Effect of Added Elements, Especially Titanium, on the Coarsening Temperature of Austenitic Grain Size.

Study on the high-temperature carburizing-I

Abstract

Theoretically, there is nothing particularly unusual about the fact that steel carburizes more rapidly at higher temperatures. Higher production rate is obviously possible. With higher temperatures all reaction rates increase but furnace parts erode more rapidly and the grain-size of the steel being treated increases with temperature. The authors experimented on the effect of additional elements especially titanium in carburizing steel on the coarsening temperature of austenitic grain size. The results are as follows:
(1) Relation between nitrogen and titanium in iron.
The behavior of titanium nitride in titanium-iron alloys with up to 0·2% titanium was observed on the quenched specimens after equilibrated with the controlled atmosphere at 1560, 1600 and 1650°C. The equilibrium constant in the reaction was determined.
(2) Effect of titanium on austenitic grain size.
The effect of titanium compounds on the grain coarsening temperature was studied with titanium-iron alloys containing oxygen, nitrogen or carbon respectively. The results are as follows:
(A) The grain size was reduced and its coarsening temperature increased by the presence of titanium nitride or carbide. The amount of added titanium required for enhancement of grain coarsening temperature was 0·01 to 0·1%.
(B) Titanium as solid solution or oxide had not any visible effect on the grain size.
(C) The steels containing aluminum, zirconium or niobium were superior to the steels containing aluminum or vanadium in the enhancement of grain coarsening temperature.