1. Core Advantages of Welding Performance
Low carbon equivalent: The carbon content of Q345NHD is ≤0.18%, and its carbon equivalent (Ceq) is usually between 0.38% and 0.45%, which is lower than the critical value for easy welding cracks (generally, the risk increases when Ceq > 0.45%). It has a low hardening tendency, and the welded joint has moderate hardness, so it is not easy to cause brittle fracture due to excessively high hardness.
Good compatibility of alloying elements: The weather-resistant elements such as Cr, Ni, and Cu contained in the steel have strong compatibility with commonly used low-alloy steel welding wires (e.g., ER50-G) and electrodes (e.g., E5015-G). No harmful compounds are easily generated during welding, which can ensure the basic mechanical properties of the weld.
2. Key Welding Issues to Focus On
Risk of cold cracks: If there is oil, rust (not thoroughly cleaned) in the welding area, or the welding environment has high humidity (>80%), hydrogen is likely to remain in the weld, which may cause cold cracks after cooling. The risk increases especially when welding thick plates (≥16mm) or in low-temperature environments (<0℃).
Matching of weld weather resistance: The core advantage of Q345NHD is its weather resistance. If ordinary carbon steel welding wires (e.g., ER50-6) are used instead of weather-resistant welding wires (e.g., ER50-GNiCrCu), the corrosion resistance of the weld will be much lower than that of the base metal. The weld is prone to rust first during long-term outdoor use.
3. Key Recommendations for Improving Welding Quality
Match weather-resistant welding materials: Prioritize the selection of welding wires/electrodes that match the weather resistance of the base metal. For example, choose ER50-GNiCrCu for welding wires and E5015-G (the letter "G" indicates weather-resistant type) for electrodes to ensure the weather resistance of the weld is consistent with that of the base metal.
Control preheating and post-heating: When welding thick plates (≥12mm) or in low-temperature environments, preheat the base metal to 80–150℃; after welding, perform post-heat treatment at 200–300℃ in a timely manner to accelerate hydrogen escape and reduce the risk of cold cracks.
Clean the welding area: Before welding, thoroughly remove oil, rust, and oxide scale from the surface of the base metal. Sandpaper grinding or pickling can be used to prevent impurities from entering the weld and causing pores or inclusions.
