超级奥氏体不锈钢的高温变形行为

 为了研究超级奥氏体不锈钢Cr20Ni24Mo6N钢的高温变形行为,采用Gleeble热模拟试验机进行了等温压缩试验,建立了合金的热加工图。结果表明,当变形温度为1 000～1 200 ℃时,Cr20Ni24Mo6N钢的流变曲线表现出典型的“加工硬化＋动态再结晶软化”特点;Cr20Ni24Mo6N钢的热激活能[Q]为678.656 kJ/mol。通过加工图与微观组织综合分析得出,超级奥氏体不锈钢Cr20Ni24Mo6N的合适热加工工艺为,应变速率10 s－1左右,应变量0.5～0.8,变形温度1 150～1 200 ℃。     

硼微合金化对6Mo超级奥氏体不锈钢微观组织及耐蚀性影响

综述了6Mo超级奥氏体不锈钢凝固、热加工和热处理阶段的微观组织演化规律,并分析了合金元素对Mo偏析和σ相析出及耐蚀性能的影响规律.结合作者前期工作,重点分析了微合金化元素硼对其凝固阶段Mo偏析、热加工和热处理阶段σ相析出以及耐蚀性能的影响.硼抑制热加工过程中σ相的析出,减小析出相数量和尺寸,有利于热塑性提高;同时还可促...     

新型奥氏体耐热不锈钢C-HRA-5的热变形行为

为了获得C-HRA-5钢轧制生产的最佳工艺参数,采用Gleeble-3800热力模拟试验机对C-HRA-5钢进行了双道次热压缩实验.实验在变形温度范围为900～1100℃,应变速率范围为0.01～1 s-1,道次间隙时间分别为1、5、15、30s的条件下获得C-HRA-5钢的真应力-应变曲线.采用0.2％补偿法计算得到...     

Precipitation behaviour of 25% Cr - 5.5% Ni austenitic stainless steel containing 0.87% nitrogen

In this paper, a 25Cr - 5.5Ni steel (mass contents in %), which originally had a ferritic-austenitic duplex microstructure (DIN material no. 1.4460), and to which mass contents of 0.87% nitrogen were added to become fully austenitic was studied. The phase transformations that occurred between 700 and 1350°C were studied using several complementary techniques. Firstly, various treatments were carried out in the range 1050-1350°C for 1h to select the best temperature for solution heat treatment. Chromium nitride dissolution and absence of ferrite were was observed at 1250°C for 1h. Subsequently, the specimens were aged in the range 700-1100°C, for 90s up to 100h. The first phase to precipitate was chromium nitride. Ferrite precipitation occurred after long aging times, followed by sigma phase precipitation. A TTT diagram has been proposed.     

Numerical simulation of Mo macrosegregation during ingot casting of high-Mo austenitic stainless steel

Mo macrosegregation was studied through the comparison of numerical simulation of the ingot pouring process and experiment on as-cast 500?kg high-Mo austenitic stainless steel ingot. The simulated results showed the evolution of temperature, melt velocity and the patterns of Mo macrosegregation, and revealed the effects of pouring temperature and cooling rate on macrosegregation. The predicted variation of Mo macrosegregation was compared with measurement values from an industrial ingot along the vertical centreline and horizontal direction. Severe normal and gravity segregation were observed. Although a basic agreement was obtained, the lack of a sufficiently fine numerical grid and the neglect of sedimentation for free equiaxed grains in the prediction brought about the absence of A-segregation and V-segregation. Further investigation would be needed to perform this investigation. The predicted results also confirmed that Mo macrosegregation in the ingot could be effectively diminished by improving cooling rate and decreasing pouring temperature.     

超级奥氏体不锈钢00Cr20Ni25Mo6N0.15的时效析出相研究

以超级奥氏体不锈钢00Cr20Ni25Mo6N0.15为研究对象,采用金相显微镜、扫描电镜等手段分析了在650℃和980℃时效温度不同保温时间条件下对其组织和性能的影响.结果表明:在650℃温度时效时,随着时效时间的延长,晶界处有少量σ相出现,力学性能没有发生明显变化;在980℃温度时效,当时效时间10 h时,晶界有大量的链状σ相出现,材料的强度显著升高,塑性及韧性明显降低.     

Nitrogen strengthening of a stable austenitic stainless steel

The low-temperature flow stress of mechanically stable austenitic stainless steels increases with increasing concentration of nitrogen in solution and with decreasing temperature. This phenomenon has been studied in a series of FeNiCrMo alloys with nitrogen contents between 0.04 and 0.36 wt% by measuring the flow stress and the thermal activation parameters for plastic flow as a function of stress, plastic strain and nitrogen concentration in stress relaxation and strain-rate change experiments. Care is taken, when analyzing the data, to distinguish between athermal and thermal effects. The significant increase of the athermal flow stress with increasing nitrogen concentration is attributed to short-range ordering of chromium and nitrogen atoms. The thermally activated component of the flow stress is also dependent on the nitrogen concentration and is thought to be due to localized, predominantly modulus interactions between lattice disturbances in the immediate vicinity of nitrogen atoms and slip dislocations. The thermally activated component is suitably described by Friedel's model of solid solution strengthening.     

含4.35%铜抗菌不锈钢的热变形行为

含铜奥氏体不锈钢具有优异的抗菌性能而广泛应用在食品加工、医疗等领域,然而铜的加入会显著影响不锈钢的加工性能。用Gleeble-3800热模拟试验机对含铜4.35%奥氏体抗菌不锈钢进行了单道次等温热压缩试验,研究了不锈钢在变形温度为900～1 150℃、应变速率为0.01～10 s^-1和变形量为50%下的高温变形行为,构建了反映其材料特性的本构方程,使用金相显微镜观察了热变形后的微观组织,分析了各变形工艺下的微观组织演化规律,为含铜不锈钢的加工成型工艺及组织优化提供了理论参考。结果表明,4.35%Cu-304L钢的流动应力对变形工艺是敏感的,应力随着变形温度的升高和应变速率的降低而减小。采用得到的应力应变曲线建立了一种基于Arrhenius的5阶多项式拟合的应变补偿本构模型,根据此模型计算了相关系数R和平均相对误差AARE分别为0.972和9.03%,这表明所构建模型可以准确地反映含铜不锈钢的流动行为。结合微观组织发现较高的温度和较快的应变速率有利于再结晶的发生,由于0.01 s^-1低应变速率提供的变形能低,在变形温度为1 100℃、应变速率为...     

奥氏体耐热不锈钢的焊接实践

通过对奥氏体耐热不锈钢的焊接性分析，提出奥氏体耐热不锈钢焊接应采取的焊接工艺及应注意的问题．     

超级奥氏体不锈钢的发展

日益增长的工业需求推动着超级奥氏体不锈钢的研发,以研发时间为序阐述超级奥氏体不锈钢3个发展阶段。第1个阶段主要是为解决硫酸介质环境的耐腐蚀性而开发的不锈钢;第2个阶段是在第1阶段研发钢的基础上添加质量分数约为0.2%的N元素、并将Mo元素质量分数增加到约6%而研发的几种耐腐蚀性能良好的超级奥氏体不锈钢;第3个阶段是在6%Mo钢的基础上将Cr、Mo、N含量都进行较大幅度的提高,其中Mo元素质量分数增加到约7%,N元素质量分数控制在0.5%左右,并加入适量Mn元素而研发出耐腐蚀性优异的超级奥氏体不锈钢。阐述了超级奥氏体不锈钢研发过程中的2个重要技术,即炉外精炼与氮合金化技术,并展望了超级奥氏体不锈钢的未来发展及推广应用。     

Hot workability of M2 type high-speed steel

The hot workability of an M2 type HSS in cast, forged and rolled condition has been studied by means of a torsion test and metallography. Continuous tests were used to determine the temperature and strain-rate dependence of the flow stress and temperature dependence of the strain to fracture, while multistage tests were used to determine the extent of interpass softening. Temperature and strain dependence of the flow stress is described by a relation of the form: in which the activation energy for hot working (Q_HW) is found to be temperature dependent. The hot ductility of the cast steel is not only lower but is also little affected by temperature in comparison to worked steels, in spite of the fact that critical strain for dynamic recrystallization is smaller, and the extent of metadynamic and static recrystallization during interpass interval is more extensive in the former. This is related to a large volume fraction of carbides, which give rise to a high stored energy and enhanced recrystallization on the one hand, and to the suppression of recrystallization within the continuous network of carbides on the other hand. Carbides give rise to an easy nucleation, growth and coalescence of cracks.     

Hot workability of three grades of tool steel

Three tool steels, a cold-work air-hardening grade, a hot-work die grade, and a high-speed type, were deformed by torsion in the range of 900 to 1100 °C at rates of 0.1 to 5 s^•1. In a series of continuous deformation tests the flow stress and ductility were determined. The exponent of the flow stress was proportional to the strain rate and to the temperature in a reciprocal Arrhenius relationship. In general the flow stress for a given deformation condition, the activation energy, and the strain for the start of dynamic recrystallization increased for the steels in the order listed above; however, the ductility of the hot-work grade is superior to the other two grades. Multistage tests were carried out on each steel to determine its softening behavior during intervals between passes. Each test was carried out under isothermal conditions with constant strain rate, pass strain, and interval duration. Softening occurred by both recovery and recrystallization with the amount increasing with temperature, strain rate, pass strain, and accumulated strain. The first two steels were similar in behavior having extensive softening at 1000 °C, whereas the high-speed steel experienced considerably less softening.     

Irradiation-produced defects in austenitic stainless steel

Metallurgical and Materials Transactions B - The microstructure of annealed AISI Type 304 and type 316 stainless steels has been characterized by transmission electron microscopy as a function of...     

Surface segregation in austenitic stainless steel

We report in this paper a study of surface segregation in austenitic stainless steel. Auger electron spectroscopy was used to measure segregation as a function of time and temperature. We have found that P, N, S, Cr, and Ni will all segregate to the surface. However, their presence on the surface often depends on the competitive and attractive interactions between the various elements. We show that thermodynamic data on ternary liquid iron alloys are quite valuable in predicting these interactions. We also discuss possible applications of these studies.     

Carbon paraequilibrium in austenitic stainless steel

Carburization of austenitic stainless steels under paraequilibrium conditions—i.e., at (low) temperatures where there is essentially no substitutional diffusion—leads to a family of steels with remarkable properties: enhanced hardness, resulting in improved wear behavior, enhanced fatigue, and corrosion resistance, and with essentially no loss in ductility. These enhanced properties arise from an enormous carbon solubility, which, absent carbide formation, is orders of magnitude greater than the equilibrium solubility. Using interaction parameters from the latest CALPHAD assessment of the Fe-Cr-Ni-carbon system, the authors have calculated the equilibrium and paraequilibrium carbon solubility in a model Fe-18Cr-12 Ni (wt pct) austenitic steel (essentially a model 316L composition), as well as the carbon solubility in this austenite when paraequilibrium carbide formation occurs (i.e., when carbides form in a partitionless manner). For temperatures in the range 725 to 750 K, the calculations predict a paraequilibrium carbon solubility of ～5.5 at. pct. Carburization of 316L stainless steel at these temperatures, however, results in significantly higher concentrations of carbon in solid solution—up to 12 at. pct. Much better agreement with experimental data is obtained by calculating the paraequilibrium carbon solubility using Wagner interaction parameters, taken from the most comprehensive experimental study of this system. The discrepancy between the two predicted solubilities arises because the CALPHAD Cr-carbon interaction parameters are not sufficiently exothermic at the low temperatures used for paraequilibrium carburization. After multiple paraequilibrium carburization cycles, carbide formation can occur. The carbides that form under these conditions do so in a near-partitionless manner (there is modest Ni rejection to the austenite/carbide interface) and have an unusual stoichiometry: M₅C₂ (the Hägg or η carbide).     

Creep mechanisms in a vanadium alloyed austenitic stainless steel

In certain alloys it is possible to stop any movement of the original or strain introduced dislocations by a strong, heterogeneous nucleation of alloying elements. Diffusion will be the only active process left to contribute to the straining during a high temperature creep test. The dislocation structure generated before or during the nucleation process resists the deformation for a very long time and therefore forbids a true secondary structure to develop. A creep resistant steel, UHB SS 724 LN of the type AISI 316, has been intensively studied for the internal structure by TEM through all the three classical stages. This steel appears to have a critical stress above which dislocations at grain boundaries are generated in the first few seconds of the testing. The secondary creep stage is significant by showing an extremely low minimum creep rate at stresses below the critical one contrary to the creep rate predicted by the Coble model. The steel has a very developed tertiary creep stage, and observations of the dislocations generated by the initial straining indicate that the dislocations during this stage climb away from the precipitated particles. The contribution from void growth to the tertiary stage will probably still exist, and this stage therefore has at least two contributions.     

奥氏体不锈钢伸长率的换算

对奥氏体不锈钢不同标距间伸长率的换算公式进行研究,结果表明：试验所得n值约为0．199,与标准中Olive公式的规定值存在一定的差异。     

Hot workability of high manganese transformation induced plasticity steel

The hot deformation behavior and microstructure evolution of high manganese transformation induced plasticity steel(Fe - 20Mn - 3Si - 3Al) were investigated by using hot compression test in a temperature range from 800℃to 1 050℃and strain rate ranging from 0.01 s~(-1) to 5.0 s~(-1).The effects of temperature,strain rate,and true strain on the flow behavior and microstructures of high manganese transformation induced plasticity steel were discussed.The results show that the dynamic recrystallization occur...     

Creep mechanisms in a vanadium alloyed austenitic stainless steel

In certain alloys it is possible to stop any movement of the original or strain introduced dislocations by a strong, heterogeneous nucleation of alloying elements. Diffusion will be the only active process left to contribute to the straining during a high temperature creep test. The dislocation structure generated before or during the nucleation process resists the deformation for a very long time and therefore forbids a true secondary structure to develop. A creep resistant steel, UHB SS 724 LN of the type AISI 316, has been intensively studied for the internal structure by TEM through all the three classical stages. This steel appears to have a critical stress above which dislocations at grain boundaries are generated in the first few seconds of the testing. The secondary creep stage is significant by showing an extremely low minimum creep rate at stresses below the critical one contrary to the creep rate predicted by the Coble model. The steel has a very developed tertiary creep stage, and observations of the dislocations generated by the initial straining indicate that the dislocations during this stage climb away from the precipitated particles. The contribution from void growth to the tertiary stage will probably still exist, and this stage therefore has at least two contributions.