Specimens of AISI 321 stainless steel (0Cr18Ni9Ti) of various martensile contents were prepared by the low temperature(-70℃) elongation method- X-ray diffraction (XRD) and transmission electron micrograph (TEM) techn...Specimens of AISI 321 stainless steel (0Cr18Ni9Ti) of various martensile contents were prepared by the low temperature(-70℃) elongation method- X-ray diffraction (XRD) and transmission electron micrograph (TEM) techniques were used to study the phase transition process and its structure. The relationship between deformation-induced martensite and stress corrosion cracking (SCC) susceptibility of the steel in 42% (boiling) MgCl2 solution was investigated using the constant load SCC test with the normalized threshold values. The results reveal that when the α'-martensite content is less than 5% and also in the range of 15%-24 % , the SCC susceptibility of this material decreases with the increase of α'-martensite content.However. whenthe α' martensite content is in the rang of 5% -15% and more than 24%, the SCC susceptibility of this material increases with the increase of the α'-martensite content. The SCC fracture surface of the specimens exhibits a stepped fracture surface and transgranular stress corrosion fracture surface morphology.展开更多
This was a feasibility study for a modified 304 steel resistant to stress corrosion cracking (SCC) in aqueous environment containing chloride. SCC tests were conducted potentiostaticaly with spot welded specimens, wh...This was a feasibility study for a modified 304 steel resistant to stress corrosion cracking (SCC) in aqueous environment containing chloride. SCC tests were conducted potentiostaticaly with spot welded specimens, which had both crevice and residual stress, mainly in 3 % NaCl solution at various temperatures to determine the critical temperature for SCC at and below which the steel would not suffer from SCC. The effects of individual alloying element of silicon, manganese and copper on SCC of 18Cr 14Ni steels which phosphor content is 0.002 % and molybdenum content is 0.01 % were examined. Addition of 1 or 2 % of copper has beneficial effect on resistance to SCC, while increasing silicon or manganese content has no significant effect. Critical temperature of the steel with 0.002 % of phosphor and 2 % of copper is 150 ℃, which is markedly higher than 50 ℃ of 304L steel. However, the beneficial effect of copper is reduced with increasing phosphor content. From practical viewpoint, the modified steel with good SCC resistance should have 0.01 %-0.015 % of phosphor and 0.3 % or more of molybdenum, because it is very difficult to reduce phosphor content below 0 008 % industrially and such molybdenum content is inevitably introduced through cost saving melting process using return steel. Aluminium is to be added as another alloying element and 3 % of aluminium combined with 2 % of copper has been found to negate the deleterious effects of increased phosphor and molybdenum content. As a candidate steel at this stage, 14Cr 16Ni 0.013P 2Cu 1Al (0.3 1)Mo steel has critical temperature of 110 ℃.展开更多
Constant load tests in NS4 solution purged with N2-5%CO2 gas mixture were conducted on American Petroleum Institute （API） X80 pipeline steel applied in the 2nd West-East （;as Pipeline project with and without prelo...Constant load tests in NS4 solution purged with N2-5%CO2 gas mixture were conducted on American Petroleum Institute （API） X80 pipeline steel applied in the 2nd West-East （;as Pipeline project with and without preload. The results show that cracks could initiate and propagate in X80 pipeline steel in near-neutral pH environment under a constant load condition. The life of crack initiation and propagation increased with decreasing applied stress. Preload did not change its corrosion behavior obviously. However, preload reduced the time for crack initiation.展开更多
基金Supported by the National Natural Science Foundation of China and State Key Laboratory for Corrosion and Protection and Study Foundation of The Hong Kong Polytechnic University.
文摘Specimens of AISI 321 stainless steel (0Cr18Ni9Ti) of various martensile contents were prepared by the low temperature(-70℃) elongation method- X-ray diffraction (XRD) and transmission electron micrograph (TEM) techniques were used to study the phase transition process and its structure. The relationship between deformation-induced martensite and stress corrosion cracking (SCC) susceptibility of the steel in 42% (boiling) MgCl2 solution was investigated using the constant load SCC test with the normalized threshold values. The results reveal that when the α'-martensite content is less than 5% and also in the range of 15%-24 % , the SCC susceptibility of this material decreases with the increase of α'-martensite content.However. whenthe α' martensite content is in the rang of 5% -15% and more than 24%, the SCC susceptibility of this material increases with the increase of the α'-martensite content. The SCC fracture surface of the specimens exhibits a stepped fracture surface and transgranular stress corrosion fracture surface morphology.
文摘This was a feasibility study for a modified 304 steel resistant to stress corrosion cracking (SCC) in aqueous environment containing chloride. SCC tests were conducted potentiostaticaly with spot welded specimens, which had both crevice and residual stress, mainly in 3 % NaCl solution at various temperatures to determine the critical temperature for SCC at and below which the steel would not suffer from SCC. The effects of individual alloying element of silicon, manganese and copper on SCC of 18Cr 14Ni steels which phosphor content is 0.002 % and molybdenum content is 0.01 % were examined. Addition of 1 or 2 % of copper has beneficial effect on resistance to SCC, while increasing silicon or manganese content has no significant effect. Critical temperature of the steel with 0.002 % of phosphor and 2 % of copper is 150 ℃, which is markedly higher than 50 ℃ of 304L steel. However, the beneficial effect of copper is reduced with increasing phosphor content. From practical viewpoint, the modified steel with good SCC resistance should have 0.01 %-0.015 % of phosphor and 0.3 % or more of molybdenum, because it is very difficult to reduce phosphor content below 0 008 % industrially and such molybdenum content is inevitably introduced through cost saving melting process using return steel. Aluminium is to be added as another alloying element and 3 % of aluminium combined with 2 % of copper has been found to negate the deleterious effects of increased phosphor and molybdenum content. As a candidate steel at this stage, 14Cr 16Ni 0.013P 2Cu 1Al (0.3 1)Mo steel has critical temperature of 110 ℃.
基金supported by the National Natural Science Foundation of China (Grant No. 51025104)
文摘Constant load tests in NS4 solution purged with N2-5%CO2 gas mixture were conducted on American Petroleum Institute （API） X80 pipeline steel applied in the 2nd West-East （;as Pipeline project with and without preload. The results show that cracks could initiate and propagate in X80 pipeline steel in near-neutral pH environment under a constant load condition. The life of crack initiation and propagation increased with decreasing applied stress. Preload did not change its corrosion behavior obviously. However, preload reduced the time for crack initiation.
