Development of grain refinement process for cast steel

Foundry industry in various industrial countries has paid more attention to grain refinement of cast steel for more than 60 years.

At the end of 1950s, M.C. Flmings, J.F. Wallace and others in the U.S. have started the research on grain refinement of cast steel.

In the early 1960s, J.F. Wallace et al., supported by U.S. Military Materials Research Department, carried out a quite comprehensive exploratory research work on grain refinement of carbon steel and low alloy steel [12].Materials with heterogeneous nuclei, such as Ti, Nb, B, V and Zr, as well as carbides, nitrides and oxide powders of various metals, which were considered possible at that time, were tested and studied.Based on the analysis of the test data:

(1) TiC can be generated as heterostructure nucleus by adding Ti into molten steel, which can refine grain size. However, there are some difficult problems in mechanical properties.

(2) Nb can also refine grains, but its effect is not as obvious as Ti.

(3) Other added materials have little effect on grain refinement.

At the beginning of 1980s, Beijing Institute of Iron and Steel (now Beijing University of Science and Technology) of China carried out a lot of research work on the application of rare-earth elements in carbon steel and low-alloy steel, and noticed that the addition of rare-earth elements in steel has grain refinement effect.

In the same period, J.J. Moore in the UK also carried out tests with rare earth elements to improve the impact toughness of low alloy steels with 0.10% C and 1.25% Mn content.Rare earth elements are added into the molten steel in the form of rare earth ferrosilicon or mixed rare earth alloys.When rare earth elements are added, the sulfur content in steel decreases greatly, about 90%. The fine non-metallic inclusions in steel are mainly RE-Mn-O-S.Moore also noticed that the grain refinement of the steel, but at that time he attributed the improvement of the steel performance to the purification effect of desulfurization without further research on the effect of grain refinement.

At the beginning of the 21st century, C.Eijk, F.Haakosen and others added alloys containing rare-earth element Ce into completely austenitic stainless steel, and found that they have good grain refinement effect.Several different alloys containing Ce were subsequently used in austenitic high manganese steels.

Continuous R.B. Tuttle research in recent years has shown that rare earth elements not only refine grains in austenitic steels, but also are suitable for carbon and low alloy steels.

It seems that the application of rare earth elements in grain refinement of cast steel has a promising prospect.Of course, a great deal of recent research work done in the United States is still a good starting point. To launch a widely applicable process technology, a lot of experiments and research work still need to be done.

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