Evaluation of Ce Addition by Different Wire inLiquid 316 Stainless Steel

Sammanfattning: It is well known that REMs are strong oxide and sulphide formers that can easily form large clusters which have harmful effect on the casting process as well as the quality of the final steel product. By adding these elements right before casting, the number of narrow transfer parts are eliminated (compared to if added in ladle) Also, the REM inclusions has less time to sinter together to form large clusters, preventing clogging. The general idea behind this alloying method in the continuous casting machine is to feed a wire of FeSiRE powder blend, coated with a metal strip, into the melt in the chilled Cu mold (CC mold) Adding REMs to the steel, in particular Ce, can increase the resistance to oxidation at high temperatures by improving the properties of the chromia layer. This is of big interest for SANDVIK as it can improve their corrosion resistant grades and may also, in the future, enable alloying in with other volatile elements such as Zr. This master thesis has the objective to find out the dissolution time of the wire, coated with three different metal strips; Steel, Cu and Al. The experiments were performed with steel grade 316L, provided by SMT, in a 2kg melt in a lab scaled induction furnace at 1500oC, 1510oC and 1530oC. The operations were performed both with and without FeSiRE powder inside. The results obtained with powder inside at 1500oC showed that the Al wire experienced the shortest dissolution time ( 0,5 to 1s) followed by Cu (≤10s) and Steel (18 to 20s). In addition to this, sampling procedures was implemented ( 1, 1, 3, 5 10 and 29mins after wire addition) in a depth of 40mm for each wire. Here, the yield of Ce 1 minute after wire addition was highest for the Steel wire (41.9%) followed by Cu wire (25%) and Al wire (<14.8%). From samples taken 1 and 5mins after wire addition in the Al wire experiment, inclusions were extracted and collected on a film filter after electrolytic extraction and filtration. The film filter was observed in SEM. The morphology and compositions were analysed and compared. It was found that Ce and La was present as Ce La oxy sulfides both individually and on Al Mg O clusters.