Page 38 - MetalForming-Jun-2018-issue

FABRICATION
Overcoming Stainless-Steel
Welding Challenges
It’s a matter of achieving proper heat, understanding alloys, choosing the right filler metal and following these best practices.
BY TRE’ HEFLIN-KING
When a component must with- stand corrosion and extreme temperatures—as low as -100 F and as high as 1800 F—manufactur- ers often turn to stainless steel. While commonly used in manufacturing, stainless steel can present welding challenges. Keeping heat input low plays a critical role, since stainless steel is less conductive to heat steel. This, along with selecting the filler metal and following proven best practices, is critical for optimal weld results.
Understanding Types
Understanding the differences between the five commonly used grades of stainless steel helps to ensure selection of the right grade. Across all five grades, chromium and nickel rep- resent the main alloy materials to vary- ing degrees. Three of the most common types: austenitic, ferritic and marten- sitic. As the material cools, the result
Tre’ Heflin-King is a welding engineer and certified welding inspector– applications at Hobart Filler Metals, Troy, OH: 937/332-4000; www.hobart- brothers.com.
36 MetalForming/June 2018
Welding stainless steel can be challenging. The weld pool can be sluggish compared to welding mild steels—making low heat input low a critical success factor.
will be one of these types, or a combi- nation of types, depending on how the metal is cooled and what temperature it reaches during cooling.
As for weldability, all stainless-steel alloys share a common challenge: slug- gishness of the weld pool. Using elec- trodes with boosted silicon content can help address this.
Strength varies across the alloys. If the material classification has an L- grade, such as 308L, this designates a lower carbon level, which can mean slightly lower tensile strength.
Choosing the right filler metal for each type of stainless steel depends on the characteristics of the base mate- rial, the properties required for the fin- ished welds and the environment to which the welds will be exposed.
The five types of stainless steel:
• Austenitic alloys have chromium content from 16 to 25 percent, and
nickel from 8 to 20 percent. Additional alloying elements include silicon, man- ganese, nitrogen and molybdenum. Austenitic stainless steels do well in highly corrosive environments and are commonly used for medical equipment and kitchen equipment, such as mixers and dishwashers. The most common austenitic steels are 304, 308, 309 and 316. For 304 and 308, a Type 308 filler metal can be used. For a 309 base mate- rial, there are numerous options, including 308, 309 or 316 filler metals. For Type 316 base materials, use a Type 316 filler metal. Pre- and post-weld heat requirements aren’t typically an issue with austenitic stainless steels. If there is a need to perform post-weld heattreat, avoid the temperature range of1200to1650F,ascarbideformation occurs rapidly in this range and causes weld embrittlement.
• Ferritic alloys have a chromium- www.metalformingmagazine.com