Prediction of Ac1 temperature in P92 steel weld metal

The effects of major alloying elements on the Ac, temperature in P92 steel weld metal were evaluated by Thermo- Calc, and a formula relating Ac1 to the content of major alloying elements was developed using multiple regression method. Results show that both C and N reduce Ac, temperature in weld metal, the effect of N on Ac, is greater than that of C, but their influence on Act is not so significant when they individually vary in the specified chemical composition ranges. Si, Cr, Mo and W increase the Acl temperature, and the descending order of their effects is determined as Si, Mo, W, Cr. Mn and Ni decrease the AcI in weld metal, the decreasing effect is especially remarkable when the （ Mn ＋ Ni） ≥ 1%. The effect of Co is moderate and is much smaller compared to Ni. The variations of Acl for the ranges of micro-alloying elements Nb and V are also evaluated, the effect of V is greater compared to Nb and the effect of Nb could be ignored in the specified chemical composition range. A prediction formula for Ac, temperature in P92 steel weld metal within the specified chemical composition ranges was developed based on the comprehensive consideration of the calculated Ac, temperatures and the experimentally measured results.

Nanoindentation Characterization of Creep-fatigue Interaction on Local Creep Behavior of P92 Steel Welded Joint

In modern fossil and nuclear power plants,the components are subjected to creep,fatigue,and creep-fatigue(CF)due to frequent start-up and shut-down operations at high temperatures.The CF interaction on the in-service P92 steel welded joint was investigated by strain-controlled CF tests with different dwell times of 30,120,300,600 and 900 s at 650℃.Based on the observations of the fracture surface by scanning electron microscope(SEM),the character-istic microstructure of fatigue-induced damage was found for the CF specimens with short dwell times(30 and 120 s).The hardness,elastic modulus and creep deformation near the fracture edges of four typical CF specimens with 30,120,600 and 900 s dwell times were measured by nanoindentation.Compared to specimens with post-weld heat treatment(PWHT),lower hardness and creep strength were found for all CF specimens.In addition,significant reduc-tions in hardness,elastic modulus,and creep strength were measured near the fracture edges for the CF specimens with short dwell times compared to the PWHT specimens.Compared to PWHT specimens(0.007),the increased strain rate sensitivities(SRS)of 0.010 to 0.17 were estimated from secondary creep.The increased values of SRS indicate that the room temperature creeps behavior is strongly affected by the decrease in dislocation density after the CF tests.

Effects of Ni and Co on the Ac1 temperature of P92 steel weld metal

The effects of the addition of O - 1.2wt. % Ni and 0 - 2wt. % Co in F92 steel weld metal on its A L temperature was analyzed using computational thermodynamic software （ Thermo-CalcTM ） in this paper. The results indicate that both Ni and Co decrease the A, of P92 .steel weld metal, and each elements has a pronounced linear relationship with the At. The il^fluence of Ni on A,I is much larger than that of Co. In order to evaluate effects of Co and Ni in combination on AI of P92 .steel weld metal, an equation Ni = Ni ＋ O. 096Co was developed. According to the formula, the decreaing effect of Co on A., is jun about 1 / 10 of that of Ni. For welding consumables of P92 steel, the .substitution of Co for Ni （part or whole） could be an appropriate way to avoid the strong reduction of A and improve the properties of weld metal.

Effect of long-term service on the precipitates in P92 steel

The precipitates in P92 steel after long-term service in an ultra-supercritical unit were investigated by field-emission scanning electron microscopy and transmission electron microscopy and were found to mainly consist of M23 C6 carbides,Laves phase,and MX carbonitrides.No Z-phase was observed.M23 C6 carbides and Laves phase were found not only on prior austenite grain boundaries,martensite lath boundaries,and subgrain boundaries but also in lath interiors,where two types of MX carbonitrides—Nb-rich and V-rich particles—were also observed but the "winged" complexes were hardly found.Each kind of precipitate within the martensite laths exhibited multifarious morphologies,suggesting that a morphological change of precipitates occurred during long-term service.The M23 C6 carbides and Laves phase coarsened substantially,and the latter grew faster than the former.However,MX carbonitrides exhibited a relatively low coarsening rate.The effect of the evolution of the precipitate phases on the creep rupture strength of P92 steel was discussed.

采用连铸坯制造的P92钢管性能试验研究

为评估采用连铸坯轧制的P92钢管的性能,对几家钢厂提供的3支采用连铸坯轧制的P92大直径厚壁钢管进行理化检测、625℃高温持久强度试验等。结果表明:采用连铸坯轧制的P92钢管的各项理化性能满足相关标准要求,625℃、10万h外推高温持久强度为93.1 MPa,高于规范推荐值。因此,连铸坯P92钢管已具备工程应用条件,可降低产业链成本。

P92钢焊接组织分析与残余应力模拟

对P92钢平板进行了4层4道焊接试验,采用X射线衍射法测量焊接残余应力,通过光学金相显微镜对焊件显微组织进行表征,利用维氏硬度计对其硬度进行测量。同时基于SYSWELD软件在相同条件下对P92钢平板进行焊接模拟,得到焊接应力场与应变场的计算结果,并使用生死单元技术对比不同焊道焊接结束后残余应力的动态变化,探究多层焊接残余应力的产生与影响因素。金相试验结果显示,焊缝(FZ)处组织为淬火马氏体,最大硬度高达436 HV;母材(BM)组织为回火马氏体,平均硬度为236 HV;热影响区(HAZ)从过热区到正火区硬度逐渐降低。有限元计算结果表明,模拟所得残余应力分布与实测值吻合良好,证明了该焊接模型的准确性;横向拉应力和纵向压应力的最大值出现在焊缝处,纵向拉应力与横向压应力最大值均出现在热影响区与母材交界处,但随着焊道高度的变化,残余应力分布趋势基本不变;上层焊道热载荷对下层焊道的残余应力分布具有较大影响,固态相变效应不仅影响残余应力分布,还会使板件在焊接时产生较大的角变形。

Hot Deformation Behavior of P92 Steel Used for Ultra-Super-Critical Power Plants

Hot compression tests of P92 steel at temperatures in the range of 1 173 to 1 523 K and at strain rates in the range of 0.1 to 10 s^-1 were carried out on a Gleeble-3500 thermal-mechanical simulator, and the corresponding flow curves were measured. The results showed that the flow stress and the peak strain increase with decreasing deformation temperature and increasing strain rate. The critical Z value, below which the complete dynamic reerystallization may occur, was determined to have 4.61 × 10^18. The hot deformation activation energy of the steel was about 437 kJ/mol. The hot deformation equation and the microstructure diagram of P92 steel were obtained. For the convenience of the practical application, the empirical equation for the peak stress can be described as σp=17. 17lnε＋902499/T-524.1.

P92钢的CCT图及组织转变

研究国外P92钢的过冷奥氏体转变具有一定理论意义和应用价值。用淬火膨胀仪结合组织形貌和硬度,用Origin软件绘制钢的过冷奥氏体连续冷却相转变曲线(CCT),分析不同冷却速度下的组织转变规律和硬度变化。结果表明:P92钢的组织在缓慢冷却速度0.01~0.03℃/s下,发生铁素体、珠光体转变。由于贝氏体转变凸出于CCT曲线左方,在一般冷却条件下即可淬火得到贝氏体、马氏体组织,硬度可达564HV_(1)。

P92钢锅炉管道焊接组织分析与残余应力模拟

对P92钢管道进行了多层多道焊接试验,采用X射线衍射法测量焊接残余应力,并对焊接接头进行金相组织分析和硬度测试。基于SYSWELD软件开发并优化了P92钢相变耦合焊接模型,并考虑马氏体相变的Satoh试验和P92钢管道多层多道焊接模拟。焊接试验结果表明,焊缝为淬火马氏体组织、硬度较高,母材为回火马氏体组织、硬度较低,热影响区为混合组织、硬度呈下降趋势。有限元模拟结果表明,模拟所得残余应力分布与实测值吻合,证明了焊接模型的准确性。残余应力的分布与演变过程表明,马氏体相变引起的体积应变与塑性应变对残余应力的形成过程和分布影响显著,且马氏体相变效应在当前焊道作用最为明显,前道焊道的压应力会被后续的热源载荷消除。

国产P92钢的蠕变裂纹扩展行为研究

对国产P92钢开展了600℃蠕变试验,得到了蠕变变形曲线、蠕变指数和蠕变延性等,再在600℃进行蠕变裂纹扩展行为试验研究,得到了蠕变裂纹萌生时间和蠕变裂纹扩展速率与蠕变断裂力学参量C^(*)的关系,将国产P92钢的性能与BS 7910数据进行比较,评估NSW模型的预测效果,计算得到材料的蠕变断裂韧性。结果表明,蠕变裂纹萌生时间和蠕变裂纹扩展速率与蠕变断裂力学参量C^(*)之间有较好的双对数线性相关性。国产P92钢的蠕变裂纹扩展性能优于BS 7910中9%Cr钢的平均性能,NSW模型的平面应力预测结果与试验数据接近,材料的蠕变断裂韧性随着服役时间的增大逐渐降低。该研究结果可以用于评估长期服役高温结构的安全性。

Ripening behavior of M_(23)C_6 carbides in P92 steel during aging at 800°C

The rapid coarsening of the M_（23）C_6 carbides has been held responsible for the creep fracture in 9-12Cr martensitic heat resistant steels.A commercial P92 steel was subjected to thermal aging at a high temperature of 800°C to investigate the ripening behavior of the M_（23）C_6 carbides.Scanning electron microscopy（SEM）and transmission electron microscopy（TEM）were employed to characterize the microstructure evolution,especially the ripening process of the M_（23）C_6 carbides.The new concept of the effective mean size,dependent on the critical radius,was introduced to correct the measured mean size and then the Ostwald theory was applied to describe the ripening behavior of the M_（23）C_6 carbides.The ripening of the M_（23）C_6 carbides was revealed to be grain boundary diffusion controlled.

考虑位错硬化效应的P92钢晶体塑性模拟研究

基于晶体塑性理论,建立了考虑位错硬化效应的P92耐热钢晶体塑性有限元模型。应用模型模拟了P92钢在拉伸过程的塑性变形行为,进一步探究了不同滑移系开动对塑性变形的影响。结果表明:P92钢变形后应力应变、位错密度和形变储存能呈现不均匀分布,证实晶粒发生不均匀的塑性变形。其中位错运动是塑性变形的载体,在晶界处存在位错塞积导致应力应变集中和形变储存能升高;同时塑性变形受滑移系开动的影响,对比模型在不同滑移系统开动下的拉伸曲线,得出{110}<111>作为主滑移系统在单轴拉伸变形过程中起决定性作用。

国产主蒸汽管道用P92钢的持久性能研究

对3个批次主蒸汽管道用P92钢开展了系列温度和应力条件下的持久试验,其中最长持久试验时间达到28000 h。分别采用等温线法、Larson-Miller参数法和Wilshire法对持久性能进行预测,采用等温线法外推的结果介于后两种方法之间,采用Larson-Miller参数法的预测结果高于实际试验数据,而采用Wilshire法的预测结果过于保守。根据试验数据和日本国立材料研究所(NIMS)数据的比较情况以及3种预测方法的10万h持久性能预测结果,认为国产P92钢的持久性能与NIMS和欧洲蠕变委员会(ECCC)的数据比较接近。在进行长时持久性能预测时应选择合适的预测方法,且采用分区处理方法可以提高预测精度。

基于磁巴克豪森效应的P92钢热老化状态检测

针对火电厂锅炉和主蒸汽管道P92钢服役时的热老化状态检测,开发了基于MBN(磁巴克豪森噪声)效应的热老化检测仪器;对不同硬度P92钢进行MBN信号测量,选择了基于启发式硬阈值原则的小波包算法作为滤波算法;得到了MBN信号4种特征值与P92钢硬度值之间的关系;以硬度作为评价热老化状态的参数,对不同服役时长的P92钢试样进行MBN信号检测。试验结果表明,当服役时间小于30000 h时,材料的硬度有小幅度的增大,当服役时间为30000~70000 h时,材料的硬度下降较快,并在服役时间达到70000 h后,硬度下降趋于平缓,微观上表现为4种强化机制对于材料硬度的影响。

P91和P92马氏体耐热钢焊缝中的黑线

借助光学显微镜、扫描电镜、能谱仪、聚焦离子束和透射电镜等设备,研究了P91和P92马氏体耐热钢埋弧焊焊缝中黑线的分布特点、结构特征和形成原因。结果表明:黑线长短不一,主要位于焊缝的柱状晶之间,由线状排列的面心立方M_(23)C_(6)碳化物组成,形成原因是焊接过程中Cr和Mo等元素在柱状晶间偏聚,焊后热处理时M_(23)C_(6)碳化物在柱状晶晶界析出,腐蚀后在光学显微镜下呈黑色线状。

多次热处理对超超临界锅炉用P92钢显微组织及硬度的影响

在超超临界机组用P92钢管道现场安装过程中,为了满足硬度标准经常对接头部位进行多次回火处理,但当前关于多次热处理对P92钢显微组织及其硬度的影响规律尚不清楚。为此,本文对P92钢进行1~4次回火处理,借助OM、SEM、XRD、TEM及硬度计等分析其显微组织特征及硬度变化规律。结果表明,多次回火处理后P92钢均主要由板条状回火马氏体、原奥氏体界面处的M_(23)C_(6)相和马氏体内的MX相组成,其物相组成无明显差异。随回火次数增加,马氏体板条宽度逐渐增加,4次热处理后提高约52.2%;界面处的M_(23)C_(6)析出相发生明显粗化,但析出相数量有所减少,主要粗化机制为Ostwald熟化;基体中Cr、Mo和W合金元素的固溶含量下降,导致回火马氏体的固溶强化作用减弱,P92钢的硬度呈现降低现象。

脉冲电弧焊P92钢接头的组织和力学性能研究

采用脉冲电弧焊对P92钢进行对接焊。检测了焊接接头的显微组织、硬度和力学性能,并在650℃以100 MPa的应力进行了持久试验。结果表明:脉冲电弧焊的P92钢焊接接头焊缝和热影响区组织细小,热影响区无明显的过热粗晶区,邻近熔合线的区域存在过热区;接头的室温和高温拉伸性能与母材相近,高温蠕变断裂强度较采用氩弧焊工艺焊接的P92钢接头提高了约11%。

P92无缝钢管内表面裂纹分析及工艺优化

采用斜轧穿孔工艺生产大口径P92铁素体耐热无缝钢管过程中,钢管内表面易产生细小裂纹。通过金相分析、高温相变计算和高温加热试验等研究表明,内表面裂纹产生的主要原因是:中心有通孔的P92管坯在坯料加热过程中,由于加热温度过高和在炉时间过长(即表面氧化脱碳加重),导致管坯通孔近内壁产生大量的高温δ-铁素体相,管坯在随后的斜轧穿孔中,裂纹在塑性较差的高温δ-铁素体处产生和扩展。根据内表面裂纹的产生机制,通过对P92钢管化学成分的铬当量、镍当量按Cr_(eq)<13%、Ni_(eq)>4%进行控制,坯料保温温度由原工艺的1220~1250℃降为1190~1220℃,对穿孔机轧辊转速、辊距和顶伸量参数优化等工艺改进措施,有效地解决了大口径P92无缝钢管内表面易产生裂纹的问题,提高了P92无缝钢管的成材率和生产效率。

超超临界机组主蒸汽管道用P92钢热压弯头应力试验分析

采用电阻应变测量法对超超临界机组主蒸汽管道用P92钢90°热压弯头进行了内压作用下的应力试验,对弯头各部位缺欠所产生的等效应力与弯头应力分布的相关性进行了分析。结果表明:该弯头在内压作用下,环向应力最大位置位于弯头内壁内弧面中心线处,轴向应力最大位置位于弯头内壁外弧面中心线处,弯头各部位缺欠所产生的等效应力与弯头的主应力分布呈正相关,且同一缺欠在弯头不同部位的危害性不同,进而为同类弯头的产品质量控制及在役弯头针对性质量检测提出了建议。

焊后热处理温度对P92钢焊缝显微组织和力学性能的影响

采用光学金相显微镜、透射电子显微镜、扫描电子显微镜和力学性能测试等方法,研究了焊后热处理温度对P92钢焊缝显微组织和力学性能的影响.结果表明:热处理前P92钢焊缝硬度高、脆性大;随着焊后热处理温度的提高,P92钢焊缝的硬度降低、缺口冲击韧性升高;采用目前的常规热处理恒温时间、焊后热处理恒温温度达到746℃后,焊缝硬度和缺口冲击韧性可以达到母材的力学性能要求;造成P92钢焊缝硬度降低、缺口冲击性能提高的原因是由于板条马氏体基体向等轴亚晶转变、M23C6及MX相的脱溶析出及M23C6的聚集球化和缓慢长大造成的.