铸钢件疲劳裂缝的冷焊修复

某电厂现役机组有6台,其中6号、7号、8号、9号机组为六十至七十年代的中温中压机组,近几年,由于设备老化和材质缺陷等原因,发生了多起危及设备安全运行的重大问题,其中7号、8号机型号为31-25额定参数,主汽温度435℃,主汽压力3.1 MPa,分别于1964年、1967年投运。在7号、8号机大修时发现汽缸上缸盖中分面的两拐角处各有一道裂缝,裂缝尺寸见表1。     

金属加工表面缺陷冷焊修复

本文介绍了冷焊修复原理,对比冷焊工艺与手工氩弧焊修复效果,并介绍了精密冷焊工艺的相关参数,确定冷焊修复应用可以达到理想的修复效果。     

汽轮机自动主汽门裂纹的分段冷焊修复

某热电厂的Ｂ2 5 - 8.83/ 0 .98型汽轮机在运行 4 .8× 10 4 ｈ后大修时发现 ,材质为ＺＧ15Ｃｒ1Ｍｏ1Ｖ的汽轮机自动主汽门结合面的螺栓孔之间存在两条裂纹 ,见图 1。主汽门内侧裂纹深度约为 30ｍｍ ,裂纹从内向外贯穿整个缸体厚度。另外 ,在裂纹的近末端还有一条较短的裂纹 ,长度约为 35ｍｍ。基于该裂纹所处的位置和裂纹的大小 ,决定采用冷焊的方法进行补焊。图 1　自动主汽门裂纹位置示意图1　焊前准备( 1)清除裂纹　用机械方法将裂纹挖除干净 ,最后形成Ｕ形焊接坡口 ,见图 2。平均宽度 2 8ｍｍ ,最深70ｍｍ。( 2 )清理坡口　用丙酮将…     

自制铜铁焊条和镍铜焊条的灰铸铁电弧冷焊研究

采用自制铜铁焊条、镍铜焊条,运用电弧冷焊工艺对灰铸铁进行焊接试验,研究了其焊后接头的金相组织、硬度。结果表明,用所研制铜铁焊条、镍铜焊条进行铸铁补焊是可行的。     

卷板机上导板电弧冷焊修复工艺

介绍了焊接修复卷板机上导板时,采用电弧冷焊修复工艺,严格控制焊接顺序及层间温度,焊后锤击焊缝以减少焊接应力,防止产生裂纹和焊缝剥离的成功经验.     

灰铸铁非铸铁型异质焊缝电弧冷焊焊条的选用

（1）镍基铸铁焊条。特点是焊缝硬度较低、熔合区白口层薄,且呈断续分布,焊缝的颜色与灰铸铁桕近,适用于加工面的焊接。     

大型锻件的激光相变强化

对大型锻件耐磨部位采用激光相变强化,能够获得一定深度的淬硬层,淬硬层组织为隐针马氏体+碳化物+少量残余奥氏体,晶粒组织明显细化,硬度显著提高。淬硬层为压应力,对提高耐磨性和抗疲劳能力有很大作用。合理的搭接,能够将软带宽度降低到最小。     

铜含量对焊缝组织和性能的影响

采用药皮过渡铜的方法,研究了碱性焊条中铜的过渡规律及其对焊缝组织和显微硬度的影响.结果表明:铜的过渡系数为79％;焊缝组织主要由晶界铁素体、侧板条铁素体和针状铁素体组成;随着焊缝铜含量的增加,针状铁素体数量增加,焊缝显微硬度增大.     

空气锤缸体裂纹电弧冷焊修复工艺设计与实践

介绍了修复空气锤缸体裂纹时采用焊条电弧冷焊配合栽丝工艺及合理的焊接顺序等措施.实践证明,大型铸件补焊的经济方法是打底、镶边过渡.采用塑性较好的异质焊缝铸铁焊奈,填充用强度较低的碳钢焊条与异质焊缝焊条分层交替焊接.该方法对铸件特别是大型铸铁件的焊接修复具有一定的借鉴价值.     

高强韧模具修复用堆焊焊条的研制

根据冲裁模具的工作条件和失效形式，设计出一种专用的局部修复用堆焊焊条。使焊缝具有高咸度和高抗裂性，满足冲裁模具局部修复用冷焊要求。     

Effects of expulsion in spot welding of cold rolled sheet steels

The effects of expulsion on microstructure and tensile shear strength of spot welds have been investigated for a high-strength cold rolled sheet steel. Spot welds with expulsion are characteristic for a “double im-age” near the fusion line, an equiaxed dendritic grain zone along the faying surface, and deep indenta-tions on the outer surfaces. Microstructural examinations and tensile shear tests of spot welding specimens were conducted to determine the correlation between microstructure and strength. It was found that the equiaxed dendritic structure was associated with significant solidification cracking. Frac-tography on tensile specimens reveals that brittle failure is associated with an equiaxed microstructure. Furthermore, the surface indentation will change the stress at the nugget edge, and deep surface inden-tations are expected to promote premature failure.     

Effect of deep cold treatment on two case hardening steels

Although cold treatments have been used to reduce the retained austenite in the cases of carburised steel for many years, there is little data on deep cold temperatures below -70℃ or treatment times longer than an hour or two. This study set out to determine the effects of such deep cold treatments at temperatures -150℃ for 24 h. The study investigated the effects of deep cold on the microstructure, hardness profile, residual stress and internal oxidation on two typical carburising steels, 16MnCr5 and 21NiCrMo2. The study found that for both 16MnCr5 and 21NiCrMo2 carburised to a case depth of approximately 0.8 mm, the longer and colder the deep cold treatment, the more the austenite retained in the case was converted to martensite and the harder it became. After low temperature tempering, the hardness difference was smaller, but still significant. In both steels, the case appeared more refined and homogeneous after deep cold treatment. Deep cold treatment had a negligible effect on the core properties of either steel.     

热镀锌高强钢电阻点焊的点蚀对熔核形成的影响

热镀锌高强钢由于高强度特性以及良好的抗腐蚀性,可满足汽车轻量化与安全性需要,在车身制造中逐渐得到广泛应用.但热镀锌高强钢点焊的电极磨损严重,点蚀磨损特征变化明显,对熔核形成产生较大影响.建立点焊过程的点蚀有限元模型,采用数值分析与试验方法研究点蚀对熔核形成影响.结果表明,点蚀的产生与发展增加了工件之间的实际接触面积,使电流密度降低,熔核直径减小;同边缘位置点蚀相比,电极中心位置点蚀由于对熔核区域的电流分流作用,更加不利于熔核的形成.随着点蚀面积的增大,形成环状熔核几率增加.     

不等厚ULC-BH钢激光拼焊接头硬化机制

采用两种激光光斑加热位置,对不等厚超低碳烘烤硬化钢板进行激光拼焊,分别测定拼焊接头的显微硬度,对比分析其组织性能差异,探讨热影响区硬化软化机制.结果表明,光斑偏向厚板时,拼焊焊缝两侧组织硬度曲线较为对称;在焊接热循环作用下,热影响区基体中饱和科特雷尔(Cottrell)气团析出细小弥散的NbC等第二相颗粒,使得热影响区强硬化;光斑置中时,容易使薄板热输入过渡,析出的第二相颗粒聚集长大,热影响区重新软化,容易导致冲压时开裂.