Investigation on Mechanical Behaviors for Bolted Connections in Carbon Steel and in Stainless Steel Using FEM

Kim, TaeSoo,Kuwamura, Hitoshi,Cho, Taejun,Shin, SungWoo,Kim, SeungHun,Lee, YongTaeg The Iron and Steel Institute of Japan 2008 ISIJ international Vol.48 No.6

<P>A finite element (FE) analysis with three-dimensional solid elements has been performed for estimating the structural behaviors of single shear bolted connections fabricated with cold-formed austenitic stainless steel by utilizing the existing test data for calibration. Failure and curling (out-of-plane deformation perpendicular to the direction of loading) criteria were proposed. Therefore, the failure mode and ultimate strength, predicted by FE analysis method, showed good agreements with those of experimental results. In this study, FE analyses for 10 test specimens fabricated with cold-formed carbon steel as well as stainless steel including failure mode of bolt shear fracture are carried out and the validity of numerical prediction for ultimate behaviors in cold-formed carbon steel bolted connections is also verified, based on the applicability of FE method for predicting the mechanical behaviors of bolted connections in cold-formed stainless steel. It is known from the coupon test results of steel materials that austenitic stainless (SUS304) steel has a higher tensile strength of material due to the effect of strength enhancements (considerable strain hardening) by means of cold-working process and much lower yield stress when compared to carbon steel. The influence of curling on the strength reduction of bolted connections is estimated quantitatively. In addition, characteristics of mechanical behaviors and the influence of curling in bolted connections between two different steel materials are compared through detailed investigation of FE analysis results.</P>

Cryogenic Fracture Toughness Evaluation for Austenitic Stainless Steels by Means of Unloading Compliance Method

Yu, Hyo-Sun,Kwon, Il-Hyun The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.1

Most research to date concerning the cryogenic toughness of austenitic stainless steels has concentrated on the base metal and weld metal in weldments. The most severe problem faced on the conventional austenitic stainless steel is the thermal aging degradation such as sensitization and carbide induced embrittlement. In this paper, we investigate the cryogenic toughness degradation which can be occurred for austenitic stainless in welding. The test materials are austenitic stainless JN1, JJ1 and JK2 steels, which are materials recently developed for use in nuclear fusion apparatus at cryogenic temperature. The small punch(SP) test was conducted to detect similar isothermally aging condition with material degradation occurred in service welding. The single-specimen unloading compliance method was used to determine toughness degradation caused by thermal aging for austenitic stainless steels. In addition, we have investigated size effect on fracture toughness by using 20% side-grooved 0.5TCT specimens.

냉간가공을 통한 중성자조사된 오스테나이트 스테인리스강의 기계적물성 모사 타당성 분석

김진원,김윤재 한국압력기기공학회 2019 한국압력기기공학회 논문집 Vol.15 No.2

The objective of this study is to investigate the feasibility of simulating the mechanical properties of irradiatied austenitic stainless steels by cold-working. In this study, the tensile properties, cyclic hardening behaviors and fracture toughness of cold-worked TP316L stainless steel were compared with those of austenitic stainless steels irradiated by neutrons. It showed that cold-working can properly simulate the increase in strength and the decrease in ductility and fracture resistance of austenitic stainless steels by neutron irradiation, even though it could not perfectly simulate the microstructures of irradiated austenitic stainless steels. Also, cold-working can appropriately simulate the hardening behaviors of neutron irradiated austenitic stainless steels under monotonic and cyclic loading conditions.

AISI 410과 304 스테인레스 강의 내식성 평가에 관한 연구

박형래(Hyung-Lae Park),최태준(Tae-Jun Choi) 산업기술교육훈련학회 2009 산업기술연구논문지 (JITR) Vol.14 No.3

In order to investigate the effect of surface treatment on the corrosion resistance of AISI 410 and 304 stainless steel, the surface roughness and corrosion were tested. The corrosion test were performed by immersion test and the corrosion rate calculated by weight loss method. Results were summarized as follows: 1. The surface roughness of electrolytic polished stainless steel were better than that of mechanically polished stainless steel. 2. The corrosion rate of surface treated AISI 410 stainless steel decreased as the value of surface roughness decreased. 3. The electrolytic polished AISI 410 and 304 stainless steels slowed lower corrosion rate than the mechanically polished stainless steels in H2SO4 solution.

The effect of molybdenum on the characteristics of surface layers of low temperature plasma nitrocarburized austenitic stainless steel

Insup Lee 한국물리학회 2009 Current Applied Physics Vol.9 No.3

The effect of molybdenum in the surface characteristics on low temperature plasma nitrocarburized layer of austenitic stainless steel was investigated. A low temperature nitrocarburized layer of AISI 316L steel (Fe–17Cr–12Ni–2.5Mo) was compared with that of AISI 304L steel (Fe–19Cr–10Ni) to evaluate the influence of molybdenum on nitrocarburizing. The low temperature plasma nitrocarburizing was performed in a gas mixture of N2, H2 and carbon-containing gas such as CH4. The influence of processing temperature (380–480 ℃) on the surface properties of the nitrocarburized layer was investigated. The resultant nitrocarburized layer produced on both 316L steel and 304L steel is a dual-layer structure, which comprises a N-enriched layer (γN) with a high nitrogen content on top of a C-enriched layer (γC) with a high carbon content, leading to a significant increase in surface hardness (about 1200 HV0.01). The chromium nitride was formed in the N-enriched layer for 316L steel treated at temperatures above 480 ℃ compared with 304L steel treated at temperatures above 430 ℃. The thickness of the hardened layer without precipitation of chromium nitride of both 316L steel and 304L steel increased with increasing temperature, and reached up to 25 ㎛ in 316L steel at 450 ℃, 10 ㎛ in 304L steel at 400 ℃, respectively. However, at same treatment temperature, the thickness of the hardened layer formed on nitrocarburized 316L steel was larger than that produced on nitrocarburized 304L steel. The specimens treated at 400 ℃ showed much enhanced corrosion resistance in terms of lower corrosion current density and a higher corrosion potential as compared to the untreated steel. The loss in corrosion resistance was observed for the specimens treated at 430 ℃ for 304L steel and 480 ℃ for 316L steel, due to the formation of chromium nitrides in the nitrogen-enriched layer. The effect of molybdenum in the surface characteristics on low temperature plasma nitrocarburized layer of austenitic stainless steel was investigated. A low temperature nitrocarburized layer of AISI 316L steel (Fe–17Cr–12Ni–2.5Mo) was compared with that of AISI 304L steel (Fe–19Cr–10Ni) to evaluate the influence of molybdenum on nitrocarburizing. The low temperature plasma nitrocarburizing was performed in a gas mixture of N2, H2 and carbon-containing gas such as CH4. The influence of processing temperature (380–480 ℃) on the surface properties of the nitrocarburized layer was investigated. The resultant nitrocarburized layer produced on both 316L steel and 304L steel is a dual-layer structure, which comprises a N-enriched layer (γN) with a high nitrogen content on top of a C-enriched layer (γC) with a high carbon content, leading to a significant increase in surface hardness (about 1200 HV0.01). The chromium nitride was formed in the N-enriched layer for 316L steel treated at temperatures above 480 ℃ compared with 304L steel treated at temperatures above 430 ℃. The thickness of the hardened layer without precipitation of chromium nitride of both 316L steel and 304L steel increased with increasing temperature, and reached up to 25 ㎛ in 316L steel at 450 ℃, 10 ㎛ in 304L steel at 400 ℃, respectively. However, at same treatment temperature, the thickness of the hardened layer formed on nitrocarburized 316L steel was larger than that produced on nitrocarburized 304L steel. The specimens treated at 400 ℃ showed much enhanced corrosion resistance in terms of lower corrosion current density and a higher corrosion potential as compared to the untreated steel. The loss in corrosion resistance was observed for the specimens treated at 430 ℃ for 304L steel and 480 ℃ for 316L steel, due to the formation of chromium nitrides in the nitrogen-enriched layer.

Effects of Ar gas Composition on the Characteristics of Surface Layers Formed on AISI 316L Stainless Steel During Low-Temperature Plasma Nitriding after Low-Temperature Plasma carburizing

이인섭 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.5

A 2-step low-temperature plasma process (the combined carburizing and post- nitriding) increases both the surface hardness and the thickness of the hardened layer and the corrosion resistance compared to individually processed low-temperature nitriding and low-temperature carburizing techniques. The 2-step low-temperature plasma process was carried out to improve both the surface hardness and the corrosion resistance of AISI 316L stainless steel. The influence of the Ar gas level in the atmosphere during the nitriding step on the surface properties was investigated. The expanded austenite (rN) was formed on all the treated surface. The thickness of rN was increased up to about 15 μm, and the thickness of the entire hardened layer was determined to be about 40 μm. The surface hardness reached 1200 HV0.1, which is about 5 times higher than that of the untreated sample (250 HV0.1). The thickness of the rN layer increased with increasing Ar gas content in the atmosphere. The corrosion resistance in the austenitic stainless steel processed by using the 2-step low temperature plasma was also much enhanced compared to that in the untreated austenitic stainless steel due to the high concentration of N on the surface. A 2-step low-temperature plasma process (the combined carburizing and post- nitriding) increases both the surface hardness and the thickness of the hardened layer and the corrosion resistance compared to individually processed low-temperature nitriding and low-temperature carburizing techniques. The 2-step low-temperature plasma process was carried out to improve both the surface hardness and the corrosion resistance of AISI 316L stainless steel. The influence of the Ar gas level in the atmosphere during the nitriding step on the surface properties was investigated. The expanded austenite (rN) was formed on all the treated surface. The thickness of rN was increased up to about 15 μm, and the thickness of the entire hardened layer was determined to be about 40 μm. The surface hardness reached 1200 HV0.1, which is about 5 times higher than that of the untreated sample (250 HV0.1). The thickness of the rN layer increased with increasing Ar gas content in the atmosphere. The corrosion resistance in the austenitic stainless steel processed by using the 2-step low temperature plasma was also much enhanced compared to that in the untreated austenitic stainless steel due to the high concentration of N on the surface.

Austenitic Stainless Steel의 應力腐蝕龜裂에 關하여 : 沸騰 MgCl₂溶液의 濃度變化를 中心으로

張禹煬 조선대학교 생산기술연구소 1981 生産技術硏究 Vol.1981 No.-

Stress corrosion cracking (SCC) of austenitic stainless steels has been investigated for several concentrations of boiling MgCl₂solutions. The cracking mode of austenitic stainless steels was investigated for several concentrations of boiling MgCl₂solutions by microscopy. The tests were conducted on stressed U-bend specimens cut from sheets. Both the periods of induction and propagation were determined by measuring the crack depth of the specimens for several concentrations of boiling MgCl₂solutions, and the mechanism was discuesed. The results obtained are as follows: 1) SCC occurs at the region of stress concentration, and it is always perpendicular to the direction of tensile stress. 2) As the concentration of boiling MgCl₂solution increases, SCC is mainly transgranular. Conversely, as the concentration of boiling MgCl₂solution decreases, SCC is intergranular. 3) As the concentration of boiling MgCl₂solution increases, the induction period increases and the propagation period decreases. Therefore, as the induction period increases, the propagation period decreases. 4) Time to failure shows a minimum at 140-150℃, and it increases below and/or above 140-150℃.

오스테나이트계 스테인리스강 용접부의 금속학적 현상에 관한 연구(2) - STS 304 용접부 조직특성 및 고온균열 감수성에 미치는 질소의 영향 -

이종섭,김숙환 대한용접접합학회 2000 대한용접·접합학회지 Vol.18 No.1

The purpose of the present study was to investigate weld metallurgical phenomena such as primary solidification mode, microstructural evolution and hot cracking susceptibility in nitrogen-bearing austenitic stainless steel GTA welds. Eight experimental heats varying nitrogen content from 0.007 to 0.23 wt.% were used in this study. Autogenous GTA welding was performed on weld coupons and the primary solidification mode and their microstructural characteristics were investigated from the fusion welds. Varestraint test was employed to evaluate the solidification cracking susceptibility of the heats and TCL(Total Crack Length) was used as cracking susceptibility index. The solidification mode shifted from primary ferrite to primary austenite with an increase in nitrogen content. Retained delta ferrite exhibited a variety of morphology as nitrogen content varied. The weld fusion zone exhibited duplex structure(austenite+ferrite) at nitrogen contents less than 0.10 wt.% but fully austenitic structure at nitrogen contents more than 0.20 wt.%. The weld fusion zone in alloys with about 0.15 wt.% nitrogen experienced primary austenite + primary ferrite solidification (mode AF) and contained delta ferrite less than 1% at room temperature. Regarding to solidification cracking susceptibility, the welds with fully austenitic structure exhibited high cracking susceptibility while those with duplex structure low susceptibility. The cracking susceptibility increased slowly with an increase in nitrogen content up to 0.20 wt.% but sharply as nitrogen content exceeded 0.20 wt.%, which was attributed to solidification mode shift fro primary ferrite to primary austenite single phase solidification.

Effect of the Holding Time during Solution Heat Treatment on Intergranular Corrosion of Unstabilized Austenitic Stainless Steels

Eun-Jong Oh,Dong-Hwa Lee,Sung-Woo Cho,Yun-Il Choi,Ki-Woo Nam 대한용접·접합학회 2020 대한용접·접합학회지 Vol.38 No.3

The holding time during solution heat treatment of unstabilized austenitic stainless steels as specified in the nuclear regulatory requirements was investigated. The sensitized 2.54㎝ thick specimens held at 675℃ for 1 h were rejected by ASTM A262 test, due to the large amount of chromium carbide precipitated in the form of 50~300㎚ particles at the grain boundaries. They also showed about 10.8% of DOS in the DL-EPR test. However, solution heat treatment of the sensitized specimens at 1,038℃ and 1,121℃ for at least 1 min resulted in the complete dissolution of chromium carbide into the grains, and they passed ASTM A262 test and showed less than 0.01% of DOS in the DL-EPR test. As a result of solution heat treatment at 1,038℃ for 5 h of the 25.4㎝ thick specimen sensitized at 675℃ for 10 h, it passed ASTM A262 and DL-EPR test at any position in the specimen thickness. While the specimen surface showed a step structure without the precipitation of chromium carbide and a DOS less than 0.01%, towards the center, a dual structure was observed. It exhibited about 0.6% of DOS due to the longer exposure time to the sensitization range of 427~816℃. Considering the minimum time in which the chromium carbide precipitated at the grain boundary at 1,038℃ was completely dissolved into the grain, and the maximum delay time for the center of the specimen to reach 1,038℃ rather than the surface, the holding time for complete solution heat treatment to the center was found to be up to 2 min per 2.54㎝ of material thickness. The solution heat treatment for 0.5~1.0 h per 2.54㎝ of material thickness at 1,038~1,121℃, which is employed in the nuclear power industry, was proven to prevent grain boundary corrosion by inhibiting the sensitization of unstabilized austenitic stainless steels.

Strength of Channel Bolted Connection with Austenitic Stainless Steel (304 Type)

김태수,김민성,조태준 한국강구조학회 2015 International Journal of Steel Structures Vol.15 No.3

Stainless steel has been widely utilized as structural materials of building due to significant characteristics in its superior corrosion resistance, durability, aesthetic appeal etc. Recently, experimental and numerical studies of structural behaviors and curling (out-of-plane deformation) influence for single shear bolted connection fabricated with thin-walled plane plates have been performed by Kim T.S. In this paper, finite element analysis (FEA) has been conducted based on the existing test result of channel bolted connections in austenitic stainless steel. The validation of numerical approach was verified to predict the structural behaviors of bolted connections such as fracture mode, ultimate strength and curling occurrence. Curling also occurred in the channel bolted connections with a long end distance like bolted connections assembled with plane plates. The curling reduced the ultimate strength and ultimate strength reduction caused by curling has been estimated quantitatively through the strength comparison of analysis results of FEA models with free edge and restrained curling. Additional parametric analysis for FEA models with extended variables has been performed. Therefore, the ultimate strengths were compared with current design strengths and modified strength formulae for channel bolted connections considering curling effect were proposed.