The market requires lower and lower carbon/sulfur content in steel, for low carbon sulfur steel like silicon steel, extra-deep drawing auto sheet, and gas pipeline steel, during the refining process, carbon sulfur content in steel sample reaches to around 0.001%. Since when the content is closed to baseline value, the baseline value will affect testing limit, also affect analyzing precision and accuracy. Therefore, it is necessary to decrease baseline value, and carbon sulfur crucible pretreatment is an important way.

In the current experiment, four different pretreatment methods are applied to carbon sulfur crucibles, and then implement carbon/sulfur content test.

Method A: without pretreatment, test directly

Method B: burn for 2 hours at 1100℃, and get it cooled in drier, then test.

Method C: burn once in high frequency furnace, get cooled, and then test.

Method D: burn the carbon sulfur crucible in oxygen flow at 1350℃ and then test

Testing instrument and material

1.LECO infrared carbon sulfur analyzer

2.Carrier oxygen: 99.995% oxygen, produced by Air Products

3.Ceramic crucible: carbon sulfur crucible（ф25×25mm）, produced by CS Ceramic Co.,Ltd

4.Tungsten flux: 40 mesh, roast the tungsten particles for 2 hours in oven at 300±10℃. produced by CS Ceramic Co.,Ltd

Test Result

Analysis and Discussion

1.By comparing the test result of 4 methods, it’s found that pretreatment affects sulfur content slightly, while has a larger effect to carbon content. In method A, carbon content is 20-30ppm, while in method B, it’s 10-20ppm, for both method C and D, carbon content is smaller than 10ppm, and average value of carbon sulfur content is less than 5ppm, which conforms to standard of YB/T 4145-2006 and available as dedicated carbon sulfur crucible.

2.During sintering fabrication, packing and transportation process, some salt like carbonate or sulphate may remain in the surface of crucibles, which may cause high carbon/sulfur content of direct test.

3.In Method B, carbon content is still 10-20ppm after burning at 1100℃, it means that the burning temperature maybe not high enough and some residuum still not removed.

Conclusion

Pretreatment method C and D are recommend, for super low carbon sulfur content test, to ensure testing precision and accuracy, carbon sulfur crucible for test should be burned in high frequency furnace or in oxygen at 1350℃.