摘要:
针对EAF-LF(VD)-VC工艺生产的大型船用S34MnV曲拐探伤不合的问题,分别在电炉还原期、LF-VD精炼期、浇注和锻造后钢锭取样对钢中夹杂物进行了研究.结果表明,精炼期间大于15μm的夹杂物比例波动在1.65%~10.34%之间;钢锭横截面上凝固前沿的柱状晶截获夹杂物的几率不同,帽口中心部位大型夹杂物含量少于边部试样夹杂物含量为5.81mg/10kg;钢锭尾部中心部位夹杂物含量高于边部试样夹杂物含量为25.9mg/10kg;锻造钢锭中夹杂物富集严重,其中尾部DS类夹杂达到了4级以上.钢锭锻造后尾部含有大型夹杂物聚集部分不能完全切除是目前导致产品探伤不合的一个主要原因.
Abstract:
The experimental samples were the marine crank steel S34MnV produced by the EAF-LF(VD)-VC production process, including the electric period, LF-VD refining period, casting period, and forging ingots from a heavy machinery factory in north China to solve the difficulty of being rejected by ultrasonic flaw detection for crank shaft. These samples were analyzed by the methods of metallographic observation, energy spectrum, and the electrolysis. The obtained results indicated that there was a large number of inclusions during the refining stage, and the proportion of inclusions with the size bigger than 15 μm accounting to total inclusions were within 1.65%-10.34% after VD process. Furthermore, the probability of inclusions captured by columnar crystal in the steel ingot cross-section was found changed obviously in different locations of ingot cap. The content of large inclusions in the center of the beginning of the ingot cap was 5.81 mg/10 kg, with increasing the distance from the center to the edge, whereas this value decreased to only 25.9 mg/10 kg in the rear center of ingot cap, with decreasing the distance form the center to the edge. In addition, large numbers of inclusions was found to exist in the forging ingot with the biggest inclusion of a 140 μm DS category, which were difficult to be cut off completely and would be the main reason of being rejected by ultrasonic flaw detection for crank shaft.
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