等温保持状态下非平衡晶界偏聚动力学的研究

海军舰艇主机及核动力设备中，壁温在570－590℃以及壁温为540℃左右的蒸气道和集箱用钢，长期在回火脆性温度范围服役，会由于磷的晶界偏聚而导致沿晶间的脆性断裂。为此介绍了等温保持状态下磷的非平稳晶界偏聚动力学的研究进展，建立了非平衡偏聚过程和反偏聚过程动力学方程，依此可计算某一温度下任意时刻的晶界偏聚量，并求出对应最大偏聚量的临界时间，从而可以预报钢的晶界脆性，为钢的晶界生控制研究提供了依据。     

低拉应力下12Cr1MoV钢中P原子的晶界非平衡偏聚

对低应力作用下12Cr1MoV钢中磷原子的晶界偏聚现象进行了俄歇能谱实验研究和动力学分析．实验获得了在30MPa拉应力作用下，磷原子在晶界处发生的非平衡晶界偏聚，临界时间是1h．分析表明，低拉应力极大地提高了磷-空位复合体在钢中的扩散速率，低拉应力引起的晶界变形对磷-空位复合体具有强烈的吸引作用．通过动力学计算给出了磷-空位复合体偏聚阶段扩散系数Dc和磷原子反偏聚扩散系数Di随时间变化的表达式．     

磷的非平衡晶界偏聚恒温动力学实验及计算研究

选用12Cr1MoV工业用钢,通过俄歇电子能谱分析方法(AES),对磷在1050℃固溶处理温度下,540℃恒温时效过程中的非平衡晶界偏聚浓度进行了测试,在国际上首次获得了磷在钢中的非平衡晶界偏聚动力学完整曲线,该曲线直接验证了由徐庭栋提出的非平衡晶界偏聚动力学理论模型.论文还进行了非平衡晶界偏聚动力学计算,求出了12Cr1MoV钢在540℃恒温过程中复合体的扩散系数Dc及磷原子的自扩散系数Di,并应用非平衡晶界偏聚动力学方程进行了动力学曲线模拟,拟合曲线与实验曲线符合完好.证实了非平衡晶界偏聚的空位-溶质原子复合体扩散机制.     

热老化对核级316LN锻造控氮奥氏体不锈钢微观组织及性能的影响

研究了热老化对核级316LN锻造奥氏体不锈钢的位错组态、电阻率及显微硬度的影响规律。结果表明,随着热老化的进行,奥氏体基体中位错密度总体下降,而始于晶界向晶内延伸的扩展位错数量增多且宽度变窄,其中,固溶态的扩展位错宽度约为1．0μm,热老化5000h后约为0．2μm。分析认为,碳原子在晶界及其附近微区的偏聚是引起位错亚结构变化的主要原因：电阻率随热老化时间的延长、检测温度的升高而增大,且热老化5000h后电阻率随温度的增长速率高于固溶态;晶内和晶界处的显微硬度值随热老化的进行均有所升高,二者之间显微硬度的差值逐渐增加。     

12Cr1MoV钢的可逆回火脆性非平衡晶界偏聚机制研究

根据实验获得的磷在12Cr1MoV钢中的非平衡晶界偏聚恒温动力学曲线,进行了12Cr1MoV钢的可逆回火脆性动力学研究.在P的偏聚过程、临界时间、反偏聚过程分别选取试样,对试样进行了系列示波冲击试验,测得了不同时效时间试样的DBTT值.实验发现该钢存在过时效现象,即钢材的脆性在开始时随时效时间的延长而逐渐增加,然后又逐渐下降。对材料的可逆回火脆性非平衡晶界偏聚(NGS)机理进行了分析,建立了12CrlMoV钢的可逆回火脆性NGS机制,并依此给出了一种预报和控制钢材晶界脆性的方法.     

热处理工艺对CrWMn冷作模具钢残余奥氏体的影响

本文采用不同热处理工艺控制CrWMn钢中残余奥氏体的含量,并用X射线物相定量分析方法测定了在不同热处理工艺下残余奥氏体的含量,发现CrWMn钢中残余奥氏体的含量随淬火温度的升高而增加,在820℃达到最大含量。在分级热处理时,残余奥氏体含量随等温温度的升高而下降,在260℃至270℃之间基本消除残余奥氏体。     

0.22C-0.45Mn钢低温奥氏体晶粒长大行为的研究

对0.22C-0.45Mn钢进行淬火工艺实验,研究加热温度、保温时间对奥氏体晶粒平均直径的影响,探究0.22C-0.45Mn钢在加热温度(870～990℃)和保温时间(15～120 min)范围内的低温奥氏体晶粒长大行为;基于Beck,Hillert和Sellars模型分别建立奥氏体晶粒平均直径的数学模型,预测0.22C-0.45Mn钢的奥氏体晶粒直径。结果表明：随加热温度的升高,0.22C-0.45Mn钢奥氏体晶粒直径近似呈指数形式增长,长大速率加快;随保温时间的延长,奥氏体晶粒增长速率减缓;3种晶粒模型中,Sellars模型的拟合精度最高,能较好地预测0.22C-0.45Mn钢奥氏体晶粒直径,可为实际生产中旋扩后的0.22C-0.45Mn钢低温热处理工艺提供参考依据。     

37Mn5钢高温形变再结晶规律的研究

本文采用定量金相的方法研究了37Mn5钢(N80石油套管)在再加热前的不同组织状态、加热温度、形变温度、形变量以及形变后在空气中的停留时间等诸参数对奥氏体高温形变再结晶规律的影响。为钢管在淬火前获得最佳奥氏体状态确定比较合理的工艺参数。     

奥氏体化温度和钛含量对20MnVBH钢奥氏体晶粒度的影响

本文研究了奥氏体化温度和钛含量对含有较高氮的20MnVBH钢奥氏体晶粒度的影响。结果表明,该钢的奥氏体晶粒随奥氏体化温度升高逐渐长大,符合一般晶粒长大规律:如果钢中的钛含量大大超过按化学计算的钛量(3.43N),可显著提高奥氏体晶粒粗化温度和细化奥氏体晶粒。     

控制轧制工艺参数对15MnV钢奥氏体状态和铁素体组织的影响

本文研究了热轧工艺参数对15MnV钢奥氏体再结晶行为,奥氏体状态和铁素体组织的影响。实验结果表明,由于奥氏体的形变和再结晶细化,铜坯的加热温度对轧后奥氏体晶粒大小影响不大。在奥氏体的完全再结晶温度范围内,形变量对再结晶百分数有显著的影响。低于完全再结晶温度范围,则热轧温度的影响将会变得更为重要。随着形变温度的下降或形变量增大,奥氏体晶粒内的形变带密度将增大,铁素体晶粒将细化。     

Theoretical progress in non-equilibrium grain-boundary segregation (I): Thermally induced non-equilibrium grain-boundary segregation and intergranular embrittlement

The research progress of non-equilibrium grain-boundary segregation theories in the last 20 years is reviewed. Based on studies by the present authors, the critical time of non-equilibrium segregation and its impact on the development of non-equilibrium segregation theories are described. Quasi-thermo-dynamics and kinetics for thermal non-equilibrium grain boundary segregation are detailed along with a non-equilibrium grain boundary cosegregation model. The experimental validation of the theories and their application to the reversible temper embrittlement of steels and the intermediate temperature brittleness in metals and alloys are also addressed. Supported by the National Natural Science Foundation of China (Grant No. 50771036)     

Effects of Phosphorus Grain Boundary Segregation and Hardness on the Ductile-to-Brittle Transition for a 2.25CrlMo Steel

The combined effect of phosphorus grain boundary segregation and hardness on the ductile-to-brittle transition was examined for a P-doped 2.25CrlMo steel by using Auger electron spectroscopy in conjunction with hardness measurements, Charpy impact tests and scanning electron microscopy. With prolonging time at 540 ~C after water quenching from 980℃, the segregation of phosphorus increases and the hardness decreases. The DBTT （FATT） increases with increasing phosphorus segregation and decreases with decreasing hardness. The effect of phosphorus segregation is dominant until 100 h aging and after that the hardness effect becomes dominant. This effect makes the DBTT （FATT） decrease with further prolonging ageing time although the segregation of phosphorus still increases strongly.     

Effects of Phosphorus Grain Boundary Segregation and Hardness on the Ductile-to-Brittle Transition for a 2.25CrMo Steel

The combined effect of phosphorus grain boundary segregation and hardness on the ductile- to-brittle transition was examined for a P-doped 2.25Cr1Mo steel by using Auger electron spectroscopy in conjunction with hardness measurements, Charpy impact tests and scanning electron microscopy. With prolonging time at 540 oC after water quenching from 980 oC, the segregation of phosphorus increases and the hardness decreases. The DBTT (FATT) increases with increasing phosphorus segregation and decreases with decreasing hardness. The effect of phosphorus segregation is dominant until 100 h aging and after that the hardness effect becomes dominant. This effect makes the DBTT (FATT) decrease with further prolonging ageing time although the segregation of phosphorus still increases strongly.     

Effect of phosphorus on the microstructure and mechanical properties of strip cast carbon steel

Carbon steel strips with different phosphorus and carbon contents were produced by using the twin roll strip casting process.Fine grains and dendrite structure were observed in high-P steels.Negative phosphorus segregation was found in strip cast high-P and high-C steels.For the steels with different carbon contents,phosphorus distribution in the thickness direction of the strip is obviously different.This is because solutes are redistributed in the melting pool and the phosphorus segregation rate is ass...     

Effect of Cu on the boron segregation at grain boundaries and vacancy-type defects in ultra-low carbon micro-alloy steels

By thermal neutron irradiation particle tracking autoradiography(PTA)technique,the development of boron segregation at grain boundaries in ultra-low carbon micro-alloy steels was investigated during cooling from 1150°C to 850°C,and the effect of Cu on boron segregation at grain boundaries was discussed.By positron annihilation lifetime(PAL)technique,the changes of vacancy-type defects with temperatures and the effect of Cu on vacancy-type defects in the cooling process were discussed.Results show that,the concentration of boron at grain boundaries increases rapidly at the beginning of the cooling;after that,it begins to decrease;and then,it increases gradually again.The addition of Cu not only increases the concentration of boron at grain boundaries but also speeds up the development process of boron segregation at grain boundaries.During the continuous cooling process,the addition of Cu significantly affects the change of vacancy-type defects with temperatures in ultra-low carbon micro-alloy steels.     

Theoretical progress in non-equilibrium grain-boundary segregation(II):Micro-mechanism of grain boundary anelastic relaxation and its analytical formula

Finding the internal-friction peak of grain boundary anelastic relaxation was one of the important breakthroughs in the study of internal friction in the last century. But the micro-mechanism of grain boundary anelastic relaxations is still obscure. Based on the observations of the grain boundary segregation or depletion of solute induced by an applied stress, the following micro-mechanism was suggested: grain-boundaries will work as sources to emit vacancies when a compressive stress is exerted on them and as sinks to absorb vacancies when a tensile stress is exerted, inducing grain-boundary depletion or segregation of solute, respectively. The equations of vacancy and solute concentrations at grain boundaries were established under the equilibrium of grain-boundary anelastic relaxation. With these the kinetic equations were established for grain boundary segregation and depletion during the grain boundary relaxation progress. Supported by the National Natural Science Foundation of China (Grant No. 50771036)     

2.25Cr1Mo钢韧脆转变温度影响因素分析

采用不同的时效工艺,运用冲击试验、俄歇能谱、扫描电镜等分析方法,研究2.25Cr1Mo钢的韧脆转变温度变化规律及其影响因素。结果表明,2.25Cr1Mo试验钢650℃时效2h后的韧脆转变温度为-55℃,560℃时效100h后的韧脆转变温度为-25℃,480℃时效1 200h后的韧脆转变温度升高至-10℃;P在晶界处的偏聚行为是导致试验钢韧脆转变温度变化的主要因素。     

The prefer red-site tendency of alloying element Nb in Fe γ phase and its effect on grain boundary cohesion

The discrete variational (DV) and DMol methods within the framework of density functional theory are used to study the effect of alloying element Nb on Fe γ phase. The impurity formation energy in bulk and segregation energies at grain boundary and free surface are calculated. The results show that Nb prefers to segregate at grain boundary. The difference in segregation energies between the grain boundary and the corresponding free surface is - 0.39 eV for solute Nb. According to Rice-Wang model, it can be predicted that Nb can enhance grain boundary cohesion. The calculated results of interatomic energy and charge density show that charge would be redistributed, and the bonds across grain boundary are strengthened by the substitution of Nb for Fe. As a result, it is difficult for the grain boundary to move. Thus the dragging effect of Nb is explained electronically.     

Mg在Ni基高温合金中的晶界偏析行为和强化机制的计算机模拟

用嵌入原子势函数和静态弛豫方法模拟了镁在高温合金中的晶界偏析行为。模拟结果指出，Ｍｇ确有晶界平衡偏析行为。Ｍｇ的晶界偏析使晶界区电子密度分布更加均匀，提高晶界结合强度和空位形成能，减少晶界位错可动性，因此推迟蠕变孔洞的形成和长大，这是Ｍｇ的主要强化机制。     

Theoretical progress in non-equilibrium grain-boundary segregation (Ⅰ): Thermally induced non-equilibrium grain-boundary segregation and intergranular embrittlement

The research progress of non-equilibrium grain-boundary segregation theories in the last 20 years is reviewed. Based on studies by the present authors, the critical time of non-equilibrium segregation and its impact on the development of non-equilibrium segregation theories are described. Quasi- thermo- dynamics and kinetics for thermal non-equilibrium grain boundary segregation are detailed along with a non-equilibrium grain boundary cosegregation model. The experimental validation of the theories and thei...