共查询到20条相似文献,搜索用时 953 毫秒
1.
A. Munitz 《Metallurgical and Materials Transactions B》1987,18(3):565-575
The effect of cooling rates on the microstructure of Fe−Cu alloys was investigated. A variety of solidification techniques
was employed, in order to obtain a wide range of cooling rates. At high cooling rates (about 104 K/sec), and in the composition range 30 to 80 wt pct Cu, the microstructures showed clear evidence of metastable liquid separation.
This indicates a melt supercooling of about 50 to 100 K. Liquid separation coupled with high interfacial velocities resulted
in solute trapping, and in a spherical morphology for one of the solids. At cooling rates lower than 104 K/sec no liquid separation was observed, and the alloys solidified in a conventional manner,i.e., with a polycrystalline or a dendritic microstructure, depending on the Cu content. The type of the γ-Fe to α-Fe solid state
transformation, taking place during cooling after solidification, depends on the cooling rates as well as on the Cu content
in the γ-Fe phase. At medium cooling rates the transformation is martensitic, while at low or high cooling rates a polycrystalline
transformed structure is obtained.
A. MUNITZ, formerly Visiting Research Associate at the University of Florida at Gainesville, FL 32611 相似文献
2.
Characterization of the peritectic reaction in medium-alloy steel through microsegregation and heat-of-transformation studies 总被引:2,自引:0,他引:2
Brij K. Dhindaw Tomas Antonsson Hasse Fredriksson Jose Tinoco 《Metallurgical and Materials Transactions A》2004,35(9):2869-2879
In the present work, the phenomenon of the peritectic reaction was characterized in a medium-alloy steel. Several directional
solidifcation and thermal-analysis experiments were done to investigate the reaction process. Directional solidification experiments
carried out did not tend to show any direct evidence of a peritectic reaction. Microsegregation studies on the directionally
solidified samples and those solidified under isothermal conditions bring out some interesting features. It has been documented
that if the segregation ratio for Ni is higher than that for Cr, there is a correlation that the peritectic reaction had occurred
in that region. On the other hand, a higher Cr segregation ratio as compared to Ni showed the possibility that the liquid
had directly transformed to γ-austenite without undergoing a peritectic reaction. Measurement of energies of transformations and the analysis of their
values in different segments of the cooling-curve differential thermal analysis (DTA) experiments have helped in understanding
the peritectic reaction. It is revealed that the transformation is more like diffusionless transformation, where γ-austenite directly precipitates from δ-ferrite. Indeed, this proposition is also supported by the segregation patterns for Cr and Ni obtained in the solidified
samples of this steel during directional solidifcation and DTA experiments and also by calculations to show the presence of
enough lattice defects or vacancies to aid the aforementioned transformation. 相似文献
3.
在钢的凝固过程中冷却速率对钢的相变具有不可忽视的影响。本研究采用Thermo-calc热力学软件,模拟计算了含Al 3.52%(质量分数)的δ铁素体相变诱导塑性(δ-TRIP)钢的相转变过程,并分别使用差示扫描量热法(DSC)和Ohnaka微观偏析模型,分析了不同冷却速率对3.52%Al δ-TRIP钢凝固过程中的包晶相变温度,以及溶质元素偏析的影响。结果表明,冷却速率越小,DSC试验所得的相变温度越接近Thermo-calc计算的热力学平衡值。随着冷却速率从10、30增加到50 ℃·min–1,L→L+δ的转变温度降低,L+δ→L+δ+γ和L+δ+γ→δ+γ的转变温度先降低后升高,前者主要受过冷度的影响,后者主要受元素偏析的影响。冷却速率对C、Mn、S的偏析影响很小,对Si、P、Al的偏析影响较大,并且随着冷却速率的增加,Si、P、Al偏析程度增加。Si和P的偏析会小幅度延缓包晶反应的进程;Al对改变包晶反应进程作用明显,随着冷却速率的增加,包晶反应区域逐渐下移,且下移趋势渐缓。 相似文献
4.
The FeS-MnS system is reexamined, both with and without excess iron. When excess iron is present, as is true for sulfide inclusions
within steel, the pseudobinary reveals a peritectic rather than the previously assumed eutectic invariant. The maximum solubility
limits (997 ± 3°C, or 1270 K) in the two solid phases are: a) 7.5 wt pct MnS in FeS, and b) 73.5 wt pct FeS in MnS. The peritectic
liquid contains 66 wt pct Fe, ∼34 wt pct S, and ∼0.4 wt pct Mn. The two solid sulfide phases are nearly stoichiometric in
the presence of excess iron; the Fe-richer sulfide is metal-deficient in the absence of a metallic iron phase. Based on this
study, it is possible to be more specific than heretofore about the Fe-FeS-MnS-Mn region of the Fe-Mn-S ternary. In addition
to the presence of a peritectic, it was concluded that the miscibility gap does not cross the univariant line between primary
metal and (Mn,Fe)S phases. The peritectic liquid and the Mn-richer solid sulfide equilibrate with a metal containing ≤ 0.36 wt pct Mn. These
data help explain the Mn/s ratios required to avoid hot-shortness in regular and resulfurized plain-carbon steels.
G. S. MANN, formerly Graduate Student
This is a part of the dissertation submitted by G. S. Mann for his Ph.D. at the University of Michigan 相似文献
5.
The droplet emulsion technique, which involves dispersal of a bulk liquid alloy into a collection of fine droplets (5 to 30μm), was applied to Sn-Sb alloys to yield high levels of controlled undercooling. The maximum undercooling levels achieved
varied from 179 °C for pure Sn to 113 °C for a Sn-16 at. pct Sb alloy. Analysis of hypoperitectic alloy samples (alloys with
an Sb content less than that of the liquid at the peritectic temperature) indicates that solute trapping occurs during solidification
at the levels of undercooling and cooling rate investigated, yielding nearly homogeneousβ-tin solid solutions with compositions approaching those of the bulk alloys. With increasing undercooling and/or cooling rate,
hyperperitectic alloys exhibit a transition from a highly segregated structure consisting of faceted primary intermetallic
phase and cellularβ to a structure consisting primarily of a supersaturated tin-rich solid solution. Lattice constant measurements confirm that
virtually complete supersaturation ofβ-tin was achieved in emulsion samples cooled at 200 °C ss−1 for compositions up to approximately 20 at. pct Sb. The development and characteristics of subsequent solid-state precipitation
were used to guide the interpretation of the often complex solidification reaction sequences in the hyperperitectic alloys.
The formation of supersaturatedβ-tin solid solutions in the undercooled samples is related to the appropriate metastable phase equilibria and the development
of solute trapping.
Formerly Graduate Student, Department of Materials Science and Engineering, University of Wisconsin-Madison 相似文献
6.
为了从凝固及相变特性角度解决微合金钢连铸坯表面裂纹问题,建立了与合金化相关联的初始凝固包晶反应度模型、奥氏体晶粒长大模型、铁素体转变量模型以及碳氮化物的析出模型。结合铸坯实际冷却条件,进一步建立了包晶反应度预测、初生奥氏体晶粒长大、铁素体转变、析出相析出等对铸坯表面裂纹敏感性的预测模型。针对某J55钢连铸板坯,奥氏体晶粒尺寸超过1 mm、铁素体析出量为10%、二次相析出量增加时,横裂纹敏感性最大。表面裂纹敏感性预测模型有助于实现基于成分微调和组织调控的微合金钢连铸、热装等生产过程表面裂纹控制技术。 相似文献
7.
N. Liu F. Liu L. M. Lu X. Y. Gao X. J. Wang 《Metallurgical and Materials Transactions B》2014,45(3):815-820
Adopting a fluxing purification and cyclic superheating technique, Co-10 wt pct Si and Co-15 wt pct Si alloys had been undercooled to realize rapid solidification in this work. It was investigated that the solidification modes and microstructures of Co-Si alloys were deeply influenced by the undercooling of the melts. Both alloys solidified with a near-equilibrium mode in a low undercooling range; the peritectic reaction occurred between the primary phase and the remnant liquids, and it was followed by the eutectic reaction and eutectoid transformation. With the increase of undercooling, both alloys solidified with a nonequilibrium mode, and the peritectic reaction was restrained. As was analyzed, a metastable Co3Si phase was found in Co-10 wt pct Si alloy when a critical undercooling was achieved. 相似文献
8.
9.
After the nucleation and sedimentation of primary Fe-rich phases, the microstructures of Al-11.5Si-0.4Mg cast alloys with
0.35–1.03Fe and 0.18–0.59Mn have been studied to investigate the solidification characteristics of Fe-rich phases. Depending
on the iron and manganese contents as well as cooling rates, Fe-rich phases may solidify as predendritic (primary), pre-eutectic,
coeutectic, and posteutectic intermetallics at the different stages of solidification through three types of reactions: (1)
predendritic (primary), (2) eutectic, and (3) peritectic reactions. It seems that Fe-rich phases may nucleate on the wetted
sides of double oxide films, while the gap of the dry sides of oxide films constitutes the cracks commonly observed in the
Fe-rich phases and aluminum matrix. Conventional metallurgical observations also suggest that the Fe-rich phases nucleated
early during the solidification might act as nuclei for those formed subsequently, although it has not been ruled out that
these phases may share the same oxide substrates. It is probable that these nucleation events may all work as suggested in
the possible nucleation hierarchy for Al-11.5Si-0.4Mg cast alloys. 相似文献
10.
11.
Junfeng Xu Feng Liu Xiaolong Xu Yuzeng Chen 《Metallurgical and Materials Transactions A》2012,43(4):1268-1276
A new method to determine directly the solid fraction using the cooling curve was proposed for solidification of undercooled
melts. Then, to construct three different baselines, a sudden function ξ
α
(x) is introduced. In terms of the ξ
α
(x) function, accordingly, the solid fractions during solidification of Ni-3.3 wt pct B, Al-7 wt pct Si, Al-14 wt pct Cu, and
Fe-4.56 wt pct Ni alloys were predicted. The predictions of the primary, the regular lamellar eutectic, the anomalous eutectic,
and the peritectic phases from cooling curves of the solidified samples coincide with the results of measurement or the available
methods. 相似文献
12.
Thermal analysis during solidification of ZA8 alloy against copper, hot die steel and stainless steel chills instrumented with thermocouples was carried out in the present work. The investigation showed that the chill material and coating had a significant effect on the cooling curve of the casting. When casting was solidified against chills, the liquidus and eutectic start temperature of the casting remained nearly the same whereas eutectoid transformation occurred at a higher temperature. Cooling rate curve of the casting solidified against coated chill indicated that formation of solid shell and subsequent re-melting in the case of high thermal conductivity coated chill whereas in lower thermal conductivity coated chill, the re-melting of solid shell was absent. It was found that chilling during solidification causes the morphology of dendrites transform to nearly rounded shape with refinement of lamellar eutectic. 相似文献
13.
Macro-microscopic models have been developed to describe the macrosegregation behavior associated with the peritectic reaction
of low carbon steel. The macrosegregation model has been established on the basis of previously published work and experimental
data. A microscopic model of a three-phase reaction L+δ→γ has been modeled by using Fredriksson’s approach. Four horizontal and unidirectional solidified experimental groups simulating
continuous casting have been performed with a low carbon steel containing 0.13 wt pct carbon. The extent of macrosegregation
of carbon was determined by wet chemical analysis of millings. It is confirmed, by comparing calculated results with experimental
results, that this model successfully predicts the occurrence of macrosegregation. The results indicate that a peritectic
reaction which is associated with a high cooling rate generates high thermal contraction and a high tensile strain rate at
the peritectic temperature. Therefore, the macrosegregation, particularly at the ingot surface, is very sensitive to the cooling
rate, where extremely high positive segregation was observed in the case of a high cooling rate. However, in the case of slow
cooling rate, negative segregation was noted. The mechanism of macrosegregation with peritectic reaction is discussed in detail. 相似文献
14.
Effects of Undercooling and Cooling Rate on Peritectic Phase Crystallization Within Ni-Zr Alloy Melt
The liquid Ni-16.75 at. pct Zr peritectic alloy was substantially undercooled and containerlessly solidified by an electromagnetic levitator and a drop tube. The dependence of the peritectic solidification mode on undercooling was established based on the results of the solidified microstructures, crystal growth velocity, as well as X-ray diffraction patterns. Below a critical undercooling of 124 K, the primary Ni7Zr2 phase preferentially nucleates and grows from the undercooled liquid, which is followed by a peritectic reaction of Ni7Zr2+L → Ni5Zr. The corresponding microstructure is composed of the Ni7Zr2 dendrites, peritectic Ni5Zr phase, and inter-dendritic eutectic. Nevertheless, once the liquid undercooling exceeds the critical undercooling, the peritectic Ni5Zr phase directly precipitates from this undercooled liquid. However, a negligible amount of residual Ni7Zr2 phase still appears in the microstructure, indicating that nucleation and growth of the Ni7Zr2 phase are not completely suppressed. The micromechanical property of the peritectic Ni5Zr phase in terms of the Vickers microhardness is enhanced, which is ascribed to the transition of the peritectic solidification mode. To suppress the formation of the primary phase completely, this alloy was also containerlessly solidified in free fall experiments. Typical peritectic solidified microstructure forms in large droplets, while only the peritectic Ni5Zr phase appears in smaller droplets, which gives an indication that the peritectic Ni5Zr phase directly precipitates from the undercooled liquid by completely suppressing the growth of the primary Ni7Zr2 phase and the peritectic reaction due to the combined effects of the large undercooling and high cooling rate. 相似文献
15.
Kinetics of the peritectic phase transformation: In-situ measurements and phase field modeling 总被引:1,自引:0,他引:1
Dominic Phelan Mark Reid Rian Dippenaar 《Metallurgical and Materials Transactions A》2006,37(3):985-994
An experimental study has been conducted into the role of cooling rate on the kinetics of the peritectic phase transformation
in a Fe-C alloy. The interfacial growth velocities of the peritectic phase transformation were measured in situ for cooling rates of 100, 50, and 10 K/min. In-situ observations were obtained using high-temperature laser scanning confocal microscopy (HTLSCM) in a concentric solidification
configuration. The experimentally measured interface velocities of the liquid/austenite (L/γ) and austenite/delta-ferrite
(γ/δ) interphase boundaries were observed to increase with higher cooling rates. A unique finding of this study was that as
the cooling rate increased, there was a transition point where the L/γ interface propagated at a higher velocity than the
γ/δ interface, contrary to the findings of previous researchers. Phase field modeling was conducted using a commercial multicomponent,
multiphase package. Good correlation was obtained between model predictions and experimental observations in absolute values
of interface velocities and the effect of cooling rate. Analysis of the simulated microsegregation in front of the L/γ and
γ/δ interfaces as a function of cooling rate revealed the importance of solute pileup. This microsegregation plays a pivotal
role in the propagation of interfaces; thus, earlier modeling work in which complete diffusion in the liquid phase was assumed
cannot fully describe the rate of propagation of the L/γ and δ/γ interfaces during the course of the peritectic transformation. 相似文献
16.
17.
Dominic Phelan Mark Reid Rian Dippenaar 《Metallurgical and Materials Transactions A》2006,37(12):985-994
An experimental study has been conducted into the role of cooling rate on the kinetics of the peritectic phase transformation
in a Fe−C alloy. The interfacial growth velocities of the peritectic phase transformation were measured in situ for cooling rates of 100, 50, and 10 K/min. In-situ observations were obtained using high-temperature laser scanning confocal microscopy (HTLSCM) in a concentric solidification
configuration. The experimentally measured interface velocities of the liquid/austenite (L/γ) and austenite/delta-ferrite
(γ/δ) interphase boundaries were observed to increase with higher cooling rates. A unique finding of this study was that as
the cooling rate increased there was a transition point where the L/γ interface propagated at a higher velocity than the γ/δ
interface, contrary to the findings of previous researchers. Phase field modeling was conducted using a commercial multicomponent,
multiphase package. Good correlation was obtained between model predictions and experimental observations in absolute values
of interface velocities and the effect of cooling rate. Analysis of the simulated microsegregation in front of the L/γ and
γ/δ interfaces as a function of cooling rate revealed the importance of solute pileup. This microsegregation plays a pivotal
role in the propagation of interfaces; thus, earlier modeling work in which complete diffusion in the liquid phase was assumed
cannot fully describe the rate of propagation of the L/γ and δ/γ interfaces during the course of the peritectic transformation. 相似文献
18.
Dominic Phelan Mark Reid Rian Dippenaar 《Metallurgical and Materials Transactions A》2006,37(13):985-994
An experimental study has been conducted into the role of cooling rate on the kinetics of the peritectic phase transformation
in a Fe−C alloy. The interfacial growth velocities of the peritectic phase transformation were measuredin situ for cooling rates of 100, 50, and 10 K/min.In-situ observations were obtained using high-temperature laser scanning confocal microscopy (HTLSCM) in a concentric solidification
configuration. The experimentally measured interface velocities of the liquid/austenite (L/γ) and austenite/delta-ferrite
(γ/δ) interphase boundaries were observed to increase with higher cooling rates. A unique finding of this study was that as
the cooling rate increased there was a transition point where the L/γ interface propagated at a higher velocity than the γ/δ
interface, contrary to the findings of previous researchers. Phase field modeling was conducted using a commercial multicomponent,
multiphase package. Good correlation was obtained between model predictions and experimental observations in absolute values
of interface velocities and the effect of cooling rate. Analysis of the simulated microsegregation in front of the L/γ and
γ/δ interfaces as a function of cooling rate revealed the importance of solute pileup. This microsegregation plays a pivotal
role in the propagation of interfaces; thus, earlier modeling work in which complete diffusion in the liquid phase was assumed
cannot fully describe the rate of propagation of the L/γ and δ/γ interfaces during the course of the peritectic transformation. 相似文献
19.
Solidification of M2 high speed steel 总被引:5,自引:0,他引:5
R. H. Barkalow R. W. Kraft J. I. Goldstein 《Metallurgical and Materials Transactions B》1972,3(4):919-926
The freezing process in AISI type M2 high speed tool steel (6 pct W, 5 pct Mo, 4 pct Cr, 2 pct V, 0.8 pct C) was studied by
metallographic and thermal analysis techniques. Unidirectional solidification of small laboratory melts in a modified crystal
growing apparatus was employed to provide metallographic sections of known macroscopic growth direction. Also cooling curves
were obtained on 40 g specimens solidified in thimble crucibles. X-ray microradiography, electron probe scanning techniques,
and quantitative microanalysis of dendrites and interdendritic carbides were extensively used to supplement conventional metallography.
Carbon and vanadium contents of M2 were varied in order to observe the effect of an austenite and ferrite stabilizer on the
thermal analysis curves and microstructure. The nonequilibrium freezing process in M2 includes three major liquid-solid reactions:
1) Liquid → Ferrite, 1435°C; 2) Liquid + Ferrite → Austenite, 1330°C; 3) Liquid → Austenite + M6C + MC, 1240°C. These reactions account for the as-cast structure of the commercial alloy. The addition of carbon depresses
the liquidus (1) and solidus temperatures (3) and narrows the gap between the liquidus (1) and peritectic transformation (2).
This gap is eliminated at > 1.39 wt pct C, where the initial freezing reaction is the crystallization of austenite. The accompanying
microstructural change is the elimination of σ eutectoid dendrite cores. The addition of vanadium promotes ferrite formation
by strongly depressing the peritectic reaction and thus widening the gap between the liquidus and the peritectic. 相似文献
20.
基于Clyne-Kurz的微观偏析公式,以物理试验结果为依据,充分考虑固、液相以及夹杂物之间相互作用,建立第3代汽车钢(TG钢)凝固过程微观偏析耦合模型,研究凝固过程钢液中溶质元素和Al2O3等夹杂物分子的质量分数变化特征。结果表明:在整个凝固过程中,Al2O3分子会不断在液相中生成,但生成量比较少,而SiO2和MnO分子不会在液相中生成;铸坯枝晶间不仅有Al2O3夹杂,还有SiO2和其他复合夹杂,凝固前钢水中夹杂物有待进一步去除;凝固末期液相中MnS析出,大大减小了残余液相中S的质量分数变化,但对Mn的质量分数变化没有明显影响;包晶反应温度为1 487℃,包晶反应后凝固的固相中溶质的质量分数明显高于包晶反应前。 相似文献