Spheroidal Graphite Nodule
Nodular graphite nodules are spherical graphite concentrations in cast iron formed by magnesium or cerium treatment. They minimize notching effects and increase mechanical elongation.
Physicochemical Mechanism of Action
Nodular graphite nodules are produced by targeted treatment of the melt with magnesium or cerium. These additions collect in the liquid melt and form spherical graphite crystals on cooling. The spherical shape minimizes stresses at the contours, which leads to less notch effect.
Metallurgical Relevance & Welding Risks
Nodular graphite nodules improve the mechanical properties of cast iron, especially elongation at break and fatigue strength. They reduce the risk of hot cracks and raise the toughness of the weld. With too high a concentration, however, the structure can be contaminated, which can lead to embrittlement.
Workshop Practice & Instructions
To produce nodular graphite nodules in cast iron, add magnesium or cerium to the melt in an amount of 0.1 to 0.3 %. Cooling should be slow and controlled to keep the spherical shape of the graphite nodules. When welding, careful cooling is required to minimize the risk of hot cracks.