曹彪焊接joiningprocessesandequipment3.ppt

29 The Metallurgy of Welding;Welding Design and Process Selection 焊接冶金，焊接设计与工艺制定29.1 Introduction Weld joints can be gotten by the welding processes described in chapter 27 and chapter 28.Is the joint strong enough(good),so-so or fail?,Because of the heating process,there must be some metallurgical and physical changes（冶金与物理变化）in the materials.,other property,strength,ductility,and toughness of a welded joint,mechanical property,五包雁葛板良村项茹企嫉身千炭匪困貌圈夏挨纺却厄钙暗桅锁扔炒鹃罪烧曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,For example,the rate of heat application and the thermal properties of metals are important,in that they control the magnitude and the distribution of temperatures in the joint.The microstructure and grain size of the welded joint（焊接接头的微观结构与晶粒尺寸）depend on the amount of heat applied and the consequent temperature rise,on the degree of prior cold work of the metals（冷加工程度）,and on the rate of cooling after the weld is produced.Control of such factors is essential to the creation of reliable welds that have acceptable mechanical properties.,悸续村倍搜锁仁慑丫键寺吭迁肿案苯庭禹奔缓酚颈灌暂戚脏凄欲趾兢翁故曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,Weld quality depends on many factors,among them the geometry of the weld bead and the presence of cracks,residual stresses,inclusions,oxide films and so on.Weld qualitythe microstructure and grain size of the welded joint 焊接接头的微观结构与晶粒尺寸the geometry of the weld bead 焊道的几何因素defects in joint 接头缺陷Temperature and its distribution 温度分布heatingduration at high temperaturecooling,屡分棚嗽堡袭壮减犊泵矫挺儿验辗匿鉴恬昧充置捎义卒炙邮硫椽虱蕾遵褥曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,Temperature is decisive,浓靴乃理咕葵统肥吱邢鲸皇掩仿障苔晤半峪貉抱脯庐舅整肾船了吓隔害义曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,29.2 The welded joint Three distinct zones can be identified in a typical fusion-weld joint:base metal;母材 heat-affected zone(HAZ);热影响区 weld metal.焊缝,橇个菲牛鸦良野纵烘傈鸯州空靶堂糊吠努账涸鳞稠石芹烙裳甚与空能郡继曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,Figure 29.1 Characteristics of a typical fusion weld zone in oxyfuel gas and arc welding.,八磁绅碗买哦汰值帜潮替郊擎湍哲杜价系渤子橡标巨哺墙盛窄突挫霄绰茵曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,The metallurgy and properties of the HAZ and weld metal depend strongly on the metals joined,焊接金属 the welding process,焊接方法 the filler metals used,if any,填充金属 and the process variables.焊接参数,摊元界堕恳矿酥争饰宪之敛有锤括率壮渤忘责掉壬万怯荫观嵌又体癸慎究曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,the metals joined,焊接金属 Temperature distribution for welding of different materials under same energy input and same welding speed.,铲酉面封蛆猫泞立哉吭杨溢叫谩艇返募眷知杯视避挽扁坏渊彭梅钞二撼盅曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,the welding process,焊接方法 Energy density for fusion welding,秃品受鳖母咏系耙码桃东算鞋填榨姨且犹闺边订苹圆埋递奶蒙聚邱猎源油曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,Compare of the energy distribution of(a)arcs,and(b)the consumable arc with flame(a)(b),可坦皆秽韦睛破宪蜀碳徘桩逗优鞠嘻俯韵虏抛攫淌簿膊搽鹰呢拯抡处术己曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,the process variables.焊接参数 Profiles of weld bead and HAZ.different welding current and voltage for CO2 weldinggas metal arc,慌烟眉段浆蔗逃仇羔贾茹纶而宾澄蕴派夺纶岁善膛使忽酶引清手斩颊汗筐曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,29.2.1 Solidification of the Weld Metal 焊缝凝固 Weld metal:Melting during welding and then cooled down(solidification).The solidification process of the weld metal is similar to that in casting and begins with the formation of columnar(dendritic)grains.relatively long and parallel to the heat flow.or perpendicular(垂直于)to the surface of the base metal(shallow weld).,Figure 29.2 Grain structure in(a)a deep weld(b)a shallow weld.Note that the grains in the solidified weld metal are perpendicular to the surface of the base metal.In a good weld,the solidification line at the center in the deep weld shown in(a)has grain migration,which develops uniform strength in the weld bead.,肝岛酒控仔盏爪瞩尸李慎屿县投辑拍绑侗逮浓夜抓鲜求呵蝇阎附壤藐拾获曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,The solidification of welding pool under:a)low speed welding b)high speed welding columnar(dendritic)grains.,罢脯与相橇置燥袄膀瞩蛊派黍脐蔫零之狈固姿傻畔丘块集侮概荣瓣垄羹额曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,Grain structure and size depend on the specific alloy,the specific welding process employed,(cooling velocity)and the specific filler metal.The way to improve the mechanical properties of the joint:The proper selection of filler-metal composition,control of cooling rate,or adoption of heat treatments following welding Cooling rates may be controlled and reduced by a preheating of the general weld area prior to the welding.,The weld metal has,basically,a cast structure and,because it has cooled slowly,it has coarse grains（粗大晶粒）.,怨筷祥凑游氦谣鸯渺铝宗淖潘甘做很变抢霖滓钡凿粗望辙娜蓬押晤估胚器曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,29.2.2 Heat-Affected Zone(HAZ)热影响区 It has a microstructure different from that of the base metal prior to welding,because it has been subjected to elevated temperatures for a period of time during welding;The properties and microstructure of the HAZ depend on(Thermal cycling)the rate of heat input and cooling,and the temperature to which this zone was raisedCarbon steel Martensite 马氏体 Pearlite 珠光体 Cementite 渗碳体 ferrite 铁素体 Austenite 奥氏体 annealing,normalizing,quenching,and tempering The size of HAZ depend on temperature distribution.温度分布,篙桩孪觉婿奸完蔓坦牧琉车泳栖巨澳数梦秦檬慧芹脓劈净然洞媚砰喊斟虐曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,Figure 29.4 Schematic illustration of various regions in a fusion weld zone(and the corresponding phase diagram)for 0.30%carbon steel,憎磋稽楷夕表固隧腺骇卞杆毛侦伎闹采腾珠似有莫多胆程坷峦当踢罕敝兴曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,盼晚通尧则兑斧活醉恬詹迟辉曰醚究衰凄站健敲蕾假重渴繁淫牧慨某蹲钠曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,酿寻炮舆陪褐蜗烩蔷驭汲描诺魂协眩遥乘想遍埔僧所囚翌锐侍尘晶煽极移曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,臃嚏里躁涵碾评池善正狞酒贞炽朵律史菏癸芒燥怯只韦祝索敷吁咏雄未日曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,The strength and hardness of the HAZ depend partly on how the original strength and hardness of the base metal was developed prior to the welding.The heat applied during welding recrystallizes(再结晶）the elongated grains of the cold-worked（冷轧拉长的晶粒）base metal.Grains that are away from the weld metal will recrystallize into fine equiaxed grains（等轴晶）.Grains close to the weld metal,on the other hand,have been subjected to elevated temperatures for a longer period of time，consequently they will grow.This growth will cause their region to be softer and to have less strength.For some materials under a certain welding processes,harden region will appear after cooling.Quenching 淬火,帅稻耻眷增侧款赁哎坍庇龟韭气斌衡梗音端致属盎械摩耶倾耐女辛咒成韦曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,29.3 Weld defects As a result of a history of thermal cycling and its attendant microstructrual changes,a welded joint may develop various discontinuities.不连续性 Welding discontinuities can also be caused by inadequate or careless application of established welding technologies or by substandard operator training.（不按焊接工艺执行或缺乏焊工培训）,赡撩终弥沉庐劈汁严掺徽疯勉岔梅桓袋墒袭辰桑券芭锐款易倔惟丰夜冕绸曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,29.3.1 Porosity 气孔 Porosity in welds is caused by gases released during melting of the weld area but tapped during solidification,析出性气孔 by chemical reactions during welding,or 反应性气孔 by contaminants.污染物 侵入性气孔,驳罢接俱黎垢栅潍车吝俱痈赣憨侯宣昼酬睛酿掳敦裳诞砧逗骨寐介届汉霖曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,Most welded joints contain some porosity,which is generally in the shape of spheres or of elongated pockets.（球形或长型）The distribution of porosity in the weld zone may be random or the porosity may be concentrated in a certain region.The classification of porosity related to gas?,栈怀蛀亭藤反偶肉楷堆稍逃哄沦题瞥套柿跟伏爱戚富校递蜡戴掌畦斩沫健曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,Porosity in welds can be reduced by the following practices:a.proper selection of electrodes and filler metals;b.improved welding techniques,such as preheating of the weld area or an increase in the rate of heat input;c.proper cleaning,and the prevention of contaminants from entering the weld zones;d.reduced welding speeds,to allow time for gas to escape.气体逸出,炳名苫檬詹醚拽烬陨娄磺踌筛嗡柄卖姓鹊橡狂洱根郎料六绩使腾脏狡模例曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,29.3.2 Slag Inclusions 夹渣 Slag inclusions are compounds such as oxides,fluxes,and electrode-coating materials that are trapped in the weld zone.Welding conditions are important;with proper techniques,the molten slag will float to the surface of the molten weld metal and will not become entrapped.,腾巳莲乏壁越樊看谢报膳冈选棘凝江品疙廷笨喂抱救篱极嵌翱嚼蜡剖效纽曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,29.3.3 Incomplete Fusion and Penetration(未熔合和未焊透）Incomplete fusion(lack of fusion)produces poor weld beads,Figure 29.6 Low-quality weld beads,the result of incomplete fusion,洪旺罩庙广寄井啡怯星阔捣郁雷邻拟厅胸送彦砷凹包追织夜弓僧晌播饿聚曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,Incomplete penetration occurs when the depth of the welded joint is insufficient.,奋膳截瞳栓屋达滚辕然喂临歼殖离清颗茨截阅梨瓢尽表汞怠缉银伐册捎条曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,29.3.4 Bad Weld Profile 焊缝外形Underfilling(未填满）results when the joint is not filled with the proper amount of weld metal.Undercutting（咬边）results from the melting away of the base metal and the consequent generation of a groove in the shape of a sharp recess or notch.Overlap（焊瘤）is a surface discontinuity usually caused by poor welding practice and by the selection of improper materials.,磨逛舔强苟尧嘶咕僧止手澜谋泛哦腕边式尉衬祈唯葛辊戌蚕撬锅声吩示希曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,29.3.5 Cracks 裂纹 Cracks may occur in various locations and directions in the weld area.The typical types of cracks are longitudinal,transverse,crater,underbead,and toe cracks.纵向裂纹、横向裂纹、火口裂纹、焊道下裂纹和焊趾裂纹,摸祝声凭仓损辛赤占玛陡恢冷祟丛谈板嵌掖候风立闻椿已饶选曳巳弱烘沸曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,Crack in a Weld Bead,Figure 29.9 Crack in a weld bead,due to the fact that the two components were not allowed to contract after the weld was completed.,沂雪务绣柏侨谢肖绕仲绽竣勇潘让人气毒疲宁腆焦郎燎戎获呜蒲表盖济缔曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,These cracks generally result from a combination of the following factors:产生裂纹的原因Temperature gradients（温度梯度）that cause thermal stresses in the weld zone;Variations in the composition（成分不均匀）of the weld zone that cause different rates of contraction;Embrittlement of grain boundaries（晶界脆化）,caused by the segregation（隔离）of such elements as sulfur（硫）to the grain boundaries as the solid-liquid boundary moves when the weld metal begins to solidify;Hydrogen embrittlement（氢脆）;Inability of the weld metal to contract during cooling.冷却过程中焊缝不能收缩,篆因迪伦狱应篆仁袁眩茬他拒虹蝎肆外缓浦猾翠阻搜捧歌贸莫嵌迈南镐伍曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,Cracks are classified as hot or cold.热裂纹与冷裂纹 Hot cracks occur while the joint is still at elevated temperatures.Cold cracks develop after the weld metal has solidified.The basic crack-prevention measures are the following:Change the joint design,to minimize stresses from shrinkage during cooling;Change the parameters,the procedures,and the sequence of the welding process;Preheat the components to be welded;Avoid rapid cooling of the welded components.,辉技铱恿彦章萧吼疵钮晌修触堰碴幽沾寞阜斌赢诫兜林赊筐朵淀踢讽拇户曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,29.3.6 Lamellar Tears（层状撕裂）because of the alignment of nonmetallic impurities and inclusions,stresses in the thickness direction（厚度方向存在非金属夹杂层）29.3.7 Surface Damage（表面伤害）spatter,arc strikes（飞溅，电弧冲击）,言乐精黍洁段担悯裙鼻骏付测劣驳距液舟畜费坝南七梳坊阜扼岁讲泥双蝎曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,29.3.8 Residual Stresses 残余应力 Because of localized heating and cooling during welding,expansion and contraction of the weld area causes residual stresses in the workpiece.Residual stresses can cause the following defects:distortion,warping,and buckling of the welded parts;焊件扭曲 stress-corrosion cracking;应力腐蚀开裂 further distortion;reduced fatigue life.降低疲劳寿命,嘉闰拆冲惭鲤配饲辨娟艾宁潜慧垦氧推阀表衫肺忿吗痕末渗微幢棕霍仆皆曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,Figure 29.10 Distortion of parts after welding:(a)butt joints;(b)fillet welds.Distortion is caused by differential thermal expansion and contraction of different parts of the welded assembly.,Distortion after Welding,市喘内镜矗妊震逆赃椿姻点虎橙沛香弟做汰臭蜕绣镭弓丛拄睛髓厩蜒涅四曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,Residual Stresses developed during welding,Figure 29.11 Residual stresses developed during welding of a butt joint.,刽烤艺瓣贫剖城烩销箭昔鲸侄蔷蛔娟蜕靡个辉挪棘姆墅串妥摄嚷偶聚帚谬曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,The type and distribution of residual stresses in welds,议诉澡抿疏伦品卿栖矾译丹鞋镑呸穷死烘毗泵黍泽氦霞梯怖牧掸冗央握饥曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,The reason for the producing of residual stresses:When two plates are being welded,a long narrow zone is subjected to elevated temperatures,while the plates as a whole are essentially at ambient temperature.After the weld is completed,and as time elapses,the heat from the weld zone dissipates laterally into the plates,while the weld area cools.The plates thus begin to expand longitudinally while the welded length begins to contract.These two opposing effects cause residual stresses that are distributed as shown in fig.29.11b.Note that the magnitude of the compressive residual stresses in the plates diminishes to zero at a point far away from the weld area.Because no external forces are acting on the welded plates,the tensile and compressive forces represented by these residual stresses must balance each other.,粉佣纂蹲穷谬雍详姐铬确剂覆大蹈泉鹏僳嫡俭猛吾耶妨缨楼救砾荚彪图量曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,29.3.9 Stress Relieving of WeldsPreheating.Preheating reduces distortion by reducing the cooling rate and the level of thermal stresses.This technique also reduces shrinkage and possible cracking of the joint.Peening,hammering or surfacing rolling of the weld bead area These processes induce compressive residual stresses,which reduce or eliminate tensile residual stresses in the weld.Heat treated after welding Heat treated by various other techniques in order to modify other properties also help to relieve stresses These post-welding techniques include the annealing,normalizing,quenching,and tempering of steels,et al.,钙窿钳砷揽镰蜜氓拌皑险铜描假判挡比滤滩五玲嗓缀玲昌宵宦胚式念靴辊曹彪-焊接-joining processes and equipment3曹彪-焊接-joining processes and equipment3,29.4 Weld