Influence of Transformation Plasticity on the Distribution of Internal Stress in Three Water-Quenched Cylinders
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NCHING is one of the most important heat-treatment processes for improving the mechanical properties of steel. During quenching, various phase transformations can occur depending on the cooling rate for a given steel, generating a variety of microstructures at different locations within a quenched component.[1] Moreover, the difference in the cooling rates at the surface and the core of a quenched component induces
YU LIU, SHENGWEI QIN, JIAZHI ZHANG, YONGHUA RONG, and XUNWEI ZUO are with the School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. YING WANG, is with School of Mechanical Engineering, Shanghai Dianji University, Shanghai 201306, P.R. China. NAILU CHEN is with the Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University. Contact e-mail: [email protected] Manuscript submitted February 12, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
thermal stress. Additionally, the expansion caused by phase transformations, such as martensitic transformation, will result in transformation stress. The interaction between the thermal and transformation stresses makes quenching stress rather complex. The quenching stress is also a source of cracking. The importance of the measurement of the residual stress distribution in a component lies not only in the determination of the location of the maximum tensile stress, which is often the cause of cracking,[2] but also in the data measured as a benchmark for examining the accuracy of computer simulations. As early as 1925, Scott[3] studied the cracking conditions of tool steel when quenched in water or oil. Using analytical calculations and experimental measurements of the axial stress distribution in the quenched cylinders, he concluded that the cracking was due to the tensional stress at the surface. Isomura and Sato[2] measured the residual stress of 18-mm-diameter and 100-mm-long cylinders after quenching in water or brine, respectively, and revealed that the quenching cracks were caused by the triaxial tension stress below the surface of the high carbon
cylinders. Moore and Evans[4] proposed the correction formulation, which is used to precisely measure the residual stress distribution along the radius of a cylinder by X-ray diffraction (XRD). The precise measurement of the residual stress distribution is the basis of process design. However, experimental measurements have three main limitations: (1) for a large and complex component, the measurement of the internal stress as a function of depth is not only difficult but also time-consuming; (2) in most cases, cracking of a quenched component is caused by transient stress during quenching, whereas the experiment can only measure the final internal stress (residual stress), rather than the transient stress; and (3) the origin of complex quenching stresses cannot fully be understood if there is no assist of computer simulation of the stress analysis. For these reasons, finite element simu
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