strength. If using a carbon-steel filler metal, stress relieving may drop the weld’s strength below the minimum specified level. A low-alloy electrode may need to be used in order to meet the required tensile and yield strengths after stress relieving. Some carbon-steel electrodes are designed specifically for stress-relieved applications. They have been alloyed to prevent an appreciable drop in strength after PWHT. These types of electrodes may have an “SR” designation in their brand name (Table 2). Refer to a particular filler metal’s literature to see if it has published mechanical property data in the stress-relieved condition. Weathering Steel Some grades of steel (ASTM A588, A606, A871, etc.) have their own corrosion resistant properties. Weathering steels are alloyed to “weather” after an extended period of exposure to the atmosphere. In essence, they are designed to rust to a controlled thickness. This rust layer or patina on the steel’s surface then helps reduce continued corrosion. Weathering steels do not require paint or some other type of surface coating. Welds on weathering steel will also be exposed and should have a similar corrosionresistant characteristic and color match to the steel. Note that the weld and base plate weather over a period of time and eventually have similar color. Filler metals used to weld weathering steels most commonly contain a minimum of 1% nickel. These are the “CX” or “NiX” (e.g., C3, C1, Ni1, Ni2) series low-alloy steel filler metals. These electrodes also typically have a minimum tensile strength rating of 80 ksi (552 MPa). While you might not require this strength level for welding on carbon-steel grades of weathering steel, you do need the nickel content. The higher strength comes along for the ride. Low-Alloy Steels Compared to medium- and highcarbon steels, low-alloy steels include additional alloying elements in place of some of the carbon in order to achieve strength and other properties, while also improving ductility and weldability. Carbon content is typically 0.05–0.25% by weight, and the steel is also alloyed with low percentages by weight of other elements, such as nickel, chromium, molybdenum, niobium, vanadium, titanium, etc. Many of these steels are heat treated or quenched and tempered to produce the desired mechanical properties. They are welded with low-alloy steel filler metals with similar alloy content — Fig. 4. Examples of low-alloy filler metals include E7018-A1 H4R, ER80SB2, E10018-D2 H4R, and E91T1- K2M-JH4. Quenched and Tempered Steels (Q&T): These steels are heat treated for strength and ductility. They include, for example, ASME A514 steels, commonly referred to by U.S. Steel’s brand name “T-1.” Do not weld them using high heat input and interpass temperatures to avoid softening the steel and losing some of its strength properties. The Q&T steels are generally welded with a 110 ksi (758 MPa) minimum tensile strength filler metal. If the plate thickness is more than 2.5 in. (63.5 mm), then a 100 ksi (690 MPa) minimum tensile strength filler metal may be used. Quenched and tempered steels are also joined to lowcarbon steels. In those cases, follow the rule outlined earlier in this article about choosing a filler metal of matching strength to the weaker material, which improves the weldability. AISI Grades of Steels: These could be referred to as “heat-treatable” grades of steel because they have no specified strength levels. Instead, they often are heat treated in different ways to produce the desired mechanical properties. The 10XX–15XX series are carbon-steel grades and the rest are low-alloy grades. The appropriate filler metal selection for all grades is dependent on the specific treatment of the steel. To illustrate this point, look at AISI 1040 carbon steel and the resulting mechanical properties when it is subjected to three different manufacturing treatments (Table 3). The appropriate matching strength filler metal you select depends on which treatment was applied to the steel you are welding. As another example, common applications for the chrome-moly grades (4130, 4140) or nickel-chrome-moly grades (4340, 8620) include rollers and shafts. There are no filler metals that exactly match the chemistry of these types of steels. However, if they must be joined, then a “DX” series (e.g., D2) manganese-molybdenumtype, low-alloy filler metal is most commonly used. Other times, the roller or shaft has worn down in an area. In these cases, the part can be restored back to the original dimensions with an overlay weld. For these applications, use a filler metal with similar chemistry, such as Lincoln Electric’s Lincore 4130, or use a “buildup” type, hardfacing filler metal and/or a “metal-tometal” type hardfacing filler metal of an equivalent hardness to the base plate. Conclusion This article provides general guidelines for selecting the proper filler metal for some common types of steel and steel alloys. These guidelines are primarily based on the steel’s chemical formulation and mechanical properties. Beyond that, other factors need to be considered for choosing the most appropriate filler metal for your particular welding application. These factors include welding process, welding position, plate thickness, plate condition, and other variables. 56 WELDING JOURNAL / APRIL 2015 WJ TOM MYERS is a senior application engineer with The Lincoln Electric Co., Cleveland, Ohio, www.lincolnelectric.com. Based on a presentation made during the AWS So You’re the New Welding Engineer Conference held during FABTECH 2014 in Atlanta, Ga. Iron Man Comic Book, Welding Career DVDs Available for Free Copies of four unique resource materials, including the Careers In Welding magazine, Iron Man comic book, and Hot Bikes, Fast Cars, Cool Careers, and Careers In Welding DVDs, may be requested for free. Just visit www.CareersInWelding. com, click on the welding publications link, and fill out the form to specify the quantity you need of each item.
Welding Journal | April 2015
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