ASM Handbook, Edited By Jon L. Dossett, George E. Totten, ASM International, 2014, p 241-252, https://doi.org/10.31399/asm.hb.v04d.a0005994
