Copyright Goodheart-Willcox Co., Inc. Chapter 8 Manual Welding Techniques 129 Forgings Forging refers to pressing a shaped die into hot metal under high pressure. The metal is heated to a plastic state before it is forged so it will take on the shape of the die that is pressed into it. Forgings are made from billets, bars, round stock, or square stock. Forgings can be identifi ed by the remnants of the fl ashing that usually extends around the center of the part. Since the forging operation is done while the part is hot, a scale forms on the surface, similar to the scale on hot-rolled steel. Steel Classifications Steels are manufactured to specifi cations devel- oped by various organizations, including ASTM International. One grouping of steels under this classifi cation is ASTM A335. The assigned designa- tion identifi es the material as high-ferritic steel alloy pipe for high-temperature applications. Other steel specifi cations include SAE International’s Aerospace Material Specifi cations (AMS), the American Iron and Steel Institute (AISI) classifi cations, and corporation specifi cations. Filler Metals Filler metals used to join carbon steels, low-alloy steels, and tool steels must be selected to produce the desired mechanical properties of the weldment after any required welding or heat treatment. Carbon and low-alloy steel fi ller metals are selected from specifi - cations, such as AWS A5.18, AWS A5.28, MIL-E-23765, MIL-S-6758, and AMS6370. When selecting a steel fi ller metal, the welder should consider the basic type of steel to be welded and the possibility of excessive porosity within the completed weld. Figure 8-1 lists three classifi cations of fi ller metal, each with a 70,000 psi tensile strength that can be used to weld porosity-prone material. Figure 8-2 lists several types of fi ller metals that can be used to weld HSLA (high-strength, low-alloy) steels. Chromium-molybdenum steels (chrome-moly steels) are a class of extremely strong and hard steels. If the chrome-moly weldment is to be hardened after being welded, one of the following fi ller metals should be used: • 1-1/4% chrome—1/2% moly fi ller metal • 2-1/4% chrome—1% moly fi ller metal • 4%–6% chrome (AISI 502) If the chrome-moly steel weldment will not be hardened after welding, the following stainless steel fi ller metals can be used: • 25% Cr—20% Ni stainless steel fi ller metal • 25% Cr—12% Ni stainless steel fi ller metal Do not use stainless steel fi ller metals for welds in service over 1000°F (538°C). Welds subjected to temperatures above 1000°F (538°C) will have carbon migration from the steel to the stainless steel, which can cause weld failure. When selecting fi ller metals for tool steels, refer to the fi ller metal manufacturer for the recommended type. These fi ller metals have been specially devel- oped for specifi c applications and are not made to precisely conform to specifi cations issued by organi- zations such as ASTM or AISI. Filler Metal Quality Steel fi ller metals are supplied by the manufac- turer with a bright fi nish, oiled fi nish, or copper fl ash fi nish. Since these materials are susceptible to rusting, store them in a dry, heated area until they are needed. Always clean the fi ller metal with acetone or alcohol just before use. Return all unused material to the storage area. Solid Wires for Carbon Steela Per AWS A5.18 Classification Composition C Mn Si Ti Zr Al ER70S-2 0.07 0.90– 0.40– 0.05– 0.02– 0.05– 1.40 0.70 0.15 0.12 0.15 ER70S-3 0.06– 0.90– 0.45– – – – 0.15 1.40 0.70 ER70S-5 0.07– 0.90– 0.30– – – 0.50– 0.19 1.40 0.60 0.90 a P, 0.025 S, 0.035 Cu 0.50. Figure 8-1. The letters E and R in the classification code identify these filler metals as solid electrode wires that can be used in the GTAW process. The letter E indicates the wire is designed to carry current for the GMAW process. Some electrode wires can also be used (without current) as filler metal for the GTAW process. If the electrode wire can also be used for GTAW, the letter E is followed by the letter R (which stands for “rod”).