Cast Iron With Improved High Temperature Properties

Abstract

A nodular, compacted graphite or other hybrid or duplex graphite morphology cast high silicon iron is disclosed which contains up to 1.5% tungsten, up to 0.8% vanadium, and up to 1.2% niobium; and at least 60.0% iron, all percentages are based on the total weight of the composition. This cast iron exhibits high strength and good ductility over a wide temperature range compared to the conventional SiMo ductile iron. The compositions may further contain, up to 1.5% molybdenum and up to 1.0% chromium to offer improvements in material strength. The compositions may include 0.2 to 0.5% by weight aluminum and up to 1.2% chromium for further oxidation resistance and 0.5 to 5.0% nickel for corrosion resistance.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims the benefit of U.S. Provisional Application No. 60 / 678,950, filed on May 5, 2006. The disclosure of the above application is incorporated herein by reference.FIELD OF THE INVENTION[0002]The present invention relates to cast iron that exhibits improved strength and high temperature properties. More specifically, the present invention relates to cast iron alloys which contain certain amounts of carbide formers selected from the group including tungsten, vanadium and niobium. Other carbide formers such as molybdenum, and / or chromium may be employed in addition to at least one of tungsten, vanadium and niobium. Other alloy additions of silicon and aluminum for oxidation resistance are also disclosed. The cast iron may include a graphite morphology that is primarily nodular, vermicular or a combination referred to herein as hybrid or duplex.BACKGROUND OF THE INVENTION[0003]Cast iron alloys, and parts cast from the alloys...

AI Technical Summary

Benefits of technology

[0012]The high silicon iron composition of the present invention contains up to 1.5 wt. % tungsten, up to 0.8 wt. % vanadium, and up to 1.2 wt. % niobium, preferably in combination with at least one of molybdenum and chromium. The cast iron alloys of the present invention yield high strength and good ductility over a wide temperature range, compared to conventional SiMo iron having nodular, compacted graphite iron or other graphite morphologies. The addition of higher silicon and aluminum offers improved hot oxidation resistance, compared to conventional SiMo iron having nodular, compacted graphite iron or other graphite morphologies. In preferred embodiments, the iron alloy of the present invention contains, from about 0.02 to 0.8% vanadium, from about 0.03% to about 1.5% tungsten, from 0.02% to about 1.2% niobium, from about 2.8 to about 5% silicon, from 2.8% to about 3.8% carbon, less than 0.06% magnesium, and less than 0.02% cerium, the balances being at least 60.0 t % iron and impurities, with all percentages based on the total weight of the composition. The compositions may further contain up to 1.5% molybdenum, up to 1.0% chromium, up to 5.0% nickel and between 0.2 and 3.0% aluminum.

Problems solved by technology

Cast iron alloys, and parts cast from the alloys are subject in use to an ever increasing range of challenging environments.

However, the high oxidation rate at high temperatures remains a problem in parts such as exhaust manifolds and turbocharger turbine housings, where the in-use temperatures can reach 850° C. and higher.

In addition, cast irons in these applications are also subject to thermal fatigue cracking.

This continued thermal cycling and associated thermal expansion / contraction is said to contribute to thermal fatigue in the part which, in time, leads to cracking.

As temperatures increase, the cast iron is more prone to damage from lower strength at high temperatures, creep and oxidation resistance.

Further, because of the high demand of molybdenum in the steel and iron industries, the price of Mo fluctuates dramatically, increasing the cost of conventional SiMo cast irons.

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