多孔Fe–C–P合金泡孔形貌、孔隙率、显微组织及力学性能的研究

Open cell steel foams were successfully fabricated through the powder metallurgy route using urea granules as the water leachable space holder in the present study. The influence of different amounts of phosphorus (0, 0.5wt%, 1wt%, 2wt%, and 4wt%) was investigated on the cell morphology, porosity, microstructure of cell walls, and mechanical properties of steel foams. The cell morphology and microstructure of the cell walls were evaluated using an optical microscope equipped with image processing software and a scanning electron microscope equipped with an energy dispersive X-ray spectrometer. In addition, the compression tests were conducted on the steel foams using a universal testing machine. Based on microscopic images, the porous structure consists of spherical cells and irregularly shaped pores that are distributed in the cell walls. The results indicated that by increasing the phosphorus content, the porosity increases from 71.9% to 83.2%. The partially distributed ferrite and fine pearlite was observed in the microstructure of the cell walls, and α-Fe and Fe₃P eutectic extended between the boundaries of agglomerated iron particles. Furthermore, elastic and long saw-toothed plateau regions were observed before fracture in the compressional stress–strain curves. According to the results, by increasing the phosphorus content from 0 to 4wt%, the plateau region of the stress–strain curves shifts to the right and upward. Therefore, increasing phosphorus content causes improvement in the mechanical properties of steel foams.     

Synthesis and characterization of copper foams through a powder metallurgy route using a compressible and lubricant space-holder material

In the present work, a compressible and lubricating space-holder material commonly known as “acrawax” was used to process Cu foams with various pore sizes and various porosities. The foams were processed without using binders to avoid contamination of their metal matrices. The lubricant space-holder material was found to facilitate more uniform flow and distribution of metal powder around the surface of the space holder. In addition, the use of acrawax as a space-holder material yielded considerably dense cell walls, which are an essential prerequisite for better material properties. The foams processed with a smaller-sized space holder were found to exhibit better electrical and mechanical properties than those processed with a coarser-sized space holder. The isotropic pore shape, uniform pore distribution throughout the metal matrix, and uniform cell wall thickness were found to enhance the properties pertaining to fine-pore foam samples. The processed foams exhibit properties similar to those of the foams processed through the lost-carbonate sintering process.     

Effects of copper content on the shell characteristics of hollow steel spheres manufactured using an advanced powder metallurgy technique

Metallic hollow spheres are used as base materials in the manufacture of hollow sphere structures and metallic foams. In this study, steel hollow spheres were successfully manufactured using an advanced powder metallurgy technique. The spheres’ shells were characterized by optical microscopy in conjunction with microstructural image analysis software, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The microscopic evaluations revealed that the shells consist of sintered iron powder, sintered copper powder, sodium silicate, and porosity regions. In addition, the effects of copper content on various parameters such as shell defects, microcracks, thickness, and porosities were investigated. The results indicated that increasing the copper content results in decreases in the surface fraction of shell porosities and the number of microcracks and an increase in shell thickness.     

铁路钢桥高强度紧固螺栓断裂分析及防护

为探求高强度紧固螺栓发生断裂的原因,对某铁路钢桥上断裂的紧固螺栓进行了失效分析。利用扫描电子显微镜、能量色散X射线谱、金相显微镜、洛氏硬度仪、X射线荧光光谱仪、电子万能试验机等技术手段,对铁路钢桥失效螺栓的断口形貌、断口微区成分、显微组织、硬度、螺栓用钢的成分以及力学性能等方面进行分析与研究。结果显示：螺栓用钢的化学成分、硬度及力学性能均符合国家标准要求;螺栓断口起裂区存在树枝状裂纹,裂纹内部有含硫的腐蚀产物,且螺栓工作时所受外力为交变载荷。因此,螺栓的断裂是在交变载荷下发生的腐蚀疲劳断裂。螺栓断裂的初始裂纹源位于螺杆上螺纹的根部或螺柱与螺母连接位置的根部,为由硫元素引起的应力腐蚀裂纹。此研究为防止螺栓发生应力腐蚀裂纹及衍生病害提供了理论依据。     

钢桥面沥青铺装层疲劳损伤分析与车辆轴载换算

采用力学近似方法,对钢桥面沥青混合料铺装层在循环荷载作用下的力学行为和疲劳损伤特性进行了理论分析.采用粘弹性损伤模型的能量转换方法对钢桥面沥青混合料铺装层应力场、应变场及损伤场分布状况进行研究.依据钢桥面沥青混合料铺装体系复合结构的应力场、应变场和损伤场在疲劳过程中的动态演变规律以及疲劳裂缝的形成机理,推导出钢桥面沥青铺装层疲劳性能方程和车辆轴载换算公式.结合南京长江第二大桥钢桥面铺装工程,应用所建立的疲劳性能方程以及轴载换算公式对钢桥面铺装层使用寿命进行预测.     

Effects of sphere size on the microstructure and mechanical properties of ductile iron–steel hollow sphere syntactic foams

The effects of sphere size on the microstructural and mechanical properties of ductile iron–steel hollow sphere (DI–SHS) syntactic foams were investigated in this study. The SHSs were manufactured by fluidized-bed coating via the Fe-based commercial powder–binder suspension onto expanded polystyrene spheres (EPSs). Afterwards, the DI–SHS syntactic foams were produced via a sand-mold casting process. The microstructures of specimens were investigated by optical microscopy, scanning electron microscopy (SEM), and energy- dispersive X-ray spectroscopy (EDS). The microscopic evaluations of specimens reveal distinct regions composed of the DI matrix, SHS shells, and compatible interface. As a result, the microstructures and graphite morphologies of the DI matrix depend on sphere size. When the sphere size decreases, the area fractions of cementite and graphite phases are observed to increase and decrease, respectively. Compression tests were subsequently conducted at ambient temperature on the DI–SHS syntactic foams. The results reveal that the compression behavior of the syntactic foams is enhanced with increasing sphere size. Furthermore, the compressed specimens demonstrate that microcracks start and grow from the interface region.     

缺口对转向架用SMA490BW钢的疲劳性能的影响

基于高速列车转向架在运行进程中常因承受各种交变载荷而导致疲劳断裂问题,针对CRH2高速列车转向架用SMA490BW钢试样进行拉伸试验,确保SMA490BW钢的力学性能符合标准要求下,对此种钢进行疲劳性能研究并通过扫描电镜进行断口分析。结果表明：与光滑试件(kt = 1)相比缺口试件(kt = 3),疲劳极限应力减小了61％,S-N曲线左侧的斜率更大;其缺口敏感系数为0.786;光滑试样的裂纹源为角部裂纹,缺口试样的裂纹源为表面裂纹。     

改进310奥氏体不锈钢长期时效后的组织与性能

借助扫描电子显微镜、透射电子显微镜以及高温、室温拉伸和硬度测试研究了实验室研发的改进310奥氏体不锈钢在700℃长期时效后的组织与性能.700℃时效1000 h后,实验钢在晶界和晶内析出了大量(Cr,Fe,Mo)23C6、(Cr,Fe)23C6、σ相和少量的χ相.析出相对实验钢的室温力学性能有明显的强化作用.强度增加,硬度升高20 Hv,同时延伸率仍保持在30%以上.高温下,析出强化效应减弱,延伸率轻微下降.通过断口表面和剖面观察发现,时效1000 h后,实验钢的高温拉伸断口为韧性断裂,未观察到裂纹和孔洞;而室温拉伸断口为脆性断裂,断口附近则观察到σ相中出现裂纹和孔洞.从σ相的脆-韧转变和实验钢基体的室温和高温强度的不同,讨论了在室温拉伸过程中产生裂纹和孔洞的原因,以及时效对室温和高温力学行为的不同影响.     

w(Co)对CB2钢显微组织和力学性能的影响

为研究w(Co)对CB2钢微观组织和力学性能的影响，调整CB2钢中w(Co)为0.5%，1.0%，1.5%，2.0%和3.0%.利用光学显微镜(OM)、扫描电镜(SEM)、室温拉伸等检测方法研究w(Co)对试验钢微观组织和力学性能的影响规律，结合Thermo-Calc和JMatpro-7.0模拟结果解释其影响机理.研究发现:w(Co)增加提高铬当量的值，使试验钢中δ铁素体含量减少，当w(Co)增加到1.5%时，δ铁素体基本消失;材料的抗拉强度随w(Co)的增加而增加，而延长率则先增加后降低;结果表明，w(Co)为1.5%时综合性能较好，即抗拉强度达到805.13MPa，延长率达到20.4%，布氏硬度为260.     

汽车用钢连铸坯的高温力学性能

运用经典热模拟的方法研究石钢电炉生产汽车用钢的连铸坯高温力学性能,获得了五个钢种热塑性曲线和强度曲线.针对不同方向铸坯取样的结果与其他研究结果作了对比.运用扫描电镜对试样拉断后的断口形貌进行观察,得出了相应钢在各温度区域的断裂机理.讨论了连铸坯质量与高温力学性能的关系.     

Effects of cold rolling on the microstructure and mechanical properties of Fe-Ni-Mn-Mo-Ti-Cr maraging steels

Effects of cold rolling on the microstructure and mechanical properties of Fe-Ni-Mn-Mo-Ti-Cr maraging steels were studied.To investigate the microstructure and mechanical properties,optical microscopy,scanning electron microscopy,X-ray diffraction,tensile test,and hardness test were used.The results show that the solution-annealing treatment in the cold-rolled steel redounds to the formation of sub-microcrystalline Fe2(Mo,Ti) Laves phase particles,which are stable at high temperatures.These secondary Laves phase particles prevent from recrystallization at high temperatures and correspond to semi-brittle fracture in the subsequent aging treatment.     

Effect of weld line positions on the tensile deformation of two-component metal injection moulding

Knowledge of the mechanical properties of two-component parts is critical for engineering functionally graded components. In this study, mono-and two-component tensile test specimens were metal injection moulded. Three different weld line positions were generated in the two-component specimens. Linear shrinkage of the two-component specimens was greater than that of the mono-component specimens because the incompatibility of sintering shrinkage of both materials causes biaxial stresses and enhances sintering. The mechanical properties of 316L stainless steel were affected by the addition of a coloured pigment used to identify the weld line position after injection moulding. For the two-component specimens, the yield stress and ultimate tensile stress were similar to those of 316L stainless steel. Because 316L and 630 (also known as 17-4PH) stainless steels were well-sintered at the interface, the mechanical properties of the weaker material (316L stainless steel) were dominant. However, the elongations of the two-component specimens were lower than those of the mono-component specimens. An interfacial zone with a microstructure that differed from those of the mono-material specimens was observed; its different microstructure was attributed to the gradual diffusion of nickel and copper.     

Ti对高强耐候钢力学性能的影响

通过光学显微镜、透射电镜(TEM)以及力学性能测试等手段分析了薄板坯连铸连轧(TSCR)工艺生产Ti微合金化高强耐候钢的成分及工艺对显微组织和力学性能的影响.研究结果表明:钢中加入Ti,屈服强度有明显的提高;钛质量分数为0.05%～0.08%时,高强耐候钢的晶粒尺寸随着钛含量的增加基本不变;高强耐候钢强度的提高主要取决于钢中有效钛的含量,有效钛不仅与钛的含量有关,而且还与S, N的含量有关;在有效钛含量一定的条件下,析出强化的大小主要取决于轧后的卷取温度.     

淬火温度对12Cr14Ni2不锈结构钢组织及力学性能的影响

使用光学显微镜(OM)、扫描电镜(SEM)、电子探针(EPMA)及透射电镜(TEM)分析研究了淬火温度对12Cr14Ni2索氏体不锈结构钢的显微组织和力学性能的影响.结果表明:热轧后的实验钢板经 900~1050℃保温0.5h淬火及710℃高温回火2h热处理后,均可以获得细小均匀的回火索氏体组织;回火索氏体晶界处存在大量直径100~200nm的富含Cr的M₂₃C₆型析出相;随着淬火温度从900℃升高到1050℃,淬火后奥氏体晶粒尺寸逐渐增大,进而导致热处理后的回火索氏体组织粗化;实验钢强度先减小后增大,延伸率和冲击功均先增加后降低;在最佳淬火温度950℃时,实验钢抗拉强度为767MPa,屈服强度为588MPa,断后延伸率为22%,在20℃时冲击功达107J,综合力学性能优异.     

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.     

高速侵彻下35CrMnSi钢失效行为实验研究

研究高速侵彻下35CrMnSi钢弹体的失效行为. 对油、水二次淬火低温回火的35CrMnSi钢材进行静态拉伸,动态压缩力学性能测试及金相分析,通过高速侵彻低碳钢板实验掌握不同侵彻速度下35CrMnSi钢弹体的失效特征,对35CrMnSi钢弹体断裂失效处进行断口形貌的扫描电镜(SEM)微观观测,分析了不同侵彻速度下圆柱形35CrMnSi钢弹体的失效行为,依据一维冲击理论分析获得了高速侵彻下35CrMnSi钢弹体断裂失效行为发生的阈值条件,为相关研究提供了参考和借鉴.     

Effects of cold rolling on the microstructure and mechanical properties of Fe-Ni-Mn-Mo-Ti-Cr maraging steels

Effects of cold rolling on the microstructure and mechanical properties of Fe-Ni-Mn-Mo-Ti-Cr maraging steels were studied. To investigate the microstructure and mechanical properties, optical microscopy, scanning electron microscopy, X-ray diffraction, tensile test, and hardness test were used. The results show that the solution-annealing treatment in the cold-rolled steel redounds to the formation of submicrocrystalline Fe₂(Mo, Ti) Laves phase particles, which are stable at high temperatures. These secondary Laves phase particles prevent from recrystallization at high temperatures and correspond to semi-brittle fracture in the subsequent aging treatment.     

Si对Al-Zn-Mg-Cu合金组织、断裂和局部腐蚀行为的影响

采用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)以及室温拉伸、剥落腐蚀等测试方法,研究了微量的Si对Al-Zn-Mg-Cu铝合金组织、性能和局部腐蚀的影响.研究表明:随着Si含量增加,合金的强度先增加再减小,0.040%Si(质量分数)时合金的强度出现峰值;合金的力学性能各向异性随Si含量的增加,先减小再增大,0.025%Si时,力学性能各向异性最小;随着Si含量的升高,合金横向断裂模式从以穿晶断裂为主向沿晶断裂转变.与合金纵向强度变化幅度比较,Si含量对合金横向强度影响显著.     

CuO/Al反应自生复合材料的机械性能研究

采用液态搅拌法制备了反应自生 Al2 O3增强金属基复合材料并研究了它的机械性能 .采用 X衍射和扫描电镜分析了相组成和断口形貌 .与基体合金比较 ,复合材料的强硬性得到较大提高 ,其中 10 % Cu O复合材料的抗拉强度提高了 5 2 .3% ,硬度提高近一倍 .复合材料中的拉伸断裂特征为韧性断裂 ,铸造缺陷渣气孔是主要的裂纹源     

易切削钢中夹杂物及锡的形态

研制了一种新型含锡易切削钢.在锡含量小于0.05%(质量分数)时,钢材具有良好的易切削性能,其力学性能也达到了国家标准.在扫描电镜下观察了钢中夹杂物和断口的形貌,利用能谱分析了夹杂物的成分.结果表明,钢中的复合夹杂物主要由氧化物和Mns组成.多数呈球形或纺锤形,在断口及夹杂物的表面上锡明显偏析.