Technical Handbook - Stainless Steel Welding

Technical Handbook - Stainless Steel Welding

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Three basic chapters of this volume, Chapter 1, Carbon and Low-Alloy Steels; Chapter 2,High-Alloy Steels; and Chapter 5, Stainless and Heat-Resistant Steels contain detailedsections on the metallurgy, composition and properties of steels, and methods of producinghigh-integrity welds in carbon steels, alloy steels, and stainless steels.

Different sets of welding conditions, challenges, and solutions are presented for the specialized steels represented in Chapter 3, Coated Steels; Chapter 4, Tool and Die Steels; Chapter 6, Clad and Dissimilar Metals; Chapter 7, Surfacing Materials; and Chapter 8, Cast Irons. The chapters provide information on the composition, metallurgy, weldability, and recommended welding procedures for these metals.

Stainless steel is the general name for the family of iron-based alloys that contain at least 10.5% chromium. When there is sufficient exposure to oxygen, an invisible protective passive chromium-rich oxide film forms on the surface. This invisible film forms automatically as long as the surface is clean and exposed to oxygen. Higher levels of chromium and the addition of other alloying elements such as nitrogen and molybdenum enhance this surface layer and improve the corrosion resistance of the stainless material.

Both of these stainless steels contain chromium and nickel alloy additions, but Type 316 also has a molybdenum (Mo) alloying addition. Molybdenum improves corrosion resistance and is particularly helpful when there is exposure to chlorides (coastal or deicing salts) or corrosive pollutants. Type 304 contains 18 to 20% chromium and 8 to 10.5% nickel. Type 316 contains 16 to 18% chromium, 10 to 14% nickel and 2 to 3% molybdenum. Corrosion resistance increases with higher alloying additions of molybdenum.

There is a common misconception that specifying low carbon will improve the corrosion resistance of surfaces outside the weld zone. This is not the case. Corrosion resistance is improved by specifying stainless steels with higher chromium, molybdenum and/or molybdenum levels. Specification of low sulfur (0.005% or less) may also improve corrosion performance.

Stainless steel gauge thicknesses are not defined by ASTM and can vary from producer to producer. Therefore, it is important to order stainless steel products by the specific thickness range, maximum or minimum that is required in either inches or millimeters. Gauge numbers can be referenced, but should not be used exclusively. A cross-reference showing the nominal thicknesses typically associated with stainless steel gauge numbers can be found in our Designer Handbook: Stainless Steel Architectural Facts available in our Library. It is important to note that the typical thicknesses associated with the gauge numbers for stainless steel, carbon steel, and aluminum are all different.

Stainless steel is 100% recyclable. An international study by the ISSF determined that the average recycled content of stainless steels is 60%, but, in areas of the world where there have been more historic use of stainless steel, the recycled content is typically higher. In North America, SSINA has issued a LEED statement indicating that the average recycled content of the 300-series stainless steel sheet, plate and reinforcing bars used in building and construction is between 75 and 85%.

No. The austenitic or 300 series stainless steels are generally non-magnetic but high levels of cold work can make them somewhat magnetic. Castings made out of these stainless steels can also be somewhat magnetic. This slight magnetism is not an indication of a problem with the stainless steel. Other stainless steels families are naturally magnetic (e.g. ferritic 400-series and duplexes).

Yes. Stainless and carbon steels can be welded together. It is important to use a filler metal that is appropriate for stainless steel. Please see our Designer Handbook Welding of Stainless Steels and Other Joining Methods, available in our library. It is important to note that galvanic corrosion may be a problem if there is an electrolyte (moisture) present on a regular basis that will connect the two metals at this welded joint. Appropriate steps, such as applying a protective coating, should be taken to prevent moisture from bridging the metals and causing selective corrosion at the welded joint. It is important to note that, if the carbon steel has been galvanized, the coating must be completely removed from the surface prior to welding or zinc embrittlement could occur.

While stainless steel is easy to fabricate, it is different from carbon steel and knowing these differences will greatly assist the fabricator in working with stainless steel.

The handbook describes fabrication methods, such as cutting, shearing, blanking, bending and forming. Compares stainless to mild steel with suggested fabrication methods. Descaling, removing mild discoloration, and the definition of passivation are discussed. Comments on handling, care in the shop, and cleaning procedures.

KOBE STEEL offers a wide range of stainless steel flux cored wires (FCWs), to meet specific requirements from various industries. The features of these wires and understanding how to choose the best stainless steel FCW(s) for a particular application is the subject of this article.

FCWs are known for a high deposition rate and excellent usability. The former contributes to shorten welding time while the latter, by decreasing spattergeneration, helps reduce time spent on treatments likeremoving spatter that sticks to steel plates duringwelding. Accordingly, both features contribute toimproving productivity. In particular, when FCWs areapplied to welding an austenitic stainless steel, thewelds have beautiful bead appearance and highcorrosion resistance.

The DW-Series stainless steel FCWs provide excellentarc stability with not only 100%CO2 but also Ar-CO2mixed shielding gases. Furthermore, as [P] DW-308L and[P] DW-316L are designed to offer easy slag removalafter welding, the temper color on bead surfaces can beavoided as shown in Figure 1. Preventing the generationof temper color can save time spent on acid treatmentand raise productivity.

As an example, how [P] DW-308L is classified undereach standard is shown in Table 2. Symbols such as 308or 316, which show the chemical compositions of allweld metal in the trade names of stainless steel FCWs,correspond to JIS and AWS classifications in general.

The DW-Series stainless steel FCWs for generalpurposes provide excellent usability in flat positionwelding as well as horizontal fillet welding. The zero (0)in the AWS and JIS classifications indicates the weldingposition. Typical DW-Series stainless steel FCWs forgeneral purposes are as shown in Table 3.

An L attached to the symbol for chemical compositionindicates low carbon type and is suited to weld a similarlow carbon base metal. A weld containing high carbonmay have reduced tensile strength because thechromium carbide that is generated at the heat affectedzone (HAZ) causes the intergranular corrosionresistance to drop. However, a low carbon stainless steelis usually superb in intergranular corrosion resistance.Therefore, attention should be paid. Typical low carbonstainless steel FCWs are shown in Table 5.

An FCW with a suffix [P] in the product name indicatesit is for all position (or positional) welding. It providesbeautiful bead shape in vertical (upward) and overheadposition welding, as shown in Figure 2. In the AWS andJIS classifications, the one (1) indicates the weldingposition. Typical DW-Series stainless steel FCWs for allposition welding are shown in Table 6.

However, Bismuth (Bi), a surface activating element,segregates at the boundary and can promote breakageunder a sustainable tensile load when it is exposed to hightemperatures for a long time. Therefore, according toAWS, a stainless steel FCW containing Bi is unsuitablefor use in circumstances exceeding 400 °C or for postweld heat treatment (PWHT) exceeding 500 °C.

Although JIS Z 3323 specifies that the Bi content inthe all weld metal be under 10 ppm (0.001%), thisamount is practically interpreted as no addition of Bi, inother word, Bi-free. Hence, BiF indicates a Bi-free typeof stainless steel welding consumable, such as inYF308C-BIF.

The DW-H-Series stainless steel FCWs are designedto produce lower ferrite than conventional stainless steelFCWs. This is because ferrite in the weld metaltransforms to a brittle sigma (σ) phase at hightemperature and causes mechanical properties of theweld metal to deteriorate. As a criterion of ferrite content, the API PR582 3rd Edition specifies that 9 FN(based on WRC Diagram-1992) or less shall bemaintained if the weld metal is exposed to temperaturesexceeding 538 °C.

Welding fumes are a complex mixture of metallicoxides, silicates, and fluorides that come from metalvapor during welding. In the case of welding stainlesssteel, the fume contains about 5 to 20% chromium (Cr)oxide, a part of which exists as the hazardous 6-valentchromium compound, Cr(VI). Accordingly, strictcontrol of Cr(VI) is now a worldwide trend.

DW-XR-Series stainless steel FCWs are designed toreduce Cr(VI) in the welding fume. 308L, 316L and 309Lstainless steel FCWs were targeted for the developmentof DW-XR-Series stainless steel FCWs for flat andhorizontal fillet welding as well as for all positionwelding. The present line-up is shown in Table 9.

DW-G-Series stainless steel FCWs enable stablewelding on sheet metals even at low welding current. Tobe more precise, though the welding of sheet metalsrequires 0.9 mm diam eter (φ) when a conventionalFCW or solid wire is used, with DW-G-Series FCWs,1.2 mmφ can be used, which is more convenient andless expensive. Table 10 shows the line-up ofDW-G-Series stainless steel FCWs.

The relationship between leg length and weldingspeed in horizontal fillet welding is shown in Figure 5,while Figure 6 shows the optimum range of weldingparameters of the DW-G-Series stainless steel FCWs(1.2 mmφ) in comparison with conventional FCWs (0.9mmφ). 781b155fdc