• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2002.05a
• /
• pp.141-146
• /
• 2002

The cast iron cylinder liner of the marine engine must be scrapped after its inner surface was definitely worn out due to the friction between the surface and piston ring during the operating. In this research, the restoring method of the worn out cast iron cylinder liner are discussed based on the results of experimental work of the thermal plastic deformation technique.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2002.04a
• /
• pp.311-318
• /
• 2002

In this study, we developed an analysis method of plate forming by induction heating and verified the effectiveness of the present method through a series of experiments. The phenomena of the induction heating is a 3D transient problem coupled with electromagnetic, heat transfer, and elastoplastic large deformation analyses. To solve the problem, we suggest a proper model and an integrated system. Using the present analysis model, we can estimate the plate deformation in heating without experiments and simulate the plate bending process of induction heating.

• Journal of the Korean Society for Heat Treatment
• /
• v.15 no.1
• /
• pp.9-15
• /
• 2002

Deformation behavior of nickel-rich Ti-51.5at.%Ni single crystals was investigated over a wide range of temperatures(77 to 440K) and strain levels(up to 9%) in compression. These alloys combined superior strength with wide range of pseudoelasticity temperature interval(~200K). The slip deformation in [001] orientation did not occur due to the prevailing slip system, and consequently, exhibited pseudoelastic deformation at temperatures ranging from 77 to 283K and 273 to 440K for the solutionized and over-aged cases, respectively. The critical transformation stress levels were in the range of 800 to 1800MPa for the solutionized case, and 200 to 1000MPa for the over-aged case depending on the temperature and specimen orientation. These stress levels are considerably higher compared to these class of alloys having lower Ni contents. The maximum transformation strains, measured from incremental straining experiments in compression, were lower compared to the phenomenological theory with Type II twinning. A compound twinning model depending on the successive austenite(B2) to intermediate phase(R) to martensite(B19') transformation predicts lower transformation strains compared to the Type II twinning case.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.21 no.2
• /
• pp.194-199
• /
• 2015

In this study, experiments of welding deformation considering dog-pieces setting were performed to assess the effect of dog-pieces on welding deformations quantitatively and an analysis method of welding deformations considering dog-pieces was proposed. Experimental results show the relationship between welding deformations and dog-pieces setting quantitatively. The maximum reduction of welding deformation was measured as 74%. The proposed numerical analysis method to predict welding deformations is one of thermal elasto-plastic analyses using a circular heat flux and finite elements model and has been verified through experiments of welding deformation. The proposed analysis method is expected to be used in a variety of fields as an analysis tool to assess or establish guidelines for a proper use of dog-pieces.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2006.05a
• /
• pp.421-424
• /
• 2006

High nitrogen steels (HNS) exhibit both high strength and ductility during tensile deformation. In the present study the Fe-18Cr-14Mn-4Ni-0.9N high nitrogen steel was heat treated at $1000^{\circ}C$ and $1100^{\circ}C$ to produce $Cr_2N$ precipitates in austenite matrix and full austenite microstructures, respectively. Tensile tests of the heat treated specimens were performed at two different strain rates of 0.05/sec and 0.00005/sec. Each tensile curve of the specimens could be well characterized by the the modified Ludwik equation. Plastic deformation of the steel was adequately represented by the four parameters of the modified Ludwik equation. At 0.05/s strain rate, the specimen with the $Cr_2N$ precipitate exhibited higher strength than the full austenite specimen, while the full austenite specimen showed better mechanical properties at 0.00005/s strain rate. It was found that the $Cr_2N$ precipitates influences deformation behavior of the high nitrogen steel significantly.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.19 no.5
• /
• pp.113-117
• /
• 2011

The frame for automotive assembly can be deformed and remained on the residual stress due to high temperature thermal attacks when in welding. The frame deformation can be made to problems when in assembly with body and the residual stress can affect the negative effect on durability performance of the automobile. In order to analyze the frame deformation, the simplified test frame which had the similar shape (form) of the real automotive frame was fabricated. The contactless optical 3D scanner was used for the shape difference measurement of the frame between before and after the welding. The FE-model of the test frame was composed and the heat transfer and thermal stress simulation were performed. The simulated results were compared with the measured results for the reference of the frame design. The deformation shape of the frame by simulation was in good agreement with that by the experimental measurement.

• Journal of the Korean Society for Heat Treatment
• /
• v.16 no.2
• /
• pp.83-89
• /
• 2003

As a research for developing fine-grained high strength low carbon steels, the effects of austenitization temperature and hot deformation on microstructure was investigated in 0.15 wt.% carbon steels with microalloying elements such as Nb and Ti. When the steels were reheated at $1250^{\circ}C$, Nb containing steel showed very coarse austenite grain size of $200{\mu}m$ whereas Nb-Ti steel did fine one of $70{\mu}m$ because Ti carbonitrides could suppress the austenite grain growth. In case of 50% reduction at $850^{\circ}C$, the austenite grains in the Nb steel partially recrystallized while those in the Nb-Ti steel fully recrystallized probably due to finer prior austenite grains.For the Nb-Ti steel, ferrite grain size was not sensitively changed with austenitization temperature and compression strain and, severe deformation of 80% reduction was not essentially necessary to refine ferrite grains to about $3{\mu}m$ which could be obtained through lighter deformation of 40% reduction.

• Proceedings of the KWS Conference
• /
• 2005.06a
• /
• pp.285-287
• /
• 2005

During fabrication of deck house block in passenger ships, the problem of unexpected large deformation and distortion frequently occurs. In this case, line and spot heating method were widely used to correct the distortion of thin plate structure. Spot heating was especially used for the case under 5mm thickness. Few papers are available on the working conditions of spot heating method but only little information on deformation control. In this study, evaluation was carried out on the temperature distribution of spot heating methods using FEA and practical experiments for various heating time. IIn FEA, heat input model was established using Tsuji's double Gaussian heat input mode (Tsuji, I., 1988). This model was verified by comparing with experimental data. Also radial shrinkage and angular distortion due to spot heating were determined and compared with experimental results. Thermo elasto-plastic analysis was performed using commercial FE code, MSC/MARC. Radial shrinkage and angular distortion were measured using 3D measuring apparatus. Based on these results, simplified analysis model for deformation by spot heating was established.

• Journal of the Korean Society for Heat Treatment
• /
• v.31 no.4
• /
• pp.180-186
• /
• 2018

High temperature flow behaviors of Fe-Cr-Mo-V-W-C tool steel were investigated using isothermal compression tests on a Gleeble simulator. The compressive test temperature was varied from 850 to $1,150^{\circ}C$ with the strain rate ranges of 0.05 and $10s^{-1}$. The maximum height reduction was 45%. The dynamic softening related to the dynamic recrystallization was observed during hot deformation. The constitutive model based on Arrhenius-typed equation with the Zener-Hollomon parameter was proposed to simulate the hot deformation behavior of Fe-Cr-Mo-V-W-C steel. An artificial neural network (ANN) model was also developed to compare with the constitutive model. It was concluded that the ANN model showed more accurate prediction compared with the constitutive model for describing the hot compressive behavior of Fe-Cr-Mo-V-W-C steel.

• Journal of the Korean Society for Heat Treatment
• /
• v.37 no.5
• /
• pp.215-220
• /
• 2024

Slip lines and dislocation structures developed by deformation at 77 K, 292 K and 500 K have been investigated by an optical microscope and a high-voltage electron microscope. Slip patterns after the deformation by 4-5% at 77 K and 500 K are compared. From the slip line geometry, operation of both primary and secondary {111} slips have been confirmed. However, the primary slip lines formed at 77 K appear coarser and more pronounced than those at 500 K. This indicates that a larger number of dislocations have moved on the same plane at 77 K. Another characteristic difference noted here is that the slip lines are straight and pass through the specimen from one end to the other at 77 K. On the contrary, slip lines are rather faint at 500 K. The typical change found at 77 K is the increase in the [$0{\bar{1}}1$] dipole dislocations and generation of the [$10{\bar{1}}$] screw dipoles upon increase in the strain from 1.2% to 5.2%. This is the indication that the straight dipole dislocations were formed by a pinning effect due to jogs generated by mutual cutting between primary and secondary dislocations. Extremely fine slip has been noted after deformation at 500 K indicating that the usual Frank-Read source is not operative at high temperatures due to the strong KW locking.