Si-Mn-Mo系低碳贝氏体钢焊接热影响区的脆化机理

用焊接热模拟,普通光学金相,透射、扫描电镜及电子探针,X射线和常规拉伸、冲出等手段研究了一种新型Si-Mn-Mo系低碳贝氏体钢焊接热影响区过热区的组织和性能的关系,重点探讨了过热区的脆化机理.结果表明,在焊接热模拟条件下,原始奥氏体晶粒尺寸是影响机械性能的主要因素.少量准下贝氏体与低碳马氏体的混合组织具有最佳的强韧性配合.随线能量增加,影响韧性的主要因素是奥氏体晶粒粗化以及高温时碳原子在奥氏体晶界及其附近的偏聚;而且碳原子的这种偏聚是经过较高线能量热循环后出现沿晶脆性断口的主要原因.粒状贝氏体及粒状组织中的M-A岛不是该钢焊接热影响区过热区脆化的原因.     

HQ130高强钢热影响区组织及韧性

采用金相、扫描电镜（ＳＥＭ）和热模拟方法，研究了不同峰值温度（Ｔｍ）和冷却时间（ｔ８／５）对ＨＱ１３０钢焊接热影响区（ＨＡＺ）显微组织、冲击韧性和断口形态的影响。试验结果表明，峰值温度１３５０℃，ｔ８／５为５～２０ｓ时，ＨＡＺ韧性较好，ｔ８／５为４０ｓ时，ＨＡＺ韧性明显降低。Ｔｍ由１３５０℃降低到８００℃时，ＨＡＺ冲击韧性相应降低；在Ｔｍ＝８００℃附近ＨＡＺ出现脆性区，冲击韧性明显较低；在Ｔｍ＝７００℃附近ＨＡＺ出现回火软化区，冲击韧性较高，硬度明显下降。实际焊接生产中应采用较小的焊接能量（ｑ／ｖ≤２０ｋＪ／ｃｍ），以防止该钢ＨＡＺ软化和脆化现象。     

低碳钢焊接热影响区TiN粗化的动力学

提出了低碳钢焊接过程中热影响区TiN颗粒粗化的动力学模型。计算结果表明:当质量分数wTi/wN>342时,wTi/wN提高、温度升高以及持续时间延长均会导致TiN颗粒粗化。通过计算发现:部分TiN颗粒的溶解较快,TiN颗粒粗化过程主要受未溶TiN界面前沿钛原子扩散控制。     

纵向焊接铝合金压杆承载力研究

大多数结构用铝合金通常要经过热处理或加工硬化以改善其力学性能。当这种合金焊接后除了产生残余应力外,在焊缝附近还将产生强度明显降低的热影响区(HAZ)。而对于钢结构,由于其热导率比铝材小得多,因此只有高强钢才可能产生强度降低的热影响区,而且其强度的降低没有铝合金显著,热影响区的宽度也比铝合金小得多。这将使得铝合金受压杆件的屈曲性能变得更为复杂。对贴角焊和剖口焊这两种焊接方式的工字型铝合金中心受压杆件进行试验研究,并将试验结果同即将颁布的国标《铝合金结构设计规范》(送审稿)及欧洲规范9(EC9)进行比较。结果表明,通常情况下,对于贴角焊构件,规范结果与试验结果吻合较好;而对于剖口焊构件,规范结果偏保守。     

Characterisation of quasi‐stationary temperature fields in laser welding by infrared thermography

In this work, high‐speed thermography is shown to effectively capture quasi‐stationary temperature fields during the laser welding of steel plates. This capability is demonstrated for two cases, with one involving the addition of a ferritic‐bainitic filler wire, and the other involving the addition of a low‐transformation‐temperature (LTT) filler wire. The same welding parameters are used in each case, but the temperature fields differ, with the spacing between isotherms being greater in the case where the low‐transformation‐temperature filler material is added. This observation is consistent with the differences in the extent of the heat‐affected zone in each sample, and the shape of the weld pool ripples on the weld bead surfaces. The characterization of temperature fields in this way can greatly assist in the development of novel methods for reducing residual stresses, such as the application of low‐transformation‐temperature filler materials through partial‐metallurgical injection (PMI). This technique reduces or eliminates tensile residual stresses by controlling the temperature fields so that phase transformations take place at the optimum times, and success can only be guaranteed through precise knowledge of the temperature fields in the vicinity of the welding heat source in real time.     

快速加热过程中Fe-40Ni-Ti合金的晶粒长大行为

利用热模拟技术、金相观察及定量统计,通过分析Fe-40Ni-Ti合金快速升温过程中试样不同部位的晶粒长大规律,模拟研究了焊接过程中奥氏体晶粒的长大行为.结果表明:温度最高的中心线附近晶粒长大显著,5 s内温度达到1350℃时,其尺寸达到了180 μm;而距离中心线4 mm处的热影响区及母材(试样端部)晶粒变化不大,在80 μm左右.金相观察发现TiN颗粒对晶界迁移产生了明显的阻碍作用.     

Effects of microstructural heterogeneity on very high cycle fatigue properties of 7050-T7451 aluminum alloy friction stir butt welds

In this study, the very high cycle fatigue (VHCF) properties of 7050-T7451 aluminum alloy and its friction stir welding (FSW) butt welds have been investigated. The results show that the failure of FSW joints still occurs at 7.0 × 10⁸ cycles. The fatigue properties of the FSW joints are superior to those of the base material, especially in the super long life regime. Most fatigue cracks initiate at the thermo-mechanically affected zone and heat affected zone on the advancing side of the FSW joints, and the susceptibility of these zones to fatigue is attributed to the metallurgical heterogeneity.     

石油储罐钢焊接热影响区模拟研究

采用焊接热模拟技术,研究不同焊接热输入条件下焊接热循环对石油储罐钢焊接热影响区粗晶区(CGHAZ)的组织和性能的影响.结果表明:实验钢在80～100kJ/cm的大热输入下,热影响区仍能够保持良好的低温韧性;随着焊接热输入的增加,实验钢CGHAZ组织变粗大,低温冲击功下降;钢中弥散分布着大量细小TiN粒子,在焊接热循环中...     

Mechanomaking of nanostructured hypereutectic white irons: powder fabrication

Abstract

White irons containing 5·7 wt-%C were produced by room temperature, high energy milling from iron and carbon elemental powders. Both iron and cementite phases have crystal sizes of less than 10 nm in the powders which have fully dense particles of 50 μm mean size. The gas content is 0·5 wt-% and the powder is stable up to 550°C. Above 550°C decomposition of cementite occurs, involving a decrease in combined carbon content from 5·7 to 3·5 wt-% (annealing at 1050°C). The crystal growth kinetics has two temperature regions with lower activation energies in the high temperature (above 800°C) region. Crystal sizes still below 100 nm were observed for annealing up to 800°C. The size distribution in mechanosynthesised powders was modified by tumbling (dry) and attritor (wet) milling down to mean sizes of 4 μm and 1·4 μm respectively. Whereas tumbling milling does not alter the properties of MS powders, wet attritor milling produced higher gas content (7 wt-%) and much decreased thermal stability. Mechanosynthesised and tumbling milled powders can be degassed prior to consolidation, while wet attritor milled ones cannot.     

Numerical method applied to duplex stainless steel welding

Abstract

Microstructure plays an essential role in the attractive properties of the duplex stainless steels (DSSs) such as toughness and corrosion resistance. These properties are obtained by an adequate balance between the fractions of the ferrite and austenite phases, which can be modified when DSSs are welded. Besides the unbalanced fractions of ferrite and austenite, the precipitation of deleterious compounds at high temperatures such as sigma phase can also occur during DSS welding. In this work, a model based on transport equations was numerically implemented by the finite volume method in a computational code in order to simulate the 2205 DSS welding. It was able to evaluate qualitatively the sigma phase precipitation and the formation of the ferrite and austenite phases by calculating the cooling rates reached during 2205 DSS welding. The results are discussed in light of the previous work, and good agreement between numerical and experimental results was obtained.