In sequence from the previons reports (TentsutoHagane, May 1951, p. 272283), the eaperiment was made and summarized as follows:
(5) Addition of zirconium refines the austenitic grain size of steel and retards the grain growth at high temperatures.
(6) 0.50.9% of zirconium into steel has no remarkable effect on A1 point, but slightly lowers A3 point both in heating and cooling conditions. But in most cases these effects are covered by the action of the silicon.
(7) In many cases zirconium refines the annealed and normalized structures of steel, but there is no remarkable effect in quenched and tempered structures.
(8) Addition of zirconium more than 1% on carbon steel and lowalloyed steel can not expect the improvement of their mechanical properties, but addition of it up to 0.5% improves the mechanical properties of steels in normalized and high temperature tempering conditions.
(9) Zirconium raises the toughness of steel at low temperature tempering and shows the temperresistance at high temperature tempering.
(10) Zirconium prevents the temper brittleness of lowalloyed etructural steels.
(11) The deoxidation with zirconium improves the low temperature brittleness of steel With the indirect effect by improvement of structure, as in the previous report.