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1.
主要研究了高Al TRIP钢的显微组织与残余奥氏体的稳定性。通过光学显微镜、SEM、TEM观察了其微观组织。通过TEM观察了钢中马氏体与贝氏体的形貌。通过电子衍射斑分析,得出了残余奥氏体与马氏体的位向关系为K-S位向关系,奥氏体母相与贝氏体的位向关系为N-W位向关系。为研究残余奥氏体机械稳定性,对试验用钢进行了不同应变量的单向拉伸,用X射线测量了残余奥氏体体积分数。结果表明,真应变小于0.11时残余奥氏体体积分数随应变量增加而减少。真应变量大于0.11后,残余奥氏体体积分数随应变量增加变化不大。为了研究残余奥氏体热稳定性,将试验用钢冷却至不同的温度。发现高Al TRIP钢残余奥氏体热稳定性很高,深冷至-196℃条件下不发生马氏体转变。 相似文献
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利用扫描电镜、连续退火模拟试验机和成形试验机研究了配分温度对Q&P钢组织和成形性能的影响,结果表明,不同的配分温度会使得Q&P钢获得不同的残余奥氏体体积分数,当配分温度为300~450 ℃时,残余奥氏体的体积分数为8.79%~12.19%,次应变相同的情况下,FLC曲线的单向应变区主应变最大提升0.09,双向应变区主应变最大提升0.05,平面应变区主应变提升不显著。配分温度主要通过影响残余奥氏体体积分数使FLC曲线位置发生变化,残余奥氏体体积分数的增加提高了Q&P钢的成形性能。 相似文献
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平面应变用于评定薄钢板成形性能的研究 总被引:2,自引:0,他引:2
对大量汽车零件进行冲压成形分析,表明平面应变在零件的危险区域中是个重要因素。用两种方法测定了薄钢板的平面应变值,其结果接近,但拉伸试验法较成形极限试验简单。此外还探讨了平面应变在评定薄钢板成形性能方面的实际应用。 相似文献
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本文结合现有实验条件,采用武钢生产的08Al和WP22,进行了单向拉伸和双向拉伸(液压胀形)试验,初步探讨了双向拉伸试验方法;单向拉伸和双向拉伸受力状态下真应力与真应变之间的关系。 相似文献
9.
通过热模拟实验、光学金相及透射电镜分析观察,研究了奥氏体化条件、变形温度、变形速率、变形量以及道次间隔时间对曲轴用非调质钢C38N2轧制道次间的静态再结晶体积分数和残余应变率的影响规律.实验结果表明:随着变形温度的升高、变形速率的增大、变形量的增大或道次间间隔时间的增长,静态再结晶的体积分数逐渐升高,道次的残余应变率逐渐降低;原始奥氏体晶粒尺寸增大,静态再结晶体积分数降低,但变化不大;在1250℃以下,随着奥氏体化温度的升高,静态再结晶体积分数降低不明显,但在1250℃以上,奥氏体化温度的升高明显降低了静态再结晶体积分数.通过线性拟合以及最小二乘法,得到静态再结晶体积分数与不同变形工艺参数之间关系的数学模型;对已有残余应变率数学模型进行修正,得到含有应变速率项的残余应变率数学模型,拟合度较好. 相似文献
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研究了冷轧退火马氏体基体TRIP钢在不同预拉伸过程中残余奥氏体向马氏体的转变。为了使残余奥氏体转变充分,试验拉伸速度设定为1mm/min。对不同变形条件下的试样进行分析,通过XRD分析残余奥氏体转变的体积分数及残余奥氏体中的碳浓度,通过SEM观察拉伸断裂后的断口形貌。分析发现:残余奥氏体转变过程与应力-应变有十分密切的关系,在变形的初始阶段和试样断裂之前,残余奥氏体的转变率较均匀变形阶段要小很多;在均匀变形阶段,即在出现颈缩之前,残余奥氏体发生稳定的马氏体相变,其转变率达到最大值,此时可以有效地提高均匀伸长率;在出现颈缩之后,残余奥氏体继续发生马氏体转变,但其转变率要较均匀转变时稍低。在整个变形过程中,残余奥氏体中的碳浓度呈线性增加。在变形的始末,虽然是应力-应变的最大梯度,但奥氏体的转变率并不是最高,反而为最低。 相似文献
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TRIP sheet steels typically consist of ferrite, bainite, retained austenite, and martensite. The retained austenite is of particular importance because its deformation‐induced transformation to martensite contributes to excellent combinations of strength and ductility. While information is available regarding austenite response in uniaxial tension, less information is available for TRIP steels with respect to the forming response of retained austenite in complex strain states. Therefore, the purpose of this work was to study the austenite transformation behaviour in different strain paths by determining the amount of retained austenite before and after forming. Forming experiments were performed on a high strength 0.19C‐1.63Si‐1.59Mn TRIP sheet steel 1.2 mm in thickness in two different strain conditions, uniaxial tension (ε1 = ‐2ε2) and balanced biaxial stretching (ε1 = ε2). Specimens were formed to strains ranging from zero to approximately 0.2 effective (von Mises) strain. Specimens were tested both longitudinally and transverse to the rolling direction in uniaxial tension, and subtle mechanical property differences were found. The volume fraction of austenite, determined with X‐ray diffraction subsequent to forming, was found to decrease with increasing strain for both forming modes. Some modification in the crystallographic texture of the ferrite was observed with increasing strain, in specimens tested in the balanced biaxial stretch condition. This trend was not evident in the uniaxial tensile test results. Slight differences were found in the transformation behaviour of the austenite when formed in different strain conditions. More austenite transformed in specimens tested parallel to the rolling direction than transverse to the rolling direction in uniaxial tension. The amount of austenite transformed during biaxial stretching was determined to be greater than the amount transformed in uniaxial tension for specimens tested transverse to the rolling direction at an equivalent von Mises strain. The amount of austenite that transformed in biaxial tension, however, was comparable to the amount of austenite that transformed in specimens tested longitudinal to the rolling direction in uniaxial tension. 相似文献
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A. M. Streicher-Clarke J. G. Speer D. K. Matlock D. L. Williamson B. C. DeCooman 《Metallurgical and Materials Transactions A》2005,36(4):907-918
Austenite and ferrite lattice parameters were monitored using X-ray diffraction subsequent to deformation in uniaxial and
biaxial tension and plane straining of a 0.19C-1.63Si-1.59Mn transformation-induced plasticity (TRIP) sheet steel. Details
from peak position results suggest the presence of stacking faults in the austenite phase, especially after deformation in
uniaxial tension. The results also indicate residual stress or composition effects (through changes in the average carbon
concentration due to selective transformation of lower carbon regions of austenite). Compressive residual stresses in the
ferrite matrix were measured, and found to increase with increasing effective strain in specimens tested in biaxial tension
and plane strain. Strain partitioning between softer ferrite and harder austenite (and possibly bainite or martensite) may
be responsible for these residual compressive stresses in the ferrite, although volume expansion from the γ → α′ transformation and texture gradients through the sheet thickness are also possible contributors. 相似文献
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���±����Ž����������ŷ壬��ΰ������� 《钢铁研究学报》2015,27(11):54-59
Forming limit diagram (FLD) of cold- rolled TRIP steel was established by experiments. The microstructures of samples before and after deformation were examined by metalloscopy and scanning electron microscopy and at the same time the contents of retained austenite after different strain ratios were measured by X- ray diffraction. The results show that the ultimate strain under plane strain state(FLD0) is 0. 397. With the strain ratio increasing, strain path changes from uniaxial stretching to plane strain and then biaxial stretching and the transformation amount of residual austenite increases gradually. Compared with dual- phase steel, the higher FLD0of TRIP steel is ascribed to TRIP effect and necking area is wider during deformation. 相似文献
14.
A metallographic study has been made of the microstructures produced by room temperature deformation of 0.6mm thick commercially
pure titanium sheet metal in uniaxial, plane strain and biaxial tension. Deformation twinning becomes increasingly important
as the deformation mode changes from uniaxial through plane strain to equibiaxial tension, and is more significant for strain
transverse to the rolling direction than for strain in the longitudinal direction. In uniaxial tension, 1122 twins are dominant
in longitudinal straining, while 1012 twins dominate in transverse straining. In plane strain and equibiaxial straining, 1012
twinning is suppressed and largely replaced by 1122 twinning. The observed changes in twin occurrence and type are attributed
to the interaction of the imposed stress system and the crystallographic texture of the rolled sheet, which alters the distribution
of the grain basal-plane poles with respect to the operative stress axes. In uniaxial tension parallel to the longitudinal
direction, twins favored by ‘c’ axis compression are produced, while in the transverse direction twins favored by ‘c’ axis
tension appear. In plane strain and biaxial tension the dominant stress is through-thickness compression, which produces twins
favored by ‘c’ axis compression in nearly all cases. The alterations in twin orientation and numbers are associated with changes
in stress-strain behavior. As twin volume fraction increases and twins are aligned more closely to the principal stress axis,
the instantaneous work-hardening rate tends to stabilize at a nearly constant value over a large strain range.
Formerly Chief Metallurgist, The APV Company. 相似文献
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Jon Scott Michael Miles David Fullwood Brent Adams Ali Khosravani Raja K. Mishra 《Metallurgical and Materials Transactions A》2013,44(1):512-516
Failure mechanisms were studied in wrought AZ31B magnesium alloy after forming under different strain paths. Optical micrographs were used to observe the shear band formation and regions of high twin density in samples strained under uniaxial, biaxial, and plane strain conditions. Interrupted testing at 4?pct effective strain increments, until failure, was used to observe the evolution of the microstructure. The results showed that shear bands, with a high percentage of twinned grains, appeared early in the samples strained under biaxial or plane strain tension. These bands are similar to those seen in uniaxial tension specimens just prior to failure where the uniaxial tensile ductility was much greater than that observed for plane strain or biaxial tension conditions. A forming limit diagram for AZ31B, which was developed from the strain data, showed that plane strain and biaxial tension had very similar limit strains; this contrasts with materials like steel or aluminum alloys, which typically have greater ductility in biaxial tension compared to plane strain tension. 相似文献
16.
《钢铁研究学报(英文版)》2017,(11)
Based on uniaxial tensile and plane strain deformation tests,the effects of strain states on the stability of RA(retained austenite)in medium Mn steels,which were subjected to IA(intercritical annealing)and QP(quenching and partitioning)processing,were investigated.The volume fractions of RA before and after deformation were measured at different equivalent strains.The transformation behaviors of RA were also investigated.The stability of RA differed across two different transformation stages at the plane strain state:the stability was much lower in the first stage than in the second stage.For the uniaxial tension strain state,the stability of RA corresponded only to a single transformation stage.The main reason was that there were two types of transformations from RA in the medium Mn steel for the plane strain state.One type was that the martensite originated in the strain-induced stacking faults(SISF).The other type was the strain-induced directly twin martensite at a certain equivalent strain.However,for the uniaxial tension state,only the strain-induced twin martensite was observed.Dislocation lines and dislocation tangles were also observed in specimens deformed at different strain states.In addition,complex microstructures of stacking faults and lath-like phases were observed within a grain at the plane strain state. 相似文献
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P. J. Jacques F. Delannay J. Ladrière 《Metallurgical and Materials Transactions A》2001,32(11):2759-2768
The mechanical stability of dispersed retained austenite, i.e., the resistance of this austenite to mechanically induced martensitic transformation, was characterized at room temperature
on two steels which differed by their silicon content. The steels had been heat treated in such a way that each specimen presented
the same initial volume fraction of austenite and the same austenite grain size. Nevertheless, depending on the specimen,
the retained austenite contained different amounts of carbon and was surrounded by different phases. Measurements of the variation
of the volume fraction of untransformed austenite as a function of uniaxial plastic strain revealed that, besides the carbon
content of retained austenite, the strength of the other phases surrounding austenite grains also influences the austenite
resistance to martensitic transformation. The presence of thermal martensite together with the silicon solid-solution strengthening
of the intercritical ferrite matrix can “shield” austenite from the externally applied load. As a consequence, the increase
of the mechanical stability of retained austenite is not solely related to the decrease of the M
s temperature induced by carbon enrichment. 相似文献
18.
70-30 brass tubes have been tested in combinations of tension/internal pressure and in pure torsion. The flow properties,
from these loading conditions, were measured from yield until local necking. We found that the pure hoop tension, plane strain,
and torsion flow curves were 15 pct lower than those in uniaxial tension and balanced biaxial tension when compared on the
basis of a von Mises effective stress-strain criterion. Microstructures, at a von Mises strain of 0.4, were examined; no differences
were observed between plane strain, torsion, and uniaxial tension deformation modes. Based on the microstructural measurements,
we estimate that at most 13 pct of the deformation at an effective strain of 0.40 was by twinning. The initial texture and
final textures, after balanced biaxial and uniaxial tension, were measured by pole figure analysis. The initial texture was
qualitatively consistent with measured flow stress levels of the axisymmetric deformation modes (uniaxial tension, balanced
biaxial tension, and hoop tension). A crystallographic effective stress-strain criterion was also applied to the torsion data.
This method of analysis gave results which were better than the von Mises criterion. 相似文献
19.
Aytekin Polat 《国际钢铁研究》2012,83(8):775-782
In the present study, the influences of temperature and strain rate on the deformation behavior of cold‐rolled TRIP800 steel were investigated. Microstructural observation and tensile tests were performed and volume fractions of retained austenite were measured at various temperatures and strain rates. The results reveal that both temperature and strain rate affect the volume fractions of retained austenite that transforms into martensite. The strain‐induced transformation of retained austenite is retarded with increasing temperature and the retained austenite becomes more stable against straining. The amount of retained austenite that transforms into martensite is not influenced significantly by strain rate. The variation in mechanical properties with temperature and strain rate was related to the effects of dynamic strain aging, tempering of banite, high temperature softening, and the volume fractions of retained austenite. 相似文献
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Deformation affects the microstructure and morphology of the parent austenite, which affects the subsequent bainite transformation. The effects of ausforming on bainite transformation and microstructure were investigated by means of thermal simulation experiment, TEM and SEM etc. Different deformation temperatures and deformation strains were designed. The amount of bainitic transformation during isothermal holding and the volume fraction of retained austenite at room temperature were analyzed. The results show that the isothermal bainitic transformation is promoted by the deformation at 300?? and 400??. Moreover, the lower deformation temperature leads to larger amount of bainite. In addition, the volume fraction of retained austenite increases with the increase of the deformation strain, and more retained austenite can be obtained by decrease the deformation temperature. It indicates that deformation at lower temperature contributes to the mechanical stabilization of austenite. 相似文献