Copyright Goodheart-Willcox Co., Inc. 128 Gas Tungsten Arc Welding Handbook Base Materials (Steel) Many types and grades of steel are included in the steel family. These materials are typically magnetic and melt at approximately 2500°F (1371°C). Carbon Steels Carbon steels are identifi ed as a group that contains the following materials: • Carbon—1.70% maximum • Manganese—1.65% maximum • Silicon—0.60% Carbon steels are further classifi ed based on the percentage of carbon: • Low-carbon (mild) steel—less than 0.20% carbon • Medium-carbon steel—0.20%–0.50% carbon • High-carbon steel—over 0.50% carbon Low-Alloy Steels Low-alloy steels contain varying amounts of carbon and a variety of alloying elements. These elements include chromium, molybdenum, nickel, vanadium, and manganese. These elements increase the strength and toughness of the material and, in some cases, increase resistance to corrosion. Heat-Treated Materials Heat-treated steels are used for many different applications. Heat treating is a process in which the material is heated and cooled to specifi c temperatures for specifi c amounts of time. A material is heat treated to obtain desirable qualities or to reduce undesir- able qualities. Many materials and alloys, including aluminum, copper, titanium, nickel, and chromium- molybdenum, can be heat treated to make the material perform in different ways. Heat treating of a material is most commonly done as part of the manufacturing process. Quenching is the process of rapidly cooling a mate- rial to obtain certain material properties that increase the material’s toughness. The quenching process changes the crystalline structure of the material. Tempering is a heat treatment that can improve the mechanical properties of a material. Tempering involves heating the metal to a certain temperature below the material’s melting temperature for a certain length of time. This process allows trapped carbon to produce a different crystalline structure. The material is then cooled at a controlled rate to a low temperature. The temperature and the duration of the tempering process determine which mechanical properties are enhanced. Annealing is a heat treatment that involves heating the material to a temperature that rearranges the crystalline structure and reduces internal stress of the material, making the material softer and more ductile. Annealing is typically done to improve the cold working properties of a material. Tool Steels Tool steels are steels with a combination of high carbon and alloy content. Tool steels are used for making dies, cutting bits, and many other types of tools. Dies and other tools are formed from annealed tool steel. Later in the manufacturing process, after the tools are formed, the metal is treated to harden or temper it as needed. The various types of tool steel include W1, W2, SI, S5, S7, 01, 06, A2, A4, and D2. Also included are H11, H12, H13, and M1, M2, M10. The numbers for the various tool steels identify the various compositions. The letters usually indicate the type of quenching required to achieve full mechanical values. Forms and Shapes of Steel Steel is supplied in many forms and shapes for welding. Some of the more common shapes are hot- rolled steel, cold-rolled steel, castings, and forgings. Hot-Rolled Steel Hot-rolled steel includes plate and structural forms which are allowed to cool in air after rolling. After cooling, the oxide fi lm on the surface is blue- gray in color. Cold-Rolled Steel This material is fi nal-rolled to the required dimen- sions in the cold condition and does not have an oxide fi lm or "mill scale" on the surface. A light coating of oil is placed on the material to prevent rusting. Cold- rolled steel requires very little preparation for GTAW welding. Castings Casting refers to pouring molten metal into a mold that has the desired shape. The metal is kept in the mold until it solidifi es, at which point the mold is removed. The cast metal inside has the same shape as the inside of the mold. Castings are usually made in a sand mold and have a rough surface. New castings are sandblasted, leaving a dull silver surface.