For alloy steel castings, the pouring temperature is generally above 1380 ℃, at this temperature, the appearance will quickly thermal pyrolysis into gas and liquid, through two times decomposition, there will also be a large number of pyrolysis products cracking elemental carbon precipitation. However, because of the high carbon content of the cast iron itself, the surface of the cast iron does not appear as a carbon deficiency, but rather as a corrugated or diliu-shaped wrinkle.
When the metal liquid filling speed is higher than the vaporization rate of the pyrolysis products of alloy steel castings, the metal liquid flow front gathers a layer of liquid polystyrene, so that the surface metal which is contacted with it is excited to form a layer of hard skin. When this layer of hard skin is broken by the metal liquid in advance, it is pressed to both sides of the casting, forming a corrugated or Diliu wrinkle defect on the casting surface. After opening the box, it can be found that the surface of the wrinkle skin has carbon powder accumulation, which is the pyrolysis elemental carbon produced after two reactions of the pyrolysis product. When the density of the pattern is too high, the adhesive surface is too heavy, and the pouring filling is unstable, the carbon inclusion defects in the castings are more serious.