Iron alloys decarburization

Stable oxides, such as those of clrromium, vanadium and titanium cannot be reduced to the metal by carbon and tire production of these metals, which have melting points above 2000 K, would lead to a refractoty solid containing carbon. The co-reduction of the oxides widr iron oxide leads to the formation of lower melting products, the feno-alloys, and tlris process is successfully used in industrial production. Since these metals form such stable oxides and carbides, tire process based on carbon reduction in a blast furnace would appear to be unsatisfactory, unless a product samrated with carbon is acceptable. This could not be decarburized by oxygen blowing without significairt re-oxidation of the refractory metal. 

Decarburization occurs in steels and cast irons in hydrogen gas by the reaction of H with C in the steel. The decarburization rate is primarily dependent on the diffusion rate of C in the steel, but is also affected by the carbon content of the steel, alloying elements in the steel, such as chromium, impurities in the hydrogen, and of course time and temperature. Carburization of steels, the reverse of decarburization, is usually conducted at temperatures of about 900°C, but decarburization can occur at temperatures as low as 800°C. " ... 

The temperature below which a ferrite surface layer forms on decarburization depends on the nature and concentration of other alloying elements in the steel, but, for plain carbon steels, can be taken to be 910 °C as for pure iron. Prediction of the effect of alloying elements on this temperature is complicated by the fact that the alloying elements will undergo either denudation or concentration at the surface during scaling. 

Using mishmetal to modify high-chromium white iron results in a refinement of the alloy structure and increases the wear resistance by 13.6% [1994Pee]. Adding Cu to the C-Cr-Fe melt decreases the decarburization reaction rate [2002Shi]. 

Kan] Kaneko, K., Sano, N., Matsushita, Y., Decarburization and Denitrogenization of Iron And Iron-Chromium Alloys by Hydrogen Plasma (in Japanese), J. Fac. Eng., Univ. Tokyo, A-13, 60-61 (1975) (Phase Relations, Thermodyn., Experimental, 2)... 

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