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Influence of martensite composition and content on the properties of dual phase steels 总被引:2,自引:0,他引:2
R. G. Davies 《Metallurgical and Materials Transactions A》1978,9(5):671-679
A study has been made of the mechanical properties of dual phase (martensite plus ferrite) structures produced when Fe-Mn-C
alloys are quenched from the austenite plus ferrite phase field, so as to give a series of alloys with constant ferrite and
martensite compositions but varying percent martensites. It is found that the strength of a dual phase structure is dependent
on the ferrite grain size and the volume fraction of martensite, and is independent of the composition and strength of the
martensite. In agreement with previous work the ductility of these steels is superior to that for standard HSLA steels at
the same tensile strength. As shown in a previous paper the strength and ductility as a function of percent martensite are
in agreement with Mileiko’s theory of composites of two ductile phases. This theory and the results indicate that the superior
ductility of dual phase steels is largely a consequence of the high strength (fine grained), highly ductile (low interstitial
content) ferrite matrix. 相似文献
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DA Chuan- li YANG Geng- wei MAO Xin- ping CAI Zhen YU Chi- bin HE Xian- ling 《钢铁研究学报》2018,30(2):132-138
Isothermal transformation behavior of CSP (compact strip production) hot rolled 50CrV4 spring steel was systematically investigated by means of Thermecmastor- Z thermal simulation testing machine, OM, SEM and Vickers hardness tester. The results show that the isothermal phase transformation of austenite to ferrite and pearlite will take place when the steel is held at the temperature in the range of 680-550??. With the decrease of temperature, the phase transformation kinetics firstly accelerates and then slows, the ferrite grains and lamellar pearlite are refined, and the hardness increases gradually. When the isothermal temperature is 620??, the phase transformation completion time is 96s. Furthermore, the kinetics of transformation model is built based on the Johnson- Mehl- Avrami (JMA) theory and parameters of JMA kinetic are obtained. The time- temperature- transformation (TTT) diagrams of 50CrV4 spring steel are obtained, the results show that the calculated results agree well with the experimental measurements. 相似文献
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Itiswellknownthattheferritetransformationisacceleratedandenhancedbyaustenitedeforma tion ,especiallyinnon recrystallizationregion ,andbysubsequentcoolingwithrelativehighrate[1] .Suchprocessobviouslyrefinestheferritegrainandotherphasetransformationproductsandbecomesaneffectivewaytoimprovethepropertiesofsteel ,basedonwhichthecontrolledrollingandcontrolledcoolingtechniquegoesforwardfurther . However ,someyearsago ,itwasfoundthatthedeformationofunder cooledaustenitecaninducefer ritetransformati… 相似文献
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HAYAKAWAMotozo PEEJae-hwan 《材料与冶金学报》2005,4(2):126-126
The phase transformation from the high temperature tetragonal phase to the low temperature monoclinic phase of zirconia had been long considered to be a typical athermal martensitic transformation until it was recently identified to be a fast isothermal transformation. The isothermal nature becomes more apparent when a stabilizing oxide, such as yttria, is doped, by which the transformation temperature is reduced and accordingly the transformation rate becomes low.Thus it becomes easy to experimentally establish a C-curve nature in a TTT (Time-Temperature-Transformation) diagram. The C-curve approaches that of well known isothermal transformation of Y-TZP (Yttria Doped Tetragonal Zirconia Polycrystals), which typically contains 3mol% of Y2O3. In principle, an isothermal transformation can be suppressed by a rapid cooling so that the cooling curve avoids intersecting the C-curve in TTT diagram. Y-TZP is the case, where the stability of the metastable tetragonal phase is relatively high and thus the tetragonal phase persists even at the liquid nitrogen temperature. On the other hand, the high temperature tetragonal phase of pure zirconia can never be quenched-in at room temperature by a rapid cooling; instead it always turns into monoclinic phase at room temperature. This suggests the occurrence of an athermal transformation after escaping the isothermal transformation, provided the cooling rate was fast enough to suppress the isothermal transformation. Thus, with an intermediate yttria composition, it would be possible to obtain the tetragonal phase which is not only metastable at room temperature but athermally transforms into the monoclinic phase by subzero cooling. The objective of the present work is to show that, with a certain range of yttria content, the tetragonal phase can be quenched in at room temperature and undergoes isothermal transformation and athermal transformation depending on being heated at a moderate temperature or under-cooied below room temperature. Because both of the product phases are essentially the same monoclinic phase, both transformations are regarded as martensitic transformation, i. e. isothermal and athermal martensite. In some steels such as Fe-Mn-Ni and Fe-Ni-C, the occurrence of both isothermal and alhermal martensitic transformations has been reported. However, in these cases, the isothermal transformation occurs at temperatures slightly above the Ms (Martensite start) temperatures, and thus these transformations are considered to conform the same C-curve. On the other hand, the Ms temperature of the present material is well below the C-curve, which suggests that completely different mechanisms are controlling the kinetics of these two modes of transformations. Other aspects on these transformations are also to be reported.. 相似文献
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The phase transformation from the high temperature tetragonal phase to the low temperature monoclinic phase of zirconia had been long considered to be a typical athermal martensitic transformation until it was recently identified to be a fast isothermal transformation. The isothermal nature becomes more apparent when a stabilizing oxide, such as yttria, is doped, by which the transformation temperature is reduced and accordingly the transformation rate becomes low.Thus it becomes easy to experimentally establish a C-curve nature in a TTT (Time-Temperature-Transformation) diagram. The C-curve approaches that of well known isothermal transformation of Y-TZP (Yttria Doped Tetragonal Zirconia Polycrystals), which typically contains 3mol% of Y2O3.In principle, an isothermal transformation can be suppressed by a rapid cooling so that the cooling curve avoids intersecting the C-curve in TTT diagram. Y-TZP is the case, where the stability of the metastable tetragonal phase is relatively high and thus the tetragonal phase persists even at the liquid nitrogen temperature. On the other hand, the high temperature tetragonal phase of pure zirconia can never be quenched-in at room temperature by a rapid cooling; instead it always turns into monoclinic phase at room temperature. This suggests the occurrence of an athermal transformation after escaping the isothermal transformation, provided the cooling rate was fast enough to suppress the isothermal transformation. Thus, with an intermediate yttria composition, it would be possible to obtain the tetragonal phase which is not only metastable at room temperature but athermally transforms into the monoclinic phase by subzero cooling.The objective of the present work is to show that, with a certain range of yttria content, the tetragonal phase can be quenched in at room temperature and undergoes isothermal transformation and athermal transformation depending on being heated at a moderate temperature or under-cooled below room temperature. Because both of the product phases are essentially the same monoclinic phase, both transformations are regarded as martensitic transformation, i. e. isothermal and athermal martensite. In some steels such as Fe-Mn-Ni and Fe-Ni-C, the occurrence of both isothermal and athermal martensitic transformations has been reported. However, in these cases, the isothermal transformation occurs at temperatures slightly above the Ms (Martensite start) temperatures, and thus these transformations are considered to conform the same C-curve. On the other hand, the Ms temperature of the present material is well below the C-curve, which suggests that completely different mechanisms are controlling the kinetics of these two modes of transformations. Other aspects on these transformations are also to be reported.. 相似文献
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变形速率对普碳钢中形变诱导铁素体相变的影响 总被引:1,自引:0,他引:1
针对普通碳素钢(Q235类型),研究在Ae3~Ar3温度区间内采用形变诱导铁素体机制获得超细晶铁素体的数量与变形速率的相互关系。实验在Gleeble 1500热模拟实验机上进行。实验方案为:1000℃保温2min,以10℃/s的速度冷却到变形温度[Ae3(840℃)至Ar3(780℃)],变形量为30%~50%,变形后立即水淬。结果表明,在840℃变形时,随着变形速率的增大,形变诱导铁素体量增多;在780℃变形时,随着变形速率的增大,形变诱导铁素体量减少;而在840-780℃之间变形时,变形速率存在最佳值,在该值下诱导生成的铁素体量最大。 相似文献
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通过等温形变研究了形变参数(形变温度、形变速率、形变量)对高强度汽车钢WHT1300HF的微观组织转变和形貌的影响规律。研究结果表明:增加奥氏体等温形变量,有利于铁素体的缺陷形核,促进了形变奥氏体向铁素体转变;奥氏体的形变强化导致马氏体相变阻力增大,马氏体相变开始温度(Ms)下降,细小晶粒数量和小角度晶界数量增多;增加奥氏体等温形变(40%)速率能同时促进马氏体和铁素体相变,但马氏体体积分数和小角度晶界数量减少,细小晶粒数量略有提高;降低等温形变温度加剧奥氏体的形变强化,导致Ms温度下降,马氏体体积分数、小角度晶界比例减少,细小晶粒数量增多,铁素体含量明显增加。 相似文献
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S. F. Dirnfeld B. M. Korevaar F. Van't Spijker 《Metallurgical and Materials Transactions B》1974,5(6):1437-1444
The transformation to austenite in a fine grained tool steel has been investigated quantitatively until the disappearance
of the ferrite. The initial structure of the steel consisted of ferrite and globular carbides. The nucleation starts at carbides
which lie at the ferrite grain boundaries. The kinetics are in good agreement with Cahn's theory of grain boundary nucleated
transformation. A constant growth rate was found up to 30 pct transformation. Site saturation occurs early in the reaction;
this was confirmed by metallographic examination. The rate law is controlled by growth and is independent of the nucleation
rate. The mechanism which is controlling this growth is the advancing ferrite-austenite interface reaction. The alloying elements
influence the atomic mobilities, increasing the necessary activation energy to about 110 kcal/mol.
Formerly Research Engineer, Metallurgical Department, Delft University of Technology 相似文献
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A combination of extrusion and equal channel angular pressing (ECAP) was used to deform a plain low carbon steel. This process consists of two successive deformations by extrusion and ECAP in a single die (Ex-ECAP). Cylindrical samples were heated to predefined temperatures (650 and 850 ℃) and then pressed through a die channel with crosshead speed of 10 mm/s. Microstructure and resultant mechanical properties of processed material were studied. The results showed that pressing temperature has a significant effect on the resultant microstructure. While at 650 ℃, the cold worked structure with elongated ferrite grains were obtained, and at 850 ℃ the microstructure consisted of elongated ferrite grains and very fine grains at their boundaries as a consequence of continuous dynamic recrystallization (CDRX) of ferrite phase. Also at 850 ℃, a particular microstructure consisted of cold worked ferrite and static recrystallized grains on shear bands was obtained. 相似文献
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A high strength steel with yield strength on the order of 600 MPa was developed successfully with only addition of titanium alloying element based on a low-carbon steel.The results showed that the hot deformation accelerated ferrite and pearlite transformation and retarded bainite transformation under continuous cooling condition.The microstructure of this steel was mainly composed of fine grained ferrite and carbides distributing along the ferrite grain boundaries.The yield and tensile strengths of steels ... 相似文献
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普通C-Mn钢超细晶中厚板的带状组织 总被引:6,自引:0,他引:6
采用Gleeble2000热模拟试验机研究了普通C-Mn钢的再结晶规律,在实验室轧机上进行了C-Mn钢超细晶中板的轧制,并且在首钢中厚板厂工业轧机上进行了超细晶中厚板的工业试制,研究了工艺条件对中厚板带状组织的影响,分析了带状组织产生的机理。研究结果表明,在靠近静态相变温度Ar3附近的未再结晶区进行大变形量轧制(形变诱导相变),不仅可以使板材的铁素体晶粒细化甚至获得超细晶组织,而且普通C-Mn钢中厚板中的带状组织减轻1~2级;降低精轧开轧温度有利于减轻板材的带状组织;在未再结晶区控轧有利于减轻板材的带状组织;随着未再结晶区形变量增加,板材的带状组织减弱。 相似文献
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I. Madariaga I. Gutierrez H. K. D. H. Bhadeshia 《Metallurgical and Materials Transactions A》2001,32(9):2187-2197
The influence of time and isothermal transformation temperature on the morphology of acicular ferrite in a medium-carbon microalloyed
steel has been studied using optical and transmission electron microscopy (TEM). This study has been carried out with the
analysis of the microstructures obtained with one- and two-stage isothermal treatments at 400 °C and 450 °C, following austenitization
at 1250 °C. The heat treatments were interrupted at different times to observe the evolution of the microstructure at each
temperature. The results show that a decrease in the isothermal transformation temperature gives rise to the development of
sheaves of parallel ferrite plates, similar to bainitic sheaves, but intragranularly nucleated. These replace the face-to-edge
nucleation that dominates the transformation at higher temperatures. The TEM observations reveal that the plates correspond
to upper acicular ferrite and the sheaves to lower acicular ferrite. In this last case, cementite precipitates are present
at the ferrite unit interiors and between the different platelets. 相似文献
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Morphology and properties of low-carbon bainite 总被引:11,自引:0,他引:11
H. Ohtani S. Okaguchi Y. Fujishiro Y. Ohmori 《Metallurgical and Materials Transactions A》1990,21(3):877-888
Morphology of low-carbon bainite in commercial-grade high-tensile-strength steels in both isothermal transformation and continuous
cooling transformation is lathlike ferrite elongated in the 〈11l〉b direction. Based on carbide distribution, three types of bainites are classified: Type I, is carbide-free, Type II has fine
carbide platelets lying between laths, and Type III has carbides parallel to a specific ferrite plane. At the initial stage
of transformation, upper bainitic ferrite forms a subunit elongated in the [−101]f which is nearly parallel to the [lll]b direction with the cross section a parallelogram shape. Coalescence of the subunit yields the lathlike bainite with the [−101]f growth direction and the habit plane between (232)f and (lll)f. Cementite particles precipitate on the sidewise growth tips of the Type II bainitic ferrite subunit. This results in the
cementite platelet aligning parallel to a specific ferrite plane in the laths after coalescence. These morphologies of bainites
are the same in various kinds of low-carbon high-strength steels. The lowest brittle-ductile transition temperature and the
highest strength were obtained either by Type III bainite or bainite/martensite duplex structure because of the crack path
limited by fine unit microstructure. It should also be noted that the tempered duplex structure has higher strength than the
tempered martensite in the tempering temperature range between 200 °C and 500 °C. In the case of controlled rolling, the accelerated
cooling afterward produces a complex structure comprised of ferrite, cementite, and martensite as well as BI-type bainite.
Type I bainite in this structure is refined by controlled rolling and plays a very important role in improving the strength
and toughness of low-carbon steels.
This paper is based on a presentation made in the symposium “International Conference on Bainite” presented at the 1988 World
Materials Congress in Chicago, IL, on September 26 and 27, 1988, under the auspices of the ASM INTERNATIONAL Phase Transformations
Committee and the TMS Ferrous Metallurgy Committee. 相似文献
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I. Madariaga Ph.D. J. L. Romero I. Gutiérrez 《Metallurgical and Materials Transactions A》1998,29(13):1003-1015
The isothermal transformation vs time of a medium-carbon microalloyed steel at 450°C, following austenitization at 1250°C for 45 minutes, has been investigated
using optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). At short times, the fine
microstructure of acicular ferrite is nucleated at MnS inclusions, which are covered by a shell of a hexagonal CuS phase.
The special orientation between MnS and the CuS crystals of this shell enables the formation of a low-energy interface between
the ferrite and the inclusion with, at the same time, the ferrite satisfying one of the 24 variants of the orientation relationship
into the Bain region with austenite. As the treatment times are increased, the increase in the volume fraction of acicular
ferrite being formed raises the carbon concentration of the austenite, such that some retained austenite instead of martensite
is observed for these intermediate treatment times. This retained austenite transforms to ferrite plus carbides at long treatment
times, resulting in a final microstructure of acicular ferrite, very similar in nature to those encountered in the case of
upper bainite formation. 相似文献
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Upper acicular ferrite formation in a medium-carbon microalloyed steel by isothermal transformation: Nucleation enhancement by CuS 总被引:3,自引:0,他引:3
I. Madariaga Ph.D. J. L. Romero I. Gutiérrez 《Metallurgical and Materials Transactions A》1998,29(3):1003-1015
The isothermal transformation vs time of a medium-carbon microalloyed steel at 450 °C, following austenitization at 1250 °C for 45 minutes, has been investigated
using optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). At short times, the fine
microstructure of acicular ferrite is nucleated at MnS inclusions, which are covered by a shell of a hexagonal CuS phase.
The special orientation between MnS and the CuS crystals of this shell enables the formation of a low-energy interface between
the ferrite and the inclusion with, at the same time, the ferrite satisfying one of the 24 variants of the orientation relationship
into the Bain region with austenite. As the treatment times are increased, the increase in the volume fraction of acicular
ferrite being formed raises the carbon concentration of the austenite, such that some retained austenite instead of martensite
is observed for these intermediate treatment times. This retained austenite transforms to ferrite plus carbides at long treatment
times, resulting in a final microstructure of acicular ferrite, very similar in nature to those encountered in the case of
upper bainite formation. 相似文献