摘要焊接残余应力是焊接结构质量评定的重要参数之一，因而探讨可无损、快速测量焊接残余应力的技术与方法对焊接结构可靠性具有重要意义。目前，常用的无损检测方法主要有：射线检测、超声波检测、磁力检测、涡流检测及渗透检测，这些方法各有其使用的限定条件且只能检测出已形成的宏观缺陷，对检测材料隐性不连续部位（即应力集中部位）存在局限。而金属磁记忆检测技术不仅可以发现宏观缺陷并且能够指示无宏观缺陷的应力集中部位，从而具有早期诊断、预警能力。84512

鉴于此，本文以Q235钢与45钢对接焊接接头为评价对象，在金属磁记忆信号对应力响应机理分析基础上，探讨Q235钢与45钢对接焊应力的金属磁记忆评价技术，结合弹塑性变形理论及压磁理论澄清其评价机理。在此基础上，本文借助真空热处理方法，获得无初始磁信号的Q235钢与45钢，进而利用金属磁记忆信号特征参量标定实验，分别建立Q235钢与45钢的磁场强度梯度与应力间对应关系，最终实现Q235钢与45钢对接焊应力的金属磁记忆评价。

结果表明，金属磁记忆信号检测位置不同，Q235钢与45钢标定试样的金属磁记忆信号随应力的变化规律基本相同，只是信号幅值略有不同；加载应力不同时，Q235钢与45钢试样Hp(y)磁信号随其摆放角度的变化规律基本相同。Q235钢与45钢试样散射磁场强度梯度随试样摆放角度的变化规律基本相同，即随试样摆放角度增大，其散射磁场强度梯度逐渐变大，当试样摆放角度达到90°时，其散射磁场强度梯度达到最大值，再随试样摆放角度增大，其散射磁场强度梯度逐渐减小；随应力σ的增加，Q235钢试样与45钢试样散射磁场强度梯度k值基本呈线性规律变大，但是Q235钢试样的k值增大的速率比45钢的大。结合试样静载拉伸断口分析理论认为，45钢与Q235钢各向异性组织引起的不均匀弹塑性变形是导致上述结果的主要原因。

毕业论文关键词: 金属磁记忆； 应力； 无损评价； 磁场强度梯度； 碳含量

Abstract The welding residual stress is an important factor for welding structure quality, so research on nondestructive method of welding stress evaluation is important for reliability for welding structure。 At present, the common nondestructive evaluation methods include radiographic testing, ultrasonic testing, magnetic testing, penetrant testing and eddy current testing。 These methods have their limited conditions and can only detect the formed macroscopic defects。 These detection methods of recessive material discontinuity (stress concentration) also have limitations。 However, metal magnetic memory testing technology can not only find macroscopic defects and can indicate non-macroscopic defects of stress concentration areas, so it owns early diagnosis and warning capacity。

In view of this, welding stress of butt joint of Q235 steel and 45 steel is evaluated in this paper。 Based on the analysis of mechanism of metal magnetic memory signal to stress response, discuss the metal magnetic memory technology on butt weld based on Q235 steel and 45 steel, explain its evaluation mechanism with elastic-plastic deformation theory and piezomagnetic theory。 On this basis, by means of vacuum heat treatment in this paper, get the zero initial magnetic signal of Q235 steel and 45 steel, and then using metal magnetic memory signal characteristic parameter calibration experiments, set up of Q235 steel and 45 steel corresponding relationship between magnetic field intensity gradient and stress respectively, finally complete the evaluation of the Q235 steel and 45 steel butt welding stress of metal magnetic memory。

The results show that the metal magnetic memory signal detection position is different, but the Q235 steel and 45 steel calibration sample of metal magnetic memory signal with stress change rule of is basically same, just a slightly different signal amplitude; Load stress is not at the same time, the Q235 steel and 45 steel samples Hp(y) magnetic signals with the different angle is basically same。 Q235 steel and 45 steel specimen scattering gradient magnetic field strength with the placement angle changing rule is basically same, namely with the increase of sample placement angle, the scattering intensity of magnetic field gradient increases gradually, when the sample is put angle 90°, the scattering magnetic field intensity gradient is the maximum, and with the increase of sample placement angle, the scattering intensity of magnetic field gradient decreases。 With the increase of stress sigma, Q235 steel samples with 45 steel samples scattering intensity of magnetic field gradient follow k value basic linear law, but the k value of Q235 steel sample rate is increased greater than 45 steel。 Combined with the sample surface analysis theory, the static load of 45 steel and Q235 steel anisotropic organization caused by uneven deformation plasticity is a major cause to the result。