Effect of alloying elements on corrosion resistance of carbon steel in compressed bentonite containing alkaline solution

Carbon steels are considered to be the most promising material for an overpack container used for the geological disposal of radioactive wastes. In order to know effective alloying elements that increase the corrosion resistance in the disposal environment, corrosion tests of a commercial carbon steel and several kinds of low alloy steels were performed in compressed bentonite containing a simulated solution of bentonite contact water with chloride at pH 8 to 13. The most effective alloying element in the solutions from pH 8 to 12 was Ni. The second effective one was Al. The addition of Ti, Cr, Si, Cu, or Nb slightly increased the corrosion resistance. The most harmful element that decreased the corrosion resistance was Mo. In the solution with pH 13, all the steels except Mo- and Si-containing steels were passivated and the difference in the effect of alloying elements was very small. An FeCO3 layer was formed on all the steels as a corrosion product in the solutions with pH 8 to 12. (author)