Abstract：During the production of 9Ni steel medium-thick plates 06Ni9DR, many batches were unqualified in ultrasonic flaw detection. The defective parts of the samples were inspected and analyzed using the metallographic microscope and scanning electron microscope. The results showed that there were a large number of CaO-Al2O3 inclusions (in length of 61-167 μm) accompanied by a small amount of MgO and sulfide in the steel, which was main reason for the unqualified flaw detection. Due to insufficient addition of aluminum in LF deoxidation, the burning loss of aluminum during refining led to further reduction of aluminum content. Aluminum was added in the later stage of LF treatment or in the process of RH treatment, thus a large number of such inclusions were generated. After taking some measures such as controlling the end-point carbon and oxygen content of the converter, extending the RH vacuum treatment time and soft blowing time, and ensuring sufficient liquid steel sedation time, the quantity of inclusions in the steel plate had been significantly reduced. Meanwhile, the proportion of unqualified ultrasonic flaw detection decreased from 8.11% to 0.2%.
韩启彪, 高龙永, 车金锋. LNG储罐用9Ni钢夹杂物控制生产实践[J]. 物理测试, 2023, 41(4): 27-30.
HAN Qibiao, GAO Longyong, CHE Jinfeng. Production practice of inclusion control in 9Ni steel for LNG storage tank. PHYSICS EXAMINATION AND TESTING, 2023, 41(4): 27-30.
2023, Vol. 41 
