HARDOX 400 is a high-performance wear-resistant steel plate produced by Swedish Steel Olympus Co., Ltd., with a hardness range of HAW370-430. It is manufactured through high-pressure water jet quenching and tempering, offering excellent wear resistance, cold formability, and weldability. This material is widely used in heavy machinery such as crushers, excavator buckets, loaders, and scraper conveyors. In recent years, its popularity has grown significantly in the domestic market due to its superior properties.
**1. Welding Analysis of HARDOX 400 Steel Plate**
The thickness of HARDOX 400 typically ranges from 3mm to 130mm, and its chemical composition and carbon equivalent vary depending on the thickness. Table 1 shows the chemical composition, while Table 2 provides the carbon equivalent values. As the thickness increases, so does the carbon equivalent, which leads to a higher tendency for hardening and an increased risk of cold cracking during welding. Therefore, it's essential to control heat input carefully and implement preheating and post-weld heat treatment to reduce hydrogen content and minimize residual stress.
**2. Development of HARDOX 400 Welding Process**
Due to its high strength, it's recommended to use low-strength welding materials. For plates thicker than 40mm, preheating before welding and post-weld heat treatment are necessary. The following process plan was developed:
- **Welding Method:** 20% Argon + 80% COâ‚‚ gas shielded welding was selected for its stability and efficiency.
- **Welding Material:** ER70S-6 wire with a diameter of φ 1.2mm was chosen for its good weldability and lower tensile strength compared to the base metal.
- **Preheating:** Preheating temperature should be between 100°C and 150°C, with at least 5 minutes per millimeter of thickness and a total heating time of at least 1 hour.
- **Heat Input:** The maximum allowable heat input depends on the plate thickness, as shown in the figure. Keeping heat input within this limit ensures good toughness and maintains the original hardness in the heat-affected zone.
- **Welding Parameters:** For a 40mm thick plate, the first layer uses current between 180–220A and voltage between 19–22V, while subsequent layers use 240–300A and 23–30V. The welding speed remains consistent at 200–300 mm/min.
**3. Practical Application**
In a recent project involving Metso Reclaimer and Reclaimer equipment, all bucket structures were made from 40mm thick HARDOX 400 steel. These buckets require high wear resistance, so the welds must maintain sufficient hardness. The welding process included 20% Ar + 80% CO₂ gas shielded welding with ER70S-6 (Jinda JQ.MG50-6) wire. Preheating to 100–150°C and slow cooling after welding ensured high-quality welds. The final product met all performance requirements, and both the customer and Metso provided positive feedback.
**4. Conclusion**
HARDOX 400 is well-regarded in both international and domestic industries for its exceptional wear resistance. Its welding performance has been extensively studied and optimized, making it a reliable choice for demanding applications. By selecting appropriate welding materials and parameters, and implementing suitable preheating and post-weld treatments based on plate thickness, it is possible to achieve strong, durable, and high-quality welded joints. This makes HARDOX 400 an ideal material for heavy-duty industrial equipment.
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