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Controlling thermal deformation using a heat sink in laser heat treatment of carbon steel sheets

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Title
Controlling thermal deformation using a heat sink in laser heat treatment of carbon steel sheets
Author
Kim, Sanseo
Advisor
Ki, Hyungson
Keywords
Thermal deformation from laser heat treatment
Issue Date
2015-08
Publisher
Graduate School of UNIST
Abstract
Objective of this study is controlling the thermal deformation from laser transformation hardening process. Unlike the laser forming process, thermal deformation behavior in laser heat treatment has rarely been studied. It is important that there is no deformation on specimen when heat treatment process is conducted. So this study was conducted. In this study, Thermal deformation tendency after laser heat treatment of steel sheets is investigated. Laser heat treatment experiments were conducted by a 3 kW diode laser on 2 mm thick DP590 dual phase steel and boron steel sheets. Also, in these experiments, there are four types of heat sink were used: steel, stainless steel 316, copper and no heat sink were considered. For each kind of heat sink, four interaction time and six levels of intensity were used for both types of steel. After experiments, deflection angle were measured by three dimension coordinate system and cross section of all specimen was captured, microstructure distribution such as martensite, bainite, ferrite and pearlite within heat treated region for all specimen were analyzed. All of deflection angle was distributed within interaction time and intensity. From this study, thermal deformation is reduced from positive value to negative value when a heat sink is used. Between positive value and negative value, zero deflection regimes, which are considered good conditions for heat treat process, are observed. In these different appearance of deflection angle, two different thermal deformation mechanisms are involved, which are plastic deformation and phase transformation. Plastic deformation cause positive deflection angle and the phase transformation cause negative bending angle. It was also observed that heat affected zone depth from surface of specimen with respect to the specimen thickness is an important factor for deciding deformation. The heat affected zone depth is approached half of specimen, the thermal deformation angle is located in zero regime region as heat sink was used.
Description
Department of Mechanical Engineering
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