Direct-reading spectral analysis of pig iron and cast steel samples requires that the surface carbon of the sample exists in the state of carbides, and no free graphite is available, that is, the analysis surface of cast iron must be completely white. When free carbon (gray iron) is present on the surface of cast iron, it will affect the analysis results, especially the carbon is as high as 3.8 to 4.0% and the silicon is as high as 2.0 to 3.6%. It is very difficult to "whiten" a sample of this composition. .
In order to achieve the goal of Baikou, Xiaobian organized the following methods for everyone:
1. Increase the temperature of the casting sample and increase the supercooling of the molten iron. This can avoid and reduce the inclusions as the graphite core, thereby increasing the degree of whitening. The pouring temperature is required to be above 1400 degrees Celsius.
2. Increasing the cooling rate of the casting sample block, improving the cooling conditions of the as-cast test block, reducing the thickness of the test block, and increasing the cooling area of the test block are effective methods to promote the whitening of the sample. The rapid cooling of as-cast hot metal makes it too late or very little to precipitate free graphite. Generally, the copper mold casting method is better.
3. Add anti-graphitizing element to the molten iron. The precipitation of graphite carbon in molten iron is closely related to its chemical composition. The addition of anti-graphitization elements can inhibit the formation of graphite cores and promote the whitening of test blocks. The elements that promote graphitization are: Al, C, Si, Ti, Ni, Cu, P, CO, Zr; the elements that prevent graphitization are: Nb, W, Mo, S, Cr, V, Te, Mg, CO, B. When casting into a sample, the whitening effect of the sample containing chromium and tellurium is good, but the higher amount of chromium affects the analysis of chromium in the matrix and iron; and the addition of 0.07% tellurium powder can make the sample completely white. And the tellurium spectrum line does not interfere with other elements, which is ideal.