The Care and Consideration of Low Alloy Gas Shielded Flux Cored Wires
On applications ranging from shipbuilding to outdoor light poles, earthmoving equipment, and to high pressure steam piping, gas shielded low alloy flux cored wire can offer a number of advantages over other low alloy welding methods.
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Typically, flux cored wire provides significant productivity increases over the stick electrode process and can be more easily alloyed than solid wire while still retaining the required mechanical and chemical properties. Due to the manufacturing process, flux cored wires can be also made in much smaller batches than solid wire. Compared to metal cored and solid wires, which are only able to be welded out of position with short circuit transfer or with a pulse power supply, flux cored wires are available to weld in all positions using spray transfer, greatly increasing the potential deposition rates. Metal cored and solid wires are only able to be welded out of position with a short circuit transfer or with a pulse power supply.
But with dozens of AWS classifications for low alloy gas shielded flux cored wire, selecting the one that’s right for your application might seem like a daunting task. Knowing the material you will be welding and the required mechanical and chemical properties for the weld will put you well on the way to selecting the right wire for the job. Plus, following a few simple care practices will ensure you get the best performance from your chosen wire.
Base Material
The most important factor in selecting a low alloy gas shielded flux cored wire is knowing the base material to be welded. Depending on the application and the requirements of the finished weldment, the wire you select should be as similar in strength, chemical composition and mechanical properties to the base material as possible. When welding two two different strength base materials togetherof different strengths, match the filler metal to the tensile strength of the weaker base metal.
Low alloy filler metals typically fall into seven basic categories based on their alloying elements, with effective ranges for each alloying element as defined in AWS A5.29/A5.29M:2005: molybdenum, chromium-molybdenum, nickel, manganese-molybdenum, manganese-nickel-molybdenum, weathering and a general classification.
Each of these alloying elements provide certain mechanical and chemical properties determined bydesigned to match the base materials specific to certain industries and applications. Molybdenum, for example, is added to improve strength and creep resistance as well to maintaining its strength after stress relieving. Chromium is added for a variety of reasons, including corrosion resistance, creep resistance at elevated temperatures, and improved strength. Chromium-molybdenum steel provides the corrosion resistance and tensile strength required for petro-chemical piping, high-pressure steam piping, steam boilers and certain types of castings.
Other examples of low alloy applications include 1 – 3% nickel-alloyed filler metals for offshore oil rigs, ship building, and light pole construction. Manganese-molybdenum filler metals for castings and applications that require extensive post weld heat treating and manganese-nickel-molybdenum metals for earth moving equipment, mining equipment and shipbuilding. Weathering steel is often used for bridges and buildings where the material is to be left exposed to the elements.
Even though wires are from the same AWS class per A5.29, A5.29:2005, the mechanical properties and chemistry can vary depending on theby manufacturer based on the amount of the alloying elements and other ingredients added to the wire. For example, all K3 flux cored wires have the same range of allowable manganese, nickel and molybdenum, but they can vary widely in terms of tensile strength, impact toughness, weldability, and other factors depending on the manufacturer.
Within the E10XT1-K3 class of wires, for example, the minimum AWS requires for thedefined CVN impact value is 20 ft-lbs at -20F. Depending on the manufacturer and the application the wire is designed for, the CVN values can vary from 20 to over 50 ft-lbs at -20F. The different properties are achieved by varying the amount of the major alloying elements in addition to other elements added to the flux.
Other factors
Low alloy flux cored wires are available in either all-position or flat and horizontal welding capabilities. The position capability can be determined bydetermined by the AWS classification. For instance, if the classification is an EXX0T1-K3, the wire can be used in the flat and horizontal positions. If the classification is an EXX1T1-K3, the wire can be used in all positions.
The recommended shielding gas can also be determined by the AWS classification. If the wire is classified as an EXX1T1-K3M the wire can should be used with argon/CO2 shielding gas. If the wire is classified as an EXX1T1-K3C, the wire can should be used with 100% CO2 shielding gas. The wire can also be classified as an EXX1T1-K3M, EXX1T1-K3C, which means it can be used with both either an Argon/CO2 mixtures as well asor 100% CO2. As a general rule, using 100 percent CO2 shielding gas with these wires will provide deeper penetration at the expense of arc quality and spatter. Using a 75/25 Argon/CO2 shielding gas mix with these wires will provide much better arc quality and reduced spatter, but with less penetration. Typically, using a mixed gas also produces a higher tensile strength weld, but reduces elongation and may effect lower CVN impact values compared to 100 percent CO2. As with any product, always check the manufacturer’s recommended shielding gas requirements.
Slag properties are another factor to consider when selecting a low alloy gas shielded flux cored wire. Slag systems are classified as either basic or acidic. A basic slag, also known as a T-5, has better mechanical properties and strength than an acid slag, but the weldability isn not as friendly. An acid slag, referred to as T-1, has very good weldability, such as less spatter and smoke and better arc stability, puddle control and bead appearance, but the mechanical properties are sometimes not as good as a T-5 slag.
Caring for your wire
The foremost rule in caring for all wires and electrodes, including low alloy gas shielded flux cored wire, is to follow the manufacturers’ recommendations. However, a few guidelines apply universally. Moisture is the biggest concern for in caring for almost all types of filler metals, with gas shielded flux cored wires being no exception. To avoid potential problems, the wires should be kept in moisture resistant packaging in an environment below 70 percent humidity and between 40 and 120 degrees Fahrenheit. Reconditioning, or baking of the wire at a specific temperature for a period of time, is not recommended even if the product is exposed toexposed to excessive moisture. Exposing these and other wires to excessive moisture will typically void their warranty.
Low alloy gas shielded flux cored wire is just one among many ways to weld low alloy steel, but if you’ve decided that it is the best process for your application, selecting and properly caring for the wire is crucial to making sound, long lasting welds. Following a few simple guidelines, starting with the base material and moving through the weld positions and desired mechanical properties, will ensure that you make the correct choice. Following the manufacturers’ care requirements will ensure that your chosen wire performs at its peak when it comes time to weld.