Thermal fatigue in H13 steel extrusion dies leads to a situation called thermal checking. It is characterized by a network of surface cracks. This phenomenon is primarily caused by cyclic thermal stress. However, several management strategies are deployed to counter it. Strategies include advanced heat treatments, precise die designing, and targeted surface engineering.
Designing Process of Die Geometries
- Integrated Cooling Channels: Modern dies are constructed using the Additive Manufacturing process. This helps to integrate conformal cooling channels within the complex geometry of the dies. This ensures that the temperature is distributed evenly. It will eventually minimize the extreme gradients that can cause fatigue.
- Avoiding Sharp Radii: While creating the die profile, sharp radii are avoided as these may act as trigger points to initiate thermal checking.
- Distance between Cooling Channels and the Die Surface: Industrial examples indicate that the distance between the wall of the die and the cooling channels is an important factor that can affect its life during cyclic thermal stress. Research shows that even a 1 mm wall thickness can offer a significant balance between heat transfer and the dimensional integrity of the die.
Applying Advanced Heat Treatment
- Pre-Tempering of the Steel: Manufacturing experts indicate that employing a pre-tempering stage before the final tempering phase can have a significant impact on balancing tensile strength and impact toughness. Generally, pre-tempering at 640 degrees for 10 minutes can achieve the intended results.
- Preferring Direct Tempering: Practical situations exhibit that direct tempering of H13 of as-built parts can be a better choice compared to the traditional quenching and tempering process. This is because the steel exhibits a higher tempering resistance. It also has a finer microstructure.
- Hardening Process: The temperature varies between 525° C and 600° C. This helps to obtain an optimal hardness level of 45-52 HRC. Application of this process has shown to resist thermal softening during the extrusion process.
Applying Material Quality Enhancements
- Correct Alloying Elements: The thermal conductivity can be enhanced easily. It needs the incorporation of more Molybdenum into the alloy. The element can facilitate better heat dissipation.
- Right Refining Processes: Processes like ESR or VAR are usually used. These help improve homogeneity. They also reduce the concentration of non-metallic inclusions. Material science indicates that the non-metallic inclusions serve as primary sites for thermal crack initiation.
Surface Engineering Applications
- Fine Particle Peening: By applying FPP, manufacturers can introduce high levels of CRS (Compressive Residual Stress) deeper within the sub-surface, thereby causing a marked improvement in fatigue life.
- Nitriding with Gas and Plasma: Gas nitriding after the FPP process can further increase surface hardness. It can reinforce the Compressive Residual Stress. These processes delay surface crack initiation.
- Applying Laser Surface Treatments: The Laser Surface Melting process includes the application of rapid heating and cooling within the surface microstructure, resulting in a harder bionic surface layer that prevents propagation of surface cracks. In addition, manufacturers may also apply laser cladding, whereby Fe-based coatings are applied to repair damaged dies and provide high fatigue resistance.
Summing Up
In view of the above conditions, you need to find the best H13 steel supplier like TGKSSL. Check out the service website of your preferred supplier to find out whether the h13 available for you has been sufficiently prepared to handle thermal stress.