微合金钢模拟焊接热影响区组织和韧性研究

采用焊接模拟试验方法，研究了不同峰值温度（Tmax）和不同冷却时间（t8/5），对合Ti-N、TI-NB-N两种微合金钢热影响（HAZ）显微组织、奥氏体晶粒度、冲击韧性影响。试验结果表明：Ti-N钢焊接热影响区比Ti-Nb-n钢具有更高的冲击韧性、更适用于大线能量的焊接条件。     

焊接热影响区微观结构演化的蒙特卡罗计算机模拟方法

焊接热影响区是影响焊接性能的主要区域。焊接热影响区的晶粒长大常常导致焊接热影响区成为性能薄弱的环节，对焊接热影响区晶粒长大的研究一直是焊接接头的重要研究课题。焊接热影响区微观结构演化与诸多因素密切相关，是一个复杂的过程。运用适当的计算机方法进行模拟，完成对晶粒生长的完全预测，具有重要的意义，可以为优化焊接工艺参数，提高焊接质量提供依据。在此对在模拟焊接热影响区微观结构的演化时采用的基本方法进行综述。     

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.     

Characterization of the microstructure and hardness of the HAZ in a 800 MPa grade RPC steel

The microstructure and hardness of the HAZ in a 800 MPa grade ultra-low-carbon microalloyed steel were studied.The results indicate that the heat affected zone (HAZ) of the RPC (Relaxation- Precipitation- Controlling) steel possesses a continuous gradient structure, and can be classified into three zones, i. e. CGHAZ ( coarse-grain HAZ ) , FGHAZ (fine-grain HAZ ) and ICHAZ ( intercritical temperature HAZ ). The microstructures in the HAZ are all composed of bainite-like structure.The microstructare in the CGHAZ mainly consists of lath-like bainite and granular bainite . The influences of heat input and t8/5 on the hardness in the HAZ of RPC steel are notable. With the increase of heat input and t8/5, the softening tendency of HAZ becomes obvious. The hardening phenomenon that normally occurs in the CGHAZ does not take place with this steel in the range of experimental conditions. The softening in the ICHAZ is bound to occur. Hence appropriate welding technologies need to be selected.     

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.     

Temperature-gradient induced microstructure evolution in heat-affected zone of electron beam welded Ti-6Al-4V titanium alloy

The heat-affected zone (HAZ) of electron beam welded (EBW) joint normally undergoes a unique heat-treating process consisting of rapid temperature rising and dropping stages, resulting in temperature-gradient in HAZ as a function of the distance to fusion zone (FZ). In the current work, microstructure, elements distribution and crystallographic orientation of three parts (near base material (BM) zone, mid-HAZ and near-FZ) in the HAZ of Ti-6Al-4V alloy were systematically investigated. The microstructure observation revealed that the microstructural variation from near-BM to near-FZ included the reduction of primary α (α_p) grains, the increase of transformed β structure (β_t) and the formation of various α structures. The rim-α, dendritic α and abnormal secondary α (α_s) colonies formed in the mid-HAZ, while the “ghost” structures grew in the near-FZ respectively. The electron probe microanalyzer (EPMA) and electron back-scattered diffraction (EBSD) technologies were employed to evaluate the elements diffusion and texture evolution during the unique thermal process of welding. The formation of the various α structures in the HAZ were discussed based on the EPMA and EBSD results. Finally, the nanoindentation hardness of “ghost” structures was presented and compared with nearby β_t regions.     

大线能量焊接用船体结构钢的研究进展

介绍了大线能量焊接在船舶建造中的应用,对比了船体结构钢与其它钢种对大线能量焊接适应性的不同要求。针对大线能量焊接热影响区韧性下降问题,提出了目前提高热影响区韧性的主要措施。指出降低碳当量、细化热影响区奥氏体晶粒尺寸、利用有益氧化物诱导晶内铁素体析出是提高船体结构钢大线能量焊接适应性的有效途径。介绍了鞍钢在热影响区组织调控技术和氧化物诱导机理研究等方面取得的成果。     

焊缝管液压成形技术及热影响区对成形的影响

结合研究成果讨论了焊缝材料性能对管材液压成形规律的影响,阐述了焊缝管液压成形的研究现状及发展趋势,以及亟待解决的关键问题.论述焊缝及热影响区材料性能的测定技术,包含焊缝及热影响区材料特性的有限元数值模拟模型的建立方法.结果表明:焊缝及热影响区的存在造成焊缝管的液压胀形特点及成形规律不同于无缝管.有缝管自由胀形后轮廓形状不对称;在距焊缝对称中心0°～15°之间的壁厚沿环向分布不均匀,在15～180°之间的壁厚基本上呈均匀分布,且壁厚值和与同种材料的无缝管在相同条件下胀形的壁厚值接近;焊缝材料比基体材料强度高,则极限胀形高度大.     

Effect of Nb on Mechanical Properties of HAZ for High-Nb X80 Pipeline Steels

The mechanical properties of heat affected zone (HAZ) of two commercial high-Nb X80 grade pipeline steels with different alloy elements were investigated using thermal simulation performed on a Gleeble-3500 thermal simulator. The results showed that the high-Nb steels have excellent weldability. Embrittlement regions appear in coarse grain heat affected zone (CGHAZ) and intercritically heat affected zone (ICHAZ); Softening region appears in fine-grain heat affected zone (FGHAZ), and the strength here was even lower than 555 MPa as required in the standard. Meanwhile, with the increase of heat input, the strength and the toughness of HAZ of steel with high Nb, C and lower alloy decrease notably. Therefore, take into account the welding procedure during manufacture of weld pipe, suitable amount of alloy elements, such as Cr, Ni, Cu, Mo and so on, is necessary for high Nb X80 heavy-thick steel plate.     

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。