FIELD

The present disclosure relates to iron-based alloys, in particular to corrosion and wear-resistant iron-based alloys with sustained strength and hardness capability in a wide temperature range that may be used, for example, in valve seat inserts.

BACKGROUND

More restrictive exhaust emissions laws for diesel engines have driven changes in engine design including the need for high-pressure electronic fuel injection systems. Engines built according to the new designs use higher combustion pressures, higher operating temperatures and less lubrication than previous designs. Components of the new designs, including valve seat inserts (VSI), have experienced significantly higher wear rates. Exhaust and intake valve seat inserts and valves, for example, must be able to withstand a high number of valve impact events and combustion events with minimal wear (e.g., abrasive, adhesive and corrosive wear). This has motivated a shift in materials selection toward materials that offer improved wear resistance relative to the valve seat insert materials that have traditionally been used by the diesel industry.

Another emerging trend in diesel engine development is the use of EGR (exhaust gas recirculation). With EGR, exhaust gas is partially routed back into the intake air stream to reduce nitric oxide (NOx) content in exhaust emissions. The use of EGR in diesel engines can change engine combustion characteristics and consequently the valve/VSI working environment. Accordingly, there is a need for lower cost exhaust valve seat inserts having suitable metallurgical and mechanical properties for use in diesel engines using EGR.

Also, because exhaust gas contains compounds of nitrogen, sulfur, chlorine, and other elements that potentially can form acids, the need for improved corrosion resistance for alloys used in intake and exhaust valve seat insert applications is increased for diesel engines using EGR. Acid can attack valve seat inserts and valves leading to premature engine failure.

There is a need for improved iron-based alloys for valve seat inserts that exhibit adequate hardness, as well as corrosion and wear resistance suitable for use in, for example, intake and exhaust valve seat insert applications.

SUMMARY

In embodiments, the present disclosure provides a low-carbon iron-based alloy containing, in weight percent, carbon from about 0.1 to about 0.8 percent; manganese from about 0.1 to about 4 percent; silicon from about 0.1 to about 0.5 percent; chromium from 14 to about 16 percent; nickel up to about 8 percent; vanadium up to about 0.1 percent; molybdenum from 14 to about 16 percent; tungsten up to about 6 percent; niobium from about 0.1 to about 0.8 percent; cobalt up to about 0.2 percent; boron up to 0.1 percent; nitrogen up to about 0.1 percent; copper up to about 1.5 percent; sulfur up to about 0.05 percent; phosphorus up to about 0.05 percent; aluminum up to about 0.005 percent; balance iron from about 50 to about 65 percent; and incidental impurities wherein the alloy contains a ratio of Cr/Mo of about 0.9 to about 1.1.

In an embodiment, the alloy comprises: carbon from about 0.15 to about 0.75 percent; manganese from about 0.2 to about 3 percent; silicon from about 0.2 to about 0.4 percent; chromium from 14.5 to about 15.5 percent; nickel from about 3 to about 6 percent; vanadium from about 0.02 to about 0.06 percent; molybdenum from 14.5 to about 15.5 percent; tungsten from about 0.02 to about 6 percent; niobium from about 0.1 to about 0.7 percent; cobalt from about 0.005 to about 0.1 percent; boron from about 0.005 to about 0.01 percent; nitrogen from about 0.04 to about 0.09 percent; copper from about 0.6 to about 1.2 percent; sulfur up to about 0.03 percent; phosphorus up to about 0.03 percent; aluminum up to about 0.005 percent; balance iron from about 53 to about 63 percent; and incidental impurities.

In another embodiment, the alloy comprises carbon from about 0.1 to about 0.8 percent; manganese from about 1 to about 3 percent; silicon from about 0.2 to about 0.4 percent; chromium from 14.5 to about 15.5 percent; nickel from about 5 to about 6 percent; vanadium up to about 0.1 percent; molybdenum from 14.5 to about 15.5 percent; tungsten about 4 to about 6 percent; niobium from about 0.1 to about 0.2 percent; cobalt up to about 0.1 percent; boron up to about 0.1 percent; nitrogen up to about 0.1 percent; copper 0.8 to about 1.2 percent; sulfur up to about 0.03 percent; phosphorus up to about 0.03 percent; aluminum up to about 0.005 percent; balance iron from about 50 to about 56 percent; and incidental impurities.

According to various embodiments, the alloy contains about 50 to about 65 weight percent iron, at least 3 percent nickel, at least 0.7 percent copper, up to 0.1 percent cobalt, up to 0.07 percent vanadium and up to 0.7 percent niobium, the alloy has a hardness of at least 47 Rockwell C, and/or the alloy has a microhardness (HV10) of at least 350 at a temperature of about 1000° F.

In an embodiment, the alloy consists essentially of, in weight percent: carbon from 0.1 to 0.8 percent; manganese from 0.2 to 3.5 percent; silicon from 0.1 to 0.4 percent; chromium from 14.5 to about 15.5 percent; nickel from 3 to 6.5 percent; vanadium up to 0.1 percent; molybdenum from 14.5 to about 15.5 percent; tungsten up to 6 percent; niobium up to 0.7 percent; cobalt up to 0.1 percent; boron up to 0.1 percent; nitrogen up to 0.1 percent; copper 0.7 to 1.2 percent; sulfur up to 0.03 percent; phosphorus up to 0.03 percent; aluminum up to 0.005 percent; balance iron from 50 to 65 percent; and incidental impurities wherein a ratio of chromium to molybdenum is 0.9 to 1.1.

In an exemplary embodiment, the alloy is cast into a cast part having a fully austenitic microstructure, a fully ferritic microstructure, or a duplex ferritic-austenitic microstructure. For example, the cast part can be a valve seat insert useful in combustion engines.

