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1.
Mine Yoji Tachibana Kazutaka Horita Zenji 《Metallurgical and Materials Transactions A》2011,42(6):1619-1629
This study addresses a hydrogen effect on the tensile properties of a type 310S austenitic stainless steel with ultrafine-grained
structures produced by high-pressure torsion (HPT) and subsequent annealing. The mean grain size was reduced to ~85 nm by
the HPT processing. The grain size was increased by the post-HPT annealing, but the grain size of ~265 nm was retained after
annealing at 1023 K (750 °C). The tensile strength of ~1.2 GPa, which is approximately twice as much as that of the solution-treated
specimen, was attained in the 1023 K (750 °C) post-HPT-annealed specimen. The elongation to failure was restored up to ~15 pct
by the post-HPT annealing, although it was still insufficient in comparison with the ~55 pct elongation of the solution-treated
specimen. There was no change in the tensile strength of the HPT-processed specimens and the post-HPT-annealed specimens by
hydrogen charging with the hydrogen content in the range of ~20 to 40 mass ppm. The HPT-processed and the 773 K (500 °C) post-HPT-annealed
specimens exhibited a ductility loss through the fully shear type fracture. The hydrogen charge into higher temperature post-HPT-annealed
specimens with σ-FeCr precipitates led to a mild hydrogen embrittlement. 相似文献
2.
Structure and properties of a β solution treated,quenched, and aged si-bearing near-α titanium alloy
The microstructure, tensile properties, and fractographic features of a near-α titanium alloy, IMI 829(Ti-6.1 wt pct Al-3.2
wt pct Zr-3.3 wt pct Sn-1 wt pct Nb-05 wt pct Mo-0.32 wt pct Si) have been studied after aging over a temperature range of
550°C to 950°C for 24 hours following solution treatment in the β phase field at 1050°C and water quenching. Transmission
electron microscopy studies revealed that aging at 625°C and above produced discrete silicides at α′ interplatelet boundaries.
However, aging at 900°C and above has also resulted in the precipitation of β phase along the lath boundaries of martensite.
The silicides have been found to have a hexagonal structure withc=0.36 nm anda=0.70 nm (designated as S2 by earlier workers). There is a significant improvement in yield and ultimate tensile strength after aging at 625°C, but
there is less improvement at higher aging temperatures. The tensile ductility is found to be drastically reduced. While the
fracture surface of the unaged specimen shows elongated dimples, the aged samples show a mixed mode of fracture, consisting
of facets, featureless parallel bands, and extremely fine dimples. 相似文献
3.
P. Sahu A. S. Hamada T. Sahu J. Puustinen T. Oittinen L. P. Karjalainen 《Metallurgical and Materials Transactions A》2012,43(1):47-55
A high-Mn austenitic steel was deformed in cold rolling to study the martensitic transformation and microstructure using X-ray
diffraction and electron backscatter diffraction. Despite heavy deformation of 70 pct reduction (1.2 true strain), α′-martensite could not be induced in this alloy, but about 90 pct of the austenite transformed to ε-martensite. However, a small fraction (~4 pct) of α′-martensite could be observed when the same alloy was subjected to low strain compression tests in a Gleeble simulator. The
stability of ε-martensite was attributed to the increase in stacking fault energy of the steel, expected to be more than 20 mJ/m2 because of the increase in temperature during the cold rolling deformation. 相似文献
4.
Bikas C. Maji Madangopal Krishnan Gouthama R. K. Ray 《Metallurgical and Materials Transactions A》2011,42(8):2153-2165
The effect of Si addition on the microstructure and shape recovery of FeMnSiCrNi shape memory alloys has been studied. The
microstructural observations revealed that in these alloys the microstructure remains single-phase austenite (γ) up to 6 pct Si and, beyond that, becomes two-phase γ + δ ferrite. The Fe5Ni3Si2 type intermetallic phase starts appearing in the microstructure after 7 pct Si and makes these alloys brittle. Silicon addition
does not affect the transformation temperature and mechanical properties of the γ phase until 6 pct, though the amount of shape recovery is observed to increase monotonically. Alloys having more than 6 pct
Si show poor recovery due to the formation of δ-ferrite. The shape memory effect (SME) in these alloys is essentially due to the γ to stress-induced ε martensite transformation, and the extent of recovery is proportional to the amount of stress-induced ε martensite. Alloys containing less than 4 pct and more than 6 pct Si exhibit poor recovery due to the formation of stress-induced
α′ martensite through γ-ε-α′ transformation and the large volume fraction of δ-ferrite, respectively. Silicon addition decreases the stacking fault energy (SFE) and the shear modulus of these alloys and
results in easy nucleation of stress-induced ε martensite; consequently, the amount of shape recovery is enhanced. The amount of athermal ε martensite formed during cooling is also observed to decrease with the increase in Si. 相似文献
5.
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
6.
Kaveh Edalati Zenji Horita Hiroshi Fujiwara Kei Ameyama 《Metallurgical and Materials Transactions A》2010,41(13):3308-3317
Pure Ti (99.5 pct) powders after processing with ball milling (BM) were consolidated to disc-shaped samples with 10-mm diameter
and 0.8-mm thickness at room temperature using high-pressure torsion (HPT). A relative density as high as 99.9 pct, high bending
and tensile strengths of 2.55 to 3.45 and 1.35 GPa, respectively, and a moderate ductility of 8 pct with an ultrafine grained
structure are achieved after cold consolidation with HPT, which exceed those of hot consolidation methods. X-ray diffraction
(XRD) analysis showed that a phase transformation occurs from α phase to ω phase during HPT under a pressure of 6 GPa as in bulk pure Ti, whereas no phase transformation is detected after processing
with BM alone. It was confirmed that the strength and ductility are improved by a combined application of BM and HPT when
compared with other severe plastic deformation methods applied to Ti and Ti-6 pct Al-4 pct V, so that no alloying elements
are required for the achievement of a comparable strength and ductility. 相似文献
7.
Mohit Sharma Sanjay Kumar Vajpai Ravindra Kumar Dube 《Metallurgical and Materials Transactions A》2010,41(11):2905-2913
In the present work, Cu-Al-Ni shape memory alloy strips were prepared successfully from premixed elemental Cu, Al, and Ni
powders in the ratio 82:14:4 (wt pct) by a novel processing route consisting of preparing powder preforms, sintering, and
unsheathed hot rolling of the sintered preforms. Subsequently, the hot rolled strips were homogenized. The as-rolled strips
consisted of two phases—α and β′. A postconsolidation homogenization of the hot rolled strips was carried out at 1173 K (900 °C) for different time periods.
It has been shown that a homogenization period of 4 hours was sufficient to achieve a single-phase material consisting of
only martensitic phase. It also has been shown that the 4-hour homogenized and quenched Cu-Al-Ni shape memory alloy strips
primarily consisted of self-accommodated β′ martensite plates, which are necessary for realizing shape memory effect (SME). The finished hot rolled Cu-Al-Ni strips
had a fracture strength of 476 MPa, coupled with 2.5 pct elongation. The shape memory tests showed almost 100 pct recovery
after 10 thermomechanical cycles in the hot rolled strips at 1 pct and 2 pct prestrain level. 相似文献
8.
Gencaga Purcek Onur Saray Ibrahim Karaman Hans J. Maier 《Metallurgical and Materials Transactions A》2012,43(6):1884-1894
Interstitial-free steel (IF steel) underwent severe plastic deformation by equal-channel angular extrusion/pressing (ECAE/P)
to improve its strength, and then it was annealed to achieve a good strength-ductility balance. The coarse-grained microstructure
of IF steel was refined down to the submicron level after eight-pass ECAE. The ultrafine-grained (UFG) microstructure with
high dislocation density brought about substantially improved strength but limited tensile ductility. The limited ductility
was attributed to the small, uniform elongation caused by early plastic instability. The annealing at temperatures below 723 K
(450 °C) for 1 hour did not lead to remarkable softening, whereas annealing at temperatures up to 923 K (650 °C) resulted
in complete softening depending on the development of recrystallization. Therefore, the temperature of approximately 923 K
(650 °C) can be considered as a critical recrystallization temperature for UFG IF steel. The annealing at 873 K (600 °C) for
different time intervals resulted in different stress–strain response. Uniform tensile elongation increased at the expense
of strength with annealing time intervals. After annealing at 873 K (600 °C) for 60 minutes, the yield strength, tensile strength,
uniform elongation, and total elongation were found to be 320 MPa, 485 MPa, 15.1 pct, and 33.7 pct, respectively, showing
the better combination of strength and ductility compared with cold-rolled samples. 相似文献
9.
D. Eliezer D. G. Chakrapani C. J. Altstetter E. N. Pugh 《Metallurgical and Materials Transactions A》1979,10(7):935-941
A study has been made of the HE and SCC of a type 304 and a type 310 austenitic stainless steel, and the results correlated
with the presence or absence of α′ martensite, determined by means of a ferrite detector. Hydrogen induced slow crack growth
(SCG) was observed at room temperature when type 304 was stressed i) in 1 psig (∼105 N/m2) gaseous hydrogen, ii) after high temperature charging, and iii) while undergoing cathodic charging. The fracture surfaces
corresponding to SCG were primarily transgranular and cleavage-like, and were found to be associated with α′. Conditions i)
to iii) did not produce SCG in the type 310 steel, in which α′ martensite was not detected, nor did SCG occur when type 304
was stressed in gaseous hydrogen above the MD temperature (∼110°C). These observations indicated that the formation of the martensitic phase was a prerequisite for SCG
under these test conditions. Stressing of type 310 while it was undergoing cathodic charging at room temperature was found
to produce shallow, nonpropagating cracks, confirming earlier reports that austenite can be embrittled by hydrogen in the
absence of α′. SCC occurred in both alloys in boiling aqueous MgCl2 (154°C) with no evidence for α′ formation. The results are discussed in terms of the mechanisms of HE and SCC.
Formerly Research Associate, Department of Metallurgy and Mining Engineering, University of Illinois.
Formerly Corrosion-Control Analyst with the Physical Plant at the University of Illinois. 相似文献
10.
The effects of carbon content and ausaging on austenite γ ↔ martensite (α′) transformation behavior and reverse-transformed
structure were investigated in Fe-32Ni-12Co-4Al and Fe-(26,28)Ni-12Co-4Al-0.4C (wt pct) alloys. TheM
s
temperature, the hardness of γ phase, and the tetragonality of α′ increase with increasing ausaging time, and these values
are higher in the carbon-bearing alloys in most cases. The γ → α′ transformation behavior is similar to that of thermoelastic
martensite; that is, the width of α′ plate increases with decreasing temperature in all alloys. The αt’ → γ reverse transformation
temperature is lower in the carbon-bearing alloys, which means that the shape memory effect is improved by the addition of
carbon. The maximum shape recovery of 84 pct is obtained in Fe-28Ni-12Co-4Al-0.4C alloy when the ausaged specimen is deformed
at theM
s
temperature and heated to 1120 K. There are two types of reverse-transformed austenites in the carbon-bearing alloy. One
type is the reversed y containing many dislocations which were formed when the γ/α′ interface moved reversibly. The plane
on which dislocations lie is (01 l)γ if the twin plane is (112)α′. The other type of reverse-transformed austenite exhibits γ islands nucleated within the α′ plates. 相似文献
11.
Remendur is an alloy of approximately equal proportions of iron and cobalt with two to four wt pct vanadium. In previous articles
by the authors, various aspects of the ternary phase equilibrium and the influence of processing variations on microstructure
were described. This paper reports on the more complete correlation among microstructure, mechanical properties, magnetic
properties, and resistivity. For strand annealed (900 to 950°C) material, the mechanical properties are only a weak function
of annealing temperature but a strong function of vanadium content. Subsequent annealing at 600°C significantly increases
the yield and tensile strengths but the mode of fracture becomes brittle cleavage, in contrast to the ductile failure of strand
annealed material. Coercivity in the strand annealed (900 to 950°C) and quenched condition is primarily determined by grain
size and transformation strains produced during the quench. Coercivity in 600°C annealed material is due to the fine dispersion
of stable γ particles in the α′1 matrix which are impediments to domain wall motion. In general, resistivity is relatively
independent of processing temperature. 相似文献
12.
To study the influence of hydrogen on the fatigue strength of AISI type 304 metastable austenitic stainless steel, specimens
were cathodically charged with hydrogen. Using tension-compression fatigue tests, the behavior of fatigue crack growth from
a small drill hole in the hydrogen-charged specimen was compared with that of noncharged specimen. Hydrogen charging led to
a marked increase in the crack growth rate. Typical characteristics of hydrogen effect were observed in the slip band morphology
and fatigue striation. To elucidate the behavior of hydrogen diffusion microscopically in the fatigue process, the hydrogen
emission from the specimens was visualized using the hydrogen microprint technique (HMT). In the hydrogen-charged specimen,
hydrogen emissions were mainly observed in the vicinity of the fatigue crack. Comparison between the HMT image and the etched
microstructure image revealed that the slip bands worked as a pathway for hydrogen to move preferentially. Hydrogen-charging
resulted in a significant change in the phase transformation behavior in the fatigue process. In the noncharged specimen,
a massive type α′ martensite was observed in the vicinity of the fatigue crack. On the other hand, in the hydrogen-charged specimen, large
amounts of ε martensite and a smaller amount of α′ martensite were observed along the slip bands. The results indicated that solute hydrogen facilitated the ε martensitic transformation in the fatigue process. Comparison between the results of HMT and EBSD inferred that martensitic
transformations as well as plastic deformation itself can enhance the mobility of hydrogen. 相似文献
13.
Heat treatments were performed using an isothermal bainitic transformation (IBT) temperature compatible with continuous hot-dip
galvanizing on two high Al–low Si transformation induced plasticity (TRIP)-assisted steels. Both steels had 0.2 wt pct C and
1.5 wt pct Mn; one had 1.5 wt pct Al and the other had 1 wt pct Al and 0.5 wt pct Si. Two different intercritical annealing
(IA) temperatures were used, resulting in intercritical microstructures of 50 pct ferrite (α)-50 pct austenite (γ) and 65 pct α-35 pct γ. Using the IBT temperature of 465 °C, five IBT times were tested: 4, 30, 60, 90, and 120 seconds. Increasing the IBT time
resulted in a decrease in the ultimate tensile strength (UTS) and an increase in the uniform elongation, yield strength, and
yield point elongation. The uniform elongation was higher when using the 50 pct α-50 pct γ IA temperature when compared to the 65 pct α-35 pct γ IA temperature. The best combinations of strength and ductility and their corresponding heat treatments were as follows:
a tensile strength of 895 MPa and uniform elongation of 0.26 for the 1.5 pct Al TRIP steel at the 50 pct γ IA temperature and 90-second IBT time; a tensile strength of 880 MPa and uniform elongation of 0.27 for the 1.5 pct Al TRIP
steel at the 50 pct γ IA temperature and 120-second IBT time; and a tensile strength of 1009 MPa and uniform elongation of 0.22 for the 1 pct Al-0.5 pct
Si TRIP steel at the 50 pct γ IA temperature and 120-second IBT time. 相似文献
14.
15.
Yihong Nie Yuuji Kimura Tadanobu Inoue Fuxing Yin Eiji Akiyama Kaneaki Tsuzaki 《Metallurgical and Materials Transactions A》2012,43(5):1670-1687
A deformation of a tempered martensitic structure (i.e., tempforming) at 773 K (500 °C) was applied to a 0.6 pct C-2 pct Si-1 pct Cr steel. The hydrogen embrittlement (HE) property
of the tempformed (TF) steel was investigated by a slow strain rate test (SSRT) and an accelerated atmospheric corrosion test
(AACT). Hydrogen content within the samples after SSRT and AACT was measured by thermal desorption spectrometry (TDS). The
tempforming at 773 K (500 °C) using multipass caliber rolling with an accumulative are reduction of 76 pct resulted in the
evolution of an ultrafine elongated grain (UFEG) structure with a strong 〈110〉//rolling direction (RD) fiber deformation texture
and a dispersion of spheroidized cementite particles. The SSRT of the pre-hydrogen-charged notched specimens and the AACT
demonstrated that the TF sample had superior potential for HE resistance to the conventional quenched and tempered (QT) sample
at a tensile strength of 1500 MPa. The TDS analysis also indicated that the hydrogen might be mainly trapped by reversible
trapping sites such as grain boundaries and dislocations in the TF sample, and the hydrogen trapping states of the TF sample
were similar to those of the QT sample. The QT sample exhibited hydrogen-induced intergranular fracture along the boundaries
of coarse prior-austenite grains. In contrast, the hydrogen-induced cracking occurred in association with the UFEG structure
in the TF sample, leading to the higher HE resistance of the TF sample. 相似文献
16.
Eun Yoo Yoon Dong Jun Lee Lee Ju Park Sunghak Lee Mohamed Ibrahim Abd El Aal Hyoung Seop Kim 《Metallurgical and Materials Transactions A》2014,45(11):4748-4752
High tensile strength of 616 MPa and improved ductility of 7.6 pct were obtained in powder-consolidated pure Cu processed by high-pressure torsion (HPT) at room temperature followed by post-annealing at 673 K (400 °C). The powder-HPT consolidation process maintained nano-crystalline microstructures even after post-annealing due to the presence of well-dispersed oxide particles in the matrix. Higher ductility in the post-annealed specimen is attributed to higher fraction of stable Σ3 coincidence site lattice boundaries than that in the HPT-processed Cu. 相似文献
17.
Javad Mola Dongchul Chae Bruno C. De Cooman 《Metallurgical and Materials Transactions A》2010,41(6):1429-1440
Anisotropic dimensional changes in a 16 pct Cr ferritic stainless steel possessing a banded structure of α + α′ obtained by hot rolling were studied. Considerable anisotropic transformation plasticity was observed during both the austenitization
and the martensite formation reactions. Anisotropy was also observed in the case of the coefficient of thermal expansion (CTE),
over a wide annealing temperature range. The observations are shown to be due to the geometrical arrangement of the phases,
with ferrite acting as a constraint against the in-rolling-plane straining of the pancaked γ, thus encouraging exaggerated dimensional changes along the normal direction (ND). Assuming isotropic dimensional change
within the rolling plane and combining the dilatometric results in the rolling and normal directions (NDs), the measured dilatation
and CTE can be used to determine the volume fraction of α′. This alternative phase analysis method is shown to have advantages compared to a conventional image analysis method especially
at low annealing temperatures where there are still residues of the tempered martensite. 相似文献
18.
The super α
2 Ti3Al-based alloy with a fine grain size of ∼2.2 μm exhibits superplastic elongations over 1000 pct at 920 °C to 1000 °C, 600 pct at 900 °C, 330 pct at 850 °C, and 140 pct
at 750 °C. Mechanical anisotropy is observed in this alloy, and relatively lower flow stresses and higher tensile elongations
are obtained in the 45 deg specimen loaded at 25 °C to 960 °C. The texture characteristics appear to impose significant influence
on the mechanical anisotropy at temperatures below 900 °C (under the dislocation creep condition), and the {111}〈2
〉 and {0001} basal textures evolve in the β and α
2 phases after tensile straining. At loading temperatures higher than 900 °C (under the superplastic flow condition), the anisotropy
effect is less pronounced and the grain orientation distribution becomes basically random in nature. Rationalizations for
the mechanical anisotropy in terms of the Schmid factor calculations for the major and minor texture components in the β and α
2 phases provide consistent explanations for the deformation behavior at lower temperatures as well as the initial straining
stage at higher temperatures. 相似文献
19.
The electron backscattered diffraction (EBSD) technique has been used to assess crystallographic features of the residual
γ phase and the strain-induced ε/α′ martensites in a 304 stainless steel, tensile tested to 10 pct strain at T=−60 °C. The martensitic transformation rate varies according to the γ-grain orientation against the applied stress and the γ-grain size. The α′-transformation textures as well as the γ-misorientation spreads observed in specific γ-grain orientations have been analyzed. Large misorientation spreads are observed in the less-transformed γ grains. This reveals an important crystallographic slip activity, even if less strain-induced martensite has been formed.
A strong γ → α′ variant selection was detected in the cube- and Goss-oriented γ grains for which the transformation is less developed. For the {110} 〈1–11〉 and copper-oriented γ grains, the amount of α′ martensite is significantly higher and the γ → α′ variant selection is less pronounced. This variant selection is then analyzed on at a local scale and is related to the presence
of {111}
γ
localized deformation bands on which further ε/α′ martensites have nucleated. 相似文献
20.
C. Ramachandra A. K. Singh G. M. K. Sarma 《Metallurgical and Materials Transactions A》1993,24(6):1273-1280
Microstructural stability in the near-α titanium alloy (alloy 834) containing Ti-6Al-4Sn-4Zr-0.70Nb-0.50Mo-0.40Si (in weight
percent), in the β and(α + β) solution-treated and quenched conditions, has been investigated. The β transus for this alloy is approximately 1333 K. Solution
treatment in the β phase field at 1353 K followed by quenching in water at room temperature resulted in the formation of α′
martensite platelets with high dislocation density and stacking faults. Thin films of β are found to be sandwiched between
interface phases, which, in turn, are sandwiched at the interplatelet boundaries of lath martensite. The interface phase is
a subject of much controversy in the literature. Solution treatment at 1303 K in the(α + β) phase field followed by quenching in water at room temperature resulted in the near-equiaxed primary α and transformed β.
Both the β and(α + β) solution-treated specimens were aged in the temperature range of 873 to 973 K. While aging the —treated specimen at 973 K,(α + β)-treated specimen, even at a lower temperature of 873 K for 24 hours, caused precipitation of suicides predominantly
at the interplatelet boundaries of martensite laths. Electron diffraction analysis confirmed them to be hexagonal suicide
S2 witha = 0.702 nm andc = 0.368 nm. The above difference in the precipitation could be attributed to the partitioning of a higher amount of β- stabilizing elements as well as silicide-forming elements to the transformed β in the(α + β) solution-treated condition. However, ordering of theα′ phase was observed under all of the aging conditions studied. The ordered domains were due to the longer aging times, which
cause local increases in the level of theα-stabilizing elements.
Formerly Research Associate, Department of Metallurgical Engineering, Baranas Hindu University. 相似文献