For a long time, pitting is a big problem. The surface quality of castings in the casting blasting, sandblasting, casting surface will have black spots, pitting, cause a large number of scrap castings. Data showed that pitting is metal oxide inclusions in aggregates of the casting surface.


1. causes of formation

(1) the metal oxide inclusions brought by the deoxidation of molten steel;

(2) complete deoxidation condition is: the dry, clean charging, melting after first with ferrosilicon ferromanganese deoxidation, plus calcium deoxidation, then power static 2min, coupled with aluminum deoxidation after heat insulation casting. After pouring immediately added sawdust or waste wax and then cover the seal cooling box.

A. in unkilled, if the cover box seal for cooling, cooling time, exist in the liquid steel in the reaction time full of oxygen, the formation of a large number of pitting is inevitable. While in the deoxidation, cover box cooling ensures no foreign oxygen is adsorbed into the liquid steel, avoid two oxidation of molten steel, to prevent pock formation. 

(1). Shell through high temperature roasting, the shell when pouring under a small amount of gas generated?, which will promote the interface reaction and the formation of pits.

(2). The increase of impurities in refractory material, especially the high content of Fe2O3, will lead directly to the interface reaction involved in shell and liquid steel, the oxygen in molten steel by two oxidation, thus increasing the formation of pitting tendency.


2. prevention measures

(1). The main factors affecting the pitting produced, is the quality of molten steel; (i.e. deoxidation and dross are completely)

(2). Operation should strictly follow the melting process. According to the bottom ash melting to cover pad melting after pre deoxidation, static electricity slag removal, before pouring the final deoxidation process is carried out. 

(3). The deoxidizing agent should be selected. In order to make steel liquid deoxidation full and can form the melting point, after deoxidation oxide is low, easy to gather and floating. The amount of Al final deoxidizer must be strictly controlled, the excess aluminum will cause pitting. The steel material should be very clean, and do not use too much and returns the primary inclusions of the steel increased, the melting process should try to avoid the time, the liquid steel surface exposed to prevent Cr, Fe, oxidation of Si elements. 


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2017年08月24日

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Causes of precision casting carbon steel surface pitting and prevention measures

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