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REM Surface Engineering

Comparative Corrosion Characteristics of Ground and Superfinished Gear Steels

By: Suren Rao, Doug McPherson, Gear Research Institute-The Pennsylvania State University and Gary Sroka, REM Surface Engineering

Technical Papers and White Papers

The described effort was undertaken to assess the impact of the isotropic superfinishing (ISF®) process on the corrosion resistance of a variety of gear steels. Alloys examined were AISI 9310 VIM VAR, AMS 6308, Pyrowear ® 675 (two variations; tempered at 925°F and at 550°F), and CSS-42L TM (tempered at 925°F) with stainless steel 440C, in hardened condition, as a base line. Except for the 440C specimens all other specimens were sectioned gear teeth. They were as ground or super finished to be line free at 10X. Various passivation techniques were evaluated and the process adopted utilized 5% citric acid followed by ultrasonic solvent bath cleaning to remove any free iron that may be present on the surface.

Tests were conducted by suspending samples above a salt water solution and exposing the assembly to 150 degrees F for 8 hours followed by exposure to 37 degrees F for sixteen hours. This was repeated for fourteen cycles. This is a low intensity corrosion test, developed in collaboration with the sponsor and expected to reveal small differences in corrosion resistance between materials. The comparative performance is assessed by evaluating the extent of the corrosion on the various samples and also the depth of corrosion penetration in the worst corroded samples. Finally the corrosion resistance of the various steels is ranked by the observed performance in the ground and super finished category.


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