控锻控冷对非调质钢38MnVS5的组织影响

采用热模拟实验技术研究控锻控冷工艺对38MnVS5微合金非调质钢组织的影响。试验工艺参数包括变形量、热变形温度以及锻后冷却速率等,并观察晶粒和组织照片。结果表明,变形量为70％、终锻温度850℃的奥氏体晶粒细化最明显;锻后冷却速度越大,铁素体含量下降,铁素体尺寸越细小。     

Nb-V复合非调质钢热变形行为的研究及其热加工图

采用Gleeble-3800热模拟试验机对Nb-V复合非调质钢在变形温度950~1 150℃、变形速率0.1~10 s-1、变形量为60%下进行单道次压缩试验,研究了Nb-V复合非调质钢的动态再结晶行为,并测得动态再结晶激活能为Qd=353.80 kJ/mol。基于动态材料模型建立了其在常见变形量之下的热加工图。结果表明,该Nb-V钢在变形温度为1 050~1 150℃、应变速率为0.1~0.3 s-1的条件下功率耗散效率值最大,可为确定最佳的热加工工艺参数提供依据。     

铁素体—珠光体型非调质钢及其控锻控冷技术

综述了国内外铁素体－珠光体型非调质钢发展现状，探讨了锻造温度、锻造变形量、变形速率及锻后冷却速度对非调质钢强韧化的影响，指出了旨在控制先共析铁素体组织参数和沉淀硬化效应的控锻控冷新技术。为稳定锻造用铁素体－珠光体型非调质钢性能，推动其规模化生产应用，开拓了前景。     

Nb-V复合非调质钢奥氏体晶粒长大行为

研究了一种新型Nb-V复合微合金非调质钢在不同加热温度和保温时间下的奥氏体晶粒长大规律,并与35MnVN非调质钢进行了对比。讨论了微合金元素Nb、V的存在形式及作用机理,并提出了该钢种较合理的加热工艺。试验结果表明,Nb-V复合微合金非调质钢在1280℃和1140℃下,其奥氏体中的Nb、V主要以NbC、VN相形式析出。利用ASTM晶粒度级别等于5.0的临界判据定义Nb-V复合非调质钢奥氏体晶粒长大温度为1150℃,比35MnVN非调质钢粗化温度提高了50℃,表明该钢种在高温加热时具有较好的抗晶粒长大能力,故其开锻前加热温度应控制在1150～1200℃,保温时间30～60min为宜。     

Nb-V微合金中碳非调质钢CCT曲线的测定与分析

在Gleeble-3500热模拟机上测定了Nb-V微合化金中碳非调质钢在不同冷却速率下的膨胀曲线,并联合金相-硬度法,绘制出了Nb-V试验钢的动态CCT曲线。依据所绘试验钢动态CCT曲线,对试验钢在不同冷却速率下组织的转变转变情况进行了分析。结果表明:冷却速率低于2℃/s时,Nb-V钢的显微组织为铁素体和珠光体,冷却速率超过2℃/s时,钢中组织可以观察到贝氏体,随着冷却速率的增加贝氏体含量也明显增加;冷却速率超过10℃/s时,组织中开始出现马氏体;冷却速率超过15℃/s后Nb-V钢显微组织全部为马氏体。贝氏体转变的临界冷却速率为7~10℃/s,马氏体转变的临界冷却速率为10~15℃/s。     

复合形变热处理对38MnVS钢组织及性能的影响北大核心CSCD

利用热变形与温变形相结合的复合形变热处理工艺对38MnVS非调质钢进行了处理,借助光学显微镜、扫描电镜、能谱仪、拉伸试验机、摆锤冲击试验机及显微硬度仪等对其组织结构及力学性能进行了表征。结果表明,当复合形变热处理工艺为1150~1200℃热变形（25%变形量）＋650℃温变形（15%变形量）时,能够显著改善其组织结构,并有效增加珠光体团位错密度及形变强化效应,其显微组织主要为珠光体和沿晶界或晶内分布的均匀细小铁素体,抗拉强度、屈服强度和冲击吸收功（25℃）分别为935.8 MPa、625.5 MPa和11.8 J,相对于传统的控锻控冷工艺分别提升9.4%,12.5%和61.6%,且试样冲击断口具有解理断裂和微孔聚集型断裂混合特征。     

终锻温度对Nb-V-Ti微合金非调质钢显微组织和冲击韧性的影响

对比研究了经控锻-控冷处理的V-Ti和Nb-V-Ti微合金非调质钢的显微组织和力学性能。结果表明,Nb-V-Ti复合微合金化和控锻-控冷处理能有效细化组织,改善珠光体形态,促进V(C,N)相析出,提高非调质钢的冲击韧性。添加Nb显著提高抗奥氏体晶粒粗化温度,使细小碳氮化物弥散分布。与传统控锻-控冷工艺相比,850~900℃再结晶-未再结晶控锻-控冷工艺,使珠光体片碎化及部分球化,是导致V-Nb-Ti非调质钢冲击韧性提高的主要原因。     

复合形变热处理对38MnVS钢组织及性能的影响

利用热变形与温变形相结合的复合形变热处理工艺对38MnVS非调质钢进行了处理,借助光学显微镜、扫描电镜、能谱仪、拉伸试验机、摆锤冲击试验机及显微硬度仪等对其组织结构及力学性能进行了表征。结果表明,当复合形变热处理工艺为1150~1200℃热变形(25%变形量)+650℃温变形(15%变形量)时,能够显著改善其组织结构,并有效增加珠光体团位错密度及形变强化效应,其显微组织主要为珠光体和沿晶界或晶内分布的均匀细小铁素体,抗拉强度、屈服强度和冲击吸收功(25℃)分别为935.8 MPa、625.5 MPa和11.8 J,相对于传统的控锻控冷工艺分别提升9.4%,12.5%和61.6%,且试样冲击断口具有解理断裂和微孔聚集型断裂混合特征。     

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.     

氮含量对25Mn2CrVS贝氏体型非调质钢组织和性能的影响

研究了N含量(0.016wt%、0.029wt%和0.049wt%)对贝氏体型非调质钢25Mn2CrVS组织和力学性能的影响。结果表明:3组试验钢均为板条贝氏体、粒状贝氏体和铁素体组织,当氮含量从0.016%增加到0.029%时,试验钢强度和韧性增加,组织发生细化,且板条束状贝氏体含量减少,M/A相由长条状变成块状且分布弥散,针状铁素体增加;而氮含量增加至0.049%时,试验钢强度基本不变,韧性急剧下降,组织明显粗化,晶界铁素体形成。固溶钒可以促进板条束状贝氏体在晶界上的形成,奥氏体中析出的VN能够促进针状铁素体的形成。     

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).     

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.     

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.     

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.