- The material should retain its greatest strength at high temperatures.
- No tendencies to air harden.
- Critical temperature above 800*C.
- No tendency of high temperature scaling.
- Hot and cold corrosion resistant.
- Able to be forged and machined easily.
- Capable of consistent and reliable heat treatment.
- Most diesel engines use an Austenitic heat-resisting alloy steel. The seating surface can be stellited.
- Heat up to 950*C and cool in air to give a Brinnel Hardness of 269.
- Surface treatment is frequently used to improve or modify valve steel characteristics. Chrome-cobalt-tungsten alloy available in various grades of hardness is widely used.
- The hardness when deposited is in the order of 375 to 425 Brinnel.
- The valve head is treated to more than 430*C to reduce contraction stresses.
- The value face is now sweated by an oxyacetylene flame and the alloy deposited continually by welding (1.02 mm to 1.52 mm).
- Alloy Irons, with high percentage of molybdenum and Chromium with a Brinnel number of Approx. 500 are best.
- Alloy steel with stellited seating surface are also in common use.
- The methods employed for fitting the inserts include screwing and shrinking.
- Valve guides are mostly made of Cast Iron.
- To avoid scaling etc at high temperatures alloy Irons are preferred.
- Phosphor Bronze and Gun metal have also been successfully used.
- Alloy Iron guides with Bronze linings also are in common use.
- Mostly made of pearlitic cast iron and provided with a chamber for cooling water.
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