高频电阻焊管用低强度钢的热处理工艺

采用Gleeble-3500型热模拟试验机研究了加热速度、加热温度以及冷却速度对高频焊管用钢的组织和性能的影响规律。结果表明:加热速度对奥氏体相变点有显著影响,随加热速度的提高,相变点呈线性增加。在850～1000℃范围内,当加热温度达到925～950℃时,强度达到最低值。随加热温度进一步升高,强度增加。随冷却速度的降低,钢的强度显著下降,组织粗化,且出现带状组织。     

残余应力和组织结构对提高感应脉冲淬火件疲劳性能的作用

结构钢经大功率感应脉冲淬火后,可获得高硬度、高的疲劳极限和高的回火抗力。分析表明,高幅值的残余压应力和“有效晶粒”细化是提高弯曲疲劳性能的主要因素。     

Dimensioning of welded structures made of strain-hardened aluminium alloys

The progress in the standardization of aluminium-welded structures' calculations leaves much to be desired. This paper presents a fundamental evolution of advanced methods of calculation for the building of structures made of strain-hardened aluminium alloys. It contains calculation procedures consistent with Eurocode 9, which account for the actual development of aluminium structural safety. Qualitative advancement in the analysis of load capacity is explicitly visible in the area of welded aluminium structures that display the thermal penetration effect in heat-affected zones; this phenomenon has a destructive impact on the mechanical properties of the structure. These effects are typical of the majority of aluminium alloys and do not happen in the case of welded steel structures.     

Effect of modifying microadditions on the corrosion resistance of welded joints in low‐alloy steel

Results of investigation of the effect of the cooling rate on the structure and mechanical properties of metal in plasma quenching are presented.     

A mathematical model to predict the strength of aluminum alloys subjected to precipitation hardening

A number of alloys, notably most of the aluminum alloys, can be heat treated by aging. This aging due to time-dependent precipitation hardening increases the strength and hardness as well as modifying other mechanical properties. Precipitation hardening has been a popular strengthening mechanism for many decades; therefore, extensive information is available in literature about the precipitation-hardening response of various series of aluminum alloys. The age-har dening response of these alloys is usually represented in graphical form as plotted between property changes and aging time for different temperatures. In designing a suitable precipitation-hardening strategy, one can refer to these graphs. However, for automatic control of aging furnaces, as well as for decision making regarding optimal selection of aging conditions (time/temperature combination), it is desirable to express these relationships in a formal mathematical structure. A mathematical model is developed in this article for widely used heat treatable aluminum alloys used in the extrusion industry. This model is a condensed representation of all σ=f(T, t) curves in different series of aluminum alloys, and the parameters of this model characterize the various compositions of the alloys in the series.     

激光-电弧复合焊接7075-T6铝合金疲劳断裂特性

研究激光一电弧复合焊接2mm板7075-T6铝合金在不同应力比尺和应力幅σa下的疲劳裂纹扩展行为．结果表明,优选的复合焊工艺参数激光功率3kW、电流110A和焊接速度3m／min条件下接头和母材的疲劳裂纹扩展速率曲线存在交叉现象,即当应力强度因子幅△K小于15．6MPa·m1/2。时,接头的疲劳裂纹扩展速率小于母材,反之则接头的疲劳裂纹扩展速率大于母材．而对应同一△K值,高应力比下的疲劳裂纹扩展速率快于低应力比条件下的扩展速率．应力幅或平均应力是影响疲劳裂纹扩展特性的主要因素．     

Coarsening rate of microstructure in semi-solid aluminium alloys

The rate of microstructural coarsening of recrystallisation and partial melting (RAP) and cooling slope (CS) processed materials in the semi-solid state is compared with rates found in the literature. The rate of coarsening depended on the liquid fraction but RAP route 2014 alloy with 37% liquid coarsened slightly more slowly than the CS route 2014 alloy with a lower liquid fraction of 17%, contrary to expectations. For the CS route, an increase in liquid fraction resulted in faster coarsening. A modified 2014 alloy with Fe, Mn and Zn stripped out of the composition gave a relatively high coarsening rate. The coarsening rate was also relatively high for CS 201 alloy in comparison with either RAP 2014 or CS 2014. Low coarsening rates are thought to be associated with the presence of particles which inhibit the migration of liquid film grain boundaries. This could be the result of pinning or of the liquid film impeding diffusion at the boundary.     

Special features of heat treatment of welded joints in large systems in the construction of nuclear power stations

Special features of heat treatment of zones of welded joints in welding of systems of nuclear power stations in the assembling conditions are described. Design features of the equipment for heating the zones of the welded joints and special features of the heat treatment conditions are outlined.     

钢轨现场焊打磨工艺对接头质量的影响

针对无缝线路换铺工程中的钢轨焊接接头踏面上出现的纵向裂纹问题,采用现代材料分析方法分析该类裂纹的特征和组织形貌;采用数控钢轨仿形精磨机进行打磨工艺的模拟对比试验,探讨该类裂纹的形成原因。结果表明,纵向裂纹的产生原因是焊后打磨操作违规导致焊接接头轨顶面打磨发蓝,形成了薄壳状马氏体硬化层,在列车车轮碾压作用下形成了沿纵向的表面裂纹,致使钢轨接头损伤。打磨压力越大,砂轮硬度越高,焊头表面越容易发生打磨发蓝现象。     

Al-Si合金熔体热处理的结构转变

用示差扫描量热分析了Al-Si合金温度处理的熔体结构变化规律及结构变化温度。结果表明,在升温阶段的Al-7%Si亚共晶、Al-12%Si共晶及Al-20%Si过共晶合金的熔体中均存在额外的热效应,范围均在798～850℃之间,额外热效应温度范围与含硅量无关,结构转变焓值随合金的硅含量增加而增加,氢含量不影响结构转变的温度;而在降温过程中仅在Al-20%Si过共晶合金中发现了额外热效应,额外热效应的出现及温度范围取决于降温速度。分析认为,升温阶段的额外热效应体现了Al的熔体结构变化,降温阶段的额外热效应与熔体中的Si-Si原子团簇的行为有关。     

Microstructural characterization of superaustenitic stainless steel surface alloys formed using laser treatment

Conventional stainless steels (SS’s) such as AISI type 304 SS are used in many industrial applications due to their excellent weldability and good mechanical properties. However, in contacts with chlorides, they suffer from localized corrosion. AISI type 304 SS was alloyed at the surface with chromium, nickel, and molybdenum using a CO₂ laser carried under varying laser processing parameters. The objective is to create a surface alloy with composition and microstructure, suitable for marine environments. The surface alloys were characterized using optical microscopy and scanning electron microscopy (SEM) and revealed the presence of the austenitic phase. Analysis by SEM-energy dispersive analysis (EDAX) revealed good compositional homogeneity with molybdenum contents in the range of 3 to 15 wt.%. The dendrite arm spacing (DAS) measured at the surface and bottom of the surface alloy using an image analyzer was found to be in good correlation with calculated cooling rates.     

Removal of Si from recycled aluminium alloys

Abstract

Recycling of aluminium alloys is beneficial to the environment since it uses less energy than primary metal production. However, some instances, such as recycling of brazing sheets used for heat exchanger applications, lead to increased silicon content in Al–Mn alloys (3xxx series) due to the presence of clad layer of eutectic Al–Si alloy. In the present study, the removal of excess Si from recycled Al alloys has been investigated. The feasibility of removing silicon was evaluated using thermodynamic calculations. This was followed by some simple experiments by adding calcium to alloys with known silicon content to reduce it. It was found that the Si content can be reduced by 50% by this process.     

焊缝的非匹配对含表面裂纹管道接头J积分的影响研究

采用有限元方法对几种匹配情况下管道接头表面裂纹的J积分值进行了计算,结果表明焊缝强度匹配以及应变硬化参数匹配的影响随载荷加大而加大,但应变参数匹配影响比强度匹配影响小。对强度匹配对J积分值的影响进行了详细讨论,其结果表明对于高匹配接头来说,J焊缝金属相似文献   

Friction welding of T-joints in sheet structures of aluminium alloys

A special tool is developed for the friction welding of T-joints which produces T-sections with smooth contact between the surfaces of the web and the flange.     

激光表面淬火强化技术的工艺基础

通过对激光与金属材料表面的交互作用规律的研究,从传热学角度得出了激光固态加热的两个基本规律,从物理冶金学角度讨论了激光快速加热作用条件下的金属晶体的缺陷特征、残余奥氏体特征、淬火马氏体特征、组织遗传性以及其各自的形成原因。     

6N01铝合金水冷MIG焊接头组织和性能

针对6N01铝合金熔化焊接头软化问题,研究了水冷对MIG焊接头组织和性能的影响,并与自然冷却条件下接头进行对比.金相试验结果表明,水冷使填充和盖面焊道部分熔化区变窄,焊缝近熔合线的柱状晶区变宽,焊缝内部等轴晶细化;显微硬度试验结果表明水冷条件下接头软化区范围明显变窄且硬度提高;软化区TEM观察显示水冷减少了β'析出相长大;水冷还提高了MIG焊接接头屈服强度和抗拉强度.结果表明,水冷能优化6N01铝合金MIG接头组织并提高力学性能.