• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.4
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• pp.354-361
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• 2008

Cold rolled steel sheet for automotive was treated by Ar/$O_2$ atmospheric pressure plasma to improve the adhesive bonding strength. Through the contact angle test and calculation of surface free energy for cold rolled steel sheet, the changes of surface properties were investigated before and after plasma treatment. The contact angle was decreased and surface free energy was increased after plasma treatment. And the change of surface roughness and morphology were observed by AFM(Atomic Force Microscope). The surface roughness of steel sheet was slightly changed. Based on Taguchi method, single lap shear test was performed to investigate the effect of experimental parameter such as plasma power, treatment time and flow rate of $O_2$ gas. Results shows that the bonding strength of steel sheet treated in Ar/$O_2$ atmospheric pressure plasma was improved about 20% compared with untreated sheet.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.5
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• pp.58-63
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• 2008

Cold rolled and high strength steel were used for vehicle bodys to satisfy environmental regulation and improve fuel ratio. This paper presented a method far determining the fatigue life of cold rolled steel sheet EZNCEN and high strength steel sheet HS40R spot weldment used in vehicles. We can estimate the fatigue life of the spot weldments from the MSC/FATIGUE using the finite element method. The maximum load is found in the nugget part of both surfaces. The cold rolled steel and the high strength steel showed the maximum stress 746MPa and 730MPa in the effective nugget part when the weld current was 8KA and 7KA, respectively. Also the some weld current of the cold rolled steel and high strength steel is applied, the fatigue life of high strength steel is obtained about four times longer than the cold rolled steel.

• Journal of the Korean institute of surface engineering
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• v.29 no.3
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• pp.203-210
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• 1996

The purpose of this study is to investigate behavior of surface oxide on the cold rolled sheet used for the drum material and its phosphatability. Phosphatability is dependent of the characteristics of surface oxide on the cold-rolled sheet and can be estimated by using the electrochemical method and measuring $\tau$ value which is the time to be exposed to substrate Fe. $\tau$ value is varied with the steel composition, width direction of the sheet and SPM length. The good phosphatability and uniform surface color can be obtained by increasing SPM elongation and decreasing FCS temperature.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.83-90
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• 2004

The drawbead is one of the most important factors in sheet metal forming for automotive parts. So clarifying the friction characteristics between sheets and drawbead is essential to improve the formability of sheet metal. Therefore in this study, drawbead friction test was performed at various panels(cold rolled steel sheets, galvanized steel sheets, electrogalvanized coating steel sheets, electrogalvanized Zn-Fe alloy steel sheets and aluminum alloy steel sheets). Circular shape bead has been used for the test. The results show that friction and drawing characteristics were mainly influenced by the nature of zinc coating.

• Journal of Power System Engineering
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• v.19 no.5
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• pp.38-44
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• 2015

The cold-rolled steel sheet for automobile is liable to corrosion, and will be painting in a variety of ways for the anticorrosive. This paper was coated on cold rolled steel (SPCC and SPFC590) for automobiles using five kinds of organic/inorganic hybrid solution. This was evaluated corrosion resistance and so on by the salt spray. Corrosion area was less according to increasing of curing time in 2 types of steel plate with 5 types of the coating solution. No.1 solution was showed the best corrosion resistance regardless of the kinds of the steel sheet. It is judged that the melamin hardner had the role of bridge between $SiO_2$ polysilicate and urethan resin. Other properties were excellent in all solution.

• Laser Solutions
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• v.11 no.2
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• pp.15-19
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• 2008

Electron beam (EB) weldability of pure grade Nb sheet was studied. One of Nb sheets was as-annealed and the other was cold rolled. Microstructures, Vickers hardness, and transverse weld tensile test were carried out for the base metal, the heat affected zone (HAZ) and weld metal. In the case of the EB welds made using the annealed Nb sheeet, fine equiaxed grains and coarse grains were dominant at the base metal and the HAZ, respectively, and columnar grains were observed at the weld metal. For the EB welds made using the cold rolled Nb sheet, elongated grains in the rolling direction at the base metal, and the microstructures of the weld metal and the HAZ are similar to those of the EB welds made using the annealed Nb sheet, respectively. For both annealed and cold rolled Nb sheet, the width of the HAZs are unusually wide in spite of using high density heat source, i.e. electron beam, and the grain sizes of both HAZs are similar. When tensile test was carried out using the transverse weld specimens, the failure occurred at the HAZ for both EB welds made using Nb sheets annealed and cold rolled, respectively and the tensile strengths of both specimens were 161MPa. Vickers hardness of EB welds made using annealed Nb was 56-57 Hv at both base metal and weld metal, 52-53 Hv at the HAZ. On the other hand, Vickers hardness of EB welds made using cold rolled Nb was 97-99 Hv at the base metal, but the hardness values of weld metal were similar to those obtained at the weld metal of annealed Nb.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.2
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• pp.73-77
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• 2004

The efforts which increase the strength of the auto-body structure and decrease its weight lead to develop a new concept of part production systems, such as Post-Form Strengthening by induction heat treatment. In this study, several cold and hot-rolled sheet steels were used to find out optimum induction heat treatment conditions. After induction heat treatment, strength of heat-treated sheet steels was increased significantly compared with that of as-rolled steels. From these results, auto-body structure which has more light and safe has been made by using this induction hardening method.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.06a
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• pp.17-24
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• 1998

This paper deals with the springback characteristics of cold rolled sheet steel through the use of the V-bending process and U-bending one. The influence of material properties on the springback of forming processes was investigated. In the V-bending process there was an optimum bend radius for each combination of parameters which produced minimal springback. In the U-bending process the blank holder force can control the degree of springback. A high blank holding force resulted in a uniform strain distribution and reduced the level of springback.

• Transactions of Materials Processing
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• v.12 no.2
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• pp.123-127
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• 2003

The cold rolling conditions for the ultra thin steel for tension mask are very important because the residual stress that affects the flatness of strip is generate during the cold rolling. The residual stress in the sheet causes etching curls when it suffers perforation process. The residual stress through the thickness. To estimate the residual stress and deformation due to etching curl. FEM analysis is performed. Numerical simulation employ a ANSY5 5.6 and an elastic-plastic constitutive equation. The simulation results indicate the distribution of residual stress in the rolled sheet can be controlled by selecting the rolling conditions properly.

• Transactions of Materials Processing
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• v.29 no.1
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• pp.5-10
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• 2020

Heat treatment conditions of 88.5% asymmetrically cold rolled oxygen free copper (OFC) sheets have been studied to obtain an equiaxed fine microstructure with a grain size of less than 10 ㎛. The commercial OFC sheets with the thickness of 10 mm were asymmetrically cold rolled by using equal speed asymmetric rolling (ESAR) processes and total rolling reduction. The thickness of the rolled sheets were 88.5% and 1.15 mm, respectively. An equiaxed fine microstructure of OFC sheets with a grain size of 6.0 ㎛ were obtained when the asymmetrically cold rolled OFC sheets were heat treated at 180℃ for 40 minutes. The tensile strength of the asymmetrically cold rolled specimen increased from 217.6 MPa to 396.1 MPa, while the elongation of the specimen asymmetrically cold rolled and heat treated increased from 29.0% to 66.9% along with an 8% increase of the tensile strength.