فولاذ الأدوات H13 is the most widely used steel among hot-work die steels, serving as a benchmark in this category. Therefore, the failure of H13 steel is a topic worthy of thorough discussion. Drawing upon our company’s over 20 years of industry experience and the latest international research findings, this article summarizes common factors contributing to H13 steel failure.
1. Failure of H13 steel caused by heat treatment
Improper heat treatment is a significant factor contributing to the failure of the H13 steel mold.
1.1 H13 Steel Failure Caused by Normalizing Treatment
Normalizing treatment is generally not recommended for H13 steel, as it increases the risk of cracking, particularly when the furnace atmosphere is uncontrolled and causes surface decarburization. Although specific methods exist for normalizing H13 steel, the risk of cracking remains.
1.2 H13 Steel Failure During Quenching
If cracking occurs in H13 material during oil إخماد, it may result from improper mold design or inadequate control during the quenching process.
For H13 hot extrusion dies with complex geometries—such as sharp corners, excessive thickness variations, or abrupt cross-sectional changes—rapid cooling during quenching causes uneven contraction across different sections. This generates significant internal stresses, which concentrate at vulnerable points and lead to cracking.
H13 material has a relatively high carbon content, resulting in greater hardness. Using water as a quenching medium can cause excessive cooling rates, leading to cracking. Therefore, oil with a relatively gentle cooling rate should be selected as the quenching medium. During quenching, cracking may still occur if the H13 material enters the oil at too high a temperature, the oil temperature is too low, or the cooling time in the oil is insufficient—all of which can cause cooling rates to be too rapid or uneven.
On the other hand, as a hot-work tool steel, H13 must also avoid excessively slow cooling during quenching, as this promotes bainite formation and carbide precipitation at grain boundaries—both factors contributing to embrittlement.
Failure to promptly temper H13 material after quenching can also cause cracking. H13 steel should be removed from the quench cycle while still warm (approx. 66–93°C or 150–200°F for water/oil-hardened, or no colder than 66°C or 150°F for air-hardening) and tempered immediately to minimize quench cracking.
There are two methods to determine whether cracks actually occurred during quenching. One is to observe the crack morphology; quenching-induced cracks exhibit intergranular fracture. The other method involves inspecting whether the inner surface of the crack contains scale. If scale is found on the inner surface of the crack during the subsequent tempering process, it confirms that the crack formed during quenching before tempering, rather than during tempering itself.
1.3 H13 Steel Failure During Tempering
During the tempering process of H13 material, improper control of tempering temperature and time can lead to failure. If the tempering temperature is too low, alloy carbides in the steel—such as those of Cr, Mo, and V—cannot precipitate sufficiently and uniformly. This results in excessively high hardness and reduced toughness. This also impairs the secondary hardening effect of H13, diminishing the heat resistance of H13 molds. Conversely, excessively high tempering temperatures or prolonged holding times can cause coarse grain growth, embrittlement at grain boundaries, and increased residual austenite, thereby reducing the toughness of H13. Some studies suggest that grain boundary embrittlement may be linked to phosphorus segregation1.
If you want to learn more about the heat treatment of H13 steel, please refer to the H13 tool steel heat treatment guide.
2. Design flaws in the H13 mold
Design flaws are a common cause of failure. H13 dies can fail due to high stresses induced by sharp changes in section thickness, inadequate material left between threaded holes and inner surfaces, or stress concentrations from deep identification stamp marks.
3. Hydrogen embrittlement
H13 steel is particularly susceptible to hydrogen embrittlement. Hydrogen embrittlement is noticeable at low strain rates and ambient temperatures, and is characterized by a delayed nature of failure. It reduces ductility and causes premature failure under static loads. Hydrogen migrates to regions of triaxial tensile stress (e.g., crack tips) and can reduce the cohesive forces between atoms. It can also enhance localized plasticity (HELP mechanism). Hydrogen can be introduced during pickling, electroplating, corrosion, and welding.
In conclusion, H13 steel failures stem from a complex interplay of inherent material properties, deficiencies in heat treatment, and processing defects.
- روبرتس، جي، وكراوس، جي، وكينيدي، ر. (1998). فولاذ الأدوات (5th ed.), p. 331. ASM International. ↩︎
