152 Gas Tungsten Arc Welding Handbook Copyright Goodheart-Willcox Co., Inc. 152 Gas Tungsten Arc Welding Handbook 152 Gas Tungsten Arc Welding Handbook • Types of steel include carbon steels, low-alloy steels, heat-treated steels, and tool steels. Carbon steels are classifi ed as low-, medium-, and high- carbon steels. Alloying elements in low-alloy steels include chromium, molybdenum, nickel, vanadium, and manganese. Heat treatments include quenching, tempering, and annealing. Tool steels are steels with a combination of high carbon and alloy content. • Common steel forms include hot-rolled steel, cold-rolled steel, castings, and forgings. Steels are manufactured to specifi cations developed by various organizations, including ASTM International. • Filler metals must be selected to produce the desired mechanical properties in the weldment after any required welding or heat treatment. When selecting a steel fi ller metal, the type of steel to be welded and the possibility of excessive porosity within the completed weld should be considered. • Joint preparation considerations include removing oxide fi lm from edges prepared by thermal cutting processes, providing weld backing where needed, and preheating. Quenched and tempered steel requires preheat and interpass temperature control to retain the original mechanical properties of the metal. • Two torch angles that affect how the weld bead is placed into the weld joint are the work angle and travel angle. Work angles usually split the weld pool evenly between the two pieces of base metal. A good travel angle allows the welder to see the weld pool. • Stringer beads, or stringer passes, are welds made without oscillation of the torch. Weave beads are welds made with torch oscillation. • Thoriated, lanthanated, ceriated, zirconiated, and pure tungsten electrodes can be used for welding steel. Lanthanated electrodes work well for either AC or DC current and have good current- carrying capacities. Higher welding amperages require larger electrodes. An electrode that is sharpened to a point with a slightly fl attened tip is recommended for welding steel. • Pure argon gas can be used when welding metal up to 1/8″ (3.2 mm) thick. For greater thicknesses, helium should be added to the shielding gas. • Manual GTAW requires a great deal of skill to perform correctly. The ability to read a weld pool must be developed so that the welder can make the appropriate adjustments to ensure a quality weld. Answer the following questions using the information provided in this chapter. 1. What are the three classifi cations of carbon steel? 2. Medium-carbon steel has a content of _____ carbon. 3. List three alloying elements commonly used to make low-alloy steels. 4. What is heat treating? 5. The oxide fi lm on the surface of hot-rolled steel is _____ in color. 6. The surface of castings that have been sand- blasted are _____ in color. 7. Why should stainless steel fi ller metals not be used for welds in service over 1000°F (538°C)? 8. List the three fi nishes available on steel fi ller metals. 9. Why must the oxide scale be removed from the edges of thermally cut joints before use? 10. What two types of backing are used for welding steel joints where 100% penetration is required? 11. Why is backing used for 100% penetration steel welds? 12. When should carbon steels less than 1″ (25.4 mm) thick with less than .30% carbon be preheated? 13. A(n) _____ that is too low causes low-alloy steels to have hard heat-affected zones after welding. 14. What is the main reason for maintaining a good travel angle? 15. The welding rod to be added to the weld pool is held at what angle? 16. Tool steels should be welded with small _____ beads to reduce the amount of heat input and expansion of the base material. 17. At what approximate temperature can postweld stress relief of carbon steel weldments be done? 18. Welds made without any side-to-side movement of the torch are called _____ beads. 19. Welds made with side-to-side movement of the torch are called _____ beads. 20. When steel is being welded, a small white dot may form on the top of the molten metal. What is this material? Summary Review Questions