焊接残余应力形成机制与消除原理若干问题的讨论

针对目前存在的一些对焊接残余应力形成机制和消除原理传统理论的质疑和不同观点，采用两端拘束杆件和长板各焊接的一维简化模型，分析比较了经受加热与冷却热循环以及直接从高温冷却下来时的应变历史和残余应力产生的机制。结果表明，前者存在残余压缩塑性应变，后者存在残余热收缩应变。两者对产生残余应力的作用完全是等价的，为了统一概念，建议引入固有应变理论。固有应变包括焊接过程中产生的塑性应变，热应变和相变应变，残余应力是在固有应变源作用下构件自动平衡的结果，消除焊接残余应力必须去除固有应变源，此外对若干容易混淆的问题进行了讨论。     

连铸坯连续矫直理论再探

本文对连续矫直作不进一步的探讨,充实了文献[7]的一些结果,使对连续矫直这一先进技术的认识前进了一大步。     

网格法用于大应变的确定

此文对网格法作了回顾总结，详细说明了网格法的基本原理，阐述了至今用于网格制作，记录和分析网格的各种实验技术和数据处理技术，简要介绍了近期国内外网格法研究和应用方面的新动向，并指出了一些研究方向。     

循环应变中钢的弹性模量损伤率的测定

根据光滑拉压疲劳试验的循环加载滞后回线,分别测得5CrNiMo和5Cr2NiMoVSi钢住拉伸半周的初始弹性模量E_0,以及经不同循环周次Ni的受损弹性模量Eni。提出了低周疲劳过程中钢的弹性模量损伤率D的表达式,D值随循环应变幅和周次的增加而增加,弹性模量损伤率对疲劳损伤过程较敏感,该值可表征材料损伤的程度,是表示疲劳损伤的一种物理参量。     

关于塑性应变比的测定

此文用直接法和间接法研究了δ值和计算方法对γ值的影响。发现γ值基本上与δ无关。δ只影响其测量精度。δ愈大愈有利于提高γ的测量精度。计算方法对γ值的影响只在δ值较小时，随δ增大，计算方法的影响逐步消除。     

应变幅与应变速率在形变加速腐蚀过程中的作用

采用应变电极技术研究了应变幅，应变速率与外加电位对形变中金属电化学腐蚀过程的影响，选用的体系为工业纯Ｆｅ－３．５％ＮａＣｌ水溶液和Ａ５３７钢－３．５％ＮａＣｌ＋１％ＮａＮＯ２水溶液，结果表明，塑性变形对阳极过程的加速作用大于对阴极过程的加速作用，这种作用主要发生在自腐蚀电位附近，在强阳极与强阴极极化区，由于强的分反应驱动力，单个反应的电流增大，导致了形变电流的增加相对不重要，活化体系的金属溶解电流     

焊接应力变形原理若干问题的探讨(一)

在焊接加热和冷却过程中,组成焊件的小窄条之间不可能存在完全刚性拘束,端面不可能保持平面,会分别产生凸出和凹进,平截面假设不成立.不用平截面假设也可以得到类似的焊接残余应力分布.焊缝不存在残余压缩塑性应变,只存在拉伸应变,焊缝和近缝区残余压缩塑性应变分布和大小的传统观点不成立.提出新的近似用熔池最宽处温度分布表示的拉伸塑性应变分布原理图及其相应的计算公式.     

Q235碳素钢应变诱导相变中的应力一应变曲线分析

分析了单向压缩热模拟条件下碳素钢应变诱导铁素体相变过程中的σ-ε曲线特征结果表明,应变诱导相变过程有自己特定的σ-ε曲线,与典型的奥氏体动态再结晶σ-ε曲线有明显差异随形变温度的降低σ-ε曲线由典型的奥氏体动态再结晶型过渡到铁素体应变诱导相变型在900℃奥氏体稳定状态应变时,随应变速率的提高,奥氏体动态再结晶被推迟,铁素体应变诱导相变提前奥氏体的动态再结晶并不能完全抑止铁素体的诱导相变在770℃奥氏体亚稳态应变时,奥氏体不能动态再结晶应变速率的变化主要与铁素体析出速率相关这时表现为过冷与应变对转变的相对贡献上粗晶奥氏体的σ-ε曲线与细晶不同,两者的差异主要表现在铁素体转变的后期应变诱导相变过程中,铁素体析出的临界应变量εc与应变峰值εp的关系受应变温度和应变速率的影响在奥氏体不能动态再结晶的条件下,εc＜0.3εp.降温单道次形变过程中,Q235碳素钢中会相继发生奥氏体的动态再结晶,铁素体应变诱导相变及铁素体的动态再结晶并反映在σ-ε曲线上     

连铸坯连续矫直理论的初步探讨

本文从弧形连铸坯连续矫直时具有低的恒定的应变速率出发,导出了矫直应变、矫直应变速率的表达式和矫直力矩的计算公式,并对理想矫直曲线的设定进行了讨论。     

基于ARAMIS的搅拌摩擦焊焊接件拉伸试验分析

利用ARAMIS光学应变测量系统分析了搅拌摩擦焊焊接件在拉伸过程中的应变分布和不同位置处的应变变化曲线,结果表明,试验前300s应变变化较缓慢,处在均匀塑性应变阶段,应变从0增加到10%左右,而当300 s时出现颈缩后,进入非均匀集中塑性应变阶段,应变在100s内从10%增加到30%左右,最后在400 s时断裂;距焊缝越近,应变变化越剧烈,离焊缝较远处,应变变化曲线相对较平缓,最大应变出现在焊缝后退侧热影响区,达到31%,而焊核和前进侧的应变最大分别达到24%和16%.     

Estimation of weld properties by Bayesian neural network

In the study of hot working processes, the knowledge of interaction between microstructural behaviour and control process parameters such as temperature, strain rate, and strain is very important. In the last decades, processing maps have been developed to design, control, and optimize the hot strain of various metallic materials. In this work, to study the hot workability of medium carbon microalloyed steel, during hot compression tests, a comparative study between two types of processing maps constructed using phenomenological and thermodynamic continuum criteria has been carried out. The analysis of the maps indicates that the studied steel does not undergo any type of plastic instability. However, the maps corresponding to the strain of ? = 0.6 reveal a domain of dynamic recrystallization, considered as the more efficient domain within the ‘safe’ region process. This domain is centred at 1150°C and 10 s^? 1. Also, the comparative study of the obtained results shows the difference between the positions of plastic strain domains predicted by the two criteria.     

中碳V-N微合金钢热变形行为

用Gleeble-1500热模拟试验机对中碳V-N微合金钢在不同变形温度(900~1050℃)及不同变形速率(0.005~30 s-1)的奥氏体区热变形行为进行研究。通过建立真应力-真应变曲线、动态再结晶图、功率耗散效率因子(η)图和应变速率敏感因子(m)图综合分析其热变形行为。结果表明,试验钢在1050℃、1 s-1变形条件下发生了动态再结晶,其真应力-真应变曲线、动态再结晶图、m图等方法得出的结果相互吻合。其中η图与m图差异很小,但由于应变速率敏感因子具有合理的物理意义,因此建议利用m图分析材料的热变形行为和选取最佳热变形工艺参数。     

Hot Deformation Behavior of an Ultra-High-Strength Fe–Ni–Co-Based Maraging Steel

Hot processing behavior of an ultra-high-strength Fe–Ni–Co-based maraging steel was studied in temperature range of 900–1200 °C and strain rate range of 0.001–10 s~(-1). Deformation processing parameters and optimum hot working window were characterized via flow stress analysis, constitutive equation construction, hot processing map calculation and microstructure evolution, respectively. Critical strain value for dynamic recrystallization was determined through theoretical mathematical differential method: the inflection point of θ–σ and -αθ/ασ-σ curves. It was found that the flow stress increased with the decrease in deformation temperature and increase in the strain rate. The power dissipation maps in the strain range of 0.1–0.6 were entirely similar with the tendency of contour lines which implied that strain had no strong effect on the dissipation maps. Nevertheless, the instability maps showed obvious strain sensitivity with increasing strain, which was ascribed to the flow localization and instability. The optimized hot processing window of the experimental steel was obtained as 1100–1200 °C/0.001–1 s~(-1) and 1000–1100 °C/0.001–0.1 s~(-1), with the efficiency range of 20–40%. Owing to high Mo content in the experimental steel, high dynamic activation energy, Q = 439.311 kJ mol~(-1), was achieved, indicating that dynamic recrystallization was difficult to occur in the hot deformation process, which was proved via microstructure analysis under different hot deformation conditions.     

300M钢的热变形行为及其变形组织演变研究

基于热压缩实验,对300M钢在应变速率为10s-1下的热变形行为及其变形组织演变进行了研究。结果表明:在试样高度压下量为50%,变形温度为700～750℃时,300M钢的应力-应变曲线呈流变失稳型,且变形组织出现绝热剪切;当变形温度为800～1000℃时,300M钢的应力-应变曲线呈双峰不连续动态再结晶型,且热变形过程出现了两轮动态再结晶;当变形温度为1050～1180℃时,300M钢的应力-应变曲线呈单峰不连续动态再结晶型,且热变形过程只发生了一轮动态再结晶。     

60NiTi合金的热压缩变形与显微组织演变（英文）

采用Gleeble-3500热模拟试验机对在变形温度500～650℃和应变速率0.001～1 s^-1条件下的60NiTi合金进行热压缩变形,分析其热变形行为和显微组织,建立变形本构模型,绘制热加工图。结果表明,当压缩温度升高或应变速率降低时,峰值应力减小。合金的热变形激活能为327.89 k J/mol,热加工工艺参数为变形温度600～650℃和应变速率0.005～0.05 s^-1。当变形温度升高时,合金的再结晶程度增大;当应变速率增大时,位错密度和孪晶数量增大,Ni₃Ti相易于聚集;Ni₃Ti析出相有利于诱发合金基体的动态再结晶。动态回复、动态再结晶和孪生是60NiTi合金热变形的主要机制。     

热变形条件对P92钢动态再结晶组织及机制的影响

采用Gleeble-1500D热力模拟压缩试验机,研究P92锻态料在温度900℃～1300℃、应变速率0.5s-1～25s-1、变形程度50%条件下的热变形行为,分析热变形参数对应力-应变曲线、动态再结晶组织演变规律和机制的影响,获得了动态再结晶分数和动态再结晶晶粒尺寸。结果表明,P92钢动态软化机制有动态回复、不连续动态再结晶和几何动态再结晶3种方式。动态再结晶分数随温度的升高而增大,且随着应变速率的增大,发生不连续动态再结晶的温度范围扩大。采用提高热变形温度和高应变速率的改进工艺,可获得P92钢优良的组织和性能。     

Hot deformation and processing maps of as-sintered CNT/Al-Cu composites fabricated by flake powder metallurgy

The deformation behaviors of as-sintered CNT/Al-Cu composites were investigated by isothermal compression tests performed in the temperature range of 300?550 °C and strain rate range of 0.001?10 s^?1 with Gleeble 3500 thermal simulator system. Processing maps based on dynamic material model (DMM) were established at strains of 0.1?0.6, and microstructures before and after hot deformation were characterized by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and high-resolution transmission electron microscopy (HRTEM). The results show that the strain has a significant influence on the processing maps, and the optimum processing domains are at temperatures of 375?425 °C with strain rates of 0.4?10 s^?1 and at 525?550 °C with 0.02?10 s^?1 when the strain is 0.6. An inhomogeneous distribution of large particles, as well as a high density of tangled dislocations, dislocation walls, and some sub-grains appears at low deformation temperatures and strain rates, which correspond to the instability domain. A homogeneous distribution of fine particles and dynamic recrystallization generates when the composites are deformed at 400 and 550 °C under a strain rate of 10 s^?1, which correspond to the stability domains.     

Hot Deformation Characteristics of 13Cr-4Ni Stainless Steel Using Constitutive Equation and Processing Map

Hot compression tests were performed to study the hot deformation characteristics of 13Cr-4Ni stainless steel. The tests were performed in the strain rate range of 0.001-10 s^?1 and temperature range of 900-1100 °C using Gleeble® 3800 simulator. A constitutive equation of Arrhenius type was established based on the experimental data to calculate the different material constants, and average value of apparent activation energy was found to be 444 kJ/mol. Zener-Hollomon parameter, Z, was estimated in order to characterize the flow stress behavior. Power dissipation and instability maps developed on the basis of dynamic materials model for true strain of 0.5 show optimum hot working conditions corresponding to peak efficiency range of about 28-32%. These lie in the temperature range of 950-1025 °C and corresponding strain rate range of 0.001-0.01 s^?1 and in the temperature range of 1050-1100 °C and corresponding strain rate range of 0.01-0.1 s^?1. The flow characteristics in these conditions show dynamic recrystallization behavior. The microstructures are correlated to the different stability domains indicated in the processing map.     

V、N、Nb微合金化对薄板坯连轧带钢组织和性能的影响

在试验室模拟薄板坯连铸连轧过程，板坯均热后被轧制到7mm厚并通过控冷来模拟辊道冷却和带钢的缓慢卷取过程。本文选用低碳钢，研究了V、N、Nb微合金化对其组织和性能的影响。通过试验证明在V-N钢中加入Nb对钢的强化机制有较大影响，使V-N-Nb钢中的析出强化增大，这表明V-N-Nb微合金化可充分地发挥微合金元素在钢中的析出强化作用，析出强化对屈服强度的贡献比V-N微合金化提高17MPa。     

Nb对低碳微合金钢动态再结晶行为的影响

利用Gleeble-1500热模拟试验机研究了3种含铌或不含铌低碳钢在850～1150℃,应变速率分别为0.05、1、10 s-1条件下的热变形行为。采用应变硬化速率-应力(θ-σ)曲线图较精确地获得了C-Mn钢的流变应力和峰值应力;用-dθ/dσ-σ曲线获取了含Nb试验钢的应变和应力值;用回归法确定了双曲线本构方程中的变形激活能,确定了3种试验钢发生动态再结晶的激活能分别为234.867、261.276、301.751 kJ/mol。随Nb含量的增加,试验钢的再结晶激活能逐渐升高。