Enhanced Spring Steel’s Strength Using Strain Assisted Tempering

Abstract

Spring steels are typical materials where enhancement of mechanical properties can save considerable mass for transport vehicles, in this way the consumption of fuel or electric energy can be decreased. A drastic change in both the resulting microstructure and mechanical properties could be achieved due to the inclusion of strain into the tempering process after quenching. The strain assisted tempering (SAT) technology was applied, i.e., the process of quenching and following a sequence of tempering operations alternating with strain operations. After the first tempering, controlled deformation by rotary swaging was carried out with a strain of 17% (strain rate is about 120 s−1). Considerably higher strength parameters after SAT compared to conventional quenching and tempering (QT) technology were nevertheless accompanied by enhanced notch toughness at the same time by the decrease of elongation and reduction of area. However, by optimizing the process it is was also possible to achieve acceptable values for those parameters. Remarkable differences are visible in resulting microstructures of compared samples, which were revealed by metallographic analysis and X-ray diffraction measurement. While the standard microstructure of tempered martensite with transition carbides was observed after QT processing, carbideless islands with nanotwins occurred in martensitic laths after SAT processing.

Design and Control of a Shape Memory Alloy-Based Idle Air Control Actuator for a Mid-Size Passenger Vehicle Application

“…Based on a predefined colourmap of the actuator's strain for the opening state, the bias spring shows the highest strain, and the SMA spring follows it. However, the recorded maximum strain of 2% is lower than the allowable working strain of the spring made from steel, which is between 15% and 20% [54,55]. This strain is also below the maximum strain transformation of the SMA spring.…”

Fatigue Properties of Spring Steels after Advanced Processing

“…The fatigue limit was calculated based on the knowledge of the constant parameter A and slope parameter B presented in Equation (1). The relationship for the fatigue limit estimation σ ∞ is presented in Equation (2).…”

“…They consisted of tempered lath martensite and retained austenite (γ). A retained austenite content of about 4 vol.% was determined for both samples using X-ray diffraction analysis in previous work [2]. Precipitation of transition carbides occurred in the martensite crystals.…”

“…This process was applied on SAT material to show the effect on the fatigue resistance. This combination is labelled This work follows from previously published results wherein a new process known as SAT was developed for medium-carbon steel 54CrMo6 to achieve enhanced tensile properties up to 3 GPa, together with good plasticity [2,12]. Compared to conventional steel, the fatigue resistance of SS is a complex material property wherein its sensitivity to processes such as post surface treatment, material purity and the component design itself all play a crucial role [4,5,7].…”

“…High strength steels include spring wire made of 54SiCr6 steel, wherein the quenching and tempering (QT) process can be replaced with strain-assisted tempering (SAT) to make the steel even stronger [1,2]. This steel has great potential for use in highly specific product sectors such as coil springs for racing purposes.…”