P355NL1钢双丝MAG焊接头组织及力学性能

对P355NL1正火钢进行双丝MAG焊,并研究了接头组织及力学性能。结果表明,P355NL1钢双丝焊接头成形良好,无未熔合、咬边等焊接缺陷;焊缝区域晶粒均匀细小,金相组织为条状和块状的先共析铁素体分布于柱状晶界上,先共析铁素体沿奥氏体晶界析出,针状和条状铁素体向晶内生长,并含有少量的珠光体组织;母材硬度约HV180,热影响区粗晶区硬度约HV300,细晶区硬度约HV220,焊缝硬度在HV200～HV220之间,无接头软化区;拉伸断裂位置均出现在母材,抗拉强度均值为542 MPa; 25℃和-40℃焊缝的平均冲击吸收功为分别为84 J和67 J,疲劳试样多断裂于焊缝,疲劳极限可达到400 MPa。     

P355NL2正火处理细晶粒钢焊接接头的组织与性能研究

采用MAG焊对P355NL2正火细晶粒钢制作了一组全熔透对接焊缝接头,通过拉伸、弯曲、冲击、硬度及显微金相试验对焊接接头的组织与性能进行研究。结果显示:P355NL2钢焊接接头抗拉性能及弯曲性能均合格,具备良好的塑性、韧性;硬度值分布,母材略低、热影响区略高一些,均在标准要求值范围内;焊缝、热影响区冲击功值均高于标准要求值,具备良好的低温冲击韧性。接头的金相显示焊缝区主要为共析铁素体组织,热影响区主要由铁素体和珠光体组成,并沿母材轧制方向呈带状分布。     

去应力退火对P355NL1钢焊接接头组织及性能的影响

对比研究P355NL1钢MAG焊接接头去应力退火前后的微观组织和基本力学性能,结果表明,通过MAG焊接方法可获得外观良好的焊接接头.去应力退火处理对焊接接头的焊缝、热影响区和母材的微观金相组织无明显影响.去应力退火处理对焊接接头的拉伸性能、断后伸长率和弯曲性能影响不大,但接头硬度有一定程度的降低.去应力退火接头焊缝冲击功变化不大,母材和热影响区的冲击功有一定程度的提高.综合来看,去应力退火处理对P355NL1钢MAG焊接接头的组织及基本力学性能无明显影响,能够保证接头具有良好的使用性能.     

P355NL1钢深熔焊与MAG焊接头力学性能对比研究

进行了10 mm厚的P355NL1钢深熔焊和熔化极活性气体保护电弧焊(MAG)试验,对比了2组焊缝在显微组织、力学性能等方面的差别。结果表明,深熔焊热影响区晶粒受到热循环的影响有一定程度的长大,但相比MAG焊热影响区晶粒仍然较为细小。2种焊接方法的接头力学性能差异明显,深熔焊焊缝拉伸性能、弯曲性能以及冲击韧性均优于MAG焊焊接接头,深熔焊焊接接头抗拉强度均在520 MPa左右,焊缝热影响区冲击吸收功可达155 J,抗弯强度在1 160 MPa左右,表明深熔焊工艺适合于P355NL1钢的焊接。     

Q235钢与316不锈钢异种钢焊接接头组织及力学性能的研究

采用手工电弧焊,填充A307焊条,对Q235钢和316不锈钢进行焊接,得到两种钢的焊接接头。利用金相显微镜对焊接接头的不同区域进行显微组织分析,通过扫描电镜能谱仪对焊接接头进行元素扫描,利用维氏硬度计对焊接接头的硬度进行测定。结果表明:在Q235钢和316不锈钢焊接接头中,焊缝组织呈柱状晶生长,在近焊缝一侧Q235钢中产生脱碳层而软化,在近Q235焊缝一侧出现增碳层而硬化,靠近焊缝的Q235钢热影响区出现针状铁素体组织,热影响区晶粒相对较粗大。316不锈钢热影响区和母材区组织均为奥氏体,Q235钢母材区组织为铁素体与珠光体。通过线扫描发现镍、铬元素在焊缝区域分布基本均匀。焊接接头中焊缝区硬度最高,约为195HV,Q235钢的硬度最低,约为121HV。     

TIG重熔对转向架用P355NL1钢焊接接头性能的影响

利用TIG重熔工艺对转向架用P355NL1钢对接接头进行处理,利用金相显微镜、维氏硬度计以及拉伸试验机研究了TIG重熔对焊接接头微观组织形貌、硬度和抗拉强度的影响。TIG重熔前后焊接接头母材及焊缝组织相同,而TIG重熔区主要为马氏体+少量的M-A组元。TIG重熔前后焊接接头母材及焊缝组织硬度相当,母材为160 HV,焊缝为190HV,而TIG重熔区的硬度显著提高到393 HV。TIG重熔前后焊接接头的抗拉强度基本不变,断裂部位均在母材上。     

X80管线钢及其接头的低温韧性和显微组织

分别利用示波冲击韧性试验、硬度试验和光学显微镜、透射电镜研究了X80管线钢及其焊管接头的力学性能和显微组织。试验结果表明，X80钢及其焊管接头具有良好的韧性，其中焊缝的韧性最高，焊接热影响区粗晶区因受焊接热效应引起晶粒粗化和形成脆性组织，故韧性最低。试验钢由针状铁素体和少量块状铁素体组成，焊缝为典型的针状铁素体组织，焊接热影响区粗晶区以粒状贝氏体为主。焊接热影响区熔合线附近的硬度值最高，越远离熔合线硬度值越低，并逐渐接近母材的硬度值。     

退火处理对P91钢管TIG焊接头组织结构及性能的影响

对P91耐热钢管结构TIG焊接头进行退火处理,并试验分析接头的显微组织和硬度分布。试验结果表明,退火后接头热影响区组织由粗大的板条马氏体转变为片状马氏体,且残余奥氏体的数量减少。退火处理后接头焊缝组织为针状或片状马氏体,且组织中存在一些铁素体组织。退火处理后接头各区域硬度变化趋于平缓,热影响区的硬度约为270~300 HV,而焊缝的硬度约为240~270 HV。770℃退火处理后焊接接头热影响区和焊缝的硬度与750℃退火处理相比稍高。硬度分布的变化与焊缝及热影响区组织结构变化密切相关。     

油气结构用S355NL钢焊接裂纹敏感性研究

采用可控热拘束(CTS)试验和测定焊接热影响区最高硬度的方法,研究了用于油气结构件的S355NL钢的焊接裂纹敏感性。试验结果表明,在不预热条件下,在可控热拘束试验时,S355NL钢焊接接头的裂纹率为0,热影响区最高硬度为318 HV10。S355NL钢的焊接裂纹敏感性较低,其焊接热影响区淬硬倾向小。     

10CrNi3MoV钢激光-MAG复合焊接头组织与力学性能

针对10CrNi3MoV钢激光-MAG复合焊接头的“脆硬”行为,借助光学显微镜、透射电镜、数显硬度仪、MTS电子万能试验机等试验手段,全面分析了接头各区域组织、合金元素分布、显微硬度和力学性能等.结果表明:复合焊接头组织硬化现象明显,焊缝区平均硬度高达324 HV,较常规MAG提高46％,过热区平均硬度高达357 HV,较常规MAG提高42％;与常规MAG焊相比,复合焊接头焊缝中心冲击韧性较低,呈现一定的脆化现象;复合焊焊缝组织主体为粒状贝氏体,多呈长条状分布,且内部分布着较多大尺寸的M-A岛,针状铁素体含量很少.针对复合焊接头“脆硬”行为,提出通过优化焊接材料成分,并对工件进行低温预热的方式进一步提高焊接接头的综合力学性能.     

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.