Products and solutions, 2007-09-11, 08:05 AM
Requirements on vehicle suspension springs are growing all the time. The goals in developing coil springs are to minimize weight, optimize packaging space, maximize strength and minimize cost. Coil springs with higher stress levels and consequently higher strength allow a further reduction in weight while maintaining part lifetime. ThyssenKrupp Bilstein Suspension is a leader in the development of such innovative components.
In Europe vehicle suspension springs are now made almost exclusively from Si steels, replacing the previously used Cr steels in line with the trend toward higher strengths. Material developers are looking to improve ductility at strengths above 2050 MPa and optimize finishes (decarburizing). Steel can be optimized in several areas; changing the chemical composition can influence strength, sag resistance, toughness, heat treatability and corrosion resistance.
The “High Performance Therm-o-Tec Process (HPTP)” is a milestone in process development in which induction austenitizing (heat treatment) is followed by thermomechanical forming in a rolling process. The springs are subsequently wound and hardened. Recrystallization during the thermomechanical forming process provides outstanding ductility and a previously unattainable strength level of 2200 MPa. Bilstein’s ThermoTecSpring® is approx. 15 percent lighter, while the lower overall spring height offers additional weight-saving potential.
Although basic ductility can be significantly increased, springs with a heat-treated strength of over 2050 MPa need special surface protection to prevent premature failure from corrosion pitting. One solution is the DualProtect® coating with a first layer (zinc primer) to protect against corrosion and a second layer to protect against mechanical damage (stone chipping etc.). The AluProtect® aluminum coating provides an alternative for surface protection.