Influence of Cryogenic Treatment on the Fracture Toughness of Conventional and Super Clean Spring Steels 2016-36-0064

Spring steels are the materials most commonly used in suspensions of vehicles and are subject to heavy efforts in terms of load, impact and also under intense fatigue solicitation. Required mechanical performance depends mainly on the chemical composition and heat treatments. Therefore, the aim of the present work was to compare SAE 5160 steel with one Super Clean steel developed in Slovenia. Searches improving mechanical properties of these steels are constantly present in the automotive industry, reducing vehicle weight and maintaining safety. In this scenario, cryogenic treatment in combination with quenching and tempering has shown interesting results in the scientific literature for tool steels and the best results for cryogenics are achieved when the treatment occurs for long duration as 24 hours. However, for the industry, the production lead time should be as fast as possible, then it is interesting to discern the influence on spring steels of cryogenics when shorter durations as 12 hours, 2 hours and 30 minutes. The parameters that measure the ability of these materials to resist the quick fracture are called fracture toughness. Standardized tests are difficult to apply, so an alternative fracture toughness testing developed in IMT (Institute of Metals and Technology), Ljubljana, Slovenia, is one of the most promising methods. Thus, after applying these tests, the Super Clean steel showed higher resistance than SAE 5160 and there was not any enhancement caused by cryogenics.