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Yb:YAG 디스크로 레이저 표면 용융 경화된 SKD61 열간금형강의 경도와 미세조직에 미치는 레이저 출력의 영향
이광현,최성원,강정윤,Lee, Kwang-Hyeon,Choi, Seong-Won,Kang, Chung-Yun 대한용접접합학회 2015 대한용접·접합학회지 Vol.33 No.3
In this study, effect of laser power on hardness and microstructure of SKD61 Hot Die steel of which surface was melted and hardened with Yb:YAG disk laser was investigated. Beam speed was fixed at 70 mm/sec and distance between them was 0.8 mm about Laser surface melting. The only thing that was changed laser power. Laser powers were 2.0, 2.4 and 2.8 kW. No defect was found under all conditions. As the laser power increased, the penetration depth were deepened and the bead width was also widened. There was no hardness deviation of fusion zone at same laser power and it was higher than that of heat affected zone. In addition, the more laser power increased, the more hardness in fusion zone decreased. Fusion zone was macroscopically dendrite structure. However, core matric in dendrite was lath martensite of 100 nm size. There were $M_{23}C_6$ of 500 nm and the VC and $Mo_2C$ of a nano meters on boundary of dendrite.
이광현(Kwang Hyeon Lee),조성근(Sung Keun Cho),허용(Yong Huh),구재민(Jae Mean Koo),석창성(Chang Sung Seok) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
The direct current potential drop(DCPD) method is the most commonly used method to evaluate the dynamic fracture resistance characteristics of a material. However, at using DCPD method in the dynamic fracture resistance test, there is a problem that the voltage drops sharply on the initiation of crack. For this reason mentioned above, the normalization method was suggested by ASTM E1820 which was revised recently, as a new method to evaluate the dynamic fracture resistance characteristic. The normalization method can be used to obtain a J-R curve directly from a load-load line displacement. In this study, we obtained two J-R curves from the dynamic fracture toughness test of two materials' weldment (SA508 Gr.lA, SA508 Gr.3A) for nuclear piping both by the DCPD and the normalization method.
Yb:YAG 디스크 레이저로 표면 오버랩 용융된 냉간금형강, STD11의 미세조직과 경도
이광현(Kwang-Hyeon Lee),최성원(Seong-Won Choi),윤중길(Jung Gil Yun),오명환(Myeong-Hwan Oh),김병민(Byung Min Kim),강정윤(Chung-Yun Kang) 대한용접·접합학회 2015 대한용접·접합학회지 Vol.33 No.5
Laser surface Melting Process is getting hardening layer that has enough depth of hardening layer as well as no defects by melting surface of substrate. This study used CW(Continuous Wave) Yb:YAG and STD11. Laser beam speed, power and beam interval are fixed at 70㎜/sec, 2.8㎾ and 800㎛ respectively. Hardness in the weld zone are equal to 400Hv regardless of melting zone, remelting zone overlapped by next beam and HAZ. Similarly, microstructures in all weld zone consist of dendrite structure that arm spacing is 3~4㎛, matrix is γ(Austenite) and dendrite boundary consists of γ and M₇C₃ of eutectic phase. This microstructure crystallizes from liquid to γ of primary crystal and residual liquid forms γ and M₇C₃ of eutectic phase by eutectic reaction at 1266℃. After solidification is complete, primary crystal and eutectic phase remain at room temperature without phase transformation by quenching. On the other hand, microstructures of substrate consist of ferrite, fine M23C₆ and coarse M₇C₃ that have 210Hv. Microstructures in the HAZ consist of fine M23C₆ and coarse M₇C₃ like substrate. But, M23C6 increases and matrix was changed from ferrite to bainite that has hardness above 400Hv. Partial Melted Zone is formed between melting zone and HAZ. Partial Melted Zone near the melting zone consists of γ, M₇C₃ and martensite and Partial Melted Zone near the HAZ consists of eutectic phase around γ and M₇C₃. Hardness is maximum 557Hv in the partial melted zone.
심현보(Hyeon-Bo Shim)이광현(Kwang-Hyun Lee),김령희(Ryeon-Hee Kim),박순규(Soon-Kyoo Park),심지나(Ji-Na Shim) 대한CT영상기술학회 2021 대한CT영상기술학회지 Vol.23 No.1
기존 반복적 재구성법의 단점을 보안하고 보다 낮은 선량으로 좋은 질의 영상을 얻기 위해 인공 신경망(Artificial Neural Network)으로 학습시킨 딥러닝 반복적 재구성법(Deep Learning Iterative Reconstruction, DLIR)이 개발되었으며 복부 CT에서 GE사의 딥러닝 반복적 재구성법(True Fidelity, TF)과 Siemens사의 모델기반 반복적 재구성법(Advanced Modeled Iterative Reconstruction, ADMIRE)을 적용한 영상의 화질평가와 선량감소 효과를 비교해 보고자 하였다. Phantom study는 CTDIvol(mGy)을 9.5로 동일하게 설정한 TF(TF-L, TF-M, TH-H)와 ADMIRE(1,2,3,4,5)이 적용된 단면영상으로 복부(A), 뼈(B) ROI를 설정하였고, Patient study는 본원에서 검사를 시행한 환자 30명의 복부조영 CT 검사에서 TF(TF-M, TF-H), ADMIRE 2 적용된 단면영상으로 복부대동맥(A), 간실질(B), 근육(C), 백그라운드(D) ROI를 설정하여 HU 및 SD값을 측정하고 SNR, CNR을 비교 평가하였다. Phantom study에서 T F-M은 ADMIRE 1, 3, 5 보다 Noise는 ROI A에서 221%, 139%, 40%, B는 104%, 66%, 19% 낮았고,(p<0.05) SNR은 ROI A에서 70%, 59%, 33%, B는 53%, 42%, 19% 높았다.(p<0.05) Patient study에서 TF-M은 ADMIRE 2 보다 Noise는 ROI A에서 7% 낮았지만 통계적으로 유의하지 않았고,(p=0.28) B는 21%, C는 45% 낮았다.(p<0.05) SNR은 ROI A에서 동일하였지만 통계적으로 유의하지않았고,(p=0.70) B는 20%, C는 28% 높았다.(p<0.05) CNR은 ROI A에서 22%, B는 25%, C는 22% 높았다.(p<0.05) 선량평가에서 TF가 적용된 환자의 평균 CTDIvol(mGy)은 4.73 ± 1.28, DLP(mGy⋅cm)는 281.43 ± 79.22, ADMIRE가 적용된 환자의 평균 CTDIvol(mGy)은 6.06 ± 1.22, DLP(mGy⋅cm)는 343.3 ± 81.34 이였고,(p<0.05) TF가 ADMIRE가 적용된 환자보다 CTDIvol(mGy)은 28%, DLP(mGy⋅cm)는 21% 낮았음을 알 수 있다.(p<0.05) 복부 CT 검사에서 딥러닝 반복적 재구성법이 적용된 TF 영상이모델기반 반복적 재구성법이 적용된 ADMIRE 영상보다 HU값의 변화는 없지만, Noise가 감소하며 SNR과 CNR은 증가하는 것으로 나타났다. 또한 선량이 같다면 딥러닝 반복적 재구성법이 적용된 TF 영상이 모델기반 반복적 재구성법이 적용된 ADMIRE영상보다 화질이 향상되고 이는 다시 말해 환자의 피폭 선량을 저감하는데 큰 기여를 한다고 할 수 있다 Deep Learning Iterative Reconstruction (DLIR), which was trained with an artificial neural network, was developed to secure the shortcomings of the traditional iterative reconstruction method and obtain a good quality image at a lower dose. The purpose of this study was to compare the effects of dose reduction and image quality evaluation using deep learning iterative reconstruction (True Fidelity; TF) and Siemens Advanced Modeled Iterative Reconstruction (ADMIRE). Phantom study is a axial image with TF (TF-L, TF-M, TH-H) a nd ADMIRE (1,2,3,4,5) with CTDIvol (mGy) set e qual to 9.5. Abdomen (A), Bone (B) ROI w as set, and the patient study was a axial image applied with TF (TF-M, TF-H) and ADMIRE 2 in the abdominal contrast CT scan of 30 patients who performed the examination in our hospital. Abdomen aorta (A), Hepatic parenchyma (B), muscle (C), background (D) ROI w as s et to measure HU, SD values, a nd SNR , CNR were compared. In t he P hantom study, TF-M w as c ompared with ADMIRE 1, 3, 5. Noise was 221%, 139%, 40% lower in ROI A, 104%, 66%, 19% lower in B.(p<0.05) SNR was 70%, 59%, 33% higher in ROI A, 53, 42%, 19% higher in B.(p<0.05) In patient study, TF-M was compared with ADMIRE 2. Noise was 7% lower in ROI A but it was not statistically significant.(p=0.28) B was 21%, C was 45% lower.(p<0.05) SNR was the same in ROI A but not statistically significant.(p=0.70) B was 20%, C was 28% higher.(p<0.05) CNR was ROI A 22%, B 25%, C 22% higher.(p<0.05) In dose assessment, the average CTDIvol (mGy) of patients with TF applied was 4.73 ± 1.28, DLP (mGy cm) was 281.43 ± 79.22, and the average CTDIvol (mGy) of patients with ADMIRE was 6.06 ± 1.22, DLP (mGy cm) was 343.3 ± 81.34.(p<0.05) It can be seen that TF was lower in CTDIvol (mGy) by 28% and DLP (mGy cm) by 21% than in patients with ADMIRE.(p<0.05) In conclusion, TF images on abdominal CT showed no change in HU values than ADMIRE images, but Noise decreased and SNR and CNR increased. If the dose is the same, the TF image is applied has better image quality than the ADMIRE image. It can be said that it contributes significantly to reducing the patient s exposure dose.
SKD61 열간합금강의 레이저 표면 합금화 경화처리 공정에서 SKH51 분말 송급속도에 따른 균열 형성에 대한 고찰
최성원 ( Seong-won Choi ),이광현 ( Kwang-hyeon Lee ),서정 ( Jeong Suh ),오명환 ( Myeong-hwan Oh ),강정윤 ( Chung-yun Kang ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.3
A laser surface-melting alloying process using a laser beam is a new surface-hardening process of obtaining an alloying layer that melts the surfaces of substrates and alloying powder at the same time. This study used SKD61 hot die steel as a substrate and SKH51 powder as an alloying powder. The laser beam speed and the laser power were fixed at 70 mm/sec and 2 kW. The power feeding rate was changed from 0 rpm to 6 rpm (step: 1 rpm). The alloying layer showed high hardness (710~830 Hv), but cracks occur at a high powder feeding rate. Cracks occur at more than 5 rpm, and the lengths of cracks become longer as the powder feeding rate increases. Moreover, cracks were observed at the dendrite boundary, and dendrite protrusions were observed on the fracture surfaces. As the powder feeding rate increases, the concentration of the Mo, V, and W in alloying layer increase. The liquidus and solidus temperatures decreased by as much as 6 ℃ and 26 ℃. As a result of calculating the aspect ratio (penetration depth/width) of the molten zone, it was found that there is no difference as the powder feeding rate increases. Therefore, strain by solidification contraction was constant with an increase in the powder feeding rate, but cracks occur, and the number of cracks increases because the solidus temperature decreases and the ductility of alloying layer reduces.
박수(Soo Park),이광현(Kwang-Hyeon Lee),조성근(Sung-Keun Cho),구재민(Jae-Mean Koo),석창성(Chang-Sung Seok) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
To J-integral calculation, first of all must idealize the stress-strain curve to a Ramberg-Osgood(R-O) equation. But a R-O constant depends on curve fitting section. So for Ramberg-Osgood fit to accurately estimate elastic-plastic J from engineering fracture mechanics analysis many methods are proposed. These method must have either full stress-strain data or yield and tensile strengths. But these methods have many difficulties for applying these to a real situation. Existing methods must know about a stress-strain curve or yield and tensile strengths. Therefore acquiring a correct R-O constant is very hard. The objective of this paper is to confirm a R-O constant determinating method.
조성근(Sung-Keun Cho),이광현(Kwang-Hyeon Lee),구재민(Jae-Mean Koo),석창성(Chang-Sung Seok),박재실(Jae-Sil Park) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Fracture resistance curves for concerned materials are required in order to perform elastic-plastic fracture mechanical analysis. Fracture resistance curve is built with J-integral values and crack extension values. The objective of this paper is to propose the estimation method of the fracture resistance curve. The estimation method of the fracture resistance curve for the pipe specimen was proposed by the load ratio method from load - displacement data for the standard specimen.