摘要因可获得可靠冶金结合连接，焊接技术在重型机械、汽车制造、石油管道、压力 容器等领域得到广泛应用。相关研究表明，影响焊接结构服役安全及其可靠性的因素 众多，而焊接应力是其关键甚至决定性因素，为此国内外对焊接应力的评价技术开展 了广泛研究。目前，广泛应用的应力测量方法可分为两大类，即机械方法和物理方法， 其中机械方法有钻孔法、切割法等，这类方法属于破坏性检测方法，物理方法有电阻 应变计法、X 射线测定法、磁弹性法和超声波法等，这类方法属于无损检测方法。 超声波检测就是近年迅速发展起来的新方法。它具有检测方便，对人体没有伤害等优 点，因此超声波检测的发展十分迅速。81345

鉴于此，本文以碳钢对接焊应力的超声波应力评价为研究目标，探讨碳含量对碳 钢超声波信号的影响规律，结合超声波声弹性理论澄清其影响机理。在此基础上，本 文借助真空热处理方法，通过加热速率、最高加温度、保温时间及冷却方式的优化， 获得相同晶粒尺寸的 45 钢和 Q235 钢试样，进而通过对材料静载拉伸，建立应力— 超声波信号时间差的关系，最终实现 45 钢和 Q235 钢对接焊应力的超声波评价。

结果表明：随载荷增大，45 钢与 Q235 钢超声波信号间时间差基本呈线性规律增 大，这与超声波声弹性理论基本相符，但与理论规律相比，超声波信号间时间差—载 荷曲线波动略微明显，且超声波信号间时间差的增大速率随载荷增大而略有降低并逐 渐趋于平稳，对比低载荷阶段 45 钢与 Q235 钢超声波信号间时间差随载荷变化的规 律可知，45 钢超声波信号间时间差波动幅度较大，导致实验结果与理论结果不同的 根本原因是静载拉伸过程中 45 钢与 Q235 钢表层不均匀变形。通过对两种试样的应 力-时间差曲线进行线性拟合，可得到其声弹性系数。由于材料的晶粒尺寸相同，影 响材料声弹性系数的因素即为材料的碳含量。所以最终得到了声弹性系数与碳含量之 间的关系。

关键词：超声波；应力；无损评价；碳含量；声弹性理论

Abstract

Because it can obtain reliable metallurgical bonding connection, welding technology in heavy machinery, automobile manufacturing, oil pipelines, pressure vessels and other fields has been widely used。 Researches show that there are lots of influence factors for welding structure service safety and reliability, but welding stress is the key decisive factor。 Therefore, welding residual stress evaluation techniques have been extensively studied。 At present, the methods for welding residual stress evaluation can be pided into two categories including mechanical and physical methods, the mechanical method consists of hole drilling method and the cutting method, and this kind of method belongs to damage detection methods, physical methods consists of resistance strain gauge method, X-ray method, magnetic elastic method and ultrasonic method and so on, this kind of method belongs to nondestructive detection method。 Ultrasonic testing is a new method that is developed rapidly in recent years, and it has  advantages of convenient detection, no  harm to the human body, so ultrasonic wave method for welding residual stress evaluation is developed  rapidly。

In view of this, this paper takes the carbon steel butt welding stress as the research objective, discusses the influence of carbon content on the ultrasonic signal of carbon steel, and clarifies the influence mechanism of the ultrasonic wave theory。 On the basis of。 With the help of vacuum heat treatment method, through the optimization of the heating rate, plus a maximum temperature, holding time and cooling way to obtain the same grain size of 45 steel and Q235 steel sample, and then through the material static tensile, should be established in the power ultrasonic signal time difference, ultimately achieve 45 steel and Q235 steel butt  welding   force  of ultrasonic evaluation。