Abstract
The effect of zirconium on the austenitic grain-size refining and its grain-coarsening temperature in electrlytic iron and low-carbon rimmed steel nfelted in nitrogen atmosphere, in argon atmosphere and in vacuum were studied. The effect of nitrogen on the austenitic grain-size was also tested with electrolytic iron melted in nitrogen atmosphere, holding it for various time. When zirconium was added, the austenitic grain-size was refined and its graincoarseniding temperature became higher.
In the case of electrolytic iron, grain size became finer in certratin range of zirconium content, but in mild steel such range could not be found. Total contents of oxygen or nitrogen did not effect directly on the grain size, but nitrogen coexisted with zirconium effected on grain size. Considering of grain-coarsening temperature, amount of inclusions which was to be cause of grain refining was calculated from thermodynamic data. It was considered that ZrN or ZrC were effective for grain refining but ZrO2 was not so. On mild steel, the authors could not obtain the obvious conclusion because of including several elements. It was presumed that the cause of grain size refining could be decided clearly if coexisted inclusions, ZrN, ZrO2, ZrC and etc., would be able to analyse separately.
