奥氏体变形及冷却速率对低碳贝氏体组织中大角晶界分布的影响

使用电子背散射衍射技术研究了低C高Mn高Nb成分设计下,非再结晶奥氏体变形及加速冷却速率对低碳贝氏体组织取向差特征和大角晶界分布的影响.结果表明,与原奥氏体晶粒内部的相变组织相比,原奥氏体晶界附近具有更高的大角晶界密度,非再结晶区奥氏体变形及快速冷却都有利于提高共格相变的驱动力、弱化变体选择以及有效增加大角晶界密度.此外,非再结晶区的大变形除了可充分压扁奥氏体晶粒和增加单位面积的奥氏体晶界密度外,还导致奥氏体晶界上细小的非共格转变铁素体晶粒生成,且这些铁素体晶粒与相邻组织表现出大取向差.      

形变对X65M管线钢形变诱导相变和微观组织的影响

主要研究了不同变形量、不同待温时间对多道次变形和单道次变形后X65M管线钢形变诱导铁素体析出的影响。结果表明:随着变形量的增加和待温时间的延长,奥氏体晶界诱导析出的铁素体量增多,而且奥氏体晶粒也被拉长和细化。研究为提高管线钢的低温韧性提供了依据。     

变形对微合金钢在两相区变形时显微组织的影响

通过热处理试验和单道次压缩热模拟试验,研究了微合金钢加热到两相区变形时的组织演变规律,并分析了变形量的影响,使用OM、SEM和EBSD技术分析了试验钢的微观组织和取向分布。结果表明,试验钢加热到两相区保温后,奥氏体相变在原铁素体晶界上发生,变形时晶界上的奥氏体发生应变诱导相变,形成细小的仿晶界铁素体,变形铁素体发生动态回复或动态再结晶。随变形量和变形温度的提高,硬度下降,800℃下增加变形量,动态回复向动态再结晶发展,动态再结晶形核机制是亚晶转动生长,名义变形量为70%时得到均匀的超细晶组织,有效晶粒平均等效直径为2.7μm,大角度晶界的体积分数达到92.8%。     

超细晶中锰钢温轧强化增塑机理

采用Gleeble-3500热模拟试验机测定了不同温度下中锰钢的变形抗力,并通过分阶段拉伸、扫描电镜、电子背散射衍射、X射线衍射等实验手段,对温轧中锰钢中逆转变奥氏体的相变行为进行观察和分析。研究发现,热轧马氏体中锰钢经过600℃温轧及退火后,获得较多较稳定的残余奥氏体,从而实现强度859 MPa和延伸率36%的优良力学性能。拉伸变形前期,锯齿状流变应力现象明显,残余奥氏体提供持续的TRIP效应来提高塑性,此过程中尺寸较大的逆转变奥氏体稳定性差,变形时先发生转变;拉伸变形后期,锯齿状波动消失,超细晶铁素体和马氏体发生塑性变形,马氏体强化及铁素体中的位错强化为主要强化方式。      

热变形双相不锈钢的微区取向及组织分析

 在变形温度为1000和1100℃,应变速率为01s-1的条件下,利用MMS-200热模拟试验机,对S32750超级双相不锈钢进行了高温压缩试验。利用电子背散射衍射(EBSD)分析了其晶体取向和微观组织。研究结果表明,铁素体在两种试验条件下均可形成<001>和<111>∥压缩轴织构,在变形温度为1100℃时,<001>织构要强一些;奥氏体在两种变形温度下均形成了<001>织构,强度很弱。在变形温度为1100℃条件下,奥氏体中存在的以Σ3为主的CSL特殊晶界数量更多。两种试验条件下,S32750超级双相不锈钢中铁素体和奥氏体均发生了动态再结晶,降低变形温度有利于细化晶粒。在铁素体向奥氏体转变过程中,奥氏体可以在铁素体晶界处生成,也可以在铁素体晶粒内部形成。     

微合金化控轧控冷钢筋纵向金相组织研究

 对微合金化控轧控冷钢筋的纵向金相组织进行了研究,并分析了不同成分试验钢纵向“条带”组织的差异及形成原因。研究结果表明：偏析元素（P、Si、Mn等）在轧制过程中沿轧制方向呈条状分布,是20MnSi、20MnSiV钢产生带状组织的原因。铌及其碳氮化物的溶质拖曳和“钉扎”作用,使20MnSiNb钢的奥氏体未再结晶轧制温度提高到1050℃,在冷却过程中,先共析铁素体在形变奥氏体晶界和内部变形带均匀析出,随后沿形变奥氏体晶界（在先共析铁素体与奥氏体的界面上）生成珠光体带,最后在形变奥氏体晶粒内部形成贝氏体条。研究条件下优势形核点的排序为：形变奥氏体晶界和形变奥氏体晶内变形带、偏析元素和夹杂、再结晶奥氏体晶界。     

09SiMnCrMo钢全奥氏体化后临界区铁素体形成动力学的研究

09SiMnCrMo钢全奥氏体化后降温到临界区等温保持时铁素体的形成可分为三个阶段:①铁素体形核于原奥氏体晶界并快速长大;②原奥氏体晶界被占满后晶界铁素体又长大到一定程度时,铁素体从原奥氏体岛内部析出:③铁素体缓慢地向奥氏体内长大直至平衡。     

超低碳钢在铁素体生长过程中硼分布的变化

通过对照显微结构与硼的自射线径迹显微照相（ＰＴＡ）,研究了一种超低碳含硼钢在铁素体生长过程中硼分布的变化,发现：在发生等温铁素体相变前,硼已偏聚在奥氏体晶界上;铁素体在奥氏体晶界形核;在有铁素体生成的奥氏体晶界上,硼偏聚减弱;沿晶界长出的小块铁素体中硼浓度明显高于奥氏体,但随铁素体长大,其硼含量逐渐与母相持平。这些现象表明,铁素体长大不受硼在奥氏体中扩散的控制     

几种形变钒钢的奥氏体—铁素体等温转变

通过对等温转变温度淬火试样的显微组织观察和铁素体体积分数的测定,研究了钒对热变形微合金钢725～775℃奥氏体-铁素体等温转变的影响。采用薄膜及碳复型透射电镜观察和电子能量损失谱分析,研究了伴随的沉淀析出。转变初期,在奥氏体晶界形成连续的细晶铁素体带。     

氧化物冶金之探析

对利用微细氧化物钉扎奥氏体晶界和诱导晶内针状铁素体进行了理论分析,认为氧化物主要是钢液的脱氧产物,具有尺寸大、体积分数小的特征,既不能有效钉扎奥氏体晶界,也难以促进针状铁素体在奥氏体晶粒内形成。微细的氮化物可以在钢中大量析出,符合有效钉扎奥氏体晶界和诱导针状铁素体的要求。     

形变及冷却条件对35钢铁素体组织的影响

利用热模拟单道次压缩形变试验研究了35钢在临界奥氏体区(Ae3～Ar3)形变后铁素体组织的变化规律。结果表明,形变后水淬,小形变时铁素体首先在原奥氏体晶粒的界隅和晶界上形核,随着形变温度的降低和应变量的增大,原奥氏体内部出现大量细小、等轴的铁素体。在此温度区间形变后缓慢冷却,能够得到超平衡数量(共析转变温度的铁素体转变量)的铁素体,并且随形变温度的降低和形变量的增大,铁素体晶粒明显细化和等轴化。当形变温度降到690℃(Ar3附近),真应变0.92时,铁素体晶粒细化到2～4μm,其体积分数达到76.86%。     

等温压缩对高强度汽车钢WHT1300HF的马氏体相变及微观组织的影响

通过等温形变研究了形变参数(形变温度、形变速率、形变量)对高强度汽车钢WHT1300HF的微观组织转变和形貌的影响规律。研究结果表明:增加奥氏体等温形变量,有利于铁素体的缺陷形核,促进了形变奥氏体向铁素体转变;奥氏体的形变强化导致马氏体相变阻力增大,马氏体相变开始温度(Ms)下降,细小晶粒数量和小角度晶界数量增多;增加奥氏体等温形变(40%)速率能同时促进马氏体和铁素体相变,但马氏体体积分数和小角度晶界数量减少,细小晶粒数量略有提高;降低等温形变温度加剧奥氏体的形变强化,导致Ms温度下降,马氏体体积分数、小角度晶界比例减少,细小晶粒数量增多,铁素体含量明显增加。     

双相不锈钢热老化前后拉伸变形行为的电子背散射衍射表征

通过电子背散射衍射实验分析方法,研究变形量和热老化因素对双相不锈钢的拉伸性能、相边界、局部应变分布、重位点阵特殊晶界和取向分布的影响.研究结果表明:热老化后,双相不锈钢的强度提高,韧性降低;在大变形条件下铁素体晶粒内小角度晶界的数量和密度略有增加;热老化材料的铁素体的塑性变形和局部应变能力下降,大变形破坏初始奥氏体和铁素体以及Σ3孪晶边界的分布.      

Inhomogeneity of the hot deformation of austenitic steel

By high-temperature metallography, the nonuniformity of deformation is studied for 08X18H10T steel with 28% δ ferrite. The mean strain of the ferrite is greater than for the austenite; this difference increases with rise in temperature. Correspondingly, the slip along phase boundaries increases. The hot-microhardness ratio of δ ferrite and austenite declines with increase in test temperature.     

Austenitization during intercritical annealing of an Fe-C-Si-Mn dual-phase steel

Partial austenitization during the intercritical annealing of an Fe-2.2 pct Si-1.8 pct Mn-0.04 pct C steel has been investigated on four kinds of starting microstructures. It has been found that austenite formation during the annealing can be interpreted in terms of a carbon diffusion-limited growth process. The preferential growth of austenite along the ferrite grain boundaries was explained by the rapid carbon supply from the dissolving carbide particles to the growing fronts of austenite particles along the newly formed austenite grain boundaries on the prior ferrite grain boundaries. The preferential austenitization along the grain boundaries proceeded rapidly, but the austenite growth became slowed down after the ferrite grain boundaries were site-saturated with austenite particles. When the ferrite grain boundaries were site-saturated with austenite particles in a coarse-grained structure, the austenite particles grew by the mode of Widmanstätten side plate rather than by the normal growth mode of planar interface displacement.     

Ferrite recrystallization and austenite formation in cold-rolled intercritically annealed steel

The recrystallization of ferrite and austenite formation during intercritical annealing were studied in a 0.08C-1.45Mn-0.21Si steel by light and transmission electron microscopy. Normalized specimens were cold rolled 25 and 50 pct and annealed between 650 °C and 760 °C. Recrystallization of the 50 pct deformed ferrite was complete within 30 seconds at 760 °C. Austenite formation initiated concurrently with the ferrite recrystallization and continued beyond complete recrystallization of the ferrite matrix. The recrystallization of the deformed ferrite and the spheroidization of the cementite in the deformed pearlite strongly influence the formation and distribution of austenite produced by intercritical annealing. Austenite forms first at the grain boundaries of unrecrystallized and elongated ferrite grains and the spheroidized cementite colonies associated with ferrite grain boundaries. Spheroidized cementite particles dispersed within recrystallized ferrite grains by deformation and annealing phenomena were the sites for later austenite formation.     

形变诱导铁素体逆相变过程中的组织及取向变化

 通过对普碳钢Q235在Gleeble1500热模拟机上变形后的微观组织分析,研究了组织中形变诱导的铁素体在变形后保温阶段转变为奥氏体的逆相变现象;并利用背散射电子衍射(EBSD)技术分析了晶粒取向变化。结果表明,在变形后的保温过程中,形变诱导的铁素体先逆相变为奥氏体,同时伴随着诱导铁素体晶粒的长大;然后随着变形后保温时间的延长,逆相变后的奥氏体由马氏体相变逐渐过渡到铁素体的平衡转变,相应地铁素体由具有少量亚结构的形变诱导铁素体逐渐转变为具有较多亚结构的先共析铁素体。     

Monte carlo-method simulation of the deformation-induced ferrite transformation in the Fe-C system

A Monte Carlo (MC) technique has been used to model deformation-induced ferrite transformation (DIFT) in an Fe-C binary system on a mesoscale. The effects of strain rate, strain, and recrystallization of the matrix on DIFT are investigated. Increasing the strain rate slightly retards the onset of DIFT. The volume fraction of ferrite increases gradually as the strain increases before the volume fraction of ferrite reaches its saturation value. After the volume fraction of ferrite becomes saturated, it oscillates around its saturation value. The recrystallization of austenite slightly retards the onset of the DIFT. Although the recrystallization of austenite reduces the equilibrium volume fraction of ferrite significantly, it cannot completely suppress DIFT. The stress concentration has been shown to induce the nucleation of ferrite near the grain boundaries and phase boundaries. The significance of the reverse transformation has been investigated. We found that there is a temporal oscillation of the volume fraction of ferrite and the stored energy after they arrive at their saturation values. We conclude that this oscillation and the effect of the strain rate on DIFT are both brought about by the reverse transformation from induced ferrite to undeformed austenite. The diffusion behavior of carbon atoms in the systems is different for different strain rates. The simulation shows that the dynamic recovery of austenite cannot occur in the system during deformation under the present conditions. The results of the simulation show that, other than the oscillation of the equilibrium volume fraction of ferrite and the unusual diffusion behavior of carbon atoms, the simulation agrees well with the corresponding experimental results. The temporal oscillation of the volume fraction of ferrite and stored energy and the unusual diffusion behavior are two new phenomena that have not been reported by other researchers.