16Mn钢中Sb析出对晶内铁素体的影响

利用扫描电镜及能谱分析研究了16Mn钢中Sb的析出行为,利用光学显微镜观察钢的显微组织。结果表明:16Mn钢中Sb的析出位置主要有两种:一是沿原奥氏体晶界析出;二是在MnS夹杂物上富集析出。Sb在MnS夹杂物上的富集析出,能促进钢中晶内铁素体的形成。适当提高S含量,降低O含量,加入Ti变质钢中MnS夹杂等方式,能增加Sb在夹杂物上富集析出,促进了晶内铁素体,尤其是晶内针状铁素体形成,减少了Sb的晶界析出。     

低碳微合金钢中晶内和晶界铁素体长大动力学

利用光学显微镜和晶体长大动力学理论对低碳微合金钢中晶内和晶界铁素体的长大动力学进行了实验测定和理论计算与分析．在实验温度范围（650-750℃）内，铁素体首先在晶界上形成，在晶内夹杂物上形成较晚．晶界与晶内铁素体形成的过冷度相差40℃以上，铁素体在晶内夹杂物上形成比在晶界上形成需要更大的过冷度．晶内铁素体长大速率常数的实测值小于计算值，晶界铁素体长大速率常数的实测值则大于计算值．     

新型微合金非调质钢的组织与性能

研制了一种新型微合金非调质钢。通过合理设计合金成分,改善熔炼脱氧过程,控制钢中氧化物的组成、分布、形状和尺寸,在研制钢中形成微细的氧化物夹杂作为晶内铁素体最有利的析出位置。晶内铁素体的析出细化了晶粒,提高了钢的强度与韧性。     

低温变形低碳钢超细铁素体的形成

在Ｇｌｅｅｂｌｅ ２０００热模拟实验机上通过变形同时水淬和减少变形量的方法,对普通低碳钢低温变形获得超细晶铁素体的机制进行了研究。结果表明：超细晶铁素体的获得主要是形变诱导铁素体和铁素体动态再结晶两种机制共同作用的结果。在８７０－７６０℃低温８０％变形可以获得的等轴均匀超细晶铁素体。形变量控制铁素体的析出量和动态再结晶。应变速率影响形变诱导铁素体所需的临界变形量。冷却过程对铁素体的析出量不产生决定     

等温处理对中碳含钒微合金钢晶内铁素体形成的影响

研究了600,550,500和450℃等温处理对中碳含钒微合金钢晶内铁素体形成的影响,及530℃下钢的组织随等温时间的转变规律.同时测量了不同等温温度处理后钢的维氏硬度,分析了钢中诱导晶内铁素体析出的夹杂物的成分.结果表明:由600℃逐渐降低至500℃进行等温处理,晶内铁素体的含量随之增加,其形状由等轴状变为针状,钢的硬度逐渐降低;但是等温温度降至450℃时,钢中出现了贝氏体,钢的硬度亦随之升高.实验中发现,在远离原奥氏体晶界处,晶内铁素体先于珠光体发生形核长大;由Si、Mn、Ti和V等元素构成的及Mn、Ti和S等元素构成的复合夹杂物可以诱导晶内铁素体形核析出.     

中碳V-N微合金钢连续冷却奥氏体分解及晶内铁素体的形成

采用Gleeble-1500热模拟实验机,对一种中碳V-N微合金钢生产过程的中间冷却、再加热、张力减径及其后冷却过程进行了物理模拟.在张力减径变形后分别在800、730、650、630、615、600、585和550℃采用水冷至室温.研究了张力减径变形后控冷过程中奥氏体的分解规律,重点分析了诱导晶内铁素体形成的因素.结果表明:奥氏体的分解转变依次为晶界铁素体、晶内铁素体和珠光体;在745～639℃范围内,奥氏体分解主要为晶界铁素体形核、长大阶段;冷却到639℃后,大量的晶内铁素体和珠光体开始形核析出.除已广泛接受的依附夹杂物形核外,析出相及先形成铁素体晶界同样是晶内铁素体的有效形核位置.能谱分析表明,诱导晶内铁素体形核的夹杂物附近没有出现贫化区,钢中夹杂物诱导晶内铁素体的形核应该是由惰性界面能和应力-应变能的共同作用.     

冷却速度对含Ti非调质钢中晶内铁素体形成的影响

观察了不同冷速下获得的含Ti非调质钢的显微组织,并绘制了静态连续冷却转变曲线(CCT曲线).结果表明,在0.5～2.5℃/s的冷速范围内,会有晶内铁素体析出,其中在2℃/s冷却时可以获得大量针状铁素体.空冷条件下获得细小无序分布的晶内铁素体,明显提高试验用含Ti非调质钢的韧性.     

低碳Mo-Cu-Nb-B系微合金钢的中温转变组织类型

利用热膨胀仪对低碳Mo—Cu—Nb-B系微合金钢进行了不同温度的等温实验．结合金相（OM）、透射电镜（TEM）研究了不同等温条件下组织转变特点．该微合金钢中温转变有三类组织：沿晶界形核并向晶内单方向生长的准多边形铁素体，晶界或晶内形核的针状铁素体和成束生长的板条贝氏体铁素体．620℃为发生准多边形铁素体转变的鼻尖；580℃只发生少量仿晶界铁素体转变，铁素体转变受到抑制；在530℃左右等温时，奥氏体将发生针状铁素体转变，这些针状组织彼此交割、独立生长，分割原奥氏体晶粒，细化了组织．     

X70微合金管线钢组织中针状铁素体细化机制的研究

以微合金管线钢XTO为研究对象，在Gleeble 1500热模拟机上，进行了不同形变量和冷却速度对合金相变行为及组织细化影响的研究。实验结果表明，形变量和冷却速度的增加，有助于针状铁素体的形成及细化。管线钢中针状铁素体组织典型的形貌为非常微细的亚结构、高位错密度以及部分细板条铁素体，基体上弥散分布着M／A岛和渗碳体。同时可以观察到在铁素体晶粒边界和铁素体晶粒内部有相的析出。可见，针状铁素体组织细化的机制主要有：形变诱导铁素体、铁素体的动态再结晶和相的析出抑制晶粒长大。     

低碳钢铁素体相变析出行为

利用高温淬火相变仪测定了EH40级船板钢晶内铁素体的相变温度区间,又利用高温共聚焦显微镜对晶内针状铁素体的相变析出行为进行了原位观察。结果表明:能得到针状铁素体的最佳降温速率为10℃/s,升温过程中奥氏体开始相变温度Ac_1=743℃,降温过程中奥氏体结束相变温度Ar_1=546℃;针状铁素体的生长过程伴随着加速和减速现象;观察到针状铁素体的3种形核方式,分别为夹杂物诱导形核、在奥氏体晶界上感生形核析出以及在晶界铁素体上感生形核析出。最后揭示了从铁素体析出生长到形成连锁组织的作用机理。     

The effects of ferritic transformation on hot ductility of medium carbon steel

The hot ductilities of Nb-bearing and Nb-free medium carbon steel have been investigated by the hot tensile tests. A high carbon steel (0.4%) was also tested as a reference to determine the relationship between transformation temperature and hot ductility. C and Nb are very effective in delaying the ferrite transformation so that the ductility trough extended to a lower temperature compared to Nb-free medium carbon steel. Decreasing the strain rate promotes the formation of grain boundary ferrite films at higher temperatures and, on the low temperature side, the intergranular failure could still occur even when the amount of ferrite reached 40% or more. The short time temperature oscillation accelerated the precipitation of grain boundary films at higher temperatures, extending the ductility trough to higher temperatures. The samples tested on different machines (direct heating and induction heating) exhibited different hot ductility behavior.     

Effect of Grain Size on the Precipitation Behaviour in Super-Ferritic Stainless Steels During a Long-Term Ageing

A 27.6Cr-3.6Mo-2Ni alloy was solution treated and then aged for a long time to study the effect of grain size on precipitation behaviour by using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The experimental results demonstrated that the average grain size increased from 46.3 ± 6.2 to 101.8 ± 13.5 μm and the grain boundary length per unit area decreased from 3.3 × 10~4 to 1.7 × 10~4 m/m~2 with an increasing annealing temperature from 1100 to 1200 ℃. After ageing at 800 ℃, the σ-phase,χ-phase and Laves phase were observed. As the ageing time increased, the σ-phase notably increased, while the χ-phase and Laves phase gradually decreased before finally vanishing after ageing for 400 h. The σ-phase precipitation kinetics curves consisted of two parts, and the grain size had a significant effect on the first stage of the precipitation curves due to the abundance of nucleation sites in the specimens with finer grains. The Laves phase was transformed from Nb(C,N) particles by Nb diffusion. As the ageing time increased, the ferrite phase decreased due to the transformation of the ferrite phase to the σ-phase, and then C was expelled into the untransformed ferrite grains. Moreover, new Nb(C,N) particles were formed by Nb diffusion from the Laves phase, resulting in the absence of the Laves phase.     

Grain boundary segregation and intergranular fracture in Ferrite containing Mo,Si or Al

Roles of molybdenum, silicon or aluminum in ferrite on grain boundary segregation and hence on intergranular fracture have been investigated by using Auger electron spectroscopy (AES) and tensile test. Competitive segregation between sulfur and carbon or nitrogen, which caused the decrease below 700°C of sulfur content at the grain boundaries, was observed in the pure iron. The intergranular brittleness of the pure iron was caused by sulfur at the grain boundaries. When molybdenum was added to the pure iron, the sulfur contents at the grain boundaries were lowered in comparison to those in the pure iron. The molybdenum-bearing alloy showed higher fracture strength than that of the pure iron, and fractured mostly in the transgranular mode. This arises from the intrinsic effect of molybdenum on the grain boundaries as well as the decrease in sulfur content. Tn the 3.37 wt.%Si alloy, silicon and carbon or nitrogen competitively segregated to the grain boundaries, and such a competitive segregation was also observed between sulfur and carbon or nitrogen. The sulfur content at the grain boundaries decreased with increasing silicon content. The fracture modes in the 3.37- and 4.26 wt.%Si alloys were transgranular in the rolling direction, but were mostly intergranular in the transverse direction and in the as-rolled condition. The intergranular characteristic in the fracture behavior may be attributed to the detrimental effect of silicon as well as sulfur on the intergranular cohesion. Carbon and aluminum only were found at the grain boundaries of the aluminum-bearing alloy. This suggests that aluminum is a strong repulser of sulfur or nitrogen at the grain boundaries. Additionally, it was found that aluminum has a detrimental effect on grain boundary strength of ferrite.     

低碳钢中晶界铁素体/原奥氏体界面对贝氏体转变的影响

采用电子背散射衍射 (EBSD) 研究了低碳Fe--C--Mn--Si钢中晶界铁素体/原奥氏体界面对贝氏体形核的影响. 通过两阶段等温热 处理, 获得了晶界铁素体和贝氏体的混合组织. 结合金相观察和取向测量, 发现晶界铁素体与贝氏铁素体之间的界面分为两种, 一种界面不清晰, 一种界面清晰. 分析表明, 在晶界铁素体/贝氏体界面不清晰一侧, 晶界铁素体与原奥氏体保持取向关系, 贝氏体在这类界面形 核生长, 且取向与晶界铁素体保持一致; 在晶界铁素体/贝氏体界面清晰一侧, 晶界铁素体与原奥氏体无取向关系, 且贝氏体与晶界铁素体之间取向差较大.     

纯铁γ-Fe到α-Fe和共析钢的珠光体转变与过渡相界铁原子个体有序位移机制

纯铁γ-Fe的α-Fe转变遵循过渡相界铁原子个体有序位移机制,这个机制本质上等同于切变而差异于扩散机制。凡是过冷含碳奥氏体的先共析铁素体析出,必然服从相界铁原子个体有序位移机制;这是固态相变第一法则;凡是无碳铁素体必然得自过冷无碳奥氏体,故过冷含碳奥氏体务必预先除碳,这是第二法则。珠光体分解实质上为过冷无碳奥氏体的珠光体铁素体层片的析出,等轴铁素体的析出亦然。在此不存在铁原子个体无序位移扩散机制。铁碳系统固态相变存在群体有序位移切变与过渡相界个体有序机制两类型机制,切变和扩散两类型的分类不具现实和理论意义,这是固态相变物理的科学发展。     

304/Q245R爆炸复合板结合界面的退火组织和硬度

针对304/Q245R爆炸焊接复合板,采用扫描电镜(SEM)和纳米压痕仪研究了消应力退火后基材侧结合界面中珠光体(P)和铁素体(F)形态的演变及对硬度的影响. 结果表明,细晶区为再结晶形成的直径为1 μm的等轴晶粒,原珠光体位置形成的等轴晶粒中,铁素体亚晶尺寸小于100 nm,亚晶界由不连续的球化渗碳体和连续分布的碳原子构成;纤维区中珠光体破碎部位分别发生渗碳体球化和铁素体亚晶析出,部分未破碎的层状珠光体发生时效软化;扭转晶粒区少量破碎的珠光体发生渗碳体球化和铁素体亚晶析出,大量未破碎的层状珠光体区域则发生时效硬化;结合界面中铁素体和珠光体的硬度依据各区域软化或硬化的机制而不同.     

Grain refinement in the process of discontinuous precipitation

The mechanism of grain refinement in the process of nucleation and growth of cells of discontinuous precipitation in the Pb-5 wt % Sn alloy has been investigated. In the case of the nucleation of cells according to an S-like mechanism, there occurs a “splitting” of the initial grain boundary into three boundaries of two adjacent cells. The boundary between the cells is fixed, the boundaries of the growing cells move into the supersaturated solid solution until the collision with other cells. The possibility of the passage of intercrystallite microcracks into the bulk of grains in the process of the discontinuous precipitation is shown.     

Grain boundary segregation of phosphorus in iron-vanadium alloys

Grain boundary segregation of phosphorus has been studied in Fe---V---P and Fe---V---P---C alloys through fracture experiments in a scanning Auger microprobe with the objective of examining the effects of vanadium on the interaction processes operative under circumstances when the structure in the interior of the grain (in the present case carbide formation) and grain boundary segregation occur simultaneously. It is understood that to predict and analyse the behaviour of an alloy, it is pertinent to consider the atomic interactions both at the grain boundaries and in the grain interior and that between the constituents and the grain boundaries. The study suggests that the determining factor for suppression or decrease in the migration of phosphorus to the grain boundaries is whether vanadium is present in the combined form (say, carbide) or is available in solid solution form. When vanadium is present in solid solution form, grain boundary segregation of phosphorus is low because of the chemical interaction of vanadium and phosphorus. However, as carbon is increasingly introduced in the alloy, vanadium now preferentially interacts with carbon in view of a higher interaction for carbon as compared to that of phosphorus. A consequence of this is an increase in the grain boundary concentration of phosphorus. In such a situation, the presence of excess carbon in addition to what is stoichiometrically required to precipitate the entire vanadium as vanadium carbides serves as a palliative with regard to the reduction in the intergranular concentration of phosphorus. This palliative behaviour is explained in terms of the site-competition model. An effort is also made to examine the behaviour of segregating elements in terms of a whole range of probable interactions (both at the grain boundaries and in the grain interior) and chemical interaction energies.     

TiNbV微合金钢焊接接头HAZ晶粒长大及相变原位观察

采用激光共聚焦显微镜原位观察方法，研究了大热输入用TiNbV微合金钢在模拟焊接热循环作用下焊接热影响区(HAZ)晶粒长大过程及相变的规律. 热循环过程中加热温度升高至860 ~ 980 ℃时，发生由铁素体和珠光体向奥氏体的转变，1 100 ℃时，奥氏体晶粒开始有明显长大的趋势，1 300 ~ 1 400 ℃时，晶粒以合并长大方式迅速长大；冷却过程中温度降低至1 400 ~ 1 350 ℃时，晶粒以晶界迁移方式缓慢长大，660 ~ 580 ℃时，发生奥氏体迅速向贝氏体转变，焊接HAZ主要由贝氏体与铁素体组成，贝氏体的尺寸是由奥氏体晶粒大小决定的. 热循环高温停留时间延长，奥氏体与贝氏体的形成、终了、转变温度区间均有下降. 结果表明，组织中先共析铁素体含量先降低后增加，贝氏体含量降低，多边形铁素体消失，先共析铁素体含量增加，冷却组织趋于均匀粗大. 焊接过程中，选择合适的高温停留时间可提高组织中IAF的含量，提高力学性能.