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Show (5). Availability - Wrought heat resisting alloys are available from stock in numerous forms, permitting immediate procurement, and minimizing the need for excessive inventory or maintenance supplies. (6). Repairability - After exposure to service, castings may lose ductility and become difficult to weld repair fra'ctures and cracks. Almost all wrought assemblies can be repaired without a 20000F anneal and in some cases straightened. (7). No pattern cost. In fabrication, the heat resisting alloys work differently than mild steel. Whether bending, forming shearing, machining, or welding, there are some differences that should be considered based on the realization of the alloy's properties. The most Important thing to keep in mind when shearing an alloy for high temperature application is to avoid cracks and rough edges. Torn metal Is the focal point for stresses which can lead to failure and a shorter service life. The yield strengths are a little higher in alloy in the hot rolled, annealed condition· and the tensile strengths are a lot higher compared to mild steel. Shearing capacity has to be approximately 50% greater. Good shearing practice is to cut 20% of the metal and the remaining 80% is fractured. A larger percent of the fracture ratio can result in tearing and develop small edge fissures which become notches when used at high temperatures due to expansion of the metal. Punching is a more critical operation and more susceptible to tearing. If economically feaSible, drill rather than punch holes and on thick plates, saw cut rather than shear. These fissures can also affect the ability to take forming. Use as large a bending radius as possible. The AISI's recommendation for austenitic steels is forming to an Inside radius twice the thickness of the material, and on more highly alloyed metal it could be four times the thickness. In the real world, this is usually much too generous for most fabrications and we often see metal bent to much smaller radii. If the Inside radius has to be sharp, it is good practice to dress the edges to reduce the amount of fissures that can be generated through shearing or punching (Figure 6). The method for best edge conditioning is saw cutting and grinding. Welding heat resisting alloys requires specific techniques easily acquired through experience, but does not require sophisticated techniques. 5 |