RESUMEN
This article deals with the effect of strain-assisted tempering (SAT) on the fatigue properties of 54SiCr6 steel used for spring steel wires in a wide variety of automotive applications, including coil springs. This steel spring wire is extremely strong, having a high elastic limit and yield point, giving the steel excellent energy accumulation and fatigue properties. This combination opens up new possibilities in helical and cylindrical coil spring design, resulting in the reduction of both size and weight. Lightweight coil springs lead to improvements in fuel consumption, stability and vehicle traction. A large plastic deformation and SAT were applied to enhance the yield point of the study material. Improvements in the static and cyclic properties of steel springs were investigated using tensile tests and 3PB fatigue tests at ambient temperature. In addition, an advanced laser shock peening (LSP) process was employed to increase the fatigue resistance of the SAT material. The results presented here show great improvements in the static and fatigue properties over commercial steel treatment. The material quality of the wires was evaluated to be insufficient for further processing with cold coiling.
RESUMEN
Continuous cooling transformation (CCT) diagrams are widely used when heat treating steels and represent which type of phase will occur in a material as it is cooled at different cooling rates. CCT diagrams are constructed on the basis of dilatometry measurements on relatively small testing samples (cylindrical shape with diameter of 4mm and length of 11 mm in this study). The main aim of this work was to demonstrate the possibility of evaluating the tensile test properties using mini-tensile tests from miniature volumes (1.4 × 10-7 m3 for one sample) subsequent to determination of the CCT diagram and to extend a standard CCT diagram with information about strength, ductility and the estimated value of the work-hardening coefficient. Mini-tensile tests (MTT) were recently developed due to the low availability of experimental material and have already been successfully used for local mechanical property characterization of metals. CCT diagrams were constructed for 42CrMo4 steel prepared by the laser-directed energy deposition (L-DED) process, for commercially available 42CrMo4 steel conventionally manufactured (for comparison of traditional processing and AM preparation) and for H13 tool steel deposited by the selective laser melting (SLM) process.