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1.
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
2.
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
3.
The tensile and corrosion behaviors of 0.13 pct N-containing CD4MCU cast duplex stainless steels with different Cr contents
ranging from 23 to 28 pct were examined in the present study. The polarization tests were conducted in 3.5 pct NaCl + 5 pct
H 2SO 4 aqueous solution for general corrosion resistance, and the in-situ slow strain rate (SSR) tests were also conducted in air and 3.5 pct NaCl + 5 pct H 2SO 4 aqueous solution to quantify the resistance to stress corrosion cracking (SCC) of the three materials. A substantial microstructural
change in 0.13 pct N-containing CD4MCU cast duplex stainless steel was observed with different Cr contents, which in turn
affected the tensile and corrosion behaviors significantly. Tensile behavior of 0.13 pct N-containing CD4MCU cast duplex stainless
steel, for example, varied in a nonlinear manner with different Cr contents due to the volume change of hard ferritic phase
and the presence of the second precipitates of soft austenitic phase in the ferrite matrix. The beneficial effect of Cr for
improving the general corrosion and the SCC resistances was largely overshadowed by this variation in microstructural characteristics.
The relationship between the microstructural evolution and the tensile and corrosion behavior of 0.13 pct N-containing CD4MCU
cast duplex stainless steels with different Cr contents was discussed based on the optical microscopy and scanning electron
microscopy (SEM) micrographic and fractographic observations. 相似文献
4.
A fracture mechanics study of stress corrosion cracking (scc) of cold worked AISI 310 austenitic steel, and an experimental
metastable austenite, was conducted in hot aqueous solutions of 44.7 wt pct MgCl 2 and the results compared with previous studies on AISI 316 steel. Attention was directed towards Region II behavior where
crack propagation rate (v) was independent of stress intensity (K I). The apparent activation energy of Region II was found to be in the range ~65 to 75 kJ/mol, independent of the relative
proportions of intergranular and transgranular cracking. Also, electron diffraction studies of fracture surfaces showed that
α′-martensite formation was not a pre-requisite for scc, although it may influence crack propagation rates. Cracking was discussed
in terms of a hydrogen embrittlement model under hydrogen transport control in the austenite lattice. However, adsorption
(chemisorption) effects on repassivation and dissolution behavior could not be eliminated from consideration.
Alan J. Russell, Formerly Research Student, University of British Columbia. 相似文献
5.
The similarities and differences in the stress corrosion cracking response of ferritic and austenitic stainless steels in
chloride solutions will be examined. Both classes of materials exhibit a cracking potential: similar transient response (to
loading) of the potential in open circuit tests or the current in potentiostatic tests and similar enrichment of chromium
and depletion of iron in the film associated with localized corrosion processes. The ferritic steels are more resistant to
localized corrosion than are the austenitic steels, which is responsible for the difference in the influence of prior thermal
and mechanical history on cracking susceptibility of the two types of steel. Similarities in the fractography of stress corrosion
cracks and those produced by brittle delayed failure during cathodic charging of the ferritic steels indicate that hydrogen
embrittlement is involved in the failure process. 相似文献
6.
Austenitic stainless steels are known to be sensitive to stress corrosion cracking (SCC) in hot chloride solutions. The aim
of the present study is to find improvements in the SCC behavior of 316L-type austenitic stainless steels in 117°C MgCl 2 solutions. Previously, the authors have proposed the “corrosion-enhanced plasticity model” (CEPM) to describe the discontinuous
cracking process which occurs in SCC. This model is based on localized corrosion (anodic dissolution, and hydrogen absorption)-deformation
(dislocations) interactions (CDI). From the framework of this model, it is proposed that a prestraining in fatigue at saturation
decreases the SCC sensitivity. This idea is experimentally confirmed for both crack initiation and crack propagation, through
the analysis of the SCC behavior by slow-strain-rate tests of single and polycrystals after different prestraining conditions. 相似文献
7.
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
8.
The tensile and corrosion behaviors of CD4MCU cast duplex stainless steels with different Mo contents of 0, 2, and 4 pct,
respectively, were examined in the present study. The polarization and the in-situ slow-strain-rate (SSR) tests were conducted in a 3.5 pct NaCl+5 pct H 2SO 4 aqueous solution to quantify the resistances to pitting corrosion and stress corrosion cracking (SCC) with different Mo contents.
The addition of Mo, which is a strong ferrite stabilizer, affected the microstructure of the present alloy and, eventually,
the tensile and corrosion behaviors in a complex manner. The tensile properties of CD4MCU cast duplex stainless steel, for
example, were found to be determined by the volume fraction of hard ferritic phase, the presence of the second precipitates
of soft austenitic phase in the ferrite matrix, and the shape of the austenitic phase. The addition of 2 pct Mo was detrimental
to the corrosion properties of CD4MCU cast duplex stainless steel due to the significant increase in the volume fraction of
ferritic phase. With the addition of 4 pct Mo, however, the resistances to pitting corrosion and SCC recovered to those of
the specimen without Mo. The relationship between the microstructural evolution and the tensile and corrosion behavior of
CD4MCU cast duplex stainless steels with different Mo contents was discussed based on the micrographic and fractographic observations. 相似文献
9.
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
10.
This article describes the corrosion behavior of special austenitic alloys for waste management applications. The special
stainless steels have controlled levels of alloying and impurity elements and inclusion levels. It is shown that “active”
inclusions and segregation of chromium along flow lines accelerated IGC of nonsensitized stainless steels. Concentration of
Cr +6 ions in the grooves of dissolved inclusions increased the potential to the transpassive region of the material, leading to
accelerated attack. It is shown that a combination of cold working and controlled solution annealing resulted in a microstructure
that resisted corrosion even after a sensitization heat treatment. This imparted extra resistance to corrosion by increasing
the fraction of “random” grain boundaries above a threshold value. Randomization of grain boundaries made the stainless steels
resistant to sensitization, IGC, and intergranular stress corrosion cracking (IGSCC) in even hot chloride environments. The
increased corrosion resistance has been attributed to connectivity of random grain boundaries. The reaction mechanism between
the molten glass and the material for process pot, alloy 690, during the vitrification process has been shown to result in
depletion of chromium from the reacting surfaces. A comparison is drawn between the electrochemical behavior of alloys 33
and 22 in 1 M HCl at 65 °C. It is shown that a secondary phase formed during welding of alloy 33 impaired corrosion properties
in the HCl environment.
This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste
Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the TMS Corrosion
and Environmental Effects and Nuclear Materials Committees. 相似文献
11.
Austenitic stainless steels (SSs) core internal components in nuclear light water reactors (LWRs) are susceptible to irradiation-assisted
stress corrosion cracking (IASCC). One of the effects of irradiation is the hardening of the SS and a change in the dislocation
distribution in the alloy. Irradiation may also alter the local chemistry of the austenitic alloys; for example, silicon may
segregate and chromium may deplete at the grain boundaries. The segregation or depletion phenomena at near-grain boundaries
may enhance the susceptibility of these alloys to environmentally assisted cracking (EAC). The objective of the present work
was to perform laboratory tests in order to better understand the role of Si in the microstructure, properties, electrochemical
behavior, and susceptibility to EAC of austenitic SSs. Type 304 SS can dissolve up to 2 pct Si in the bulk while maintaining
a single austenite microstructure. Stainless steels containing 12 pct Cr can dissolve up to 5 pct bulk Si while maintaining
an austenite structure. The crack growth rate (CGR) results are not conclusive about the effect of the bulk concentration
of Si on the EAC behavior of SSs. 相似文献
12.
The effects of tempering temperature and carbon content on the stress corrosion cracking (SCC) behavior of high-strength CrMo
steels in 3.5 pct NaCl aqueous solution have been studied by means of Auger electron spectroscopy (AES) and scanning and transmission
electron micros- copy (SEM and TEM). Experimental results show that the specimens with higher carbon content and tempered
at lower temperatures have a higher tendency for intergranular fracture and lower threshold stress intensity K ISCC The SCC behavior is significantly affected by the distribution of carbide particles, especially carbide coverage on prior
austenitic grain boundaries, through a carbide-matrix interface mechanism as the interface is the preferential site for the
nucleation and propagation of microcracks because of its strong ability to trap hydrogen atoms. In low- temperature tempered
states, there is the serious segregation of carbon in the form of carbide particles at prior austenitic grain boundaries,
causing low-stress intergranular fracture. After tempering at high temperatures (≥400 °C), both the coalescence of the carbide
particles at the grain boundaries and the increase of carbide precipitation within grains cause the decrease of the tendency
for intergranular fracture and the rise of K ISCC. The higher the carbon content in steels, the more the carbide particles at the grain boundaries and, subsequently, the higher
the tendency for low-stress intergranular fracture. The carbide effect on K ISCC makes an important contribution to the phenomenon that K ISCC decreases with the rise of yield strength of the steels. 相似文献
13.
This article discusses the intricacies associated with the determination of threshold stress intensity for stress corrosion cracking ( K ISCC) of narrow regions such as the sensitized microstructure of austenitic stainless steel and presents a simple approach to the accurate determination of K ISCC of a sensitized stainless steel. K ISCC and crack growth rates of solution-annealed and sensitized AISI 304 stainless steel in the 42 wt pct MgCl 2 environment at 427 K (154 °C) were determined using the circumferential notch tensile (CNT) technique. The results presented here validate the ability of the CNT technique to overcome some of the fundamental difficulties in determination of the K ISCC of narrow regions, using the traditional techniques. This article also discusses the mechanistic aspects of the difference in fractographic features of the sensitized and solution-annealed stainless steels. 相似文献
14.
A new test specimen configuration, designated the T-notch double cantilever beam (TNDCB), was developed, calibrated and employed
for a fracture mechanics study of stress corrosion cracking (SCC) of cold worked Type-316 austenitic stainless steel exposed
to hot aqueous solutions of 44.7 wt pct MgCl 2. The effects of stress intensity ( K
I
), temperature ( T) and electrochemical potential ( E) upon the crack velocity ( v) and fractography were investigated. The stress intensity ( K
ISCC
) below which v became immeasurably small was ∼12 MN·m −3/2. Above this value, three regions of behavior were observed. Region I exhibited K
I
dependent cracking followed by Region II which exhibited K
I
independent cracking and an apparent activation energy of 63 to 67 kJ/mol, followed by Region III where cracking again became
dependent upon K
I
. The relative proportions of intergranular and transgranular crack paths were markedly dependent upon both K
I
and E, and less sensitive to T. Crack velocity was insensitive to small changes in E with respect to the free corrosion potentials ( E
corr), but could be terminated by an applied active potential of ∼−0.35 V SCE. The pH within the propagating crack was estimated to be <1.0 at E
corr, rising to ∼4.5 at −0.35 V SCE. The mechanism of SCC was discussed with respect to film rupture events caused by crack tip plastic deformation, adsorption
controlled processes on the metal surface, and hydrogen diffusion in the metal lattice.
Alan J. RUSSELL, formerly Research Student, University of British Columbia 相似文献
15.
The linearly increasing stress test (LIST) was used to study the stress corrosion cracking (SCC) behavior of a range of pipeline
steels in carbonate-bicarbonate solution under stress rate control at different applied potentials. Stress corrosion cracking,
at potentials below -800 mV(SCE), was attributed to hydrogen embrittlement. Stress corrosion cracking, in the potential range
from about-700 to -500 mV(SCE), was attributed to an anodic dissolution mechanism. In the anodic potential region, the SCC
initiation stress was larger than the yield stress and was associated with significant plastic deformation at the cracking
site. The relative SCC initiation resistance decreased with in-creasing yield strength. In the cathodic potential region,
the SCC initiation stress was smaller than the yield stress of steel; it was approximately equal to the stress at 0.1 pct
strain (@#@ Σ 0.1pct) for all the steels. The original surface was more susceptible to SCC initiation than the polished surface. 相似文献
16.
The behavior of hydrogen induced slow crack growth in type 310 and type 16-20-10 stable austenitic stainless steels along
with type 321 unstable austenitic stainless steel were investigated. It was found that slow crack growth could occur in all
three types of stainless steels, and the threshold values were K
H/K c = 0.55, 0.7, and 0.78 for type 321, 310, and 16-20-10 stainless steel respectively, when charged under load. Slow crack growth
could also occur if the precharged specimens were tested under constant load in air. No slow crack growth occurred in the
precharged and then out-gassed specimens. This indicates that delayed cracking in stable austenitic stainless steels is induced
by hydrogen. Since there is no hydrogen induced α’ martensite in type 310 and 16-20-10 stainless steel, the existence of a’
martensite is not necessary for the occurrence of slow crack growth in the austenitic stainless steels, although it can facilitate
slow crack growth. The mode of hydrogen induced delayed fracture in either the stable or unstable austenitic stainless steel
is correlated with the K, value; the fracture surface is changed from ductile to brittle as K
1 is decreased. 相似文献
17.
This paper reports a study of grain boundary segregation, intergranular corrosion, and intergranular stress corrosion cracking
in austenitic stainless steels. The results show that phosphorus, nitrogen, and sulfur all segregate to grain boundaries in
these materials and that they can affect one another's segregation through site compctition. In particular, the results demonstrate
that phosphorus segregation can be lowered by the presence of nitrogen and sulfur in the steel. Also, if manganese is present
in the steel, sulfur segregation will be greatly decreased as a result of formation of manganese sulfides. Phosphorus, sulfur,
and nitrogen will not initiate intergranular corrosion in the modified Strauss test, although if corrosion is initiated by
chromium depletion, these elements might enhance the corrosion process. Phosphorus segregation does enhance corrosion in the
Huey test, even in steels that have not undergone grain boundary chromium depletion, although there does not appear to be
a precise correlation between the depth of corrosion penetration and phosphorus segregation. Intergranular stress corrosion
cracking in 288 °C water at a pH of 2.5 and electrochemical potential of OV SHE can occur in these steels even in the absence of chromium depletion if sulfur is present on the grain boundaries. Phosphorus
segregation appears to have very little effect. 相似文献
18.
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
19.
The effect of nitrogen additions upon the pitting resistance of 18 pct Cr, 18 pct Mn stainless steel has been investigated
by potentiokinetic techniques in a 1000 ppm NaCl solution. Nitrogen additions increased the pitting resistance of the steel
irrespective of structure, however, the ferritic steel was less pit resistant than the (duplex) steels containing both austenite
and ferrite which, in turn, were less pit resistant than the totally austenitic steels. For steels having a duplex structure,
the effect of nitrogen on the pitting resistance was observed to follow a linear function of the relative amount of austenite
in these steels due to the area effects of the austenite and ferrite which are galvanically coupled in these steels. The addition
of nitrogen was found to increase the amount of austenite at a rate of approximately 200 times the percent nitrogen addition
from 36 pct austenite for the 0.02 pct N steel to 100 pct for the 0.40 pct nitrogen steel. The addition of nitrogen to the
totally austenitic steels increased the pitting resistance at the rate of approximately 0.31 volts per pct nitrogen added,
but no mechanism was found for the increased resistance.
This paper is based on a presentation made at a symposium on “New Developments in Ferritic and Duplex Stainless Steels,” held
at the Fall Meeting in Cleveland, Ohio, on October 19, 1972, under the sponsorship of the Corrosion Resistant Metals Committee
of TMS-IMD and the Corrosion and Oxidation Activity of the ASM. 相似文献
20.
The effects of electroplated and hot-dip zinc coatings on the fracture of low-alloy steel AISI 4140 bars tempered to hardnesses
in the range Rc 33 to 49 were studied. Either electroplated or hot-dip zinc coatings decrease resistance to stress corrosion
cracking, i.e., they reduce K
sc, the threshold stress intensity for stress corrosion cracking in 3.5 wt pct NaCl solution. Above K
scelectroplated-zinc coatings do not appear to affect the crack-growth rate, although the incubation period prior to the onset
of crack growth is reduced. Hot-dip zinc coatings increase stress corrosion crack growth rates slightly because of the additive
effect of internal dissolved hydrogen. Hot-dip zinc coatings reduce the critical stress intensity for fracture in the absence
of a corrosive environment because of embrittlement by internal hydrogen which is released from traps during hot-dip coating
and confined by the inter metallic coatings which form on the steel surface in the hot dip bath. A simple fracture mechanics
analysis indicates that either increasing diameter or the presence of a zinc coating lowers the critical hardness at which
the stress corrosion cracking of structural bolts can occur. 相似文献
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