蠕变过程中P91钢晶界析出相的变化行为

对600℃和650℃蠕变持久断裂试验过程中P91钢组织演变及晶界析出相的变化规律进行了研究。结果表明，在蠕变过程中，P91钢马氏体板条组织随蠕变断裂时间增加逐渐趋于分散，晶界析出相的数量及尺寸增加。晶界上的析出相主要为M₂₃C₆相和Laves(Fe₂Mo)相，Laves相的形核点主要位于晶界上M₂₃C₆相界面处，晶界上的M₂₃C₆相与基体相比具有更高含量的Mo,为Laves相的形成和粗化提供了有利条件，同时晶界上偏聚的Si增加了钢的自扩散系数，促进了Laves相的形成，也使得Laves相的粗化速率较M₂₃C₆相更高。在蠕变过程中P91钢的硬度随断裂时间的延长呈下降趋势，且试验温度越高硬度下降越明显。     

C-HRA-3耐热合金850 ℃持久性能及组织特征

研究了C-HRA-3耐热合金在850 ℃持久试验过程的碳化物特征。结果表明:当持久应力为120 MPa时,持久寿命为37.8 h,主要析出相包括M₂₃C₆相和Ti(C, N)相,高应力状态下,M₂₃C₆相沿变形带析出。当持久应力为80 MPa时,持久寿命延长至491 h,晶界处M₂₃C₆相部分回溶,导致晶界特征不明显,同时细小M₂₃C₆相重新析出,晶内析出的Ti(C, N)相尺寸增加。不同应力下试样的断裂方式均为沿晶断裂,裂纹源优先在尺寸较大的析出相(M₂₃C₆和Ti(C, N))周围萌生,导致伸长率随持久寿命延长而减小。     

不同C和W含量低合金Cr-Mo钢焊缝金属组织及性能

采用扫描电子显微镜(SEM)、X射线衍射(XRD)和透射电子显微镜(TEM)等手段研究了四代钠冷快堆蒸汽发生器用低合金Cr-Mo钢熔敷金属微观组织及冲击韧性。结果表明：熔敷金属主要为贝氏体组织,焊后回火过程中主要形成的析出相为M₂₃C₆和M₃C型碳化物,但随着C和W含量升高,开始出现M₆C型碳化物;受多道次焊接热循环影响,熔敷金属在不完全相变区内形成链状结构+铁素体组织,链状结构内的马奥岛在回火作用下发生分解,内部析出大量碳化物;当w(C)在0.02%～0.08%,w(W)在0.04%～0.06%范围内变化时,熔敷金属冲击韧性均较高,随着C含量的升高,碳化物尺寸和数量增多,使得冲击韧性略有下降;随着W含量的升高,碳化物发生细化,使得冲击韧性略有提高。     

Y12Cr18Ni9Cu易切削钢的平衡凝固相变与MnS析出行为

采用Thermo-Calc热力学软件对Y12Cr18Ni9Cu易切削钢在500～1800℃的析出相进行了热力学计算并得到了平衡凝固相变路径图。结果表明,Y12Cr18Ni9Cu易切削钢的平衡相主要有MnS、液相、δ-铁素体、奥氏体、M₂₃C₆、M₂(C,N)、σ相。平衡凝固和冷却相变路径：液相→液相+MnS→液相+δ-铁素体+MnS→液相+δ-铁素体+MnS+奥氏体→δ-铁素体+MnS+奥氏体→MnS+奥氏体→MnS+M₂₃C₆+奥氏体→MnS+M₂₃C₆+奥氏体+M₂(C, N)→MnS+M₂₃C₆+σ相+奥氏体+M₂(C, N)。随着S含量增加,MnS的析出量逐渐增加,析出温度也逐渐升高,Mn含量变化对MnS相的析出量几乎没有影响,但Mn含量增加会使MnS析出温度升高。Y12Cr18Ni9Cu易切削钢中的硫化物呈球形、椭球形、纺锤形或短棒状并以...     

宽束激光熔覆Ni60/WC复合层显微组织及抗剪强度

利用宽束激光在Q550钢表面制备Ni60/WC复合熔覆层,分析熔覆层显微组织、元素分布和物相组成,通过剪切试验定量表征熔覆层/基体界面结合强度,并对断口形貌进行分析阐述界面断裂机制.结果表明,熔覆层中WC颗粒部分溶解,形成了具有复杂结构的析出相,内核为M₂₃C₆碳化物（M代表Cr,W,Fe）,外部为M₂₃C₆复合碳化物和γ-Ni共晶.平面晶和树枝晶在界面上生长,形成牢固冶金结合.激光功率大于2.8 kW时,熔覆层抗剪强度达到279.8 MPa以上,超过母材的75%.断口分析表明,熔覆层界面具有脆性-韧性混合断裂特征,低功率下WC颗粒在界面上沉积,削弱了界面结合强度.     

焊后回火温度对G115钢熔敷金属组织及室温力学性能的影响

采用G115钢焊条焊接了熔敷金属试板,然后分别在760、780、800、820 ℃下进行了焊后回火热处理,并对不同回火温度下试样的力学性能和显微组织进行了分析。结果表明,G115钢熔敷金属的最佳回火温度为800 ℃,随着回火温度的升高,析出相M₂₃C₆有长大的趋势。760~820 ℃回火后的冲击断口表现为韧窝断裂和准解理断裂特征,在韧窝内存在焊接冶金脱氧过程中形成的球形第二相粒子。     

时效时间对S30432钢组织的影响

利用扫描电镜、透射电镜研究了S30432钢在650 ℃不同时效时间处理后的微观组织演变。结果表明,未经时效的S30432钢组织为均匀奥氏体,晶内有很多未溶的大片状一次Nb（C,N）和细小的二次Nb（C,N）,M₂₃C₆型合金碳化物极少;300 h时效后组织出现明显回复过程,有少量的富铜相和M₂₃C₆型碳化物的析出;时效1000 h后,富铜相和M₂₃C₆碳化物数量急剧增加,M₂₃C₆颗粒逐渐长大并呈链状分布。随时效时间延长,孪晶逐渐消失。TEM照片显示,随着时效时间的延长,富铜相颗粒长大,并和M₂₃C₆相、孪晶一起阻碍位错运动,提高了S30432钢的高温性能。     

固溶处理对53Cr21Mn9Ni4N耐热钢组织及碳化物的影响

利用FactSage软件中的FSstel数据库对53Cr21Mn9Ni4N耐热钢的相图进行计算,分析了氮元素对凝固及冷却过程中相变及析出相的影响,得到了53Cr21Mn9Ni4N耐热钢平衡凝固及冷却相变路径图,并用OM、SEM、XRD、EDS等对53Cr21Mn9Ni4N耐热钢在1200 ℃固溶3、10、20、40和60 min后的显微组织及碳化物演变规律进行了研究。结果表明,53Cr21Mn9Ni4N耐热钢由1600 ℃平衡冷却至300 ℃的过程中完整的平衡相变路径为:液相+气体→液相→液相+δ铁素体→液相+δ铁素体+奥氏体→液相+奥氏体→奥氏体→奥氏体+M₂₃C₆→奥氏体+M₂(C,N)+M₂₃C₆→奥氏体+M₂(C,N)+M₂₃C₆+α铁素体→奥氏体+M₂(C,N)+M₂₃C₆+α铁素体+σ相。M₂₃C₆的析出温度随着氮含量的增加而降低,M₂(C,N)的析出物温度随着氮含量的增加而升高,M₂₃C₆会因M₂(C,N)的析出受到抑制。53Cr21Mn9Ni4N耐热钢的铸态组织非常不均匀,奥氏体呈树枝晶状生长,枝晶间析出大量层片状碳化物。随着固溶时间的增加,分布在枝晶间的层片状碳化物逐渐变成块状及短棒状,碳化物的数量逐渐减少,粗壮的树枝晶也逐渐变得细小。53Cr21Mn9Ni4N耐热钢在1200 ℃固溶后的组织及碳化物均得到明显改善。     

P91钢焊缝650 ℃时效黑线缺陷分析

将P91钢焊缝在650 ℃分别时效210、1000、3000和5000 h,采用扫描电镜-X射线能谱分析(SEM-EDS)和复相分离技术(MPST)研究了焊缝黑线/正常组织区域的合金元素(Cr、Mo)的分布变化以及M₂₃C₆体积分数变化。结果表明,焊缝黑线缺陷区域组织由δ-铁素体和周边析出相M₂₃C₆组成,黑线组织上有显微裂纹和显微孔洞;黑线组织区域的Cr_eq较大,促进了δ-铁素体的生成;随着时效时间的延长,黑线组织区域基体中贫Cr较正常区域严重,M₂₃C₆相所占体积分数更多,且颗粒更易粗化。     

Fe51Mn30Cr19低活化双相多主元合金中χ相与M23C6碳化物在475 ℃回火过程中的析出行为

通过XRD、SEM、EBSD和TEM等手段研究了低活化双相多主元合金Fe₅₁Mn₃₀Cr₁₉在475 ℃回火过程中χ相与M₂₃C₆的析出行为。结果表明,试验材料在回火过程中χ相与M₂₃C₆碳化物析出行为既有相似性又存在差异性。两种析出相的相似性是χ相与其基体铁素体相和M₂₃C₆与其基体奥氏体相都满足立方-立方位向关系,且析出相与基体晶格常数比值都十分接近3∶1。两种析出相在回火过程中差异性在于χ相首先以点状析出相形式于铁素体内部产生,析出过程不存在元素偏聚,而M₂₃C₆的析出总起始于铁素体/奥氏体界面,然后逐渐向铁素体区域扩展,析出过程存在明显的铬元素偏聚。根据两种析出相晶格结构并与其母相对比,分析了两种析出相的形成机理。通过对低活化双相多主元合金析出特征的分析,能够为析出相的控制与材料性能设计提供重要的参考依据。     

Effects of chemical compositions and microstructure on hydrogen embrittlement of austenitic stainless steel weld metal in high-pressure gaseous hydrogen environment

The effect of chemical compositions and microstructures on hydrogen embrittlement of austenitic stainless steel weld metals in high-pressure hydrogen gas was surveyed by using the slow strain rate test (SSRT). As a result, hydrogen embrittlement of the weld metal was hardly influenced by δ ferrite in the weld metal, but by stability of austenite phase, which was estimated by Md30 value or Ni equivalent. In the weld metal with poor stability of austenite, α′-martensite was formed near a crack induced by SSRT. In addition, although the crystal structure of α′-martensite is as same as δ ferrite, susceptibility of hydrogen embrittlement became higher with the increase in α′-martensite. The mechanism to explain the difference between δ ferrite and α′-martensite was considered as following. The hardness, which increases the hydrogen embrittlement susceptibility in bcc structure, is higher in α′-martensite than in δ ferrite. In addition, α′-martensite might be formed continuously with propagation of a crack. Therefore, the effect of α′-martensite on hydrogen embrittlement could be larger compared with δ ferrite.     

Precipitation Behavior and Mechanical Properties of a 16Cr-25Ni Superaustenitic Stainless Steel Weld Metal During Post-weld Heat Treatment

A 16Cr-25Ni superaustenitic stainless steel weld metal for austenitic stainless steel/ferrite heat-resistance steel dissimilar metal weld was designed and prepared through tungsten inert-gas welding. The precipitate evolution and its correlation with mechanical properties were investigated during post-weld heat treatment (PWHT) at 690 °C for up to 12 h. The primary precipitates in the as-welded weld metal were identified as Mo-rich M₆C carbides in the interdendritic region and semicontinuous fine-sized M₂₃C₆ carbides along grain boundary. After PWHT, three types of precipitates coexisted in the interdendritic region: primary M₆C carbides, newly precipitated Mo-rich M₂X carbonitrides and some of the secondary M₂₃C₆ carbides. Additionally, mass secondary M₂₃C₆ carbides formed and coarsened along grain boundary. No undesirable intermetallic phases formed during the whole period. The M₂X and interdendritic M₂₃C₆ improved the strength of the weld metal after PWHT, but the elongation and impact toughness degraded, which were mainly owing to the intergranular M₂₃C₆ carbides that changed the fracture mode from ductile transgranular mode to mixed mode of transgranular and intergranular fracture. Meanwhile, the coarsening of M₂X carbonitrides may lead to the elongation loss during 8 h to 12 h. Evolution of impact toughness was also related to the M₂X carbonitrides, which made the crack easier to propagate compared with austenitic matrix and contributed to the decline of impact toughness. However, due to the sluggish precipitation of M₂X carbonitrides with longer holding time, the decreasing trend became slow from 4 to 12 h. The results showed that PWHT should be controlled within 8 h to obtain better combination of strength and ductility.     

双相不锈钢CMT-P复合焊接微区组织特征

引入CMT-P复合焊接方法成功制备了成形质量优异的UNS S32750超级双相不锈钢焊接接头,选用金相显微镜、X射线衍射仪、扫描电镜、能谱仪及透射电镜等设备研究了接头不同区域的微观组织. 结果表明,焊缝、热影响区和母材组织呈现显著差异. 与母材和焊缝相比,热影响区内奥氏体含量最低(32.3%),但焊接接头各微区的奥氏体含量均满足不低于30%的标准要求．由于焊接热循环过程中再加热的作用,焊根及热影响区中析出了尺度和形貌均不同的晶粒内γ₂和晶粒边界γ₂,而焊缝填充区没有γ₂析出．此外,焊根和热影响区均析出了短棍状Cr₂N,主要分布在铁素体晶粒内和晶粒边界,Cr₂N析出致使相邻铁素体基体形成了明显的贫Cr区．     

Inconel 690焊材熔敷金属热裂倾向分析

针对ERNiCrFe-13焊丝熔敷金属拉伸过程中的微观组织演变规律和微裂纹的萌生扩展机制,采用SEM原位拉伸结合扫描电子显微镜(scanning electron microscope,SEM)观察和能谱(energy dispersive spectrometer,EDS)分析对熔敷金属组织及断裂行为等进行分析.结果表明,ERNiCrFe-13焊丝熔敷金属组织主要由柱状晶γ相(NiCrFe固溶体)、枝晶间富Nb和Mo元素的Laves相(Cr,Fe,Ni)₂(Nb,Mo)、MC碳化物与共晶组织组成,Laves相的形成主要与凝固过程中Nb和Mo元素的偏析有关,且具有尺寸效应,水平方向Laves相尺寸大于4 μm易发生开裂,断裂机制为枝晶间析出相在切应力作用下本体断裂萌生微裂纹,在轴向拉应力的作用下进一步沿晶界扩展连通至断裂失效,断口呈韧性断裂,碳化物偏析(NbC、TiC)和大尺寸Laves相是晶界裂纹产生的主要原因.     

UNS S32750超级双相不锈钢激光焊接头微观组织与耐蚀性能

以UNS S32750超级双相不锈钢为研究对象,采用光学显微镜、扫描电子显微镜、透射电子显微镜、电子探针显微分析仪对激光焊接头微观组织和元素分布进行表征,采用临界点蚀温度测试方法研究激光功率对激光焊接头点蚀行为的影响规律.结果表明,提高激光功率可显著增加焊缝中奥氏体含量,并且在一定程度上抑制Cr₂N析出.此外,激光焊焊缝具有比母材更低的耐点蚀性能.但随着激光功率的增加,焊缝中耐蚀的奥氏体含量增加,同时降低了Cr₂N析出倾向,因此其耐点蚀性能也逐渐增强.与双相钢母材相比,激光焊焊缝中Cr,Ni,Mo等合金元素在铁素体与奥氏体中的分配差异性显著减小,而N原子的分配差异性增加,因此焊缝中铁素体具有比奥氏体更低的耐点蚀指数,进而优先被选择性腐蚀.对于双相钢母材,点蚀主要发生在δ/γ相界和夹杂处,而激光焊焊缝的点蚀主要以铁素体内大量析出的Cr₂N作为点蚀萌生位置,并向弱相铁素体内快速发展.     

T92/HR3C异种钢接头的蠕变损伤演化

对T92/HR3C异种钢焊接接头进行温度为650℃、应力为90 MPa的系列蠕变中断试验,利用光学显微镜、扫描电子显微镜对经过不同蠕变寿命分数试样的显微组织和蠕变孔洞损伤进行了观察与定量,并测试了接头蠕变断裂后的硬度分布.结果表明,T92/HR3C异种钢接头断裂在T92侧细晶粒热影响区(FGHAZ),断裂方式为IV型开...     

焊缝金属中针状铁素体晶粒长大行为

以针状铁素体(AF)组织为基体组织的大热输入焊缝金属作为研究对象,采用金相显微镜(OM)、扫描电子显微镜电子背散射衍射装置(EBSD)、全自动静态相变仪等手段表征了焊缝金属内细长状的针状铁素体(AF)组织晶粒的取向特征,分析不同焊接热输入对焊缝金属内AF晶粒形核以及长大行为的影响规律.?结果表明,在大热输入焊接条件下,...     

Martensite microstructure of 9–12%Cr steels weld metals

Several new grades of steel have been developed in recent years, which have been based on the high-strength 9–12%Cr steels. These steels were developed to meet the proposed demand by power generation companies to increase efficiency to operating at higher temperatures by and thus burning less fossil fuel, principally coal, and thereby reducing costs and also meeting the increasingly stringent environmental requirements.

The 9–12Cr steels used for high temperature components in power plants are generally required to possess good mechanical properties, corrosion resistance, creep strength and fabricability. Although such steels normally have a fully martensite microstructure, they are also susceptible to the formation of delta ferrite, mainly during the welding process. Delta ferrite has several detrimental effects on such properties as creep, ductility and toughness. Thus, it is important to avoid its formation.

In this study the formation of delta ferrite in the weld metal of high-strength 9–12%Cr steels has been analysed for several samples with variations of key alloying elements. The results indicate that the most effective way to avoid delta ferrite in the weld metal is to reduce the chromium equivalent value to as low a value as possible. A fully martensite microstructure is obtained when both the Schneider chromium equivalent is lower than 13.5 and the difference between the chromium and nickel equivalent is lower than 8.     

低合金高强钢焊缝熔敷金属强韧化机理

向焊缝熔敷金属过渡微量的Ti-B和稀土元素,可以有效地抑制先共析铁素体的析出,使焊缝获得细小、均匀的针状铁素体组织.从而提高了焊缝的低温冲击韧性.通过透射电镜观察,发现焊缝中合金元素能形成细小、难溶的非金属夹杂物,成为针状铁素体的形核核心;Ti能形成细小、难溶而弥散分布的化合物(TiO)质点,对针状铁素体的形核更为有利.针状铁素体由许多亚结构组成,这相当于进一步细化了晶粒,是提高焊缝熔敷金属低温韧性微观原因.     

GH4169D合金电子束焊接接头显微组织和持久断裂特征

采用金相显微镜和扫描电镜分析了GH4169D合金电子束焊接接头的显微组织,利用显微硬度计测试了母材、热影响区和焊缝的显微硬度,采用体式显微镜和扫描电镜研究了焊接接头持久断裂特征.结果表明,GH4169D 母材中的主要析出相为1～20 μm 长的片层状晶界η相、30～80 nm 的颗粒状γ'相和少量的碳氮化物.热影响区中...