Abstract：When the mass fraction of hydrogen in steel was low to 0.Xμg/g, the uncertainty problem for determination would be serious. The influence factors were discussed for determination of ultralow hydrogen in steel. The ultrasonic cleaning comparison test was conducted with rare earth steel sample by induction heat extraction method. The results showed that the simple immersion in solvent could not fully eliminate the influence of surface pollution, and the procedures of ultrasonic cleaning were necessary. The interaction between graphite crucible and steel sample could also influence on the accuracy of ultralow hydrogen analysis. With the help of filling blank, the positive interference of 0.1μg/g could be observed. The analysis results of actual samples and certified reference materials indicated that the graphite single crucible had obvious interference at high power, and the interference also existed in duplex crucible. During the routine analysis of hydrogen in new steel sample, the sample of abnormal “zero peak value” appeared, which challenged for the current pulse melting method and existing instruments. The use of instrument based on induction heat extraction method could solve this problem. The volatilization pollution of rare earth elements could cause “zero peak value” phenomenon, which had been proved by experiments. The similar abnormal phenomenon was also observed during the analysis of certified reference materials. At present, both thermal conductivity detector and infrared detector were suitable for the analysis of ultralow hydrogen. In conclusion, the pretreatment by ultrasonic cleaning, the nonuse of graphite single crucible and elimination of sample volatilization interference were three major factors for accurate determination of ultralow hydrogen in steel. The induction heat extraction combined with ultrasonic cleaning could meet the determination requirements of ultralow hydrogen in various steel samples.
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