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Solidification modeling and solid-state transformations in high-energy density stainless steel welds
J. A. Brooks M. I. Baskes F. A. Greulich 《Metallurgical and Materials Transactions A》1991,22(4):915-926
The solidification and solid-state transformations which occur during the high-energy density (HED) welding of austenitic
stainless steel were studied. Comparisons were made between structures observed in gas tungsten arc (GTA) welds and those
of electron beam (EB) and laser welds using Fe-Ni-Cr ternary alloys with Cr/Ni ratios ranging from 1.5 to 1.85. Weld solidification
and microsegregation was modeled using a finite difference analysis and compared with experimental results. These calculations
were also used to help interpret the origin of the observed microstructures. Calculations showed that little solid-state diffusion
occurs during the solidification and cooling of primary austenite solidified welds, whereas structures which solidify as ferrite
may become almost completely homogenized as a result of diffusion. A change in solidification mode from primary austenite
to primary ferrite was found to occur at higher Cr/Ni ratios with the HED welds than with GTA welds and is attributed to dendrite
tip undercooling. A nearly segregation-free, single-phase austenite structure which appears to be unique to the rapid solidification
velocities and cooling rates of HED welds was also observed. It is suggested that this structure is a product of ferrite solidification
which transforms to austenitevia a massive transformation. 相似文献
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The solidification behavior of three heats of nitrogen-strengthened austenitic stainless steel was examined and was correlated
with solidification mode predictions and with hot cracking resistance. The heat of NITRONIC* 50 solidified by the austenitic-ferrite
mode, and the NITRONIC 50W and NITRONIC 50W - Nb heats solidified by the ferritic-austenitic mode. This behavior was in good
agreement with predictions based on Espy’s formulas for Cr and Ni equivalents. Both the NITRONIC 50W and NITRONIC 50W + Nb
welds contained primary delta-ferrite, with the latter weld and the NITRONIC 50 weld also containing some eutectic ferrite.
Solute profiles in austenite near the eutectic ferrite showed decreasing Fe and increasing Cr, Ni, Mn, and Mo relative to
austenite in the dendrite cores. Numerous Nb-rich precipitates were found on the eutectic ferrite/austenite interfaces and
within the eutectic ferrite. The precipitates were mainly Nb(C, N), with some Z-phase, a Nb-rich nitride, also detected. One
instance of the transformation of eutectic ferrite to sigma-phase was observed to have occurred during cooling of the NITRONIC
50 weld. Hot cracking was seen in the NITRONIC 50 and NITRONIC 50W + Nb welds and resulted from the formation of a niobium
carbonitride eutectic in the interdendritic regions. In the absence of Nb, the NITRONIC 50W heat formed no observable eutectic
constituents and did not hot crack. The presence of hot cracks in the NITRONIC 50W + Nb weld indicates that solidification
by the ferritic-austenitic mode did not counteract the effects of small Nb additions. 相似文献
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高硅奥氏体不锈钢因其较高的Si元素含量所表现出的优异耐蚀性能而成为制酸行业普遍应用的一种特殊钢种。然而,高含量Si元素的加入会引发铸造缺陷和成分偏析加剧以及钢中析出相增多,热加工过程中易产生热裂纹等问题。高硅奥氏体不锈钢凝固过程中δ铁素体的含量、形态和分布与合金化学成分和热加工历史紧密相关,其室温组织取决于析出相的析出顺序和随后的固态相变,因此,奥氏体不锈钢的凝固模式势必会影响合金的热塑性。为此通过调整高硅奥氏体不锈钢中Si元素与Cr元素的含量,采用金相显微镜(OM)、X射线衍射仪(XRD)、扫描电镜能谱分析(SEM/EDS)、电子探针(EPMA)、JMatPro软件计算等方法,探究了合金成分变化与冷却速率对高硅奥氏体不锈钢凝固模式的影响,并对经典铬镍当量算法进行了评估。结果表明,Schneider铬镍当量算法相较于Rajasekhar铬镍当量算法对大多数合金的凝固模式预测较为准确;随着合金中Si元素与Cr元素含量的提高,合金凝固模式由AF模式转变为FA模式,合金凝固过程中经历更多的“δ→γ”固态相变,其中质量分数为6.0%Si成分的合金对应的δ铁素体增幅减缓;随着质量分数为5.0%的Si铸锭冷却速率的提高,合金凝固模式由AF模式转变为A模式;Hammar and Svensson凝固路线判据可以准确预测高硅奥氏体不锈钢的初始析出相。研究为合理制定高硅奥氏体不锈钢的合金成分与成形工艺提供理论依据。 相似文献
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Weld solidification structure of three different types of stainless steel,i.e., 310 austenitic, 309 and 304 semiaustenitic, and 430 ferritic, was investigated. Welds of each material were made without
any quenching, with water quenching, and with liquid-tin quenching during welding. The weld micro-structure obtained was explained
with the help of the pseudobinary phase diagrams for Fe-Cr-Ni and Fe-Cr-C systems. It was found that, due to the postsolidification
5 → γ phase transformation in 309 and 304 stainless steels and the rapid homogenization of microsegregation in 430 stainless
steel, their weld solidification structure could not be observed unless quenched from the solidification range with liquid
tin. Moreover, the formation of acicular austenite, and hence, martensite, at the grain boundaries of 430 stainless steel
welds was eliminated completely when quenched with liquid tin. The weld solidification structure of 310 stainless steel, on
the other hand, was essentially unaffected by quenching. Based upon the observations made, the weld microstructure of these
stainless steels was summarized. The effect of cooling rate on the formation of primary austenite in 309 stainless steel welds
was discussed. Finally, a simple method for determining the relationship between the secondary dendrite arm spacing and the
solidification time, based on welding speeds and weld pool configurations, was suggested. 相似文献
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Heat transfer during Nd: Yag pulsed laser welding and its effect on solidification structure of austenitic stainless steels 总被引:2,自引:0,他引:2
T. Zacharia S. A. David J. M. Vitek T. Debroy 《Metallurgical and Materials Transactions A》1989,20(5):957-967
Theoretical and experimental investigations were carried out to determine the effect of process parameters on weld metal microstructures
of austenitic stainless steels during pulsed laser welding. Laser welds made on four austenitic stainless steels at different
power levels and scanning speeds were considered. A transient heat transfer model that takes into account fluid flow in the
weld pool was employed to simulate thermal cycles and cooling rates experienced by the material under various welding conditions.
The weld metal thermal cycles and cooling rates are related to features of the solidification structure. For the conditions
investigated, the observed fusion zone structure ranged from duplex austenite (γ)+ferrite (δ) to fully austenitic or fully
ferritic. Unlike welding with a continuous wave laser, pulsed laser welding results in thermal cycling from multiple melting
and solidification cycles in the fusion zone, causing significant post-solidification solid-state transformation to occur.
There was microstructural evidence of significant recrystallization in the fusion zone structure that can be explained on
the basis of the thermal cycles. The present investigation clearly demonstrated the potential of the computational model to
provide detailed information regarding the heat transfer conditions experienced during welding. 相似文献
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根据铬当量、镍当量的计算结果推断了06Cr19Ni10奥氏体不锈钢的凝固模式,并采用差热分析技术(DTA)对06Cr19Ni10奥氏体不锈钢在10和30℃/min的加热冷却速度下的凝固过程进行了研究,对DTA曲线中的吸热峰和放热峰进行了分析,并采用激光共聚焦显微镜(LSCM)和扫描电子显微镜(SEM)对样品进行了测定。分析结果表明:06Cr19Ni10奥氏体不锈钢的实际凝固模式为FA型,即铁素体奥氏体型。随着冷却速率的增加,奥氏体形核率增大,残余的δ铁素体在形态上更加细小分散。该研究结果对实际生产中改善铸坯组织,提高铸坯质量具有着一定的意义。 相似文献
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The effect of hydrogen on the tensile behavior of austenitic stainless steel welds was studied in two AISI 300 series alloys
and two nitrogen strengthened alloys. The microstructure of these welds typically contained several percent ferrite in an
austenite matrix. Hydrogen was found to reduce the ductility of all welds; however, the severity of ductility loss increased
with increasing tendency to deform via a planar slip mode. In materials exhibiting large degrees of slip planarity, 304L and
308L, hydrogen changed the fracture mode from dimple rupture to a mixed mode of ductile and brittle fracture associated with
the austenite-ferrite interface. The two alloys, 22-13-5 and 309S, which tend to deform by cross slip mechanisms, showed smaller
losses in ductility even though hydrogen assisted the ductile rupture process by aiding void growth and coalescence, without
changing the fracture mode. Varying the amount of ferrite from approximately one to 10 pct had no significant effect on performance
in hydrogen. 相似文献
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Five different stress levels between 70 and 240 MPa were used together with a range of temperature (550 °C to 700 °C) for
creep testing on E308H and E316H austenitic stainless steel weld deposits. The test results show that the Ferrite Number (FN)
exhibits a linear relationship with the Larson-Miller parameter (LMP) after creep testing. More sigma phase formed in commercial
E316H weld deposits than in commercial E308H because of the difference in molybdenum content. 相似文献
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Structure Evolution and Solidification Behavior of Austenitic Stainless Steel in Pulsed Magnetic Field 总被引:1,自引:0,他引:1
To understand the solidification behavior of austenitic stainless steel in pulsed magnetic field, the solidification process is investigated by means of the self made high voltage pulse power source and the solidification tester. The results show that the solidification structure of austenitic stainless steel can be remarkably refined in pulsed magnetic field, yet the grains become coarse again when the magnetic intensity is exceedingly large, indicating that an optimal intensity range existed for structure refinement. The solidification temperature can be enhanced with an increase in the magnetic intensity. The solidification time is shortened obviously, but the shortening degree is reduced with the increase of the magnetic intensity. 相似文献
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K. L. Chao H. Y. Liao J. J. Shyue S. S. Lian 《Metallurgical and Materials Transactions B》2014,45(2):381-391
The purpose of the current study is to develop austenitic nickel-free stainless steels with lower chromium content and higher manganese and nitrogen contents. In order to prevent nickel-induced skin allergy, cobalt, manganese, and nitrogen were used to substitute nickel in the designed steel. Our results demonstrated that manganese content greater than 14 wt pct results in a structure that is in full austenite phase. The manganese content appears to increase the solubility of nitrogen; however, a lower corrosion potential was found in steel with high manganese content. Molybdenum appears to be able to increase the pitting potential. The effects of Cr, Mn, Mo, and N on corrosion behavior of Fe-16Cr-2Co-Mn-Mo-N high nitrogen stainless steels were evaluated with potentiodynamic tests and XPS surface analysis. The results reveal that anodic current and pits formation of the Fe-16Cr-2Co-Mn-Mo-N high nitrogen stainless steels were smaller than those of lower manganese and nitrogen content stainless steel. 相似文献
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Effect of Grain Size on Mechanical Properties of Nickel-Free High Nitrogen Austenitic Stainless Steel 总被引:1,自引:0,他引:1
The fine grained structures of nickel-free high nitrogen austenitic stainless steels had been obtained by means of cold rolling and subsequent annealing.The relationship between microstructure and mechanical properties and gain size of nickel-free high nitrogen austenitic stainless steels was examined.High strength and good ductility of the steel were found.In the grain size range,the Hall-Petch dependency for yield stress,tensile strength,and hardness was valid for grain size ranges for the nickel-free high nitrogen austenitic stainless steel.In the present study,the ductility of cold rolled nickel-free high nitrogen austenitic stainless steel decreased with annealing time when the grain size was refined.The fracture surfaces of the tensile specimens in the grain size range were covered with dimples as usually seen in a ductile fracture mode. 相似文献
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The micro- and macrostructures of about 50 different stainless welds of the AISI/AWS 300 series are analyzed. The results
indicate that in welding condition corresponding to a typical SMA welding those and only those welds in which the ratio Creq/Nieq≲1.48, where Nieq and Creq are the nickel and chromium equivalents on the Schaeffler diagram, solidify with the austenite as the primary or leading
phase and the delta ferrite, if any, formed from the rest melt between growing cells or cellular dendrites of the austenite.
At room temperature these welds are characterized by a regular general microstructure, soft forms of the ferrite and relatively
large compositional differences mainly caused by solidification.
T. TAKALO, formerly Research Staff Member, University of Oulu 相似文献
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The microstructures of austenitic stainless steel strip were studied using color metallographic method and electron probe micro analysis (EPMA). In the cast strips, there are three kinds of solidification structures: fine cellular dendrite in the surface layer, equiaxed grains in the center and fine dendrite between them. The solidification mode in the surface layer is the primary austenite AF mode because of extremely high cooling rate, with the retained ferrite located around the primary cellular austenite. In the fine dendrite zone, the solidification mode of molten stainless steel changes to FA mode and the residual ferrite with fish-bone morphology is located at the core of the dendrite. The retained ferrite of equiaxed grains in the center is located in the center of broken primary ferrite dendrite with vermicular morphology. 相似文献
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Cr‐Mn steel grades with high nitrogen contents are becoming increasingly important in the field of austenitic stainless steels. Industrial production facilities allow to use two different strategies to reach a high nitrogen content. The first involves taking advantage of the pressurised‐electroslag remelting process, which is operated at elevated nitrogen partial pressure; the second consists of adding elements which increase the nitrogen solubility of the melt so that high nitrogen contents can be achieved at atmospheric pressure. This paper focuses on nitrogen solubility and austenite stability. These have been observed as important and in some cases restricting for the successful implementation and production of high alloyed Cr‐Mn austenitic steels. The precondition for a stable austenitic microstructure can be predicted with the help of equations using chromium and nickel equivalents. Different formulae were tested and their results compared to the microstructure of the alloys. The nitrogen solubility in the melt is particularly important for the steel grades cast under atmospheric conditions. It has been found feasible to produce steel grades up to 0.9 mass percent nitrogen at atmospheric pressure on an industrial scale. Several theoretical approaches for calculating the nitrogen solubility in the melt were tested for atmospheric conditions and compared to the chemical analyses of conventionally cast Cr‐Mn steel grades. 相似文献
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The effect of severe hydrogen environments on the tensile fracture behavior of a variety of austenitic stainless steel welds was investigated. In all cases, second phases or particulates common only to the weld microstructure were the origin of fracture initiation in hydrogen. These second phases formed as a result of microsegregation during solidification and/or solid state transformations during cooling or aging. In addition to second phases the weld microstructure matrix phase also influences fracture behavior. The fracture behavior is discussed in terms of localized chemical variations and the presence of second phases, and th interaction of dislocations with internal boundaries. 相似文献
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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