溶质在晶界的平衡与非平衡偏聚

在含硼约15ppm 的 Fe-30wt-%Ni 合金中,硼在奥氏体晶界存在平衡与非平衡两类偏聚。等温偏聚动力学曲线上出现极大值,是晶界非平衡偏聚的重要特征。在较低温度下等温,非平衡偏聚促进了晶界硼相的析出和平衡偏聚的建立。在连续冷却的试样中,硼在晶界的偏聚是保温时形成的平衡偏聚和冷却时形成的非平衡偏聚的叠加。加热温度升高,其控制因素由前者转变为后者;冷却速度降低,后者增强。     

EQUILIBRIUM AND NONEQUILIBRIUM SEGREGATION OF SOLUTE AT GRAIN BOUNDARIES

在含硼约15ppm 的Fe-30wt-%Ni 合金中,硼在奥氏体晶界存在平衡与非平衡两类偏聚。等温偏聚动力学曲线上出现极大值,是晶界非平衡偏聚的重要特征。在较低温度下等温,非平衡偏聚促进了晶界硼相的析出和平衡偏聚的建立。在连续冷却的试样中,硼在晶界的偏聚是保温时形成的平衡偏聚和冷却时形成的非平衡偏聚的叠加。加热温度升高,其控制因素由前者转变为后者;冷却速度降低,后者增强。     

Inconel 600及Inconel 718合金晶界偏聚研究进展

高温合金中的溶质晶界偏聚是影响合金多方面性能的重要因素.以高温合金Inconel 600和Inconel718为研究对象,总结了合金中溶质晶界偏聚的研究现状,并对已有的研究成果进行了深入分析,结果发现:溶质在Inconel 600合金中的偏聚规律对舍金性能的影响还需要进一步研究晶界偏聚特性、基本物理参量以及晶间腐蚀抗力的作用;溶质在Inconel 718合金中的晶界偏聚对合金性能的影响依然有待于进一步研究其作用机理、偏聚动力学和共偏聚特性.同时,指出今后高温合金中溶质晶界偏聚的研究方向为溶质晶界偏聚动力学以及溶质问晶界共偏聚行为.     

利用APT研究RPV模拟钢中相界面原子偏聚特征

提高了Cu含量的核反应堆压力容器(RPV)模拟钢经调质处理(880℃保温0.5h,水淬;660℃保温10h)以及400℃时效1000h后,采用原子探针层析技术(APT)研究了碳化物/α-Fe基体,富Cu相/α-Fe基体以及富Cu相/碳化物界面处溶质或杂质原子的偏聚特征。结果表明:在碳化物/α-Fe基体界面处P原子偏聚最明显;在富Cu相/α-Fe基体界面处Ni原子偏聚最明显,Mn原子也有微弱的偏聚;在富Cu相/碳化物界面处未发现溶质或杂质原子的偏聚现象。不同相界处原子偏聚不仅与界面本身微观结构有关,也与相界附近化学特性有关。     

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.     

J75钢的时效处理工艺

本工作研究了时效处理工艺对沉淀强化奥氏体不锈钢J75的显微组织及力学性能的影响。在固定其他热处理工艺参数的情况下,分别对时效温度及时效时间进行研究,结果表明:随着时效温度由600℃升高到760℃,J75钢晶粒度变化不明显,但沉淀强化相的形状和数量均受到影响,强度及硬度在时效温度为720℃时出现峰值;随着时效时间由8h增加到48h,J75钢的显微组织及性能均未发生明显变化。     

超低碳微合金钢中硼的偏聚

用硼径迹显微照相技术研究了超低碳微合金钢从1150℃以5℃/s冷却到850℃过程中硼晶界偏聚的形成与发展过程,测量了不同温度时硼富集因子与贫化区宽度,分析了铜元素对硼晶界偏聚的影响.结果表明:在冷却初始阶段,晶界硼偏聚量迅速增加,在1000℃左右达到最大值后,随着温度的降低,硼晶界偏聚量开始逐渐减少,在910℃左右达到最小,温度继续降低,晶界上硼的偏聚量又开始增加.实验结果还表明添加铜元素能促进硼向晶界的偏聚.     

18Cr9Ni3CuNbN奥氏体耐热钢中富Cu相的早期析出行为

应用三维原子探针技术研究了600℃超超临界电站锅炉过热器/再热器用18Cr9Ni3CuNbN奥氏体耐热钢中强化相富Cu相的早期析出行为,并绘制出富Cu相在18Cr-9Ni型奥氏体耐热钢中的C曲线。结果表明:在高温时效过程中富Cu相无论在650℃还是在700℃均能较快地析出,其形成过程都是在短时间内先形成富Cu偏聚区,随着时效时间的延长Cu原子继续扩散到富Cu偏聚区,其它原子如Fe,Cr,Ni等则被排出富Cu偏聚区而扩散到奥氏体基体中,最终形成富Cu相。     

Inconel 600合金中不同类型晶界处铬的浓度

应用TEM、EDS和EBSD等技术研究了Inconel 600合金在715℃时效过程中不同类型晶界处碳化物的结构、形貌和晶界附近Cr浓度的分布。结果表明,不同类型晶界处碳化物的结构和形貌有较大的不同：在Σ3_c晶界析出的碳化物很少,在Σ3_i晶界析出不规则形状的M₂₃C₆碳化物,在Σ9晶界析出较大的M₂₃C₆碳化物颗粒,在Σ27晶界随机析出粗大的M₇C₃碳化物颗粒。富Cr碳化物在晶界的析出使晶界附近贫铬,在相同的时效条件下晶界的Σ值越高其附近贫铬越严重。随着时效时间的延长各晶界附近贫铬区的宽度不同程度地增大,时效15 h贫铬区的深度最大,时效50 h后深度不同程度地减小。     

X20CrMoV12.1钢长期高温时效的逆回火脆性研究

X2 0CrMoV12 .1耐热合金钢是热电厂主蒸汽管线的主要用材之一。该管材经 16×10 4 h长期高温载荷运行后 ,性能明显退化 ,常温下呈完全脆性状态。试验结果表明 ,管材的脆化是可逆的 ,属于逆回火脆现象。运用透射电镜和俄歇电子能谱等方法对其显微组织结构进行了研究 ,发现晶界碳化物的球化以及有害元素磷在晶界的偏聚是材料性能退化和致脆的原因     

Non-equilibrium grain-boundary segregation of phosphorus in an Ni-Cr steel

In order to confirm the segregation characteristic of phosphorus in Ni-Cr steel at grain boundary, a grain boundary segregation kinetic curve of phosphorus is obtained using Auger electron spectroscopy. The results show that a peak concentration of phosphorus appears at about 60 min during isothermal ageing at 600 °C after quenching from 1000 °C. The boundary concentration of phosphorus decreases with decreasing (increasing) ageing time, when the ageing time is shorter (longer) than 60 min. These results are analyzed by the model of non-equilibrium grain boundary segregation, indicating that this peak is corresponding to the critical time for phosphorus non-equilibrium grain boundary segregation.     

Non-equilibrium grain boundary segregation kinetics of phosphorus in 12Cr1MoV steel at different solution temperatures

The non-equilibrium grain boundary segregation (NGS) concentrations of phosphorus in an industrial steel, 12Cr1MoV, at different solution temperatures, 1050 and 1300°C, were measured. The NGS kinetics curves of phosphorus at the isothermal holding temperature of 540°C are given. These results provide direct support for a NGS kinetic model, and also show that the higher the solution temperature, the higher the segregation concentration of phosphorus at the grain-boundaries, and also the longer the critical time.     

Thermal stability of additively manufactured austenitic 304L ODS alloy

Thermal stability and high-temperature mechanical properties of a 304L austenitic oxide dispersion strengthened(ODS)alloy manufactured via laser powder bed fusion(LPBF)are examined in this work.Additively manufactured 304LODS alloy samples were aged at temperatures of 1000,1100,and 1200℃for 100h in an argon atmosphere.Microstructure characterization of LPBF 304L ODS alloy before and after the thermal stability experiments revealed that despite the annihilation of dislocations,induced cellular substructure by the LPBF process was partially retained in the ODS alloy even after aging at 1200℃.The size of Y-Si-O nanoparticles after aging at 1200℃increased from 25 to 50 nm.EBSD analysis revealed that nanoparticles retained the microstructure of LPBF 304L ODS and hindered recrystallization and further grain growth.At 600℃and 800℃,the yield stress of the 290 and 145 MPa were measured,respectively,which are substantially higher than 113 MPa,and 68 MPa for 304L at the same temperatures.Furthermore,the creep properties of LPBF 304L ODS alloy were evaluated at a temperature of 700℃under three applied stresses of 70,85,and 100 MPa yielding a stress exponent(n)of～7.7;the minimum creep rate at 100 MPa was found to be about two orders of magnitude lower than found in the literature for wrought 304L stainless steel.     

The sensitivity of surface crack initiation to surface roughness in low-cycle fatigue at high temperature

Low-cycle fatigue tests have been carried out on AISI 304L stainless steel and Cr---Mo---V steel specimens with two different modes of surface roughness at 823 K. In the case of Cr---Mo---V steel, grain boundary cavities were not formed during the test. Transgranular cracks were formed and then propagated. The number of cycles required for the crack initiation was observed to be a very large fraction of the toral fatigue life. In the case of AISI 304L stainless steel, grain boundary cavities formed and intergranular crack initiation and propagation was also observed to occur. The number of cycles required for crack initiation was negligible in comparison with the total low-cycle fatigue life.     

Relation of ductile-to-brittle transition temperature to phosphorus grain boundary segregation for a Ti-stabilized interstitial free steel

Equilibrium grain boundary segregation of phosphorus in a Ti-stabilized interstitial free (IF) steel is measured using Auger electron spectroscopy (AES) after the specimens are aged for adequate time at different temperatures between 600 and 850 °C. Based on the experimental data of equilibrium grain boundary segregation along with the McLean equilibrium segregation theory, the free energy of segregation of phosphorus is evaluated to be ∼44.8 kJ/mol, being independent of temperature. With the AES results being combined with the ductile-to-brittle transition temperatures (DBTTs) determined by impact tests, a relationship between DBTT and phosphorus boundary concentration is established. Predictions with the relationship indicate that cold work embrittlement may be severe if the steel is annealed at relatively low temperatures after cold rolling.     

正火处理对304和304L不锈钢在硝酸中耐蚀性的影响

开展热处理对304和304L不锈钢在硝酸中耐蚀性的影响研究,可为不锈钢现场使用过程中的焊接和热处理提供指导.利用正火处理模拟不锈钢在焊接或者热加工过程的受热过程,考察304和304L不锈钢在硝酸中的耐蚀性随受热温度和时间的变化规律.利用电化学动电位再活化法(DL-EPR)与交流阻抗谱法(EIS)研究了不同正火处理条件对304和304L不锈钢在硝酸中耐蚀性的影响.结果表明:2种材料经650℃正火处理后敏化度均为最大值.经900℃正火处理后,304不锈钢的晶粒略有减小,敏化度与未经正火处理的试样相比略有增大,304L不锈钢的晶粒略有增大,敏化度与未经正火处理的试样相比略有减小.304和304L不锈钢经650℃正火处理后,在硝酸介质中其钝化膜的保护能力变差.随保温时间的延长,其在硝酸中的耐蚀性也逐渐降下降.     

Non-equilibrium intergranular segregation in ultra low carbon steel

Abstract

Impurity segregation to grain boundaries in ultra low carbon steel was investigated by Auger electron spectroscopy and SEM during isothermal annealing at 900°C and continuous cooling. The results of isothermal annealing at 900°C show that a concentration peak appears at different times for phosphorus, sulphur, and boron, which is contrary to the equilibrium segregation theory of McLean. The phenomena could be satisfactorily explained by the non-equilibrium segregation theory based on the impurity–vacancy complex mechanism. Under continuous cooling, the segregation concentration at the grain boundary largely depends on the cooling rate. At a low cooling rate the concentration of phosphorus and boron at the grain boundary is higher than that of sulphur, while at the higher cooling rate the concentration of sulphur is higher.     

800MPa级别钢熔敷金属热处理脆化机理研究

用于制造船体结构的10Ni5CrMoV钢,为了消除焊接残余应力,在焊后需对其焊接接头进行热处理。试验采用纯氩气体保护焊接10Ni5CrMoV钢,焊后热处理后发现其熔敷金属-50℃冲击韧性大幅下降。利用扫描电镜(SEM)、透射电镜(TEM)和俄歇电子能谱分析方法(AES)对熔敷金属热处理前后的组织和冲击断口进行分析,找出其冲击韧性下降的原因。试验结果表明:10Ni5CrMoV钢熔敷金属热处理后由于回复作用板条状组织变粗或消失,在晶界磷元素的偏聚和大量的碳化物在晶界析出导致其冲击韧性下降。     

Microstructural aspects of phosphorus grain boundary segregation in low alloy steels

The influence of microstructure on phosphorus grain boundary segregation in 2.6Cr–1Mo–0.3V low alloy steel was investigated. Measurement of the phosphorus grain boundary concentration and characterization of the steel microstructure (substructure) were performed by means of Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). It was found that the phosphorus grain boundary segregation during the aging of the steel at 773 K is faster in as-tempered microstructure than in as-quenched material. The lower dislocation density and the indirectly evidenced lower carbon content in ferrite matrix were considered to accelerate the kinetics of phosphorus segregation.     

纳米Al2O3和TiO2改性有机硅涂层对304不锈钢高温氧化行为的影响

本文以纳米Al₂O₃和TiO₂为主要填料,采用物理混合方法制备了两种纳米改性有机硅涂料,将涂料喷涂于马口铁和304不锈钢表面并室温干燥,获得了两种涂层样品。测试了两种涂层的常规机械性能,研究了600℃空气中涂层对304不锈钢抗氧化性能的影响。结果表明：两种涂层均具有良好的附着力、柔韧性和耐冲击性能。两种涂层均能有效减缓304不锈钢在600℃下的氧化;当纳米Al₂O₃和TiO₂含量比例为4:1时,纳米改性有机硅涂层对304不锈钢的防护效果最佳。