Effects of Ti Addition on As-cast γ Grain Structure in Hyper-peritectic Carbon Steel

Abstract

Effects of titanium addition on as-cast austenite grain size in 0.2 mass% carbon steel cooled at 0.03°C/s has been studied. The average austenite grain size was reduced from 4.3 to 1.9 mm by increasing the titanium concentration from 0 to 0.13 mass%. Two different shapes of Ti(C, N) particles were observed in the solidified samples; one was a facet shape which were dispersed over the whole observation area and the other was a filmy shape, most of which were located on the austenite grain boundary. Thermodynamic calculations and EPMA analyses showed that the facet shaped Ti(C, N) particles crystallize at relatively high temperatures, while the filmy shaped ones form from the last solidifying liquid in the inter-dendritic regions at lower temperatures. The latter Ti(C, N) is considered to provide the grain refinement effect of austenite grain structure. The grain refinement effects of titanium are further discussed by comparing the results of 0.2 mass% carbon steel with those of 0.45 mass % one, which supports the substantial effect of the filmy shaped Ti(C, N) on the as-cast austenite grain structure.

Effects of Ti Addition on Austenite Grain Growth during Reheating of As-Cast 0.2 mass% Carbon Steel

“…The addition of 0.1 mass% Ti does not lead to substantial changes in pearlite colony size and lamellar spacing of pearlite. As discussed in our previous report, 6) the prior γ grain size is reduced from about 4 mm to about 2 mm by the addition of 0.1 mass% Ti. Furthermore, the size of proeutectoid α phase, which is acicular shape, is slightly reduced by Ti addition in Fig.…”

“…When the temperature reached 1 100°C, the sample was put out of the furnace and it was cooled to room temperature. This melting and cooling processes are the same as those reported in the previous study for the investigation of effects of Ti addition on the as-cast γ grain structure, 6) except that the sample was air cooled to obtain α + pearlite structure in this study. The average cooling rate during the air cooling was 0.76°C/s.…”

“…Our recent study demonstrated that the addition of Ti is effective in reducing the size of as-cast γ grains in 0.2 mass% C steel which is prone to exhibit coarse γ grains because of its high value of Tγ . 6) Figure 1 shows the phase diagram of Fe-0.2 mass% C-0.006 mass% © 2012 ISIJ N-xTiTi calculated by the CALPHAD method 7) with a thermodynamic database reported in Ref. 8).…”

Effects of Second Phase Particle Dispersion on Kinetics of Isothermal Peritectic Transformation in Fe–C Alloy

“…Therefore, the decrease in Tγ corresponds to a decrease in the temperature for onset of rapid grain growth, thereby retarding γ grain growth at high temperatures. In fact, it has been reported in several studies [2][3][4][5] that reduction of Tγ by alloying element addition leads to grain refinement of as-cast γ structure. It should be noted that these early works focused on the reduction of Tγ due to stabilization of liquid or δ phase in a low temperature region.…”

Effects of Al and P Additions on As-cast Austenite Grain Structure in 0.2 mass% Carbon Steel

“…[8][9][10][11][12][13][14] The addition of d-ferrite stabilizing elements such as Nb, V and Mo extends the dϩg region in the phase diagram toward lower temperatures, which leads to refinement of as-cast g grain structure due to pinning effect of the d phase on the g grains. 15,16) Moreover, it was reported that P addition led to the refinement of as-cast g grain structure in 0.1 mass% C steel.…”