Machining overheated materials is not recommended. Due to irreversible damage such as grain boundary oxidation, voids, or localized melting, the material is extremely brittle and prone to fracture, chipping, or tool damage during machining. Machining accuracy and safety cannot be guaranteed.
1. Extremely High Machining Risks
High Risk of Fracture: Overheated materials almost completely lose intergranular bonding, and cutting stress directly triggers intergranular fracture, causing the workpiece to suddenly crack during machining.
Severe Tool Damage: Uneven hardness within the material (coexistence of localized softening and hard oxides) accelerates tool wear and can even cause tool tip chipping.
Uncontrolled Machining Accuracy: Uneven microstructure leads to unstable cutting performance, making it difficult to guarantee dimensional accuracy and surface quality.
Real-world Case: Overheated H13 steel exhibited "stone-like fracture" fracture during milling, resulting in the scrapping of an entire batch of molds.
2. No repair value, should be scrapped directly.
Performance cannot be restored through machining: Machining only changes the shape and cannot eliminate internal grain boundary damage; the part will still fail rapidly during service.
Safety hazards exist: Even if it is forcibly machined, its fatigue life and load-bearing capacity are extremely low, and it may suddenly break during use, causing equipment damage or safety accidents.
Poor economic efficiency: Machining costs are high, but the finished product has no practical value, constituting a waste of investment.
Correct practice: Once overheating is confirmed, it should be scrapped immediately, and the cause of the temperature control abnormality should be traced to prevent recurrence.
3. Recommended alternatives:
Replace with new parts: Remanufacture using materials resistant to grain growth (such as H13+Ti, PM-H13);
Optimize process control: Strictly limit heating temperature (H13 steel ≤ 600°C), regularly calibrate thermocouples to avoid overheating risks;
Incoming inspection: Conduct metallographic sampling inspection on newly purchased materials to ensure there are no original defects.
Prevention tips: Establishing a hot runner temperature monitoring record and conducting metallographic sampling inspections every 6 months can effectively avoid the risk of overheating.
