SM45C 환봉 용접재의 피로거동에 관한 실험적 연구

이용복(Yong-Bok Lee),정재근(Jae-Keun Jung) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.6

For this study, SM45C steel rods using generally for power transmission shafts and machine components was selected and welded by butt-GMAW method. And then it was studied about estimation of fatigue strength and the region of infinite life by Haigh diagram using Goodman's equation. Fatigue strength in weld zone presents highly in order of the boundary between deposited metal zone and heat affected zone, deposited metal zone, heat affected zone. This result agrees with distribution of hardness in weld zone. Fatigue strength in base metal zone presents highly compared with weld zone in low cycles between 10⁴ cycles and 10?cycles, but it presents the lowest fatigue strength on the order of heat affected zone in the vicinity of 10?cycles. It is the result that the first high compressive residual stress distributed by drawing process of the steel rods is released and the base metal is softened by alternating stresses. The region of infinite life by Haigh diagram presents highly in order of the boundary between deposited metal zone and heat affected zone, deposited metal zone, heat affected zone. From this results, it is demanded that the stress for safety design of machine components using SM45C butt-welded steel rods must be selected in the region of the lowest infinite life of heat affected zone.

Ti-Nb첨가 저합금강 용접열영향부에서의 열-응력 이력이 미세조직 및 기계적 성질에 미치는 영향에 관한 연구

문준오,이창희,Moon, Joonoh,Lee, Changhee 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.6

The influence of thermo-mechanical cycling on the microstructure and strength in the weld coarse-grained heat affected zone (CGHAZ) of Ti-Nb added low carbon HSLA steel was explored through Vickers hardness tests, nanoindentation experiments, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Undeformed and deformed CGHAZs were simulated using Gleeble simulator with different heat inputs of 30kJ/cm and 300kJ/cm. At high heat input of 300kJ/cm, the CGHAZ consisted of ferrite and pearlite and then their grain sizes were not affected by deformation. At low heat input of 30kJ/cm, the CGHAZ consisted of lath martensite and then the sizes of prior austenite grain, packet and lath width decreased with deformation. In addition, the fraction of particle increased with deformation and this is because the precipitation kinetics was accelerated by deformation. Meanwhile, the Vickers and nanoindentation hardness of deformed CGHAZ with 30kJ/cm heat input were higher than those of undeformed CGHAZ, which are due to the effect of grain refinement and precipitation strengthening.

Analysis of microstructure characteristics of welded zones and heat-affected zones for offshore steel materials

사바야사치,백영곤,박영도 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5

The objective of the present study is to investigate the microstructure and toughness of weldment and simulated HAZ of offshore steels. Weldment of 420 MPa steel was done in 1G, 2G and 3G positions with varying inter-pass temperature and different heat input. Crack tip opening displacement (CTOD) tests were conducted to obtain the fracture toughness of weldments at different weld positions. The microstructural characterization of as deposited and reheated zones of the weldment are conducted and analyzed. Coarse grained heat affected zones and Inter-critically coarse grained heat affected zones are simulated using Gleeble thermo-mechanical simulator. Secondary heating of Inter-critically coarse grained heat affected zone samples were done at lower and higher temperature region between Ac1 and Ac3 temperatures. The effect of Martensite-Austenite constituents and surrounding microstructure on the low temperature impact toughness of simulated samples are studied.

고강도 구조용 철강소재의 대입열 용접 시 열영향부의 조직 미세화 및 기계적 특성 향상에 미치는 TiN 및 B의 효과

박진성,황중기,조재영,한일욱,이만재,김성진,Park, Jin-seong,Hwang, Joong-Ki,Cho, Jae Young,Han, Il Wook,Lee, Man Jae,Kim, Sung Jin 한국재료학회 2019 한국재료학회지 Vol.29 No.2

In the current steel structures of high-rise buildings, high heat input welding techniques are used to improve productivity in the construction industry. Under the high heat input welding, however, the microstructures of the weld metal (WM) and heat-affected zone (HAZ) coarsen, resulting in the deterioration of impact toughness. This study focuses mainly on the effects of fine TiN precipitates dispersed in steel plates and B addition in welding materials on grain refinement of the HAZ microstructure under submerged arc welding (SAW) with a high heat input of 200 kJ/cm. The study reveals that, different from that in conventional steel, the ${\gamma}$ grain coarsening is notably retarded in the coarse grain HAZ (CGHAZ) of a newly developed steel with TiN precipitates below 70 nm in size even under the high heat input welding, and the refinement of HAZ microstructure is confirmed to have improved impact toughness. Furthermore, energy dispersive spectroscopy (EDS) and secondary-ion mass spectrometry (SIMS) analyses demonstrate that B is was identified at the interface of TiN in CGHAZ. It is likely that B atoms in the WM are diffused to CGHAZ and are segregated at the outer part of undissolved TiN, which contributes partly to a further grain refinement, and consequently, improved mechanical properties are achieved.

핵융합로 구조용 저방사화강의 용접열영향부 후열처리 균열 감수성

이진종(Jinjong Lee),문준오(Joonoh Moon),이창훈(Chang-Hoon Lee),박준영(Jun-Young Park),이태호(Tae-Ho LEE),홍현욱(Hyun-Uk Hong),조경목(Kyung-Mox Cho) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.6

Post-Weld Heat Treatment (PWHT) cracking susceptibility in the weld heat-affected zone (HAZ) of reduced activation ferritic-martensitic (RAFM) steels was evaluated through stress-rupture tests. 9Cr-1W based alloys including different C, Ta and Ti content were prepared. The coarse grained heat-affected zone (CGHAZ) samples were simulated with welding condition of 30 kJ/cm heat input. CGHAZ samples consisted of martensite matrix. Stress rupture experiments were carried out using a Gleeble simulator at temperatures of 650-750℃ and at stress levels of 125-550 MPa, corresponding to PWHT condition. The results revealed that PWHT cracking resistance was improved by Ti addition, i.e., Ti contributed to the formation of fine and stable MX precipitates and suppression of coarse M23C6 carbides, resulting in improvement of stress rupture ductility. Meanwhile, rupture strength increased with increasing solute C content.

고주파 유도 열원 적용 선상가열 유기 조선용 후판 이중곡률 성형기술

이광석(K. S .Lee),이정환(J. H. Lee) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5

Line heating-induced permanent deformation behavior of a SS400 thick plate has been investigated through both numerical analysis and experimental testing by applying high frequency induction as a heat source after generating dual-curvature by secondary line heating. Electromagnetic-thermal-structural coupling numerical analysis was first utilized for the prediction of temperature distribution and subsequent permanent deformation over the SS400 carbon steel plate. Also experimental line heating was carried out to validate the feasibility of the numerical analysis by applying newly designed laboratory-scale high frequency (HF) induction heating (IH) equipment. Both the numerical and experimental results indicate that depth and width of the heat affected zone (HAZ), generated by the interaction between I-IF induction heat source and upper surface of the workpiece, tend to increase with the increase in the input power. Also the numerically calculated depth of HAZ coincides well with experimentally obtained HAZ profiles. Permanent vertical deformation is increased with an increase in the input power regardless of both concave and saddle-type doubly curved plates. Transverse curvature determined in both simulation and experiment were investigated, and the results indicate that the transverse curvature after HF IH achieves good agreements between the FE analysis and experimental measurement regardless of input power and shape of plate, indicating the effectiveness of the eco-friendly designed HF IH-based line heating apparatus established in KIMS.

A516-65급 압력용기용 강재의 용접모사 열처리를 통한 용접열영향부의 수소확산 및 황화물응력균열 거동 연구

조동민,박진성,이진우,김성진 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.9

Hydrogen diffusion and sulfide stress cracking of simulated heat-affected zone (HAZ) of A516- 65 grade steel were examined using an electrochemical permeation technique, glycerin volumetric method, and constant loading method. HAZ samples were fabricated using a metal thermal cycle simulator with a welding heat input of 20, 35, and 50 kJ/cm. The fractions of bainite and martensite-austenite (M-A) constituent in coarse-grained HAZ (CGHAZ) and intercritical HAZ (ICHAZ) obtained by a simulated thermal cycle with a low heat input (20 kJ/cm) were higher than those with a higher heat input. These fractions contributed to the increase in the reversible hydrogen trap density (N[H]rev) and reversibly trapped hydrogen concentrations (Crev). Although CGHAZ had higher N[H]rev and Crev meaning that it is more likely to be vulnerable to brittle failure by hydrogen, actual fracture by sulfide stress cracking (SSC) occurred in ICHAZ composed of a mixture of soft ferrite/pearlite, and hard bainite and M-A. The hydrogen diffusion/ trapping parameters, which were obtained from the electrochemical permeation or glycerin method, cannot be directly indicative of the resistance to SSC of the steel in a H2S environment. The susceptibility to SSC was more influenced by the level of M-A-localization and localized corrosion attack, acting as a stress intensifier under a tensile load.

2.25Cr-1Mo강 용접 열영향부의 기계적 특성과 미세조직에 미치는 용접후열처리 온도의 영향

강용준,서강명,이준호,오창영,이승건 대한용접접합학회 2023 대한용접·접합학회지 Vol.41 No.3

The effect of post-weld heat treatment (PWHT) temperature on the mechanical properties of the heat-affected zone (HAZ) of 2.25Cr-1Mo steels was investigated. SA-387 Gr. 22 Cl. 2 steel was employed, and the specimens taken from the steel were thermally cycled using Gleeble to simulate the coarse-grained HAZ (CGHAZ), fine-grained HAZ (FGHAZ), and intercritical HAZ (ICHAZ). Before the PWHT, the simulated HAZs exhibited poor impact toughness as compared with the base metal. The base metal and simulated HAZ specimens were heat treated in a furnace at 610, 650, 690, and 730℃ for 8 h; their impact toughness improved significantly irrespective of the PWHT temperature. The microstructural changes owing to the PWHT were observed using scanning electron microscopy and correlated with the mechanical properties.

Corrosion Characteristics of Welding Zones by Laser and TIG Welding of 304 Stainless Steel

( Kyung Man Moon ),( Myung Hoon Lee ) 한국부식방식학회(구 한국부식학회) 2010 Corrosion Science and Technology Vol.9 No.6

Two types of welding methods were performed on austenitic 304 stainless steel: laser welding and TIG welding. The differences of the corrosion characteristics of the welded zones from the two welding methods were investigated with electrochemical methods, such as measurement of the corrosion potential, polarization curves, cyclic voltammogram, etc. The vickers hardness of all laser-welded zones (WM:Weld Metal, HAZ:Heat Affected Zone, BM:Base Metal) was relatively higher while their corrosion current densities exhibited a comparatively lower value than those which were TIG welded. In particular, the corrosion current density of the TIG-welded HAZ had the highest value among all other welding zones, which suggests that chromium depletion due to the formation of chromium carbide occurs in the HAZ, which is in the sensitization temperature range, thus it can easily be corroded with an active anode. Intergrenular corrosion was also observed at the TIG-welded HAZ and WM zones. Consequently, we can see that corrosion resistance of all austenitic 304 stainless steel welding zones can be improved via the use of laser welding.

플라스마 아크 용접에 의한 STS317L 용접부의 기계적 특성에 관한 연구

이일준(Il-Jun Lee) 산업기술교육훈련학회 2012 산업기술연구논문지 (JITR) Vol.17 No.3

Austenitic stainless steel(STS317L) were selected as base metal. The base metal were jointed by plasma arc welding(PAW) under proper welding conditions. Specimens were cut out from transverse line of welded respectively. Tensile, micro vickers hardness, bending test and microstructure inspection were preformed and the mechanical properties and microstructures investigated. The results of analyses are as follows: Tensile strength was the high in weld metal(565MPa) and elongation was the low(41.0%) then base metal. Hardness was the highest in bond(HV252) and decreased to the base metal gradually and the average hardness in heat affected zone was HV207. In bending test deformation was the largest in heat affected zone and smaller in weld metal zone. The microstructure of weld metal zone showed dual phase of austenite-ferrite contains σ phase and δ-Ferrite, and grain size was largest in heat affected zone then in base metal.