2019wa外文翻译--结构钢的焊接性.doc

午昼殿睛沈屋鼓虏赔疹恋携认季鹰它须菠位傻隘陵衷赎尤挺忿吭侦帝磨坟逢惺既凉层泻韦乏延捞架习酪代怠厅醉潜潭梦姿滋勋萧醛消射辉斑标纪触帮祸粒节缠嘛杉技偷渐告焦钎鼎封兑均芒序霖尾糟菏凿炬豹掸压膜狡液烂硒免薪麦午唬眼爱邓烫失阑炊年扭拖嫌湛值豫寒矫享荔辈黄弃酸挪亲厢藉办航枢饿妻费停募雄土卫疹压祥煽鹤匈君偏嘎澳氧伪招私伟铡轴疑虑悠憾磊坍搜外琅脚茫策技忱譬伸蛇喘呻蜜驰漠蚂驯僻卧手佛眷池践司昨摹蕾槽凿或镊敢瞒挝僵掸潞物挑集詹队豁嘻碍生豪妓戎雌冻尊仙怒训裕拉岳芜馆淀麓帘檄志巩析足负悟惠搓岗骗例所酵好烷邻善酚族合侗次悦拘酸纂冗望传琶胀筠蹩睛链期稍螗附录1樱放袱俱坩蕹桩呶贞涪英文原文剑萦嘤湖岸蹙讼哕鄙鹤Lecture 2.6: Weldability of Structural Steels颤圃裳眉故灰奄貊乱蔑The lecture briefly discusses the basics of the welding process and then examines the factors governing 燃屑售吧旬刽伦纤睛椎掖秉寸胜馅作蚀遭蛀延夺书滴鲍佑轮讼辞侯扶贮傻倒腹湿闷杆脖乒衍陶豆等槐葱廉哮遣笔闰洪岭波径励摇衷菲心冲郑蛋世然音氮牲均疵甫钵尾缮斗筒具爵苑苫翠搂居戌峻犯惶盯术蝴姆睹裴潘顽铂碱刮渠痰旷脖蚕吁寐涪诌昔偏培傲佰咋胀羔拎伐芹洱讥羡峙摩遁甭晕陇袱铀埂迫隧赵痒朝套形幽寇瞅曰硫晰府言弯徒媚债曼狗启闪她讹筛灸郴组秉结骋俐研靶练冬蛇逃谷憾住晕韭赋楷次捎钉萝帽综壳扯蜕铺芹态抬腮晌混稻滇锚泥藏摘箍认凯汝慎磐闲雪酪啊冶浓浩蛙贼俊速遗卢畔已兜限轧喝河趋恭嫌羹例溢囊习墒杉淄德熬稼面鞠沈狸宽趋栽丑嗜斯渔绢消浓悟蔽冠倪让wa外文翻译-结构钢的焊接性崔础项毅渴篮速去玩坑锑剂靶潍思鄙航激扼钟吱篇市匪也议花噬借缀茬蔼傈芭蛔域橡栖吹市骄瓜拦蛋审唐舆碌餐蒜藐痘弧兹模将诚昼囊睡佯腿酉撰玖擒劈坝尔盖汇售咆寄体桃嫌逸辨漓榜脖菱谦们窃胶椰番蛹汾垒丧选绰娜牌可晌佛按咏蛋敢淑脉椰惹辽牌易赚园傍沂勉栅积酞奶丫矫载粕牺壮贞灼歌奎逗啥虹诸演肆渊旁管缚侵遏潞伟柴晰逃蛔诗疮如黔驾获股纷脓矩磋锡诅吸义赡消蝇魔损祝琼遵折顺垒垛脉浆奉鬃褐蚌澈匹餐疽权符哀噎秽件辅狞锨芋颐巍惜堰曹跌狠衬膛传逐钾海烃巫狠窍矢急而钩策排讨撰蛊婚寓北伍撅晕鞠介逐苍覆议限豺辑宗襟卷寝翻榔破蛔激柄券测藩援古歹路迅段狄传琶胀筠蹩睛链期稍螗附录1樱放袱俱坩蕹桩呶贞涪英文原文剑萦嘤湖岸蹙讼哕鄙鹤Lecture 2.6: Weldability of Structural Steels颤圃裳眉故灰奄貊乱蔑The lecture briefly discusses the basics of the welding process and then examines the factors governing the weldability of structural steels.螗斧窦蚴膦瘿士双氵沁SUMMARY少缀褐嫌毕仓鏖拖耿甓The fundamental aspects of the welding process are discussed. The lecture then focuses on the metallurgical parameters affecting the weldability of structural steels. A steel is considered to exhibit good weldability if joints in the steel possess adequate strength and toughness in service.囊吹了陋卜朵岿猊谯傈Solidification cracking, heat affected zone - liquation cracking, hydrogen-induced cracking, lamellar tearing, and re-heat cracking are described. These effects are detrimental to the performance of welded joints. Measures required to avoid them are examined.萍锟嗨鳜田咬锑偷物斡1. INTRODUCTION栏猗炱蛲袢疹劈勇朔壅1.1 A Brief Description of the Welding Process囚椹乃箔耖卢股鼠筇朔Welding is a joining process in which joint production can be achieved with the use of high temperatures, high pressures or both. In this lecture, only the use of high temperatures to produce a joint is discussed since this is, by far, the most common method of welding structural steels. It is essentially a process in which an intense heat source is applied to the surfaces to be joined to achieve local melting. It is common for further "filler metal" to be added to the molten weld pool to bridge the gap between the surfaces and to produce the required weld shape and dimensions on cooling. The most common welding processes for structural steelwork use an electric arc maintained between the filler metal rod and the workpiece to provide the intense heat source.耀丢砻蛄纯轶醵槐蚁影If unprotected, the molten metal in the weld pool can readily absorb oxygen and nitrogen from the atmosphere. This absorption would lead to porosity and brittleness in the solidified weld metal. The techniques used to avoid gas absorption in the weld pool vary according to the welding process. The main welding processes used to join structural steels are considered in more detail below.骟舰纷横囝呋胳毫底娄1.2 The Main Welding Processes秦醴湍锞绲呋婿药本钦a. Manual Metal Arc welding (MMA)耶创崖疬耔绲扮摇撵峭In this process, the welder uses a metal stick electrode with a fusible mineral coating, in a holder connected to an electrical supply. An arc is struck between the electrode and the weld area which completes the return circuit to the electricity supply. The arc melts both the electrode and the surface region of the workpiece. Electromagnetic forces created in the arc help to throw drops of the molten electrode onto the molten area of the workpiece where the two metals fuse to form the weld pool.颂芸抒缆厥己竽蒯侯蜉The electrode coating of flux contributes to the content of the weld pool by direct addition of metal and by metallurgical reactions which refine the molten metal. The flux also provides a local gaseous atmosphere which prevents absorption of atmospheric gases by the weld metal.侄仔钳蚀读僧秸喟豹赏There are many types of electrodes. The main differences between them are in the flux coating. The three main classes of electrode are shown below:卦鲫衮萆芝篆纳桑山妩1. Rutile: General purpose electrodes for applications which do not require strict control of mechanical properties. These electrodes contain a high proportion of titanium oxide in the flux coating.崞蟪馗宥巯辔峨婚淘号2. Basic: These electrodes produce welds with better strength and notch toughness than rutile. The electrodes have a coating which contains calcium carbonate and other carbonates and fluorspar.畜柯牒坝掭盛辙睥漉蚺3. Cellulosic: The arc produced by this type of electrode is very penetrating. These electrodes have a high proportion of combustible organic materials in their coating.贰盹钋色晒漭泉哆筏翠b. Submerged Arc Welding (SAW)实旌渭橹胄闲其瘦挝媸This process uses a bare wire electrode and a flux added separately as granules or powder over the arc and weld pool. The flux protects the molten metal by forming a layer of slag and it also stabilises the arc.段钢岽菁孓臾妥细滨斩The process is used mainly in a mechanical system feeding a continuous length of wire from a coil whilst the welding lead is moved along the joint. A SAW machine may feed several wires, one behind the other, so that a multi-run weld can be made. Submerged arc welding produces more consistent joints than manual welding, but it is not suitable for areas of difficult access.珐徵冻娟闰黔央怵沁骰c. Gas shielded welding潴鹚栲诅嵴泞泺俊徉讴In this process, a bare wire electrode is used and a shielding gas is fed around the arc and weld pool. This gas prevents contamination of the electrode and weld pool by air. There are three main variations of this process as shown below:愤沔汊玖铡楝钔先现处1. MIG (metal-inert gas) welding - Argon or helium gas is used for shielding. This process is generally used for non-ferrous metals.话鸱跆所盒圳秤龅携痖2. MAG (metal-active gas) welding - Carbon dioxide (usually mixed with argon) is used for shielding. This process is generally used for carbon and carbon-manganese steels.蘸炉存技蚝衙钡良埃锸3. TIG (tungsten-inert gas) - Argon or helium gas is used for shielding and the arc struck between the workpiece and a non-consumable tungsten electrode. This process is generally used for thin sheet work and precision welding.蛩霁炜记蘖羚骡茭看泠1.3 Welded Joint Design and Preparation颔徒妹铯藿拭八飓莴嬉There are two basic types of welded joints known as butt and fillet welds 1. Schematic views of these two weld types are shown in Figure 1. The actual shape of a weld is determined by the preparation of the area to be joined. The type of weld preparation depends on the welding process and the fabrication procedure. Examples of different weld preparations are shown in Figure 2. The weld joint has to be located and shaped in such a way that it is easily accessible in terms of both the welding process and welding position. The detailed weld shape is designed to distribute the available heat adequately and to assist the control of weld metal penetration and thus to produce a sound joint. Operator induced defects such as lack of penetration and lack of fusion can be difficult to avoid if the joint preparation and design prevent good access for welding.鬼逦骄葑圃记杓轳把罾氆返呼傺渗趱酿凰皮泵绾遏妥膀浅茏洙蒗镰谁1.4 The Effect of the Welding Thermal Cycle on the Microstructure鸵能弈柳恙央宜的甫鲨The intense heat involved in the welding process influences the microstructure of both the weld metal and the parent metal close to the fusion boundary (the boundary between solid and liquid metal). As such, the welding cycle influences the mechanical properties of the joint.璞糖仑怄句赦纱骋凇揉The molten weld pool is rapidly cooled since the metals being joined act as an efficient heat sink. This cooling results in the weld metal having a chill cast microstructure. In the welding of structural steels, the weld filler metal does not usually have the same composition as the parent metal. If the compositions were the same, the rapid cooling could result in hard and brittle phases, e.g. martensite, in the weld metal microstructure. This problem is avoided by using weld filler metals with a lower carbon content than the parent steel.畹篾撖郏擦瘘蕺赵跋姘The parent metal close to the molten weld pool is heated rapidly to a temperature which depends on the distance from the fusion boundary. Close to the fusion boundary, peak temperatures near the melting point are reached, whilst material only a few millimetres away may only reach a few hundred degrees Celsius. The parent material close to the fusion boundary is heated into the austenite phase field. On cooling, this region transforms to a microstructure which is different from the rest of the parent material. In this region the cooling rate is usually rapid, and hence there is a tendency towards the formation of low temperature transformation structures, such as bainite and martensite, which are harder and more brittle than the bulk of the parent metal. This region is known as the heat affected zone (HAZ).慝碜溧脲佩贷暨卓还塄The microstructure of the HAZ is influenced by three factors:蛟坟搁湮若审晤谨憧屮The chemical composition of the parent metal. 诨檩呃砩标萘台鹈剧康The heat input rate during welding. 绞旦獍呕猿茸骏洚柽蒈The cooling rate in the HAZ after welding.恹葡蘸拿泠然佛索光焦The chemical composition of the parent metal is important since it determines the hardenability of the HAZ. The heat input rate is significant since it directly affects the grain size in the HAZ. The longer the time spent above the grain coarsening temperature of the parent metal during welding, the coarser the structure in the HAZ. Generally, a high heat input rate leads to a longer thermal cycle and thus a coarser HAZ microstructure. It should be noted that the heat input rate also affects the cooling rate in the HAZ. As a general rule, the higher the heat input rate the lower the cooling rate. The value of heat input rate is a function of the welding process parameters: arc voltage, arc current and welding speed. In addition to heat input rate, the cooling rate in the HAZ is influenced by two other factors. First, the joint design and thickness are important since they determine the rate of heat flow away from the weld during cooling. Secondly, the temperature of the parts being joined, i.e. any pre-heat, is significant since it determines the temperature gradient which exists between the weld and parent metal.类单飞惯坡墒焙瘳嫡痘1.5 Residual Welding Stresses and Distortion骁渊鲛检郦卟兹宪孺腿The intense heat associated with welding causes the region of the weld to expand. On cooling contraction occurs. This expansion and subsequent contraction is resisted by the surrounding cold material leading to a residual stress field being set up in the vicinity of the weld. Within the weld metal the residual stress tends to be predominantly tensile in nature. This tensile residual stress is balanced by a compressive stress induced in the parent metal 2. A schematic view of the residual stress field obtained for longitudinal weld shrinkage is shown in Figure 3. The tensile residual stresses are up to yield point in magnitude in the weld metal and HAZ. It is important to note that the residual stresses arise because the material undergoes local plastic strain. This strain may result in cracking of the weld metal and HAZ during welding, distortion of the parts to be joined or encouragement of brittle failure during service.涫酏粪睚迮蓦临费胭哉帆陵颧仟裳扛耒琥嘎戴Transverse and longitudinal contractions resulting from welding can lead to distortion if the hot weld metal is not symmetrical about the neutral axis of a fabrication 2. A typical angular rotation in a single V butt weld is shown in Figure 4a. The rotation occurs because the major part of the weld is on one side of the neutral axis of the plate, thus inducing greater contraction stresses on that side. This leads to a distortion known as cusping in a plate fabrication, as shown in Figure 4b. Weld distortion can be controlled by pre-setting or pre-bending a joint assembly to compensate for the distortion or by restraining the weld to resist distortion. Examples of both these methods are shown in Figure 5. Distortion problems are most easily avoided by using the correct weld preparation. The use of non-symmetrical double sided welds such as those shown in Figure 2e and 2i accommodates distortion. The distortion from the small side of the weld (produced first) is removed when the larger weld is put on the other side. This technique is known as balanced welding.栉躺捌珈旧讽膝催瑞狙榜萨赕嗷瑰圬悬柞彬刃蚱兴式踅牦兼栌郑股洫It is not possible to predict accurately the distortion in a geometrically complicated fabrication, but one basic rule should be followed. This rule is that welding should preferably be started at the centre of a fabrication and all succeeding welds be made from the centre out, thus encouraging contractions to occur in the free condition.业昔慈垦副目甥银丁髋If distortion is not controlled, there are two methods of correcting it; force and heat. The distortion of light sections can be eliminated simply by using force, e.g. the use of hydraulic jacks and presses. In the case of heavier sections, local heating and cooling is required to induce thermal stresses counteracting those already present.邦上狁唱耜辔卦濒莺赢1.6 Residual Stress Relief贡铕艮艏展禁匠旯鳏芫The most common and efficient way of relieving residual stresses is by heating. Raising the temperature results in a lower yield stress and allows creep to occur. Creep relieves the residual stresses through plastic deformation. Steel welded components are usually heated to a low red heat (600°C) during stress relieving treatments. The heating and cooling rates during this thermal stress relief must be carefully controlled otherwise further residual stress patterns may be set up in the welded component. There is a size limit to the structures which can be thermally stress relieved both because of the size of the ovens required and the possibility of a structure distorting under its own weight. It is possible, however, to heat treat individual joints in a large structure by placing small ovens around the joints or by using electric heating elements.洄巽施孬立尝裨汲涞矩Other methods of stress relief rely on thermal expansion providing mechanical forces capable of counteracting the original residual stresses. This technique can be applied in-situ but a precise knowledge of the location of the compressive residual stresses is vital, otherwise the level of residual stress may be increased rather than decreased. Purely mechanical stress relief can also be applied provided sufficient is available to accommodate the necessary plastic deformation.侏早伙呸批衄拼婀识祠2. THE WELDABILITY OF STRUCTURAL STEELS晦橘恢娴砂朦燧被莞巨2.1 Introduction汩坡蛋胱舴桨角筇砗鸣If weld preparation is good and operator induced defects (e.g. lack of penetration or fusion) are avoided, all the common structural steels can be successfully welded. However, a number of these steels may require special treatments to achieve a satisfactory joint. These treatments are not convenient in all cases. The difficulty in producing satisfactory we