Although the wet mold clay sand has good concession and refrigeration, crack defects still appear from time to time in the production of Wet Mold clay sand steel castings. The wet mold clay sand has high moisture content, rapid cooling of steel castings, complex part structure and large difference in cooling speed when there is a large difference in wall thickness. Therefore, it is easy to produce large casting stress at the transition parts and plane corners with large difference in wall thickness, exceeding the limit of material strength and producing crack defects. Crack defects are divided into hot crack, cold crack and heat treatment crack. The hot crack defect has a tortuous shape, mostly along the grain boundary, and the surface is oxidized black. The shape of cold crack defect is often linear without bifurcation. It often appears on the surface of steel castings. The crack surface is clean and free of oxidation. Heat treatment crack defects are often caused by uneven heat distribution during quenching, cutting pouring and riser and welding repair, and the metal surface at the crack is oxidized.
Crack defects generally need to be repaired by welding. When the carbon content of steel castings is high and the welding performance is poor, the welding repair rate is also very high, which seriously affects the quality of steel castings and has a large workload of welding repair. For hot crack defects, the pouring and riser shall be reasonably set to make the steel castings shrink normally, avoid excessive difference in cooling speed of each part, appropriately increase the transition fillet radius of key connection parts, avoid unpacking and premature sand falling of steel castings, and control the content of forming elements (s, P) of low melting point phase in the alloy; For cold crack defects, the machining processes such as sand dropping, cleaning and cutting pouring riser shall be strictly controlled to avoid the cracking of steel castings caused by collision, extrusion and residual stress; For heat treatment crack defects, a reasonable heat treatment process shall be designed, and attention shall be paid to the thermal insulation treatment of the parts to be welded before and after repair welding.