热变形条件对F40MnV钢冷却相变点及产物的影响

利用Gleeble3500热模拟试验机对非调质钢F40MnV不同热变形条件下的相变过程进行了实验研究,得出了Zener-Hollomon参数对相变转变点、相变组织及硬度的影响规律。结果表明,随形变条件Z因子值增大,先共析铁素体和珠光体的转变温度增高、珠光体的转变区间减小,而铁素体的转变区间基本不变;当完全再结晶时,随Z因子值增大,相变前奥氏体晶粒尺寸减小,转变后先共析铁素体的体积分数增大;在完全再结晶和Z参数值较高(大于1.1×1011)的情况下时,相变后组织的硬度随Z值增大而提高,而在形变中部分再结晶时由于组织处于混晶状态导致该钢的硬度较低。     

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     

Q235碳素钢应变诱导相变中的应力—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换素体的诱导相变，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，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 的关系受应变温度的和应变速率的影响，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的动态再结晶并反映在σ-ε曲线上。     

Q235碳素钢应变诱导相变中的应力-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,铁素体应变诱导相交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σ－ε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．     

Q235碳素钢应变强化相变过程中铁素体晶粒取向分析

利用Ｘ射线衍射和背散射电子衍射（ＢＳＥＤ）分析了单向热压缩条件下碳素钢Ｑ２３５应变强化相变产生的铁素体及 先共析铁素体在应力作用下的晶粒取向分布特点,结果表明,通过应变强化相变产生的铁素体晶粒取向并非完全随机分布,而有较 强的（１１１）／／ ＮＤ线织构 这明显不同于形变铁素体和部分动态再结晶的铁素体晶粒取向待征,先共析铁素体的相对量与（１００） ／／ＮＤ线织构的强度对应。ＢＳＥＤ局部取向（差）定量分析表明,（１１１）取向既可来自应变强化相变,也可来自形变的先共析 铁素体。虽然先井析铁素体形变后外形为形变长条状,但内部仍存在一定的大角晶界;表明先共析铁素体在大应变下进行了一定程 度的动态再结晶     

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.     

低碳钢过冷奥氏体形变过程中的组织及取向变化

利用ＳＥＭ,ＴＥＭ及ＥＢＳＤ研究了低碳钢在７５０℃ ,１０ｓ－１应变速率条件下形变过冷奥氏体的组织及取向变化．结果表明,组织演变由二个阶段组成,形变前期是以形变强化相变铁素体转变为主;当应变达到一定时,以铁素体的动态再结晶为主．应变量较小时,形变强化相变铁素体晶粒优先在原奥氏体晶界形核,随应变量的增加,以相界前沿畸变区的反复形核为主,铁素体转变量逐渐提高,同时珠光体等第二组织增多,铁素体晶粒内部位错密度提高．铁素体连续动态再结晶初期亚晶在珠光体与铁素体交界处优先形成．随应变增加频率提高．形变前期＜００１＞织构为相变铁素体在取向上的特征;形变后期＜１１１＞织构是动态再结晶铁素体在取向上的特征．     

低碳钢过冷奥氏体形变过程超细铁素体的形成

采用过冷奥氏体在A3-Ar3之间变形工艺，获得平均晶粒尺寸约为2μm的微细铁素体晶粒组织，过冷奥氏体形变过程的组织演变包括两个阶段，形变前期以形变强化相变铁素体转变为主导；当相变基本完成后，形变后期以铁素体的动态再结晶为主，形变强化相变是一以形核为主的过程，是晶粒细化的主要原因，应变量较小时，铁素体主要沿原奥氏体晶界及晶内变形带等位置形核，随应变量的增加，以铁素体转变前沿畸变区的反复形核为主。     

铝硅合金化耐候钢的晶粒细化和组织控制

通过热模拟试验研究了铝硅合金化耐候钢在形变强化相变及冷却过程中的组织演变规律。结果表明．其组织演变符合低碳钢形变强化相变的基本规律，形变温度较低时，铁素体转变量较高，晶粒尺寸较小。奥氏体晶粒细化促进形变强化相变过程的发生。经高温奥氏体和形变强化相变两道次变形并控制后续冷却工艺可以获得细晶铁素体和不同第二组织——直接淬火为铁素体（F）＋马氏体（M），以30℃／s冷却为铁素体（F）＋贝氏体（B），以2℃／s冷却为铁素体（F）＋珠光体（P）。当冷却速度大于30℃/s时，细晶铁素体长大不明显。     

Q235碳素钢应变强化相变过程中的动力学问题

利用热模拟单向压缩实验,分析了Q235碳素钢应变强化相变过程中应变对铁素体晶粒数目及铁素体长大速率的影响,同时考察了铁素体转变动力学与应变速率、形变温度、奥氏体晶粒尺寸、纯净度的关系,并与无应变时进行比较,结果表明,应变使铁素体转变动力学发生一定的变化,应变作用下奥氏体晶界的形核率明显增加,但未[观察到应变明显提高铁素体长大速率的现象,应变作用下铁素体的长大速率被周围铁素体快速形成或铁素体的动态再结晶所抑制或掩盖,应变速率的提高主要使铁素体转变时间提前;形变温度越高,应变对铁素体转变的促进作用越明显;原始奥氏体晶粒尺寸不同,转变动力学曲线的斜率稍有不同,这主要由转变初期的形核益的多少引起。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.