Handbook-Welding Ferrous Metals

1 WELDING OTHER FERROUS METALS In the preceding chapters, we’ve been talking chiefly about the welding of the two kinds of ferrous materials (iron alloys) most frequently encountered: low-carbon mild steels, and gray cast iron. Now let’s take a look at the problems involved in the oxy-acetylene welding of several other ferrous materials, specifically: Cast Steel Stainless Steels High-Carbon Steel Wrought Iron Galvanized Steel Cast Steel Many castings are made from steel, rather than cast iron, in order to arrive at finished parts which have high shock resistance and good ductility, properties in which cast iron is generally deficient. Cast steel can often be distinguished from cast iron by its surface color. The ”gray” color of steel is so distinctive that the term ”steely” is often used to describe the color of other materials. When surface identification isn’t possible, the color of a freshly fractured surface will distinguish cast steel from cast iron. If necessary, use a cold chisel on the surface of the casting, and attempt to cut off a thin chip. From steel, you can cut a curling chip of some length; from cast iron, even a short continuous chip is unusual. Finally, the behavior of the two materials when raised to melting temperature by the torch flame is quite different. The steel appears to be nearly white-hot before it melts; cast iron starts melting at a red heat. A puddle of molten steel is straw-white in color; a puddle of cast iron is reddish-white. Most cast steels are similar to low-carbon or medium-carbon rolled steels in composition, and can be welded with ease. In fact, the welding of rolled (wrought) steel to steel castings is often a production application. When welding cast iron, the major problem is to avoid cracking the cast iron, or leaving it with locked-in stresses that might cause cracking in service. When welding cast steel, you normally need not worry about cracking, but you must be concerned about distortion, since steel will stretch – become permanently elongated – before it will break. Distortion can often destroy the utility of a casting just as completely as cracking.