If the Ductile Iron is subjected to hardening treatment, the surface hardness of castings can be increased, resulting in castings with good abrasive resistance and improved hardness. The usual quenching and tempering treatment results in increased surface hardness from approx. HRC 30 to HRC 40 of Rockwell hardness. In this process, the heat is treated to 880C-930C, next quenched in the oil, and then subjected to tempering treatment between 500C-600C.

Even improved abrasive resistance and higher hardness can be obtained in the carburising furnace. The surface hardness can increase to HRC 50 to HRC 55. The hardness depth is 2mm. Many foundries do the foundry by themselves, while some others outsource the job to locally available heat treatment workshops for completion. 

The carburising furnace is used for ductile iron. Because the mild steel has a low carbon content between 0.1% and 0.30%, therefore, it should be treated in the carburising furnace so as to raise its carbon content level on the surface—this is the usual method. In the case of ductile iron, the carbon content is quite high between 3.00% and 3.90%, which means that its carbon content needn’t be increased.

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However, when subjected to heat treatment, there will be some reduction in carbon content. Therefore, only normal tempering and quenching processes could increase its hardness level from HRC 30 to HRC 40. But if it is heated in the carburising furnace, the carbon content is maintained, so as to raise the hardness level from HRC 50 to HRC 55. We, at VR Foundries, found that it can provide increased hardness, improved abrasive performance and mechanical properties.