• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.11 no.1
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• pp.33-38
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• 2015

The effects of post weld heat treatment(PWHT) on the mechanical properties of 2.25Cr-1Mo steels were investigated. As the PWHT temperature or holding time increased, the strength of low alloy steels progressively decreased due to softening process. After the conventional PWHT, the strength was larger than the minimum value of materials specification. The Charpy impact energy was hardly affected by the conventional PWHT. The trend of mechanical properties was analyzed in terms of tempering parameter. Most materials replaced from a power plant met the requirements of materials specification except for one heat. Same heat of materials with low impact energy were attributed to the voids formed during casting process.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.2
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• pp.66-75
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• 2003

This paper describes about the estimation method of die lift by wear and plastic deformation in hot forging process. The thermal load and the thermal softening are happened by the high temperature in hot forging process. Tool lift decreases considerably due to the softening of the surface layer of a tool caused by high thermal load and long contact time between tool and billet. Also, tool life is to a large extent limited by wear, heat crack and plastic deformation in hot forging process. Above all, the main factors which affects die accuracy and tool lift are wear and the plastic deformation of a die. The new developed technique for predicting tool life applied to estimate the production quantity for a spindle component and these techniques assist to improve the tool life in hot forging process.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.4
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• pp.97-103
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• 1992

An experimental investigation has been carried out to determine the effect of tempering temperature on the fatigue crack propagation behavior and mechanical properties using the quenched and tempered STS420 martensitic stainless steel. Heat treatments of tempering for two hours at the five different temperatures of 150.deg.C, 300.deg.C, 450.deg.C, 600.deg.C and 700.deg.C have been performed on the martensite obtained by air cooling the specimens austenitized for one hour at 1010.deg.C. Tensile strength, yield strength, hardness, .DELTA.K$_{th}$, C and m values of differently tempered specimens have been investigated by tensile, hardness and fatigue tests.s.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.4
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• pp.266-277
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• 1997

Near-threshold fatigue crack growth characteristics was investigated on the Ni-Cr-Mo-V low alloy steel, which has the different microstructure obtained by tempering at various temperature. The specimens were austenized at $950^{\circ}C$ and then followed by tempering at $200^{\circ}C$, $530^{\circ}C$ and $600^{\circ}C$. Strain rate was obtained from strain gauge attached on the crack tip and crack opening point was observed through load-strain curve. Threshold stress intensity range(${\Delta}K_{th}$) was increased with increasing tempering tempuerature, but the effective threshold stress intensity rage (${\Delta}K_{eff,\;th}$) was not affected with the increasing temperature. Grain size increased with increasing tempering temperature.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.3
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• pp.159-164
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• 1997

Non-alloyed and 1.0%Ni alloyed ductile cast iron were cast into the sand mold and metal mold, and finer graphite size was obtained in case of metal mold casting. Direct tempering after casting showed the slight increase of absorbed energy, which is largely due to the relieving of residual stress that is developed during casting. After austempering heat treatment, higher impact energy was obtained in case of metal mold casting than sand mold casting, which is due to the finer graphite size.

• Korean Journal of Materials Research
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• v.5 no.5
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• pp.532-543
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• 1995

박용 디젤엔진 부품 크랭크샤프트의 기계적 성질에 미치는 화학 성분과 열처리 공정의 영향을 인장시험기, 경도시험기, 충격시험기와 광학현미경으로 조사연구하였다. 시행된 4가지 열처리공정중 다음의 열처리 공정인 노말라이징$\longrightarrow$TR단조$\longrightarrow$\ulcorner칭$\longrightarrow$템퍼링이 최적의 기계적 성질을 나타냈다. 이때 기계적인 성질은 오스테나이트 결정입도 크기, 냉각 속도, 오스테나이트화 온도와 오스테나이트화 유지 시간에 의존하였다. 오스테나이트 결정입도는 TR단조 후의 초기 결정입도 크기에 의존하고, 냉각 속도는 C-곡선 Nose를 지나야 하고, 오스테나이트화 온도는 탄소 함량에 의존하고 그리고 오스테나이트화 유지 시간은 저어널지름에 의존하는 것으로 나타났다.

• Journal of Ocean Engineering and Technology
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• v.25 no.5
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• pp.40-46
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• 2011

This study carried out a series of experiments involving impact tests (Drop weight type & Charpy type with a standard specimen and newly designed I-type specimen), hardness tests, and fracture surface observations of French-made roll shell steel (F), abnormal roll shell steel (M), reheated roll shell steel (R), and S25C steel under heat treatment conditions ($570^{\circ}C$) to analyze the cause and prevent the roll shell steel's brittle fracture and its damage.

• Journal of Ocean Engineering and Technology
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• v.25 no.5
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• pp.33-39
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• 2011

This study involved a series of experiments, which included impact tests (drop weight & Charpy) and hardness tests under various heat treatment conditions, followed by fractography observations of Normal Roll Shell steel (NRS), Abnormal Roll Shell steel (ARS), and S25C steel, in order to analyze the cause of brittle fracture and damages in Roll Shell steel. The optimal tempering temperature was characterized for ARS and NRS.

• Proceedings of the KAIS Fall Conference
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• 2003.06a
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• pp.83-86
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• 2003

SKD11은 자이로 펌프의 로타와 붓싱 재질로 사용되는데, 자이로펌프는 임펠러의 회전이 없고 원판의 기울기 운동으로 흡입과 토출을 반복하는 고압용적식 펌프이다. 이 펌프의 내구성을 향상시키기 위하여 우수한 내압성과 내마모성을 갖는 재질선정이 요구한다. 따라서 현재 가장 널리 사용되고있는 SKD11에 심냉처리를 통하여 미세조직의 개선을 수행하였고, 가스질화처리에 의한 표면경화로 내압성과 내마모성을 증가시키고자 하였다. SKD11의 미세조직 변화를 조사하기 위하여 광학현미경과 X-선 회절기를 사용하여 미세조직 관찰과 상변화를 조사하였으며, Rockwell 경도기틀 사용하여 각 변수에 따른 경도변화를 조사하였다. 연구 결과 기지조직은 모두 마르텐사이트로 나타났으며, 이 이외에 각각의 조건에 따라 크롬탄화물, PFZ, 잔류오스테나이트가 확인되었다. SKD11을 액화질소로 냉각한 후 500℃에서의 템퍼링으로 가장 큰 경도값을 얻을 수 있었다. 또한 가스질화처리에 의하여 표면경도를 크게 증가시킬 수 있었다.

• Composites Research
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• v.34 no.5
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• pp.311-316
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• 2021

In this study, TiC/steel metal matrix composites were fabricated by powder metallurgy process using Fealloy powders with 3 wt.% Cr and 10 wt.% Cr, respectively, as matrix material. Subsequently, the composite samples were heat treated by the annealing and quenching-tempering(Q-T), respectively, to understand the effect of heat treatment on the mechanical properties of the composites. The correlation between microstructure and structural strength depending on the chromium content and the heat treatment conditions was studied through tensile, compressive, and transverse rupture test and microstructural analysis. In the case of TiC/steel composite containing 10 wt.% Cr, the tensile strength and transverse rupture strength at room temperature were significantly lowered by the influence of coarse chromium carbide formed at the TiC/steel interface. On the other hand, both TiC/steel composites containing 3 wt.% Cr and 10 wt.% Cr showed much higher compressive strength of about 4 GP after quenching-tempering compared to the annealed specimens regardless of the presence of the chromium carbide.