Acoustic emission detection of 316L stainless steel welded joints during intergranular corrosion

This study analyzes acoustic emission (AE) signals during the intergranular corrosion (IGC) process of 316L stainless steel welded joints under different welding currents in boiling nitric acid. IGC generates several AE signals with high AE activity. The AE technique could hardly distinguish IGC in stainless steel welded joints with different welding heat inputs. However, AE signals can effectively distinguish IGC characteristics in different corrosion stages. The IGC resistance of a heat-affected zone is lower than that of a weld zone. The initiation and rapid corrosion stages can be distinguished using AE results and microstructural analysis. Moreover, energy count rate and amplitude are considered to be ideal parameters for characterizing different IGC processes. Two types of signals are detected in the rapid corrosion stage. It can be concluded that grain boundary corrosion and grain separation are the AE sources of type 1 and type 2, respectively.     

Morphology,size and distribution of MnS inclusions in non-quenched and tempered steel during heat treatment

This article reports the morphology, size, and distribution evolution of MnS inclusions in non-quenched and tempered steel during heat treatment. The variation of single large-sized MnS inclusions at high temperature was observed in situ using a confocal scanning laser microscope (CSLM). The slender MnS inclusions first changed to pearl-like strings. These small-sized pearls subsequently coalesced and became closer together as the temperature increased. Large-sized MnS inclusions in non-quenched and tempered steel samples with different thermal histories were investigated with respect to the evolution of their morphology, size, and distribution. After 30 min of ovulation at 1573 K, the percentage of MnS inclusions larger than 3 μm decreased from 50.5% to 3.0%. After a 3 h soaking period, Ostwald ripening occurred. Most MnS inclusions moved from the grain boundaries to the interior. The present study demonstrates that heat treatment is an effective method of changing the morphology, size, and distribution of MnS inclusions, especially large-sized ones.     

Titanium effect on the microstructure and properties of laminated high boron steel plates

High-boron steel is an important material used for thermal neutron shielding. The appropriate amount of added boron must be determined because excessive boron may deteriorate the steel's workability. A uniform microstructure can be formed by adding titanium to boron steel. In this study, casting and hot rolling were used to fabricate laminated high-boron steel plates whose cores contained 2.25wt% boron and 0wt%-7.9wt% titanium. The effects of titanium content and hot-rolling and heat-treatment processes on the microstructure and properties of the laminated plates were studied. The results indicated that the optimum titanium content was 5.7wt% when the boron content was 2.25wt%, and that the best overall properties were obtained after heat treatment at 1100℃ for 4 h. The tensile strength, yield strength, and elongation at the specified temperature and holding time were as high as 526.88 MPa, 219.36 MPa, and 29%, respectively.     

Effects of H content on the tensile properties and fracture behavior of SA508-III steel

SA508-Ⅲ steel was charged with different hydrogen (H) contents using a high-pressure thermal charging method to study the effects of H content on the tensile properties and evaluate the H embrittlement behavior of the steel. The results indicate that the ultimate tensile strength remains nearly unchanged with the addition of H. In contrast, the yielding strength slightly increases, and the elongation significantly decreases with increasing H content, especially at concentrations exceeding 5.6×10-6. On the basis of fractographic analysis, it is clear that the addition of H changes the fracture mode from microvoid coalescence to a mixture of river patterns and dimples. Carbides are strong traps for H; thus, the H atoms easily migrate in the form of Cottrell atmosphere toward the carbides following moving dislocations during tensile deformation. In addition, stress-induced H atoms accumulate at the interface between carbides and the matrix after necking under three-dimensional stress, which weakens the interfacial bonding force. Consequently, when the local H concentration reaches a critical value, microcracks occur at the interface, resulting in fracture.     

一种新型结构材料S280

 S280 是一种超高强度不锈钢, 采用低碳马氏体相变强化和时效强化叠加, 靠析出强化获得所需的强度。使用状态下的基体组织为低碳板条马氏体, 主要强化相为Fe₂Mo 等, 抗拉强度σ_b为1920～1930 MPa, 断裂韧度K_IC为95～100 MPa √m, 具有比300M 和AerMet100 更好的耐腐蚀性能, 主要用于抗腐蚀性能要求高的超高强度构件。     

干侵入在云南一次全省性暴雨中的触发作用

利用常规观测资料和NCEP再分析资料,对2013年8月2425日发生在云南的强降水事件进行诊断分析.结果表明热带低压西行过程中来自中高层的干冷空气侵入造成了大范围强降水的发生.稳定而持续的水汽输送和水汽辐合是暴雨形成的重要因素,高层冷空气南下并向低层渗透造成的对流抬升又使得对流加强,利于暴雨的产生.冷空气与偏东急流长时间交汇于滇东北,造成滇东北暴雨维持时段较长;而滇西南干舌与热带低压交汇时段和区域正好对应着暴雨时段.干舌前侧与暴雨落区有较好相关性,暴雨发生在干空气与湿空气交界处,暴雨区与MPV异常值对应关系较好.     

基于模糊综合评价法的农产品冷链绿色物流综合评价研究

随着人类保护环境和绿色消费的意识不断增强,农产品冷链绿色物流得到了快速发展.农产品冷链物流的绿色发展,对减少环境污染、提高居民生活水平的意义重大.通过分析农产品冷链物流绿色发展的重要性,基于国内外研究和实际调研,选取合适的农产品冷链物流绿色发展影响因子,构建湖南农产品冷链绿色物流的模糊综合评价模型,并运用具体的算例验证构建的评价模型,得出现阶段农产品冷链绿色物流的发展程度.算例结果表明,农产品冷链绿色物流综合评价指标体系符合实际情况,具有参考价值和现实意义.     

基于OpenSees的钢管混凝土柱-钢梁错层节点抗震性能有限元分析

为研究钢管混凝土柱-钢梁错层节点抗震性能,基于已有试验研究成果,利用OpenSees有限元软件,对钢管混凝土柱-钢梁错层节点进行数值模拟,将模拟结果与试验结果进行对比,两者较吻合。通过数值模拟,分析了轴压比、混凝土强度等级和钢材强度等参数对钢管混凝土柱-钢梁错层节点抗震性能的影响。结果表明:在轴压比为0.3～0.7范围内,随轴压比增大,结构承载力降低明显;随混凝土强度等级提高,试件极限承载力特征值增大较为明显,最大增幅达9.39%;通过对比发现,合理提高钢材强度可以有效增加结构承载力和延性,当模拟计算Q345钢材时,试件极限承载力增加了26.08%,破坏点位移值增加了8.41%。     

多次分段控制注浆斜向预应力钢锚管锚索组合结构加固技术现场试验研究

对多次分段控制注浆斜向预应力钢锚管锚索组合结构新型边坡加固技术的结构形式、适用范围、加固作用机理、现场试验进行分析,对比分析预应力锚索、多次分段控制注浆预应力钢锚管及多次分段控制注浆预应力钢锚管锚索承载力,研究结果表明：1)该结构特别适用岩土体破碎、松散、易塌孔地层于边坡,通过钢锚管劈裂注浆,提高边坡岩土体的强度指标,充填了和挤密破碎地层间的空洞和孔隙,有效提高锚固段锚固力;2)通过预应力锚索和预应力钢锚管极限承载力对比分析表明预应力钢锚管没能够充分发挥该地层的锚固力。预应力钢锚管施加的预应力只能传到浅表层,且破坏模式为钢管被拉断或者钢管接头处断裂;3)三组不同根数的钢绞线预应力钢锚管锚索极限承载力结果与普通的预应力锚索相比来看,单束钢绞线预应力锚索承载力由200kN增加到235kN,锚固力提高17.5%;两根钢绞线预应力锚索承载力由295kN增加到378kN,锚固力提高28.14%;三根钢绞线预应力锚索承载力由336kN增加到432.26kN,锚固力提高28.65%。表明预应力钢锚管锚索通过劈裂注浆挤密锚固段岩土体,浆液充填裂隙,形成“树根状”,有效的提高了锚固段锚固力。     

On-line spheroidization process of medium-carbon low-alloyed cold heading steel

Conventionally manufactured 35CrMo cold heading steel must undergo spheroidization annealing before the cold heading process. In this paper, different types of deformation processes with various controlled cooling periods were operated to achieve on-line spheroidal cementite using the Gleeble-3500 simulation technique. According to the measured dynamic ferrite transformation temperature (A_d3), the deformation could be divided into two types: low temperature deformation at 810 and 780℃; “deformation-induced ferrite transformation” (DIFT) deformation at 750 and 720℃. Compared with the low temperature deformation, the DIFT deformation followed by accelerated cooling to 680℃ is beneficial for the formation of spheroidal cementite. Samples subjected to both the low-temperature deformation and DIFT deformation can obtain granular bainite by accelerated cooling to 640℃; the latter may contribute to the formation of a fine dispersion of secondary constituents. Granular bainite can transform into globular pearlite rapidly during subcritical annealing, and the more the disperse phase, the more homogeneously distributed globular cementite can be obtained.