H13钢CCT曲线的测定与分析

利用DIL805A型淬火变形膨胀仪对H13钢进行连续冷却转变试验。利用膨胀法结合金相-硬度法绘制H13钢的连续冷却转变(CCT)曲线。研究了冷速对试样组织和硬度的影响。比较分析980、1030℃两种奥氏体化温度所测CCT曲线的异同。结果表明:马氏体转变的临界冷速为1℃/s。随奥氏体化温度降低,Ms点升高,贝氏体转变区域减小,珠光体转变区域增大且向左偏移;随冷却速度增大和奥氏体化温度升高,试验钢硬度增大。     

ST52-3G钢CCT曲线的测定与分析

在Gleeble-1500D热模拟试验机上,测定了ST52-3G钢在不同冷却速率下过冷奥氏体连续冷却的膨胀曲线,利用膨胀法结合金相-硬度法,绘制了试验钢过冷奥氏体连续冷却相转变曲线(CCT曲线),研究了试验钢组织及硬度与冷却速率之间的影响规律。结果表明,试验钢的Ac_1和Ac_3分别为760℃和940℃;微观组织主要有铁素体、珠光体和贝氏体。较慢冷却速率时发生铁素体和珠光体转变,其中铁素体含量较多;当冷却速率大于20℃/s时发生贝氏体转变;随着冷却速率的提高,各组织或晶粒变细,试验钢的硬度随着冷却速率的增加呈先快后慢趋势。     

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。     

铸态GCr15钢在连续加热过程中的奥氏体化动力学特征与组织演变

利用DIL805A热膨胀仪记录了铸态GCr15钢在不同的加热速率下(0.5、3、5、30、100 ℃/s)的线膨胀量,获得了不同加热速率下的热膨胀曲线和奥氏体体积转变分数曲线,研究了加热速率对奥氏体化的影响。采用高温光学显微镜对该钢在连续加热过程中的奥氏体转变过程进行了观察分析。研究表明:GC15钢在连续加热过程中的奥氏体转变可分为3个阶段:在760~790 ℃为珠光体向奥氏体的转变、(Fe, Cr)₃C_II向奥氏体中的溶解和奥氏体的成分均匀化温度分别为790~890 ℃及890 ℃以上。并且随着加热速率提高,相变临界温度提高,相变速率提高。在连续加热过程中,铸态GCr15钢的奥氏体转变是一个形核和长大交替进行的过程。     

SPCC钢CCT曲线测定与分析

结合膨胀法和金相-硬度法,利用Gleeble-1500D热模拟试验机测定了SPCC钢的临界点Ac_1、Ac_3,测得该钢在不同冷速连续冷却时的膨胀曲线﹑相转变点;分析了连续冷却过程中相转变及组织转变的规律;测定了不同冷速下相转变后的硬度,获得了SPCC钢连续冷却相转变曲线(CCT曲线)。结果表明:SPCC钢在连续冷却过程中发生了奥氏体向铁素体和珠光体的转变,且室温金相组织基本为铁素体,而珠光体量比较少;随冷却速率的增加,相变温度降低,晶粒尺寸从24μm减小到12μm,硬度变化不显著。     

P92钢的焊接连续冷却转变曲线

利用热膨胀法,通过Gleeble1500热模拟机测定了P92钢焊接连续冷却转变过程中的膨胀曲线。采用共聚焦显微镜,扫描电镜对不同冷却速度下的试样进行显微组织观察及分析;利用显微硬度计测量了不同冷速下的显微硬度。通过对P92钢连续冷却特性分析和比较得出P92钢的焊接连续冷却转变曲线(SH-CCT曲线)。结果表明,P92钢的焊接CCT曲线分为两个区域,在高温区的类珠光体转变区,在低温区的马氏体转变区。P92钢在0.01~0.1℃/s的冷速范围内获得类珠光体+马氏体+残留奥氏体的混合组织;当冷却速度大于等于0.5℃/s时,获得马氏体与残留奥氏体的混合组织。     

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。     

低碳贝氏体钢AH80DB过冷奥氏体连续冷却转变与等温转变

利用DIL805A淬火相变膨胀仪测定了AH80DB低碳贝氏体钢的连续冷却转变(CCT)曲线与等温转变(TTT)曲线,并结合金相-显微硬度法确定了过冷奥氏体在不同冷速冷却及不同温度等温时的组织转变。结果表明,连续冷却转变时,在0.2~30℃/s冷速范围内,可得到贝氏体组织;AH80DB钢的等温转变曲线为珠光体区在右,贝氏体区在左的双鼻型,在Ms~600℃等温可获得贝氏体组织。     

气保焊丝钢ER70S-G过冷奥氏体的连续冷却转变

利用DIL805A膨胀仪测定了ER70S-G钢的过冷奥氏体连续冷却转变（CCT）曲线,并结合金相-硬度法确定过冷奥氏体在不同冷却速率下的组织转变。结果表明,ER70S-G钢连续冷却过程中,冷速在0.1~0.6 ℃/s范围内时,组织为铁素体+珠光体;冷速为0.8 ℃/s时,组织为铁素体+珠光体+贝氏体;冷速在1~20.0 ℃/s范围内时,组织为铁素体+贝氏体。     

一种超高碳钢的连续冷却转变

在Formastor-FⅡ型全自动相变测定记录仪上,利用膨胀法测定超高碳钢UHCS-6Al的膨胀曲线,结合金相-硬度法,获得了其连续冷却转变(CCT)曲线,并对不同冷速下的组织、硬度进行了研究。结果表明:超高碳钢UHCS-6Al的奥氏体转变温度范围为650~820℃,比GCr15钢奥氏体转变温度明显提高;其马氏体转变临界冷却速度为0.81℃/s,而UHCS-6Al钢的Ms点温度比GCr15钢低。UHCS-6Al钢可获得高硬的马氏体组织,并且其密度比GCr15钢轻9%,是一种良好的轴承钢备选材料。     

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.