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Step 1 involves heating the steel to a red-hot temperature then Quenching to a critical temperature, which results in partial transformation of the structure of the steel to strike just the right balance between strong martensite and softer but more formable austenite. In this work, a temperature–microstructure–stress coupled finite element model is established to simulate the quenching process of cold-rolled high-strength steel strips using a UMAT subroutine in ABAQUS. for a 50 mm diameter bar, the cooling rate at center is about 27°C/s in water, but, 13.5 °C/s in oil. The assumption of a completely immobile interface was incorporated into the equilibrium calculations, allowing quantification of the possible levels of carbon enrichment. See our User Agreement and Privacy Policy. The fundamental aspects related to Q&P processing have been reviewed in more depth elsewhere (29,32). Schematic illustration of the Q&P thermal processing concept. To reach temperatures below RT, dry ice mixed with alcohol can be used to reach up to −70 °C. The gear is partially modeled appl ying the cyclic symmetry constraint (MPC type CYCLSYM) in order to reduce the calculation time and to improve the accuracy. Unfortunately, rapid cooling can introduce residual stresses in parts by inhomogeneous plastic flow (inelastic strains) due to severe thermal gradients.73 These residual stresses can lead to warping during quenching, degradation of dimensional stability during machining, and reduced fatigue life during service.74 The aftermath of residual stress is distortion. Quenching: During cooling, heat must be extracted at a very fast rate from the steel piece. M.M.A. The idealized conditions, where the martensite and austenite fractions are fixed (i.e., the interface is constrained) and the chemical potential of carbon is uniform in the two phases, are now known as constrained carbon equilibrium (CCE), which defines the endpoint of equilibrium partitioning (12,27,30). For example, during machining, in a part with residual stress, the equilibrium state of stress is distorted and a new equilibrium results; local plastic deformation is then unavoidable. After removing from liquid nitrogen tank, the part is sprayed by either boiling water or water vapor, or it is dipped into the boiling water tank again. If you wish to opt out, please close your SlideShare account. The gases most commonly used today in connection with hardening are air and nitrogen. In addition, micropillar compression specimens were extracted from the individual ferrite grains and the martensite particles, and using a flat-punch nanoindenter, stress-strain curves were obtained. For AA7010 aerospace alloy, it was observed that 1% cold compression could relieve most of the residual stress developed during quenching.78 However, this could not diminish tensile stresses from the core, and susceptibility of SSC remains. The cooling sequence has considerable influence on properties such as microstructure, hardness uniformity, residual stresses, and the strength of the hardened part as well as on the distortion caused by the hardening.

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