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# Mold Thermal Fatigue Crack Generation Mechanism & Prevention Strategy Thermal fatigue crack is the main long-term failure mode for hot work molds. Alternatin

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  • Release time: 2026-09-29

Mold Thermal Fatigue Crack Generation Mechanism & Prevention Strategy

Thermal fatigue crack is the main long-term failure mode for hot work molds. Alternating rapid heating and cooling generates cyclic thermal stress, initiating microcracks and expanding into macro cracks. This article describes crack evolution and mold design, material and process prevention methods.

Thermal stress forms when mold surface expands upon contacting hot aluminum melt and contracts rapidly during cooling. Repeated tension-compression cycles create microcracks starting from stress concentration points.

High risk locations: sharp corners, fillets below R2.8, vent edges, parting lines and cooling holes near cavity surface.

H13 material purity matters: ESR electroslag remelted H13 reduces non-metallic inclusions, slowing crack initiation by 26% compared with conventional forged H13.

Heat treatment specification: HRC44–48 for thermal fatigue resistance. Hardness above HRC49 sacrifices toughness and accelerates crack propagation.

Fillet optimization: all sharp transitions must be modified to R≥3.0. Fillet radius R3.2 is recommended for high cyclic load molds.

Cooling channel distance from cavity ≥12 mm. Too close cooling channels create steep temperature gradient and increase thermal stress.

Cryogenic treatment after quenching reduces retained austenite, stabilizes mold dimension and improves thermal fatigue resistance by 32%.

Mold preheating must reach 280℃ and above. Cold mold starting produces extreme thermal shock and rapidly generates microcracks in early casting cycles.

Nitriding layer over 0.12 mm is brittle. Thick nitriding layer easily develops network microcracks under thermal cycling.

Once micro thermal cracks appear, timely local welding repair and post-weld tempering can stop crack expansion. Delayed repair leads to large crack and mold scrap.

FAQ

Q1: Where do thermal fatigue cracks usually start on casting molds? A1: Sharp corners, small fillets, vent edges and parting lines with high stress concentration. Q2: How to improve thermal fatigue resistance of H13 mold steel? A2: Use ESR H13, proper heat treatment hardness HRC44–48 and cryogenic treatment. Q3: Why over-thick nitriding layer accelerates thermal crack? A3: Over-thick nitriding layer has high brittleness and easily generates network microcracks under thermal cycles.

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