TiNi薄膜马氏体稳定化及其形状记忆效应研究

用DSC研究了预变形对Ti51Ni49形状记忆合金薄膜的相变行为的影响，结果表明：预变形后薄膜的马氏体发生了稳定化现象，第一次逆相变温度T^1A随预应变量增加而升高，而在第二次相变循环中，马氏体稳定化现象消失，逆相变温度T^2A基本恢复到变形前的温度值，马氏体相变温度随预应变量增大而降低，但R相变受预变形影响不大，形状记忆效应研究表明，Ti51Ni49合金薄膜的可恢复应变随预应变量的增加而增大，其最大值4．5％在预应变量为6％时获得。     

高铬铁素体耐热钢的热疲劳与相变

试验研究了高铬铁素体耐热钢的热疲劳与γ、α相变的关系，发现有相变的热循环热疲劳裂纹发生在试样外缘，裂纹长度及变形量均较小，无相变的热循环疲劳裂纹发生在试样中心，裂纹长度及变形量均较大，无相变的Ｃｒ２６钢表面呈严重的龟裂现象，试验证明，相变并不加剧高铬铁素体耐热钢的热疲劳破坏，其机理是相变应力部分抵消热循环过程中产生的热应力。     

预变形对CuAlMnLa形状记忆合金组织及相变性能的影响

以低铝含量的Cu8.8Al5.9Mn0.3La合金为研究对象,探究了不同拉伸预变形量对合金组织、相变点、阻尼特性的影响规律。结果表明:变形量为5.0%时,马氏体再取向已经完全,此后的变形产生了大量的变形孪晶和马氏体旋转破碎,对原马氏体界面的连续性产生不利影响。预变形会不同程度地提高马氏体正逆相变的温度,并且预变形量大于5.0%时,变形产生的大量位错增加了相变的摩擦阻力,导致相变热滞陡增。变形量在3.5%以下时,变形量增加可以提高马氏逆相变能力,阻尼峰值升高,但是变形量过大导致马氏体不连续,会阻碍马氏体逆相变,阻尼峰值下降。     

变形对贝氏体钢等温相变动力学影响

奥氏体预变形影响后续贝氏体相变,采用SEM、膨胀法和XRD衍射分析等实验方法,研究了奥氏体预变形对等温贝氏体相变动力学的影响规律。结果表明,300℃变形25%加速贝氏体相变,且贝氏体最终转量增多,室温组织中残留奥氏体量与贝氏体转变量相关,随贝氏体转变量增大而增多,变形对等温贝氏体相变的影响与变形温度和变形程度有关。此外,首次提出了变形条件下贝氏体相变动力学Avrami修正模型,为下一步系统建立变形条件下贝氏体相变动力学模型提供了参考。本文的结果为缩短高强塑积无碳化物贝氏体钢生产时间提供了有效途径。     

热锻TiNi形状记忆合金膨胀分析

用膨胀法研究了热锻变形非平衡状态TiNi合金的相变特征，结果表明：热锻变形态TNi合金有两类截然不同的膨胀曲线，第1类在降温时膨胀，对应B2→M相变；第Ⅱ类在降温时收缩，对应B2→R相变。热锻变形更有利于R相变发生。热锻变形态合金的相变温度较高，在OC乃至室温以上。其发生相变时的线伸长变化量比较大。固溶处理后，合金的相变温度降低，线伸长变化量减小。     

低碳钢低温变形γ→α相变行为的预测模型

从变形使孕育期缩短的角度，讨论了形变诱导相变的发生条件，计算了不同变形条件下几种成分的低碳钢变形过程析出铁素体的开始温度Ar3d，发现同样变形条件下，碳含量越低的钢种，其Ar3d越高；同一成分钢种，随着变形量增加或变形速率减小，Ar3d提高，基于相变动力学理论，在形核速率计算中充分考虑变形和过冷的双重作用，探索了低温变形诱导铁素体相变的动力学模型，用该模型进行的计算机模拟结果和实验结果吻合良好，表明这种理论处理方法可用来模拟这种相变过程。     

低温变形对Fe-C-Mn-Si超级贝氏体钢组织的影响

研究了Fe-C-Mn-Si超级贝氏体钢低温变形对等温转变贝氏体组织的影响。结果表明,低温下变形会明显缩短贝氏体等温转变的孕育期,同时与未变形等温相变相比,25%的小变形显著促进了贝氏体相变,50%的大变形则阻滞贝氏体相变,低温变形对超级贝氏体相变的影响存在临界变形量。同时,变形等温处理后,贝氏体束由规则的超细板条束改变为断续状,随着变形量的增加,贝氏体断续特征更加明显。     

2205双相不锈钢热变形过程中 形变诱导相变的探讨

对不同热变形工艺的热轧2005双相不锈钢试样进行了WBSD分析,结果表明,在2205双相不锈钢热轧变形过程中,发生了α-β逆相变。进一步的分析显示,工艺参数对这种逆相变的影响规律是;随着变形量的增加和变形温度的降低,该相变的转变量增大。     

海洋平台用钢E40的连续冷却转变

采用热膨胀法测定了未变形和不同变形条件下海洋平台用钢E40的连续冷却转变曲线,对E40钢的显微组织与硬度进行观察。通过分析不同变形量及冷却速度对试验钢相变及组织的影响规律,研究了变形工艺参数对铁素体相变和贝氏体相变的影响。结果表明,随着冷却速度的增加,贝氏体量增多,铁素体量减少,铁素体的晶粒变细;随着变形量增加,铁素体与贝氏体晶粒均能得到细化。     

热变形处理对建筑用HRB400钢筋微观组织与性能的影响

利用热模拟试验机对HRB400钢筋进行单道次热压缩实验,研究变形温度、变形量和变形速率对其微观组织和性能的影响。结果表明,高温变形时,大变形高应变速率有助于形变诱导相变的发生。低温变形时,大变形低应变速率有助于形变诱导相变的发生。在变形温度和变形量不变的前提下,变形速率具有某一最佳中间值。     

变形对低合金钢珠光体→奥氏体相变的影响

采用DSC法研究了变形对低合金钢组织中珠光体→奥氏体相变的影响。结果表明：变形可降低低合金钢的相变温度和相变激活能，缩短相变时间，有利于该低合金钢的相变。     

Reverse Transformation in [110]-Oriented Face-Centered-Cubic Single Crystals Studied by Atomic Simulations

Bidirectional transformations, which are achieved by triggering both dynamic forward transformation from the face-centered-cubic (fcc) austenite to the hexagonal-close-packed (hcp) martensite and the reverse transformation from martensite to austenite during cold deformation, have been previously reported in FeMnCoCr-based high-entropy alloys (HEAs). This leads to the permanent refinement of microstructure and hence enhances the work-hardening capacity of alloys. In order to reveal the microscopic mechanism of the reverse transformation in HEAs under deformation, the effect of the sample aspect ratio, i.e., Z/X, on the evolution of deformation systems in the equi-atomic FeMnCoCrNi alloy with [110] orientation during uniaxial tensile loading along the Z direction is investigated by atomic simulations in this study. When the aspect ratio is 0.5, the reverse transformation is more significant compared with other models, while a good plasticity can still be maintained. We then compare the micromechanical behavior of three fcc single crystals, i.e., FeMnCoCrNi, FeCuCoCrNi, and pure Cu. The results show that the stacking fault energy plays a major role in the activation of different deformation mechanisms; however, the lattice distortion in the HEA does not significantly affect the activation of deformation systems. Furthermore, for all materials dislocation slip leads to the softening, while strain hardening is attributed to the initiation of multiple deformation mechanisms. The Shockley partials slip leads to bidirectional phase transition, twinning and detwinning in the three materials. Thus, the reverse transformation can occur in all metallic materials where the fcc to hcp phase transformation is the dominant deformation mechanism. These findings contribute to an in-depth understanding of the deformation mechanism in fcc-structured materials under severe plastic deformation and provide theoretical guidance for the design of alloys with superior strength-plasticity combinations.     

FTSR产线快冷模式下薄规格高强钢扁卷原因分析及控制

配置短距离、快速冷却层流系统的FTSR生产线具备较好的控轧控冷条件,可充分利用细晶强化生产高强度低合金热轧带钢,但薄规格钢卷普遍出现扁卷缺陷,影响后续加工6为探究扁卷机理,计算了试验钢的连续冷却转变曲线,并通过热模拟试验,研究了试验带钢轧后冷却的相变行为.结果表明,短距离快冷模式下热轧带钢在层冷线上相变孕育期缩短,相变...     

MATHEMATICAL MODELLING OF PHASE TRANSFORMATION FROM HOT—DEFORMED AUSTENITE IN LOW CARBON STEELS

On the basis of superelement model, Cahn's transformation kinetics theory and Scheil's additivity rule, the CCT diagrams and transformation kinetics in low carbon steel were predicted considering both undeformed and deformed conditions. The influence of deformation on phase equilibria and transformation incubation period was evaluated quantitatively. The recrystallization kinetics and the evolution of dislocation density were calculated during continuous cooling. The results show deformation considerably shortens transformation incubation period, accelerates transformation kinetics and makes CCT curve shift leftwards. The calculated CCT diagrams and the volume fraction of each phase are in good agreement with measurements.     

工艺参数对过共析钢过冷奥氏体动态转变的影响

利用Gleeble 1500热模拟试验机进行单轴热压缩实验,研究了含Al过共析钢和不含Al过共析钢过冷奥氏体形变过程中,形变温度和应变速率对组织演变的影响。结果表明:过共析钢过冷奥氏体形变过程中的动态转变经历动态相变和相变所得珠光体的动态球化、超细化。过冷奥氏体动态相变抑制晶界网状渗碳体的形成。动态转变所经历的两个过程均为热激活过程,受形变温度和应变速率的影响。降低形变温度,使过冷度增加;降低应变速率,使完成应变的时间延长,两者均减小了过冷奥氏体完成动态相变所需的应变量,使相变所得的珠光体经历的变形程度增加,有利于珠光体实现球化、超细化。合金元素Al的添加阻碍铁、碳原子的扩散,推迟过冷奥氏体动态相变的发生,细化所得的球化、超细化复相组织。     

Influence of Deformation Degree and Cooling Rate on Microstructure and Phase Transformation Temperature of B1500HS Steel

To study the effects of the deformation degree and cooling rate on the microstructure and phase transformation temperature for the B1500 HS steel, the samples were heated at 900 °C for 5 min, compressed by 10, 20, 30 and 40% at the strain rate of 0.1 s~(-1), and then cooled down at the rates of 50, 40, 25, 20 and 15 °C/s by the thermo-mechanical simulator,respectively. The start and finish temperatures of the phase transformation were determined by the tangent method, and the volume fraction of the phase transformation was ascertained by the level principle according to the dilatometric curves.The volume fraction of the retained austenite was determined by X-ray diffraction. The results show that the volume fraction of the bainite rises with an increase in the deformation degree as the cooling rate is lower than the critical rate. At the same cooling rate, the phase transformation temperature rises with an increase in the deformation degree, and the sizes of both the martensite and bainite phases reduce due to the austenite grain refinement induced by the deformation. The volume fraction of the retained austenite reduces as the deformation degree increases. The critical cooling rate of the undeformed samples is approximately 25 °C/s and the critical cooling rate rises as the deformation degree increases.     

SPHE钢连续冷却过程相变和组织演变规律

采用热模拟方法结合组织观察和硬度测试,绘制出了微碳铝镇静钢热轧板(SPHE)的连续冷却转变(CCT)曲线,分析了SPHE钢动态及静态连续冷却过程的相变及组织演变规律。结果表明,随着冷却速率的增加,SPHE钢的硬度增加,连续冷却相变温度降低,晶粒尺寸减小;同一冷速下,动态连续转变时的相变点明显高于静态;变形条件下的γ+α两相区温度范围小于未变形条件下的,而且变形后的晶粒和渗碳体更加细小。     

热变形参数对α→γ逆相变再结晶晶粒细化的影响

利用Gleeble-1500热模拟试验机,研究了热变形参数对低碳微合金钢α→γ逆相变再结晶的影响及其晶粒细化的机制。结果表明,试验钢中非平衡态组织马氏体在再加热过程中,原奥氏体晶粒发生了逆相变再结晶,并随变形温度的降低,再加热淬火后的奥氏体晶粒逐渐细化;在部分再结晶区变形得到的混晶组织,可以通过逆相变再结晶得到消除;随变形量的增加,再加热淬火后的奥氏体晶粒逐渐细化。     

Evolution of lattice strain and phase transformation of β III Ti alloy during room temperature cyclic tension

An in situ high-energy X-ray diffraction cyclic tension test was carried out on a β III Ti alloy to study its micromechanical behavior and the stress-induced phase transformation. Pre-strained material showed a microscopic multi-stage re-loading behavior following the sequence of elastic deformation, stress-induced martensite (SIM) transformation, a second stage of elastic deformation followed by a final stage of SIM transformation. Based on the relationship of internal strains and diffraction intensities between the β phase and the SIM, it is concluded that after a small strain deformation, the austenite is divided into two different sets of grains with different properties. Those that previously experienced phase transformation have a lower critical stress for the SIM transformation due to residual martensite and dislocations, while the rest have a higher trigger stress and only transform to martensite after the stress is back to levels comparable to where transformation was seen in the previous cycle. The different properties within the same austenite grain family cause the multistage re-loading behavior. The reverse phase transformation during unloading was impeded by the combination of increased dislocation density in the austenite and the increased tensile strain in the martensite prior to unloading.     

相变与超塑性固态焊接

通过对不同工艺参数的超塑固态焊接结合层金相组织的分析，阐明了相变在焊接过程中的重要作用。由于相变时伴随着大量的晶界移运动，造成了小应力一上的超塑变形，细化了晶粒，促进了空位及间隙原子的扩散以及部分晶粒穿过结合面生长，使结合面逐渐消失，形成了一个高质量的整体接头。