Sanicro25耐热钢中析出相的热力学计算与平衡相分析

利用热力学软件Thermal-Calc计算了Sanicro25耐热钢中的平衡态析出相,分析讨论了关键元素含量变化对析出相的影响规律.研究结果表明:增加钢中W、C含量可以升高M23C6的回溶温度以及增加M23C6的析出量,Cr、Co含量对M23C6的析出量没有明显影响;Cr含量越低,W含量越高,Laves相的回溶温度越高,析出量越大;Cr、N含量越低,Nb含量越高,MX相的析出量越高;Nb含量越高,N含量越少,Z相的析出量越大;W、Cr含量越高,σ相析出量越大,回溶温度越高.     

Si对9Cr型铁素体/马氏体钢析出相和力学性能的影响

研究了Si含量对9Cr型铁素体马氏体(F/M)钢析出相和力学性能的影响。结果表明：在不同Si含量的9Cr型F/M钢中析出相均为M₂₃C₆、MX和Laves相，Si能促进Laves相和M₂₃C₆型碳化物的析出。Si含量为0.9%～1.2%的这种钢其拉伸强度和延伸率略有降低，冲击性能维持稳定；Si含量为1.2%～1.8%时，Si的固溶强化和析出相的沉淀强化使钢的拉伸强度提高。但是，随着Si含量的进一步提高Laves相和M₂₃C₆型碳化物大量析出，使其冲击功显著衰退。     

Mn对22%Cr双相不锈钢700℃时效σ相及韧性的影响

利用光学显微镜(OM)、X射线衍射仪(XRD)、扫描电镜(SEM)、透射电镜(TEM)结合析出动力学和冲击实验,研究了不同Mn含量(4.3%,6.9%,9.7%,质量分数,下同)对22%Cr节镍型双相不锈钢700℃时效析出相形成和韧性的影响。结果表明:随Mn含量由4.3%增加至9.7%,时效76h,析出形貌分别为铁素体/奥氏体(δ/γ)界面细小σ相颗粒析出和铁素体晶内σ相/二次奥氏体(γ_2)共析组织。Mn含量增加使Avrami指数n减小,反应常数B增大,Mn元素参与并促进σ相析出,σ相开始析出和完全析出时间均提前,开始析出与完全析出的时间间隔增大,析出速率降低。时效过程中δ相分解量低于1%(体积分数,下同)对冲击韧度影响不大,δ相分解量由1%增至5%会显著降低冲击韧度。Mn含量增加在时效前期对冲击韧度有利,时效中期则会促使δ相分解量更早超过1%,导致冲击韧度快速下降。     

P92钢高温时效过程中Laves相量化分析

在650℃条件下,对P92钢进行1 000,2 000,3 000 h高温时效试验,通过SEM拍摄显微照片,并用IMAGEJ软件对P92钢高温时效过程中析出的Laves相进行量化分析。量化结果表明:在1 000 h就已经发生Laves相的聚集,且在1 000~3 000 h内,随着高温时效试验时间的延长,Laves相平均截圆直径与面积分数不断增加,而数量密度逐渐减少。动力学研究外推法表明,Laves相析出面积分数在3000 h后变化不大,10 000 h达到0.8%后基本不变。     

Ti和Co对9Cr3W低活化耐热钢组织及性能的影响

用低活化元素Ti替代高活化的Co制备9Cr3W系列钢,用金相观察、SEM观察、拉伸实验及蠕变实验等手段对其进行表征,研究了分别加入Ti和Co对9Cr3w钢力学性能的影响。结果表明,Co和Ti的添加促进析出相的析出,Ti使品粒细化,使拉伸性能和蠕变性能显著提高;Ti的添加使基体中出现少量的δ铁素体,但选择单相奥氏体区间热处理可使其消除,得到单一马氏体组织的低活化钢。对低活化9Cr3W钢进行Ti的微合金化,可获得与添加1%Co相当的良好蠕变性能。     

1Cr11Ni2W2MoV钢长期时效时组织性能的变化EI

本文研究了1Cr11Ni2W2MoV钢在不同温度下长期时效后组织与性能的变化。试验证明,该钢经1010℃、1.5h后保温淬火并于570℃、1.5h空冷回火后,分别在250℃和450℃下经500～1000h时效,发生明显的脆化现象。在450℃延长时效时间至4000h,冲击功逐步回升。     

超高强度马氏体时效钢的力学行为与微观组织演化的关系

用高分辨透射电镜(HRTEM)和原子探针层析技术(APT)等手段研究了2.4 GPa级超高强度马氏体时效钢在时效过程中析出相的演化规律及其与材料力学性能的关系。对组织观察的结果表明,马氏体时效钢在时效过程中析出相的演化规律分为三个阶段：时效初期富Ni和富Ti团簇的形成、峰时效期金属间化合物Ni₃Ti及其界面处富Mo相的形成、过时效阶段Ni₃Ti的粗化和富Mo相过渡为Ni₃Mo。力学性能的实验结果表明,随着时效时间的延长抗拉强度呈现先提高后降低的趋势,时效时间为4 h时抗拉强度达到最大值2560 MPa。断裂韧性呈现与抗拉强度相反的变化趋势,时效时间为4 h时的断裂韧性值最低,仅为20 MPa·m^1/2。根据不同时效阶段材料中析出相的演化规律,探讨了马氏体时效钢的力学行为与析出相的关系。     

P92钢奥氏体化后的冷却方式对650℃时效组织及硬度稳定性的影响

采用扫描电镜二次电子/背散射成像模式(SEM-SE/BSE)、能谱分析(EDS)和复相分离技术(MPST)研究P92钢试样于1060℃/1h奥氏体化后以不同方式冷却(空冷/置炉门口冷:缓冷)经760℃/2h回火(空冷)后再经650℃时效后的组织及硬度的稳定性。结果表明:P92钢时效后的显微组织均为基体相与析出相(M₂₃C_6相和Laves相);奥氏体化后冷却方式对650℃时效后组织及试样硬度有明显影响:缓冷时效试样的析出总量大而硬度低,且Laves相的体积分数/颗粒粗化倾向明显较大,M₂₃C_6相体积分数较小;在650℃时效1000h和3000h期间,空/缓冷时效试样的硬度基本不变/下降;此外,650℃时效试样组织及硬度的稳定性与过冷奥氏体及马氏体的稳定性有关。因此,工业现场管道奥氏体化后应尽快散热。     

新型耐热钢Super304H高温时效后的组织与性能

采用光学显微镜、扫描电子显微镜及X射线衍射等手段并通过显微硬度和冲击实验,研究了Supre304H钢经750～1350℃时效后的微观组织和性能.结果表明:高温时效后Super304H钢的微观组织为γ相+析出相;随时效温度的不同,基体晶粒尺寸及析出相的种类、分布发生不同的变化.在750℃左右因微细沉淀强化及细晶组织使得显微硬度达到最大值,而后随温度升高以及析出相、晶粒尺寸与固溶元素的变化,显微硬度呈现先快速下降后缓慢下降的趋势;时效试样的冲击功值随温度升高在850℃左右,由于M23C6沿晶界大量析出导致晶界脆化而达到最低值,后又因析出相的再溶解致使晶界脆化效果趋弱而逐渐升高.     

三维原子探针表征10Ni3MnCuAl钢时效过程中析出相NiAl和Cu的变化规律

本研究使用三维原子探针表征了10Ni3Mn Cu Al钢在540℃时效过程中析出相随时间的变化规律,使用透射电镜分析了Ni Al析出相的晶体结构及其在基体上的分布状态。结果表明:10Ni3Mn Cu Al钢在540℃时效过程中,Ni Al析出相由时效2 h后的近球状转变为时效100 h后的长条状,平均粒子半径由1. 13 nm长大到2. 13 nm,数量密度由1. 70×10~(22)m~(-3)降低到3. 40×10~(21)m~(-3); Cu析出相由时效2 h后的球状转变为时效100 h后的长条状,平均粒子半径由1. 04 nm长大到2. 08 nm,数量密度由6. 04×10~(21)m~(-3)降低到2. 00×10~(21)m~(-3)。两种析出相由相邻位置转变为以Cu为核心,Ni Al为外壳的壳状结构。B2结构的Ni Al相对基体的强化作用大于Cu相对基体的强化作用,Ni Al相弥散分布在马氏体板条上,并在基体的[200]方向存在超结构反射斑点。     

On Laves phase in a 9Cr3W3CoB martensitic heat resistant steel when aged at high temperatures

9Cr3W3CoB steels are developed to serve at the temperature range of 620-650℃,and have been recog-nized as the most promising martensitic heat-resistant steels for supercritical power plants.Due to the high W and Co contents,the Fe2W Laves phase in such 9Cr3 W3CoB steel possesses some specialties in thermodynamics.In the present research,it was found that even when aged at 800℃in the 9Cr3W3CoB steel,instead of dissolving,Laves phase formed after 50 h and kept on increasing in size and number density until 1000 h,indicating that the Laves phase was marching for the thermodynamic equilibrium during aging.In this thermodynamic process,the W-rich M3B2 borides in as-received steel and M23C6 carbides were revealed to dissolve,supporting the growth of Laves phase.SEM investigation indicates that Laves phase tended to form clusters,and finally grow as a unit bulk Laves phase with an irregular shape.Besides,Laves phase nucleated next to M23C6 carbides and enwrapped them inside at 800℃.In addition,the growth processes of Laves phase and M23C6 carbides were a competitive procedure,the coarsening of M23C6 carbides was prior to the growth of Laves phase at 750℃while the growth of Laves phase was prior to the coarsening of M23C6 carbides at 800℃.     

Characterisation of Laves phase precipitation and its correlation to creep rupture strength of ferritic steels

The Laves phase precipitation process was characterised by means of field emission scanning electron microscopy to demonstrate its effect on creep rupture strength of steels with a fully ferritic matrix. To eliminate the effects of carbide and carbonitride precipitations so that the creep rupture data can be analysed exclusively in relation to the Laves phase precipitation process, an alloy Fe–9Cr–3Co–3W (wt.%) without C and N additions was used for the study. Creep rupture strengths were measured and volume fraction and particle size of Laves phase precipitates in the ruptured specimens were analysed. It was found that the creep rupture strength started to collapse (or decrease more rapidly) long before the Laves phase precipitation reached equilibrium fraction. This was related to the onset of the coarsening of Laves phase particles, which precipitated only on grain boundaries and hence contributed little to precipitation strengthening. Creep deformation had no effect either on the precipitation kinetics or on the growth kinetics of Laves phase particles.     

时效温度对00Cr12Ni10MoTi马氏体时效不锈钢组织与性能的影响

使用X射线衍射(XRD)、扫描电镜(SEM)、电子背散射衍射(EBSD)、透射电镜(TEM)和拉伸和冲击实验等手段,研究了时效温度对00Cr12Ni10MoTi马氏体时效不锈钢的组织和力学性能的影响。结果表明：随着时效温度的升高,实验钢的强度逐渐提高,析出强化效应明显增强。在500℃时效后基体中析出大量棒状Ni₃Ti,实验钢的强度达到峰值。随着时效温度的升高,实验钢的室温和低温冲击韧性衰减,在400℃时效后低温(-196℃)冲击功出现最低值51 J。时效温度升高到500℃后,实验钢的冲击韧性回升,因为马氏体基体中生成的逆转变奥氏体抑制了裂纹萌生并缓解其扩展。在500℃时效产生了Ni₃Ti析出强化效应和逆变奥氏体韧化效应,使实验钢具有良好的强韧性匹配。     

Effect of aging treatments on microstructure and impact properties of tungsten substituted 2205 duplex stainless steel

Abstract

The effects of partial substitution of tungsten for molybdenum on the microstructure and impact properties in 22Cr–5Ni–3Mo (wt-%) duplex stainless steel (DSS) have been investigated following aging heat treatments in the temperature range 600–1000°C. During aging the intermetallic σ and χ phases were precipitated, and the impact toughness was significantly decreased with an increase in the σ phase content. The χ phase had been precipitated on the α/γ boundary in the early stages of aging. Ferrite and χ phases in tungsten substituted duplex stainless steel contain a large amount of tungsten, and their decomposition rates are much lower compared with those in steel containing only molybdenum. Consequently, the precipitation of the σ phase is retarded in tungsten substituted DSSs, which results in high impact toughness. However, after aging for a long time, the α and χ phases transformed to the σ and austenite phases in the tungsten substituted steels, and the steels showed low impact toughness.     

Study on Laves phase in an advanced heat-resistant steel

The Laves phase is one of the most significant precipitates in ferritic/martensitic heat-resistant steels. Laves phase precipitates in the creep rupture specimens with different rupture life were studied on a 10 wt.% Cr heat-resistant steel. JMatPro thermodynamic and kinetic calculations were carried out to simulate and predict the precipitation behavior of the Laves phase in the steel at the equilibrium state. The morphologies of the Laves phase developed with creep time were characterized under both scanning electron microscope (SEM) and transmission electron microscope (TEM). Effects of Co on the growth behavior of Laves phase and the corresponding fracture mode were analyzed. It was found that the Laves phase in the steel grew to 200 nm in size after only 1598 h at 600°C, indicating that the addition of Co in the steel could accelerate the growth of Laves phase, and the coalescence of large Laves phase would lead to the brittle intergranular fracture.     

Study on Laves phase in an advanced heat-resistant steel

The Laves phase is one of the most significant precipitates in ferritic/martensitic heat-resistant steels. Laves phase precipitates in the creep rupture specimens with different rupture life were studied on a 10 wt.% Cr heat-resistant steel. JMatPro thermodynamic and kinetic calculations were carried out to simulate and predict the precipitation behavior of the Laves phase in the steel at the equilibrium state. The morphologies of the Laves phase developed with creep time were characterized under both scanning electron microscope (SEM) and transmission electron microscope (TEM). Effects of Co on the growth behavior of Laves phase and the corresponding fracture mode were analyzed. It was found that the Laves phase in the steel grew to 200 nm in size after only 1598 h at 600°C, indicating that the addition of Co in the steel could accelerate the growth of Laves phase, and the coalescence of large Laves phase would lead to the brittle intergranular fracture.     

Microstructure Evolution of a 10Cr Heat-Resistant Steel during High Temperature Creep

The microstructure evolution of a 10Cr ferritic/martensitic heat-resistant steel during creep at 600℃ was investigated in this work.Creep tests demonstrated that the 10Cr steel had higher creep strength than conventional ASME-P92 steel at 600℃.The microstructure after creep was studied by transmission electron microscopy,scanning electron microscopy and electron probe microanalysis.It was revealed that the martensitic laths were coarsened with time and eventually developed into subgrains after 8354 h.Laves phase was observed to grow and cluster along the prior austenite grain boundaries during creep and caused the fluctuation of solution and precipitation strengthening effects,which was responsible for the two slope changes on the creep rupture strength vs rupture time curve.It was also revealed that the microstructure evolution could be accelerated by stress,which resulted in the lower hardness in the deformed part of the creep specimen,compared with the aging part.     

双相不锈钢00Cr25Ni7Mo4N敏化过程中的脆化机理研究

研究了双相不锈钢00Cr25Ni7Mo4N在晶间腐蚀试验中发生的脆断现象,采用金相法、扫描电镜和透射电镜对材料的脆断机理进行了分析。研究发现双相不锈钢00Cr25Ni7Mo4N在敏化时有R相、Fe3Cr3Mo2Si2相等脆性相析出,导致材料脆化,冲击韧性下降。最后,给出了双相不锈钢00Cr25Ni7Mo4N热加工后的使用要求。     

Al_2O_3-ZrO_2/W/Cr/Ni/Co金属陶瓷的断裂韧性

以Al2O3-ZrO2复合粉末、W、Cr、Ni、Co粉末为原料,采用热压烧结工艺制备了性能优良的Al2O3-ZrO2/W/Cr/Ni/Co金属陶瓷复合材料。通过SEM,EDS,XRD等手段分析其微观组织,单边梁开口法(SENB)测量其断裂韧性。实验结果表明在1320℃,20MPa条件下热压烧结制备的Al2O3-ZrO2/W/Cr/Ni/Co金属陶瓷的断裂韧性为7.16±0.4MPa.m1/2,硬度为83.3HRA,横向断裂强度为540MPa,相对致密度为97.4%;对维氏压痕下裂纹扩展进行了分析,其增韧机理为延性金属对裂纹的桥梁作用和氧化锆相变增韧,在裂纹通过时硬质相以沿晶断裂为主。     

Microlaminated dual phase steel presenting with high strength and ultrahigh toughness

In the present study, a steel with the chemical composition of Fe–0·15 wt-%C–5 wt-%Mn–3 wt-%Al was designed. Its microstructure and mechanical properties were examined by optical microscopy, scanning electron microscopy and mechanical tests. It was found that hot rolling in the dual phase region of ferrite and austenite at high temperature resulted in microlaminated dual phase microstructure. An excellent combination of high strength (～1200 MPa) and ultrahigh impact toughness (～400 J) of the microlaminated dual phase steel was obtained. Based on the measurement of the phase volume fraction and the analysis of the fractography, it was shown that the high strength was mainly dependent on the high martensite volume fraction, while the ultrahigh impact toughness was attributed to the microlaminated microstructure.