Invar 36 is a rare type of steel used for its low thermal expansion coefficient, making it the ideal choice for applications requiring a high level of dimensional stability. The metal has several advantages, including maintaining its dimensions when exposed to thermal fluctuation. However, welding Invar 36 can be challenging due to its specific composition. This blog post will discuss the steps required to properly weld Invar 36 round bars for optimal performance.
What is Invar 36-Round Bars?
36 round bars refer to steel or iron rods that are shaped into cylindrical bars of uniform size and weight. These bars are used for structural reinforcement in a variety of construction projects, including foundations, bridges, buildings, and ships. They can also create furniture frames, girders, gates, fences and railings. They provide excellent strength and durability at an economical cost when compared to other materials such as timber or concrete. Depending on the application required, 36 round bars can come in various sizes from 4mm up to 100mm in diameter, ranging from 1m – 6m long.
How to Properly Weld Invar 36-Round Bars
Preparation:
Before welding Invar 36, it is essential to prepare the material properly. The bars must be clean, free of any contaminants, and the surface must be smooth. Any impurities can compromise the quality of the weld. Therefore, it is recommended to use a solvent to clean the bars thoroughly. The surface must also be polished to remove any oxides or debris.
Choose the Right Filler Wire:
Invar 36 requires a specific type of filler wire to achieve optimal results. The ideal filler wire is similar in composition to the Invar 36 bars. The welding wire must also have the same purity level as the Invar 36 bars. This helps to ensure that the weld material will have similar properties to the Invar 36 bars. To properly weld Invar 36 round bars for optimal performance, choosing the right type of filler wire is important. The most common welding processes used with Invar 36 are TIG and MIG, so selecting a low-alloy stainless steel filler wire that is appropriate for both methods will ensure the best results. Filler wires with higher molybdenum content can also be beneficial in preventing or reducing cracking at elevated temperatures. Additionally, preheating the material before welding is essential for working with this alloy to improve joint strength and reduce distortion.
Welding Process:
Invar 36 must be welded at a low heat input to avoid cracking, distortion, and other complications. The recommended welding method is gas tungsten arc welding (GTAW), also known as TIG welding. TIG welding provides precise control of the heat input and allows the welder to produce a clean, seamless weld. The optimal way to weld Invar 36 round bars is to preheat the material before welding, use a low hydrogen electrode and AWS E347 filler wire, keep your travel speed consistent, avoid weaving and maintain constant arc length. When possible, use pulse welding or the double pulse step-down technique. Be sure to use a post-weld heat treatment process following the specific guidelines for this material. Finally, apply proper fixturing during assembly to ensure that the finished product meets your desired specifications.
Post-Weld Heat Treatment:
Post-weld heat treatment is necessary to minimize the risk of distortion and residual stress. The Invar 36 bars must be heat-treated at a temperature of around 600°C. The heat treatment helps to relieve residual stress and ensures that the weld material has similar properties to the Invar 36 bars. Post-weld heat treatment is an important part of welding Invar 36 round bars for optimal performance. This process involves heating the metal to a specific temperature (usually between 800°F and 1000°F) and then quickly cooling it with water, oil, or air quenching before gradually returning to room temperature. Properly preheating and post-weld heat treating the material can drastically improve its mechanical properties.
Testing and Inspection:
Once the welding and heat treatment processes are complete, it is essential to carry out testing and inspection. The welds must undergo visual inspection and non-destructive and possibly destructive testing. This helps to ensure that the welds meet the required dimensional stability, hardness, and toughness specifications. Welding Invar 36 round bars requires following a specific process to ensure optimal performance. The entire weld joint should be properly prepared and cleaned before welding with an approved flux; then, each bead should be monitored while welding for proper penetration, fusion and alignment. After the weld is complete, it must be inspected with visual and mechanical testing methods to ensure no flaws or porosity.
Conclusion:
Welding Invar 36 round bars can be challenging, but following the right steps can help you achieve optimal performance. Proper preparation, choosing the right filler wire, using the recommended welding method, post-weld heat treatment, and testing and inspection are the key steps to successful Invar 36 welding. By following these steps, you can ensure that your welds meet the highest quality standards and provide the necessary dimensional stability for which Invar 36 is known.
