1. Overview
30CrNiMo8 is a high-quality alloy steel originally developed in West Germany. It belongs to the category of medium-carbon steels, and is produced by adding one or more alloying elements to the base material of high-quality carbon structural steel 30Cr2Ni2Mo. Due to its excellent mechanical properties, it finds application in high-pressure chemical vessels. On the other hand, S355JR is a low-alloy high-strength steel commonly used in structural applications. Both materials are part of the European standard system. In recent years, our company has implemented 30CrNiMo8 in quenched and tempered conditions for use in the ring gear of welding gears, while S355JR is applied to the web section of the same components. To ensure the quality and reliability of the welded joints between these two dissimilar steels, this study focuses on analyzing their weldability, establishing an appropriate welding process, and conducting a welding procedure qualification according to the EN ISO 15614 standard. This approach helps guide the production of high-performance welding gears with improved structural integrity and durability.2. Pre-test Preparation
(1) Weldability Analysis Test: The chemical composition and mechanical properties of the base metals 30CrNiMo8 and S355JR are summarized in Table 1. According to the carbon equivalent (Ce) and cold crack sensitivity index (Pcm) recommended by the International Institute of Welding, the values for 30CrNiMo8 are 0.74% and 0.44%, respectively, while for S355JR, they are 0.54% and 0.37%. Both values exceed the critical thresholds of 0.40% for Ce and 0.20% for Pcm, indicating a higher susceptibility to hardening and cold cracking, especially in 30CrNiMo8. If not properly controlled during welding, the heat-affected zone may develop a significant amount of martensite, leading to embrittlement and increased risk of cold cracks in the joint.
(2) Welding Method and Materials: Submerged arc welding was selected as the welding method. The welding wire used was H08MnA, and the flux was HJ431. The mechanical properties of the welding materials are listed in Table 2. Before welding, the flux was dried at 400°C for 90 minutes to ensure optimal performance and reduce the risk of porosity or defects in the weld.
(3) Weld Groove Form and Parameters: The welded joint was designed as a butt joint with a backing plate, as shown in Figure 1. The welding parameters and sequence are detailed in Table 3 and Figure 2, respectively.
Please refer to the attachment for more details or read the 18th issue of Metalworking (Hot Processing).
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