摘  要在现代工业中，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，焊接技术早已成为各大工业的必不可缺的核心技术。焊接 结构的质量是保证推动焊接技术不断发展、应用领域不断扩展的关键。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，焊接结构的质量是保证推动焊接技术不断发展、应用领域不 断扩展的关键，为此国内外对焊接应力的评价技术开展了广泛研究。80634

鉴于此，本文以碳钢对接焊应力的金属磁记忆评价为研究目标，探讨晶粒 尺寸对碳钢金属磁记忆信号的影响规律，结合弹塑性变形理论及压磁理论澄清 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，获得不同晶粒尺寸的 Q235 钢试样，进而利 用金属磁记忆信号特征参量标定实验，建立其与晶粒尺寸间对应关系，最终实 现 Q235 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；晶粒尺寸不同，Q235 钢金属磁记忆信号随应力的变化规律基本相同，未加载时，Q235 钢金属磁记忆 信号幅值较小，随应力增大，Q235 钢金属磁记忆信号即呈逆时针规律转动，其 金属磁记忆曲线具有唯一过零点，且此时不同应力的 Q235 钢金属磁记忆曲线基 本相交于过零点 30mm 处，当应力都达到 320MPa 时，Q235 钢金属磁记忆曲线 斜率随应力增大而略有降低。采用线性拟合，对六组不同晶粒尺寸 Q235 钢试样 符合线性规律阶段的磁场强度梯度 K 与应力结果进行拟合，得到金属磁信号曲 线斜率变化率 S 与 Q235 钢晶粒尺寸间对应关系。

毕业论文关键词:金属磁记忆；应力；无损检测；晶粒尺寸；磁场强度梯度

Abstract Welding technology has been widely used in the field of heavy machinery, automobile manufacturing, oil pipelines, pressure vessels and so on, so quality assurance of welding structures is important for applied field and development of welding technology。 Research shows that lots of factors affect the safety of the welding service, reliability of the structure, while welding stress is a key factor in determining the quality of welded structures, that is the key to promote the continuous development of welding technology, expanding applications of assurance, so many researchers both at home and abroad develop the technology of welding stress。

In view of this, welding stress measurement with metal magnetic memory technology is researched in this paper, and the influence of grain size on welding stress evaluation is discussed。 Based on the theory of elastic and plastic deformation, the mechanism is obtained。 In this paper, the Q235 steel samples with different grain sizes were obtained by heat treatment。 By using the  characteristic  parameters of metal magnetic memory signal calibration experiment, the relationship between the grain size and the corresponding relationship was established。 Finally, the evaluation of the metal magnetic memory of Q235 steel welding stress was achieved。

The results show that effect of metal magnetic memory signal detection position on Q235 steel metal magnetic memory signal can be ignored。 When the grain size is different, the relationship between the metal magnetic memory signal and the  stress of Q235 steel is consistent。 When Q235 steel is not under pressure, the Q235 steel metal magnetic memory signal amplitude is small。 When the stress increases, the magnetic memory signal of Q235 steel increases。 While the stress increases to the yield stage, the Q235 steel metal magnetic memory signal is reduced。 From the foregoing, the law is rotating counterclockwise。 In order to obtain the relationship between magnetic field intensity gradient and stress, this paper be based on linear fitting。