What is the cause of pitting on the surface of carbon steel precision casting castings?
(1) Metal oxide inclusions caused by poor deoxidation of molten steel;
(2) The conditions for complete deoxidation are as follows: select a dry and clean charge, first add ferromanganese, then ferrosilicon for deoxidation, then add silicon calcium for deoxidation, then cut off the power for 2 minutes, then add aluminum for deoxidation, and then heat preservation and pouring. Immediately after pouring, add sawdust or waste wax, cover the box, seal, and cool.
Carbon steel precision castingIn the case of incomplete deoxidation, if the box is sealed and cooled, due to the long cooling time, the large amount of oxygen in the molten steel has sufficient reaction time, and a large number of pits will inevitably be formed. In the case of complete deoxidation, the cooling of the cover box ensures that no outside oxygen is absorbed into the molten steel, thereby avoiding secondary oxidation of the molten steel and preventing the formation of pitting corrosion.
(1) When the shell is not fully baked, a small amount of gas will be generated at high temperature during pouring, which will promote the interface reaction and form pitting corrosion.
(2) The increase of impurities in refractory materials, especially the high content of Fe2O3, will directly cause it to participate in the interface reaction between the shell and molten steel, causing oxygen to enter the molten steel to cause secondary oxidation, thereby increasing the tendency of pitting corrosion.
Preventive measures for carbon steel precision casting.
(1). An important factor affecting pitting corrosion is the quality of molten steel; (that is, whether the deoxidation and scum are complete)
(1). The smelting process should be strictly followed. That is, bottom slag→cover during melting→pre-deoxidation after melting→slag removal after power failure→final deoxidation before pouring. The process is executed.
(2) The choice of deoxidizer should fully deoxidize molten steel so that the deoxidized oxide has a low melting point and is easy to aggregate and float. The amount of deoxidizer aluminum added must be strictly controlled, too much aluminum will promote the formation of pitting corrosion ③. The steel should be very clean, do not use too much recycled material to increase the primary inclusions in the steel. During the melting process, try to prevent the exposure time of the molten steel surface and prevent the oxidation of chromium, iron and silicon elements.
