Abstract
To meet the requirement for higher allowable design stress of the suspension springs, new steel were developed placing emphasis on corrosion fatigue resistance. Corrosion fatigue life proved to be increased by improvement of hydrogen embrittlement resistance as well as corrosion resistance. Corrosion resistance was improved through the control of rust composition by the addition of copper and nickel. Hydrogen embrittlement resistance was improved through the improvement of toughness and the introduction of hydrogen trapping sites by the addition of titanium. Newly developed steel (UHS1900) subjected to a 1200MPa maximum shear stress has the same corrosion fatigue life as that of SUP7 steel subjected to a 1100MPa maximum shear stress. In addition, UHS1900 demonstrated better toughness, ductility, hydrogen embrittlement resistance, fatigue life in the air, fatigue life in the corrosion atmosphere, and sag resistance when it was tempered relatively lower temperature of 200∼300°C. This suggests that application of the lower tempering temperature enables higher stress design for UHS1900 springs.
