Sulfur printing is a method of displaying sulfur segregation on a sample using photographic paper.
The principle is that sulfuric acid on the paper reacts with sulfides (FeS, MnS) on the sample to generate hydrogen sulfide gas, which then reacts with silver bromide on the paper to generate silver sulfide precipitates at corresponding positions on the paper, forming black or brown spots.
The reaction formula is FeS+H2SO4 → FeSO4+H2S ↑ MnS+H2SO4 → MnSO4+H2S ↑ H2S+2AgBr → Ag2S ↓+2HBr. Longitudinal or transverse specimens can be taken from the die casting aluminum billet, and the smoothness of the test surface processing should not be less than ▽ 6. Use silver bromide glossy paper with high contrast. Soak the paper of the same size as the sample in dilute sulfuric acid for 1-2 minutes before removing it. Then, align the paper with the inspection surface and gently cover it. Remove the bubbles between the sample and the paper and allow it to come into contact for 2-5 minutes. Rinse the paper in flowing water, then fix and dry it to complete a sulfur print. The sulfur imprinting test can display the distribution of cracks, segregation lines, macrostructures, and inclusions in steel ingots and continuous permanent mold casting billets.
Link to this article：Principle and Method of Sulfur Stamp Inspection for Continuous Casting Billets
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