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1.
《Acta Metallurgica Materialia》1994,42(9):3149-3156
Samples of unalloyed silicon and aluminium spheroidal graphite cast iron have been studied in the austempered condition. Austempering times of up 3 h at 400°C for Al SG and 1 h at 350°C for Si SG gives a typical ADI microstructure consising of carbide-free banitic ferrite and stable, high carbon enriched, retained austenite. This has an attractive combination of elongation and strength. For longer austempering times transition carbides are precipitated in the bainitic ferrite, η-carbide in the upper bainitic range, i.e.400°C for Al SG and 350°C for Si SG, and ϵ-carbide in the lower bainite range. Increasing amounts of transition carbide reduce the ductility and produce a mixed model of fracture. For longer austempring times X-carbide is precipitated at the ferrite/austenite boundaries leading to a more brittle fracture mode. 相似文献
2.
设计了一种0.7C的低合金超细贝氏体钢,并通过膨胀仪、二体磨损实验、光学显微镜、扫描电镜、X射线衍射、激光扫描共聚焦显微镜及能谱仪,研究了不同等温淬火温度对超细贝氏体钢的贝氏体相变动力学、微观组织以及干滑动摩擦耐磨性的影响,揭示超细贝氏体钢在二体磨损条件下的耐磨性能和磨损机理.研究结果表明,不同等温温度下的超细贝氏体钢都由片层状贝氏体铁素体和薄膜状以及块状的残留奥氏体组成;随着等温温度的升高,超细贝氏体的相变速率提高,相变孕育期及相变完成时间缩短,但贝氏体铁素体板条厚度增加,残留奥氏体含量增加,硬度值有所降低;超细贝氏体钢磨损面形貌以平直的犁沟为主,主要的磨损机理为显微切削;不同等温温度下所获得的超细贝氏体的耐磨性能都优于回火马氏体,且随着等温温度的降低,耐磨性能提高.其中在250℃等温所获得的超细贝氏体钢具有最优的耐磨性能,其相对耐磨性为回火马氏体的1.28倍.这主要与超细贝氏体钢中贝氏体铁素体板条的细化及磨损过程中残留奥氏体的形变诱导马氏体相变(TRIP)效应有关. 相似文献
3.
Hiroshi Matsuda Fusato Kitano Kohei Hasegawa Toshiaki Urabe Yoshihiro Hosoya 《国际钢铁研究》2002,73(6-7):211-217
The effects of heat‐treatment conditions on mechanical properties are comprehensively investigated to optimise the industrial process of the 590 MPa grade TRIP steel sheet with the metallurgical understanding. The substantial effect of the thermal conditions are first clarified by laboratory investigation, which includes the effects of annealing conditions, cooling conditions from intercritical temperature to austempering temperature and austempering conditions. The results indicate that the optimum annealing temperature is between 800 and 850 °C and the mechanical properties are hardly influenced by the annealing time between 30 and 120 s at an annealing temperature of 825 °C. It is also suggested that the optimum quenching rate is 45 °C/s to obtain the stable properties of the products and the optimum austempering conditions are 425 °C with over 300 s in case of a constant temperature austempering. Based on the laboratory investigation, mill trial is performed using the NKK No.4‐CAL in Fukuyama works. The heat treatment conditions are intentionally varied to examine minutely the stability of the production. The mechanical properties are sensitive to the austempering start temperature, when the austempering temperature is gradually decreased during austempering in the industrial conditions for the stable operation without meanders. Excellent mechanical properties can be obtained by controlling the austempering start temperature between 445 and 460 °C. On the contrary, the properties deteriorate in case of the austempering start temperature over 470 °C although the amount of retained austenite is the same or slightly larger than the material which exhibits excellent properties. This is because the retained austenite is less stable in the high‐temperature austempered material caused by less bainite transformation. 相似文献
4.
In order to understand the influence of high-temperature aging effects and those of the superimposed creep stress on the microstructural
variations in a 1.25Cr-0.5Mo steel, the shoulder as well as gage portions of specimens subjected to stress-rupture tests at
520 °C and 560 °C have been studied by transmission electron microscopy. In the normalized and tempered condition, the microstructure
of the steel consists of 90 pct ferrite and 10 pct bainite, and M3C is the only carbide present in bainite and at a few ferrite grain boundaries. On aging at 520 °C for 5442 hours, Cr2N precipitates in a fibrous form at ferrite-bainite interfaces, and the creep stress has enhanced this mode of precipitation.
On holding for 13,928 hours at 520 °C, fibrous carbide is still present but its composition has changed to Mo2C, while the superimposed creep stress has promoted the precipitation of Mo2C needles with fine globular precipitates of M23C6. Aging at 560 °C for 1854 or 10,338 hours has resulted in the precipitation of longer Mo2C needles and ellipsoidal M23C6 carbide precipitation; the superimposed creep stress has resulted in a more dense precipitation of shorter needles in both
cases. There is some recovery of bainitic ferrite at 560 °C, though the cementite coarsening is negligible. 相似文献
5.
Dependence of fracture toughness of austempered ductile iron on austempering temperature 总被引:1,自引:0,他引:1
Ductile cast iron samples were austenitized at 927 °C and subsequently austempered for 30 minutes, 1 hour, and 2 hours at
260 °C, 288 °C, 316 °C, 343 °C, 371 °C, and 399 °C. These were subjected to a plane strain fracture toughness test. Fracture
toughness was found to initially increase with austempering temperature, reach a maximum, and then decrease with further rise
in temperature. The results of the fracture toughness study and fractographic examination were correlated with microstructural
features such as bainite morphology, the volume fraction of retained austenite, and its carbon content. It was found that
fracture toughness was maximized when the microstructure consisted of lower bainite with about 30 vol pct retained austenite
containing more than 1.8 wt pct carbon. A theoretical model was developed, which could explain the observed variation in fracture
toughness with austempering temperature in terms of microstructural features such as the width of the ferrite blades and retained
austenite content. A plot of K
IC
2
against σ
y
(X
γ, C
γ)1/2 resulted in a straight line, as predicted by the model. 相似文献
6.
Application of Rietveld Refinement to Investigate the High Chromium White Cast Iron Austempered at Different Temperatures 总被引:1,自引:0,他引:1
The effect of austempering temperature on the microstructure and properties of a high chromium white cast iron was investigated with the Rietveld refinement method. The result shows that the upper bainite exists in the sample austempered at 623 K and the martensite, lower bainite, M7C3, and retained austenite exist in the samples austempered at 563 K and 593 K. The relative content of the retained austenite increases with increasing the austempering temperature from 563 K to 623 K. The higher hardness, impact toughness and impact abrasive wear resistance can be obtained for the specimen austempered at 593 K. 相似文献
7.
For the purpose of achieving the reasonable rolling technology of 780 MPa hot‐rolled Nb‐Ti combined ultra‐high strength steel, the effect of deformation and microalloy elements Nb and Ti on phase transformation behaviors was investigated by thermal simulation experiment. The results indicated: the deformation promoted ferritic transformation; due to the carbon content of the experimental steel was lower (<0.12% wt), the deformation indirectly impacted perlitic transformation through promoting ferritic transformation; the effect of the deformation on bainitic transformation was subject to condition whether proeutectoid ferrite precipitated before bainitic transformation. At low cooling rate of 0.5 °C/s, Nb and Ti promote transformation process γ → α, but that not good for refining the ferrite grain; at high cooling rate of 25 °C/s, Nb and Ti to a certain extent promote bainitic transformation. The recrystallization stop temperature of experimental steel was greater than 1000 °C, and phase transformation point Ar3 was 764 °C. In order to obtain the fully bainite microstructure in the practical rolling process, the cooling rate should be controlled above 15 °C/s, the start finish rolling temperature between 950–980 °C, the finishing temperature between 830–850 °C, the coiling temperature between 450–550 °C. 相似文献
8.
Masoud Zandira 《钢铁研究学报(英文版)》2010,17(2):31-35
The fracture characteristics of austempered spheroidal graphite aluminum cast iron had been investigated. The chemical content of the alloy was C 3.2, Al 2.2, Ni 0.8 and Mg 0.05 (in mass percent, %). Impact test samples were produced from keel blocks cast in CO2 molding process. The oversized impact samples were austenitized at 850 and 950 ℃ for 2 h followed by austempering at 300 and 400 ℃ for 30, 60, 120 and 180 min. The austempered samples were machined and tested at room temperature. The impact strength values for those samples austempered at 400 ℃ varied between 90 and 110 J. Lower bainitic structures showed impact strength values of 22 to 50 J. The fractures of the samples were examined using SEM. The results showed that the upper bainitic fracture revealed a honey Comb-like topography, which confirmed the ductile fracture behavior. The lower bainitic fractures of those samples austempered for short times revealed brittle fracture. 相似文献
9.
Influence of the amount and morphology of retained austenite on the mechanical properties of an austempered ductile iron 总被引:1,自引:0,他引:1
J. ARanzabal I. Gutierrez J. M. Rodriguez-Ibabe J. J. Urcola 《Metallurgical and Materials Transactions A》1997,28(5):1143-1156
High Si contents in nodular cast irons lead to a significant volume fraction of retained austenite in the material after the
austempering treatment. In the present work, the influence of the amount and morphology of this phase on the mechanical properties
(proof stress, ultimate tensile strength (UTS), elongation, and toughness) has been analyzed for different austempering conditions.
After 300 °C isothermal treatments at intermediate times, the austenite is plastically stable at room temperature and contributes,
together with the bainitic ferrite, to the proof stress and the toughness of the material. For austenite volume fractions
higher than 25 pct, the proof stress is controlled by this phase and the toughness depends mainly on the stability of γ. In these conditions (370 °C and 410 °C treatments), the present material exhibits a transformation-induced plasticity (TRIP)
effect, which leads to an improvement in ductility. It is shown that the strain level necessary to initiate the martensitic
transformation induced by deformation depends on the carbon content of the austenite. The martensite formed under TRIP conditions
can be of two different types: “autotempered” plate martensite, which forms at room temperature from an austenite with a quasi-coherent
epsilon carbide precipitation, and lath martensite nucleated at twin boundaries and twin intersections. 相似文献
10.
A debate on the bainite reaction 总被引:3,自引:0,他引:3
R. F. Hehemann K. R. Kinsman H. I. Aaronson 《Metallurgical and Materials Transactions B》1972,3(5):1077-1094
11.
对一种新型70Si3MnCrMo钢进行了等温和连续冷却贝氏体相变热处理。利用拉伸和冲击试验研究试验钢的力学行为,利用XRD、SEM和TEM等方法对试验钢进行了相组成分析和微观组织形貌观察。研究结果表明,试验钢经等温贝氏体相变,其最佳综合力学性能出现在200 ℃回火,强塑积为26.4 GPa·%。经连续冷却贝氏体相变,其最佳综合力学性能出现在300 ℃回火,强塑积达到28.6 GPa·%。回火温度较低的情况下,热处理后的组织为由贝氏体铁素体和残余奥氏体组成的无碳化物贝氏体组织,这种无碳化物贝氏体由超细贝氏体铁素体板条而获得超高强度,由一定量的高碳残余奥氏体来保证较高的塑性和韧性。试验钢经连续冷却贝氏体相变,其贝氏体铁素体板条中出现了超细亚单元,并且残余奥氏体呈薄膜状和小块状两种形态分布于贝氏体铁素体板条之间,这两种形态残余奥氏体的稳定性不同。拉伸试样在变形过程中残余奥氏体持续发生TRIP效应,直至全部残余奥氏体都发生转变生成应变诱发马氏体,从而使钢得到更好的强、塑性配合,表现出十分优异的综合性能。 相似文献
12.
13.
The Bainite reaction in Fe-Si-C Alloys: The primary stage 总被引:4,自引:0,他引:4
B. P. J. Sandvik 《Metallurgical and Materials Transactions A》1982,13(5):777-787
The morphology, crystallography, and substructure of bainitic ferrite formed in silicon alloyed high-carbon steels in the
temperature range 290 to 380 °C have been studied. The bainite exhibits a plate shaped morphology, an irrational habit plane,
and an irrational orientation relationship. The bainitic ferrite is heavily dislocated, while the surrounding austenite contains
thin twins, the density of which is highest in the austenite between closely spaced ferrite plates. The bainite plates can
cross these twins in such a manner that the twinned region remains in a crystallographic orientation, which is quite different
from that of the other regions of the bainitic ferrite plates. Epsilon carbide subsequently precipitates on the austenite
twin/bainitic ferrite boundaries. The bainitic ferrite shape strain direction and magnitude are estimated from displacements
of austenite twins inherited in the ferrite. All results, including measurement of the austenite carbon content, are consistent
with a shear mode of transformation.
B.P.J. SANDVIK, formerly with Laboratory of Physical Metallurgy at Helsinki University of Technology, Finland and Ovako OyAb,
Imatra, Finland 相似文献
14.
Kaneaki Tsuzaki Aki Kodai Tactashi Maki 《Metallurgical and Materials Transactions A》1994,25(9):2009-2016
The bainite transformation at 723 K in an Fe-2 pct Si-0.6 pct C alloy (mass pct) was investigated with transmission electron
microscopy (TEM) and quantitative metallography to clarify the growth mechanism of the ferritic component of bainite. In early
stages of transformation, the bainitic ferrite was carbide free. The laths of bainitic ferrite within a packet were parallel
to one another and separated by carbon-enriched retained austenite. The average carbon concentration of the bainitic ferrite
was estimated to be 0.19 mass pct at the lowest, indicating that the ferrite was highly supersaturated with respect to carbon.
The laths did not thicken during the subsequent isothermal holding, although they were in contact with austenite of which
the average carbon concentration was lower than the paraequilibrium value. In the later stage of transformation, large carbide
plates formed in the austenite between the laths, resulting in the decrease in the carbon concentration of the austenite.
Subsequently, the ferrite with a variant different from the initially formed ferrite in the packet was decomposed for the
completion of transformation. The present results indicate that the bainitic ferrite develops by a displacive mechanism rather
than a diffusional mechanism.
Formerly Graduate Student, Kyoto University, Kyoto 606-01, Japan
This article is based on a presentation made at the Pacific Rim Conference on the “Roles of Shear and Diffusion in the Formation
of Plate-Shaped Transformation Products,” held December 18-22, 1992, in Kona, Hawaii, under the auspices of ASM INTERNATIONAL’S
Phase Transformations Committee. 相似文献
15.
J. Chakraborty P.P. Chattopadhyay D. Bhattacharjee I. Manna 《Metallurgical and Materials Transactions A》2010,41(11):2871-2879
This study attempts to determine the scope and extent of microstructural refinement through complete/partial recrystallization
of prior cold deformed ferrite during austenitizing (1223 K (950 °C), 15 minutes) and/or austempering (543 K (270 °C), 30 minutes)
followed by water quenching to obtain ultrafine bainitic sheaves along with thin martensitic plates in SAE 52100 steel. The
volume fraction and sheaf/plate dimension (thickness/length) of bainitic ferrite and martensite were determined by optical
and scanning/transmission electron microscopy studies coupled with compositional microanalysis. Marginal improvement in the
tensile strength and significant improvement in the impact properties is obtained at an optimum level of prior cold deformation
by tension in comparison to that recorded in austempered condition without prior deformation. 相似文献
16.
Hyo Kyung Sung Sang Yong Shin Byoungchul Hwang Chang Gil Lee Sunghak Lee 《Metallurgical and Materials Transactions A》2012,43(10):3703-3714
The effects of B and Cu addition and cooling rate on microstructure and mechanical properties of low-carbon, high-strength bainitic steels were investigated in this study. The steel specimens were composed mostly of bainitic ferrite, together with small amounts of acicular ferrite, granular bainite, and martensite. The yield and tensile strengths of all the specimens were higher than 1000?MPa and 1150?MPa, respectively, whereas the upper shelf energy was higher than 160?J and energy transition temperature was lower than 208?K (?C65?°C) in most specimens. The slow-cooled specimens tended to have the lower strengths, higher elongation, and lower energy transition temperature than the fast-cooled specimens. The Charpy notch toughness was improved with increasing volume fraction of acicular ferrite because acicular ferrites favorably worked for Charpy notch toughness even when other low-toughness microstructures such as bainitic ferrite and martensite were mixed together. To develop high-strength bainitic steels with an excellent combination of strength and toughness, the formation of bainitic microstructures mixed with acicular ferrite was needed, and the formation of granular bainite was prevented. 相似文献
17.
18.
Mattia Franceschi Luca Pezzato Claudio Gennari Denise Hanoz Rachele Bertolini Alberto Fabrizi Marina Polyakova Katya Brunelli Franco Bonollo Manuele Dabalà 《国际钢铁研究》2023,94(9):2200821
The microstructural evolution of a novel high-silicon carbide-free bainitic steel at different austempering temperatures is investigated. The microstructure is evaluated by means of optical and electron microscopy, X-ray diffraction, microhardness, and nanohardness. Results show a variation in the amount of stabilized retained austenite changing the temperature of the isothermal treatment. In particular, it is observed an increase in the retained austenite volume fraction increasing the temperature up to 350 °C, while further increase leads to a reduction. Moreover, increasing the isothermal holding temperature from 250 °C, through 300, 350, and 370 °C, a progressive bainite coarsening and an increase in the amount of stabilized carbon-enriched retained austenite are observed. Tensile tests reveal an excellent combination of mechanical properties: mechanical strength in the range 1276–1988 MPa and total elongation 0.18–0.44. 相似文献
19.
Microstructural development and austempering kinetics of ductile iron during thermomechanical processing 总被引:1,自引:0,他引:1
A new method of refining the microstructure of austempered ductile iron (ADI) by thermome chanical processing is investigated.
Refinement of microstructure is effected by grain refinement of parent austenite by hot deformation in the austenitizing temperature
range, before the austempering treatment. The effects of austenite deformation on the kinetics of austempering reaction and
the microstructure development were studied using metallography and X-ray diffraction (XRD), at different austempering temperatures
and deformations. The process window for optimum microstructure was determined in terms of the parameters involved. Deformation
of 40 to 60 pct could be imparted in the temperature range 900 °C to 1025 °C, resulting in a reduction in the prior austenite
grain size by 35 to 50 pct and ferrite size in ausferrite by 70 to 75 pct. The effects of austenitization temperature on the
austempered microstructure were also studied. 相似文献
20.
I. Gutierrez J. Aranzabal F. Castro J. J. Urcola 《Metallurgical and Materials Transactions A》1995,26(5):1045-1060
The transformation of a ductile iron at 410 °C for different times, after austenitization for 30 minutes at 900 °C, is analyzed
in detail. Upper bainite and a high volume fraction of austenite are formed for intermediate annealing times. A certain amount
of martensite is observed after quenching not only for short transformation times but also for intermediate times. The formation
of the martensite on cooling after intermediate transformation times is due to the decrease in carbon concentration of the
retained austenite because of the homogeneous precipitation of epsilon carbides within. This homogeneous precipitation of
epsilon carbide inside austenite is unambiguously observed. The epsilon carbide, pre-precipitated in austenite, which transforms
to martensite on cooling, continues growing in the martensite after transformation. For long times of austempering at 410
°C, some complex large carbides or silicocarbides are formed, probably from the epsilon carbide, which result in the total
decomposition of austenite. 相似文献