The necessity of quality inspection for large and medium-sized stainless steel castings:
In recent years, the rapid development of the casting industry has led to the problem of inconsistent product quality. However, if we manufacture a product and immediately sell it without considering its quality, the product quality is insufficient, and customers will feel uneasy using it. This principle also applies to large and medium-sized stainless steel castings. It's not necessary to investigate the reasons for substandard large and medium-sized stainless steel castings or complete the process during manufacturing; the goal should be to continuously improve overall application capabilities by enhancing product quality. Naturally, this involves continuously improving the advantages of the product's specific characteristics based on its application capabilities, with the overall application effect of the product as the target, so that the quality of large and medium-sized stainless steel castings, such as a top-level product, has excellent quality or testing capabilities, reflecting the advantages of the product's overall characteristics and making it competitive. So how exactly should we do this? To improve the quality inspection of large and medium-sized stainless steel castings, enterprises can increase the scope of product quality inspection during the implementation process, establish specific requirements for product quality inspection, and strengthen the processing standards of large and medium-sized stainless steel castings, etc.
Forging process of large and medium-sized stainless steel castings:
1. Due to the poor flowability of molten steel, the thickness of cast steel parts should not be less than 8mm to better avoid insufficient insulation and pouring. The gating system should be simple, with cross-sectional dimensions exceeding those of pig iron. Dry forging or hot forging should be used. The pouring temperature should be moderately increased, generally to 1520~1600℃. Due to the high pouring temperature, the hydrogen pressure of the molten steel is high, the liquid retention time is long, and the flowability is good. However, excessively high pouring temperatures can lead to defects such as coarse crystals, hot cracking, porosity, and inclusions. Therefore, the pouring temperature for small and medium-sized thick-walled complex castings is approximately 150℃ above the melting point of steel; the pouring temperature for large and medium-sized thick-walled pipe castings is about 100℃ higher than the melting point.
Second, because the shrinkage capacity of cast steel exceeds that of pig iron, in order to avoid shrinkage defects in the casting quality, risers, chills and other measures can be used in most forging processes to achieve solidification in a growth sequence.
Figure 3. To better avoid shrinkage porosity, shrinkage cavities, shrinkage cavities and cracks in cast steel parts, the thickness of cast steel parts should be uniform, and oblique angles and oblique structures should be avoided. Wood chips should be added to the molding sand, and coke should be added to the core. Hollow cores and oil cores should be used to produce sand molds or cores with compromise and occupancy.
Fourth, cast steel has a high melting point, and the pouring temperature is correspondingly high. At high temperatures, the interaction between the molten steel and the mold steel can easily cause inclusion defects. Therefore, the mold should be made of highly refractory synthetic silica sand, and the surface of the mold should be coated with a coating made of lime or zircon sand powder. In order to reduce the pneumatic valve and improve the flow of molten steel and the compressive strength of the mold, most cast steel parts are cast using dry or quick-drying molds, such as CO2 hardened water glass sand molds.
