Investment casting-Carbon equivalent

Carbon equivalent, also called as Equivalent carbon content and C.E., is a major factor for determining the weldability of alloy steel castings, carbon steel castings and iron castings.

Some products we made by investment casting or sand casting processes will be welded with other components for assembling purpose. Such investment castings and sand castings require for good weldability. Carbon element is the main factory to determine the strength and weldability of carbon steel. But for alloy steel, besides carbon, other alloy elements also affect the strength and weldability of the castings much.

To identify the weldability of certain steel or iron materials, we get the C.E numbers for each kinds of material after lots of tests. Below there are the formulas for getting the C.E. numbers,

1)Cast carbon steel and cast Alloy steel

C.E.=[C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15]*100%

2)Cast iron

CE=[C+0.3（Si+P）+0.4S－0.03Mn]% 

S elements takes small percent of cast irons. Mn element affects the strength and wedability of iron castings little. So, the forumlas for cast iron is also shorted as CE=[C+0.3(Si+P)]%.

According to our casting experience,

*CE≤0.4%, weldability of the material or castings are very good

*CE=0.4~0.6%, weldability of the material or castings are a little bad. Before welding, the castings should be preheated. 

*CE≥0.6%, the weldability is bad. Such material or castings are difficult to be welded. Cracks or other defects will be happened during welding process. To solve such problems, castings should be preheated with high temperature, and the welding process should be ollow close to the line of certain welding specification.