[Difficult Issue] 40Cr has poor weldability; what welding electrode is best to use?

40Cr is a quenched and tempered steel, and it is difficult to maintain its quenched and tempered properties after welding. You are likely going to carry out repair welding; if it is local repair welding, J507 or austenitic welding electrodes can be used, but quenching and tempering cannot be performed after welding in either case. Welding is carried out using R307 welding rod, which provides higher weld strength and good joint performance. Some experience is shared for reference: use J507 welding rods, which should be dried at 300 degrees for 2 hours before use; the base material needs to be cleaned thoroughly as usual. The type of groove should be selected based on the joint requirements. During tack welding, the temperature should be around 150 degrees, and the tack welds should be at least 80 MM long. Before starting the actual welding, the temperature should be raised to around 250 degrees; the temperature on the 40Cr side should be slightly higher to prevent delayed cracking. During welding, it is important to use a short arc, and the welding current should be kept at a low level. Try to minimize the fusion ratio on the 40Cr side. After welding, there is no need to remove slag – instead, keep the welded area insulated to allow it to cool slowly.

You must first conduct a welding procedure qualification for your company; once it is approved, a welding procedure sheet will be issued, and you can follow that to carry out the work.