1988 Volume 74 Issue 7 Pages 1509-1516
A continuous casting and direct rolling process for Al-killed cold-rolled steel sheets was examined. AlN precipitation in steels which were melted before precipitation treatment was studied in the laboratory and AlN precipitation diagrams (TTP) were obtained. AlN precipitation in melting-treated steels is delayed and a larger amount of aluminum and nitrogen are kept in solution in comparison with that in AlN solution-treated steels. When the temperature of steels after casting and solidification is kept above Ar3 transformation temperature, AlN hardly precipitates. Production-scale tests of the process were performed by using the continuous casting machine and the hot strip mill. AlN precipitation in hot-rolled steel sheets was also observed. Enough amount of solute aluminum and nitrogen for obtaining high r-value after cold-rolling and box-annealing were maintained in hot-rolled steel sheets. Even in case of high content of aluminum and nitrogen, most of them are in solution in hot-rolled sheets and cold-rolled steel sheets which have high r-value are obtained by using the process.