Key Technologies and Applications of High-Chromium Cast Iron Casting

High-Chromium Cast Iron Casting Properties
High-chromium cast iron has low thermal conductivity, poor plasticity, and large shrinkage, along with a significant tendency to hot and cold cracking. During the casting process, the characteristics of both cast steel and cast iron must be considered comprehensively, with particular attention paid to shrinkage feeding of the casting, following the same principles as for steel castings (i.e., using risers and chills, and adhering to the principle of sequential solidification). Although the high chromium content in the alloy can cause filming on the molten iron surface, thus affecting its fluidity, its fluidity is actually relatively good.
Casting Quality Control Measures
 
Sand Mold and Coating Selection
To ensure casting quality, high-strength and air-permeable sand molds and refractory coatings, such as water glass silica sand, should be selected. Highly refractory coatings, such as a mixture of high-aluminum powder or magnesium powder and alcohol, should also be used.
 
Metal Mold Casting Methods
In addition, metal mold casting is also a commonly used and effective method for achieving a fine grain structure and good surface quality when the casting shape is not complex.
 
Shrinkage and Mold Design
Given that the shrinkage of high-chromium cast iron is similar to that of cast steel, estimate a linear shrinkage of 1.8% to 2% when creating the mold. For sand mold production, riser size can be calculated based on the specifications for carbon steel, while the gating system should be calculated based on the calculation method for gray cast iron, but with a 20% to 30% increase in cross-sectional area.
 
Riser Design
Because the risers of high-chromium castings are difficult to remove, side risers or easy-to-cut risers are recommended during molding.
 
Preventing Shrinkage Cracking
In the casting process design, avoid conditions where the casting shrinks in an obstructed manner to prevent cracking. Use slow cooling below 540°C to ensure that the casting is fully cooled in the mold before unpacking and sand removal.
 
Unpacking Temperature and Ambient Humidity
Control the unpacking temperature and maintain a dry environment to prevent moisture-induced cracking in the casting.
 
Controlling Pouring Temperature
Controlling pouring temperature is also critical. Lower pouring temperatures help refine dendrites and eutectic structures and avoid defects such as excessive shrinkage and surface sand adhesion caused by high temperatures. Typically, the pouring temperature is set approximately 55°C above its liquidus (1290 to 1350°C). For light and small parts, the temperature is controlled between 1380 and 1420°C, while for heavy parts with wall thickness exceeding 100mm, the temperature is controlled between 1350 and 1400°C.