Table 3 — Varying Heat Input and Shielding Gases can Compound or Offset Effects on Mechanical Properties High Heat Input with 100% CO2 Low Heat Input with 75% Argon/25% CO2 Difference Tensile 81,500 lb/in.2 104,400 lb/in.2 22,900 lb/in.2 Yield 70,200 lb/in.2 98,600 lb/in.2 28,400 lb/in.2 Elongation 29% 22% 7% cal properties (reducing strength and increasing ductility), and lower heat inputs and high argon content gas will do the opposite (push strength up and ductility down), these variables can be used together to compound these effects or to offset each other. For example, in an application where a high heat input is causing strength to drop, selecting a gas with a higher argon content can help increase strength levels. Conversely, lower heat input may cause a lack of ductility and CO2 shielding gas can be used to minimize that effect. Using the same carbon steel gasshielded wire as in the previous examples, a high heat input with 100% CO2 combination results in a tensile strength of 81,500 lb/in.2, a yield strength of 70,200 lb/in.2, and 29% elongation. That compares to a low heat input with 75% argon gas, which results in 104,400 lb/in.2 tensile strength, 98,600 lb/in.2 yield strength, and 22% elongation (which is the minimum requirement) — Table 3. Whether or not combining these factors to work together is the right solution depends upon the filler metal, as some are more or less affected than others. Also, certain filler metals are formulated for dual gas usage, while others can only be used with a single gas. Understanding the Dynamics There are no absolutes regarding the choice of high heat or low heat, or using an argon or CO2 shielding gas — which option is the better choice all depends on the needs and requirements of the specific application and wire. That makes it especially important to understand the relationship between these variables and the impact each has on the mechanical properties of the weld. Knowing how to adjust heat and the impact of shielding gas to help produce the desired effect can help welding operators refine their process and ultimately improve their results. WJ BLAINE GUY is welding engineer/CWI, welding engineering and applications, Hobart Filler Metals, Troy, Ohio. For info, go to aws.org/adindex For info, go to aws.org/adindex JULY 2016 / WELDING JOURNAL 45
Welding Journal | July 2016
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