1000 MPa级冷轧双相钢的热处理工艺与性能研究

从高强度冷轧双相钢的冶金成分设计出发,设计了三种不同成分的C-Mn-Si系冷轧双相钢,通过在(α γ)两相区不同温度的加热淬火,获得(Ferrite Martensite)双相组织;探讨了1000 MPa级冷轧双相钢的热处理工艺、性能与组织;研究了退火温度、冷却速度对双相钢性能的影响,分析了双相钢的强化机理,并且优化了退火工艺参数.结果表明,1000MPa级冷轧双相钢最优退火温度为780～800℃,680℃开始快冷,缓冷速度为10℃/s.     

连续退火工艺和合金元素对800 MPa级冷轧双相钢组织性能的影响

在实验室试制了800MPa级别的高强度低成本C-Mn-Si系双相钢,研究了双相钢的双相处理工艺、组织和性能.通过对三种不同成分的双相钢在( γ)两相区的加热淬火处理获得了不同比例的F M双相钢钢板,其性能可通过调整双相处理工艺来确定.结果表明,800 MPa级冷轧双相钢最优加热温度为760～800℃,缓冷速度为10℃/s.     

780 MPa级冷轧双相钢的组织与性能研究

在实验室试制了780MPa级冷轧双相钢,介绍了其成分设计、轧制工艺和连续退火工艺。研究了过时效温度对钢板力学性能和显微组织的影响,并利用扫描电镜和透射电镜对钢的显微组织进行了分析。结果表明,试制的冷轧双相钢经820℃保温,320℃过时效处理,可以获得综合力学性能优良的冷轧双相钢,其屈服强度为408MPa,抗拉强度为812MPa,伸长率达到了23.1%。     

800 MPa级冷轧双相钢的工艺与组织性能研究

在实验室试制了800 MPa级别的高强度低成本C-Mn-Si系双相钢,研究了双相钢的双相处理工艺、组织和性能。通过对三种不同成分的双相钢在（α＋γ）两相区的加热淬火处理获得了不同F＋M比例的双相钢钢板,其性能可通过调整双相处理工艺来调节。结果表明,800 MPa级冷轧双相钢最优加热温度为760～800℃,缓冷速度为10℃/s。     

冷轧含Cr DP800双相钢的组织与性能

设计了两种不同成分的C-Mn和C-Mn-Cr冷轧双相钢。研究了在两相区温度热处理后其不同比例的F+M双相组织与力学性能的关系。结果表明,C-Mn-Cr钢在770℃保温5min后以10℃/min缓冷至690℃再水冷,可获得由平均晶粒尺寸为6.8μm的铁素体和体积分数约为31%的马氏体组成的双相组织,并具有抗拉强度为825MPa、屈服强度为451MPa和断后伸长率为15.4%的良好力学性能。     

退火温度对镀锌780MPa级双相钢组织性能的影响

研究了不同退火温度对780 MPa级冷轧双相钢组织性能的影响。试验表明:试验钢热轧态组织为铁素体、贝氏体和少量的珠光体,经过冷轧后形成纤维状组织,退火后组织为铁素体和岛状马氏体。对不同退火温度和速度下带钢组织性能进行了分析,带钢在820℃退火、保温100s后,可以获得双相组织且抗拉强度大于780 MPa。     

高强度冷轧热镀锌用双相钢组织及性能研究

在实验室试制了高强度冷轧热镀锌用双相钢,并且优化了模拟连续镀锌退火工艺.利用扫描电镜(SEM)、透射电镜(TEM)以及电子背散射(EBSD)观察了双相钢组织及其微观结构,探讨了不同退火温度对双相钢力学性能和组织的影响规律.研究结果表明,试制的冷轧双相钢具有高的强度和良好的延伸率,其组织主要由板条马氏体和铁素体两相组成,铁素体晶粒间多为大角度晶界,有一半以上的晶粒都是{111}//Z型取向.     

退火对980 MPa级镀锌双相钢组织和性能的影响

研究了不同退火制度下980 MPa级冷轧双相钢的微观组织和力学性能的影响。试验表明,热轧态的微观组织由铁素体、贝氏体和少量的马氏体组成,经过冷轧后形成纤维状组织。通过热模拟不同退火温度和保温时间下带钢微观组织与性能的变化,得出最佳的工艺制度:保温时间约为210 s,退火温度为780~820℃。带钢经退火温度为780℃、保温时间为210 s的热镀锌退火后,可以获得抗拉强度大于980 MPa的冷轧热镀锌双相钢。热镀锌退火后,扫描电镜下观察其室温组织为典型的铁素体+马氏体组织,在铁素体基体中观察到了含Mo元素的第二相,呈球状。     

汽车用450 MPa级冷轧双相高强度钢研制

冷轧双相钢是典型的先进高强钢,因而双相钢在汽车超轻车身设计中的应用比例大幅增加。为适应汽车工业实现轻量化对先进高强钢的市场需求,本钢进行了450 MPa级冷轧双相钢研制开发。文章介绍了汽车用450 MPa级双相高强度钢的化学成分以及热轧、冷轧、热处理工艺等的设计。实验表明:试验钢成品力学性能符合450 MPa级DP钢技术标准要求,显微组织为铁素体加约8%的马氏体,具有典型的双相钢组织特征。目前本钢已正式商业化生产该产品,并得到了多家汽车厂家的认可。     

600MPa级含钒冷轧双相钢的组织性能研究

在实验室试制600 MPa级低碳Si-Mn含钒冷轧双相钢,研究了连续退火后试验钢的组织和力学性能。结果表明:经800℃保温,300℃过时效处理,可以获得综合力学性能优良的冷轧双相钢,其屈服强度为358 MPa,抗拉强度为637 MPa,伸长率达到了23.7%,BH值为55 MPa;钢中V主要以析出物和在铁素体中以固溶态两种状态存在,主要起到析出强化和细化晶粒的作用。     

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.     

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.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

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.