Stronger with Aluminum
2014 R&D 100 Winner
Thermal fatigue is one of the most important properties in materials used as automobile’s exhaust parts, particularly near the hotter manifold section. When the exhaust gas passes through these parts, they thermally expand or shrink. But they can’t do this freely because of surrounding parts, which leads them to deform or fracture. The solution has long been to add molydenum to the ferritic heat-resistant stainless steels typically used for automobile exhausts. JFE Steel Corp., however, has achieved resistance to thermal fatigue fracture without the use of high-cost molydenum in its JFE-TF1 steel.
The new steel is based on the fact that aluminum has a large effect on high-temperature properties through so-called solid solution hardening. One of the primary alloying elements in JFE-TF1 steel is copper, which provides strength by precipitating as fine particles. However, copper’s benefits are limited beyond 800 C where it instead solutes into the steel matrix. JFE Steel’s engineers discovered that by adding a small percentage of silicon, they enhance the anti-corrosion ability of aluminum, providing protection beyond 800 C. The result substantially reduces alloying costs, increases fatigue limits and permits a gauge reduction of 30% for steel exhaust parts.
JFE Steel Corp.
|JFE Steel Corp.'s JFE-TF1 development team.|
The JFE-TF1 Development Team from JFE Steel Corp.
Hiroki Ota, Principal Developer