Welding process test and application of Hardox400 wear-resistant steel plate for cutter suction dredger
Surface Preparation for Welding Hardox400 Steel Plates
Before welding Hardox400 steel plates, the welding surface must be free from oil, grease, dust, rust, paint or any other impurities that can reduce the strength and the quality of the joint. The best way to clean the surface is to use an abrasive blasting using Aluminium Oxide or other suitable abrasive media. This can be followed by hand cleaning with a wire brush, as well as cleaning with a solvent like acetone or methanol, to remove any stubborn spots of dirt or rust. It is important to note that air arc gouging is not an appropriate technique for the surface preparation of Hardox400 steel plates.
Hardox400 Steel Plates Process Selection
GTAW (TIG) and SMAW (MMA) processes are two common welding process used for Hardox400 steel plates, due to their low heat input and ability to yield high quality and strength joints. SMAW welding is preferred for welding thicker plates, while GTAW is suitable for welds from 1-3mm materials. In hard surfacing and clad welding, the Flux Core Arc Welding (FCAW) process can be used for filling-in gaps or for covering the entire plate with a wear resistant electrode.
Hardox400 wear-resistant steel Welding Parameters
While welding parameters may vary from application to application, the welding current, arc voltage, travel speed, and number of passes should be optimized for the specific application. Generally, for GTAW, a welding current of up to 220 A is ideal, with an arc voltage of 18-22 V and a welding speed of around 10-15 cm/min. Whereas for SMAW, electrode sizes of 4.0-6.3 mm can be used with a welding current up to 200-350 A and arc voltage around 26-30 V.
Joint Design
The coefficient of thermal expansion (CTE) between the component materials must be taken into consideration during joint design. The joint design should also be optimized in such a way that the maximum welding stress and distortion are minimized. When welding thicker materials, a double V-groove joint with a J-groove root can be used. Generally, a root gap of 3 mm is used for a double V-groove joint and 2.4 mm for a single V-groove joint.
Hardox400 wear-resistant steel Post-Weld Treatment
Post-weld treatment like stress relief annealing is recommended after welding Hardox400 steel plates, in order to reduce welding stresses, relieve welding deformations, and eliminate internal residual stresses. The stress relief annealing procedure consists of preheating, soaking and cooling. The preheating temperature should be kept 40-50°C above the transformation temperature of the heat affected zone, which is usually around 550-600°C for Hardox400 steel.
Hardox400 wear-resistant steel Welding Inspection
The welding quality of high strength steel components is of great importance for their performance and durability. Visual inspection and non-destructive testing (NDT) methods can be used to check the quality of the welds. Magnetic Particle Test (MPT), Ultrasonic Test (UT) and Radiographic Test (RT) are some of the common NDT techniques used for quality assurance of hardox400 welds.
Conclusion
Hardox400 wear-resistant steel plates are widely used for fabrication work for cutter suction dredgers. Welding parameters and joint design must be considered carefully in order to obtain high quality and sturdy welded components. Appropriate surface preparation, process selection and post-weld treatment are essential for ensuring reliable operation of the cutter suction dredger. Furthermore, proper welding inspection techniques must be executed before commissioning the CSD.
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