Several heavy truck Cr-Mo steel steering arms in service less than three years fractured during stationary or low-speed turning maneuvers that required power-assisted steering. Metallographic examination of the cracked AISI 4135 arms, heat treated to a hardness of 285 to 341 HB, revealed that fatigue crack initiation occurred from the tip of oxide scale inclusions forged into the U-shaped arm at the inside radius. Corrective action involved redesigning the steering arm to increase the minimum forging radius and reduce the stress level at the inner-bend radius, and reducing the level of power assistance to the wheels to encourage the driver to put the vehicle in motion prior to turning.
Roy G. Baggerly, Fatigue Failure of Steering Arms Due to Forging Defects, Handbook of Case Histories in Failure Analysis, Vol 2, Edited By Khlefa A. Esaklul, ASM International, 1993, p 67–70, https://doi.org/10.31399/asm.fach.v02.c9001005
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