Development history of grain refinement of cast steel

In the early 1920s, both a.m. Meehan and Crosby of the United States began to discuss the inoculation treatment technology of cast iron. In 1922, Meehan applied for a U.S. patent, which was approved in June 1924. The inoculation treatment of cast iron, which has a history of nearly 100 years, has already become an indispensable conventional production process in the production of cast iron in the world.

Before adopting inoculation technology, the tensile strength of grey cast iron was only 60-80 MPa in the middle of 1880s. After adopting inoculation technology and making other improvements, the strength of grey cast iron has been greatly improved, which can reach 350-400 MPa at present.

In the casting of non-ferrous alloys, the modification of aluminum alloy and magnesium alloy has a history of 60 to 70 years. At present, they are all conventional processes, which are indispensable measures to ensure the high quality of castings.

The modification of copper alloy was studied more than 60 years ago. Adding a small amount of zirconium (mass fraction, 0.02% – 0.06%) can improve the strength and hot cracking resistance of the alloy. However, the plasticity of the alloy and the air tightness of the casting are significantly reduced, and the influencing factors are complex, which remains to be further explored.

It is not too late to study the grain refinement of cast steel. However, due to the high temperature of molten steel, the formation of crystal nucleus is affected by many factors. Moreover, most of cast steel precipitated δ – ferrite at the beginning of crystallization, and then transformed into austenite through peritectic transformation. Austenitic steel precipitates austenite directly from liquid phase, and there is no solid phase transformation during solidification.

In a word, the situation of cast steel is very complex, the means of early detection and control are not enough, and the research work is very difficult. Therefore, although the exploration and research work of various countries have been uninterrupted for the grain refinement of cast steel, up to now, there is no stable technology that can be popularized and applied.

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