Optimizing structure-property relationship in ductile iron

Through a global review of the cast iron literature and a multiphase physical metallurgy study, Element’s metallurgical experts characterize the relationship between the metal matrix, alloy content, and tensile properties in ductile iron to achieve a higher combination of strength and ductility.

A literature review showed that no extensive research work had been conducted to determine what is required to achieve 80-50-06 properties consistently. Our experts’ research developed an understanding of the relationship between alloying elements, matrix microstructure and properties in ductile iron that is not yet available to ductile iron producers.

An overall goal of the study was to determine what alloy content and metal matrix conditions could result in above-standard tensile properties for 80-55-06 ductile iron, i.e, elongation greater than 12% with yield strength greater than 55 ksi (380 MPa).

研究和测试

The research involved the application of standard physical metallurgical tools, including拉伸性质, optical microscopy, and automated image analysis to measure ferrite content, grain size, nodule count, nodule size, and nodularity. In addition to applying standard statistical parameters such as mean and standard deviation, the investigators also employed Pearson correlation coefficient analysis, transmission electron microscopy, andX-ray diffraction.

The first phase of the study consisted of an initial survey of the properties in commercial castings from several foundries. A key thrust was to investigate the chemistry and microstructural parameters that produced combinations of high strength and elongation.

Representative samples of grades 80-55-06 and 65-45-12 ductile iron were analyzed. A total of 53 samples were subjected tohardness和机械测试和26个样品进行成分，微观结构和应变硬度行为进一步测试。

Conclusions

The results of the study were as follows:

• 具有铁氧体含量的球墨铸铁的力学性能。作为铁氧体含量的增加，极限强度和屈服强度的形式的强度降低，伸长率增加;
• The combination of high strength (>80 ksi ultimate and >55 ksi yield) and high elongation (>12%) occurred when ferrite content was between 35 and 60%, and the ferrite colonies were discontinuous;
• The alloying elements copper, manganese, copper + manganese, and silicon strongly influence the occurrence of ferrite and, just as importantly, can be numerically correlated to the resulting mechanical properties. An ‘ideal’ range for these elements can be related to achieving yield strengths over 55 ksi combined with elongations that exceed 12%;
• 铁氧体菌落的连续性似乎与机械性能有关。铁氧体落区连续性的增加降低了标称相同的铁氧体含量和石墨参数的样品的强度和延展性。

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