• Journal of the Korean Society for Heat Treatment
• /
• v.31 no.6
• /
• pp.290-299
• /
• 2018

The microstructure of a newly developed alloy tool steel (KV1) for casting cold-work press dies was analyzed using advanced scanning electron microscopy. Its mechanical properties and durability in use as piercing inserts were tested. It contained a continuous network structure which originated from the micro-segregation during solidification and was composed of retained austenite and primary carbides. However, after quenching and tempering, its continuity was destroyed due to the decomposition of austenite. The discontinuous spatial distribution and the smaller amount of primary carbide in the network presented KV1 enhanced ductility compared to the common alloy (HK700). The reduced C and Cr, the addition of V resulted in a small amount of primary carbides which primarily consisted of MC, as well as fine and uniform dispersion of precipitates. Owing to these features, KV1 exhibited delayed initiation of chipping when used for piercing inserts.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1999.10a
• /
• pp.74-80
• /
• 1999

Work roll wear in the cold rolling of mild steel strip is strongly affected by rolling materials, rolling conditions such as roll arrangement in the cold rolling mill and lubrication. The tests were performed to find the effects of roll arrangement n the cold rolling mill on the work roll wear under the same lubricating conditions. The obtained results are as follows:If the distance of cold rolling is about 60km, the surface roughness of its was reduced by half(Ra 0.49${\mu}{\textrm}{m}$) and Pc(peak count) also was decreased to 60 ea/cm.It is easier for CC(Continuous casting) to make a slip on rolling than IC(Ingot casting). It is due to surface mirror in which first residual product appears and iron powder included Al2O3 is sticked. Because bending degree of 4Hi-rolling mill is higher than 6Hi-rolling mill, the first surface mirror was occurred to its center-point which is loaded strongly. 6Hi-rolling mill shape-controlled by intermediate roll doesn't need the initial crown to work roll. Therefore, fatigue and wear would appear a little bit.

• Journal of the Korean Society for Heat Treatment
• /
• v.16 no.2
• /
• pp.90-96
• /
• 2003

The effect of betatizing temperature on microstructure and transformation characteristics in a Cu-AI-Ni based pseudoelastic alloy fabricated by heated mold continuous casting by using metallography, XRD and calorimetry. The microstructure of cast rod betatized at $600^{\circ}C$ revealed a ${\beta}_1$ parent phase and a ${\gamma}_2$ phase precipitated along the casting direction. When the cast rod was betatized at the elevated temperature above $600^{\circ}C$, the ${\gamma}_2$ phase is completely dissolved into the matrix so that the volume fraction of the ${\gamma}_2$ phase was decreased. The parent phase was stabilized by betatizing at $600^{\circ}C$. However, the ${\beta}_1$ parent phase was transformed to both ${{\beta}_1}^{\prime}$ and ${{\gamma}_1}^{\prime}$ martensites with increasing betatizing temperatures above $600^{\circ}C$, while $M_s$ and $A_s$ temperatures were decreased. The stress-strain curves for compression test were not same with betatizing temperature; the stress-strain curves of the specimen betatized at $600^{\circ}C$ and $700^{\circ}C$ were linear but those of the specimen betatized at $800^{\circ}C$ and $900^{\circ}C$ were not linear.

• Proceedings of the Korean Operations and Management Science Society Conference
• /
• 2002.05a
• /
• pp.109-113
• /
• 2002

Steel industry is the most capital intensive and the largest energy consuming industry, which operate huge and complex facilities to supply various steel products as the primary materials to almost every manufacturing industry Major steel products are hot-rolled and cold-rolled coils, plates, and wires that are produced through molten iron making, molten steel making, casting, and rolling. Each process runs in batch between setups and the specifications or bach are different with each other High energy consuming and heavy material handling require careful synchronization or processes, as well. Considering the synchronization or processes, the lot planning and scheduling problem in the integrated steelmaking process rovers the roll grouping with given casts. the sequencing or rolls over time, and the machine assignment and time scheduling or charges and casts. The problem is investigated by dividing it into two cases whether single or parallel machines at the molten steel making and the continuous casting processes. Problem descriptions and solution approaches or each instance are introduced. To test their performance and conformity, implementation or the algorithms and numerical experiments are carried out with real world and constructed data sets.

• Journal of Korea Foundry Society
• /
• v.27 no.5
• /
• pp.224-227
• /
• 2007

원자로에 장전되는 $^{99}Mo$ 조사표적을 제조하기 위한 우라늄박판은, 박판 품질, 생산성, 경제성 문제로 인해, 기존의 열간압연방법에 의해 실험실 규모로는 제조가 가능하나, 상용 규모로는 제조되기 어려운 실정이므로, 새로운 제조방법의 개발이 요구되고 있다. 이와 같은 상황에서, $^{99m}Tc$의 모핵종인 방사선 동위원소$^{99}Mo$ 생산하기 위하여 planar flow casting (PFC) 법에 의해 다결정질 우라늄박판에 대한 새로운 제조방법이 연구되었다. $100{\sim}150\;{\mu}m$의 두께 및 너비 약 50mm의 연속적인 다결정질 우라늄박판이 하나의 batch에서 5m 이상의 길이로 제조되었다. 우라늄박판은 불순물이 거의 없었으며 양호한 표면조도를 가지고 있었다. 우라늄박판의 냉각를 접촉표면은 자유표면 보다 매끈한 자유표면을 가지고 있었다. 우라늄박판은 제조공정변수와는 상관없이 ${\alpha}-U$ 상을 가진 약 10 ${\mu}m$ 이하의 미세한 다결정립을 가지고 있었다.

• Transactions of Materials Processing
• /
• v.11 no.1
• /
• pp.24-35
• /
• 2002

Recent trend and future prospect of flat rolling of steel has been summarized based on the earlier reports. Key technology in the plate rolling is to have ultra fine microstructure having high resistance against crack propagation during application. Heavy accelerated cooling facility and high power rolling mill will be helpful to develope the high toughness steel. Precise modeling of properly prediction based on deformation and transformation imposed on microstructure of steel during processing is highly anticipated. For the hot strip rolling process, new trend is lies on the production of ultra-thin gauged hot strip to substitute cold rolled strip. For the substitution of cold rolled strip into hot rolled strip widely, high formable property of hot strip is highly required. For the formabilit, the ferritic rolling of extra low carbon steel under high lubricated condition is essential. Recently introduced semi-continuous thin slab and rolling mill line is very plausible to develope those kinds of products easily In the view groin facility combination. New idea to modify the existing continuous hot strip mill line to produce the ultra thin-gauged hot strip in an economic way is suggested in this report.

• Structural Engineering and Mechanics
• /
• v.17 no.2
• /
• pp.245-266
• /
• 2004

Incremental launching method is one of the highly competitive techniques for construction of concrete bridges. It avoids costly and time consuming form work and centralizes all construction activities in a small casting yard, thus saving in cost and time against conventional bridge construction. From the quality point of view, it eliminates the uncertainty of monolithic behaviour by allowing high repetitiveness and industrial environment. But, from analysis and design point of view, the most characteristic aspect of incrementally launched bridges is that, it has to absorb the stresses associated with the temporary supports that are gradually taken on by the deck during its launch. So, it is necessary to analyse the structure for each step of launching which is a tedious and time consuming process. Effect of support settlements or temperature variation makes the problem more complex. By using transfer matrix method, this problem can be handled efficiently with minimal computational effort. This paper gives insight into method of analysis, formulation for optimization of the structural system, effect of support settlement and temperature gradient, during construction, on the stress state of incrementally launched bridges.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2004.08a
• /
• pp.216-222
• /
• 2004

The caster roll shells have the good thermal conductivity and the low thermal expansion and have to exhibit high enough strength and good ductility at temperature up to $600^{\circ}C$. Thermal stress in particular is very high due to the contact with the liquid aluminium. The main stresses are of thermal origin, which bring a plastic fatigue on surface. This paper will represent one survey about the investigation of the failure of roll shells for continuous casters and an analysis using the simulation of the temperature distribution and the state of stress during hot rolling. Moreover, there will be a discussion on the roll shell of Mod. HAR 5 which is developed by heat treatment process. Mod. HAR 5 has advantages of high strength, high toughness and increased thermal stress resistance while maintaining the same productivity as the conventional roll.

• Journal of Korea Foundry Society
• /
• v.20 no.3
• /
• pp.173-180
• /
• 2000

The microstructure changes of the matrix and the graphites were observed by optical microscope and the average hardness number was investigated according to the heat-treatment conditions of the cast iron rods by the horizontal continuous casting process in 35 mm diameter. The three kinds of heat-treatments were introduced. The first treatment was performed at 900, 950, and $1000^{\circ}C$ for 2 hours and the second treatment was conducted during 5, 10, and 15 hours at $1000^{\circ}C$ respectively. The third treatments were the two-cyclic heat-treatment and the three-cyclic heat-treatment at $1000^{\circ}C$ during 2 hours. The matrix microstructure of the specimens to be treated at various temperatures for 2 hours was the ferrite to be transformed from the pearlite The hardness number of the center of the samples according to the heat treatment time at $1000^{\circ}C$ was higher than that of the surface area because of the martensite formation in the center. Also, in the cyclic heat-treatments, the hardness number of the two-cycle treatment specimens increased because of the martensite formation in the center.

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