异种钢接头中氢扩散行为的研究

本文运用氚自射线照相法和接头充氢后释放规律的观察，研究了Ｃｒ３０Ｎｉ９／高碳钢接头不均匀混俣区中的富奥氏体带的形成及其对接头氢扩散和聚集行为的影响，并建立了相应的氢扩展模型。试验和分析结果表明：富粤氏体带的形成将延缓和阻焊缝中的氢向材侧扩散；母材侧仅在熔池阶段及结晶后的高温阶段扩散进行了少量的氢，所得结论，对研究异种钢接头熔合线两侧的冷裂纹的形成机及有其理论指导作用。     

退火处理对异种钢激光焊接头组织及性能的影响

目的 通过研究相同时间不同退火温度下304/Q345激光焊接头的组织和性能,得到优化后的退火处理制度,为制定异种钢激光焊退火工艺提供一定的理论指导和技术支撑。方法 基于前期大量试验,在激光功率和离焦量不变的情况下,调节焊接速度由15 mm/s到35 mm/s,通过改变焊接速度获得性能优异的焊接接头。由于异种钢物理化学性能差异较大,接头组织不均匀,因此还需对激光焊接头进行退火处理。结果 焊缝区显微组织由板条马氏体与残余奥氏体组成,Q345低碳钢热影响区显微组织为多面体状铁素体与黑色珠光体,其中铁素体含量更多,304奥氏体不锈钢热影响区在奥氏体晶界上析出了铁素体。不同退火温度下碳元素均由Q345低碳钢侧向焊缝迁移,在Q345低碳钢侧形成脱碳层,在焊缝中形成黑色条带状增碳层。随着退火处理温度的升高,峰值温度升高,高温停留时间变长,碳迁移强度随之增加,黑色条带状区域增碳层宽度增大。拉伸性能测试结果表明,试样均断裂于Q345母材一侧,且断口存在韧窝,属于典型韧性断裂。此外,焊缝区硬度(390HV左右)最高,热影响区硬度(300HV)次之,母材的硬度(130HV左右)最低。结论 在给定试验参数范围内,优化后的最佳退火工艺参数为550 ℃-1.5 h。     

熔化焊接头“不均匀混合区”的形貌特征研究

通过对大量熔化焊接头的金相观察，研究了熔化焊接头焊缝底部附近“不均匀混合区”的形貌特征，归纳金相观察结果，发现不均匀混合区由小岛，后续熔化滞留层，扩散过渡层四种形貌构成，文中关于熔化焊接头“不均匀混合区”的形貌划分方法，能很好地解释熔化焊接头中焊缝底部附近的成分，组织．性能不均匀性的形成原因，有助于正确理解熔化焊接头的特征区域构成。     

异种铝合金搅拌摩擦焊材料流动行为研究

采用异种铝合金交替排列的方法,研究了搅拌摩擦焊接过程中材料的变形和流动行为。结果表明:采用垂直焊缝交替排列的焊缝表面形成了两套弧纹,其中粗大弧纹是由于在焊接方向上两种铝合金交替排列而产生的周期性变化所致;受焊速和转速的影响,材料在前进侧流动剧烈且混合均匀,而后退侧因材料流动较弱仍与母材保持连续分布状态;由于材料塑性变形程度的差异,在轴肩影响区、搅拌针影响区和母材之间形成了明显的分界面。     

WC含量对真空熔覆镍基合金涂层组织及性能的影响

为了强化45钢表面性能,在45钢表面于1 225℃下通过真空熔覆制备了WC颗粒增强的镍基合金涂层,利用SEM观察了熔覆层组织形貌,结合EDS分析了各元素扩散情况及WC含量对过渡层结合情况的影响,通过硬度测试和磨损试验,研究了不同WC含量对熔覆层性能的影响。结果表明:熔覆过程中元素互扩散使母材与熔覆层达到冶金结合,同时WC颗粒发生沉降;当WC含量低于20%时,WC颗粒偏聚在母材过渡层附近,且颗粒越大,越靠近母材侧;随着WC含量逐渐增加,颗粒之间相互支撑形成骨架可减少沉降,使分布逐渐趋于均匀,但当WC含量过多时,WC聚集形成熔池使熔覆层中气孔率提高;WC含量达到40%时,出现大量分布在WC颗粒之间或周围的空洞,同时,WC的加入可大大提高材料的耐磨性;当WC含量为30%时,平均磨损失重约为21.5 mg,仅为母材的15%左右。将WC颗粒增强的镍基合金熔覆于45钢表面,在保证母材基本性能的同时可显著提高45钢的表面硬度及耐磨性。加入30%WC既能保证涂层与母材良好的冶金结合,又能显著提高其表面耐磨性,具有一定的研究价值。     

高温长期加热对异种钢焊接接头碳迁移及组织性能的影响

本文用热处理方法对奥氏体和珠光体异种钢接头的碳迁移现象及其对接头组织和机械性能的影响进行了研究,认为:焊缝金属有析出物出现;熔合区形成一个增碳层;热影响区形成一个脱碳的铁素体带。随回火参数 P 值增加,焊缝析出物增多,晶界加厚;增碳层加宽;脱碳层铁素体晶粒长大;接头拉伸强度,弯曲角和梅氏冲击值均降低,但这种降低在一定温度(如490℃)下逐步达到饱和。     

Ti/Al异种金属微电阻点焊接头的形成过程及形成机理研究

目的对0.2 mm厚的TC4和2A12薄板进行微电阻点焊研究,分析其接头的形成过程及形成机理。方法通过EDS以及微区XRD等测试手段对熔核与母材界面各区域进行分析,研究界面处的元素扩散以及成分分布。结果对熔核与界面进行EDS线扫描可以发现,熔核内部区域Ti,Al含量比较均匀,说明熔核内部的元素扩散较为充分。熔核与铝侧母材界面处的针状化合物经过分析,推测其主要成分为Ti-Al金属间化合物。熔核内部的主要成分为Al_3Ti金属间化合物。熔核与Ti侧母材界面处生成了AlTi_3和AlTi_2金属间化合物。结论熔核内部以及熔核与母材交界处均生成了Ti-Al系金属间化合物。接头形成过程基本可以分为"固相连接"、"钎焊连接"、"熔化连接"、"熔核的形成与长大"4个阶段。     

热电耦合对铝/钢连续驱动摩擦焊接头组织的影响机理

采用连续驱动摩擦焊技术焊接纯铝1060/Q235低碳钢异质接头,开展两个周期(30天/60天)热电耦合实验(静载392 N+高温300 ℃+直流60 A),研究热电耦合对铝/钢异质接头焊缝微观组织、力学性能及界面生长的影响。结果表明：原始态接头界面径向金属间化合物(IMCs)层厚度不均匀,中心区域无明显IMCs生成。热电耦合30天后界面中心生成宽度为0.3~0.5 μm且以颗粒状由钢侧向铝侧弥散分布的IMCs层,整体拉伸断裂在铝母材的热力影响区。热电耦合60天后IMCs层与钢侧之间出现腐蚀沟槽,IMCs破碎,钢侧无裂纹产生,铝侧形成大量由IMCs层向铝母材内部扩展的裂纹和孔洞,焊缝及裂纹尖端处成分偏析,整体拉伸断裂在焊缝处。界面腐蚀和失效速率与界面IMCs层的厚度成正比,即v_center＜v_1/2R＜v_2/3R。由于原始态接头界面组织不均匀以及热电耦合实验过程中界面不同位置组织生长速率的差异,使得热电耦合后接头界面2/3R位置出现不同断裂形貌的分界线,2/3R内侧以准解理断裂方式为主,2/3R外侧为韧窝断裂和准解理断裂的综合结果。     

粉煤灰/二氧化硅活性剂在Q235钢A-TIG焊中的应用

为了探究粉煤灰作为A-TIG焊活性剂的可行性,以粉煤灰和不同含量的二氧化硅制备复合活性剂在Q235钢基体表面进行A-TIG焊,研究了复合活性剂成分含量对焊缝截面形貌、显微组织和元素分布的影响.结果表明:采用粉煤灰-40%SiO_2作为复合活性剂进行A-TIG焊时,可将6 mm厚Q235钢板一次性焊透,焊缝深宽比可达到0.85;焊缝出现明显的中间收缩倾向,呈"深口杯"状,可实现单道焊双面成型的效果;其焊缝柱状晶数目较多、组织排列规则且具有方向性,熔合区和热影响区组织均匀细小,可降低焊接母材的过热倾向;相对于100%SiO_2活性剂,Si元素的溶入量和溶入深度显著增加,这说明粉煤灰中其他成分的存在对Si元素溶入焊缝、进而增加焊缝熔深起到促进作用.采用粉煤灰-40%SiO_2为活性剂进行A-TIG焊时焊缝熔深的增加机理可能是以电弧收缩理论为主,但考虑到Al元素溶入较深且溶入量较多,粉煤灰中其他物相又十分复杂,在高温电弧作用下各物相之间相互反应放热致使电弧热输入增加、其他组分在熔池中改变了熔池表面张力温度梯度等均可能致使焊缝熔深增加.     

钛合金等离子和MIG复合焊接技术研究

研究了TA2板材等离子和MlG复合焊接工艺,通过高速摄影技术对熔池形貌进行观察,结果表明:在试验参数下,熔池主要是射流过渡和射滴过渡;对焊接试板进行了接头微观组织、力学性能、工艺性能等测试,结果表明:等离子和MlG复合焊接接头组织无明显缺陷,焊缝既有PAW焊缝高熔深的特性,也有MlG焊缝大熔宽的特点;相对母材,焊缝抗拉强度略有降低,但是满足母材相关标准;工艺性能良好;相对母材,焊缝冲击吸收功略有降低.TA2板材等离子和MlG复合焊接具有良好的应用前景.     

Microstructure characterization and properties of carbon steel to stainless steel dissimilar metal joint made by friction welding

Dissimilar metals of 1045 carbon steel and 304 stainless steel are joined successfully by friction welding. The microstructure variation and mechanical properties are studied in detail. The weld interface can be clearly identified in central zone, while the two metals interlock with each other by the mechanical mixing in peripheral zone. On carbon steel side, a thin proeutectoid ferrite layer forms along weld interface. On stainless steel side, austenite grains are refined to submicron scale. The δ-ferrite existing in stainless steel decreases from base metal to weld interface and disappears near the weld interface. Severe plastic deformation plays a predominant role in rapid dissolution of δ-ferrite compared with the high temperature. Carbide layer consisting of CrC and Cr₂₃C₆ forms at weld interface because of element diffusion. Metastable phase CrC is retained at room temperature due to the highly non-equilibrium process and high cooling rate in friction welding. The fracture appearance shows dimple fracture mode in central zone and quasi-cleavage fracture mode in peripheral zone. Further analysis indicates that welding parameters govern tensile properties of the joint through influencing the thickness of carbide layer at weld interface and heterogeneous microstructure in thermo-mechanically affected zone on carbon steel side.     

316L/S32101异种金属焊接接头的显微组织与力学性能研究

目的 研究乏燃料水池用钢板316L与覆板S32101双相不锈钢的焊接性、接头不同区域显微组织特征及接头与母材之间的性能差异.方法 利用氩弧焊接技术对5 mm厚的316L底板与3 mm厚的S32101覆板以搭接的形式进行焊接,利用金相显微镜、扫描电镜、维氏显微硬度仪和电子万能材料试验机对焊接接头的宏观形貌、显微组织以及力学性能进行研究.结果 316L/S32101焊缝组织主要由铁素体基体、晶界树枝状奥氏体以及晶内细小片状奥氏体所组成;316L侧靠近焊缝处存在一个较窄的熔合区,其组织由奥氏体基体和少许细小分散的铁素体组成,而S32101侧靠近焊缝处组织则由粗大铁素体晶粒和沿晶粒边界分布的若干小块状奥氏体组成.从316L母材区到焊缝区,硬度显著增大,而从焊缝区到S32101母材区,硬度变化很小;焊接接头的抗拉强度高达510 MPa,为两侧316L和S32101母材强度的87.9％和88.6％.结论 在焊接电流为240 A和焊接速度为300 mm/min的条件下,可以通过氩弧焊获得成形良好的搭接接头,且接头的力学性能优异.     

不同强度级别双相不锈钢激光焊接头的组织与力学性能

目的 为了合理制定不同强度等级DP钢同种和异种接头的激光焊接工艺,研究激光焊接工艺对接头组织性能的影响。方法 采用SEM、硬度试验、拉伸试验等手段,研究不同强度等级DP钢同种和异种激光焊接接头的微观组织和力学性能。结果 对于同种DP钢激光焊接,由于接头各个区域经历的热循环不同,因此其马氏体体积分数和形态、含碳量等存在明显差异。在焊缝熔合区,由于冷却速度较高,因此马氏体体积分数较高且为细条状,硬度高于母材硬度。在热影响区,由于马氏体发生了回火分解,因此其硬度值低于母材硬度,且软化的程度和范围大小与DP钢的强度级别相关。软化的热影响区成为接头的薄弱区域,降低了接头的拉伸性能。在异种DP钢激光焊接接头中,焊缝熔合区的硬度也明显高于母材硬度。靠近高强度级别母材侧的热影响区范围更大,软化程度更明显,接头硬度分布不再对称。接头的抗拉强度与低等级DP钢母材的抗拉强度基本一致。结论 激光焊接工艺对不同强度等级DP钢同种和异种接头组织性能的影响存在较大的差异,DP钢强度级别越高,接头或接头对应侧的热影响区软化程度越明显,这在制定焊接工艺以及焊后处理工艺过程中需要予以考虑。     

Comparison of creep behaviour of 2.25Cr–1Mo/9Cr–1Mo dissimilar weld joint with its base and weld metals

Abstract

Evaluation of the creep behaviour of 2.25Cr–1Mo and 9Cr–1Mo ferritic steel base metals, 9Cr–1Mo steel weld metal, and 2.25Cr–1Mo/9Cr–1Mo ferritic–ferritic dissimilar weld joints has been carried out at 823 K in the stress range 100–260 MPa. The weld joint was fabricated by shielded metal arc welding using basic coated 9Cr–1Mo electrodes. Investigations of the microstructure and hardness variations across the joint in the as welded, post-weld heat treated (973 K/1 h), and creep tested conditions were performed. The heat affected zone (HAZ) in both the steels consisted of a coarse prior austenitic grain region, a fine prior austenitic grain region, and an intercritical structure. In the post-weld heat treated condition, a white etched soft decarburised zone in 2.25Cr–1Mo steel base metal and a black etched hard carburised zone in 9Cr–1Mo steel weld metal around the weld fusion line developed. Hardness troughs also developed in the intercritical HAZ regions of both the steels. The width of the carburised and decarburised zones and hardness differences of these zones were found to increase with creep exposure. The 9Cr–1Mo steel weld metal showed higher creep strength compared to both the base metals. The 9Cr–1Mo steel base metal exhibited better creep resistance than the 2.25Cr–1Mo steel base metal at lower applied stresses. The dissimilar joint revealed lower creep rupture strength than both the base metals and weld metal. The creep strain was found to concentrate in the decarburised zone of 2.25Cr–1Mo steel and in the intercritical HAZ regions of both the steels. Creep failure in the stress range examined occurred in the intercritical HAZ of 2.25Cr–1Mo steel even though this region showed higher hardness than the decarburised zone. Extensive creep cavitation and cracks were observed in the decarburised zone.     

母材碳含量对异种钢焊接熔合区形态的影响

利用扫描电镜及能谱分析技术，系统地研究了相同焊接工艺条件下，母材碳含量对异种钢焊接熔合区形态的影响。结果发现随碳含量增加，熔合区中的类马氏体层消失，呈锯齿状的部分熔合区增宽。对其产生机理现进行了探讨，认为一般的焊接特征区划分方案不完全适用于异种钢焊接情况。     

Evaluation of variation of tensile strength across 316LN stainless steel weld joint using automated ball indentation technique

Tensile strength variation across 316LN stainless steel fusion welded joint comprising of base metal, deposited weld metal and heat affected zone (HAZ) has been evaluated by Automated Ball Indentation (ABI) technique. Automated Ball Indentation tests were conducted on the various zones of the steel weld joint at 300, 523 and 923?K. The flow curves obtained from ABI results were consistent with corresponding conventional uniaxial tensile test results. The HAZ exhibited higher tensile strength than the other regions of the steel weld joint at all investigated temperatures. The ratio of ultimate tensile strength to yield stress (YS), which represents the work hardening behaviour, increased with an increase in temperature for the base metal and HAZ; whereas it remained nearly the same for the weld metal.     

Origin of hard and soft zone formation during cladding of austenitic/duplex stainless steel on plain carbon steel

Abstract

Weld cladding of corrosion resistant materials is an attractive alternative to bulk usage. Such processes are generally associated with potential deterioration of mechanical properties at the clad/metal interface, often attributed to the formation of hard and soft zones which is usually minimised by control of dilution and use of a buffer layer. To ascertain the origin of the hard and soft zones, weld cladding of austenitic stainless steel (309L) was attempted on plain carbon (0.28 wt-%) steel base metal at various heat inputs, and correspondingly different dilution percentages for the weld metal were obtained. The formation of hard and soft zones was observed mainly on the austenitic stainless steel (i.e. weld metal) side. Typically close to the welding interface (i.e. visible fusion line) a hard zone was observed, followed, but only at higher dilution, by a soft zone. In general, with increasing dilution, the peak hardness and width of the hard zone increased, and the chromium and nickel concentrations of the soft zone significantly decreased. The hard zones were martensitic regions which, at higher dilution, contained chromium carbide precipitates. These precipitates may explain the chromium depletion in the adjacent soft zone. The nickel depletion may be a result of the positive interaction coefficient between nickel and carbon. Since hard/soft zone formation was least at lower dilution, cladding of duplex and superduplex stainless steel was conducted on the same plain carbon base with and without a 309L buffer at an optimum dilution of about 15%. Even at this dilution, direct cladding always resulted in hard and soft zone formation, which was significantly reduced or eliminated by indirect cladding. The hard zones were identified as regions with extensive carbide precipitation (no evidence of martensite formation was found), which occurred in duplex/superduplex grades even at 15% dilution.     

Ultrasonic Analysis of Cracking Propagation Morphology in the Fusion Zone of High Strength Steel

Cracking morphology in the fusion zone of HQ130 high strength steel was researched by “the y-slit test“and “three-point bend test“,ultrasonic test and microscope.HQ130 and Q163 high strength steel welded by Ar CO2 gas shielded arc welding under the condition without preheating.Experimental results indicated that welding cracks were produced in the partially melted zone of the weld root ofHQ130 steel side and propagated parallel to the fusion zone.The cracks were developed alternatively between the weld and the partially melted zone, and are not strictly ruptured at W/F(weld metal/fusion zone) boundary surface.Controlling weld heat input(E) about 16kJ/cm could make the cracking rate lowest and satisfy the performance requirement of welded joint zone.