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Ductile iron castings after high temperature annealing heat treatment

Our foundry performed high temperature annealing heat treatment to ductile iron castings, in order to remove massive free carbide, improve elongation (toughness), improve welding property, remove inverse chill defects, reduce hardness, and make the material more uniform.

Ductile iron fragile and solution:

Ductile iron is good because it has good elongation, so is very tough, however, for some ductile iron castings with thin wall thickness, low production temperature outside, there may be some problems with the material, such as extra high hardness, fragile because of inverse chill defects, and poor welding property. All these problems are difficult to be solved by adjustment of casting process, so further heat treatment will be necessary.

High temperature annealing heat treatment is a very good heat treatment to solve these problems. We introduce a mature annealing heat treatment process. 100 degree per hour to "A" Celsius degree, then keep for "B" hours, then reduces temperature in the furnace to "C" degree, and then pull the castings out of furnace. (As for ABC, they are our technical data, so we are not convenient to reveal them in this article.)

Heat treatment result:

After heat treatment, we found the mechanical properties and metallographic structures have been improved significantly.

1. Elongation has been increased largely. Could be improved from 12% to 20%, however, their tensile strength was not reduced as theoretical estimation.
2. Inverse chill defects have been solved. Hardness has been reduced largely.
3. Free carbide has been removed, so welding property has been improved too.

In conclusion, material has become more tough and soft. All properties have been improved significantly.

Metallographic photos:

The followings are some metallographic photos before and after heat treatment. You could see the material has become very uniform after heat treatment.

Because our Dandong foundry checked the inverse chilling areas on the samples directly, not inspected the single specimen, so the photos are not clear enough. If you want to learn more information, please feel free to contact Galen Wang.

The above photos are showing the metallographic structures of ductile iron 500-7 before and after annealing heat treatment. 

The above photos are showing the metallographic structures of ductile iron 400 before and after annealing heat treatment.

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