1Cr22Mn16N高氮钢激光焊接I.焊接保护气体组成和热输入对焊缝氮含量及气孔性的影响

利用CO2激光对1Cr22Mn16N高氮钢进行了焊接,研究了焊接热输入和保护气体组成对焊缝氮含量、气孔的影响。结果表明,在相同激光焊接热输入条件下,随着保护气体中氮含量的增加,高氮钢焊缝中的氮含量略有增加。当采用纯氩作为焊接保护气体时,焊缝氮含量随热输入的增加而减小;当保护气体中的氮比例达到一定比例时,焊缝氮含量随热输入的增加而增大。焊接热输入较小的条件下焊缝易产生气孔,较大的热输入将抑制焊缝中气孔的产生,而且保护气体中氮含量越高,焊缝中产生气孔的倾向越小。     

Microstructures of gas metal arc weld metal of 950 MPa class steel

Abstract

The effects of shielding gas composition on the properties and microstructure of single pass weld metals produced by GMA (gas metal arc) groove welding of 950 MPa class steel plates have been investigated. The shielding gas employed was a mixture of argon (Ar) and carbon dioxide (CO₂) (0–25%), and the weld heat input was ～3 kJ mm. With increasing CO₂ content, the hardness of the weld metal decreased from 380 HV to 280 HV, and the absorbed energy of the Charpy impact test decreased from 130 J to 90 J. The microstructures of the weld metal, consisting primarily of low carbon martensite and carbide free bainite, became more bainitic as the CO₂ content of the shielding gas was increased. It was also found that the MA constituent, embrittling microstructure, was formed in the granular bainitic area, the volume fraction of which increased with the CO₂ content of the shielding gas.     

Effect of nitrogen addition to shielding gas on residual stress of stainless steel weldments

Abstract

The objective of the present study was to investigate the effect of nitrogen additions to the shielding gas on the ferrite content and residual stress in austenitic stainless steels. Autogenous gas tungsten arc (GTA) welding was applied on austenitic stainless steels 304 and 310 to produce a bead on plate weld. The delta ferrite content of the weld metals was measured using a Ferritscope. The residual stress in the weldments was determined using the hole drilling strain gauge method. The present results indicated that the retained delta ferrite content in type 304 stainless steel weld metals decreased rapidly as nitrogen addition to the argon shielding gas was increased. The welding residual stress increased with increasing quantity of added nitrogen in the shielding gas. It was also found that the tensile residual stress zone in austenitic stainless steel weldments was extended as the quantity of added nitrogen gas in the argon shielding gas was increased.     

Weld shape comparison with iron oxide flux and Ar–O2 shielding gas in gas tungsten arc welding

Abstract

The influence of iron oxide flux and O₂–Ar mixed shielding gas on weld shape and penetration in gas tungsten arc welding is investigated by bead-on-plate welding on SUS 304 stainless with low oxygen and low sulphur contents. The oxygen content in the weld metal is measured using a HORIBA EMGA-520 oxygen/nitrogen analyzer. The results show that both the iron oxide flux and the O₂–Ar mixed shielding gas can significantly modify the weld shape from shallow wide to deep narrow. A large weld depth/width ratio around of 0.5 is obtained when the oxygen content in the shielding gas is in the range of 3000–6000 vol. ppm. Oxygen over a certain critical value, i.e. 70 wt. ppm, in the weld pool alters the temperature coefficient of the surface tension on the pool surface, and hence changes the Marangoni convection. A thick oxide layer on the weld pool surface is generated when the oxygen content in the shielding gas is over 6000 vol. ppm, which becomes a barrier for the oxygen conveyance to the liquid pool and prevents the liquid pool from freely moving, and therefore, decreases the intensity of the Marangoni convection on the pool surface.     

Effect of nitrogen on corrosion of duplex stainless steel weld metal

Abstract

A type 329Jl duplex stainless steel was gas tungsten arc welded without filler material in an Ar–N₂ gas mixture atmosphere with the aim of changing only the nitrogen content in the weld metal. The effect of nitrogen on the microstructure and corrosion properties of the weld metal was examined. An increase in nitrogen partial pressure increased the nitrogen content of the weld metal and brought reductions in the ferrite content and the quantity of Cr₂N nitride precipitates. Three corrosion parameters, namely, critical pitting temperature (CPT), pitting potential, and corrosion rate, were measured for weld metals having different nitrogen contents. The CPT and pitting potential increased and corrosion rate decreased with increasing nitrogen content of the weld metal. The corrosion behaviour was explained in terms of changes in microstructure and pitting index depending on the nitrogen content of the weld metal.     

Nitrogen absorption phenomenon of GTA welding with nitrogen-mixed shielding gases: effect of plasma characteristics on nitrogen content in GTA welded metal

In order to clarify the nitrogen absorption mechanism in gas tungsten arc welding, the measurement of the weld metal nitrogen content under nitrogen mixture shielding gases, and the numerical analysis of plasma heat source characteristics in nitrogen dissociation phenomenon were conducted. The nitrogen content of weld metal produced by He arc reduces to approximately a half relative to that by Ar arc in the shielding gas condition of less than about 1% mixture ratio. Additionally, it is assumed that a decline in the plasma temperature in the vicinity of the molten pools due to the generation of metal vapour, accompanied by a reduction in atom-like nitrogen content, cause intense impact on the reduction mechanism of weld metal nitrogen content in a He arc.     

气体保护焊保护效果研究综述——氮含量对气孔及焊缝性能的影响

研究了气体保护焊时氮含量对气孔及力学性能的影响,试验结果表明:采用实心焊丝和ψ(Ar)20％ψ(C02)80％组合时,随着环境中氮含量的增加最容易产生气孔.因此,必须把保护气体中氮的含量控制在1％以下.采用药芯焊丝和C02组合时,耐气孔性良好,但是,随着氮含量的增加冲击吸收功下降.因此,应把熔敷金属中氮的含量限制在0.01％以内.     

低镍含氮奥氏体不锈钢激光-电弧焊电弧特性及组织性能

采用100%Ar_2,98%Ar + 2%N_2,92%Ar + 8%N_2,85%Ar + 15%N₂四种混合比例的保护气体对08Cr19MnNi3Cu2N低镍含氮奥氏体不锈钢进行激光-脉冲MAG电弧复合焊接,研究保护气体中氮气比例对焊缝中气孔数量、焊缝熔深和熔宽、电弧形态、微观组织及铁素体含量等影响机制. 结果表明,随着保护气体中氮气比例的增加,焊缝气孔数量增多,气孔的体积也随之增大;焊缝熔深显著增加,而焊缝熔宽变窄,焊缝平均硬度有所下降,电弧收缩明显,电弧弧柱宽度随着氮气比例的增加而减小,焊接飞溅数量随之增加且体积增大,电弧稳定性变差;焊缝中铁素体含量由6.91%,6.80%减少至5.38%和4.62%,铁素体枝晶也逐渐变细,二次枝晶臂变短. 焊缝组织中只仅存在少量δ和γ两相;从4个晶面观察奥氏体晶粒的尺寸也随着氮气比例的增加而逐渐减小.     

Systematic study of effect of cross-drafts and nozzle diameter on shield gas coverage in MIG welding

Abstract

A shield gas flowrate of 15–20 L min^?1 is typically specified in metal inert gas welding, but is often adjusted to as high as 36 L min^?1 by welders in practice. Not only is this overuse of shield gas wasteful, but uncontrolled high gas flows can lead to significant turbulence induced porosity in the final weld. There is therefore a need to understand and control the minimum shield gas flowrate used in practical welding where cross-drafts may affect the coverage. Very low gas coverage or no shielding leads to porosity and spatter development in the weld region. A systematic study is reported of the weld quality achieved for a range of shield gas flowrates, cross-draft speeds and nozzle diameters using optical visualisation and numerical modelling to determine the shield gas coverage. As a consequence of the study, the shield gas flow has been reduced to 12 L min^?1 in production welding, representing a significant process cost saving and reduced environmental impact with no compromise to the final weld quality.     

Weld shape variation and electrode protection under Ar–(Ar–O2) double shielded GTA welding

Abstract

Double shielded gas tungsten arc welding (GTA welding or TIG welding) of an SUS304 stainless steel with pure inert argon as the inner layer shielding and the Ar–O₂ active gas as the outer layer shielding is proposed in this study in order to investigate its effect on the tungsten electrode protection and the weld shape variation. The experimental results show that the inner inert argon gas can successfully prevent the outer layer active gas from contacting and oxidising the tungsten electrode during the welding process. The active gas, oxygen, in the outer layer shielding is decomposed in the arc and dissolves in the liquid pool, which effectively adjusts the active element, oxygen, content in the weld metal. When the weld metal oxygen content is over 70 ppm, the surface tension induced Marangoni convection changes from outward into inward, and the weld shape varies from a wide shallow one to a narrow deep one. The effect of the inner layer gas flowrate on the weld bead morphology and the weld shape is investigated systematically. The results showed that when the flowrate of the inner argon shielding gas is too low, the weld bead is easily oxidised and the weld shape is wide and shallow. A heavy continuous oxide layer on the liquid pool is a barrier to the liquid pool movement.     

Pulsed flash welding strips of nickel alloys

Summary

Type 329J1 duplex stainless steel was welded by gas tungsten arc welding in argon‐nitrogen mixed gas atmospheres. The tensile properties and microstructures of the weld metals were examined. The nitrogen content increases and the ferrite content decreases with increasing nitrogen partial pressure of the atmosphere. The ferrite content linearly decreases with an increasing nitrogen content. The tensile strength and elongation of the weld metal produced in the argon atmosphere are much lower than those of the base metal, but they increase with an increasing nitrogen content and approximate those of the base metal at around 0.4 mass% nitrogen content. The fractographs suggest that only the base metal and high‐nitrogen weld metal clearly show dimple patterns. The tensile‐tested base metal and high‐nitrogen weld metal have complex crack paths, whereas the other weld metals have relatively straight paths. The tensile properties of the weld metal are affected by the ferrite content and chromium nitride.     

Comparative evaluation of tungsten inert gas and laser welding of AZ31 magnesium alloy

Abstract

Welding of AZ31 Mg alloy was conducted using various welding techniques, namely, tungsten inert gas (TIG) welding with Ar shielding gas, TIG welding with He shielding gas, CO₂ laser welding, and YAG laser welding. The results were comparatively evaluated in terms of weld bead formation and microstructural characterisation. It was found that TIG welding with both Ar and He gas shielding produced good welds without major defects. The penetration capacity can be improved using He gas shielding. Owing to their high energy density, CO₂ and YAG lasers can produce weld beads having high aspect ratio. Among the four techniques used, the YAG laser produced the finest weld microstructure, whereas TIG with Ar gas shielding produced the coarsest microstructure. Shielding is a key factor controlling the O contents in the welds. The more effective the shielding provided the lower the O content in the weld. Hardness reduction in the weld metals and heat affected zones was observed for all the techniques owing to the elimination of strengthening effects by the welding operation. In summary, the present study demonstrated advantages and limitations of the various welding techniques and provided an in depth understanding of the weldability of AZ31 Mg alloy.     

Solidification and solidification structure control of weld metals

Summary

The influence of the shielding gas and laser irradiation conditions on porosity formation in CO₂ laser welding of aluminium alloy were investigated. Bead-on-plate welding tests were performed on 7 mm thick Al-Mg alloy (A5182) plates. The weld beads were inspected by X-ray and the number of pores was counted as a function of the pore diameter. We found that the number of pores was minimised when the dew point of the shielding gas was kept at as low as ?50°C at the welding nozzle tip. At a dew point of ?50°C the number of pores decreased when the flow rate of the shielding gas (Ar) was reduced and the nozzle diameter was increased, presumably because of less air mixing in the welding region. We also found that porosity formation was reduced when He/Ar mixtures were used as the shielding gas instead of pure Ar or He shielding gas. But porosity also depended on the defocused distance of the laser beam at a given laser power. With Ar shielding gas, the number of pores increased when the beam was focused above the specimen surface/while with He shielding gas it increased when the beam was focused in the weld pool. These dependencies may be attributed to the unstable keyhole formation due to laser absorption through the intense plasma formed on the specimen surface and due to the strong boiling of the molten metal respectively. The results indicate that both the hydrogen and the unstable keyhole behaviour cause porosity formation in laser welding of aluminium alloys. Under the optimised conditions, however, the number of pores was significantly reduced.     

Weld porosity in fibre laser weld of thixomolded heat resistant Mg alloys

Abstract

Porosity in fibre laser welds of two thixomolded heat resistant magnesium alloys AE42 and AS41 was investigated in detail, and porosity formation mechanism was discussed in terms of gas compositions in porosity. It is found that the area percentage of porosity in welds decreases with increasing welding speed, and can be correlated to width of weld metal. Microstructure observation and gas composition analysis in porosity show that the porosity in welds is mainly attributed to the micropores pre-existing in base metals during melting of AE42 and AS41 alloys by fibre laser welding, which are formed due to air entrapment during thixomolding process. Hydrogen rejection and Ar shielding gas entrapment are also the possible reasons for the porosity formation; however, their contribution is much smaller than that of pores in base metals. Furthermore, the addition of rare earth element may probably decrease porosity amount in the thixomolded Mg alloys and their welds.     

氮氧联合过渡对GPCA-TIG焊焊缝的影响

针对外层引入氮氧混合气体的气体熔池耦合活性TIG焊,通过改变焊枪内外喷嘴的相对位置,分别研究了外层气体与熔池表面的耦合程度不同时焊缝成形、焊缝中氮氧含量及焊缝组织性能的变化规律.结果表明,氮氧联合过渡时气体熔池耦合活性TIG焊焊缝窄而深;低温冲击韧性高于母材及传统TIG焊的7.5%以上,而抗拉强度和屈服强度均略低于母材;焊缝组织晶粒细小,奥氏体上沿晶界分布着少量铁素体.气体熔池耦合活性TIG焊焊缝中的氮氧含量可以通过调节焊枪内外喷嘴的相对位置进行微量控制.     

2219铝合金FSW/VPPA交叉焊缝气孔缺陷

2219铝合金在搅拌摩擦焊（FSW）后,进行变极性等离子弧焊（VPPA）十字交叉焊接,其交叉接头存在气孔缺陷.针对6 mm 2219铝合金进行FSW/VPPA交叉焊接试验,探究了交叉焊缝的气孔类型,分别对比不同FSW热输入量、不同的VPPA焊接速度对交叉焊缝气孔缺陷程度的影响.结果表明,FSW热输入量越大,交叉焊缝气孔缺陷程度呈下降趋势,这与FSW过程产生瞬时空腔有关;而VPPA焊速越大,交叉焊缝气孔缺陷程度呈上升趋势.因此,为了抑制FSW/VPPA交叉焊缝气孔的产生,可以对FSW过程进行惰性气体保护、适当地提高FSW热输入量以及降低VPPA焊接速度.     

焊丝含氮量及焊接电流对高氮钢焊缝组织和性能影响

针对高氮奥氏体不锈钢焊接过程中由于N元素逸出引起气孔、导致力学性能恶化的问题,利用相图计算软件设计并制备了含氮量为0.35%和0.85%两种奥氏体不锈钢焊丝,系统地研究了氮含量和焊接电流对高氮钢焊缝气孔倾向性、微观组织以及力学性能的影响规律. 结果表明,高氮钢焊缝气孔倾向和力学性能与焊接电流、焊丝氮含量密切相关:随着焊接电流增加,氮含量0.35%的高氮钢焊缝抗拉强度和断后伸长率均增加,未出现气孔;而氮含量0.85%的高氮钢焊缝具有很高的气孔倾向,抗拉强度和断后伸长率变化不大,当焊接电流增大到一定值后,气孔倾向性明显降低.     

High power laser welding of Nb microalloyed steel plates

Abstract

Laser welding studies on 12 mm thick Nb microalloyed steels were done using a 25 kW CO₂ laser at welding speeds of up to 3 m min^?1 with the aim of identifying the influences of Nb and carbon on laser weldability and weld properties. Welds were examined for solidification flaws, penetration characteristics, microstructure and mechanical properties. Solidification cracking did not appear to be influenced by carbon or Nb in the ranges studied when welding at power levels between 22 and 25 kW. The area fraction of martensite was shown to increase with decreasing energy input and increasing carbon content. Weld metal toughness was improved by reducing carbon content in the range 0·08–0·05%C but was little influenced by Nb. Weld metal and heat affected zone hardness levels were reduced, as expected, by reducing carbon content. The results show that increasing Nb content leads to higher strength material without significant loss of toughness, while lowering carbon content can improve toughness without loss of strength. Thus low carbon Nb microalloyed steels with about 0·05%C can achieve a good combination of parent plate and laser weld properties and appear to be suitable for high power laser welding situations.     

SiO2增加铝合金交流A-TIG焊熔深的机理

采用单组元活性剂进行铝合金交流A-TIG(Activating flux TIG)焊时,SiO2增加熔深最明显,对其增加熔深的机理进行了研究.进行正散焦真空电子束焊试验,SiO2对焊缝成形几乎没有影响;进行系列直流正接A-TIG焊试验,研究了活性剂对电弧的影响,发现SiO2使得氧化膜厚度增加,电弧极性区收缩,弧柱区扩展,电弧电压升高;进行氦气保护交流A-TIG焊试验,发现SiO2使活性剂或金属蒸发的区域变窄且蒸发量变小,熔池表面凹陷,并且在焊接过程中SiO2涂层始终存在于熔池表面,只在熔池凹陷中央区域出现很窄的裂缝,蒸气主要集中在电弧中下部.认为电弧极性区收缩和热输入增加是SiO2增加铝合金交流A-TIG焊熔深的主要机理.     

Gas contamination during plasma welding in Al–Li alloy 2195

Abstract

Keyhole and cover pass variable polarity plasma arc welds were made on aluminium alloy 2195 with measured contamination levels of nitrogen, oxygen, and hydrogen. Contamination levels ranged from less than 10 to 500 ppm in both the argon plasma gas and the helium shield gas. It was found that nitrogen leads to more severe porosity than either hydrogen or oxygen, and that rear shielding is required for keyhole welding of Al–Li 2195 alloy to protect the weld from nitrogen in the atmosphere. Both nitrogen and oxygen contamination produced a dark surface on the weld bead, which comprised metallic aluminium particles, nucleated in the melt, that had aggregated at the surface of the weld pool.