Overheating causes a comprehensive and drastic decline in the performance of the workpiece. The core manifestations are that strength, toughness, fatigue life, and thermal stability approach zero due to permanent structural damage caused by grain boundary oxidation and localized melting.
1. Collapse of Mechanical Properties
Sharp Drop in Strength: Grain boundaries are isolated by oxides, interrupting the continuity of the metal, resulting in a decrease of over 70% in tensile and yield strength.
Loss of Toughness: The material becomes brittle, impact energy approaches zero, and it is prone to sudden, unannounced fractures during service.
Hardness Instability: Softened and hard phases coexist in the heat-affected zone, with fluctuations exceeding 20 HRC, exacerbating stress concentration.
Actual Data: After overheating, the average fracture toughness of H13 steel drops from 25 MPa·m¹/² to less than 5 MPa·m¹/².
2. Loss of Thermal and Structural Stability
Zero resistance to thermal fatigue: Crack initiation already exists; cracks propagate rapidly under thermal cycling, unable to withstand normal temperature changes.
Dimensional stability failure: Grain boundary voids and microcrack clusters cause localized deformation, affecting mold alignment and sealing.
Deterioration of thermal conductivity: Oxides hinder heat conduction, causing localized overheating and further accelerating failure.
Special Reminder: Overheated workpieces may crack upon initial heating and should not be put into production.
3. Dual Loss of Service Safety and Economy
|
Risk Dimension |
Manifestation |
|
Sudden Failure |
Spontaneous fracture without external load, threatening personnel and equipment safety. |
|
Production Interruption |
Replacement of workpieces leads to downtime of several hours, with losses reaching tens of thousands of yuan. |
|
Quality Control Loss |
Molded parts exhibit defects such as flash and insufficient material, resulting in a significant decrease in yield. |
Safety Principle: Once overheating is confirmed, the workpiece must be scrapped immediately; any form of unauthorized use is strictly prohibited.
