• 대한치과교정학회지
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• 제28권3호
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• pp.371-377
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• 1998

TiN 피막처리된 Elgiloy (Co-Cr계 선재)의 임상 적용을 검토하기 위하여 제조된 상태의 Elgiloy, $250^{\circ}C$에서 30분간 가열처리된 Elgiloy, TiN 피막처리된 Elgiloy 각각의 4가지 temper, 그리고 비교를 위하여 스테인레스강 선재의 인장 강도와 경도를 측정한 결과 다음과 같은 결론을 얻었다. $\cdot$인장강도는 모든 temper에서 TiN 피막처리된 군이 가장 높았고, 가열처리된 군, 제조상태의 군의 순으로 나타났으나 가열처리된 군과 제조상태의 군간에는 통계학적으로 유의한 차가 없었다(p>0.05). $\cdot$인장강도는 각 temper에서 TiN 피막처리시 제조상태의 Elgiloy보다 약 $10kgf/mm^2$정도의 증가를 보였다. $\cdot$경도값은 Yellow, Green, 그리고 Red temper에서는 TiN 피막처리된 군이 가장 높았고, 가열처리된 군, 제조상태의 군의 순으로 나타났으나(p<0.05), Blue temper에서는 가열처리된 군과 제조상태의 군간에 통계학적으로 유의한 차가 없었다(p>0.05). $\cdot$경도값은 각 temper에서 TiN 피막처리시 제조상태 Elgiloy보다 약 $50\~90VHN$ 정도의 증가를 보였다. $\cdot$스테인레스강의 선재와 비교할 때 제조상태에서는 Red temper와, TiN 피막처리한 경우는 Green temper와 비슷한 인장강도를 나타내었다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2010년도 춘계학술발표대회
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• pp.39.2-39.2
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• 2010

Recently, hot stamping process has been paid attention greatly by automobile makers in accordance with the fuel efficiency and environmental issues as well as crash safety issue. The hot-stamped parts, however, demand extreme mechanical properties such as tensile strength of over 1470 MPa or equivalently Vickers hardness of around 450. In this work, to meet the demand efficiently, a method to predict mechanical property of hot-stamped parts based on numerical phase transformation scheme has been proposed associated with the thermo-mechanical coupled finite element analysis. This work deals with various phase transformation equations and validates them to select appropriate model for 0.2C-0.1Si-1.4Mn-0.5Cr-0.01Mo-0.002B steel sheet. The authors show that an efficient method saving time and cost to develop hot-stamped automobile parts ensuring suitable mechanical properties such as Vickers hardness and strength.

• 한국해양공학회지
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• 제3권2호
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• pp.638-638
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• 1989

It has been very important in various industry fields to improve the fatigue strength characteristics of bearings such as bearing life, fatigue limit, etc., because such poor properties could result in shortening the machinery life as well as in decreasing the accuracy. However, no successful heat treatment criterion seems to be available at present. In this study, the effect of the $170^{\circ}C\times120min$ tempering cycles repeated after $380^{\circ}C\times80min$ oil quenching for $800^{\circ}C$ spheroidizing-annealed bearing steel (STB2) as base metal on the $120^{\circ}C$ high temperature rotary bending fatigue strength characteristics were investigated, including the effects on hardness, Charpy impact value and micro-structure, in order to seek for the best heat treatment condition finally. The important results obtained are as follows : 1) The optimal cycle of tempering so that the fatigue strength .sigma. could become the highest was the 4th cycle. And it is confirmed that this $\sigma_{F}$ is about 6 times more increased than that of base metal, and about 1.3 times more increased than the case of the 1 cycle tempered. 2) As a result of the investigation for the effects of tempering cycles on hardness, the hardness at the tempering number of 2 thru 5 cyles was not decreased severely ; only about 10% decrease from those of the quenched and 1 cycle tempered case. Such hardness is equivalent to $H_{R}$/C61-62 with no bad effect on anti-abrasion of bearing steel. 3) In the case of 2 thru 5 cycle tempering as well as 1 cycle tempering, the impact value was not so improved comparing with the case of quenching, but an increase of 5 to 10% could be expected at least. 4) It was experimentally confirmed that the control of the mechanical properties improvement such as fatigue strength and fatigue life for bearing steels could be possible by the number of tempering cycles.

• 열처리공학회지
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• 제7권2호
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• pp.77-87
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• 1994

Roles of fundamental and additional hardening precipitates on the changes of mechanical properties and electrical resistivity during precipitation decomposition in binary Al-Li, ternaty Al-Li-Cu and multi-Li-Cu-Mg-Zr alloys have been investigated by the detailed measurement of electrical resistivity, hardness and tensile strength and the observation of transmission electron micrographs. Peek hardness and tensile strength in multi-component Al-Li-Cu-Mg-Zr Alloy had higher than that of the other alloys and the results of measurement of hardness, strength and electrical resistivity in each alloys aged at 90 and $190^{\circ}C$, precipitation behaviors and mechanical properties in binary, ternary and multi-component Al-Li alloys were contributed to the ${\delta}^{\prime}$ precursory phase of ${\delta}^{\prime}$, $T_1$, G.P.B. zone and S' phases, repectively.

• Journal of the Korean Wood Science and Technology
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• 제52권4호
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• pp.383-392
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• 2024

Laminated bamboo is an engineered bamboo technology to maintain its mechanical durability for both construction and furniture materials. This study was conducted to assess the properties of laminated bamboo made from Betung bamboo at different culm positions and laminate orientations. The materials used in this study were 4-year Betung bamboo (Dendrocalamus asper) obtained from a community forest in Yogyakarta and polyvinyl acetate resin as adhesive. Two factors were applied for this study, i.e., culm position (lower, middle, and upper) and laminate orientations (vertical and horizontal direction). To examine the mechanical properties, a static bending test and the hardness test were performed in accordance with ASTM D1037-99. Moisture content and density were determined in accordance with BS 373-1957. The results indicated that there was no interaction between the culm position and laminate orientation on the moisture content, density, static bending properties and hardness. The culm position affected the static bending and hardness, with the higher position of the culm resulting a greater strength. The laminate orientation also affected the strength of laminated bamboo, with the vertical direction resulting in higher strength than the horizontal.

• 한국공작기계학회논문집
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• 제15권1호
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• pp.63-69
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• 2006

This study deals with the friction welding of A2024- T6 to A6061- T6; The friction time was variable conditions under the conditions of spindle revolution of 2000rpm, friction pressure of 50MPa, upset pressure of 100MPa, and upset time of 5.0seconds. Under these conditions, the microstructure of weld interface, tensile fracture surface and mechanical tests were studied, of friction weld, and so the results were as follows. 1. When the friction time was 1.5seconds under the conditions, the maximum tensile strength of the friction weld happened to be 292MPa, which is $94.2\%$ of the base material's tensile strength(310MPa). At the same condition, the maximum shear strength was 2l2MPa, which is equivalent to $103\%$ of the base material's shear strength (205MPa). 2. At the same condition, the maximum vickers hardness was Hv 146 at A2024- T6 nearby weld interface, which is higher Hv3 than condition of the friction time 0.5seconds, and the maximum vickers hardness was Hvl20 from weld interface of A6061-T6, which is higher Hv28 then base material's. 3. The results of microstructure analysis show that the structures of two base materials have fractionized and rearranged along a column due to heating and axial force during friction, which has affected in raising hardness and tensile strength.

• 한국해양공학회지
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• 제3권2호
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• pp.138-144
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• 1989

It has been very important in various industry fields to improve the fatigue strength characteristics of bearings such as bearing life, fatigue limit, etc., because such poor properties could result in shortening the machinery life as well as in decreasing the accuracy. However, no successful heat treatment criterion seems to be available at present. In this study, the effect of the $170^{\circ}C\times120min$ tempering cycles repeated after $380^{\circ}C\times80min$ oil quenching for $800^{\circ}C$ spheroidizing-annealed bearing steel (STB2) as base metal on the $120^{\circ}C$ high temperature rotary bending fatigue strength characteristics were investigated, including the effects on hardness, Charpy impact value and micro-structure, in order to seek for the best heat treatment condition finally. The important results obtained are as follows : 1) The optimal cycle of tempering so that the fatigue strength .sigma. could become the highest was the 4th cycle. And it is confirmed that this $\sigma_{F}$ is about 6 times more increased than that of base metal, and about 1.3 times more increased than the case of the 1 cycle tempered. 2) As a result of the investigation for the effects of tempering cycles on hardness, the hardness at the tempering number of 2 thru 5 cyles was not decreased severely ; only about 10% decrease from those of the quenched and 1 cycle tempered case. Such hardness is equivalent to $H_{R}$/C61-62 with no bad effect on anti-abrasion of bearing steel. 3) In the case of 2 thru 5 cycle tempering as well as 1 cycle tempering, the impact value was not so improved comparing with the case of quenching, but an increase of 5 to 10% could be expected at least. 4) It was experimentally confirmed that the control of the mechanical properties improvement such as fatigue strength and fatigue life for bearing steels could be possible by the number of tempering cycles.

• 한국생산제조학회지
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• 제9권4호
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• pp.131-136
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• 2000

This study deals with the mechanical properties of STS304-Al351 friction welding zone. Main results are as follows ; under the condition of upset pressure 75MPa, the tensile strength of STS304-al6351 friction weld interface was higher than that of Al6351 base metal, and the highest tensile strength(290MPa) was obtained at upset pressure 125MPa. The hardness profile across the weld interface shows that the hardness of both STS304 and Al6351 is higher around the weld interface, and sharply increased hardness on the STS304 side is related with the plastic deformation of micro volume. As the result of analyzing the tensile fracture, it showed perfect soft fracture.

• 소성∙가공
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• 제6권6호
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• pp.508-516
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• 1997

Forging process on sintered powder metals has been applied to produce automotive parts which require a high level of strength. In those parts, the measurement of relative density is very important because a low relative density density causes deterioration of strength. In the present study, an indentation force equation was proposed by which the result obtained from the hardness measurement is used to evaluate the relative density. This equation was applied to the prediction of the relative density in cylindrical specimens which were first sintered and then forged at the room temperature and at an elevated temperature. The experimental results were compared with predictions with and without consideration of the workhardening effect on the powder.

• 한국분말재료학회지
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• 제10권3호
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• pp.172-175
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• 2003

Mechanically-alloyed NiAl powder was sintered by Spark-Plasma Sintering (SPS) process. Densification and behavior mechanical property were determined from the experimental results and analysis ,such as changes in linear shrinkage, shrinkage rate, microstructure, and phase during sintering process, Victors hardness, and transver.ie-rupture-strength (TRS). Above 97% relative density was obtained after sintering at 115$0^{\circ}C$ for 5 min. Crystallite size determined by the Scherrer method was approximately 50 nm. From the X-ray diffraction analysis it was confirmed that the sintered bodies were composed mainly of NiAl phase together with Ni$_3$Al phase. Measured Vickers hardness and TRS value were 555$\pm$10 $H_v$ and 1393$\pm$75 MPa , respectively.