Influence of Phosphorus on Solidification Structure in Continuously Cast 0.1 mass% Carbon Steel.

Abstract

In 0.1 mass% carbon steels with phosphorus contents ranging from 0.01 to 0.2 mass%, slabs were continuously cast to a thickness of 100 mm with a laboratory scale caster. Their macro-and micro-structures were characterized, focusing on the effects of phosphorus addition on the structural evolution during solidification and subsequent cooling. Cast slabs of high phosphorus steels have a fine columnar-g-grain structure. The mean width of the columnar grain was approximately half of that in the cast slabs without the phosphorus addition. Dispersed globular a grains were observed in the a grain structure of high phosphorus steels. The globular grains evolved at the phosphorus-rich spots in the prior-g grain. The micro-segregation of phosphorus results in these structural evolutions. Since the phosphorus enrichment stabilizes bcc (d or a) phase locally at the inter-dendritic region, the phosphorus-rich spot makes d phase retained to lower temperature for the d/g transformation, and provides a predominant site for the g/a transformation. In the high phosphorus casts, therefore, the dispersed d phase are thought to pin the g grain growth more effectively in the dϩg region when the completion of the d/g transformation is remarkably suppressed by the phosphorus segregation.

Effect of Manganese Segregation on Fine-grained Ferrite Structure in Low-carbon Steel Slabs

“…Figure 12 shows the prediction of the growth rate of the interface between the austenite and ferrite in holding at given temperatures for the 0.4 and 0.8 % Mn compositions. 16) The present prediction says that although the difference is not large, a lower growth rate is expected for the 0.8 % Mn than for the 0.4 % Mn. When we assume that the transformation starts after the compression below 1 093 K and finishes above 973 K, the ferrite size may reach a value between 2 and 5 mm in 3 s. The lower the transformation temperature range, the more the growth.…”

“…A continuous cast slab made in a laboratory-scale was prepared for the present study. The details of the casting are reported in the literature by Yoshida et al 16) and also mentioned in Table 3 with other preparations for GRP samples. The average spacing of the primary dendrite arms was 318 mm and the average spacing of the secondary dendrite arms was 137 mm.…”

“…The average spacing of the primary dendrite arms was 318 mm and the average spacing of the secondary dendrite arms was 137 mm. 16) Using this slab, each specimen with or without the elimination of micro-segregation was prepared. The former was cut directly from a quarter thickness of the slab for the Type 3 microstructure, and the latter was rolled to a plate by 70 % in nominal reduction ratio and reheated for 86.4 ks at 1 623 K to eliminate the Mn micro-segregation for the Type ISIJ International, Vol.…”

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

“…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. [8][9][10] It was discussed that the increase in P concentration significantly lowers T g and P segregation developed during casting process provides the pinning effect. In our previous study, we investigated the effects of Al addition on the as-cast g grain structure in 0.2 mass% C 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.…”