Si含量对9%Cr铁素体马氏体钢微观结构和力学性能的影响

铁素体马氏体（F/M）钢是铅冷快堆堆芯的主要候选材料之一,提高Si含量可提高其抗腐蚀性能,但影响其微观结构和力学性能。为研发兼顾力学性能和抗腐蚀性能的高Si含量F/M钢,本文对Si含量（质量分数为034%、061%、080%、098%和120%）对9%Cr F/M钢微观结构和力学性能的影响进行了研究。结果显示,室温下通过正火（1 050 ℃,05 h,空冷）+回火（760 ℃,15 h,空冷）热处理制备的F/M钢均为全马氏体组织。钢的屈服强度和抗拉强度均随Si含量的增加而增加。Si含量对钢的组织及冲击性能的影响可分为两个阶段,当F/M钢中Si含量为034%~080%时,其组织、冲击性能变化很小;Si含量为098%~120%时,F/M钢中的第二相尺寸、数量增加,沿马氏体板条界面析出少量的Laves相,F/M钢的冲击韧性降低。本研究9%Cr F/M钢中Si元素的最优添加量应低于08%,使钢在保持较高强度的同时兼具良好的韧性。     

FeCr合金中Cr含量对微观结构影响的原子尺度模拟研究

低温辐照脆化是影响铁素体/马氏体（F/M）钢服役的主要问题之一。F/M钢低温辐照脆化的主要机理是辐照产生的纳米缺陷（如位错环、α′相(富Cr团簇)等）阻碍位错运动。本文利用分子动力学方法和迈氏蒙特卡罗方法对F/M钢模型材料--FeCr合金（Fe7%Cr、Fe9%Cr、Fe14%Cr）中Cr元素析出成团簇及在位错环上偏析的机理进行研究，并分析Cr团簇析出与合金成分的关系以及位错环尺寸、位错环类型和合金中Cr含量对位错环上Cr偏析量的影响。模拟结果表明：热力学模拟后，高Cr含量（>9%)的FeCr合金中会析出Cr团簇，且基体内Cr含量越高，析出的Cr团簇尺寸越大；在所研究的3种FeCr合金中，受位错环张应力场作用，合金元素Cr均会在位错环的外围偏析，且FeCr合金中Cr含量越高，Cr在位错环上偏析量越高。低Cr的FeCr合金中Cr对其辐照硬化的影响需考虑位错环上Cr偏析的影响，高Cr的FeCr合金中Cr元素对其辐照硬化的影响需综合考虑Cr团簇及位错环上Cr偏析。     

热老化温度对高Si含量F/M钢中Laves相析出行为和冲击性能的影响

铁素体马氏体钢（F/M钢）是铅冷快堆堆芯的主要候选材料之一,提高材料中的Si含量可提高其抗腐蚀性能,但同时会促进Laves相的析出从而影响材料韧塑性。针对一种Si含量为0.98%的F/M钢,开展了3种温度（500、550、600℃）下5000 h的热老化实验,研究了温度对Laves相析出行为和冲击性能的影响。结果表明,热老化温度升高能够促进Laves相的形核和粗化,且温度从550℃提高至600℃,Laves相的粗化速率从3.7 nm/h1/3提高至9.0 nm/h1/3。另一方面,热老化温度升高将加速冲击性能的退化,在550℃和600℃下热老化500 h,冲击功（A_KV）值分别下降至热老化前的51%和39%,而在500℃下热老化2500 h,A_KV值仍保持热老化前的75%。Laves相的析出与冲击性能退化有强烈的对应关系,是冲击性能退化的主要原因。      

低活性F/M钢形变退火过程中的组织演化

作为超临界水堆燃料包壳管用候选材料,设计和制备了一种高Cr低活性铁素体/马氏体钢（0.14C-11.06Cr-2.3W）,实验钢经淬火回火热处理后为回火马氏体组织。对实验钢进行60%冷变形,并随后在750～820℃下退火10～720min。通过显微组织观察和硬度测量,研究了变形前后板条马氏体在回复、再结晶、奥氏体化中的组织演化规律。结果表明,预变形既影响板条马氏体的再结晶行为,又影响奥氏体化行为。无变形的板条马氏体退火时难以发生再结晶,奥氏体直接在回火马氏体的原奥氏体晶界生成;60%预变形后易发生再结晶,奥氏体在完全再结晶的铁素体晶界上形核长大。     

9Cr3W低活性马氏体钢微观组织及力学性能的初步研究

通过提高W含量，调整V、Ta、Ti、N等微合金元素含量，设计了9Cr3W型低活性马氏体钢。研究了该钢的微观组织结构与硬化、时效及相转变行为，对其进行了拉伸性能和冲击韧性测试。与Eurofer97钢相比，该钢表现出优良的高温拉伸性能。分析了9Cr3W钢用作超临界水堆堆芯内部件及包壳材料的可行性，其高温力学性能远优于Zr合金包壳材料;拉伸性能与T91钢相当，且韧脆转变温度低于T91钢，冲击吸收功上限高于T91钢，具有优良的冲击韧性;9Cr3W钢的高温瞬时强度低于奥氏体316不锈钢，成为制约其用于超临界水堆堆芯内部件及包壳的因素之一。     

双束同时辐照低活性Fe-Cr-Mn(W、V)合金微观组织损伤的影响

研究了时效热处理低活性Fe Cr Mn(W、V)钢双束同时辐照损伤行为 ,结果表明 :92 3K/ 3 0 0 0h时效合金 ,经单独电子辐照 (1 0a- 1)出现低密度空洞 ,而经双束同时辐照的时效合金 ,在辐照初期就形成间隙型位错环和微小空洞。与无时效合金相比 ,随时效温度增加 ,空洞尺寸、空洞密度和空洞肿胀量增大。随时效温度的提高碳化物析出数量增多 ,奥氏体中合金元素Cr、Mn、W、V降低 ,He的存在有效地促进空洞肿胀量增大。     

先进反应堆用ODS F/M钢的强韧性匹配研究进展

氧化物弥散强化（ODS）铁素体/马氏体（F/M）钢具有极高的缺陷阱密度，加之体心立方结构基体，使其具有优异的抗辐照性能，被确定为包括聚变堆和第4代裂变堆在内的先进核能系统关键部件候选材料，成为核材料领域的研究热点。有利于ODS钢抗辐照性能的显微组织特点同时也赋予了ODS钢优异的室温和高温强度。但和其他高强度材料类似，ODS钢也存在强度高，而塑韧性不足的矛盾，不利于复杂部件的加工，因此，实现ODS F/M钢的高强高韧成为面向工程应用的ODS F/M钢研究的一大热点和难点。目前，针对ODS F/M钢强韧化的研究还较少，已有的相关研究也不够系统和深入，本文主要对抗辐照ODS F/M钢的显微组织结构要求及其强韧化研究现状进行总结和分析，为先进反应堆用抗辐照ODS F/M钢的强韧化设计提供思路和参考。     

F/M钢在超临界水环境中的腐蚀性能

本文研究了F/M钢在超临界水（SCW）环境中的腐蚀性能。实验结果表明,F/M钢在SCW中的抗腐蚀性能较差,温度、溶氧浓度以及材料中的Cr含量对其腐蚀性能有较大影响。对12Cr表面进行盐浴复合处理（QPQ）、电镀Cr和磁控溅射Cr处理,以研究其对F/M钢在SCW中抗腐蚀性能的影响。研究表明,经电镀Cr和磁控溅射Cr处理的12Cr试样在SCW中具有优良的抗腐蚀性能,尤其是经磁控溅射Cr处理的试样,1 000 h后其表面氧化膜依然完整致密,而经QPQ的试样腐蚀严重。     

氦对低活性Fe-Cr-Mn(W,V)合金焊接热影响区辐照损伤的影响

采用高能离子加速器和超高压电镜连接装置 ,研究注入He后电子辐照和同时辐照 (He+ e-)低活性Fe Cr Mn(W ,V)合金焊接热影响区 (HAZ)损伤组织特点 ,测定He对损伤组织内晶界附近合金元素浓度变化的影响。实验结果表明 :He强烈促进辐照初期位错环和位错密度增加 ,促进HAZ辐照空洞核心形成及空洞肿胀增大。He有效抑制HAZ内晶界附近Cr、Mn浓度降低 ,对Ni,Si,V ,W元素浓度变化也有抑制作用。Fe Cr Mn(W ,V)合金焊接HAZ具有优良抗He气氛下的辐照损伤性能     

采用高能重离子辐照研究铁素体/马氏体钢脆化效应

正铁素体/马氏体钢作为快堆组件的候选结构材料,辐照脆化是降低其堆内应用性能的关键问题,采用离子模拟辐照方法可大幅降低材料研究成本。对应于快堆服役环境的要求,采用高能重离子模拟辐照结合小冲杆测试技术对一种9Cr铁素体/马氏体钢的抗辐照性能进行了评价。     

Determination of nitrogen partitioning coefficients in superduplex stainless steels by NRA using a nuclear microprobe

Superduplex stainless steels (SDSSs) combine the good mechanical behavior and the high corrosion resistance of the ferrite (α-Fe) and austenite (γ-Fe) phases. The SDSSs properties depend strongly on the partitioning of the elements that form the alloy. The ferrite is generally enriched in P, Si, Cr and Mo while the content of Ni, Mn, Cu and N in the austenite phase is higher. Nitrogen is known to be a strong austenite stabilizer and its presence increases the strength and the pitting corrosion resistance of the stainless steels. While the global nitrogen content in SDSSs can be readily determined using elemental analyzers, it cannot be measured at a microscopic scale.In this work, the nuclear microprobe of the Centro Nacional de Aceleradores (Sevilla) was used to obtain the quantitative distribution of nitrogen in SDSSs. A deuteron beam of 1.8 MeV was employed to determine the overall elemental concentration of the matrix by deuteron-induced X-ray emission, whereas the nitrogen partitioning coefficients were obtained by using the ¹⁴N(d, α₀)¹²C nuclear reaction. Mappings of this element show that the nitrogen ratio between the ferrite and austenite phases ranges from 0.3 to 0.6 in the analyzed samples.     

A study on NDE method of thermal aging of cast duplex stainless steels

To maintain the integrity of applications of the duplex stainless steels currently in service, a study was conducted to develop a method to nondestructively estimate their Charpy-impact energy at room temperature. It was found that hardness of the ferrite phase is a reliable indicator of the process of embrittlement during long-term heating of duplex stainless steels. However, further information on the ferrite phase and the austenite phase is required for the estimation of Charpy-impact energy. An equation composed of the hardness values of ferrite and austenite phases, the ferrite content and the average spacing of ferrite phase islands was presented as a method applicable to the nondestructive estimation of Charpy-impact energy at room temperature.     

A SANS investigation of the irradiation-enhanced α–α′ phases separation in 7–12 Cr martensitic steels

Five reduced activation (RA) and four conventional martensitic steels, with chromium contents ranging from 7 to 12 wt%, were investigated by small angle neutron scattering (SANS) under magnetic field after neutron irradiation (0.7–2.9 dpa between 250 and 400 °C). It was shown that when the Cr content of the b.c.c. ferritic matrix is larger than a critical threshold value (∼7.2 at.% at 325 °C), the ferrite separates under neutron irradiation into two isomorphous phases, Fe-rich (α) and Cr-rich (α^′). The kinetics of phase separation are much faster than under thermal aging. The quantity of precipitated α^′ phase increases with the Cr content, the irradiation dose, and as the irradiation temperature is reduced. The influence of Ta and W added to the RA steels seems negligible. Cold-work pre-treatment increases slightly the coarsening of irradiation-induced precipitates in the 9Cr–1Mo (EM10) steel. In the case of the low Cr content F82H steel irradiated 2.9 dpa at 325 °C, where α^′ phase does not form, a small irradiation-induced SANS intensity is detected, which is probably due to point defect clusters. The α^′ precipitates contribute significantly to the irradiation-induced hardening of 9–12 wt% Cr content steels.     

Development and characterization of advanced 9Cr ferritic/martensitic steels for fission and fusion reactors

This paper presents the results on the physical metallurgy studies in 9Cr Oxide Dispersion Strengthened (ODS) and Reduced Activation Ferritic/Martensitic (RAFM) steels. Yttria strengthened ODS alloy was synthesized through several stages, like mechanical milling of alloy powders and yttria, canning and consolidation by hot extrusion. During characterization of the ODS alloy, it was observed that yttria particles possessed an affinity for Ti, a small amount of which was also helpful in refining the dispersoid particles containing mixed Y and Ti oxides. The particle size and their distribution in the ferrite matrix, were studied using Analytical and High Resolution Electron Microscopy at various stages. The results showed a distribution of Y₂O₃ particles predominantly in the size range of 5-20 nm. A Reduced Activation Ferritic/Martensitic steel has also been developed with the replacement of Mo and Nb by W and Ta with strict control on the tramp and trace elements (Mo, Nb, B, Cu, Ni, Al, Co, Ti). The transformation temperatures (A_c1, A_c3 and M_s) for this steel have been determined and the transformation behavior of the high temperature austenite phase has been studied. The complete phase domain diagram has been generated which is required for optimization of the processing and fabrication schedules for the steel.     

Development of 9Cr-ODS Martensitic Steel Claddings for Fuel Pins by means of Ferrite to Austenite Phase Transformation

For use as fuel cladding of liquid metal fast reactors, Fe-0.12C-9Cr-2W ODS martensitic steel claddings were developed by cold-rolling under the softened ferrite phase induced by slow cooling from austenite phase, subsequently by ferrite to austenite phase transformation to break up substantially elongated grains produced by cold-rolling at the final heat-treatment. The produced claddings showed noticeable improvement in tensile and creep rupture strength that are considerably superior to PNC-FMS and even austenitic PNC316 at higher temperature and extended time to rupture. The strength improvement is mainly attributed to titanium addition in ODS martensitic steels through its reduction of Y₂O₃ particle size and shortening inter-particles spacing. The behavior of oxide particle size reduction is associated with stoichiometry between Y₂O₃ and TiO₂.     

The effect of carbon on 2.25 Cr-1 Mo steel: (I). Microstructure and tensile properties

The microstucture, hardness, and the tensile properties of 2.25 Cr-1 Mo steel with 0.009, 0.030, 0.120, and 0.135 wt % C were determined on steels in the annealed (furnace-cooled from 927°C), normalized (air-cooled from 927°C), and normalized-and-tempered conditions. As annealed, the microstructure was primarily proeutectoid ferrite with spherical carbides and pearlite, the amounts increasing with increasing carbon content. During normalization ($\text{7}\text{8}$ in rods or 1 in plates were heat-treated), granular bainite formed: 1 to 2 and 15 to 20% bainite (remainder proeutectoid ferrite) for the 0.009 and 0.030 wt % C steels, respectively; the 0.120 and 0.135 wt % C steels were entirely bainite. On tempering, carbides precipitated. In all heat-treated conditions, there was little difference in the room temperature hardness of the 0.009 and 0.030 wt % C steels and between the 0.120 and 0.135 wt % C steels. Tensile tests from 25 to 565°C indicated that strength depends on microstructure, which is determined by carbon content.     

The effects of tungsten addition on the microstructural stability of 9Cr–Mo Steels

The effects of tungsten addition on the microstructure and high-temperature tensile strength of 9Cr–Mo steels have been investigated by using three different steels: M10 (9Cr–1Mo), W18 (9Cr–0.5Mo–1.8W), and W27 (9Cr–0.1Mo–2.7W) steels. The tungsten-added 9Cr steels have revealed better high-temperature tensile strength. Microchemical analysis for (Cr,Fe)₂ (C,N) revealed that the tungsten addition increased the Cr/Fe ratio, which resulted in the lattice expansion of (Cr,Fe)₂ (C,N), and then the enhanced pinning effect on the glide of dislocation. In addition, in M10 steel, the M₂₃C₆ carbides quickly grew and agglomerated, while the tungsten-added 9Cr steels revealed a fine and uniform distribution of M₂₃C₆ carbides. Dislocation recovery during tempering treatments was delayed in tungsten-added 9Cr steels, which was correlated with the stabilized precipitates and the decreased self-diffusivity of iron. It is, thus, believed that the excellent high-temperature tensile strength of tungsten-added 9Cr steels is attributed to the stabilized M₂X carbo-nitrides and M₂₃C₆ carbides and the decreased self-diffusivity of iron.