• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.163-172
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• 2004

A fast, accurate model for calculating roll gap variables are critical to the implementation of computer based automation systems for cold rolling mills. Based on the work of Fleck and Johnson, rollgap simulator with non-circular arc model was developed using the influence function. This developed model is capable of predicting values of force, torque and slip which can be applied over the wide range of rolling conditions including cold rolling/DR/temper mill with high execution speed. Friction coefficient was obtained as a function of operation conditions through analyzing measured data. After combination of rollgap simulator with production strategy, draft schedule for No.3 RCM (Reversible Cold Rolling Mill) in Incheon works of Dongbu Steel was developed. This draft schedule will be installed in the setup computer of No.3 RCM replacing old Hitachi model.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.317-317
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• 2000

The mathematical set-up model was developed to reduce the mechanical property deviation in annealed and slightly rolled steel strip. The mechanical peculiarities of temper rolling process, such as high friction value and non-circular contact arc, Low reduction and non-negligible entry and exit elastic zones as well as central restricted deformation zone are all taken into account. The deformation of work rolls is calculated with the influence function method and arbitrary contact arc shape is permitted. The strip deformation is modeled by slab method and the entry and exit elastic deformation zones are included. The restricted deformation Bone near the neutral point is also considered. It was revealed that the new model has better accuracy than present regression model by statistical analysis with actual mill rolling data.

• Journal of Welding and Joining
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• v.7 no.2
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• pp.49-59
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• 1989

The effect of non-metallic inclusions on the HAZ hydrogen induced cracking was investigated. Quench and temper high tensile strength steels containing various sulphur contents were employed. The sulphur contents range between 0.007% and 0.040%. Non-metallic inclusions were mainly MnS type sylphide and Mn-Al-Si type. The sensitivity of HAZ delayed cracking was evaluated by implant testing. Diffusible hydrogen content was varied by controlling the moisture absorbing condition of manual arc welding electrodes. The one was asreceived condition, the other was dipping the electrodes in the water for ten minutes. The main results obtained were as follows; 1) The results of implant test showed that critical stress increased with increasing S content up to 0.013%. But steel containing 0.040%S showed lower critical stress than that of 0.013% S. These result suggest that there will be optimum S content to prevent HAZ delayed cracking of high strength steels. 2) Under the lower D.H.C. level, critical stress was increased with rolling reduction, but higher D.H.C. level, effect of rolling reduction was not recognized.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.7
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• pp.36-43
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• 1998

Surface roughness of cold rolled steel sheet as well as the coating technique itself is quite important in obtaining high image clarity of electronic products and car outer panels. Especially, surface characteristics of steel sheet have acquired increasing attention from the steel and automotive industries. While the influence of such characteristics on paintability formability and painted surface appearance is important in defining steel surface requirements for automotive industries. Therefore this paper is dedicated primarily to the issue of paint appearance and reviews for improvement of roughness and peak count about the surface of work roll for the actual temper mill. The conclusions were obtained as follows ; 1) Roughness and peak count about the surface of steel sheet is strongly affected by surface condition of work roll. 2) The electro-discharge textured roll has more uniform roughness distribution than shot blasted roll and it's painted appearance of steel sheet has more improvement than that of the shot blasted because it has more harmonic wave roughness, and the higher peak count of surface roughness.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.4
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• pp.208-218
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• 2006

The effects of the grain size on the magnetic properties in extra-low carbon steel after strain annealing were investigated. Two kinds of sample were prepared. One is the annealed sheet, which was annealed at $670^{\circ}C$ and $850^{\circ}C$ for various time periods after cold rolling. The other is the strain annealed sheet, which was temper rolled by 0.4% and subsequently strain annealed at the temperature ranging between $670^{\circ}C$ and $850^{\circ}C$ for various time periods. The grains after strain annealing became more coarse than those after primary annealing. The grains were coarsened due to the strain induced grain boundary migration (SIGM). It was found that the permeability tended to be increased and coercivity tended to be decreased with the increase of grain size. The optimum magnetic properties was achieved after strain annealing at $850^{\circ}C$ for 30 minites. Under this condition, the coercivity was measured to be 0.6 and the permeability was measured up to be 13000.