冷却速率对ES355Al钢相变行为及组织的影响

采用DIL805淬火膨胀仪、金相显微镜及显微硬度计,研究了ES355Al钢连续冷却过程的相变及组织转变规律,分析了冷却速率对ES355Al钢相变及组织演变的影响。结果表明:过冷奥氏体在冷却过程中发生铁素体转变、珠光体转变、贝氏体转变和马氏体转变。在冷速为0.2~1℃/s时,发生铁素体析出和珠光体转变;在冷速为2~7℃/s时,发生铁素体析出、珠光体转变和贝氏体转变,其中7℃/s为珠光体转变结束的临界冷速;,2℃/s、15℃/s分别为贝氏体、马氏体开始转变的临界冷速。ES355Al钢的显微硬度随着冷速增加而增加,由冷速0.2℃/s时的170 HV5增加到20℃/s时的350 HV5。     

齿轮钢16MnCr的过冷奥氏体连续冷却转变规律

利用DIL805L淬火相变膨胀仪研究了齿轮钢16Mn Cr的过冷奥氏体连续冷却转变行为,结合金相-硬度法,绘制静态CCT曲线。结果表明:试验钢在冷速小于0.2℃/s时,室温下获得铁素体+珠光体组织,冷速大于0.5℃/s,室温下试验钢中出现贝氏体组织,冷速大于5℃/s,试验钢中出现马氏体组织;随着冷速的增加,铁素体、珠光体减少,铁素体的形态由多边形向针状发展,硬度由146 HV30增大至380 HV30。由于Mo推迟了铁素体、珠光体转变,降低了获得铁素体的临界冷速,试验钢获得铁素体+珠光体组织的冷速范围较窄。     

SDP2新型贝氏体模具钢的相变及动力学

对新开发大截面贝氏体塑料模具钢SDP2在极低冷速下的过冷奥氏体连续冷却转变过程和相变动力学进行了研究。采用DIL805A高精度差分热膨胀仪测量SDP2钢线膨胀行为,利用SEM分析冷却转变产物;根据JMA公式计算SDP2钢贝氏体相变激活能和Avrami指数。结果表明,SDP2钢过冷奥氏体连续冷却过程包含珠光体、贝氏体和马氏体转变,而无铁素体转变;当冷速大于0.02℃/s时,转变产物以下贝氏体或马氏体为主;小于0.02℃/s时,以上贝氏体或粒状贝氏体为主,并出现珠光体。SDP2钢贝氏体转变的激活能为117 k J/mol,SDP2钢在不同冷速下贝氏体转变动力学指数Avrami指数n≈2~3,经分析计算所得的Avrami指数值所对应的显微组织形态和实验所观察到的显微组织相符合。     

高性能桥梁钢Q370qE-HPS过冷奥氏体连续冷却相变行为

利用Gleeble 1500D型数控动态热-力学物理模拟试验机,针对新近研发的Q370q E-HPS高性能桥梁钢进行了过冷奥氏体连续冷却相变行为研究。结果表明,当冷却速度小于5℃/s时,形成铁素体+珠光体组织,当冷却速度在8℃/s~15℃/s时,形成针状铁素体+贝氏体组织。Q370q E-HPS高性能桥梁钢铁素体转变温度区间为700~800℃,贝氏体转变温度区间为550~700℃,与传统正火工艺桥梁钢Q370q E相比较,Q370q E-HPS钢转变开始温度高。Q370q E-HPS钢两阶段变形后的冷速≤5℃/s时形成均匀细小的铁素体+珠光体组织,可作为控冷阶段的参考冷速。     

960MPa级高强钢的连续冷却转变

采用DIL805L淬火相变膨胀仪,结合光学和扫描电镜组织观察,对960 MPa级高强钢的连续冷却转变进行了研究。结果表明:冷速在0.1~2 ℃/s时,室温组织为铁素体+珠光体+贝氏体,冷速在2~10 ℃/s时,组织为铁素体+贝氏体;当冷速在20~80 ℃/s时,获得全贝氏体组织。在连续冷却转变曲线中,高温转变区和中温转变区未分开,且相变温度随着冷速的增大而减小。     

非调质NM400复相耐磨钢的相变行为

为进一步优化非调质NM400复相耐磨钢不同组织配比,利用Gleeble-3800热模拟试验机探究了试验钢在连续冷却条件下的组织转变规律,并结合金相法和硬度法,绘制出试验钢的动态连续冷却转变(CCT)曲线。结果表明,当冷速低于1 ℃/s时,试验钢组织为铁素体+粒状贝氏体+珠光体,部分粗大的原奥氏体晶粒转变为粒状贝氏体和珠光体。在冷却速率为5~40 ℃/s时,试验钢不再发生珠光体转变,显微组织均为铁素体+贝氏体+马氏体。并随着冷速的增加,马氏体含量不断增加,硬度升高;此外,不同分段冷却方案下,较低的中冷温度以及较长的空冷时间均有利于铁素体和贝氏体的转变。同时,残留奥氏体含量则随铁素体含量的增大而增大;由于试验钢的Ms点较高,马氏体板条较宽,并且有自回火现象发生。     

12Mn钢CCT曲线的测定与分析

采用热膨胀仪测定了12Mn钢在不同冷速下过冷奥氏体连续冷却转变的膨胀曲线,采用膨胀法结合金相-硬度法获得了12Mn钢过冷奥氏体冷却转变曲线(CCT曲线),研究了冷却速率对12Mn钢组织及硬度的影响规律,并应用JMatPro软件模拟了CCT曲线。结果表明,12Mn钢的Ac1和Ac3分别是692和855℃;组织主要有铁素体、珠光体和贝氏体。冷速较低时发生铁素体和珠光体转变;当冷速大于4.25℃/s时发生贝氏体转变;随着冷速提高,各组织变细,12Mn钢的硬度随冷速提高而增大。MatPro模拟结果与所测CCT曲线基本一致。     

500 MPa级高建钢形变奥氏体连续冷却转变行为研究

采用Gleeble-3500热模拟试验机模拟了屈服强度500 MPa级高建钢热变形奥氏体的动态连续冷却转变过程,结合金相法绘制试验钢的CCT曲线,并对相变组织进行维氏硬度测试。试验结果表明,当冷速低于2.5℃/s时,形成多边形铁素体、针状铁素体和珠光体的混合组织;在5~30℃/s的冷速范围内,形成针状铁素体和粒状贝氏体的混合组织;在冷速50℃/s时,开始出现少量板条贝氏体组织。随着冷速的增大,组织细化,连续冷却转变组织硬度增加。试验钢两阶段变形后的控冷工艺窗口为5~25℃/s。     

Q420qE钢形变奥氏体连续冷却转变研究

采用膨胀法在Gleeble-3500型热模拟试验机上测定了Q420qE桥梁钢以不同冷速连续冷却时的膨胀曲线,并结合显微组织观察和维氏硬度测量,绘制出了试验钢的形变奥氏体连续冷却转变曲线(CCT曲线)。研究表明,随着冷速的增加,试验钢的显微组织由铁素体+珠光体逐步转变为针状铁素体+粒状贝氏体;并初步确定试验钢两阶段变形后的控冷工艺窗口为5~10℃/s。在该冷速范围内,试验钢组织为由针状铁素体、粒状贝氏体和M-A岛构成的多相组织。     

压铸用模具钢4Cr5Mo2V的过冷奥氏体连续冷却转变

通过测定不同冷却速度下的相变膨胀曲线、显微组织和硬度,得到了4Cr5Mo2V钢的过冷奥氏体连续冷却转变(CCT)曲线;结合CCT曲线,研究了不同冷却速度下组织形貌演变及硬度变化的规律;比较分析了4Cr5Mo2V钢与H13钢过冷奥氏体连续冷却转变的异同。结果表明:经过不同冷却速度冷却后,4Cr5Mo2V钢的相变产物主要为贝氏体(B)和马氏体(M);冷速小于0.06℃/s时,相变产物主要是贝氏体组织;冷却速度在0.06~0.14℃/s之间,相变产物中出现了贝氏体和马氏体的混合组织;当冷速大于0.14℃/s时,相变产物为马氏体组织。4Cr5Mo2V钢与H13钢的CCT曲线相比,位置向右整体偏移,无铁素体+珠光体转变区,且贝氏体生成区变小,相同冷速下硬度明显提高。     

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.