为保障特高压变压器油箱的防爆性能，本工作聚焦其关键结构Q345钢焊接接头在动态冲击载荷下的变形行为和失效机制，采用数字图像相关辅助的拉伸测试、冲击测试、SEM观察以及计算机断层扫描等方法，研究了油箱用Q345钢焊接接头在不同应变速率下的变形行为和失效机制。结果表明，与Q345钢母材相比，焊接接头的变形行为对应变速率更为敏感。当应变速率提升至1.0 × 10-1 s-1时，其延伸率显著降低，撕裂位置由母材区域转移至焊缝区域。在冲击载荷作用下，变形过程中的绝热升温现象促使材料内部形成氧化物颗粒，这些颗粒作为潜在的裂纹源，易造成应力集中，从而加剧油箱焊缝的结构失效。Q345钢母材的冲击韧性为(326.1 ± 14.1) J/cm2，焊接接头的冲击韧性仅为 (52.7 ± 2.7) J/cm2，母材的冲击韧性约为焊接接头的6倍，表明焊缝区域是增强油箱防爆性能的关键部位。在模拟接近电弧放电产生的超高速冲击速率载荷下，焊缝区域观察到典型的解理断裂，是导致其冲击韧性大幅降低的原因。
Ultra-high-voltage
transformer tanks are critical structural components of large-scale power and
converter transformers and require exceptional explosion-proof performance to
ensure grid stability. These tanks are typically fabricated from low-alloy
high-strength steels such as Q345 and are characterized by complex geometries
and a high density of welded joints. During internal arc discharge events,
welded joints serve as primary sites for crack initiation and propagation under
transient impact loading, ultimately leading to structural failure. Although
welded joints are recognized as potential weak links, their strain rate-dependent
deformation behavior and underlying failure mechanisms have not been
systematically elucidated. In particular, it remains unclear how dynamic
loading conditions affect fracture initiation sites and the evolution of
microstructural damage within welded joints. In this study, the deformation
behavior and failure mechanisms of Q345 steel welded joints were systematically
investigated. Uniaxial tensile tests were conducted over a strain rate range of
1.0 × 10−4 s−1–1.0 × 10−1 s−1, coupled with digital image correlation to monitor the evolution
of localized strain fields. Impact toughness was evaluated using standard
Charpy tests, and microstructural characterization was conducted using optical
microscopy and SEM. Furthermore, X-ray computed tomography was employed to
visualize and quantify internal defect evolution. The results indicate that
Q345 steel welded joints exhibit more pronounced strain rate sensitivity than
the base metal (BM). As the strain rate increased to 1.0 × 10−1 s−1,
a substantial reduction in elongation was observed. Meanwhile, the fracture
initiation site shifted from the BM to the weld
metal (WM) with increasing strain rate. Digital
image correlation analysis revealed a transition in fracture location. At lower strain rates, plastic deformation was primarily accommodated by the BM, leading to
necking and final failure within the BM region. In
contrast, at higher strain rates, strain localization rapidly developed
within the heat-affected zone and WM, resulting in fracture initiation in the weld region. Quantitative impact testing further demonstrated a
substantial disparity in toughness. The BM exhibited a high impact toughness of
(326.1 ± 14.1) J/cm2, whereas the welded joints showed a
significantly lower value of (52.7 ± 2.7) J/cm2, corresponding to an
approximately sixfold reduction. This marked decrease identifies the weld
region as the dominant failure site and underscores its critical role in improving
explosion resistance. SEM fractography confirmed a transition from ductile
dimple morphology to brittle cleavage fracture, characterized by distinct
cleavage facets and river patterns. Adiabatic heating during rapid plastic
deformation was found to promote the formation of oxide particles within the
welded joint. These oxides induced localized stress concentrations and acted as
critical crack initiation sites, ultimately triggering structural failure. In
addition, X-ray computed tomography results verified that large internal
defects within the WM served as preferential sites for strain concentration and
crack propagation under dynamic loading. This study clarifies the intrinsic
mechanisms governing dynamic failure in Q345 steel welded joints and provides
essential theoretical insights for improving the explosion resistance and
structural integrity of welded steel components under extreme dynamic conditions.
