D2 tool steel is a popular and widely used material in the manufacturing industry due to its excellent hardness, wear resistance, and dimensional stability. To fully unlock its potential, proper heat treatment is essential.
In this blog post, we will explore the heat treatment process for D2 tool steel, along with its benefits and considerations.
What is D2 Tool Steel?
D2 steel, known for its high wear resistance, is a micro-deformation cold work die steel and wind hard tool steel. It has a carbon content of up to 1.5% and chromium content of up to 11.5%. One of its notable characteristics is its excellent processability, allowing for the production of cold work die steel with large cross-sections, complex shapes, high impact force, and exceptional wear resistance.
D2 tool steel is a popular choice for various industrial applications, including cutting tools, molds, and dies. Its name, represented by the “D” in D2, signifies its classification as a tool steel. This versatile steel is known by different names, such as SKD11 and Hitachi SLD, depending on regional standards and manufacturers.
D2 tool steel is often referred to as “semi-stainless steel” due to its chromium content of 12%. While it offers some level of corrosion resistance, it falls short of the protection provided by fully stainless steels like 416 stainless steel or 410 stainless steel, which contain higher levels of chromium. However, D2 tool steel surpasses other tough steels like O1 tool steel in terms of corrosion resistance.
The high carbon content in D2 tool steel, typically around 1.5%, contributes to its excellent wear resistance and hardness. This makes it well-suited for applications that require resistance to abrasive wear, such as cutting, shearing, and forming tools. The high chromium content further enhances its wear resistance and provides good dimensional stability, allowing for precise and reliable performance.
In addition to its wear resistance, D2 tool steel exhibits high toughness, enabling it to withstand impact and shock loads. This combination of hardness and toughness makes it suitable for demanding applications where both strength and durability are essential.
Examples of applications include silicon steel sheet dies, cold cut scissors, and trimming dies. Additionally, D2 steel exhibits stable heat treatment size, ensuring consistent performance.
Heat Treatment Guidelines
To achieve optimal performance and properties in D2 steel, a specific heat treatment process is recommended. Here are the general steps:
- Rough the workpiece and heat it to a temperature of 600-650°C for 2 hours.
- Cool the workpiece to 500°C using the furnace, followed by gradual cooling.
- Hardness specifications: In the annealed state, the hardness should be ≤255HB with an indentation diameter ≥3.8mm. After quenching, the hardness should be ≥59HRC.
It is essential to promptly temper the quenched steel to prevent cracking and surface decarburization. Cryogenic treatment (-70°C) is recommended for gauges and high-precision molds to minimize deformation. The workpiece should be subjected to high-temperature tempering at 500-560°C, resulting in a hardness greater than 58HRC.
Heat Treatment Specifications
- Quenching: Preheat at 820±15°C, then heat at 1000±6°C (salt bath) or 1010±6°C (furnace controlled atmosphere) for 10-20 minutes.
- Air cool the quenched steel.
- Tempering: Perform tempering at 200±6°C to achieve the desired hardness and properties.
Annealing of D2 Tool Steel
The first step in the heat treatment of D2 tool steel is annealing. This process involves heating the steel to a temperature of around 800-950°C and holding it at that temperature for a sufficient duration. The purpose of annealing is to relieve internal stresses, improve machinability, and refine the steel’s microstructure.
Hardening of D2 Tool Steel
After annealing, the next stage is hardening. D2 tool steel is typically hardened in a controlled atmosphere furnace or vacuum heat treatment furnace. The steel is heated to a temperature between 1000-1050°C and held at that temperature for a specific time to ensure uniform heating. Then, it is rapidly quenched in a suitable medium such as oil or air. This rapid cooling transforms the steel’s microstructure, resulting in high hardness and excellent wear resistance.
Tempering of D2 Tool Steel
Hardened D2 tool steel is extremely hard but also brittle. To improve its toughness and reduce brittleness, tempering is performed. The steel is reheated to a temperature between 150-500°C, depending on the desired hardness and toughness.
The tempering time and temperature must be carefully controlled to achieve the desired balance of hardness and toughness. Tempering not only enhances the steel’s mechanical properties but also relieves internal stresses induced during hardening.
Cryogenic Treatment (Optional) of D2 Tool Steel
For further enhancement of D2 tool steel’s performance, cryogenic treatment can be employed. This process involves subjecting the steel to ultra-low temperatures (-120 to -196°C) for an extended period. Cryogenic treatment helps refine the steel’s microstructure, improve dimensional stability, and increase wear resistance, resulting in longer tool life.
Surface Coating (Optional) of D2 Tool Steel
To enhance the performance and durability of D2 tool steel, surface coatings such as nitriding, TiN (Titanium Nitride), or DLC (Diamond-Like Carbon) can be applied. These coatings provide additional hardness, wear resistance, and reduced friction, prolonging the tool’s lifespan and improving its performance in demanding applications.
Conclusion
Proper heat treatment is crucial for maximizing the performance and durability of D2 tool steel. Through annealing, hardening, tempering, and optional processes like cryogenic treatment and surface coating, the steel can achieve exceptional hardness, wear resistance, toughness, and dimensional stability. Manufacturers and toolmakers can harness the full potential of D2 tool steel by carefully controlling the heat treatment process, leading to superior tools and components capable of withstanding the most demanding applications.
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