EFFECT OF Nb ON STRENGTHENING OF Fe-BASE SUPERALLOY AT INTERMEDIATE HIGH TEMPERATURES

Because Nb accelerates the uniform distribution of MC phase and the grain refinement,aswell as,increases the amount and stability of γ-phase,the tensile strength,ductility,stressrupture life and fatigue limit of Fe-30Ni-13Cr-1.2W-1.5Mo-2.5Ti-0.4AI superalloy at650℃ can be improved with increase of Nb content up to 1.22 wt-%.The precipitation ofsmall Laves phase particles dispersed along grain boundaries may be favourable to combinedproperties of the superalloy containing 1.22 wt-% Nb.It will be worsened only that the pre-cipitation of Laves phase particles'dispersed along grain boundaries may be favourable forcombined properties of the superalloy containing 1.22 wt-% Nb.It will be worsened onlythat the precipitation of Laves phase is too more because of too high Nb content existhing.     

Phase Characterization and Formation Behavior in 6 wt% Si High-silicon Austenitic Stainless Steel during Isothermal Aging

The precipitation behavior of different phases in a high-silicon stainless steel (6 wt%Si) during aging at 600–1050℃ for24 h was investigated.The morphology,crystal structure and composition of various precipitates were detailly characterized using optical microscopy,scanning electron microscopy and transmission electron microscopy.Four phases were mainly identified:χ-phase,M_6C carbides,σphase and a new type of fcc-phase.During aging at 600–900℃,the main precipitate was(Cr,Mo and Si)-richχ-phase which was directly precipitated fromγmatrix.Theχ-phase was calibrated as bcc structure with a lattice parameter of 8.90?.The peak temperature for the precipitation ofχ-phase was 800℃,and it was dissolved when aging at temperatures above 1000℃.Theσ-phase was observed only at 700℃ and grew next toχ-phase.Above 700℃,a new fcc-phase was found to be precipitated along withχ-phase,with a space group of Fd3c and a lattice parameter of 12.56?.The M_6C carbides started to be precipitated at 700℃ in the vicinity ofχ-phase.And its amount basically increased with the increasing of temperature.An orientation relationship between M_6C/γwas found:[100]c//[100]γ,(001)c//(001)γ,i.e.,the cube-on-cube relationship.     

The influence of solution treatment temperature on microstructure and corrosion behavior of high temperature ageing in 25% Cr duplex stainless steel

In 25% Cr duplex stainless steels, the effect of prior-solution treatment temperature (STT) on the microstructure and corrosion behavior with ageing at 750 °C and 850 °C was investigated. The results revealed that the precipitation rate of σ-phase was fast in the early stage of ageing for 80 min, and then got slower with ageing time up to 330 min. The σ-phase formation was effectively suppressed by raising STT from 1060 °C to 1230 °C especially for ageing at 750 °C. Consequently, the corrosion rate of specimen was dependent on the amount of σ-phase precipitation, and was lowered due to higher STT, and more σ-phase precipitation can lead to the transition from metastable to stable pitting with ageing at 750 °C up to 330 min. Pitting occurred easily around coarse σ precipitates and caused selective dissolution in ferrite. The longer ageing time increased intergranular corrosion (IGC) susceptibility, whereas higher STT contributed to better resistance to IGC.     

Conversion of MX nitrides to Z-phase in a martensitic 12% Cr steel

A 12% Cr model steel was designed with the purpose of studying the nucleation and growth of modified Z-phase, Cr(V,Nb)N. The model alloy develops Z-phase after relatively short ageing times and contains only nitrides of Cr, V and Nb. Interferences from the presence of carbides and the development of Laves phase were avoided by keeping the C, W and Mo contents as low as possible. Transmission electron microscopy and X-ray diffraction analysis of extracted particles were used to follow the evolutions of phase composition, phase morphology and phase fraction, particularly of the precipitation of Z-phase, during ageing at 600, 650 and 700 °C for up to 10³ h. The development of Z-phase appears to be accomplished by the diffusion of Cr atoms into (V,Nb)N particles and their subsequent conversion into cubic or tetragonal Z-phase. Studies at various temperatures indicate that Z-phase development proceeds fastest at 650 °C and that Z-phase forms faster at prior austenite grain boundaries.     

变形条件和冷却速率对低碳含Nb钢的相变及纳米析出的影响

利用Gleeble 3800热模拟试验机,研究了奥氏体再结晶和未再结晶组织对低碳含Nb钢连续冷却转变行为的影响,并对不同变形温度及冷却速率下Nb(C, N)的纳米析出行为进行了研究。结果表明,未再结晶区奥氏体的变形能够为多边形铁素体提供更多的相变形核点,扩大铁素体相变区,并且能够细化铁素体晶粒;相比于再结晶区1050℃单道次变形,未再结晶区的第二道次变形能够促进Nb(C, N)的析出,其中910℃变形时Nb(C, N)的析出量最多,850℃次之;冷却速率的增大能够抑制Nb(C, N)在奥氏体中的析出,但能够促进其在铁素体中析出;对于本试验钢,10℃/s的冷却速率即可抑制Nb(C, N)的析出;Nb(C, N)的析出粒子平均粒径随着冷却速率的增加而减小。     

Effect of R-phase on impact toughness of 25Cr-7Ni-4Mo super duplex stainless steel

Effect of R-phase at an initial stage of aging on impact toughness was investigated in this study. Microstructure observation and energy dispersive x-ray analysis obviously clarified that the R-phase was mainly precipitated at interface of ferrite and austenite phases and inside of the ferrite phase at the initial stage of aging, and it was transformed into σ-phase with an increase of aging time. The ferrite phase was decomposed into new γ₂-phase and σ-phase by aging treatment. These variations of phase during the aging affected the mechanical property. In other words, the impact toughness value rapidly decreased with an increase of the R-phase at the initial stage of aging while it sharply decreased and then slowly decreased with an increase of the σ-phase. This decrease of the toughness at the initial stage of aging was predominantly due to the precipitation of R-phase.     

退火对Fe-Cr-Al-Mn双相不锈钢组织及性能的影响

设计制备了一种新型的Fe-Cr-Al-Mn资源节约型双相不锈钢,对其进行高温单相铁素体热轧,研究冷轧后不同退火工艺对其显微组织、力学性能和耐腐蚀性的影响。结果表明,Fe-Cr-Al-Mn钢冷轧后,粗大α相晶粒破碎细化,退火后奥氏体在铁素体晶界形核长大,随退火时间的增加,奥氏体体积分数逐渐增加。随退火温度升高,奥氏体含量减少,伸长率和耐点蚀性能均表现出先增强再减弱的趋势。经800 ℃×4 h退火后,表现出均匀的铁素体和奥氏体相比例和晶粒尺寸,试验钢的强度、伸长率和抗点蚀性能综合性能良好。     

GH4169合金铸态组织特征及均匀化处理工艺

通过CLSM、OM和SEM等测试方式,研究了GH4169合金铸态组织和均匀化热处理工艺对晶粒尺寸、析出相、氧化层厚度以及溶质元素均匀性的影响。研究表明,铸态组织枝晶间存在Laves相、δ相、γ′相和MC碳化物等析出相,主要偏析元素Nb在铸锭中心偏析最严重;在第一段1160 ℃×16 h,第二段1190 ℃×30 h均匀化处理后,合金铸锭可以达到最合适的均匀效果,Nb元素残余偏析系数δ在0.2左右,晶粒尺寸约6117 μm,氧化层厚度约为41.6 μm。     

Effect of Heat Treatment on the Microstructure and Mechanical Properties of the Modified 718 Alloy

M718 alloy with an extra high Mo content of 7.50 wt% which reduced Nb addition and increased Al and Ti additions within the composition specifications of 718 alloy has been designed to increase the service temperature of 718 alloy. And the effect of the heat treatment on the microstructure and mechanical properties of M718 alloy has been investigated in this study. The results showed that Laves phase precipitated on the grain boundaries of M718 alloy instead of d-Ni_3 Nb phase in718 alloy, and y'and y'phases precipitated in the matrix of M718 alloy as that in 718 alloy. Increasing the solution temperature from 960 to 1050 ℃ noticeably reduced the intergranular precipitation of Laves phase. The precipitation of Laves phase was appropriate at 1020 ℃ for improving the grain boundary cohesion. Increasing the two-stage aging temperatures markedly increased the sizes of y' andy'phases. As a result, the strength of M718 alloy increased.     

����˫�಻���00Cr25Ni7Mo4N�����ȴ�����֯���о�

 研究了950~1300℃固溶处理对00Cr25Ni7Mo4N超级双相不锈钢组织的影响。结果表明,≤1000℃固溶处理时,钢中有σ相析出,要消除热轧态的σ相,固溶温度应大于1050℃;随着固溶温度升高,铁素体相含量增加,奥氏体相含量下降。最佳固溶处理温度在1050℃~1100℃之间,此时两相比例接近1：1;随着固溶温度的提高,两相的晶粒尺寸在逐渐增大,到了1250℃晶粒明显长大。     

Nb、Al含量对GH706合金组织及力学性能的影响

研究了降Nb提Al对GH706合金组织和力学性能的影响。当合金中Al含量由0.35%提高至1.26%(质量分数,下同),Nb含量由2.88%降低至1.98%后,可抑制晶内主要强化相γ″-Ni3Nb相的析出,促进γ′-Ni3Al相的析出,显著降低合金的室温屈服强度,但明显改善了合金的室温冲击性能。同时提Al降Nb还抑制了晶界强化相η-Ni3(Ti,Nb)相的析出,使得富Nb的Laves相及富Nb、Cr的Cr2Nb相析出,弱化了高温下的晶界强度,极大地恶化了合金的持久性能。     

G115马氏体耐热钢平衡析出相的热力学计算和分析

为了制备超10 t级G115马氏体耐热钢的大型铸件,需科学评估合金元素对析出行为的影响。采用Thermo-Calc软件的TCFe9数据库对G115马氏体耐热钢的平衡析出相进行热力学模拟计算,研究了主元素对G115钢平衡态析出相类型、析出量和析出温度的影响。计算结果表明:G115马氏体耐热钢在650 ℃下的析出相主要有MX相(FCC-A1#2:NbC)、M₂₃C₆、Laves相和富Cu相。其中NbC的析出温度为1148 ℃,M₂₃C₆的析出温度为871 ℃,Laves相的析出温度为811 ℃,富Cu相的析出温度为734 ℃。其中C和Cr对M₂₃C₆的析出有影响,C和Nb对NbC的析出有影响,W对Laves相的析出有影响,B对各相的析出均无明显影响。     

MODELLING OF MICROSTRUCTURE EVOLUTION AND PROPERTIES OF LOW-CARBON STEELS

1.IntroductionMicrostructureprocessmodelsareincreasinglyonhotstriprollingofste.l[1--7].Thesemodelsfrequentlyincorporateagreatdealofempiricismwithcomparativelytightprocessrangesofapplicability.Morefundamentallybasedprocessmodelsarerequiredtodeveloppredictivetoolstooptimizetheproductionforawiderangeofmilldesignsandprocessingconditions.Theprocessofhotstriprollingoflow--carbonsteelscanbesubdividedintothreeprin-cipalstages:(i)reheating,(n)rollingand(iii)cooling(watercoolingontherun--outtableandsubs…     

Precipitation related anomalies in kinetics of phosphorus grain boundary segregation in low alloy steels

It has been shown that particles of M₆C in Cr–Mo–V low alloy steels can influence phosphorus grain boundary segregation in a similar manner to Laves phase particles in 12CrMoV steel. The influence of these particles arises from their ability to dissolve non- metallic elements such as phosphorus and silicon. As phosphorus is progressively segregated to the grain boundaries during prolonged ageing, the precipitation of M₆C particles leads to an anomalous decrease in the phosphorus grain boundary concentration as the ageing time is extended. This phenomenon originally observed for the Laves phase in long-term aged 12CrMoV steel at temperatures of 753, 773, and 803 K has now been observed for M₆C carbide in a 2.5Cr–0.4Mo–0.25V low alloy steel aged at 853 K.     

控轧控冷对Ti-Mo-Nb复合微合金化低碳钢组织和力学性能的影响

研究了控轧控冷的冷却速度对Ti-Mo-Nb微合金高强钢组织与性能的影响。结果表明,随着冷却速度的降低,试验钢中铁素体逐渐等轴化,铁素体的体积分数、晶粒尺寸逐渐增加。冷却速度的降低可显著细化析出相尺寸并增加其体积分数,析出方式由弥散析出向相间析出转变。铁素体通过析出强化实现提升材料强度的同时,成形性能得到改善。当冷却速度为28℃/s时,试验钢获得了优异的综合力学性能,抗拉强度为853 MPa,屈服强度为750 MPa,伸长率为18.6%,扩孔率为68.5%。组织细化与析出强化是试验钢的主要强化机制,当冷却速度为28℃/s时,细晶强化和析出强化强度增量分别为206 MPa和328 MPa。     

Nb和Cr对冷轧低碳低硅双相钢组织性能的影响

研究了在不同双相处理工艺条件下加Nb(0.033%)和加Cr(0.44%)两种低碳低硅冷轧双相钢的组织演变规律和性能特点。分析了合金元素Cr和Nb对双相组织中马氏体体积分数、马氏体形态和铁素体晶粒尺寸的影响。结果表明,Nb的作用主要是通过NbC粒子的析出阻碍再结晶晶粒的长大,从而在同样较低温度热处理工艺条件下,加Nb双相钢中的铁素体晶粒较细。随着处理温度的升高,当相变先于再结晶发生时,NbC对细化晶粒的作用不明显,因而加Nb和加Cr钢具有相近的铁素体晶粒尺寸。Cr提高奥氏体形成温度,导致双相处理时奥氏体的体积分数以及淬火后马氏体的体积分数的减少。力学性能分析表明,在同样的双相处理条件下,加Nb钢具有较高的强度和较低的屈强比;而加Cr钢则表现出较好的塑性。     

Inconel783高温合金螺栓的组织与织构

研究了Inconel783高温合金螺栓的组织结构与织构特点,重点关注β相的分布与析出特征,并研究了高温应力松弛前后组织与织构的变化情况。结果表明,螺栓试样γ相晶粒分布较为均匀,同时存在弥散分布的γ′相析出。大颗粒的β相沿螺栓轴向成串分布,其分布特征与γ相晶粒取向及尺寸无关,主要由冶炼方式与热加工过程决定;较小的β相在γ相晶界与晶内、连续或孤立析出。织构方面,γ相与β相均未表现出强织构,与热加工过程中变化的多向应力状态有关。以螺栓轴向(x方向)为试样参考方向,γ相存在一定的<111>//x与<100>//x择优,其中前者强度稍高。高温应力松弛试验后,γ相组织、β相分布与各相织构均较为稳定。对该合金中发挥重要作用的小尺寸β相分析发现,其析出行为受到γ相基体取向与晶界特征影响,其中<111>取向晶粒内析出较多,孪晶界上β相析出不占优势。因此,通过控制热加工与固溶处理过程中γ晶粒尺寸与取向择优,有望调控其析出特征。     

Nb含量和变形量对水电站用800 MPa高强钢淬火再加热奥氏体晶粒尺寸及其分布的影响

利用Gleeble 3500热/力模拟试验机,通过1000℃+820℃两阶段热变形+900℃淬火再加热联合模拟试验,研究了Nb含量和不同热变形量对水电站用800 MPa级高强度试验钢淬火再加热晶粒尺寸及其分布的影响规律,并通过透射电镜(TEM)对形变诱导析出的Nb(C,N)的粒子尺寸、分布进行了观测。结果表明,热变形态奥氏体晶粒尺寸(D)对于再加热淬火态奥氏体晶粒尺寸(D′)具有重要遗传性影响,二者以及900℃再加热保温时间t之间存在函数关系D′=(1.0057D-6.9785)×(t/300)^0.215,用于预测800 MPa高强钢再加热淬火态晶粒尺寸时具有较高精度。增加Nb含量可同时细化晶粒尺寸D和D′,并改善晶粒尺寸分布、显著降低个别粗大晶粒出现的概率。在常用的淬火加热制度下,添加0.03%Nb和0.05%Nb的晶粒细化效果基本相当,兼顾其经济性应优选0.03%Nb。TEM观测结果表明,含Nb变形态试样中存在大量10～30 nm尺寸的Nb(C,N)粒子,其数量和密度随Nb含量增加而增加,但粒子尺寸并未随之明显增大。通过热力学计算并综合粒子尺寸和形成时间推断,...     

Effect of Zr addition on precipitates in K4169 superalloy

In order to investigate the effect of Zr addition on the precipitations of K4169 superalloy,a manual electric arc furnace was used to prepare the superalloy with different Zr addition from 0.03wt.% to 0.07wt%.After standard heat treatment and long-time aging,the microstructures of the alloys were observed using XRD,SEM and TEM.The results show that Zr not only inhibits the precipitation of Laves phase at the grain boundary,but also significantly promotes the precipitation of earlobe-like γ’ and γ″ phases.After long time aging at 680℃ for 500 h,the γ″ phase grows up obviously and forms a γ’/γ’’ clad microstructure when the Zr addition is 0.03 wt.%.A large number of fine orbed γ’ particles precipitate in the grains and some γ″ phase transforms to disk-like δ phase when the Zr addition increases to 0.05wt.%.The nano-polycrystalline γ’ phase precipitates in the grains and there is a little δ phase when the Zr addition is 0.07wt.%.As the Zr addition increases,the amount of Laves phase at the grain boundary decreases at first,and then increases and forms flaky morphology.     

高强韧工程机械用钢Q690D的淬火工艺优化

通过全自动相变仪、光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)等,研究880~1100 ℃淬火温度对30 mm厚Q690D钢显微组织、原始奥氏体晶粒尺寸、-20 ℃低温冲击性能和冲击断口形貌的影响。结果表明,当淬火温度低于950 ℃时,试验钢奥氏体平均晶粒尺寸小于10 μm,随着淬火温度的升高,Nb、V、Ti微合金碳化物溶入奥氏体量增加,-20 ℃低温冲击吸收能量逐渐升高;当淬火温度由950 ℃升高至1100 ℃,随着奥氏体晶粒快速长大,试验钢-20 ℃冲击吸收能量由最大值150 J降低至19 J;Q690D钢的最佳淬火工艺为950 ℃×20 min,水冷。