共查询到20条相似文献,搜索用时 31 毫秒
1.
Koh-ichi Sugimoto Shin-nosuke Hidaka Hikaru Tanino Junya Kobayashi 《Metallurgical and Materials Transactions A》2017,48(5):2237-2246
The warm stretch formability and flangeability of 0.2 pct C-1.5 pct Si-5 pct Mn transformation-induced plasticity-aided sheet steel with annealed martensite matrix were investigated for automotive applications. Both formabilities were enhanced by warm forming at peak temperatures of 423 K to 573 K and 423 K to 523 K (150 °C to 300 °C and 150 °C to 250 °C), respectively. The superior warm formabilities were mainly due to the stabilization of a large amount of retained austenite by warm forming and the consequent considerably suppressed void growth at the interface between the matrix and transformed martensite, despite there being large hole punching damage for the stretch flangeability. High peak temperatures for stretch formability and flangeability were associated with apparently increased M S of the retained austenite resulting from the increased mean normal stress on stretch forming and hole expansion. 相似文献
2.
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
3.
Mahmoud Ahmadein M. Wu J. H. Li P. Schumacher A. Ludwig 《Metallurgical and Materials Transactions A》2013,44(6):2895-2903
A two-stage simulation strategy is proposed to predict the as-cast structure. During the first stage, a 3-phase model is used to simulate the mold-filling process by considering the nucleation, the initial growth of globular equiaxed crystals and the transport of the crystals. The three considered phases are the melt, air and globular equiaxed crystals. In the second stage, a 5-phase mixed columnar-equiaxed solidification model is used to simulate the formation of the as-cast structure including the distinct columnar and equiaxed zones, columnar-to-equiaxed transition, grain size distribution, macrosegregation, etc. The five considered phases are the extradendritic melt, the solid dendrite, the interdendritic melt inside the equiaxed grains, the solid dendrite, and the interdendritic melt inside the columnar grains. The extra- and interdendritic melts are treated as separate phases. In order to validate the above strategy, laboratory ingots (Al-4.0 wt pct Cu) are poured and analyzed, and a good agreement with the numerical predictions is achieved. The origin of the equiaxed crystals by the “big-bang” theory is verified to play a key role in the formation of the as-cast structure, especially for the castings poured at a low pouring temperature. A single-stage approach that only uses the 5-phase mixed columnar-equiaxed solidification model and ignores the mold filling can predict satisfactory results for a casting poured at high temperature, but it delivers false results for the casting poured at low temperature. 相似文献
4.
S. Neogy A. Laik M. T. Saify S. K. Jha D. Srivastava G. K. Dey 《Metallurgical and Materials Transactions A》2017,48(6):2819-2833
Diffusion couple formed between U-9 wt pct Mo and Zr-1 wt pct Nb alloys, proposed as fuel and clad materials, respectively, in nuclear research reactors, was annealed to investigate the microstructural evolution of the interdiffusion zone (IZ) as a function of temperature. A layered-type IZ microstructure was observed, the mechanism of development of which was elucidated. Mo2Zr phase, present as dispersoids, in the U-rich part of the as-bonded IZ evolved into a continuous layer and into a “massive” morphology upon annealing. The discontinuous precipitation reaction in the matrix adjoining the Mo2Zr phase, instigated by Mo depletion, generated lamellae of α-U phase within the γ-U(Mo,Zr) matrix. Zr-rich α-Zr(U) precipitates were observed in U-rich U-Mo-Zr matrix in the IZ next to the U-9Mo base material due to the clustering tendency of the matrix phase. The IZ next to Zr-1Nb base material comprised a “basket weave” microstructure of α-Zr laths with β-Zr(Nb,U) interlath boundaries, wherein an omega like transformation of the latter to δ-UZr2 was also noticed. The growth rates of the IZ were orders of magnitude lower when compared with the ones reported between the compositionally similar U-10 wt pct Mo alloy and the presently used Al or Al-Si cladding alloys. 相似文献
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6.
Chang Wook Lee Bruno Charles De Cooman 《Metallurgical and Materials Transactions A》2014,45(10):4499-4509
Press hardening is increasingly being used to produce ultra-high strength steel parts for passenger cars. Al-Si, Zn, and Zn-alloy coatings have been used to provide corrosion protection to press hardening steel grades. The use of coatings has drawbacks such as coating delamination or liquid metal-induced embrittlement. In the present work, the microstructural evolution of Al-Zn coating during press hardening was studied. The 55 wt pct Al-Zn coating can in principle provide both Al barrier protection and Zn cathodic protection to press hardened steel. During the heat treatment associated with the press hardening, the 55 wt pct Al-Zn alloy coating is converted to an intermetallic surface layer of Fe2Al5 and a FeAl intermetallic diffusion layer. The Zn is separated from both intermetallic compounds and accumulates at grain boundaries and at the surface. This Zn separation process is beneficial in terms of providing cathodic protection to Al-Zn coated press hardening steel. 相似文献
7.
Ardeshir Golpayegani Fang Liu Henrik Svensson Marcus Andersson Hans-Olof Andrén 《Metallurgical and Materials Transactions A》2011,42(4):940-951
The microstructure of a trial martensitic chromium steel containing a high content of boron (250 ppm) was characterized in
detail in the as-tempered and aged conditions. This steel has a similar composition and heat treatment as the TAF steel that
still is unsurpassed in creep strength among all 9 to 12 pct chromium steels. Characterization was performed by using scanning
electron microscopy, energy-filtered transmission electron microscopy, secondary ion mass spectroscopy, and atom probe tomography.
Focus was placed on investigating different types of precipitates that play a key role in improving the creep resistance of
these steels. The low tempering temperature of 963 K (690 °C) is enough for the precipitation of the full volume fraction
of both MX and M23C6. A high boron content, more than 1 at. pct, was found in M23C6 precipitates and they grow slowly during aging. The high boron level in the steel results in metal borides rather than BN
with the approximate formula (Mo0.66Cr0.34)2(Fe0.75V0.25)B2. Two families of MX precipitates were found, one at lath boundaries about 35 nm in size and one dense inside the laths, only
5 to 15 nm in size. 相似文献
9.
As interest increases in incorporating Nitinol alloys in different microapplications and devices, the development of effective
procedures for laser microwelding (LMW) these alloys becomes necessary. Laser welding processes applied to Nitinol have been
shown to lower strength, induce inclusions of intermetallic compounds (IMCs), and alter the pseudoelastic and shape memory
effects. Inconsistency in reported weld properties has also suggested that further studies are required. The current study
details the mechanical, microstructural, and phase transformation properties of Nd:YAG LMW crossed Ti-55.8 wt pct Ni Nitinol
wires. The effects of surface oxide on joint performance were also investigated. Fracture strength, weld microstructure, and
phase transformation temperatures at varying peak power inputs were studied and compared to the unaffected base metal. Results
showed good retention of strength and pseudoelastic properties, while the fusion zone exhibited higher phase transformation
temperatures, which altered the active functional properties at room temperature. 相似文献
10.
The transformations of a high-strength 9Ni-Cr-Mo-V steel were characterized as a function of cooling rate by dilatometry, microhardness measurements, and microstructural characterization. The results demonstrate that this steel is extremely insensitive to changes in cooling rate, generating a duplex microstructure of coarse autotempered martensite within a matrix of fine lath martensite at nearly all cooling rates. The coarse autotempered martensite is observed even at very slow cooling rates, although the lath martensite becomes replaced by lath (or bainitic) ferrite. 相似文献
11.
The influence of weld-simulated heat treatments of 9 to 12 pct steels is evaluated by a fundamental model for creep. The heat-affected
microstructure is predicted by considering particle coarsening, particle dissolution, and subgrain coarsening. Particle coarsening
is predicted for a multicomponent system, showing significant M23C6 coarsening in the bcc matrix. Dissolution simulations of MX and M23C6 are performed by considering a size distribution of particles, indicating that the smallest particles can be dissolved already
at relatively low welding temperatures. Recovery in dislocation networks will take place due to the coarser particles. Creep
rate modeling is performed based on the heat-affected microstructure, showing strength reduction of weld-simulated material
by 12 pct at 1123 K (850 °C) and 30 pct at 1173 K (900 °C). The main cause of this degradation is believed to be the loss
of the smallest carbonitrides. 相似文献
12.
Catherine N. Tupper Don W. Brown Robert D. Field Thomas A. Sisneros Bjorn Clausen 《Metallurgical and Materials Transactions A》2012,43(2):520-530
The large strain deformation of polycrystalline uranium 6 wt pct niobium (U6Nb) was studied in situ during uniaxial tensile and compressive loading by time-of-flight neutron diffraction. Diffraction patterns were recorded
at incremental strains to a maximum of approximately 0.13 tensile and 0.15 compressive true strain. A discrete reorientation
of the crystallographic texture under tensile straining between 0.04 and 0.08 true strain is consistent with a previously
unobserved mechanical deformation twinning mechanism, identified as either a (100) or (010) mechanical twin system. Beyond
this, a continuous texture reorientation towards an (010) crystal orientations indicates that a slip mechanism is likely predominant.
An analogous mechanical twin system was not observed in compression at large strain. 相似文献
13.
Alexandra Fedoseeva Nadezhda Dudova Rustam Kaibyshev 《Metallurgical and Materials Transactions A》2017,48(3):982-998
The effect of tempering on the mechanical properties and fracture behavior of two 3 pct Co-modified 9 pct Cr steels with 2 and 3 wt pct W was examined. Both steels were ductile in tension tests and tough under impact tests in high-temperature tempered conditions. At T ≤ 923 K (650 °C), the addition of 1 wt pct W led to low toughness and pronounced embrittlement. The 9Cr2W steel was tough after low-temperature tempering up to 723 K (450 °C). At 798 K (525 °C), the decomposition of retained austenite induced the formation of discontinuous and continuous films of M23C6 carbides along boundaries in the 9Cr2W and the 9Cr3W steels, respectively, which led to tempered martensite embrittlement (TME). In the 9Cr2W steel, the discontinuous boundary films played a role of crack initiation sites, and the absorption energy was 24 J cm?2. In the 9Cr3W steel, continuous films provided a fracture path along the boundaries of prior austenite grains (PAG) and interlath boundaries in addition that caused the drop of impact energy to 6 J cm?2. Tempering at 1023 K (750 °C) completely eliminated TME by spheroidization and the growth of M23C6 carbides, and both steels exhibited high values of adsorbed energy of ≥230 J cm?2. The addition of 1 wt pct W extended the temperature domain of TME up to 923 K (650 °C) through the formation of W segregations at boundaries that hindered the spheroidization of M23C6 carbides. 相似文献
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15.
Sangwon Lee Bruno Charles De Cooman 《Metallurgical and Materials Transactions A》2014,45(11):5009-5016
Intercritically annealed 10 pct Mn steel has been shown to exhibit an excellent combination of strength and ductility due to the plasticity-enhancing mechanisms of mechanical twinning and strain-induced martensite transformation occurring in sequence. This mechanical behavior is only achieved for a multi-phase microstructure obtained after annealing within a specific intercritical temperature range. A model for the selection of the optimal intercritical annealing temperature was developed to achieve a high strength-ductility balance for 10 pct Mn multi-phase steel. The model considers the room temperature stacking fault energy and the thermodynamic stability of the retained austenite. 相似文献
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18.
Electropulsing induced texture evolution in the primary recrystallization of a Fe-3 pct Si alloy strip was studied using the
electron backscattered diffraction technique. The results revealed that the electropulsing strengthened considerably the recrystallization
of a cold-rolled Fe-3Si alloy strip. Various textures with high-energy storages, such as α (100)〈110〉, γ (111)〈110〉, γ (111)〈112〉, and G-texture (110)〈001〉, formed after several seconds of electropulsing treatment (EPT), depending on the intensity of electropulsing.
The athermal effect of electropulsing is 319 times stronger than the thermal effect of electropulsing for the formation of
the G texture. The mechanism of electopulsing induced texture evolution is discussed from the point of view of Gibbs free energy
and dislocation dynamics. 相似文献
19.
Yan-Zhong Tian Qi-Qiang Duan Hua-Jie Yang He-Fei Zou Gang Yang Shi-Ding Wu Zhe-Feng Zhang 《Metallurgical and Materials Transactions A》2010,41(9):2290-2303
Equal channel angular pressing (ECAP) is applied to investigate the microstructural evolution and mechanical properties of
Cu-8 wt pct Ag alloy subjected to one to four passes via four different routes (A, BA, BC, and C). It is demonstrated that better mechanical properties, a higher fraction of high-angle boundaries, and a smaller
grain size can be obtained most rapidly with route A, whereas the specimen processed by route BC contains relatively inhomogeneous microstructure and has poor mechanical properties. The ultimate tensile stress (UTS) of
the Cu-Ag alloy processed by route BC saturates after four passes; in contrast, the UTS of the Cu-Ag alloy processed by route A increases continuously in relation
to the number of ECAP passes. Based on the experimental results, the strengthening mechanisms of the Cu-8 wt pct Ag alloy
processed by different routes as well as the efficiency of different routes in refining the binary alloy are discussed. 相似文献