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1.
A. Piñol-Juez A. Iza-Mendia I. Gutiérrez 《Metallurgical and Materials Transactions A》2000,31(6):1671-1677
In the present work, the mechanical properties and the microstructural evolution of a duplex stainless steel in the as-cast
and wrought conditions during deformation under hot-working conditions have been studied. Hot torsion tests, at strain rates
of
= 1 s−1, have been carried out using prepolished samples on which surface parallel scratches have been practiced. The observation
of the surface of the samples shows a large displacement of the scratches produced by two different mechanisms, sliding on
the δ/γ interface, and shearing of the ferrite. The displacements in the as-cast condition have been found to concentrate in a reduced
set of ferrite/austenite interfaces leading to the formation of cracks along them. In the wrought material, the distribution
of the sliding is more homogeneous over all the ferrite/austenite interfaces, and no damage has been produced. These behavioral
differences between both materials have been related in the present work, to the characteristics of the corresponding microstructures,
to the spatial phase distribution, and to the nature of the ferrite/austenite interface, among others. 相似文献
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A determination of stacking fault energy (SFE) of the austenite phase of a duplex stainless steel, material no. 1.4462, has been carried out using transmission electron microscopy (TEM). Furthermore, cold rolling tests and microstructural analysis have been realized in order to allow a detailed discussion of the obtained SFE-values. The results of this Investigation indicate that the stacking fault energy of the austenite phase within the duplex stainless steel Is lower than those of single-phase austenitic stainless steels. This is justified by the chemical composition; mainly by the Cr and Ni alloying contents. Nevertheless, work hardening of the austenite during cold deformation is not as accentuated as expected by the low SFE-values, because at higher deformation levels the deformation mainly occurs within the ferrite phase. 相似文献
4.
《Acta Metallurgica Materialia》1993,41(12):3421-3434
The transformation interfaces of pearlite, allotriomorphic cementite, M23C6, and Widmanstätten cementite plates in high-Mn high-C alloy steels have been studied by TEM. Linear striations in the interface have been analysed and related to intersections with stacking faults in the parent austenite phase. Emphasis is given to the pearlite interface where it is found that the striations at the interface increased as a result of thermomechanical treatment of the austenite prior to isothermal transformation, consistent with an increased density of planar defects. The effect of heat treatment, and Si alloying additions, are also considered. Both conventional and in situ TEM of the pearlite interface showed that the linear defects stretched across both ferrite and cementite phases at the pearlite interface, apparently without any deviation or change in image contrast. The results are compared with similar ones made of the static γ/α interphase boundaries in duplex stainless steel. The effect of prior deformation structure in the parent austenite on the growth and interface structure of Widmanstätten cementite plates has also been considered. 相似文献
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The present investigation is concerned with modeling of the microstructure evolution in duplex stainless steels under thermal
conditions applicable to welding. The important reactions that have been modeled are the dissolution of austenite during heating,
subsequent grain growth in the delta ferrite regime, and finally, the decomposition of the delta ferrite to austenite during
cooling. As a starting point, a differential formulation of the underlying diffusion problem is presented, based on the internal-state
variable approach. These solutions are later manipulated and expressed in terms of the Scheil integral in the cases where
the evolution equation is separable or can be made separable by a simple change of variables. The models have then been applied
to describe the heat-affected zone microstructure evolution during both thick-plate and thin-plate welding of three commercial
duplex stainless steel grades: 2205, 2304, and 2507. The results may conveniently be presented in the form of novel process
diagrams, which display contours of constant delta ferrite grain size along with information about dissolution and reprecipitation
of austenite for different combinations of weld input energy and peak temperature. These diagrams are well suited for quantitative
readings and illustrate, in a condensed manner, the competition between the different variables that lead to structural changes
during welding of duplex stainless steels. 相似文献
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Luis E. Hernandez‐Castillo John H. Beynon Christophe Pinna Sybrand van der Zwaag 《国际钢铁研究》2005,76(2-3):137-141
A modified microgrid technique has been applied to a laboratory‐made duplex stainless steel, to experimentally simulate the local state of deformation of the austenite‐ferrite microstructure of low‐alloy steels subject to intercritical deformation. A sample containing such a microgrid was deformed by plane strain compression at high temperature under conditions representative of hot rolling processes. The distortion of the microgrid after hot deformation revealed, in a quantifiable manner, the plastic flow of both phases and different deformation features. The micro‐strain distributions measured can be used to validate the models predicting the hot deformation of low alloyed C‐Mn steels during intercritical rolling. 相似文献
9.
研究了四种不同N含量的18Mn18Cr N不锈钢的凝固模式、显微组织和元素分布.结果表明:N含量影响18Mn18Cr N合金系的凝固模式和显微组织.氮的质量分数由0.07%增加至0.72%时,实验钢的凝固模式由F模式转变为A模式,显微组织由铁素体和奥氏体魏氏两相组织转变为铁素体和奥氏体两相组织以及单相奥氏体组织.N含量影响奥氏体相形貌,随N含量增加,奥氏体由板条状、针状转变为枝晶间和等轴状.枝晶间和等轴状奥氏体晶粒中存在褶皱形貌,且随着氮含量增加,褶皱数量增多.褶皱的产生与凝固过程中奥氏体相内部Fe、Mn、Cr元素的偏析有关,且该凝固偏析被保留至室温组织中. 相似文献
10.
为研究热变形参数对铸态超级双相不锈钢S32750热变形行为和显微组织的影响,运用Gleeble-3800热模拟试验机对S32750进行不同温度和应变速率下的高温拉伸和压缩试验。结果表明,S32750在1000~1200℃范围内具有较好的热塑性。在变形温度较低、应变速率较低时,流变曲线表现出不同于单相不锈钢的“类屈服平台”特征;当应变速率较高或变形温度较高、应变速率较低时,流变曲线为典型的动态再结晶特征。微观组织演变显示,铁素体和奥氏体两相都发生动态再结晶,且铁素体的再结晶先于奥氏体。降低应变速率,提高变形温度,可促进动态再结晶发生。基于热变形动力学模型建立了本构方程,表观应力指数为3.99,热变形激活能为393.75kJ/mol。S32750的高温软化机制与Zener-Hollomon(Z)参数有关,随Z参数增加,热变形峰值应力增加。 相似文献
11.
《Acta Metallurgica Materialia》1991,39(3):273-285
A thermodynamic analysis which is capable of estimating the austenite/ferrite equilibria in duplex stainless steels has been carried out using the sublattice thermodynamic model. The partitioning of alloying elements between the austenite and ferrite phases has been calculated as a function of temperature. The results showed that chromium partitioning was not influenced significantly by the temperature. The molybdenum, on the other hand, was found to partition preferentially into ferrite phase as the temperature decreases. A strong partitioning of nickel into the austenite was observed to decrease gradually with increasing temperature. Among the alloying elements, average nitrogen concentration was found to have the most profound effect on the phase balance and the partitioning of nitrogen into the austenite. The partitioning coefficient of nitrogen (the ratio of the mole fraction of nitrogen in the austenite to that in the ferrite) was found to be as high as 7.0 around 1300 K. Consequently, the volume fraction of austenite was influenced by relatively small additions of nitrogen. The results are compared with the experimentally observed data in a duplex stainless steel weld metal in conjunction with the solid state δ → δ + γ phase transformation. Particular attention was given to the morphological instability of grain boundary austenite allotriomorphs. A compariso between the experimental results and calculations indicated that the instability associated with irregular austenite perturbations results from the high degree of undercooling. The results suggest that the model can be used successfully to understand the development of the microstructure in duplex stainless steel weld metals. 相似文献
12.
经济型双相不锈钢的研发进展 总被引:1,自引:0,他引:1
经济型双相不锈钢是一种高性能低成本的氮合金化不锈钢新材料,具有典型的铁素体-奥氏体双相组织。利用氮取代镍元素的奥氏体化作用,降低成本的同时获得优良的力学性能和耐腐蚀性能。介绍了经济型双相不锈钢的发展历史,重点讨论了合金元素和热处理对相变、力学性能和耐腐蚀性能的影响规律,并与304和316进行对比;同时,分析了经济型双相不锈钢焊接性能和焊接工艺的研究进展。经济型双相不锈钢S32101、S32003、S32202等,已用于核电、桥梁、建筑、热交换器等行业,取代传统奥氏体不锈钢AISI 304和316。由于经济型双相不锈钢具有高强度和优良耐蚀性,同时镍、钼等贵金属的含量都较低,已成为未来不锈钢发展的方向之一。 相似文献
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将316L奥氏体不锈钢粉末与430铁素体不锈钢粉末分别按照80:20、65:35、50:50质量比混合, 采用冷等静压成型方法制备了双相不锈钢, 研究了奥氏体和铁素体起始粉末质量比对双相不锈钢组织结构和力学性能的影响。结果表明: 当奥氏体和铁素体起始粉末质量比为65:35, 烧结温度1350℃, 保温时间60min时, 双相不锈钢综合力学性能较好, 其中, 抗拉强度为847MPa, 屈服强度为281MPa, 硬度为HV207, 断后伸长率为37.5%。 相似文献
15.
M. B. Cortie E. M. L. E. M. Jackson 《Metallurgical and Materials Transactions A》1997,28(12):2477-2484
The precipitation of sigma phase within the ferrite component of a duplex stainless steel has been simulated using a two-dimensional
computer model which takes into account the partitioning of alloy elements between ferrite and austenite. The model is based
on a cellular automaton and, despite having a rather simple set of transition rules, is able to simulate changes in the volume
fractions of the austenite, ferrite, and sigma phases. The microstructures produced are similar in appearance to those in
the real system. Comparison of the model and the real system may assist in the assessment of the various phenomena occurring.
Use is made of the model to examine many of the factors that might conceivably be harnessed to retard precipitation of the
sigma phase in duplex stainless steels. 相似文献
16.
Influence of microstructure on the flow behavior of duplex stainless steels at high temperatures 总被引:1,自引:0,他引:1
O. Balancin W. A. M. Hoffmann J. J. Jonas 《Metallurgical and Materials Transactions A》2000,31(5):1353-1364
Three kinds of duplex stainless steel, with different ferrite-to-austenite ratios, were deformed in torsion over the temperature
range 900 °C to 1200 °C; the corresponding microstructural evolution was observed and correlated with the deformation conditions.
The shapes of the high-temperature flow curves depend strongly on the volume fractions of the phases, the characteristics
of the ferrite-austenite interface, and the active softening mechanism. At low volume fractions of austenite, the mechanical
behavior is determined by the ferrite matrix and the flow curves are typical of materials that soften by continuous dynamic
recrystallization. When the volume fraction of austenite is increased, coherent γ particles distributed within the grains and at the grain boundaries hinder the deformation of the softer α matrix, increasing both the yield and the peak stress. These peaked flow curves are characterized by rapid work hardening
followed by extensive flow softening; under these conditions, the hard austenite particles become aligned with the deformation
direction after large strains. At high volume fractions of austenite (∼50 pct), the material tends to form a duplex structure,
with the flow curves displaying extended work-hardening and work-softening regions; however, a drastic decrease is observed
in ductility because of the dissimilar plastic behaviors of the two phases. 相似文献
17.
《Baosteel Technical Research》2010,(Z1):123
Super duplex stainless steels(SDSS) show complex precipitation and transformation behavior during heat treatment processes,which affects both mechanical and corrosion properties. This report presents some data on the microstructures that develop after folding and subsequent precipitation during heat treatment of UNS S32750 SDSS sheet samples.The microstructural and textural changes have been followed using SEM/EBSD techniques.Upon folding,both a texture and strain gradient form in the folded/bent region,subsequent heat treatment at 845℃results in the ferrite phase to transform to sigma,austenite and chi phases.Transformation was found to be accelerated by strain.Complete transformation of the ferrite phase occurred within half the annealing time required in the unstrained regions.The local mis-orientations in the ferrite and austenite phases reduced during annealing,however,the reduction in the austenite was not very high and a significant amount remained even after the longest annealing time.The texture components that developed during the folding process remained unchanged even after one hour annealing at 845℃.The implication of these findings could have a bearing on the formation of sigma phase during welding of SDSS that may have residual stresses introduced during final processing. 相似文献
18.
Mohammad Moallemi Abbas Zarei-Hanzaki Mostafa Eskandari Andrew Burrows Hossein Alimadadi 《Metallurgical and Materials Transactions A》2017,48(8):3675-3691
A new metastable Ni-free duplex stainless steel has been designed with superior plasticity by optimizing austenite stability using thermodynamic calculations of stacking fault energy and with reference to literature findings. Several characterization methods comprising optical microscopy, magnetic phase measurements, X-ray diffraction (XRD) and electron backscattered diffraction were employed to study the plastic deformation behavior and to identify the operating plasticity mechanisms. The results obtained show that the newly designed duplex alloy exhibits some extraordinary mechanical properties, including an ultimate tensile strength of ~900 MPa and elongation to fracture of ~94 pct due to the synergistic effects of transformation-induced plasticity and twinning-induced plasticity. The deformation mechanism of austenite is complex and includes deformation banding, strain-induced martensite formation, and deformation-induced twinning, while the ferrite phase mainly deforms by dislocation slip. Texture analysis indicates that the Copper and Rotated Brass textures in austenite (FCC phase) and {001}〈110〉 texture in ferrite and martensite (BCC phases) are the main active components during tensile deformation. The predominance of these components is logically related to the strain-induced martensite and/or twin formation. 相似文献
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