A Class 8 diesel fuel application experiences deformation wear when using a traditional nickel-base exhaust insert material after increasing the load and cylinder pressure parameters. The engine loading can exceed 450 hp at an engine speed of 1900 rpm and cylinder pressure near 2800 psi.
The coupling of W240 nickel-base insert material with a cobalt-base common trade material substitute facing results in heavy recession wear related to a combination of deformation and horizontal adhesive wear. The wear surface of the faced valve surface shows deformation lines near the middle and voids of removed material near the valve outside diameter. The W240 insert surface confirms deformation related to shear stress. The wear is approximately equal on both components. It is evident that the contact pressure exceeded the strength of the nickel insert material creating material deformation flow. The substitution of W77T6-P® iron-base material with the same valve facing reduces the total wear by approximately 80 percent from 0.25 to 0.05 mm in a severe 1000 hour dynamometer test set. The W77T6-P® exhaust insert is now relatively smooth and shiny with mild wear. The improvement is attributed to the exhaust temperature strength of the iron-base material, which exceeds the nickel alloy strength by a factor of four times, and the distribution and blend of wear-resistant carbide materials that retain hardness at these temperatures. The hot hardness value of W77T6-P® is 50.0 HRC at 427°F, while W240 drops to 36.9 HRC, and M2 tool steel is 30.0 HRC. This illustrates the value of the carbide blend in an iron-base that is less susceptible to deformation.