"Precipitation of Copper Sulfide in Strip Casting Steel Containing High Phosphorous”

超鉄鋼研究センター　冶金グループ　劉中柱

With the steel scrap continuously increasing, the contents of impurities in steel, such as Cu and Sn, increase gradually since they are difficult to be removed during steel making process. In addition, the processes for removing sulfur and phosphorous produce a large quantity of slag and expend large amounts of resources and energy.
So, inverse utilization of such impurities in steel is of great significance.


Direct near net shape casting is an attractive process for the production of sheet metal. Post-treatment like heating and/or rolling is omitted, and the faster solidification rates associated with the direct near shape casting may produce new microstructures.

The finer microstructures are generally expected through the faster solidification and cooling rates. This process may have some advantages as one of the future approaches for the efficient utilization of steel scraps because it considers the detrimental effects caused by the impurities in the scraps.


The precipitation behavior of sulfides (manganese sulfide and copper sulfide) in strip casting steel containing high phosphorous (0.1%P) was investigated. The differences in the mechanical properties between the as-cast and annealed strips were also investigated with an emphasis on the microstructural effects.

It was found that the strip casting process not only produced fine microstructures but also resulted in nano-scale copper sulfides. The as-cast strip has higher yield and tensile strengths and maintains high work hardening ability at higher stress levels than that of the annealed strip. Both the as-cast and annealed strips have a superior balance of strength and work hardening ability compared with the strips without the impurities.

The nano-scale copper sulfide particles in the as-cast strip contributed most to the difference in the yield strength between the as-cast strip and annealed strips. The as-cast strip also could not produce the good work hardening ability without the nano-size particles.

Further improvements in strength and work hardening ability can be attained by controlling the particles’ size and the volume fraction in the strip.


Reference:

1. Z. LIU, Y. KOBAYASHI and K. NAGAI, 埼玉工業大学若手研究フォーラム 第1回研究フォーラム---21世紀の新しい創造性を支えるハイ・テクノロジー:83-86.
   
   
2. Z. LIU, Y. KOBAYASHI and K. NAGAI, submitted to Materials Transactions.