“金焊缝”的焊前准备与焊接要点

通过对长输管线施工过程中影响焊接质量因素的分析,针对"金焊缝"的特点,提出"金焊缝"焊接前需要特别关注的焊前准备事项和焊接实际操作要点。对长输管线"金焊缝"及所有连头焊缝的焊接提供借鉴。

二次热循环对晶内铁素体的影响

采用物理模拟的方法研究了二次热循环对晶内铁素体的影响。用自动图像分析仪测量了夹杂物的大小、分布和密度 ,用透射电镜观察了晶内铁素体的形貌 ,并用能谱对诱导晶内铁素体形核的夹杂物进行了成分分析。研究结果表明 ,二次热循环对夹杂物的直径大小、分布和密度几乎没有影响。经过二次热循环过程后 ,诱导晶内铁素体形核、长大的夹杂物为MnO、TiO、SiO2 、Al2 O3 和MnS、CuS、(Mn ,Cu)S的复合物。 80 0～ 5 0 0℃的时间为 10s时 ,出现了晶内铁素体的感生形核。晶内铁素体的感生形核是由于一次晶内铁素体有较高的界面能和高密度的位错 ,两者共同促进晶内铁素体的感生形核。

Effects of weld reinforcement on tensile behavior and mechanical properties of 2219-T87 aluminum alloy TIG welded joints

Tungsten inert gas （TIG） welded joints for 2219-T87 aluminum alloy are often used in the fuel tanks of large launch vehicles. Because of the massive loads these vehicles carry, dealing with weld reinforcement on TIG joints represents an important issue in their manufacturing and strength evaluation. Experimental and numerical simulation methods were used to investigate the effects of weld toe shape and weld toe position on the tensile behavior and mechanical properties of these joints. The simulation results indicated that the relative difference in elongation could be as large as 96.9% caused by the difference in weld toe shape. The joints with weld toes located in the weld metal or in the partially melted zone （PMZ） exhibited larger elongation than joints with weld toes located at the juncture of the weld metal and the PMZ.

THRESHOLD STRESS INTENSITIES FOR HYDROGEN-INDUCED DELAYED FAILURE OF WELD METAL OF AUSTENITIC STAINLESS STEEL

It was found that hydrogen induced delayed failure could occur in 308L and 347L weld metals,and the threshold stress intensities of 308L and 347L welds were lower than that of 304L austenitic stainless steel.When dynamically charged under load on a single edge notched specimen,the threshold stress intensities of 308L,347L and 304L decrease with the increase in the diffusible hydrogen content C 0 and the experimental results are as follows:K ⅠH =85.2-10.7 ln C 0 (308L),K ⅠH =76.1-9.3 ln C 0 (347L),K ⅠH =91.7-10.1 ln C 0 (304L).The morphology of the hydrogen induced delayed fracture in the three materials are correlated with the K Ⅰ and C 0 values.

Effects of weld penetration on tensile properties of 2219 aluminum alloy TIG-welded joints

Numerical simulation and experimental methods were used to investigate the effects of weld penetration on tensile properties of 2219 aluminum alloy tungsten inert gas(TIG)welded joints.The results show that when other geometric parameters are consistent,within a certain range,the deeper the weld penetration of the capping weld is,the lower the tensile strength of the j oint is.The deeper weld penetration of the capping weld can cause the more concentrated stress at the weld toe and the joint is more likely to crack accordingly.Based on necessary assumptions,a model for analyzing the mathematical relation between the weld penetration of the capping weld and the tensile strength of the joint was proposed to validate the experimental results. The decrease of weld penetration of capping weld can be controlled by decreasing welding current,helium content or increasing welding voltage.

Effects of activating flux on CO_2 laser welding process of 6013 Al alloy

In order to increase the absorption of laser energy and improve the weld appearance in laser welding of Al alloy, 1.8 mm- 6013 Al alloy plate was welded by activating flux CO2 laser welding. Activating flux includes oxide and fluoride, which was coated on the workpiece surface before welding. The experimental results show that the activating flux can effectively improve the absorption of CO2 laser energy and increase the amount of the molten base metal. The improvement on the absorption of laser energy by oxide activating flux is greater than that by fluoride activating flux or two-component activating flux, but the slag detachability made from both the single activating flux and two-activating flux is poor. The gas pore sensitivity with oxide activating flux is much higher than that with fluoride activating flux in CO2 laser welding of 6013 Al alloy.

Microstructure and grain boundary engineering of a novel Fe-Cr-Ni alloy weldment made with self-developed composition-matched weld filler metal

The microstructure,texture,and yield strength of an advanced heat-resistant alloy weldment made with composition-matched weld filler were investigated.Scanning electron microscopy,energy dispersive spectroscopy,and electron backscatter diffraction were used to characterize the microstructural and textural changes.Various grain boundary engineering(GBE)processes were performed on the weldment.The yield strengths of the weldment at 973 K were obtained before and after GBE processing,and were mostly consistent with the theoretically predicted values.The coincident-site lattices,misorientation,and recrystallization of the weld metal after GBE were analyzed,and the results indicate that the increase in dislocation density and the improvement in special grain boundaries in the weld metal are the main reasons for the yield strength elevation of the weldment after GBE.The variation in elongation after high-temperature tests has the same tendency as that in the impact toughness with different GBE parameters,which is related to the coarsening behavior of carbides.

Microstructures and mechanical properties of a martensitic steel welded with flux-cored wires

This study was focused on wear-resistant material prepared by CO2 GMAW method to basically determine the alloys and hardfacing technology which could be employed into mining equipment. Three flux-cored wires with different chemical compositions, marked by DM-I, DM-II and DM-III were used in welding a martensitic steel for the comparison of the microstructures and mechanical properties of the welding metals and HAZ. The results show that DM-I weld metal contains martensite plus other reinforced phases, while both DM-II and DM-III alloys lead to mainly martensitic microstructures with little precipitates. Among all of the tested materials the DM-I alloy has the highest hardness and wear resistance but the lowest impact toughness among the experimental weld metals. Meanwhile, the hardness, impact toughness and wear resistance of the DM-II and DM-III alloys are close to those of the base metal but the DM-III is not as strong as DM-II. Dimples can be found on the impact fracture of the weld metals, but the steel fracture consists of both cleavage and dimples. Thus HAZ has less risk for cracking than the welds, and the DM-II wire which produces the weld having identical mechanical properties to the base metal is suitable for further application.

Effect of heat input on microstructure and mechanical properties of butt-welded dissimilar magnesium alloys joint

The effects of heat input on the microstructures and mechanical properties of tungsten inert gas （TIG） butt-welded AZ31/MB3 dissimilar Mg alloys joint were investigated by microstructural observations, microhardness testing and tensile testing. The results reveal that with the increase of heat input, the width of welding seam increases obviously and the grains both in the fusion zone and the heat affected zone coarsen during TIG welding process. The tensile strength of butt-welded joint increases with the increase of heat input and the maximum joining strength of 242 MPa is obtained with wedding current of 90 A. However, lots of welding pores occur with the further increase of heat input, which results in the decrease of joining strength. It is experimentally demonstrated that robust joint can be obtained by TIG welding process.

Study on J-integral with SENB specimens in a condenser material

A series of tests was performed with three-point single-edge-notched-bend (SENB) specimens in a condenser material (Titanium alloy). Results show that the J-integral values of welded joint and HAZ are obviously smaller than those of the base metal. It signifies that the welding process can result in a reduced toughness of Titanium alloy and the effect of crack orientation on toughness value is not negligible for engineering applications. Besides, the J-integral values of L-T direction specimens are much higher than those of L-S ones. The J-integral values of rolled ring are:JC-R>JC-L>JL-R.

Latest Development and Application of High Strength and Heavy Gauge Pipeline Steel in China

Over the past twenty years, significant advances have been made in the field of microalloying and associated applications, among which one of the most successful application cases is HTP practice for heavy gauge, high strength pipeline steels. Combined the strengthening effects of TMCP and retardation effects of austenite recrystallization with increasing Nb in austenite region, HTP conception with low carbon and high niobium alloy design has been successfully applied to develop X80 coil with a thickness of 18.4 mm used for China＇s Second West-East pipeline. During this process, big efforts were made to further develop and enrich the application of microalloying technology, and at the same time the strengthening effects of Nb have been completely unfolded and fully utilized with improved metallurgical quality and quantitative analysis of microstructure. In this paper, the existing status and strengthening effect of Nb during reheating, rolling and cooling have been analyzed and characterized based on mass production samples and laboratory analysis. As confirmed, grain refinement remains the most basic strengthening measure to reduce the microstructure gradient along the thickness, which in turn enlarges the processing window to improve upon low temperature toughness, and finally make it possible to develop heavy gauge, high strength pipeline steels with more challenging fracture toughness requirements. As stated by a good saying that practice makes perfect. Based on application practice and theoretical analysis, HTP has been extended to develop heavy gauge and high strength pipeline steels with increasing requirements, including X80 SSAW pipe with a thickness of 22.0 mm and above, X80 LSAW pipe combining heavy gauge and large diameter, heavy gauge X80 LSAW pipe with low temperature requirements, as well as X90 steels. In this paper, alloy design, production processing, as well as mechanical properties and microstructure used for these products would be illustrated.

Microstructure and creep properties of high Cr resisting weld metal alloyed with Co

A 9% Cr ferritic steel weld metal containing 1% Co, partially substituted for nickel, was prepared by submerged arc welding (SAW) processing. The microstructure and creep properties of the weld metal were investigated. The microstructure exhibited a fully tempered martensitic structure free of δ-ferrite. The creep properties of the obtained weld metal were inferior to those of the P92 base metal at 600 and 650 °C. The values of A and n for weld metal in the Norton power law constitution at 650 °C are 1.1×10?21 and 8.1, respectively.