Acid resistant austenitic alloy for valve seat insert

Abstract

A high carbon austenitic iron base alloy for wear and corrosion resistant applications is developed for valve seat insert applications when corrosion resistance is required. The alloy comprises 1.8-2.8 wt % carbon, 0.5-3.5 wt % silicon, 10.0-25.0 wt % chromium, less than 1.5 wt % manganese, 2.0-10.0 wt % molybdenum and tungsten combined, 1.0-4.0 wt % niobium and vanadium combined, 0-1.0 wt % titanium, 0.01-0.2 wt % aluminum, 12-25 wt % nickel, 0.5-3.0 wt % copper, and the balance being iron and a small amount of impurities.

Description

BACKGROUND OF THE INVENTION [0001] 1. Technical Field [0002] This invention relates to an acid corrosion resistant and wear resistant austenitic iron base alloy that possesses excellent resistance to sulfuric acid and is superior to high speed steels for many applications where both sulfuric acid corrosion and wear occur simultaneously. This invention further relates to such a corrosion resistant alloy useful for making valve seat inserts used in internal combustion engines with exhaust gas recirculation (EGR) system. [0003] 2. Description of Related Art [0004] Internal combustion engines equipped with EGR systems require intake valve seat insert materials with excellent corrosion resistance due to formation of sulfuric acid in intake insert area when sulfur oxide that comes from diesel fuel after combustion meets with moisture from incoming air. Sulfur content in diesel fuel seems relatively low, however, the concentration of sulfuric acid will likely increase with engine running t...

AI Technical Summary

Benefits of technology

[0012] It is the object of this invention to develop an austenitic iron base alloy with excellent corrosion resistance to meet the specific demand from more severe corrosion condition in diesel engines with EGR systems.

[0013] It is another object of this invention to develop a corrosion resistant iron base alloy with good wear resistance.

Problems solved by technology

Sulfur content in diesel fuel seems relatively low, however, the concentration of sulfuric acid will likely increase with engine running time as combustion deposits from exhaust gas accumulated around inner wall area of an intake insert will absorb more sulfuric acid.

Severe corrosion can occur on intake valve seat inserts made from M2 tool steel once the amount of high concentration acid is enough.

However, more severe corrosion conditions in some engines with high sulfur fuel and high humidity demands materials with corrosion resistance much better than the above iron base alloys.

High carbon and high chromium type nickel base alloys normally do not exhibit good wear resistance under intake valve seat insert working conditions due to lack of combustion deposits and insufficient amount of metal oxides to protect valve seat insert from direct metal-to-metal wear.

However, the cost of these cobalt base alloys only allows these alloys to be used in limited applications.