Abstract
The recent trends on corrosion protection technology for improvement of strength on steels, especially in automotive application, are reviewed. The decrease of susceptibility to environmental cracking, such as, delayed fracture, and corrosion fatigue is the key point for the improvement of strength for quench and temper type high strength steels for high tensile bolts, suspension springs, door beams, etc. Delayed fracture of high tensile bolt steels is minimized by change of lubricant, improvement of Zn electroplating condition, materials improvement such as precipitation of hydrogen trapping site, etc. Corrosion improvement is also very effective for decrease of delayed fracture of door beam steel. Corrosion fatigue life improvement of high strength spring steel is achieved by improving resistance to pitting corrosion and hydrogen embrittlement. Its pitting corrosion is minimized by rust control, and the hydrogen embrittlement by the introduction of a hydrogen trapping sites in the matrix. Corrosion protection of steel sheet for automotive body, tire steel cord, etc. are also reviewed.
