Federal-Mogul Powertrain has introduced new materials for inlet and exhaust valves in response to the challenges of higher loads, increased intergranular and oxidation corrosion risk and continued downward cost pressure. Federal-Mogul state that the materials, are the result of a ‘twin-track’ approach by the company to define both an upgrade to conventional austenitic steel and also a more cost-effective alternative to high nickel ‘superalloys’.
As in the light vehicle market, the quest for improved fuel economy is driving the trend of downsizing and boosting in heavy-duty diesel engines. Previous generations of 16 litre engines have been replaced by 12 and 13 litre units, with even 10 or 11 litre engines now producing 500hp. This has led to a requirement for valves with increased high temperature strength that can withstand combustion pressures of 220-bar and above, while at the same time emissions reduction strategies are increasing the levels of exhaust gas recirculation (EGR) exposing the valves to greater risk of wet corrosion.
“For demanding applications the conventional answer is a premium material such as Federal-Mogul Powertrain’s ECMS-Ni80A, but with a Nickel content greater than 70% this is not always an economic solution,” explained Gian Maria Olivetti, chief technology officer, Federal-Mogul Powertrain. “We have established new ways to make more effective use of the expensive alloying elements such as Nickel by validating materials with equivalent hot strength to ECMS-Ni80A, but a lower alloy content.”
The main factors that differentiate the new materials in the range are the percentages of Nickel (Ni), Chrome (Cr) and Manganese (Mn) that they contain. One of the upgraded alloys, ECMS-2512NbN, is a development from standard CrMn austenitic steel designed to suit both inlet and exhaust applications experiencing elevated temperatures. By increasing the Nickel content from the usual 3 to around 12% while fine-tuning the combination of other elements in the alloy, both hot strength and corrosion resistance are significantly enhanced.
For higher temperature applications, ECMS-Ni36 high performance austenitic steel alloy has a superior resistance to hot oxidation than its industry standard equivalent, ECMS-3015D (austenitic steel with 15% Chromium and 31 percent Nickel). Additionally, despite having only 36 percent Nickel content, it has similar tensile strength to the superalloy ECMS-Ni80A, which contains more than 70% Nickel.
“The very high level of alloying elements present makes these materials quite special,” commented Guido Bayard, director, global valvetrain technology, Federal-Mogul Powertrain. “In order to predict reliability and conformity to engine applications, a wide range of rig and laboratory tests on wear, corrosion and durability are conducted, with a series of engine application trials on dynamometers also completed.”