Cracking Cause of Tin Plate for Easy-Opening Lid and Improvements

The tin plate for easy-opening lid produced by a steel factory cracked at the rivet during the lid making process, and the cracking rate was about 0.08%, which was lower than the customer's expected quality requirements. The cracking reasons were analyzed by chemical composition analysis, mechanical property testing, microstructure observation and inclusion analysis, and the improvements were suggested. The results show that the ductile fracture occurred on the rivets of easy-opening lids. The presence of large Al₂O₃ and CaO inclusions at the edge of the rivets and the obvious thickness thinning were the direct and indirect causes of the lidding cracking of the tin plate, respectively. After the ladle refining furnace (LF) refining process during the smelting process changed to the molten steel vacuum circulating degassing (RH) refining process, the number of inclusions per square millimeter in the finished tin plate was 4.7, and the maximum size was 15.5 μm, which were significantly lower than the 49.8 per square millimeter and 38.9 μm before the process improvement, and no cluster large inclusions were found, indicating that the RH refining process had a better control effect on the inclusions. The chemical composition, hardness, tensile properties and microstructure with the RH refining process were all met the requirements for easy-opening lids, and the cracking rate of lidding was reduced to less than 0.01%.