Effects of testing variables on stress corrosion cracking susceptibility of Al 2024-T351

Lee, Hyunjung,Kim, Youngjoo,Jeong, Yooin,Kim, Sangshik Elsevier 2012 Corrosion science Vol.55 No.-

<P><B>Abstract</B></P> <P>In the present study, the effects of testing variables on stress corrosion cracking (SCC) susceptibility of Al 2024-T351 in 3.5% NaCl solution were examined using slow strain rate test (SSRT) method with controlled applied potentials and a constant load test (CLT) method. The SSRTs were conducted at various strain rates and applied potential, while the CLTs were performed with different exposure time, with different grain directions of ST (short-transverse) and L (longitudinal) to understand how the testing parameters affected on the SCC susceptibility of Al 2024-T351. The percent reductions in tensile elongation in an SCC-causing environment over those in air tended to express the SCC susceptibility of Al 2024-T351 most properly for both SSRT and CLT. The present fractographic examination suggested that both anodic dissolution and hydrogen embrittlement played a role in the SCC process of Al 2024-T351 in 3.5% NaCl solution at both anodic and cathodic applied potentials, and the contribution of each mechanism could vary with different testing variables. It was also found that the SCC susceptibility of Al 2024-T351 obtained from the CLT result could provide the similar SCC evaluation result obtained by SSRT with a proper selection of testing variables. The metallurgical aspect of SCC behaviour of Al 2024-T351 was also discussed based on the microstructural and fractographic examinations.</P> <P><B>Highlights</B></P> <P>► Effects of testing variables on SCC susceptibility of Al 2024-T351 in 3.5% NaCl solution were examined. ► Slow strain rate test (SSRT) method and a constant load test (CLT) method were utilised. ► Percent reductions in tensile elongation increased with decreasing strain rate. ► Anodic dissolution and hydrogen embrittlement played a role in the SCC process. ► CLT showed the similar SCC susceptibility obtained by SSRT.</P>

An experimental study for qualifying hydrogen compatibility of austenitic stainless steel under low temperature

Thanh Tuan Nguyen,박재영,Seung Hoon Nahm,백운봉 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.1

Hydrogen compatibility of materials refers to the ability to exhibit reliable mechanical integrity and a probability of failure in a given hydrogen-exposed environment. Currently, no experimental methods for qualifying the hydrogen compatibility of materials have been standardized, and testing expertise has been restricted to only a few laboratories. With international coordination, this paper presents the experimental activities and results to establish a code of practice. The experimental campaign included a slow strain rate tensile (SSRT) test and a notched fatigue life test on SUS316L-grade austenitic stainless steel, which has been widely used in structural components in hydrogen service. Sub-sized tensile specimens were machined from a bar with a gauge diameter of 4.00 mm and a gauge length of 20 mm. A notched specimen with a notch angle of 60°, notch radius of 0.12 mm, and net section diameter of 4 mm was prepared for the fatigue life test. The net section stress in the notched specimen at maximum load (σ max ) was 444 MPa in a tension–tension loading condition with a loading ratio of R = 0.1. The tests were performed at a temperature of 233 K (-40 °C) in two environmental conditions: high-pressure hydrogen gas at 90 MPa and nitrogen gas at 0.1 MPa (three tests for each condition). No noticeable degradation in yield strength and tensile strength was observed in the specimens tested under hydrogen pressure of 90 MPa H 2at -40 °C compared to that tested 0.1 MPa N 2 at -40 °C, however, hydrogen had a remarkable effect on reduction area (RA), and strain at fracture. The consistency of the experimental conditions and results from different laboratories with a distinct testing system were closely compared and discussed.

산-염소이온 분위기의 인자전위에 따른 내후성강 용접부의 부식파괴에 관한 연구

최윤석,김정구,김종집,이병훈 대한용접접합학회 2000 대한용접·접합학회지 Vol.18 No.3

The stress corrosion cracking(SCC) and hydrogen embrittlement cracking(HEC) characteristics of a weathering steel weldment were investigated in aerated acid-chloride solution. The electrochemical properties of weldment were investigated by polarization test and galvanic corrosion test. Weathering steel did not show passive behavior in the acid-chloride solution. Galvanic corrosion between the weld metal and the base metal was not observed because the base metal was anodic to the weld metal. The slow-strain-rate tests(SSRT0 were conducted at a constant strain rate o 7.87×{TEX}$10^{-7}${/TEX}/s at corrosion potential, and at potentiostatically controlled anodic and cathodic potentials. The weldment of weathering steel was susceptible to both anodic dissolution SCC and hydrogen evolution HEC.

양극산화된 5083-H321 합금의 천연해수 내 전기화학적 부식 및 응력부식균열 특성에 관한 연구

황현규,신동호,정광후,김성종 한국부식방식학회 2020 Corrosion Science and Technology Vol.19 No.5

Many studies have been conducted to improve the corrosion resistance and durability of various aluminumalloys through the anodizing technique. It is already used as a unique technique for enhancing the propertiesof aluminum alloys in various industries. This paper investigated the electrochemical corrosion and stresscorrosion cracking characteristics of anodized aluminum 5083-H321 alloy in natural seawater. The corrosioncharacteristics were assessed by the electrochemical technique and potentiodynamic polarization test. Thestress corrosion cracking characteristic was evaluated with a slow strain rate tensile test under 0.005 mm/minrate, which showed that the hard anodizing film had a thickness of about 16.8 μm. Although no significantcharacteristics of stress corrosion cracking were observed in the slow strain rate test, the anodized specimenpresented excellent corrosion resistance. The corrosion current density was measured to be approximately4.2 times lower than that of the base material, and no surface damage was observed in the anodic polarizationtest.

다층 FCA 용접금속의 강도 및 입열량에 따른 저온균열 민감도와 수소 트랩 특성

유재석,안형진,이정훈,박종민,윤광희,Sourav Kr. Saha,강남현 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11

저온균열은 탄소강 구조물 제작 시 가장 주의해야 될 용접 균열로 조선/해양 구조물 제작 시에는 맞대기 이음부 다층 용접부의 횡균열과 초고강도강 필렛 이음부의 종균열 및 횡균열 형태로 주로 발생되고 있다. 저온균열 민감도 평가 방법 중 대표적인 방법은 ISO 17642-2와 JIS Z 3158의 y-groove test이며 이 시험법을 활용한 많은 연구가 수행되었지만, 다층 용접부 횡균열을 평가하기에는 적합하지 않다는 보고들이 다수 존재하며, 저입열 조건에서 균열 민감도가 더 높은 일반적인 y-groove test의 평가 경향과는 달리 다층 용접부 횡균열은 고입열 조건에서 더 민감도가 높다는 보고도 있다. 이에 본 연구에서는 다층 FCA 용접금속의 강도 및 입열량별 저온균열 민감성을 평가하였다. 적용 가능한 가장 낮은 입열량과 높은 입열량으로 용접금속을 제작 해 시편에 수소가 포화될 수 있도록 전기화학적으로 수소를 주입 후 in-situ SSRT(Slow Strain Rate Test)를 수행하여 수소취성 저항성을 평가하고, 그 평가 결과가 실 용접부의 저온균열 발생 경향과 일치하는지 확인하기 위해 window type restrained weld cracking test을 진행하여 그 결과를 비교 하였다. 또한 permeation test를 수행하여 수소 트랩 특성을 확인하였다. 평가 결과 용접금속을 형성하는 미세조직에 따라 횡균열 민감도가 상이하였는데, in-situ SSRT와 window type restrained weld cracking test 모두 AWS spec E71T-1C FCW를 적용한 용접금속은 고입열 조건에서 균열 민감도가 높았고, E91T1-Ni2C FCW를 적용한 용접금속은 저입열 조건에서 균열 민감도가 높았다. E81T1-K2C FCW를 적용한 용접금속은 저입열, 고입열 조건에서 모두 횡균열 민감도가 낮았다. 평가 결과와 AWS D1.1 및 EN1011-2의 추천 예열온도를 비교하여 고찰하였다.

전기화학적 및 고압 수소 분위기하 템퍼드 마르텐사이트강의 수소취화 특성 비교

Sang-Gyu Kim,Jae-Yun Kim,Hyun-Joo Seo,Hwan-Gyo Jung,Jaeyoung Park,Un-Bong Baek,황병철 대한금속·재료학회 2023 대한금속·재료학회지 Vol.61 No.11

The effect of hydrogen charging methods on the hydrogen embrittlement characteristics of tempered martensitic steels were discussed in terms of hydrogen diffusion behavior. Two tempered martensitic steels with different Si content were fabricated by quenching and tempering. The steel with high Si content had a lower cementite fraction because the addition of Si changed the morphology of cementite from a long film-like shape to a short-rod shape by suppressing the precipitation and growth of the cementite. To evaluate the hydrogen embrittlement resistance of the two tempered martensitic steels with different Si content, slow strain-rate tensile testing was employed after introducing hydrogen using three types of hydrogen charging methods (ex-situ electrochemical hydrogen charging, in-situ electrochemical hydrogen charging, and in-situ high-pressure gaseous hydrogen environment). For the hydrogen pre-charged tensile specimens using the ex-situ electrochemical charging method, the steel with high Si content had a better hydrogen embrittlement resistance, with a higher relative reduction in area. On the other hand, there was no significant difference in the relative notch tensile strength of the two tempered martensitic steels with different Si content, regardless of the hydrogen charging methods. In addition, the ex-situ hydrogen charging method exhibited higher relative notch tensile strength compared to the in-situ hydrogen charging method due to the release of hydrogen during the tensile test, after exsitu hydrogen charging. This implies that hydrogen embrittlement resistance can be differently estimated depending on the kind of hydrogen charging methods.

템퍼드 마르텐사이트강의 수소취성에 미치는 Cr 및 Mo 함량의 영향

김상규,김재윤,신희창,황병철 한국재료학회 2022 한국재료학회지 Vol.32 No.11

The effect of Cr and Mo contents on the hydrogen embrittlement of tempered martensitic steels was investigated in this study. After the steels with different Cr and Mo contents were austenitized at 820 °C for 90 min, they were tempered at 630 °C for 120 min. The steels were composed of fully tempered martensite with a lath-type microstructure, but the characteristics of the carbides were dependent on the Cr and Mo contents. As the Cr and Mo contents increased, the volume fraction of film-like cementite and prior austenite grain size decreased. After hydrogen was introduced into tensile specimens by electrochemical charging, a slow strain-rate test (SSRT) was conducted to investigate hydrogen embrittlement behavior. The SSRT results revealed that the steel with lower Cr or lower Mo content showed relatively poor hydrogen embrittlement resistance. The hydrogen embrittlement resistance of the tempered martensitic steels increased with increasing Mo content, because the reduction in the film-like cementite and prior austenite grain size plays an important role in improving hydrogen embrittlement resistance. The results indicate that controlling the Cr and Mo contents is essential to achieving a tempered martensitic steel with a combination of high strength and excellent hydrogen embrittlement resistance.

Microstructural evolution and stress-corrosion-cracking behavior of thermally aged Ni-Cr-Fe alloy

Yoo, S.C.,Choi, K.J.,Kim, T.,Kim, S.H.,Kim, J.Y.,Kim, J.H. Pergamon Press 2016 Corrosion science Vol.111 No.-

To understand the effect of long-term thermal aging in power plant systems, representative thick-walled Alloy 600 was prepared and thermally aged at 400<SUP>o</SUP>C to fabricate samples with thermal aging effects similar to service operating conditions. Changes of microstructures, mechanical properties, and stress corrosion cracking susceptibility were investigated mainly through electron backscatter diffraction, nanoindentation, and high-temperature slow strain rate test. The formation of abundant semi-continuous precipitates with chromium depletion at grain boundaries was observed after thermally aged for 10 equivalent years. Also, alloys thermally aged for 10 equivalent years of thermal aging exhibited the highest susceptibility to stress corrosion cracking.

고강도 7xxx 알루미늄 합금의 응력부식균열에 미치는 부식환경과 응력속도의 영향

윤여완(Yeo-Wan Yun),김상호(Sang-Ho Kim) 한국표면공학회 2008 한국표면공학회지 Vol.41 No.3

High strength 7xxx aluminum alloys have been applied to automotive bump back beam of the some limited model for light weight vehicle. The aluminum bump back beam is manufactured through extrusion, bending and welding. The residual stress given on these processes combines with the corrosive atmosphere on the road spreaded with corrosive chemicals to melt snow to occur the stress corrosion cracking. The composition of commercial 7xxx aluminum has Zn/Mg ratio about 3 and Cu over 2 wt% for better strength and stress corrosion cracking resistivity. But this composition isn't adequate for appling to the automotive bump back beam with high resistance to extrusion and bad weldability. In this study the composition of 7xxx aluminum alloy was modified to high Zn/Mg ratio and low Cu content for better extrusion and weldability. To estimate the resistivity against stress corrosion cracking of this aluminum alloy by slow strain rate test, the corrosion atmosphere and strain rate separate the stress corrosion cracking from conventional corrosion must be investigated. Using 0.6 Mol NaCl solution on slow strain rate test the stress corrosion cracking induced fracture was not observed. By adding 0.3% H₂O₂ and 0.6M Na₂SO₄ to 1M NaCl solution, the corrosion potential and current density of polarization curve moved to active potential and larger current density, and on the slow strain rate test the fracture energy in solution was lower than that in pre-exposure. These mean the stress corrosion cracking induced fracture can be estimated in this 1M NaCl + 0.3% H₂O₂ + 0 .6M Na₂SO₄ solution. When the strain rate was below 2×10??, the stress corrosion cracking induced fracture start to be observed.

질소첨가에 따른 주조용 CD4MCU 이상 스테인레스강의 분위기에서의 저속인장 거동

孫晋日,金祥植,李在鉉,崔秉鶴 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.7

The effect of nitrogen contents on the microstructure, tensile and corrosion behaviors of CD4MCU (Fe-25Cr-5Ni-2.8Cu-2Mo) cast duplex stainless steel was examined in the present study. The slow strain rate test was conducted at a nominal strain rate of 1×10^-6/sec in air and 3.5%NaCl+5% H_2SO_4 solution for studying the stress corrosion cracking behavior of the present alloy. It was observed that the volume fraction of austenitic phase in CD4MCU alloy increased from 49% to 65% with increasing nitrogen content from 0.13 to 0.27 wt.%. The yield strength decreased, while the ultimate tensile strength and the tensile elongation increased, with increasing nitrogen contents. The variation of tensile behavior appeared to be strongly related to the volume changes in ferritic and austenitic phases associated with different nitrogen contents. The increase in the volume fraction of austenitic phases was beneficial for both general corrosion and stress corrosion cracking in 3.5% NaCl+5% H_2SO_4 solution. It was believed that the selected corrosion of ferritic phases in high austenitic duplex stainless steel smoothened the initial stress corrosion cracks and, consequently, increased the resistance to stress corrosion cracking.