What Material Can Be Used to Braze Cast Iron?

About Cast Iron

• “Cast iron” is a term used for a variety of iron materials with similar carbon content. It generally contains between 2 and 4 percent of carbon with a variety of alloys to enhance certain properties. Generally, cast iron may be any of four different varieties, such as white, gray, malleable and graphite cast irons, according to Johnson Matthey Metals. By virtue of the components within the material, cast iron can exhibit a variety of different reactions when heated. This variability can make joining pieces of cast iron during welding or brazing unpredictable.

What Is Brazing?

• Brazing is a technique of joining metals that uses a filler material that is heated above its boiling point with an oxyacetylene torch. The liquid material then fills the gap between the two pieces by a capillary action. To braze cast iron, the material must be clean and free of grease or other contaminants. The parts often are pre-heated to around 1000 degrees Fahrenheit to allow the heat from brazing to be distributed evenly across the surface of the cast iron, according to the Brazing website. A flux is applied in paste, powder or liquid form. This material gives off a gas that helps to protect the area being brazed from contaminants in the atmosphere. Brazing requires less heat than traditional welding.

Materials For Brazing Cast Iron

• Because the composition of cast iron products can vary, homeowners attempting to braze them may have to experiment with a number of filler materials. Nickel often is used to braze cast iron. This material may be in a number of alloys with different percentages of nickel in the composition. Copper alloys also are used as filler material for brazing cast iron and steel. Some silver alloys also can be used to braze cast iron items. Silicon bronze is another material that often is used for cast iron welding.

Cast Iron Brazing Problems

• Cast iron contains more carbon and silicon than ordinary steel, which makes it less ductile and more prone to deformity during joining. Cast iron is susceptible particularly to cracking after brazing operations. Much of this problem can be eliminated with sufficient pre-heating of the materials before brazing.