Effects of Ni and Mn addition on critical crack tip opening displacement (CTOD) of weld-simulated heat-affected zones of three high-strength low-alloy (HSLA) steels

Lee, Seok Gyu,Lee, Dong Ho,Sohn, Seok Su,Kim, Woo Gyeom,Um, Kyung-Keun,Kim, Ki-Seok,Lee, Sunghak Elsevier Sequoia 2017 Materials science & engineering Structural materia Vol.697 No.-

<P><B>Abstract</B></P> <P>In order to understand and improve fracture toughness of heat affected zones (HAZs) of high-strength low alloy (HSLA) steels, complex microstructures including quasi-polygonal ferrite (QPF), acicular ferrite (AF), granular bainite (GB), bainitic ferrite (BF), and martensite-austenite (MA) constituent should be identified, quantified, and then correlated with critical crack tip opening displacement (CTOD). In this study, microscopic analysis methods were achieved for identification and quantitation of microstructures in the HAZs of three HSLA steels. The coarse-grained HAZ (CGHAZ) consisted of AF, GB, and BF together with a small amount of MA, while the inter-critically heated HAZ (ICHAZ) consisted of QPF, GB, and MA. In the CGHAZ, Ni promoted the formation of AF, while it prevented the formation of GB, and the addition of Ni resulted in very high critical CTOD. In the CGHAZ, both Ni and Mn promoted the formation of AF and prevented the formation of GB, while Ni was more effective than Mn. Thus, the addition of Ni resulted in very high critical CTOD. In the ICHAZ, both Ni and Mn promoted the formation MA. However, in the high-Ni-containing steel, a number of MAs were densified along Ni-segregated bands, and thus readily provided void initiation sites. This played an important role in reducing the mean free path for coalescence of voids and crack propagation, which easily led to the serious deterioration of critical CTOD.</P>

Microstructure and Mechanical Property in the Weld Heat-affected Zone of V-added Austenitic Fe-Mn-Al-C Low Density Steels

Joonoh Moon,Seong-Jun Park 대한용접·접합학회 2015 대한용접·접합학회지 Vol.33 No.5

Microstructure and tensile property in the weld heat-affected zone (HAZ) of austenitic Fe-Mn-Al-C low density steels were investigated through transmission electron microscopy analysis and tensile tests. The HAZ samples were prepared using Gleeble simulation with high heat input welding condition of 300 kJ/cm, and the HAZ peak temperature of 1200℃ was determined from differential scanning calorimetry (DSC) test. The strain- stress responses of base steels showed that the addition of V improved the tensile and yield strength by grain refinement and precipitation strengthening. Tensile strength and elongation decreased in the weld HAZ as compared to the base steel, due to grain growth, while V-added steel had a higher HAZ strength as compared than V-free steel.

Microstructure and Mechanical Property in the Weld Heat-affected Zone of V-added Austenitic Fe-Mn-Al-C Low Density Steels

Moon, Joonoh,Park, Seong-Jun The Korean Welding and Joining Society 2015 대한용접·접합학회지 Vol.33 No.5

Microstructure and tensile property in the weld heat-affected zone (HAZ) of austenitic Fe-Mn-Al-C low density steels were investigated through transmission electron microscopy analysis and tensile tests. The HAZ samples were prepared using Gleeble simulation with high heat input welding condition of 300 kJ/cm, and the HAZ peak temperature of $1200^{\circ}C$ was determined from differential scanning calorimetry (DSC) test. The strain- stress responses of base steels showed that the addition of V improved the tensile and yield strength by grain refinement and precipitation strengthening. Tensile strength and elongation decreased in the weld HAZ as compared to the base steel, due to grain growth, while V-added steel had a higher HAZ strength as compared than V-free steel.

HT 후판강재의 용접 열영향부(HAZ)에서 발생하는 용접균열의 민감도에 관한 고찰

안현모(Hyun-Mo Ann),이종식(Jong-Sik Lee) 산업기술교육훈련학회 2012 산업기술연구논문지 (JITR) Vol.17 No.1

The welding crack susceptibility around of heat affected zone in welded thick(HT80 steel) joint is very important, and especially the welded structure for industrial structure such as plant, shipping, bulding, car parts welding is needed various welding method. In joining method of welding structure, welding residual stresses inevitably occur welded joints after welding, the evaluation of welding cracking susceptibility in HT80 steel was performed using thermally simulated heat affected zones. So, this paper deals with investigations into the testing of electric shield metal arc welding(SMAW) process that is frequently in welding HT80 steel that are quenched and tempered after welding. It has been carried out to study the weldability using test of welded specimen in welding cracking of HT80 steel that frequently occur after reheating. Also, are selected for examining the mechanism of welding crack-occurrence and way to reliability in cracking of the welded metal. This examinations were carried out in terms of micro-structural characterization, micro-hardness measurement and welded bend test. It was found that welding cracking susceptibility increased as hardness increased and cooling speed of weld heat cycle, Cooling curve Diagram HT80 steel shows what can be prevented in the weld metal and heat-affected zone when be controlled by hardness value in heat treatment from 800℃ to 500℃, and welding crack susceptibility of HT80 is not occur when bead pass below about multi 10 pass. It evident that welding cracking susceptibility can be eliminated or reduced by controlling the welding parameters such as the realation of cooling cycly, max. hardness value in HAZ, affect of residual stress according to reheating cycle or In view of the results, welding crack is not occur below about 490MPa(50kgf/mm2) in reinforcement and welding pass is below about 10 pass. For the improving of Welding crack can be controlled of various parameters(decrease of HAZ hardness, stress-relief in HAZ, micro-structural characterization, cooling cycle, etc.) in welding.

용접방법에 따른 DP780 용접부의 저주기 피로특성

이정훈(Jeong Hun Lee),박성혁(Sung Hyuk Park),권혁선(Hyuk Sun Kwon),김교성(Go Sung Kim),이종수(Chong Soo Lee) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10

This study aims to investigate low-cycle fatigue (LCF) behavior of welds of DP780 steels processed by different welding methods: Laser, TIG (tungsten inert gas) and MAG (metal active gas) methods. The LCF properties were analyzed in the context of microstructure and hardness of heat affected zone (HAZ). With an increase in the amount of welding heat inputs, the width of weld metal zone and HAZ increased but hardness decreased. The results of fatigue test showed that the fatigue resistance of as-received material without welding was most superior and that of MAG welded material having the highest heat input was the worst. The Laser and TIG welded materials showed similar fatigue properties. For the Laser welded metal, the fatigue fracture occurred in the parent metal away from the welded zone because the HAZ region had nearly identical characteristic with the parent metal. In case of TIG and MAG welded materials, however, the fatigue crack initiated from the HAZ region due to the relatively lower hardness of HAZ.

Assessment of the sulfide stress corrosion cracking characteristics in the multi-pass weld of the A106 Gr B steel pipe

이규영,박광진,배동호 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.5

Sulfide stress corrosion cracking (SSCC) in crude oil field environment containing hydrogen sulfide (H2S) has been recognized as a material degradation and damage mechanism. Laboratory data and field experience have demonstrated that extremely low concentration of H2S may be sufficient to lead to SSCC failure of susceptible materials. In some cases, sulfides may act synergistically with chlorides to produce SSCC failures. SSCC mechanism is a form of hydrogen embrittlement that occurs in high strength steels and in localized hard zones in weld of susceptible materials. In the heat-affected zones adjacent to the weld, there are often very narrow hard zones combined with regions of high residual stress that may become embrittled to such an extent by dissolved atomic hydrogen. On the basis of this understanding, SSCC tests were conducted with smooth specimens of the multi-pass welded ASTM A106 Gr B steel pipe used in the oil industries. And SSCC resistance according to the welding processes was evaluated. From the results, the weld by GTAW+FCAW showed the largest resistance against SSCC.

SS400강 및 STS304강의 열재현 특성

정정환(J. H. Jeong),안석환(S. H. Ahn),남기우(K. W. Nam) 한국동력기계공학회 2004 한국동력기계공학회 학술대회 논문집 Vol.- No.-

Simulated heat of heat affected zone and researched a mechanical properties in used the SS400 and the STS304. As the result, mechanical properties of steel that make drawing decreased because of residual stress by strain hardening due to the heat-simulated temperature rises, but by the temperature rising in materials that have done heat-simulated after annealing, the mechanical properties ware improved.

Oxidation and fatigue crack propagation in the range of low stress intensity factor in relation to the microstructure in P122 Cr-Mo steel

Bae, S.Y.,Kang, H.G.,Yun, H.S.,Kim, C.W.,Lee, D.B.,Lim, B.S. Elsevier Sequoia 2009 Materials science & engineering. properties, micro Vol.499 No.1

Fatigue strength and life of weldment at high temperatures are important for the materials in power plants. The fatigue crack growth rate is accelerated by oxidation. Similarly, the high-temperature fatigue life is influenced by oxidation. The base metal, the weld metal and the heat-affected zone (HAZ) of the P122 (Cr-Mo steel) weldment were oxidized between 600<SUP>o</SUP>C and 700<SUP>o</SUP>C for up to 500h in air, and their oxidation behavior was examined. The oxidation resistance increased in the order of HAZ, base metal and weld metal. The scales were mainly Fe<SUB>2</SUB>O<SUB>3</SUB>. Fatigue tests were performed to measure the fatigue crack growth rate in the range of low stress intensity factor, and the results are discussed from the viewpoint of different microstructures and oxidation.

P92강 용접부의 피로균열 성장거동에 미치는 미세조직의 영향

김범준(Bumjoon Kim),임병수(Byeongsoo Lim) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.8

Fatigue strength and life of weldment at high temperature is very important for high temperature materials used in power plants. In this study, fatigue crack growth tests were performed to examine the effect of microstructure on the crack growth resistance in P92 steel weldment. Microhardness of the weldment was also investigated for better analysis. Residual stresses were removed by heat treatment to focus the study on the microstructural effect. CT specimens were made from the welded plate with notch at different distances from the fusion line. The fatigue crack growth rate was found highest along the fusion line and fusion line+2㎜ line into the heat affected zone.

오스테나이트계 Fe-Mn-Al-C 경량철강의 용접열영향부 고온연성 거동 및 첨가 원소의 영향

문준오(Joonoh Moon) 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.6

Three austenitic Fe-Mn-Al-C alloys containing different Mo, Cr, and Si contents were prepared to evaluate the effects of alloying elements on the hot ductility behavior of the weld heat-affected zone (HAZ) of austenitic lightweight steels. HAZ simulations and hot tension tests were performed using a Gleeble simulator. The hot tension tests were conducted at 500 - 1220 ℃ during on-heating and on-cooling cycles. The results showed that the hot ductility significantly varied according to the behavior of κ-carbide precipitation with a decrease in temperature. The tensile ductility values of all the alloys were high at elevated temperatures above 1000 ℃ because of dynamic recrystallization. At intermediate temperatures of 700 - 900 ℃, significant ductility drops occurred in all alloys because κ-carbide precipitation, and the addition of Si resulted in more significant of ductility loss than in Cr or Mo added alloys. These different effects occurred because Mo and Cr suppressed κ-carbide precipitation, whersase Si promoted it. Ductility was recovered at low temperatures of approximately 500 ℃.