Stainless Steel Casting Analysis Shows
Stainless Steel Casting The hemp spot also has called the Hemp spot, the hemp Pit, the oxidation hemp spot and so on, is one of common surface defects of the stainless steel melt die castings.
In general, Stainless Steel Casting this defect cannot be repaired and can only be scrapped. Not only improve the production costs, but also affect the normal production schedule and delivery. Therefore, how to reduce and eliminate the defect of castings and pitting is one of the main tasks of foundry workers.
The hemp spot usually appears on the stainless steel castings containing WCR and Wni. There are many round shallow pits on the surface of the castings, Stainless Steel Casting the diameter of pits is 0.3.0mm, Pit depth 0.3.5mm.
According to the relevant information, the castings before the cleaning, pits filled with slag material. The analysis of petrographic facies shows that there are some chemical substances such as ferric silicate, manganese silicate and chromium silicate in the slag in the defect. Stainless Steel Casting The results of electron diffraction show that the black pitting is composed of magnetite ($literal) and iron-chromium spinel (Feo Cr2o3). The results of spectral analysis showed that the content of silicon in the defect was increased, but the manganese content was very low.
In electron diffraction and spectral analysis, it can be seen that the pitting is mainly caused by the chemical reaction of oxide in the metal oxide and the shell material. Stainless Steel Casting In particular, the type of shell surface refractory selection, or into the plant's shell surface refractory materials do not meet the quality requirements, or the type of shell after the failure of the management of refractory materials such as the reasons, after pouring more easily on the surface of a batch of castings to produce different degrees of pitting defects. The main reasons for this are as follows:
(1) Too much oxide in the metal liquid is Shan in the burden. The use of induction furnace smelting, the burden of corrosion more, heavier, or the use of recycled material in a larger proportion, the number of reuse, will increase the metal liquid oxide. Shan Metal Liquid is not fully deoxidation. Stainless Steel Casting The choice of deoxidation agent is to achieve the aim of not only reducing the metal liquid sufficiently, but also reducing the oxide melting point which is formed after deoxidation, which is easy to assemble and float. The addition of deoxidation agent is less, which affects the deoxidation effect, so that the residual oxides in the metal liquid are too much. Shan smelting process improper or improper operation, the metal liquid oxide does not remove the clean and so on; During the melting process, the metal liquid surface is exposed for a long time, which increases the chance of oxidation of the alloying elements. After deoxidation, the static time of the power outage is short, Stainless Steel Casting the oxides in the molten metal are not in time and completely buoyant, the final deoxidation is not sufficient, and the casting process produces two times of oxidation.
(2) The oxide in the shell surface layer material according to the related data, Stainless Steel Casting because the zirconium sand has the good thermal conductivity, the thermal storage capacity, the fire resistance high advantage, in the production of stainless steel melt die Castings, the use of zirconium sand as shell surface refractories. The fire resistance of pure ZrSiO4 is more than 2000 Shan, but with the increase of impurity content, the degree of fire resistance decreases correspondingly. When the zirconium sand contains CA, Stainless Steel Casting mg oxide impurities decomposition temperature will drop to 1300 Shan, when containing K, Na oxide, the decomposition temperature will drop to 900 Shan or so. Zircon sand is the only compound in the Zro Sio2 two-element system, Stainless Steel Casting and the amorphous SiO2 with high activity when decomposed, can react with the alloy elements such as CR, Ni, Ti, MN and AL in the metal at high temperature, which causes the surface of the castings to produce pitting.
such as a casting factory production of stainless steel castings, the original shell layer material selection quartz sand/powder, serious castings of the defects accounted for about 80%. After the replacement of zircon sand/powder (no incoming inspection) and ethyl silicate hydrolysate as binder, Stainless Steel Casting the defect of the castings was reduced, but still about 50%. When taking incoming inspection and controlling the oxides in zircon sand/powder, the defects of the castings are not only significantly less, but also the degree of pitting defects is obviously reduced.
(3) The shell baking quality related to the full roasting can remove water from the shell, residue wax, saponification, organic matter and volatile, Stainless Steel Casting and the residual ammonium chloride hardening liquid and sodium salt in the shell. If these substances are left in the shell, the molten metal is produced two times in the pouring process, producing a large amount of gas or new oxides, which react chemically to the oxides in the shell and easily produce pitting defects on the surface of the castings.