Can Overheated Materials Be Machined?

Machining of hot materials is not recommended. The material is very brittle and susceptible to fracture, chipping or tool damage during machining due to irreversible damages like grain boundary oxidation, voids or localised melting. Machining accuracy and safety can not be guaranteed.

1. Very High Risks of Machining

High risk of fracture . Overheated materials lose practically all intergranular bonding and the cutting force directly induces an intergranular fracture. This results in the rapid cracking of the workpiece during machining.

Severe Tool Damage: The non-uniform hardness of the material (localised softening and hard oxides) can cause increased tool wear and possibly chipping of the tool tip.

The non-uniform microstructure results in unstable cutting performance and uncontrollable machining precision, hence it is difficult to ensure the dimensional accuracy and surface quality.

Real Case: H13 steel was overheated and showed "stone-like fracture" fracture during milling, which led to scrapping a whole batch of moulds.

2. No repair value, should be directly discarded.

Machining does not improve performance because it simply alters the shape and cannot reduce internal grain boundary damage and the part will still break quickly during service.

Safety hazards: Even if it is machined forcibly, its fatigue life and load-bearing capacity are extremely low, and it may break suddenly during operation, causing equipment damage or safety mishaps.

Low economic efficiency: The machining cost is large and the end product has no practical utility, which is a waste of investment.

Correct practice: After confirming the overheating, the equipment should be discarded immediately, and the reason for the anomaly of temperature regulation should be found to avoid recurrence.

3. Alternative suggestions:

Replace with new parts: Remanufacture with grain growth resistant materials (H13+Ti, PM-H13);

Optimise process control: Heating temperature is strictly limited (H13 steel ≤ 600°C), thermocouple calibration is carried out routinely to reduce overheating concerns;

Incoming inspection: Conduct a sampling metallographic examination of newly obtained material to confirm the absence of an original flaw.

Prevention tips: Keeping a record of hot runner temperature monitoring and doing metallographic sample examination every 6 months can effectively avoid the risk of overheating.