Sep 17, 2020
Filler Metal Must-Knows for New Welders
Filler metals are often a confusing part of the welding operation, particularly for new welders. Understanding some key factors about these products, however, can help ensure the proper selection and use of these welding consumables.
As with any part of welding, education and training are important for working with filler metals. Choosing the right filler metal for the job and using it properly it supports high weld quality and productivity and helps reduce downtime for rework.
To help along the way, here are five filler metal must-knows for new welders to help ensure success.
Understand filler metal classifications
There are several different organizations that classify filler metals, with the American Welding Society (AWS) being among the more widely recognized — not just in the United States, but also in Canada.
A filler metal classification provides details about a product’s characteristics and usability, including the type of filler metal, allowable welding positions, tensile strength, shielding gas (if needed) and chemistry or composition. It is the standard for filler metals that informs welders what type of weld a specific product will produce.
Each classification contains a series of designators that signify specific details. By way of explanation (and due to AWS classifications being well known), consider an E71T-1C/M H8 gas-shielded flux-cored wire. Under the AWS A5.20/A5.20M Specification for Carbon Steel Electrodes for Flux Cored Arc Welding, it breaks down as follows:
*E signifies the wire is an electrode.
*7 indicates the wire provides 70,000 psi tensile strength.
*1 shows the wire can be welded in all positions (0 would signify it is usable only for flat and horizontal welding).
*T-1. Here the T identifies this as a tubular wire and the 1 is the usability designator that indicates it is a DCEP multi-pass wire with a rutile base slag. Note: T-1 wires can produce high deposition rates, operate in a spray transfer mode, and are typically used in applications where toughness requirements are not below 0°F.
*C/M indicates the wire can be used with either 100% CO2 or mixed gases
*H8 signifies the wire produces a weld with a maximum of 8 ml of hydrogen per 100 g of weld deposit.
For this same wire, the Canadian Welding Bureau (CWB) classification would be E491T1-(C1A2, M21A2,)-CS1-H8. Although the designations vary, the wire provides the same properties and characteristics.
Stick electrodes, solid wires and metal-cored wires all have similar designations within their specifications. Each classification system is tailored to the filler metal alloy (for example, carbon, low carbon or stainless steel) and the process being used.
Match the filler metal to the base material
No single filler metal will do the job for every material; the two must be compatible.
To create a sound weld when welding two pieces of metal that are the same, it is critical to match the properties of the filler metal to the base material as closely as possible. When the chemistry is a good match, it follows that the mechanical properties — tensile and yield strength — will also match. This provides peace of mind that the weld deposit will be sound if it is also created using the proper technique.
Here are some other common scenarios welders may encounter when trying to match filler metals to the base material, along with their solutions:
1. In the event a welder is joining base materials of differing strength, the filler metal should be matched to the lower strength of the two base materials. This is because a weld design is limited by its weakest material.
2. If a material needs to be stress relieved or requires post-weld heat treatment (PWHT) based on the welding procedure, the chosen filler metal must be able to withstand these additional conditions.
3. If the welder is not certain what base material is being welded, there are ways to identify it. These include using a spectrometer for chemical analysis, assessing the general appearance, and observing its reaction to magnets, fracturing or flame. Sometimes the easiest way to get information on the material, and its recommended fabrication practices, is by contacting the manufacturer of the workpiece.
Pair the filler metal and welding process
Welding applications require the filler metal and welding process to match, meaning that new welders need to know not only their machine’s capabilities, but also how the filler metal is intended to operate. Each filler metal has processes in which it excels and others where it may present limitations.
For example, metal-cored and solid wires are generally used for welding in the flat and horizontal positions. If welders are required to weld out of position with either wire, they would need to use a pulse or short circuit procedure to prevent the molten weld pool from falling out of the joint before the weld solidifies. Another option, if the application allows, would be to use a flux-cored wire, as this filler metal welds well when out of position.
Additionally, the maximum current and duty cycle offered by a power source will determine what filler metal size and parameters a welder can use. A power source must be able to provide sufficient electrical output for the filler metal being used. The larger the filler metal diameter, the more power output is required from the power source.
Use the correct welding parameters for the filler metal
Filler metal manufacturers formulate every stick electrode and welding wire to operate within specific welding parameters. Depending on the code being welded to, if any, these parameters could vary for the same filler metal.
Welders can find recommended welding parameters on the product data sheet, which is often sent within the filler metal package or can be found on the filler metal manufacturer’s website. Data sheets provide critical information for proper use, including:
1. The required shielding gas or shielding gas mixture (if needed)
2. Type of welding current – Direct Current Electrode Positive (DCEP) or Direct Current Electrode Negative (DCEN)
3. Wire feed speed, amperage and voltage requirements according to filler metal type and diameter
4. Recommended welding positions and techniques
5. Filler metal chemistry
6. Filler metal testing data
7. Recommended applications
8. Contact-tip-to-work-distance (CTWD)
If a filler metal is capable of welding in all positions, the welding parameters for flat, horizontal and out-of-position welding will also be provided.
Along with following the proper welding parameters, welders should always use the correct technique for welding. For example, solid wire and metal-cored wire require a push technique; whereas a flux-cored wire, which produces slag, requires a drag technique to help prevent slag inclusions.
Store filler metals properly
Filler metals must be stored according to the manufacturer’s recommendation to ensure that they perform well and create high-quality welds. Proper filler metal storage also helps eliminate waste due to damaged products (and the associated cost for replacement) and prevents voiding warranties.
Moisture and other foreign contaminants are the enemy of filler metals — they can lead to porosity, hydrogen-induced cracking or other weld defects. Welders should store filler metals in a clean, dry and preferably climate-controlled area, in their original packaging, until ready for use. If the storage area is a different temperature than the area where welding will take place, it’s important to allow the filler metal to acclimate to the temperature in the shop before opening the packaging. For example, when moving from a cold area to a warm one, condensation can occur and needs to dissipate prior to welding.
Stick electrodes should also be stored in their original package until ready for use. Once a carton has been opened, it’s imperative that welders follow the instructions for reconditioning them to remove moisture. To recondition stick electrodes, they must be placed in an approved oven for a specific temperature and time.
While these five filler metal must-knows are a good start for new welders to build their knowledge, the list is by no means exhaustive. There are many classifications and codes for filler metals, and all the details of each welding application must be taken into consideration. If questions arise about choosing or using a specific product, filler metal manufacturers and welding product distributors are available to help.