• 대한금속재료학회지
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• 제47권8호
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• pp.474-481
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• 2009

The effects of final heat treatment on the mechanical and corrosion properties of a Zr alloy strip incorporating Nb were investigated. The chemical composition of the strip was Zr-1.49Nb-0.38Sn-0.20Fe-0.11Cr, and strip specimens were subjected to final heat treatment in a temperature range of $580{\sim}700^{\circ}C$. Tensile tests at room temperature and $316^{\circ}C$, along with corrosion tests in a simulated PWR loop and a 70 ppm LiOH solution environment at $360^{\circ}C$, were performed on the specimens. The mechanical properties of the strip were saturated when the specimens received final heat treatment at an elevated temperature of more than $640^{\circ}C$. However, the corrosion resistance of the strip in the simulated PWR loop and in the 70 ppm LiOH solution environment was improved with a decrease of the final annealing temperature. It is recommended that the alloy strip be finally heat-treated at a temperature of less than $620^{\circ}C$ for longer than 10 minutes in order to obtain fully recrystallized microstructures, and thereby attain enlarged tensile elongation, and to prevent the precipitation of ${\beta}-Zr$, which is known to deteriorate the corrosion resistance.

• 대한기계학회논문집A
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• 제20권12호
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• pp.3856-3870
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• 1996

The objective of this study is to evaluate heat transfer coefficient distribution during heat treatment by inverse analysis. As a first procedure, the inverse heat transfer formulation by using two dimensional finite element method has been developed. The formulation can handlematerial nonlinearity and allow arbitrary placement and number of sensors. The formulation was verified through application to simulated exact and inexact measurements.

• 농업과학연구
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• 제43권4호
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• pp.656-664
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• 2016

Gear reducers are widely used for various agricultural machinery applications such as greenhouses, tractors, and agricultural vehicles. However, thermal deformation and surface pitting at gear tooth flank frequently occur in gear reducers due to high torque. Thus, surface heat treatment of gears is required to improve wear and fatigue resistance. The objective of this study was to simulate the load capacity of the agricultural gear reducer. The simulation was performed for the following three surface heat treatment methods: untreated gears, nitriding heat treatment, and induction hardening method, those mostly used for agricultural gear reducers. The load capacity of the gear reducer was simulated using the safety factor, limit bending stress, and limit contact stress of the gear. The simulation of the load capacity was conducted using KISSsoft commercial software for gear analysis. The main results of simulation test were as follows: first, the nitriding heat treatment resulted in the highest safety factor for bending stress, which was increased about 77% from those of the untreated gears. Second, the induction hardening was the highest safety factor for contact stress, which was increased about 150% from those of the untreated gears. The safety factor for contact stress of the induction hardening was increased about 64% from those of the nitriding heat treatment. The study result suggested that the surface heat treatments could enhance load capacity and that the method of surface heat treatment should be determined based on simulation results for appropriate use scenarios.

• Food Science and Biotechnology
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• 제15권4호
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• pp.523-528
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• 2006

The digestibility of heat- or high-pres sure-treated beef extracts was evaluated with an in vitro simulated gastric digestion model and each sample also underwent immune assay to detect its antigenicity with the sera of beef allergic patients. Heat treatment of the beef extracts considerably decreased their digestibility, whereas high-pressure treatment at 200 MPa improved their digestibility compared with the control, but the difference was not significant. The digestibility of the high pressure-treated beef extract was generally higher than that of the heat-treated samples. Depending on the degree of digestion, the degree of antigenicity of the main beef allergens decreased. On the basis of these results, we hypothesized that the allergenicity of beef could be eliminated if the allergenic proteins are sufficiently digested in the digestive organ, leading to the suggestion that the digestibility of allergenic proteins must be improved in food processing. In conclusion, high-pressure processing is a more acceptable food processing technique for beef considering its digestibility.

• Journal of Welding and Joining
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• 제3권2호
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• pp.16-26
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• 1985

Post weld heat treatment(PWHT), at more than 600.deg. C, is essential to remove residual stress and hydrogen in weld HAZ and improve fatigue characteristics. However, residual stress during PWHT is responsible for PWHT embitterment and it promotes precipitation of impurities to grain boundary. In this paper, the effect of stress simulated residual stress on fatigue failure was evaluated by fatigue test, microhardness test and fractograph. The obtained results are summarized as follows; (1) The fatigue crack growth rate(da/dN) of parent and heat treated parent was affected by microstructure due to heat treatment and it depended on stress intensity factor (.DELTA.k). (2) The fatigue strength of weld HAZ was dependent on applied stress during PWHT and da/dN after PWHT was slower than as-weld. (3) Softening amount of weld HAZ was bigger than any other due to PWHT. Hardness value of weld HAZ was affected by heat treatment under the applied stress of 10 $kgf/mm^2$, but beyond 20 $kgf/mm^2$ it was increased by the applied stress rather than heat treatment. (4) Beyond the applied stress of 20 $kgf/mm^2$ during PWHT, intergranular fracture surface was observed and its amount was increased with applied stress during PWHT. (5) Effect of applied stress during PWHT on aspect of fracture surface was larger rather than that on fatigue crack growth behavior.

• 한국안전학회지
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• 제25권1호
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• pp.22-26
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• 2010

Material degradation should be considered to assess integrity and residual life of high temperature equipments. However, the property data reflecting degradation are not sufficient for practical use. In this study, mechanical properties of 1Cr-1Mo-0.25V casting steel generally used for turbine casing were measured and variation of microstructure was observed. Degradation was simulated by isothermal heat treatment.

• 열처리공학회지
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• 제17권4호
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• pp.216-222
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• 2004

Study was focused on the quenching embrittlement property of Zircaloy-4 cladding simulated Loss Of Coolant Accident (LOCA) environment in terms of high temperature oxidation and phase transformation. Property in LOCA condition of advanced cladding that contained Nb element was also investigated. Claddings were oxidized at given temperature and given time followed by water quenching. The results showed that ${\beta}$ phase which formed at quenching stage has an influence on cladding property. In case of advanced cladding, Nb retards cladding oxidation, thus enhances quenching resistance.

• 열처리공학회지
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• 제32권1호
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• pp.17-28
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• 2019

Jominy hardenability curves of low alloy steel containing less than 5 wt.% of alloying elements in total were calculated by applying Scheil's rule of additivity to pre-calculated isothermal transformation curve. Isothermal transformation curve for each phase in steel was approximated as a simple mathematical equation by using Kirkaldy's approach and all coefficients in the equation were estimated from experimental temperature-time-transformation (TTT) and/or continuous cooling transformation (CCT) data in the literature. Then jominy test with simple boundary conditions was performed in computer by applying the finite difference scheme. The resultant cooling curves at each location along a longitudinal direction of Jominy bar were applied to calculate phase fractions as well as mechanical properties such as micro Vickers hardness. The simulated results were compared with experimental CCT data and Jominy curves in the literature.

• 한국주조공학회지
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• 제36권5호
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• pp.167-173
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• 2016

The effect of various types of heat-treatment on the mechanical properties of cast Alloy 718 has been investigated. Cast Alloy 718 bars were subjected to 'standard heat-treatment'_(SHT), 'HIP (Hot Isostatic Pressing) heat-treatment'_(HHT), and 'HIP-simulated heat-treatment'_(HS). In the absence of long time high temperature heat-treatment, a small amount of Laves phase remained in the 'SHT' specimen, and needle shaped ${\delta}$ precipitated in the vicinity of the Laves phase. Due to the formation of the Laves and ${\delta}$ phases in the 'SHT' specimen, it exhibited lower tensile properties than those of the others_specimens. On the other hand, the Laves phase was completely dissolved into the matrix after 'HHT' and 'HS' treatments. It is known that isostatic pressure reduces the self-diffusion coefficient, because of the lower self-diffusivity under HIP conditions in the interdendritic region, Nb segregation and the high amount of ${\gamma}^{{\prime}{\prime}}$ precipitation that occurs. Due to the higher fraction of coarse ${\gamma}^{{\prime}{\prime}}$ phases, the 'HHT' treated Alloy 718 showed excellent tensile strength.

• 대한치과보철학회지
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• 제35권1호
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• pp.130-143
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• 1997

A heat-pressed technique(IPS-Empress, Ivoclar) has been described to construct single unit crown, inlay/onlay and veneers using a partially pre-cerammed and pre-colored glass-leucite ingot that has the greateast strength by the combination of heat-pressed procedure through the smalldiameter sprue and heat treatment procedure. The purpose of this study was to evaluate the flexure strength of a heat-pressed ceramic material(IPS-Empress) without simulated firing treatments according to pontic designs. Two groups of 9 disks(1.4mm thick, 14mm in diameter) each using two types of sprues with different diameters($({\Phi}2.8\;,{\Phi}1.8)$) and numbers were prepared. The specimens were mounted in the testing jig. The flexural strengths were determined, by means of the bi-axial bending test, by loading the center of disk to failure using a universal testing machine(Zwick 145141, Zwick, Germany) at a cross-head speed of 1.0 mm/min. The means flexural strength value of one group using a sprue with ${\Phi}2.8$ was $140.4{\pm}8.0Mpa$. That of the other group using two sprues with ${\Phi}1.8$ was $151.8{\pm}10.3Mpa$. After analysis, results showed that there was a statistical difference between groups(t=2.33m p<0.05). No clnical implications were drawn from these data because of absence of simulated firing treatment.