Strict Control of Sulfur Content and Sulfide Morphology: Maintain the sulfur content in castings below 0.03% and prevent the formation of Type Ⅱ sulfides. In steel castings, sulfides exist in three forms: Type Ⅰ (spherical, harmless), Type Ⅱ (distributed along grain boundaries in a discontinuous pattern, highly crack-inducing), and Type Ⅲ (strip-shaped, low risk). Adjusting the manganese-sulfur ratio (Mn/S) helps form spherical Type Ⅰ sulfides, minimizing Type Ⅱ sulfides.

Restricting the Synergistic Effect of Sulfur and Phosphorus: For carbon steel castings, ensure S + P ≤ 0.07%. Phosphorus significantly reduces the high-temperature plasticity of steel, and its combination with sulfur amplifies hot cracking risks, requiring simultaneous control of both elements.

Controlling Residual Aluminum Content: When using aluminum for deoxidation, keep residual aluminum (Al_residual) ≤ 0.1%. Excessive residual aluminum leads to the formation of Al₂S₃ or AlN, resulting in a "rock-like" fracture in the steel and drastically reducing the hot cracking resistance of castings.

Grain Refinement to Enhance Crack Resistance: Add rare earth + calcium-silicon composite inoculants to the molten steel. This not only achieves deoxidation and desulfurization but also refines grains through heterogeneous nucleation. Tests on NiCrMoV steel show that molten steel treated with rare earth + calcium-silicon exhibits over twice the crack resistance compared to untreated steel, as refined grains disperse shrinkage stress and reduce intergranular cracking.

Lowering Pouring Temperature: Minimize the pouring temperature of molten steel while ensuring complete filling of the casting. For carbon steel with 0.19% carbon content, the hot cracking resistance at 1550°C is nearly double that at 1600°C. Excessively high pouring temperatures prolong solidification time, increase the casting’s residence time in the high-temperature brittle zone, and widen the temperature difference between the casting and the mold, raising shrinkage stress.

Increasing Pouring Speed for Thin-Walled Castings: For thin-walled castings (e.g., a 125kg steel casting with a 15mm wall thickness), a higher pouring speed is necessary to avoid cracks caused by excessive temperature gradients during solidification. Tests show no hot cracking occurs when the pouring time is controlled at 14 seconds, while obvious cracks appear when extended to 40 seconds.

Installing Crack-Preventing Ribs: Add crack-preventing ribs at areas prone to cracking (e.g., wall thickness transitions, corners). These ribs redirect and disperse stress, serving as a direct and effective method to prevent hot cracking.

Timely Mold Opening: Open the sand mold promptly after the casting solidifies to release constraints on the casting, reducing internal stress caused by restricted shrinkage and lowering hot cracking risks.

Improving Resin’s High-Temperature Performance: Reduce resin dosage or modify furan resin to maintain thermoplasticity at high temperatures, minimizing coking (coking makes the mold hard and brittle with no cushioning). This ensures the mold provides sufficient "space" for casting shrinkage.

Enhancing Mold Cushioning: Add additives like wood flour or foam beads to furan resin sand, or place plastic cushion blocks at areas where casting shrinkage is most restricted to improve the mold’s compressibility at high temperatures. Use hollow sand cores to reduce the thickness of sand cores (molds), lessening mold constraints on the casting. For example, hot cracking in a certain type of valve casting was completely eliminated simply by reducing core sand thickness and improving core frame connections.

Avoiding Sulfur Penetration-Induced Microcracks: Use phosphoric acid curing agents instead of sulfonic acid-based ones. Sulfonic acid-based curing agents easily cause sulfur penetration on the casting surface, forming microcracks (crack initiation points), while phosphoric acid curing agents effectively prevent sulfur penetration. Additionally, use sulfur-proof coatings on the mold surface to block sulfur infiltration into the casting.

Selecting Low-Expansion Molding Materials: Replace quartz sand (which has a high volume expansion rate at high temperatures and easily exerts compressive stress on the casting) with low-expansion materials such as chromite sand to reduce mold expansion constraints on the casting.

Using Chilling Measures Appropriately: Place chillers or adopt other chilling methods at crack-prone areas to adjust the casting’s solidification sequence, avoiding concentrated stress from slow solidification in local regions.

Enlarge Corner Fillets: Avoid sharp corners (which easily cause stress concentration and are high-risk areas for hot cracking). Change right angles or small fillets to fillets with R ≥ 3mm.

Optimize Wall Thickness Transitions: Avoid sudden wall thickness changes (e.g., "step-like" transitions from thick to thin walls). Adopt "gradual" transition structures to reduce uneven solidification rates caused by thickness differences and lower stress concentration.