Material behaviour and plant experience of P91/P92 components

In several lignite-fired power plants of the ‘Vattenfall Generation AG’ in Germany components of P91/P92 material are used in long-time operation. About this experience in operation of selected components will be reported. In this context own experimental results of a research project in the damage evolution will be presented. The project ‘Damage development III’ was edited together with the MPA Stuttgart and was supported by Vattenfall and AVIF. The aim of the project was to improve the knowledge about the process of creep damage by experimental tests and additional numerical calculations. An instruction was given for planning, implementation and analysis of recurrent investigations on components consisting of 9% Cr steels which are subjected to high operation loading. Finally, the damage phenomena are presented by two case studies, a damage in a pipe bend due to faulty heat treatment and the creep-crack assessment of a lack of side-wall fusion in a reheater weld by fracture mechanics.     

Effect of thickness and chemical composition on thermal resistance of steel dilatometric specimens under heating-cooling cycles by Joule heating

The effect of thickness and chemical composition on the electrical power and thermal resistance of dilatometric specimens heated by Joule heating are analyzed in different steels, using stepped tests of constant temperature and electrical current. In the stepped constant temperature tests, the electric current necessary to maintain the target temperature in a specific time is measured, while in the electric current tests the electrical current is maintained until the maximum temperature stabilizes. The results show that the electrical power behaves linearly with the thickness associated with the transfer area, while the thermal resistance behaves potentially; both values depend on the chemical composition due to electrical resistivity. The steels with a higher concentration of alloying elements have a better response to Joule heating. However, thickness is the parameter that most influences electrical power due to changes in transfer area and electrical current density, as well as in the mass of the specimen to be heated. Finally, based on the results obtained, predictions are realized for the design of thicker specimens, maintaining the observed behavior; i. e., as the thickness of the specimen increases, the increase in electrical power and thermal resistance is maintained.     

ODS钢的抗辐照设计及纳米第二相粒子表征的研究进展

先进裂变反应堆及聚变堆要求材料在高温高压、强中子辐照、长服役周期等苛刻服役环境下具有卓越的结构和性能稳定性。氧化物弥散强化(ODS)钢由于具有优异的耐高温及耐辐照性能成为第四代反应堆包壳及核聚变包层最有希望的候选材料。基于材料的中子辐照损伤特性,主要介绍了ODS钢的抗辐照设计及纳米第二相粒子的表征方面的研究进展。     

Macro to nanoscale deformation of transformation-induced plasticity steels: Impact of aluminum on the microstructure and deformation behavior

This work aims to elucidate the impact of aluminum-content on microstructure and deformation mechanisms of transformation-induced plasticity(TRIP) steels through macroscale and nanoscale deformation experiments combined with post-mortem electron microscopy of the deformed region.The solid-state transformation-induced mechanical deformation varied with the Al contents,and influenced tensile strength-ductility combination.Steels with 2–4 wt% Al were characterized by TRIP effect.In contrast to 2 Al-TRIP and 4 Al-TRIP steels,twinning-induced plasticity(TWIP) was also observed in conjunction with strain-induced martensite in 6 Al-TRIP steel.This behavior is attributed to the increase in stacking fault energy with the increase of Al content and stability of austenite,which depends on the local chemical variation.The study addresses the knowledge gap with regard to the effect of Al content on austenite stability in medium-Mn TRIP steels.This combination is expected to potentially enable cost-effective alloy design with high strength-high ductility condition.     

Enhancement of work‐hardening behavior of dual phase steel by heat treatment

The work‐hardening response and mechanical properties of dual phase steels originated from different initial microstructures under low and high martensite volume fractions were investigated using a typical carbon‐manganese steel. The modified Crussard‐Jaoul analysis was used for studying the work‐hardening stages and the deformation behavior of ferrite and martensite. It was revealed that the initial martensitic microstructure before intercritical annealing is much better than the full annealed banded ferritic‐pearlitic and spheroidized microstructures in terms of work‐hardening capacity and strength‐ductility trade off. By increasing the amount of martensite, via intercritical annealing at higher temperatures, the ductility decreased but the tensile toughness of dual phase steels increased toward reaching the domain of extra‐advanced high‐strength steels due to the enhancement of work‐hardening rate.     

中国RAFM钢中驻留氘的热脱附行为研究

分别研究了中国自主研发的2种低活化铁素体/马氏体钢(CLAM钢和CLF-1钢)中氘的驻留情况,利用金相显微镜对材料的金相组织进行分析。结果表明,CLAM钢为等轴的回火马氏体相,而CLF-1钢金相组织为保持了板条马氏体形态的细小回火马氏体。通过氘的扩散常数计算2种钢中氘浓度分布,结果显示,CLAM钢和CLF-1钢在500℃、500kPa条件下,氘充饱和情况下氘浓度分别为7.43μg/g和5.7μg/g。在室温下放置0.5h后,CLAM钢和CLF-1钢中的氘分别损失了23%和51%。TDS实验结果表明,CLAM钢中的氘只有1个解吸峰,激活能为21kJ/mol,对应的氢陷阱为晶界和位错。CLF-1钢中的氘有2个解吸峰,解吸峰激活能为31kJ/mol,高温段解吸峰激活能为94kJ/mol。2种钢中低温段解吸峰对应的氢陷阱为晶界和位错,CLF-1钢低温段解吸峰的激活能略高是因为其晶粒尺寸小,氘原子的扩散路径更多。CLF-1钢样品高温段解吸峰对应的氢陷阱是由晶界和位错等缺陷与MC碳化物复合形成的新的氢陷阱。     

冷轧压下率对 ELC-BH 钢板织构的影响

通过极图分析方法研究了冷轧压下率（８０％～９０％）对Ｎｂ＋Ｔｉ处理的ＥＬＣ－ＢＨ钢板冷轧和退火织构的影响．结果表明,冷轧和退火织构的基本特性与冷轧压下率无关,冷轧压下率增大对于退火织构的有利组分与不利组分的强度比影响不大．     

Improvement in the oxidation behavior of austenitic stainless steels by superficially applied,cerium oxide coatings

The influence of superficially applied CeO₂ coatings on the isothermal-oxidation behavior, preceded by nonisothermal heating, as well as cyclic-oxidation behavior of three grades of austenitic stainless steel (AISI-316, –321, and –304), in dry air is reported. The superficial coating had a thickness of 2.1 m. The linear heating rate employed was 6 K min^–1 up to a maximum temperature of 1423 K, and the isothermal holding temperature was 1273 K. The results clearly depict that CeO₂ coatings not only reduced the rates of scale growth for all three varieties of steel but also imparted improved scale adhesion to the respective alloy substrates, as evident from the fact that the coated steels could withstand a number of thermal cycles without scale rupture. In the bare condition, 321-grade steel exhibited the best performance. However, in the presence of the coating, the improved performances of 316 and 321 grades were almost identical, whereas the 304 variety showed improvement only in the first cycle of exposure. The kinetics results have been substantiated by postoxidation analyses of the alloy/scale combinations by SEM, EDS, EPMA, and XRD techniques to reveal the role of rare-earthoxide coatings on the observed behavior.