Abstract：The preparation, sampling and analysis methods of ultralow oxygen and nitrogen in high-cobalt cast superalloy by pulse fusion-infrared absorption/thermal conductivity were limitied. The high-cobalt cast superalloy round bar was cut into round cakes with a thickness of 15-25 mm using an interactive cutting machine. The round cake was firstly cut into sector segments with a center angle of 90° using a water-cooled metallographic cutting machine. Then the sector segment was cut into slices with thickness of about 5 mm using the water-cooled metallographic cutting machine along the two arc ends of the segment. Finally, the strips with width of about 5 mm were cut from the slices. The water-cooling protection was used during cutting. The strip was polished with a diamond file to remove the oxide layer on the surface, and then cut into pellets (0.50-0.90 g) using a sample cutting machine followed by cleaning with acetone. The calibration cure was established using certified reference material of steel and superalloy. The determination method of ultralow oxygen and nitrogen in high-cobalt cast superalloy by pulse fusion-infrared absorption/thermal conductivity was established. Three methods were used for sampling from the round bar, including air-cooled cutting, interactive cutting, and water-cooled cutting. The results indicated that the air-cooled cutting was seriously overheated, which could affect the determination of oxygen content in the samples. The methods of interactive cutting and water-cooled cutting could effectively avoid this problem. Four methods were used to prepare samples, including wire cutting-cylindrical grinding, wire cutting-lathe, wire cutting-file polishing, and water-cooling cutting-file polishing. The results showed that the wire cutting sample preparation had an influence on the determination of oxygen in the small test bar sample, but the water-cooled cutting could effectively avoid this effect. The above-mentioned methods for sampling and preparation had no obvious influence on the determination results of nitrogen. The effect of analytical power of instrument, integral time and sample mass on the analysis results of oxygen and nitrogen in the samples were investigated. The following experimental conditions were selected: the analytical power of instrument was 5.5 kW; the integral time for oxygen and nitrogen was 40 s and 55 s, respectively; the sample mass was in range of 0.55-0.90 g. Under the selected experimental conditions, the limits of detection for oxygen and nitrogen were 0.000 006% and 0.000 007%, and the limits of quantification were 0.000 019% and 0.000 024%, respectively. The experimental method was applied for the determination of ultralow oxygen and nitrogen (the content was less than 0.002 0%) in high-cobalt cast superalloy samples. The measured results were basically consistent with the results obtained by other companies according to ASTM E 1019-18. The range of six measurements was not more than 0.000 3%, and the standard deviation (SD, n=6) was 0.000 1%.
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