• Steel and Composite Structures
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• v.21 no.2
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• pp.289-302
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• 2016

A new kind of partially precast or prefabricated castellated steel reinforced concrete beam, which is abbreviated here as CPSRC beam, was presented and introduced in this paper. This kind of CPSRC beam is composed of a precast outer-part and a cast-in-place inner-part. The precast outer-part is composed of an encased castellated steel shape, reinforcement bars and high performance concrete. The cast-in-place inner-part is made of common strength concrete, and is casted with the floor slabs simultaneously. In order to investigate the shear performance of the CPSRC beam, experiments of six CPSRC T-beam specimens, together with experiments of one cast-in-place SRC control T-beam specimen were conducted. All the specimens were subjected to sagging bending moment (or positive moment). In the tests, the influence of casting different strength of concrete in the cross section on the shear performance of the PPSRC beam was firstly emphasized, and the effect of the shear span-to-depth ratio on that were also especially taken into account too. During the tests, the shear force-deflection curves were recorded, while the strains of concrete, the steel shapes as well as the reinforcement stirrups at the shear zone of the specimens were also measured, and the crack propagation pattern together with the failure pattern was as well observed in detail. Based on the test results, the shear failure mechanism was clearly revealed, and the effect of the concrete strength and shear span-to-depth ratios were investigated. The shear capacity of such kind of CPSRC was furthermore discussed, and the influences of the holes on the steel shape on the shear performance were particularly analyzed.

• Journal of Advanced Marine Engineering and Technology
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• v.15 no.3
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• pp.57-65
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• 1991

The quenching of steels by water is one of the important problems in engineering for the applications of heat treatment or continuous casting process, but the fundamental researches by the theoretical approaches have not been satisfactorily improved yet. The very rapid cooling problems by the thermal conduction including the latent heat of phase transformation in steel and the transient boiling heat transfer of water on the surface of the steel covering from $850^{\circ}C$ to $20^{\circ}C$ are the key problems of heat treatment. The present quenching experiments are performed for the cylindrical specimens of carbon steel, S45C of diameters (12-30). Nonlinear transient heat conduction and transient boiling heat transfer problem of water on the surface of specimens is analyzed by the numerical method of inverse heat conduction problem. The conditions for the calculation are that the initial temperature of specimens is $820^{\circ}C$ and the cooling water in bath are $20^{\circ}C$,$40^{\circ}C$,$60^{\circ}C$,$80^{\circ}C$,$95^{\circ}C$ with no agitation.

• Journal of the Korean Society for Heat Treatment
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• v.30 no.5
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• pp.197-206
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• 2017

The microstructure of a high-carbon and high-chromium cast steel (HK700) for cold-work die inserts was analyzed by advanced scanning electron microscopy. A continuous network of primary $M_7C_3$ carbide was developed among austenitic matrix after casting. A small amount of $M_2C$ was added to the carbide network owing to the enrichment of Mo and W during the solidification. After quenching in which the austenitization was performed at $1030^{\circ}C$ and double tempering at $520^{\circ}C$, the network structure of $M_7C_3$ was preserved while most of the matrix was transformed to martensite because of additional carbide precipitation. The $M_2C$ in the as-cast microstructure was also transformed to $M_6C$ due to its instability. The continuous network of coarse carbides owing to the absence of hot-working had little influence on the hardness after quenching and tempering, whereas it resulted in severe brittleness upon flexural loading.

• Journal of Korean Institute of Industrial Engineers
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• v.24 no.4
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• pp.649-660
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• 1998

Steel making in Mini Mill consists of three major processing stages: molten steel making in an electric arc fuenace, slab casting in a continuous caster, and hot rolling in a finishing mill. Each processing stage has its own lot grouping criterion. However, these criteria in three stages are conflicting with each other. Therefore, delveloping on efficient lot grouping algorithm to enhance the overall productivity of the Mini Mill is an extremely difficult task. The algorithm proposed in this paper is divided into three steps hierarchically: change grouping, cast grouping, and roll grouping. An efficient charge grouping heuristic is developed by exploiting the characteristics of the orders, the processing constraints and the requirements for the downstream stages. In order to maximaize the productivity of the continuous casters, each cast must contain as many charges as possible. Based on the constraint satisfaction problem technique, an efficient cast grouping heuristic is developed. Each roll consists of two casts satisfying the constraints for rolling. The roll grouping problem is formulated as a weighted non-bipartite matching problem, and an optimal roll grouping algorithm is developed. The proposed algorithm is programmed with C language and tested on a SUN Workstation with real data obtained from the H steel works. Through the computational experiment, the algorithm is verified to yield quite satisfactory solutions within a few minutes.

• Journal of Korea Foundry Society
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• v.28 no.3
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• pp.119-123
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• 2008

Wear test on two die steels for aluminum die casting was carried out by dipping and rotating the specimens into the molten aluminum maintained $680^{\circ}C{\sim}780^{\circ}C$. The rotating speed of the specimen was $4.5rpm{\sim}20.0rpm$. Diffusion layer was formed between the die steel and molten aluminum, and became thicker with dipping time. Wear rate was not proportional with the thickness of the diffusion layer, but was closely related to the density of the diffusion layer. Wear rate was little affected by the kind of die steel and by the microstructure such as martensite, tempered martensite, and pearlite. Specimen with nitrided surface showed good wear resistance, and its wear rate was decreased with increase in the thickness of nitrided layer. While whole surface was worn in heat treated specimens, wear of nitrided specimens was proceeded by pitting partially.

• Korean Journal of Metals and Materials
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• v.46 no.10
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• pp.662-671
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• 2008

The behavior of hydrogen in the steel making process was investigated. The relation between the composition of ladle slag and hydrogen concentration in molten steel was considered. The hydrogen distribution ratio between ladle slag and molten steel was increased with increasing basicity of the slag; it was about 20 when the basicity of slag was 15. Hydroxyl capacity measured from the hydrogen distribution ratio between slag and the molten steel was comparatively corresponding to the value of hydroxyl capacity measured by the equilibrium reaction of slag and $H_2O$ gas. However, it is considerably different from the value calculated by regular solution model. The influence of hydrogen on a sticking type breakout is considered. The effect of hydrogen and $H_2O$ gas on the crystallization behavior of mold powder was investigated by DHTT (Dual hot thermocouple technique). As a result, it was proved that mold powder could be crystallized by $H_2O$ gas in the atmosphere. Therefore, it is concluded that $H_2O$ gas in the atmosphere can be a possible cause of the sticking type breakout that occasionally occurs in the continuous casting process.

• Journal of Korea Foundry Society
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• v.41 no.2
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• pp.132-138
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• 2021

In this study, the power basic units to produce cast iron by using the press and shredded scrap are compared in 16t/h low-frequency induction melting furnace. Charging the shredded scrap instead of the press scrap was confirmed that the power basic unit is improved by about 5%. The energy characteristics according to the shape and size of scrap steel and the effect of the furnace size were investigated. Finally, the strategy to improve the utilization of this technology was proposed.

• 제어로봇시스템학회:학술대회논문집
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• 1991.10a
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• pp.1161-1168
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• 1991

The purpose of this project is to develop an automatic cutting robot system of cast steel, which raise productivity with improvement of working circumstances, overcomming labor deficiency, reduction of process and cycle time by applying cutting automation at inferior working circumstances and condition of a foundry. This system consisted of a 5 DOF tool system, an improved conveyer system and the HR-8608 ROBOT, makes it possible to get the reduction of 12 manpowers and 30% productivity up.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.325-329
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• 2002

This study targets mainly to reduce the manufacturing costs of cam spindles and manufacturing of mechanical components with longer service durations through application of surface engineering techniques on cam spindles. Within the frame of this study, we have attempted to establish the performances of cam spindles manufacture from forged steel and SGCI, through performance of wear tests in plate-disk system, metalographic investigations, SEM imaging, EDS analyses and micro hardness scans on test samples having the same sizes with original cam that once obtained from casting of Spherical Graphite Cast Iron (SGCI) are subjected partially to Boronising and partially to hardening in a salt solution and cam spindles currently manufactured from CK 45 through cauterization based reshaping.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.3
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• pp.695-703
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• 1998

The crack problem of continuous casting slab due to the thermal stresses during the reheating process is analyzed using FEM. In this study, the C(t)-integral is calculated. As a result, the values of the C(t)-integral decrease by increasing the initial temperature of the slab and decreasing total heat flux. And those decrease by decreasing the heat flux of pre-heating zone and increasing the heat flux of heating zone.