• Journal of the Society of Naval Architects of Korea
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• v.45 no.6
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• pp.703-709
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• 2008

In the shipyard, line heating and triangle heating are two major processes for forming curved plates in various shapes. While there have been many studies on line heating, triangle heating has been rarely studied due to its complicated heating process with irregular multi-heating paths and highly concentrated heat input. As the triangle heating process is one of the most labor-consuming jobs in shipyards, it is essential to study the automation as well as improvement of triangle heating process in order to increase hull forming productivity. In this study, a pioneering attempt to simulate triangle heating was made. A circular disk-spring model was proposed for elasto-plastic analysis procedure of triangle heating and the inherent strain method was also used to analyze the deformation of plates. Simulation results were compared with those of experiments and showed good agreement. It is shown that the present approach including analysis model used in this study is effective to simulate the triangle heating for plate forming process in shipbuilding.

• Proceedings of the KWS Conference
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• 1996.05a
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• pp.186-189
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• 1996

A study was made to examine the characteristics of base metal and stress relief cracking(SRC) of heat affected zone(HAZ) for HY-100 and Cu-bearing HSLA-100 steels. The Gleeble thermal/mechanical simulator was used to simulate the SRC/HAZ. The details of mechanical properties of base plate and SRC tested specimens were studied. The specimens were aged at $650^{\circ}C$ for HSLA-100 steel and at 66$0^{\circ}C$ for HY-100 steel and thermal cycled from 135$0^{\circ}C$ In $25^{\circ}C$ with a cooling time of $\Delta$ $t_{800^{\circ}50}$ $0^{\circ}C$/=21sec. corresponds to the heat input of 30kJ/cm. The thermal cycled specimens were stressed to a predetermined level of 248~600MPa and then reheated to the stress relief temperatures of 570~62$0^{\circ}C$. The time to failure( $t_{f}$) at a given stress level was used as a measure of SRC susceptibility. The strength, elongation and impact toughness of base plate were greater in HSLA-100 steel than in HY-100 steel. The time to failure was decreased with increasing temperature and/or stress. HSLA-100 steel was more susceptible to stress relief cracking than HY-100 steel under same conditions. It is thought to be resulted from the precipitation of $\varepsilon$-Cu phase by dynamic self diffusion of solute atoms. Therefore, greater strain concentration at grain boundary of HSLA-100 steel results in the increased SRC susceptibility.y.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.4
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• pp.639-647
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• 2022

The use of flames is essential in cutting, bending, and welding steel during a ship's construction process. While acetylene fuel is commonly used in steel cutting and the manufacturing process in shipyards, the use of propane as an alternative fuel has recently been increasing, due to the lower risk of explosion and propane's relatively low calorific value. However, propane fuel has a relatively slow processing speed and high slag generation frequency, thereby resulting in poor quality. Propylene is another alternative fuel, which has an excellent calorific value. It is expected to gain wider use because of its potential to improve the quality, productivity, and efficiency of steel processing. In this study, the combustion characteristics of propane and propylene fuel during steel plate processing were analyzed and compared. The reduction of greenhouse gases and other harmful gases when using propylene flame was experimentally verified by analyzing the gases emitted during the process. Heat distribution and tensile tests were also performed to investigate the effects of heat input, according to processing fuel used, on the mechanical strength of the marine steel. The results showed that when propylene was used, the temperature was more evenly distributed than when propane fuel was used. Moreover, the mechanical tests showed that when using propylene, there was no decrease in tensile strength, but the strain showed a tendency to decrease. Based on the study results, it is recommended that propylene be used in steel processing and the cutting process in actual shipyards in the future. Additionally, more analysis and supplementary research should be conducted on problems that may occur.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.53-62
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• 1987

High power lasers provide a controllable and precise energy source in surface transformation hardening. A careful control of the process is needed in order that the surface layer of the material reaches the austenizing temperature, but that it does not melt. In order to achieve this the results of theoretical and experimental studies on the laser surface hardening of a medium carbon steel are described. A two-dimensional computer program, which can be used generally for the determination of transient temperature distributions in welding and heat treatment, was established on the basis of the finite element method. For the confirmation of the accuracy of the numerical analysis, a medium carbon steel (SM 45C) of 5mm thickness was heat-treated with a 1kW CW CO$_{2}$ laser machine, while the traverse speed and the distance from the focal point (defocused distance) were varied. Experimental and numerical results showed a similar tendency in correlations between the hardened zone shape and the process parameters. With increasing beam spot diameter the width and depth of the hardened zone increased for relatively small beam spot diameters, but decreased rapidly after reaching the maximum value, while with increasing traverse speed the width and depth of the hardened zone decreased monotonously. Too small beam spot diameters are to be avoided, since the surface melting would lower the surface hardness and produce an uneven surface which may be unacceptable because of the possible requirement for subsequent machining. It could be observed that for a given traverse speed and laser power input there exists a optimal range of the beam spot diameter, which produce a large width of the hardened zone but no melting on the surface.