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1.
The corrosion behaviour of 304LN stainless steels containing three different nitrogen content (0.132, 0.193, 0.406 wt% N) was investigated by potentiodynamic anodic polarization technique, in 1, 4, 6 M nitric acid and simulated high level waste (HLW) medium. The results showed that all three alloys exhibited good corrosion resistance in nitric acid and simulated HLW and the corrosion properties were found to be similar. Owing to the spontaneous formation of the protective chromium oxide passive film in nitric acid and simulated HLW, increasing the nitrogen content of the alloy did not indicate any discernable effect on the corrosion resistance in both media. It was also found that the oxidizing ions present in simulated HLW did not deteriorate the passive film stability of the nitrogen containing alloys. In chloride medium, the highest nitrogen content 304LN stainless steel showed a profound increase in pitting corrosion resistance when compared to the lower nitrogen content alloy. Optical and scanning electron microscopy was carried out to obtain information about the microstructure. The results of the investigation are discussed in the paper. 相似文献
2.
Intergranular corrosion (IGC) resistance of types 304LN and 316LN stainless steels (SS) thermally aged at 823, 873, and 923
K for various durations was assessed by ASTM A262 practice A test (electrolytic etch test) and electrochemical potentiodynamic
reactivation (EPR) test. The results indicated that the type 316LN SS has significantly improved IGC resistance compared to
304LN SS. Based on the results of these tests, time-temperature-sensitization (TTS) diagrams were developed for both alloys.
The secondary precipitates formed during thermal aging treatments were electrochemically extracted and analyzed by X-ray diffraction
(XRD) to determine the types of precipitates formed during the aging treatments. The results indicated that the precipitates
were mostly of M 23C 6 carbides. 相似文献
3.
This study investigates the sensitization behavior of AISI 304LN deformed previously by cold rolling (CR) to 5 pct to 25 pct
reduction in thickness and aged at 673 K to 873 K (400 °C to 600 °C). The emphasis was on revealing the degree of sensitization
(DOS) resulting from low-temperature sensitization (LTS) on the orthogonal surfaces and correlation thereof with the changes
in various metallurgical properties caused by cold rolling. It was found that the DOS differs among the orthogonal surfaces
such as the rolling surface (RS), transverse surface (TS), and cross transverse surface (CTS). RS showed lower DOS compared
with CTS and TS. The differences in the DOS were attributed to the combined effect of deformation-induced martensite (DIM),
grain size, and slip band formation. A deformation of 5 pct was critical to the susceptibility of AISI 304LN to intergranular
(IGC) and transgranular corrosion (TGC). The sensitization kinetics was slow or saturated leading to desensitization beyond
5pct deformations at 773 K (500 °C) and 873 K (600 °C). It was, however, uniformly accelerated over 5 to 25 pct deformation
when aged at 673 K (400 °C). 相似文献
5.
Mechanical properties of stainless steels increase with increasing nitrogen concentration. Currently, the maximum nitrogen
concentration in commercial stainless steels is 0.8 wt pct. In this study, type 304 and 316 stainless steels were melted and
cooled in a hot-isostatic-pressur(HIP) furnace using nitrogen as the pressurizing gas, producing alloys with nitrogen concentrations
between 1 and 4 wt pct. These nitrogen levels exceeded the alloys’ solubility limits, resulting in the formation of nitride
precipitates with several different microstructures. A new phase diagram for high nitrogen stainless steel alloys is proposed.
Several properties of these nitrogen stainless steel alloys with chromium nitrides present were studied: tensile strength
was proportional to the interstitial nitrogen concentration; hardness, wear, and elastic modules were proportional to the
total nitrogen concentration.
Formerly Research Scientist, National Institute of Science and Technology, Boulder, CO, is retired. 相似文献
7.
An experimental design method was used to determine the effect of factors that significantly affect the response of the double
loop–electrochemical potentiokinetic reactivation (DL-EPR) test in controlling the susceptibility to intergranular corrosion
(IGC) of UNS S43000 (AISI 430) ferritic stainless steel. The test response is expressed in terms of the reactivation/activation
current ratio ( I
r
/ I
a
pct). Test results analysed by the analysis of variance (ANOVA) method show that the molarity of the H 2SO 4 electrolyte and the potential scanning rate have a more significant effect on the DL-EPR test response than the temperature
and the depassivator agent concentration. On the basis of these results, a study was conducted in order to determine the optimal
operating conditions of the test as a nondestructive technique for evaluating IGC resistance of ferritic stainless steel components.
Three different heat treatments are considered in this study: solution annealing (nonsensitized), aging during 3 hours at
773 K (500 °C) (slightly sensitized), and aging during 2 hours at 873 K (600 °C) (highly sensitized). The aim is to find the
operating conditions that simultaneously ensure the selectivity of the attack (intergranular and chromium depleted zone) and
are able to detect the effect of low dechromization. It is found that a potential scanning rate of 2.5 mV/s in an electrolyte
composed of H 2SO 4 3 M solution without depassivator, at a temperature around 293 K (20 °C), is the optimal operating condition for the DL-EPR
test. Using this condition, it is possible to assess the degree of sensitization (DOS) to the IGC of products manufactured
in ferritic stainless steels rapidly, reliably, and quantitatively. A time–temperature–start of sensitization (TTS) diagram
for the UNS S43000 (France Inox, Villepinte, France) stainless steel was obtained with acceptable accuracy by this method
when the IGC sensitization criterion was set to I
r
/ I
a
> 1 pct. This diagram is in good agreement with the time–temperature–start of precipitation (TTP) diagram that delineates
the domain of low dechromization consecutive to chromium carbide precipitation. 相似文献
8.
In recent years,nitrogen-alloyed stainless steels have been a research hotspot in the field of stainless steel product and technology. Nitrogen-alloyed austenitic stainless steels developed by Baosteel and their applications are introduced. These steels are nitrogen-controlled products 304 N and 316 LN,nitrogen containing economical products BN series and high-nitrogen stainless steel( HNS) series. The results show that the presence of nitrogen can significantly improve the strength and corrosion resistance of steel produced. By nitrogen alloying,economical austenitic stainless steels w ith considerably less nickel than 304 can be obtained; the corrosion resistances of these steels are almost the same as 304. Furthermore,by a scientific approach of nitrogen alloying,high-nitrogen steel of0. 8% nitrogen content is fabricated under the non-pressurized conditions,and the pitting potential of this steel is 1. 0 V. At present,nitrogen-alloyed steels developed by Baosteel are w idely utilized in the manufacture of cryogenic storage containers,transportation containers,and many household w ares. 相似文献
9.
The metallurgical influences on the stress corrosion resistance of many commercial stainless steels have been studied using
the fracture mechanics approach. The straight-chromium ferritic stainless steels, two-phase ferritic-austenitic stainless
steels and high-nickel solid solutions (like alloys 800 and 600) investigated are all fully resistant to stress corrosion
cracking at stress intensity (K 1) levels ≤ MN • m- 3/2 in 22 pct NaCl solutions at 105 °C. Martensitic stainless steels, austenitic stainless steels and precipitation hardened
superalloys, all with about 18 pct chromium, may be highly susceptible to stress corrosion cracking, depending on heat treatment
and other alloying elements. Molybdenum additions improve the stress corrosion cracking resistance of austenitic stainless
steels significantly. The fracture mechanics approach to stress corrosion testing of stainless steels yields results which
are consistent with both the service experience and the results from testing with smooth specimens. In particular, the well
known “Copson curve” is reproduced by plotting the stress corrosion threshold stress intensity (AT ISCC) vs the nickel content of stainless steels with about 18 pct chromium.
Formerly with the BBC Brown Boveri Company, Baden, Switzerland 相似文献
10.
The mechanical and fracture properties of austenitic stainless steels (SSs) alloyed with gallium require assessment in order
to determine the likelihood of premature storage-container failure following Ga uptake. AISI 304 L SS was cast with 1, 3,
6, 9, and 12 wt pct Ga. Increased Ga concentration promoted duplex microstructure formation with the ferritic phase having
a nearly identical composition to the austenitic phase. Room-temperature tests indicated that small additions of Ga (less
than 3 wt pct) were beneficial to the mechanical behavior of 304 L SS but that 12 wt pct Ga resulted in a 95 pct loss in ductility.
Small additions of Ga are beneficial to the cracking resistance of stainless steel. Elastic-plastic fracture mechanics analysis
indicated that 3 wt pct Ga alloys showed the greatest resistance to crack initiation and propagation as measured by fatigue
crack growth rate, fracture toughness, and tearing modulus. The 12 wt pct Ga alloys were least resistant to crack initiation
and propagation and these alloys primarily failed by transgranular cleavage. It is hypothesized that Ga metal embrittlement
is partially responsible for increased embrittlement. 相似文献
12.
Steels containing about 12 pct Cr, 10 pct Mn, and 0.2 pct N have been shown to have an unstable austenitic microstructure
and have good ductility, extreme work hardening, high fracture strength, excellent toughness, good wear resistance, and moderate
corrosion resistance. A series of alloys containing 9.5 to 12.8 pct Cr, 5.0 to 10.4 pct Mn, 0.16 to 0.32 pct N, 0.05 pct C,
and residual elements typical of stainless steels was investigated by microstructural examination and mechanical, abrasion,
and corrosion testing. Microstructures ranged from martensite to unstable austenite. The unstable austenitic steels transformed
to α martensite on deformation and displayed very high work hardening, exceeding that of Hadfield’s manganese steels. Fracture
strengths similar to high carbon martensitic stainless steels were obtained while ductility and toughness values were high,
similar to austenitic stainless steels. Resistance to abrasive wear exceeded that of commercial abrasion resistant steels
and other stainless steels. Corrosion resistance was similar to that of other 12 pct Cr steels. Properties were not much affected
by minor compositional variations or rolled-in nitrogen porosity. In 12 pct Cr-10 pct Mn alloys, ingot porosity was avoided
when nitrogen levels were below 0.19 pet, and austenitic microstructures were obtained when nitrogen levels exceeded 0.14
pct. 相似文献
13.
In order to improve the low ductility of nanostructured materials,a layered and nanostructured (LN) 304 SS (stainless steel)is prepared from warm co-rolled 304 SS pre-treated by surface mechanical attrition treatment.The microstructure and mechanical properties,as well as strain hardening,are analyzed in details.The LN steels exhibit both high strength and large ductility resulting from good strain hardening behaviors.The strain hardening can be subdivided into two stages,which involves a multiple cracking along interlaminar at the first stage and a strain-induced martensite(SIM)transformation at the second stage.The SIM transformation of nanocrystallines and ultrafine grains induces a larger work hardening exponent by the formation of nanoscaled martensite phase.The effect of grain size on the transformation dynamics is discussed. 相似文献
14.
The aim of this report is to examine the influence of sensitization on the mechanical properties of AISI grade 304LN stainless
steel with special emphasis on its fracture toughness. A series of stainless steel samples has been sensitized by holding
at 1023 K for different time periods ranging from 1 to 100 hours followed by water quenching. The degree of sensitization
(DOS) for each type of the varyingly heat-treated samples has been measured by an electrochemical potentiodynamic reactivation
(EPR) test. The microstructures of these samples have been characterized by optical metallography, scanning electron microscopy,
transmission electron microscopy (TEM), and X-ray diffraction (XRD) analyses, together with measurements of their hardness
and tensile properties. The fracture toughness of the samples has been measured by the ball indentation (BI) technique and
the results are validated by conducting conventional J-integral tests. It is revealed for the first time that the fracture toughness and ductility of AISI 304LN stainless steel
deteriorate significantly with increased DOS, while the tensile strength (TS) values remain almost unaltered. The results
have been critically discussed in terms of the depletion of solid solution strengtheners, the nature of the grain boundary
precipitations, and the strain-induced martensite formation with the increasing DOS of the 304LN stainless steel. 相似文献
15.
Low-temperature nitridation is a widely used surface heat treatment. Low-temperature liquid nitridation was applied to 316 austenitic stainless steel and an S-phase (expanded austenite) layer was achieved on the alloy surface. The effect of the S-phase layer on corrosion resistance and stress corrosion cracking was investigated in a sour environment. When a bending stress of 164 MPa (80 pct yield stress, YS) was applied, no macroscopic corrosion cracking and pits were observed on the nitrided samples and the S-phase layer stayed intact. Although no macroscopic corrosion cracking was observed on the non-nitrided samples under 205 MPa (100 pct YS), some pits were formed on the alloy surface. This could be attributed to the high stresses and hardness, and the excellent corrosion resistance of the S-phase layer introduced by low-temperature nitridation. Supersaturated nitrogen atoms in the S-phase layer can effectively prevent the decrease in pH of the corrosive medium and accelerate the alloy repassivation kinetics. However, when the bending stress was increased to 205 and 246 MPa (100 pct YS, 120 pct YS), macroscopic cracks were observed in the presence of both tensile stress and a corrosive medium. 相似文献
16.
Sodium cooled fast reactors (SFRs) are designed to operate at high temperatures with an initial design life of about 40 years. Austenitic stainless steel (SS) types 304 and 316 and their variants have been generally used for out-of-core structural components of the reactor assembly system. The choice of these two grades of stainless steels is decided by several important factors such as high temperature mechanical properties like creep, low cycle fatigue and creep-fatigue interaction, compatibility with liquid sodium coolant, weldability, fabricability and cost. The components which operate in the creep temperature range are made of 316 SS. This material has been used extensively in the early SFRs. Studies on long term creep properties of 316 SS have clearly established the good creep resistance of this material and the microstructural stability at temperatures below 873 K. In view of the susceptibility of welded components to stress corrosion cracking, low carbon grades of 304 and 316 SS with alloying addition of nitrogen (designated as 304L(N) SS and 316L(N) SS) are used for structural components of later generation of SFRs. Nitrogen addition in the range of 0.06–0.08 wt% produces significant improvement in the creep properties of this material through solid solution strengthening and lowering of stacking fault energy. In view of the recent trends to increase the design life of SFRs to 60 years and more, it is necessary that non-replaceable structural components of reactor assembly have sufficient high temperature mechanical properties over such very long periods of operation. Increasing the nitrogen content from 0.06–0.08 wt % to levels of 0.12–0.14 wt% has been found to increase creep rupture life of 316LN SS by an order of magnitude. The beneficial effects of nitrogen are also extended to type 316 SS weld metal. This paper discusses the progressive improvements in the creep properties of 316 SS grade by varying the amounts of interstitial elements carbon and nitrogen. 相似文献
17.
The influence of cold work (prestraining) in the range 2.3 to 56 pct on stress corrosion cracking (SCC) properties of types
304 and 316 stainless steels in boiling MgCl2 solution at 154 °C was investigated using a constant load method. In both materials,
SCC initiation was in transgranular mode. Transition in stress corrosion cracking mode from transgranular to intergranular,
as the crack proceeds, was observed at all cold work levels in 316 stainless steel and at cold work levels of 26 pct and 56
pct in 304 stainless steel. Both prestraining and increase in the initial applied stress facilitated the transition in crack
morphology to intergranular mode. Increased tendency to intergranular SCC at high applied stresses and in cold worked specimens
appears to be mechanistically analogous. 相似文献
19.
To assist in the understanding of micromechanisms for corrosion fatigue crack growth in metastable austenitic steels, the
relationships between the crack paths and the underlying microstructure were investigated for annealed and cold-rolled (CR)
304 stainless steels that had been tested in a deaerated 3.5 pct NaCl solution, air, and vacuum. Corrosion fatigue in the
deleterious environments (3.5 pct NaCl and air) was brittle and occurred primarily by {001} γ and other unidentified, quasi-cleavage (QC), accompanied by preferential cracking along {111} γ twin and grain boundaries. In contrast, fatigue cracking in vacuum was ductile, fully transgranular, and noncrystallographic.
Transformation to alpha prime (α′-) martensite by fatigue was found to be essentially complete in the CR steel, which contained
ε-martensite, and in the annealed steel tested in vacuum, but was substantially less in the annealed steel tested in air and
3.5 pct NaCl solution. These results, taken in conjunction with the crack growth and electrochemical reaction data, support
hydrogen embrittlement (HE) as the mechanism for corrosion fatigue crack growth in 304 stainless steels in 3.5 pct NaCl solution.
Martensitic transformation appears not to be the only responsible factor for embrittlement. Other microstructural components,
such as twin and grain boundaries, slip bands, and cold work-induced lattice defects, may play more important roles in enhancing
crack growth rates. 相似文献
20.
The effect of N addition 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 tests were also conducted at a nominal strain rate
of 1 × 10 −6/s in air and 3.5 pct NaCl+5 pct H 2SO 4 solution for studying the stress corrosion cracking (SCC) behavior. It was observed that the volume fraction of austenitic
phase in CD4MCU alloy varied from 38 to 59 pct with increasing nitrogen content from 0 to 0.27 wt. pct. The tensile behavior
of CD4MCU cast duplex stainless steels, which tended to vary significantly with different N contents, appeared to be strongly
related to the volume changes in ferritic and austenitic phases, rather than the intrinsic N effect. The improvement in the
resistance to general corrosion in 3.5 pct NaCl+5 pct H 2SO 4 aqueous solution was notable with 0.13 pct N addition. The further improvement was not significant with further N addition.
The resistance to SCC of CD4MCU cast duplex stainless steels in 3.5 pct NaCl+5 pct H 2SO 4 aqueous solution, however, increased continuously with increasing N content. The enhancement in the SCC resistance was believed
to be related to the volume fraction of globular austenitic colonies, which tended to act as barriers for the development
of initial pitting cracks in the ferritic phase into the sharp ones. 相似文献
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