20SiMn铝镇静钢夹杂物演变及探伤缺陷分析

Inclusion Evolution and Flaw Detection Defect Analysis of 20SiMn Aluminum Killed Steel

20SiMn材质常用于水电水轮机、发电机轴锻件上,钢水纯净度的提升是提高轴类锻件使用寿命的关键所在。通过采用Al镇静钢工艺生产下注20SiMn钢锭的试验,分析了各个节点炉渣成分、夹杂物形貌及成分变化。研究表明:精炼结束炉渣碱度为6.3,VD后炉渣中CaO含量降低、SiO_(2)含量升高,炉渣碱度降低至4.9。整个精炼过程夹杂物主要为CaO-SiO_(2)-Al_(2)O_(3)-MgO、SiO_(2)-MnO-Al_(2)O_(3)两类,不同节点夹杂物类型单一。精炼结束、软吹后钢水中夹杂物以CaO-SiO_(2)-Al_(2)O_(3)-MgO为主,软吹后夹杂物中SiO_(2)、Al_(2)O_(3)含量有所增加。VD后钢水中夹杂物以SiO_(2)-MnO-Al_(2)O_(3)为主,Al_(2)O_(3)含量较低,该类夹杂物在软吹后大量去除。通过对锻件无损检测缺陷处进行取样分析,缺陷处形貌为微裂纹,缺陷区域未发现夹杂物和元素偏析,说明缺陷是由于锻造或锻后热处理过程内应力过大导致开裂造成的。

20SiMn material is commonly used in hydropower turbine and generator shaft forgings.The improvement of molten steel purity is the key to improve the service life of shaft forgings.The slag composition,inclusion morphology and composition change of each node have been analyzed by the experiment of 20SiMn steel ingot produced by Al killed steel process.The results show that the basicity of slag is 6.3 at the end of refining.After VD,the content of CaO in slag decreases,the content of SiO_(2)increases,and the basicity of slag decreases to 4.9.The inclusions in the whole refining process are mainly CaO-SiO_(2)-Al_(2)O_(3)-MgO and SiO_(2)-MnO-Al_(2)O_(3),and the types of inclusions in different nodes are single.At the end of refining and after soft blowing,the inclusions in molten steel are mainly CaO-SiO_(2)-Al_(2)O_(3)-MgO,and the contents of SiO_(2)and Al_(2)O_(3)in inclusions increase after soft blowing.The inclusions in the molten steel after VD are mainly SiO_(2)-MnO-Al_(2)O_(3),and the content of Al_(2)O_(3)is low.The inclusions have been largely removed after soft blowing.By sampling and analyzing the flaw detection defects of forgings,the morphology of the defects is micro-cracks,and no inclusions and element segregation have been found in the defect area,indicating that the defects are caused by excessive internal stress during forging or post-forging heat treatment.