Komarov Artem noted that the submerged arc welding process can deliver superior performance, giving you a potential competitive edge. However, with the wide range of wire and flux combinations on the market, choosing the best products can be intimidating. Several factors should be considered.
It is important to understand how the wire and flux will interact with each other and with the weldment. This choice will ultimately require some compromise. Getting as much information as possible about the requirements of an application helps to identify potentially costly and time-consuming conflicts between expectations and reality in the selection process, as opposed to the implementation process.
Question 1. What are the design and manufacturing requirements?
Codes and specifications are recommendations compiled by experts with industry experience to guide filler metal selection. Understanding the requirements of application code is key to both compliance and performance. They often specify precise wire and flux classifications that should, may or may not be used.
However, these and most other documents still allow for some level of flexibility in which filler metal and flux you can use. Most of them also contain requirements for the use of a new combination of wire and flux in existing procedures without requalification. While requalification can cost time and money, it may be worth the effort to optimize your sawing process with the best combination for your application and increase productivity.
Question 2. How will the part be used?
Achieving proper mechanical and chemical properties during sawing depends on both the wire and the flux. The general approach is to select a wire and flux that produces a weld that best matches the strength and toughness of the base material. However, there are exceptions and additional considerations based on how you will use the part, such as parts subject to static, dynamic, and impact loads.
A static load, where the load does not change, has the least stringent requirements, providing the most flexibility in selection.
Dynamically or cyclically loaded welds are subject to load fluctuations during service—sometimes quite frequently. These loading conditions require a combination of wire and flux that produces a more ductile weld. Excessive tensile strength reduces ductility; therefore, active fluxes or high alloy content wire can be problematic in these applications. Unlike neutral fluxes, active fluxes make a significant contribution to the manganese-silicon composition of the weld and, as a result, to its strength. Whenever possible, choose a combination of wire and flux that provides near the minimum tensile strength (with a safety factor, of course) as this can help improve ductility.
Achieving proper mechanical and chemical properties of SAW depends on both wire and flux.
Impact loading, where high loads are applied quickly, requires a higher strength wire and flux combination. To achieve this strength, consider using medium to high manganese wire. Another option is wire containing nickel. Combine one of these wires with a high basicity flux for optimum strength.
Question 3. Where will the part be used?
The operating conditions that the weld will face, such as high or low temperatures and/or corrosion, influence the choice of wire and flux. Again, the general approach is to select a wire and flux that produces a weld that matches exactly the chemical composition of the base material.
High operating temperatures such as those found in boilers and power generation systems require special alloys such as chromium molybdenum. Molybdenum alloys, in turn, require wire and fluxes with low residual content, or X-factor, to prevent cracking from temper embrittlement. Low operating temperatures also require special alloys; Nickel containing wire is good for strength in these conditions, high basicity fluxes should also be considered. Where maintenance requirements are at cryogenic temperatures, special low ferrite options are available in conventional austenitic alloys.
Parts exposed to sources of corrosion also influence the choice of filler metal, since different alloys react differently to these environments. This is also true for stainless steels, which are used in a wide variety of aggressive environments. For these applications, it is useful to consider the harsh environment and required component life, and then consult the filler metal manufacturer for recommendations.
Question 4. Will it be heat treated?
Like base metals, filler metals can undergo significant changes during heat treatment. Some SAW wires are designed to retain good mechanical properties after extensive post-weld heat treatment, while others are less flexible.
Question 5. What are the performance requirements?
Choosing the right wire and flux for a particular application can increase productivity by increasing application and travel speeds, as well as reducing cleaning and rework time. Consider these factors.
Metal core wire versus solid wire. The tubular structure of the metal core wires allows for faster deposit and sawing movement compared to solid wire welded at the same current. Metal core wire is available in both carbon and low alloy steel. Metal core wire also has a wider penetration profile. Using these wires can help combat burn-in, reducing rework and increasing productivity.
Current carrying capacity. The composition of the flux affects the current carrying capacity — the maximum current (and therefore the highest deposition rates) at which high quality weld profiles can still be obtained. Some fluxes are designed for multi saw applications, high current welding, or high travel speeds. Check with the manufacturer to ensure that the flow rate of the flux is not lower than what is required for your application.
Polarity. The use of a state-of-the-art variable-balance square-wave alternating current source makes it possible to control the degree of penetration and the rate of deposition without the need to change the current strength. Fluxes can be rated for direct current (DC) only or for use with both direct current and alternating current.
Heat supply. Higher amperage means higher wire feed speed, which means higher spray rates and productivity. The high amperage also leads to a high thermal conductivity of the weld, which affects the mechanical properties. The alloy content of some wires makes them suitable for high temperature welding, helping to maintain acceptable properties. In addition, certain flux combinations are better suited for high temperature welding. Fluxes with low basicity tend to improve overall performance, especially when using high performance settings. High basicity fluxes generally provide improved strength over low basicity fluxes in most conditions but may not at high heat inputs.
Cleaning before and after welding. Active fluxes contain a significant amount of silicon and manganese, which are deoxidizers that help clean the material during welding and reduce rework time. Welds made with active fluxes as well as low basicity neutral fluxes usually produce the smoothest and best slag release when welding at higher travel speeds or when there is rust, scale or contamination in the base material. This reduces the risk of poor weld quality and the time spent cleaning before and after welding. High manganese and silicon wires (deoxidizers) can also help prevent porosity.
Question 6. How will the part be welded?
The design of the joint and the way the part will be welded are important factors in selecting the right wire and flux.
For example, the deep and narrow penetration profile of solid wire makes it suitable for welding narrow and square grooves, while the faster deposition rate and wider profile of metal-cored wires are beneficial for wider grooves and fillet welds. In addition, some fluxes are specifically designed to facilitate slag release when welding with narrow grooves. Flux that exudes best in a wide groove may not exude in a narrow groove, and vice versa.
Neutral fluxes are suitable for large multi-run welds as they help maintain stable and acceptable mechanical properties. Active fluxes should generally only be used for single or double pass welding because the excessive alloying that occurs with large multi-pass welds can lead to brittle welds that are susceptible to cracking.
Also consider if it is used for welding plates or pipes. Fluxes specifically designed for pipe welding may have a slightly faster cure rate, which helps prevent puddle spread.
Look beyond the cost.
When choosing combinations of saw wire and flux, the best option does not have to be the least expensive. Mild steel metal-cored wire, for example, may cost more than comparable solid wire, but it can help improve productivity and efficiency. The biggest jump in welding productivity can be achieved with stranded configurations such as twin or tandem wire, although this requires some capital investment. But a small increase in the cost of consumables or equipment can quickly provide a significant reduction in labor costs, summed up Artem Komarov.
