Handbook-Braze Welding

5 Advantages and Disadvantages of Braze Welding Braze welding is faster than fusion welding, since the heat input required is much less. The rod normally used for braze welding has a melting point of about 875⁰ C (1600⁰F). In the braze welding of steel, the base metal must be heated only to a temperature of about 900⁰C, rather than to a temperature of more than 1500⁰C. The saving in time and the saving in gas consumption may frequently be more than enough to counterbalance the substantially higher cost of the filler metal. The reduction in heat input has other advantages, especially in the welding of cast iron, which will be covered in the next chapter. It minimizes the amount of preheating required. Since the bronze filler metal is extremely ductile, it can absorb stresses created during cooling which might, in the case of a cast iron fusion weld, cause cracking of the base metal or the weld. When used on steel, braze welding reduces distortion of the base metal due to forces of contraction and expansion. When mild steel or cast iron are properly braze welded, the strength of the joint, at normal temperatures, is likely to be equal to, or even superior to, the strength of the base metal. Braze welding can sometimes be used to join dissimilar metals which cannot be successfully fusion welded together. Steel can be braze welded to cast iron. Copper can be joined to brass by a braze weld. However, the joining of dissimilar metals by any welding process is something to be approached cautiously. The fact that you can turn out what appears to be a good-looking weld is no proof that the overall result is satisfactory. Essential properties of one or both of the metals joined may have been adversely affected by the act of welding. So much for advantages. What are the disadvantages? One is quite obvious, although often of no significance; you can’t match the color of the weld to the color of the base metal. Another, less obvious, is that bronze loses strength at relatively low temperatures. At 500⁰C, steel and cast iron are nearly as strong as they are at room temperature (20⁰C). Any bronze has lost a great deal of its strength at 500⁰C. Never use braze welding to repair parts that must operate at temperatures above 200⁰C. In Chapter 18 we shall talk more about the technique and advantages of bronze-surfacing, which is very closely related to braze welding.