Quenching of Carbon Steel Plates with Water Impinging Jets: Differential Properties and Fractography

The demand for steel components with tailored properties is constantly growing. To obtain a specific variation of microstructuresand mechanical properties along the component it must undergo a controllable cooling. One way to control the cooling rates alongthe component is by using different simultaneous water jet impingements on a hot austenitized surface. This can be done by anewly developed test rig for water Impinging Jet Quenching Technique (IJQT). This work discusses the effect of IJQT onmechanical properties and fracture behavior of 15 mm steel plates containing 0.27 and 0.38 mass-% carbon. The samples werecooled in a specifically designed setup of the technique to obtain simultaneous water and air cooling resulting in diversemicrostructures. The mechanical property gradients of both steels were analyzed through hardness measurements and tensile tests.The fracture surfaces and the near fracture regions were observed using scanning electron microscope and light optical microscoperespectively.The results from tensile tests showed that the larger part of the sample with higher carbon content was fully hardened, howeversmoothly transitioning to a more ductile region. The sample with lower carbon content combined various degrees of hardening andtransitioned from higher to lower ultimate tensile strength values. Fracture behavior of higher carbon steel was predominantlybrittle transitioning to a ductile, while the lower carbon steel had a small region showing brittle fracture transitioning to a largerregion of predominant ductile fracture behavior.