Fe-15Mn-4.5Si-10Cr-5Ni系形状记忆合金中Cr23C6的析出行为

第二相粒子Cr₂₃C₆作为Fe-15Mn-4.5Si-10Cr-5Ni系形状记忆合金中奥氏体主要强化相,对形状记忆性能起到重要影响。根据经典晶界形核长大动力学理论,分析解决包括Cr₂₃C₆相变化学自由能、界面能等一系列相关参量的理论计算及关键参数选择原则等问题。提出了Cr₂₃C₆在Fe-15Mn-4.5Si-10Cr-5Ni系形状记合金奥氏体基体中沉淀析出的相对定量理论计算方法,计算结果和试验结果吻合较好。计算出的PTT曲线(沉淀量-温度-时间曲线)可以作为Fe-15Mn-4.5Si-10Cr-5Ni系形状记忆合金时效处理参数选择的理论依据。     

两种铁基形状记忆合金抗空蚀性能比较

对Fe-26Mn-6Si-7Cr-1Cu和Fe-20Mn-6Si-7Cr-1Cu两种Fe基形状记忆合金进行了超声波振动空蚀试验，结果表明，两种合金都具有优良的抗空蚀性能，比较而言，Fe-26Mn-6Si-7Cr-1Cu合金的抗空蚀性能优于Fe-20Mn-6Si-7Cr-1Cu合金。在局部载荷作用下可吸收较多弹性变形能及在空蚀过程中有较高应变诱发马氏体相变能是前者抗空蚀性能优于后者的主要原因。     

The corrosion behavior of Fe-based shape memory alloys

Fe-30Mn-6Si, Fe-30Mn-6Si-5Cr and Fe-13Mn-5Si-12Cr-5Ni shape memory alloys were prepared by a VIM technique. The various corrosion tests were conducted to investigate the corrosion behaviors of these alloys. Experimental results show that in 3.5% NaCl solution, the Fe-13Mn-5Si-12Cr-5Ni alloy had the best chemical corrosion resistance, whereas the Fe-30Mn-6Si-5Cr alloy was locally attacked, forming many corrosion pits after immersion test. In addition, the detachment of the corrosion product covering the Fe-30Mn-6Si alloy caused an abrupt increase in the weight loss. After 2 h of heat treatment at 1000 °C, the corrosion potential of the Fe-30Mn-6Si alloy increased due to the formation of α-ferrite, while the Fe-30Mn-6Si-5Cr alloy became more active. In the stress-corrosion cracking test, the Fe-13Mn-5Si-12Cr-5Ni alloy, having the highest fracture stress in the atmosphere among these alloys, exhibited the largest decrease in fracture stress in the saturated H₂S solution due to the existence of α-martensite.     

Effect of Quenching Process on Microstructures and Mechanical Properties of Fe-0.9Mn-0.5Cr-2.4Ni-0.5Mo-C Steel

To develop an appropriate quenching process to produce Fe-0.9Mn-0.5Cr-2.4Ni-0.5Mo-C steel, the microstructures and mechanical properties of this steel were investigated under the direct quenching and tempering (DQT) and the direct quenching, reheated quenching and tempering (DQQT) heat treatment processes. The microstructure of the DQQT specimen was basically tempered sorbite with spherical precipitates, while quite a bit of tempered martensite was in the DQT specimen with dispersive nanoscaled precipitates. The yield strengths of the DQT and DQQT specimens were 1154 and 955 MPa, respectively. The yield strength of the DQT specimen was higher than that of the DQQT specimen because of its finer grain size, higher density of dislocations and dispersed precipitates. The DQQT specimen had spherical precipitates, which hindered the propagation of the crack. Moreover, the high-angle grain boundaries in the DQQT specimen took a higher proportion. Therefore, the Charpy impact values of DQT and DQQT specimens at ? 60 °C were 38 and 75 J, respectively. Consequently, the mechanical properties of the Fe-0.9Mn-0.5Cr-2.4Ni-0.5Mo-C steel, which met the standard of 1000 MPa grade steel plate for hydropower station, were acquired by the DQQT process.     

Cyclic oxidation of yttria dispersed austenitic stainless steels

Cyclic oxidation of austenitic steels (Fe-20Ni-14Cr-2.5Mo-2Mn-2.5Al-wt.%) dispersed with 0, 0.5 and 5 wt.% yttria was carried out at 800 °C in air. The scale surface and cross-section were characterized using X-ray diffraction, scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). Yttria additions improve the resistance to spallation. The increase in the resistance to spallation appears to be related to the presence of mixed oxides between yttria and base metal oxides.     

高锰奥氏体不锈钢的晶界强化

研究了高锰奥氏体不锈钢不同状态下奥氏体晶粒尺寸对硬度的影响，给出了硬度与奥氏体晶粒尺寸的关系式。     

Grain refinement of primary silicon in hypereutectic Al-Si alloys by different P-containing compounds

The grain refinement behavior of Si-3 P,Si-25 Mn-10 P,and Al-10 Si-2 Fe-3 P master alloys on hypereutectic Al-24 Si alloy was studied.Microstructure analysis indicates that the P-containing compounds in the three master alloys are Si P,Mn P,and Al P,respectively.The coarse flower-like primary silicon in the Al-24 Si alloy transforms into smaller,well-distributed blocks with the addition of various master alloys.When pouring at 840°C,the average grain size of the primary silicon refined by Si-25 Mn-10 P master alloy with a holding time of 30 min is about 18μm,which is significantly smaller than those refined by Si-3 P and Al-10 Si-2 Fe-3 P master alloys.The grain size shows an increasing trend when the holding time is further prolonged.Higher holding temperature has a positive effect on the grain refinement of Si-25 Mn-10 P master alloy.The grain refinement mechanism of the three master alloys was also discussed.     

含有Nb、Ce的形状记忆合金FeMnSiCrNi在3.5%NaCl溶液中的空蚀行为

利用超声波振动仪研究形状记忆合金Fe-14Mn-6Si-9Cr-5Ni-Nb-Ce在3.5%NaCl溶液中的空蚀行为,并探讨合金在3.5%NaCl溶液中处于静态和空蚀情形下的自腐蚀电位和极化曲线.结果表明,Fe-14Mn-6Si-9Cr-5Ni-Nb-Ce合金在3.5%NaCl溶液中呈现优异的抗空蚀性能,空蚀率为0.37 mg/h.空化能使Fe-14Mn-6Si-9Cr-5Ni-Nb-Ce合金的自腐蚀电位变负,变化量为-65 mV.在静态和空化两种条件下,Fe-14Mn-6Si-9Cr-5Ni-Nb-Ce合金在3.5%NaCl溶液中的自腐蚀电流密度都很低,因此合金具有优异的抗腐蚀性能,其纯腐蚀率和力学效应诱导的腐蚀率仅占空蚀率的2.24%.     

形变时效时间对FeMnSiCrNi合金微观组织和形状记忆效应的影响

研究了直接时效和形变时效时间对Fe-13Mn-5Si-8Cr-4Ni-0.2C合金微观组织和形状记忆效应的影响.结果表明.直接时效后只有少量Cr23C6第二相在晶界和晶内弥散析出,而形变后再时效有大量的Cr23C6在晶内沿某些特定的方向析出.形变时效时间不仅影响第二相的析出数量,还影响第二相析出的方向性,从而影响合金的形状记忆效应.形变时效时间存在最佳值.室温10%形变后再经1 073 K×300min时效,第二相数量多且在晶内析出的方向性好,合金的形状记忆效应达到最大值80%.     

Improved Shape Memory Characteristics of Fe-14Mn-6Si-9Cr-5Ni Alloy Via Mechanical Alloying

In this work, the aim was to investigate how the deformation by cold rolling affects the microstructure and transformation temperatures of Fe-14Mn-6Si-9Cr-5Ni alloy prepared by powder metallurgy route. The characteristic of the martensitic transformation in the given alloy composition was investigated in terms of the amount of deformation via cold rolling. Mechanical alloying was applied for reaching better chemical homogenization level in powder state and for this purpose the as-blended powder mixture having target composition was mechanical alloyed for 4 h under protective atmosphere. Compacted samples were sintered at 1150 °C for 2 h under Ar atmosphere. After applying different amounts of cold deformation to the sintered samples, the changes in microstructure of the shape memory alloys were characterized by x-ray diffraction and scanning electron microscopy. With increasing amount of cold deformation, shape memory recovery ratios increased remarkably and ε-martensite phase was simultaneously detected during phase analysis.     

基于马氏体区域化形成的免训练铸造Fe-Mn-Si-Cr-Ni形状记忆合金 Ⅱ.退火对形状记忆效应的影响

采用OM和铁素体测量仪研究了铸态Fe-18Mn-5.5Si-9.5Cr-4Ni合金的微观组织随退火温度的改变及其对合金形状记忆效应的影响.结果表明,在773-1173 K之间退火处理能进一步提高合金的形状记忆效应.经973 K退火30 min后,合金的可恢复变形量达到了6.4%,比训练4次的常规Fe-14Mn-5Si-8Cr-4Ni合金高1.2%.当铸态合金在低于1173 K退火30min后,δ铁素体仍为条状,变形时能使应力诱发ε马氏体以区域化的方式形成,合金具有良好的形状记忆效应;当退火温度高于1273 K时,δ铁素体将固溶到奥氏体中,体积分数减少.当退火温度进一步升高到1423 K时,δ铁素体的体积分数显著增加,形态由条状演变为岛状.条状δ铁素体体积分数的减少和岛状δ铁素体的形成导致δ铁素体不能有效分割奥氏体晶粒,合金的形状记忆效应显著下降.     

Microstructure and Electrochemical Corrosion Behavior of Fe-Cr System Alloys as Substitutes for Ni-Based Brazing Filler Metal

Two new Fe-Cr system alloys,Fe-20Cr-43Ni-10P(mass%)and Fe-20Cr-20Ni-8P-5Si-2Mo(mass%),have been developed as substitutes for the expensive Ni-based brazing filler metal used in brazing exhaust gas recirculation coolers.The microstructures and melting properties of the alloys were analyzed by electron probe X-ray microanalyzer and differential scanning calorimetry.The electrochemical characteristics of the alloys were investigated by potentiodynamic polarization testing in an electrolyte solution made in accordance with the standards of the Automobile Manufacturers Association of Germany.Furthermore,the corrosion behaviors of the alloys were investigated by constant-potential polarization testing and surface characterization.It is found that both alloys are composed of solid-solution phases and phosphide phases.The solid-solution phases serve as the anode,and the phosphide phases serve as the cathode in the corrosion reaction for both alloys.Fe-20Cr-43Ni-10 P exhibits galvanic corrosion on the entire surface.In contrast,Fe-20Cr-20Ni-8P-5Si-2Mo is attacked at a few localized areas so that the cavities form on the surface.The corrosion potential(E_(corr)) is lower than that of Ni-29Cr-6P-4Si(mass%)for both alloys.This means that the Fe-Cr system alloys are more easily corroded than Ni-29Cr-6P-4Si.The corrosion rate and corrosion resistance cannot be investigated by the corrosion current density(i_(corr)) and polarization resistance(R_p),respectively,because of localized corrosion of the two alloys.     

Effect of alloy element contents on caustic stress corrosion cracking of several stainless steels

The stress corrosion cracking behavior in caustic solutions (200 g/l sodium hydroxide, 10 g/l sodium chloride) of three austenitic (18Cr-10Ni-2.5Mo, 20Cr-25Ni-4.5Mo, 27Cr-31Ni-3.5Mo) and three duplex (23Cr-4Ni, 22Cr-5Ni-3Mo, 25Cr-7Ni-4Mo-N) stainless steels was examined. U-bend and Slow Strain Rate (SSR) tests were performed at 200–250°C. The negative influence of nickel in the lower range content for the 18Cr-10Ni-2.5Mo and 20Cr-25Ni-4.5Mo has been shown; when the nickel content is significantly increased (>30%), as in the case of the steel 27Cr-31Ni-3.5Mo, an increase of SCC resistance has been detected. The negative effect of molybdenum, mainly on the behaviour of duplex stainless steels, has also been evidenced. The duplex stainless steels show better caustic SCC resistance than austenitic stainless steels type 18Cr-10Ni-2.5Mo and 20Cr-25Ni-4.5Mo. The best behaviour has been found for the less-alloyed steel 23Cr-4Ni.     

形变时效温度对Fe-Mn-Si-Cr-Ni合金形状记忆效应的影响

研究了直接时效和形变时效温度对Fe-13Mn-5Si-8Cr-4Ni-0.2C合金形状记忆效应和微观组织的影响.结果表明,直接时效后Fe-Mn-Si-Cr-Ni合金在奥氏体晶界和晶内只有少量Cr23C6第二相弥散析出,而形变后再时效有大量的Cr23C6在奥氏体晶内沿某些特定的方向析出,显著强化基体的同时提高了ε马氏体的可逆逆转变性.形变时效温度影响第二相的析出数量和方向性,从而影响合金的形状记忆效应,存在一个最佳的时效温度.当形变后在1073 K时效300 min时,不仅第二相数量多且在晶内析出的方向性好,合金的形状记忆效应达到89%.     

热机械“训练”工艺对Fe-20Mn-5Si-8Cr-5Ni-0．05N合金组织及形状记忆效应的影响

利用透射电镜、扫描电镜等设备研究了Fe-20Mn-5Si-8Cr-5Ni-0．05N合金在不同“训练”工艺下的组织,得到结论如下:“训练”2次时,试验合金的形状记忆效应最佳,此时可恢复的ε马氏体含量最大,并呈单一切变模式生长:“训练”3次时试验合金的母相中产生位错缠结,抑制了ε马氏体的逆转变,合金的形状记忆效应开始下降。     

Mn和Ce对Fe-Ni-Mn-C-Si-Ce系合金组织和性能的影响

采用熔炼法制备出新型高耐磨的Fe-20Ni-xMn-3.5C-2.5Si系固体自润滑材料,研究稀土元素Ce对Fe-20Ni-xMn-3.5C-2.5Si系合金中石墨的球化作用及Mn含量对力学性能及摩擦磨损性能的影响。结果表明：随着Mn含量的增加,合金凝固组织中奥氏体的硬度逐渐增大,特别是Fe-20Ni-xMn-3.5C-2.5Si-0.75Ce系合金在摩擦过程中的表面硬度大幅度提高,呈现出高锰钢特有的表面加工硬化性质,通过TEM可以观察到磨损表面生成孪晶型马氏体;添加0.75%（质量分数）的稀土Ce可以使结晶的石墨球化,使抗拉强度和抗弯强度大幅度提高,大约比未经球化处理的提高3～5.8倍;稀土Ce的加入可以促进Fe1.1Mn3.9C2型碳化物的生成,使材料的耐磨性进一步提高,其中Fe-20Ni-16Mn-3.5C-2.5Si-0.75Ce合金的磨损率最低,大约是QT500球墨铸铁的1/13。     

Role of chromium on mechanical properties of Fe-Mn-Ni-Mo-Ti maraging steels

This experiment investigated the role of chromium in the mechanical properties of Fe-5Mn-9Ni-5Mo-1.5Ti maraging steels containing up to 3% chromium. Remarkable age-hardening responses were observed in the Fe-5Mn-9Ni-5Mo-1.5Ti and Cr-bcaring alloys. A ductile-brittle-ductile transition occurred in the Cr-bearing alloys during isothermal aging below 510°C. This was due to the segregation of titanium and manganese to prior austenite grain boundaries and their subsequent desegregation into the matrix. The addition of chromium to the base alloy considerably improved its ductility after aging at 520°C. From microstructure and AES analyses, it is suggested that chromium addition augments the volume fractions of (Fe,Mn)₂Mo and η-Ni₃Ti precipitates in the Fe-5Mn-9Ni-5Mo-Cr alloys, which act as sinks of manganese and titanium in the matrices. This resulted in the reduction of the alloying elements concentration in the matrix, which is followed by the reduction in the segregation level of the elements at prior austenite grain boundaries, and consequently enhanced intergranular fracture strength. The optimum combination of strength and ductility was obtained in the Fe-5Mn-9Ni-5Mo-3Cr-l.5Ti alloy aged at 520°C for 2 hr. and was σ_{0 2}=1721 MPa, σ_LS=1756 MPa. and ε,= 10.2%.     

The effect of microstructure on the shape recovery of a Fe–Mn–Si–Cr–Ni stainless steel shape memory alloy

In this work the effect of varying the microstructure on the shape memory properties of a Fe-15Mn-7Si-9Cr-5Ni (wt.%) stainless steel shape memory alloy was evaluated using a simple bend test. The best shape recovery was obtained for a single-phase austenite microstructure and for a two-phase microstructure composed of an austenite matrix and Fe₅Ni₃Si₂ type intermetallic grain boundary phase. The maximum shape recovery was achieved at the reversion temperature of 600 °C and when the pre-stain was less than 2%.     

Mn18Cr18N奥氏体不锈钢平衡凝固过程中的相变与析出行为

借助Thermo-calc软件对Mn18Cr18N奥氏体不锈钢所属的Fe-(16~19)Cr-(16~19)Mn-(0.4~0.7)N-(0.04~0.1)C-(0.1~0.4)Si-(0.1~0.4)Ni多元体系在凝固过程中的相变及析出行为进行了研究。采用Thermo-calc中TCFE9数据库对该体系的垂直截面图进行计算,分析了不同组元对凝固和冷却过程中相变的影响,并得到了Mn18Cr18N奥氏体不锈钢的平衡凝固相变路径图。结果表明:C、N、Si和Ni含量的提高可扩大γ奥氏体区,Cr和Mn具有稳定铁素体作用。平衡凝固相变路径与M₂₃C₆相析出温度主要取决于C含量;Cr₂N相析出温度主要取决于N含量;σ相析出温度主要受Cr含量影响。     

A comparison between the corrosion resistances of some HVOF-sprayed metal alloy coatings

This study compares the corrosion resistance of one Co-based alloy coating, namely Co-28Mo-17Cr-3Si (similar to Tribaloy-800), four Ni-based alloy coatings, namely Ni-17Cr-4Fe-4Si-3.5B-1C (Diamalloy-2001), Ni-20Cr-10W-9Mo-4Cu-1C-1B-1Fe (Diamalloy-4006), Ni-22Cr-9Mo-4Nb-5Fe (similar to Inconel-625), Ni-32Mo-16Cr-3Si-2Co (similar to Tribaloy-700), and a (WC-12Co)-33Ni-9Cr-3.5Fe-2Si-2B-0.5C cermet-Ni alloy blend coating. They were produced by liquid-fuelled HVOF spraying onto AISI1040 steel plates. Electrolytic hard chrome (EHC) plating was characterised as a reference material, to verify whether some HVOF coatings are suitable as an EHC replacement. The microstructure of the coatings was examined by SEM and XRD. Electrochemical polarization tests and free corrosion tests were performed in 0.1 M HCl aqueous solution; the corrodkote test (ASTM B380-97R02) was also performed, to rank coatings qualitatively.The lowest corrosion current densities (I_corr) were recorded for EHC and Tribaloy-700. The latter coating contained few secondary phases and little porosity; the damage was mainly due to corrosion activation along lamellae boundaries. Diamalloy-2001 exhibited the highest I_corr and was significantly damaged after the polarization test, as its multi-phase microstructure had triggered severe galvanic corrosion. During free corrosion in 0.1 M HCl, Tribaloy-700 and Diamalloy-4006 retained rather stable polarization resistance (R_p), whereas the R_p of EHC decreased significantly. Tribaloy-700 survived 40 h of corrodkote test with no apparent damage and EHC underwent limited pitting corrosion. All other coatings had visible corrosion. The Inconel-625 coating failed to protect the substrate after 20 h of testing, due to inadequate processing conditions.