• Journal of Welding and Joining
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• 제27권2호
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• pp.76-81
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• 2009

Tandem GMAW is one of the high performance welding process and used in many industries to increase the productivity. An evaluation is presented of the mechanical properties and microstructural characteristics of the Tandem GMAW and conventional Single GMAW welds in 30mm thickness 490MPa grade steel by comparison method. Welding sequence and bead with and hight was kept, avoiding the effect of the bead shape and welding sequence. Tension, bending, hardness and Charpy impact test results of Tandem GMAW met the requirement of specification and showed similar distribution with conventional Single GMAW. Volume fraction of ferrite phase in weld metal showed little difference between Tandem GMAW and Single GMAW

• Nuclear Engineering and Technology
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• 제52권4호
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• pp.811-818
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• 2020

Y-containing CLAM steels were melted via vacuum induction melting and electroslag remelting. In this study, the evolution, microstructure, and mechanical properties of the alloy inclusions (ESR-1 (0 wt.% Y), ESR-2 (0.016 wt.% Y) and ESR-3 (0.042 wt.% Y)) were investigated. Further, the number of inclusions in ESRed steel was observed to obviously decrease, and the distributions were more uniform. The fine Y-Al-O inclusions (1-2 ㎛) were the main inclusions in ESR-2. The addition of Y affected the prior austenite grain size (PAGZ), increasing the tensile strength at test temperature. Low ductile-brittle transition temperature (DBTT) was obtained because of the fine PAGZ and dispersive inclusions. For the ESRed CLAM steel with 0.016 wt.% Y, the yield strengths were 621 MPa at 20 ℃ and 354 MPa at 600 ℃ in air. Further, the uniform elongation and elongation of the ESR-2 alloy were 5.5% and 20.1% at 20 ℃, respectively. Meanwhile, the DBTT tested using full-size Charpy impact specimen (55 cm × 10 cm × 10 cm) was reduced to -83 ℃.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2010년도 춘계학술발표대회 초록집
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• pp.25-25
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• 2010

8 wt.% 망간 (Mn) 이 함유된 마르텐사이트계 고 Mn강은 고강도용 강재로 산업현장에 적용될 수 있는 유용한 재료이다. 그러나, 다량의 망간의 함유로 인한 용접성 저하로 상용화를 위해서는 용접성 평가가 필요하다. 본 연구에서는 gleeble simulator 를 통해 열영향부를 재현한 후 local brittle zones(LBZs) 을 규명하였다. 모재는 Electron Probe Micro Analyzer (EPMA) 및 X-Ray Diffractometer(XRD) 로 분석결과 다량의 Mn 함유로 인해 lath마르텐사이트 미세조직과 소량의 잔류 오스테나이트로 구성되어 있었다. 용접부에서 모재까지 Vickers 경도계로 경도 분포를 측정한 결과 coarse-grained heat affected zone (CGHAZ) 에서 fine-grained heat affected zone (FGHAZ) 까지 경도 증가 후 subcritical heat affected zone (SCHAZ) 까지 급격한 경도 감소 거동을 보였다. 열영향부의 미세조직은 투과전자현미경 (TEM)으로 분석하였다. 연성취성천이온도 (DBTT) 측정을 위해 온도 구간을 상온, $0^{\circ}C$, $-20^{\circ}C$, $-40^{\circ}C$, $-60^{\circ}C$, $-80^{\circ}C$으로 설정하여 charpy impact test를 시행하였다. 그 결과 coarse-grained heat affected zone(CGHAZ) 에서 조대한 결정립으로 인해 낮은 충격값을 보였다.

• Journal of Welding and Joining
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• 제17권3호
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• pp.55-65
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• 1999

Metallurgical factors influencing toughness of the Intercritically Reheated Coarse-Grained Heat Affected Zone (ICCG HAZ) of multiple welded SA508-cl.3 Reactor Pressure Vessel Steel were evaluated. The recrystallized austenite formed along the prior austenite grain boundaries and late interfaced on heating to the intercritical range was transformed to bainite and/or martensite during cooling. The newly formed martensite always included some retained austenite(M-A constituents). The characteristics(amount, hardness, density, and size) of M-A constituents were found to be strongly associated with both peak temperature and cooling time(△t8/5(2)) of last pass. Toughness in the ICCG HAZ was deteriorated with increasing amount of M-A constituents which was increased with increasing the last peak temperature within the intercritical temperature range. Meanwhile, for the same intercritical peak temperature, toughness was decreased with increasing cooling time. When cooling time was short, the dominant factor influencing toughness of the ICCG HAZ was amount of M-A constituents. However, when cooling time was lengthened, the hardness difference between M-A constituents and softened matrix(tempered martensite) was found to be the dominant factor.

• Journal of Welding and Joining
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• 제18권2호
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• pp.232-232
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• 2000

The hydrogen attack characteristics of 3Cr-1Mo-V steel as simulated weld heat affected state were studied in this paper. The hydrogen attack susceptibility was evaluated by the ratios of Charpy impact absorbed energy at 0℃($vE_{0HA}$/$vE_{0}$) and reduction of area by tensile test ($RA_{HA}$/RA) before and after exposure to hydrogen at 600℃ under 450kgf/㎠ for 300hr. The values of $vE_{0HA}$/$vE_{0}$ and $RA_{HA}$/RA were aggravated as the peak temperature of the simulated heat affected zone(HAZ) raised. These results were due to the increase of the possession of bubbles along the grain boundaries, which were resulted in the reduction of grain boundary area to be precipitated carbides due to grain coarsening and the carbon dissolved in the martensite-austenite constituent near by the prior austenite grain boundary. The possession ratio of methane bubbles formed along prior austenite grain boundaries were increased with raising the peak temperature. (Received February 22, 2000)

• Journal of Welding and Joining
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• 제18권2호
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• pp.105-111
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• 2000

The hydrogen attack characteristics of 3Cr-1Mo-V steel as simulated weld heat affected state were studied in this paper. The hydrogen attack susceptibility was evaluated by the ratios of Charpy impact absorbed energy at 0℃({TEX}$vE_{0} {HA}_/vE_{0}${/TEX}) and reduction of area by tensile test({TEX}$RA_{HA}/RA${/TEX}) before and after exposure to hydrogen at 600℃ under 450kgf/㎠ for 300hr. The values of {TEX}$vE_{0} {HA}_/vE_{0}${/TEX} and {TEX}$RA_{HA}/RA${/TEX} were aggravated as the peak temperature of the simulated heat affected zone(HAZ) raised. These results were due to the increase of the possession of bubbles along the grain boundaries, which were resulted in the reduction of grain boundary area to be precipitated carbides due to grain coarsening and the carbon dissolved in the martensite-austenite constituent near by the prior austenite grain boundary. The possession ratio of methane bubbles formed along prior austenite grain boundaries were increased with raising the peak temperature.

• Steel and Composite Structures
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• 제31권4호
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• pp.409-417
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• 2019

The choice of individual material for industrial application is primarily based on knowledge of its behavior in similar applications and similar environmental conditions. Contemporary design implies knowledge of material behavior and knowledge in the area of structural analysis supported by large capacity computers. Bearing this in mind, this paper presents and analyzes the experimental results related to the mechanical properties of the material considered (30CrNiMo8/1.6580/AISI 4340) at different temperatures as well as its creep and fatigue behavior. All experimental tests were carried out as uniaxial tests. The test results related to the mechanical properties are presented in the form of engineering stress-strain diagrams. The results related to the creep behavior of the material are shown in the form of creep curves, while the fatigue of the material is shown in the form of stress - life (S - N) diagram. Based on these experimental results, the values of the following properties are determined: ultimate tensile strength (${\sigma}_{m,20}=696MPa$), yield strength (${\sigma}_{0.2,20}=355.5MPa$), modulus of elasticity ($E_{,20}=217GPa$) and fatigue limit (${\sigma}_{f,20,R=-1}=280.4MPa$). Results related to fatigue tests were obtained at room temperature and stress ratio R = -1.

• 대한기계학회논문집A
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• 제25권7호
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• pp.1064-1072
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• 2001

It is very important to evaluate material degradation like temper and carbide embrittlements to secure the reliable and efficient operational conditions and to prevent brittle failure in service. The extent of material deterioration can be accurately evaluated by mechanical test such as impact test or creep test. But it is almost impossible to sample a large specimen from in-service plants. Thus, the material degradation evaluation by a non-destructive method is earnestly required. Recently the non-destructive test technique which uses the grain boundary etching characteristics owing to the variation of material structures has been proposed. However the program for material degradation evaluation using the grain boundary etching method(GEM) in Windows 98 domain doesnt be developed now. The aims of this paper are to develop the program and to complete the new master curve equations for the evaluation of material degradation on in-serviced high temperature components.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.40-40
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• 2009

The Cu-bearing PFS-700 steel which has yield strength over 700 MPa was developed to replace the existing submarine structural material, HY-100. PFS-700 steel has good combination of mechanical properties and superior weldability which can be welded without pre-heating before welding. Application PFS-700 steel to submarine or battle ship will give a great reduction of cost by removing or lowing pre-heating. To develop pre-heat free welding consumables that matches and take advantage of PFS-700 steel, new welding consumables have been designed for the GMAW, SAW processes and explosion bulge test(EBT) were conducted to see the reliability of welded structure. All welding was conducted without pre-heating before welding, the inter-pass temperatures were below $50^{\circ}C$ for SAW50 and $150^{\circ}C$ for GMAW and SAW150. All EBT specimens show over 14% reduction of thickness without through-thickness crack or propagation of crack to the hole-down area. Tensile properties for all welding conditions show higher(GMAW) or similar values(SAW50, SAW150) to the base metal. Charpy impact values for the weld metal also show 163.5J(GMAW), 95.4J(SAW50) and 69.0J(SAW150), which meet the goal, 50J, of this project.

• Journal of Welding and Joining
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• 제27권6호
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• pp.80-86
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• 2009

The Cu-bearing PFS-700 steel which has yield strength over 700 MPa was developed to replace the existing submarine structural material, HY-100. The PFS-700 steel has a combination of good mechanical properties and superior weldability. Becaus of that, it can be welded without pre-heating. The application of PFS-700 steel to submarine or battle ship will give a great reduction of cost by omitting pre-heating or lowering pre-heat temperature. To develop pre-heating free welding consumables that match and take advantage of PFS-700 steel, new welding consumables have been designed for the GMAW, SAW processes and explosion bulge test(EBT) was conducted to see the reliability of welded structure. All welds were made without pre-heating, and the inter-pass temperature was below $50^{\circ}C$ for SAW50 and $150^{\circ}C$ for GMAW and SAW150. All EBT specimens show over 14% thickness reduction without through-thickness crack or crack propagation to the hole-down area. Tensile properties for all welding conditions show higher(GMAW) or similar values(SAW50, SAW150) to the base metal. Charpy impact values for the weld metal also show 163.5J(GMAW), 95.4J(SAW50) and 69.0J(SAW150), which meet the goal(higher than 50J) of this project.