HARDOX 400 is a high-performance wear-resistant steel plate, manufactured by Swedish Steel Olympus Co., Ltd., with a hardness range of HAW370-430. It is produced through high-pressure water jet quenching and tempering, which ensures excellent wear resistance, cold formability, and weldability. This steel is widely used in heavy machinery such as crushers, excavator buckets, loaders, and scraper conveyors. In recent years, it has gained significant popularity in the domestic market due to its outstanding mechanical properties.
**1. Welding Analysis of HARDOX 400 Steel Plate**
The thickness of HARDOX 400 steel plates typically ranges from 3 to 130 mm. As the thickness increases, both the chemical composition and carbon equivalent change accordingly, as shown in Table 1 and Table 2.
Table 1: Chemical Composition of HARDOX 400 Steel Plate
Table 2: Carbon Equivalent of HARDOX 400 Steel Plate
According to the data in Table 2, as the thickness of the steel plate increases, the carbon equivalent also rises. This leads to a greater tendency for hardening, increased susceptibility to cold cracking, and reduced weldability. Due to this sensitivity, it's crucial to control the heat input during welding and implement preheating and post-weld heat treatment to allow hydrogen to escape and reduce residual stress.
**2. Development of the HARDOX 400 Welding Process**
Given the high strength of HARDOX 400, the welding process should follow the principle of low-strength matching. For plates thicker than 40 mm, preheating is required before welding, followed by post-heating. Heat input must be strictly controlled. The following steps are recommended:
(1) Use 20% Argon + 80% COâ‚‚ gas shielded welding.
(2) Select ER70S-6 welding wire with a diameter of φ 1.2 mm. This wire offers excellent weldability, strong resistance to cold cracks, and tensile strength slightly lower than the base material.
(3) Preheat the material to 100–150°C before welding, and maintain the same temperature after welding. Ensure that each millimeter of thickness is heated for at least 5 minutes, with a total heating time of at least 1 hour. The interpass temperature should be maintained between 150–175°C, as shown in Table 3.
Table 3: Preheating and Interpass Temperature
(4) Control the heat input carefully. Using a heat input below the specified limit helps achieve good toughness and maintains the original hardness in the heat-affected zone.
Maximum heat input allowed for different plate thicknesses
(5) Set appropriate welding parameters. For a 40 mm thick steel plate, the first layer of weld should be cleaned and polished, and root cleaning should be done using carbon arc gouging. Multi-layer, multi-pass welding is recommended, with the first pass using current of 180–220 A, voltage of 19–22 V, and speed of 200–300 mm/min. Subsequent passes use current of 240–300 A, voltage of 23–30 V, and speed of 200–300 mm/min.
**3. Practical Application**
In our company’s project involving Metso Reclaimer and Reclaimer systems, all bucket structures are made of 40 mm thick HARDOX 400 steel. These buckets require high wear resistance and therefore demand high-quality welds. To meet these requirements, we used 20% Ar + 80% CO₂ gas shielded welding with ER70S-6 (Jinda welding consumable grade JQ.MG50-6), φ 1.2 mm. The preheating temperature was set between 100–150°C, and slow cooling was applied after welding. This process ensured the structural integrity and performance of the components. During on-site operation, the customer provided positive feedback and was satisfied with the results.
**4. Conclusion**
HARDOX 400, known for its excellent wear resistance, has gained widespread recognition in both international and domestic machinery industries. Research and development of its weldability are of great importance. By selecting suitable welding materials and parameters, and applying appropriate preheating and post-weld heat treatment based on plate thickness, it is possible to achieve welded joints with superior overall performance.
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