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  • Martensitic alloys, commonly used for steam and gas pipes, turbine blades and other applications that may encounter steam and moisture buildup, provide a good combination of high tensile strength and corrosion resistance. Keep in mind that materials with high tensile strength tend to have lower ductility. Martensitic stainless steels typically have an 11.5 to 18-percent chromium range and higher levels of carbon and other alloying elements that promote the formation of martensite. Common martensitic stainless steels, 410 and 420, can be matched with 410 and 420 filler metals with similar characteristics. Susceptible to hydrogen-induced cracking, controlling the heat input through proper preheat, interpass and post-weld temperature requirements minimizes cracking as does reducing the amount of restraint on the weld. A post-weld heattreatment, when used on these types of stainless steels to temper the martensite formed, will impact the hardness, tensile strength and ductility of the weld.
  • Precipitation-hardening (PH) stainless steels go through heattreatments to obtain their strength and hardness. Grades of PH stainless steels can have strengths of more than 200 ksi, making them the strongest types of stainless steel. A common PH stainless steel, 17-4, finds use in applications needing high strength and corrosion resistance, such as missile-launch tubes, aircraft frames and high-pressure bottles, and matches well with a 17-4 PH filler metal or 630 filler metal. Because it goes through a controlled cooling to achieve its properties, bringing a 17-4 PH stainless steel to a solution-treated condition before welding is recommended. This requires a temperature usually within the range of 1650 to 1800 F for 1 to 2 hr., followed by a quench. Post-weld heattreating brings the material back to the desired properties after welding. Contact the supplier of the PH stainless steel to get recommendations on post-weld heating temperatures and times to achieve the desired properties.
  • Duplex alloys, designed to have a microstructure of 50-percent ferrite and 50-percent austenite in their finished form, have a service temperature range of about -40 to 535 F and strengths above 60 ksi, which provide a mix of abrasion and corrosion resistance. Used in a range of applications, including oil and gas pipelines, use of the newer duplex filler metals is growing.

  • There are five commonly used grades of stainless steel. Understanding the differences between them helps ensure use of the right one in a welding application. Across all five types, credit chromium and nickel as the material’s main alloys in varying degrees.

    Best Practices

    In addition to proper filler-metal selection, successful stainless-steel welding requires following these best practices:

    • Increase silicon levels to help with weld, pool flow and fluidity. The more sluggish weld pool of stainless steel in the filler metal, due to less fluid, can cause some issues, especially for welders not familiar with the material. If the less-fluid weld pool causes concern, choose a filler metal with more silicon in the classification, such as ER308LSi versus a standard ER308L filler metal. Increased silicon levels help with weld-pool flow and fluidity.
    • Use faster travel speeds to help keep heat input low. Slow travel speed increases heat input, which can burn alloying elements out of the metal and impact weld properties including strength, ductility and corrosion resistance. While a travel speed of 3 to 8 in./min. is typical with other materials, welding stainless steel with flux-cored or metal-cored wires calls for travel speeds of 8 to 11 in./min. Consider, too, the final appearance of the weld. A weld bead using flux-cored or metal-cored wires will have a distinct gold color or rainbow sheen. Gas-tungsten-arc welds should not have this bead appearance.
    • Avoid contamination of the weld using a dedicated stainless-steel brush to clean stainless welds. Using the same brush to clean stainless steel and mild steel can cause cross-contamination and result in rust. Similarly, don’t use a brush for stainless steel to clean aluminum, or vice versa. 
    • Use proper safety systems and protective gear. Some filler metals produce higher levels of weld fume than others, so it’s important to have proper ventilation or weld-fume-source capture in place when using them. In some applications, the welder may want to wear a helmet equipped with a respirator. MF
    Industry-Related Terms: Alloys, Austenite, Color, Corrosion Resistance, Ductility, Electrodes, Ferritic, Form, Martensite, Stainless Steel, Tensile Strength, Weldability
    View Glossary of Metalforming Terms

     

    See also: Hobart Brothers Co.

    Technologies: Welding and Joining

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