Steel structure: macroanalysis of chemical heterogeneity

Steel structure: macroanalysis

To determine the chemical heterogeneity of rolled or forged become macroslice cut longitudinally.

Bauman's method: gray print

The sulfur distribution is determined by the Bauman method. For this photographic (bromide silver) paper is moistened in the light or kept for 5-10 minutes in 5 %-a solution of sulfuric acid and lightly dry between sheets of filter paper to remove excess solution.

Then photo paper is placed on the prepared macrosection and carefully, preventing it from shifting, iron by hand or with a rubber roller to remove air bubbles remaining between the paper and the macrosection. Remaining bubbles can leave white spots and mask test results. Photo paper is kept on a macrosection for 2-3 minutes.

Sulfur inclusions (FeS, MnS), available in the surface areas of the metal, react with sulfuric acid, remaining on photo paper by the following reaction:

MnS(FeS) + H2SO4 → H2S + MnSO4 (FeSO4).

The resulting hydrogen sulfide directly opposite the foci of its release affects the crystals of silver bromide of the photoemulsion:

H2S + 2 Ag2S + 2 HBr.

Dark areas of silver sulfide, formed on photographic paper, show the shape and distribution of sulfides.

The photographic paper removed from the macrosection is washed under running water, fix for 20-30 minutes in hyposulfite solution, then washed for about 10 minutes in water and dry.

If steel and cast iron contains an increased amount phosphorus, then, with significant liquation in some areas, it will also participate in the reaction with silver bromide to form dark-colored silver phosphides.

Elimination of carbon and phosphorus in steel

The same reagent is used to determine the segregation of carbon and phosphorus., as for detecting continuity violations: 85 g of copper chloride and 53 g of ammonium chloride per 1000 ml of water.

The method for determining the segregation of phosphorus and carbon is based on the unequal etching of areas with different contents of these elements.. Plots, enriched with carbon and phosphorus, colored in a darker color. The best results are obtained for steels with a carbon content of up to 0,6 %. In steels with a higher carbon content, copper sludge, pickling, poorly washed off from the surface of the thin section.

Source: Metallurgy and heat treatment of steel