Cold-rolled Carbon Steel Sheets Research Articles

Evaluation of Tensio n - Shear Stress for zig -zag spot welds by using indirect resistance spot weld technique for fabrication industries

All resistance welding processes are based on the heat that is produced at the interface due to resistance for the flow of electric current through the metal parts being joined. The amount of heat generated basically depends on the magnitude of the current, the duration of current flow and the load transmitted to the inter face. Spot welding is now a very established process in which two sheets to be welded are kept one over the other to get a nugget at the interface. The contact resistance at the interface dictates the quantum of heat that is generated . New concept namely indirect resistance spot welding was developed for applications where the surface appearance on sheet can be critical. In this process outer surface, limiting the extent of electrode indentation is traditionally managed by controlling the heat balance and electrode size. Trials were conducted, for optimum weld parameters for cold rolled carbon steel sheet, for Zig – zag spot weld for the indirect spot welding and also observed the Reduced Tensile stress for the base metal. This research paper reports the results of the trials, under optimum weld parameters. indirect resistance spot welding .The observations on Tension – shear breaking load , nugget diameter ,yield stress, reduced tensile stress, working stress or design stress by considering minimum factor of safety of two, for Tension shear application for indirect resistance spot welding were discussed. Peel test was done to find quantitatively, the formation of nugget and nature of failure. This paper reveals the results for the Zig – zag spot for the indirect spot welding, process were observed more Safe joint specially for tension shear application .Since spot welds during design considerations , for Zig – Zag spots for lap joint for tension shear applications these results will be most useful for optimum design.

Improving the plasticity of thin cold-rolled steel sheet for cold stamping

Two methods of surface treatment are proposed to improve the technological plasticity of thin cold-rolled carbon-steel sheet: ionic bombardment by low-energy titanium atoms; and epilam coating. Both methods markedly increase the extensibility of the sheet (by a factor of 1.2–1.3), as estimated by the maximum crater depth without cracking in Erichsen tests (from the VG group to values exceeding those for the VOSV group, which corresponds to extremely complex extension, in State Standard GOST 9045–93). This is associated with change in the behavior of the sheet on deformation (with change in the properties of the material) as a result of two processes: the healing of surface defects; and the creation of hybrid nanocrystalline and submicrocrystalline structure in the surface layer. In epilam coating, only the first process occurs; in ionic bombardment, both are observed.

레이저 드릴링을 통한 강판 가공 시 응력 모델링

Key Words: Topology Laser Drilling(레이저구멍가공), Hole-Drilling Method(홀드릴링기법), Stress(응력)초록: 레이저정밀가공은고품질의집속광에너지를이용하여재료를미세하게가공하는특수가공으로정밀제조분야에적용되고있다. 그러나레이저가공시열적효과로인해재료특성을저하시킬수있다. 또한, 압연강재및강판의경우공정단계에서강한압력으로제작하기때문에반드시잔류응력이존재한다. 하지만압연강재에존재하는잔류응력의양은정량적인예측이불가능하다. 이러한잔류응력이존재하는재료의레이저가공시레이저에의한부가적인응력발생및재료에미치는열적영향의예측및평가는정밀가공에있어서반드시고려해야하는사항이다. 본연구에서는레이저홀가공시발생되는온도및응력을유한요소해석과실험적방법으로분석하였다. 재료의열응력을예측하기위해레이저홀가공실험을수행하여가열및냉각등의대한결과를도출하였다. 또한냉각시간에따른응력의변화를파악하였고유한요소해석으로예측된응력을홀드릴링응력측정기법에의해도출된응력과비교검증하였다.Abstract: A laser machining process has been applied in many manufacturing fields and it provides anexcellent energy control for treating materials. However, a heat effect during laser machining can deterioratematerial properties. Specifically, a thermally induced stress can be a problem in laser-machined structures ona metal surface. In this study, temperature and stress on cold-rolled carbon steel sheet machined with laserhole drilling were explored in an experimental approach and a numerical method. Stresses by temperaturegradients inside the materials were generated in fast cooling. The stresses were measured by using ahole-drilling method and the material properties of carbon steel (SCP1-S) were obtained in the experiment. Itwas found that the stress predicted from the numerical analysis was in agreement with the stresses measuredby using the hole-drilling method. The analysis can be applied for evaluating structure characteristicsmachined with a laser.

TS형 박강판 용접 구조물의 자동화설계를 위한 피로특성에 관한 연구

Cold-rolled carbon steel sheets are commonly used in railroad car or commercial vehicles such as the automobile. These are mainly fabricated by spot welding which is a kind of electric resistance welding. But fatigue strength of spot welding joint is lower than that of base metal due to high stress concentration at nugget edge of the spot welded part. And fatigue strength of them is especially influenced by not only geometrical and mechanical factors but also welding conditions of the spot welded joint. So for fatigue design of gas welded joints such as TS-type joints, it is necessary to obtain design information on stress distribution at the weldment as well as fatigue strength of spot welded joints. And also, the influence of the geometrical parameters of spot welded joints on stress distribution and fatigue strength must be evaluated. And analysis approach for fatigue test using design of experiment are evaluated optimum factor in TS-type welded joint and geometrical parameters of materials. Using these results, that factors applied to fundamental information for automation of fatigue design.

냉연강판의 기계적 물성과 자기적 특성의 상관관계

구조 강이나 터빈로터 강의 기계적 물성은 자기적 특성과 관계되므로, 비파괴적으로 자기적 특성을 측정하여 기계적 물성을 평가하는 연구가 많이 수행되었다. 따라서 자동차용 강판으로 사용되는 냉연강판에서도 비파괴적으로 자기적 특성을 측정함으로써 냉연강판의 기계적 물성을 유추할 수 있을 것이고, 냉연강판 생산 라인에서 자기적 특성을 측정하여 온라인상에서 냉연강판의 기계적 특성을 모니터할 수 있을 것이다. 기계적 특성이 다른 세 종류의 냉연강판 CBQ 3060, CBQ 3041 및 CBQ 3036의 시편을 준비하고 교류 섭동 자기장을 인가하여 자기적 특성인 가역투자율을 비파괴적으로 측정함으로서 기계적 물성인 경도와의 상관관계를 규명하였다. 세 종류의 냉연강판 시편에서 기계적 물성인 비커스 경도, 항복강도 및 인장강도를 측정하였다. 주파수가20 Hz일 때, surface type 프로브로 측정한 섭동자기장의 제 1차 고조파인 가역투자율의 피크 간 간격에서 구한 보자력은 비커스경도, 항복강도 및 인장강도가 증가할 때 선형적으로 증가하였다. 주파수 20 Hz에서 lift-off에 대한 가역투자율 측정을 하였는데,lift-off가 증가함에 따라 고조파의 amplitude가 급격히 감소하였다. Measurement methods in order to measure the mechanical properties nondestructively have been studied. The mechanical properties of the structural and turbine rotor steels are related with their magnetic properties. If the magnetic properties of the cold rolled carbon steel sheet (CR) for a car are measured nondestructively, its mechanical properties are analogized by their magnetic properties. And then the mechanical properties are monitored on-line by measuring the magnetic properties. We prepared three CR materials, CBQ 3060, CBQ 3041, and CBQ 3036, were prepared in order to measure their mechanical and magnetic properties. The Vickers hardness,yield strength, and tensile strength were measured by ASTM E 8M, and the reversible magnetic permeability was measured by the surface type probe. The coercivity calculated by the peak interval of reversible magnetic permeability increased linearly with the increase of Vickers hardness, yield strength, and tensile strength. The amplitude of the peak interval of reversible magnetic permeability drastically decreased when the lift-off was increased.

スポット溶接継手の曲げ疲労強度に及ぼす溶接条件の影響

Some effects of welding conditions on the strength of spot welded joints were studied. Spot welds under various welding conditions were performed on SPC-1 (cold rolled carbon steel sheets). Static tensile and bending fatigue tests were carried out, and the following results were obtained:(1) A dominant facto: on bending fatigue strength was different from that of static tensile fracture strength. The static tensile strength increased with nugget diameter. The bending fatigue strength changed with HAZ angle (θ), which is the angle between the heat-affected zone and the plate surface.(2) It was found that the fatigue crack propagated along the parallel direction to heat-affected zone.(3) The welding condition of R.W.M.A. class A gave the maximum static tensile strength but the minimum for bending fatigue strength.