Coarsening behavior of MX carbonitrides in type 347H heat-resistant austenitic steel during thermal aging

In this work, the growth kinetics of MX （M - metal, X - C/N） nanoprecipitates in type 347H austenitic steel was systematically studied. To investigate the coarsening behavior and the growth mechanism of MX carbonitrides during long-term aging, experiments were performed at 700, 800, 850, and 900℃ for different periods （1, 24, 70, and 100 h）. The precipitation behavior of carbonitrides in specimens subjected to various aging conditions was explored using carbon replicas and transmission electron microscopy （TEM） observations. The corresponding sizes ofMX carbonitrides were measured. The results demonstrates that MX carbonitrides precipitate in type 347H austenitic steel as Nb（C,N）. The coarsening rate constant is time-independent; however, an increase in aging temperature results in an increase in coarsening rate of Nb（C,N）. The coarsening process was analyzed according to the calculated diffusion activation energy of Nb（C,N）. When the aging temperature was 800-900℃, the mean activation energy was 294 kJ·mol -1, and the coarsening behavior was controlled primarily by the diffusion of Nb atoms.

Effect of contact thermal resistance on temperature distributions of concrete-filled steel tubes in fire

To predicate the temperature distribution of concrete-filled steel tubes(CFSTs) being exposure to fire,a finite element analysis model was developed using a finite element package,ANSYS.A suggested value of contact thermal resistance was therefore proposed with the supporting of massive numbers of collected test data.Parametric analysis was conducted subsequently towards the cross-sectional temperature distribution of CFST columns in four-side fire,in which the exposure time,width of the cross section,steel ratio were taken into account with considering contact thermal resistance.It was found that contact thermal resistance has little effect on the overall temperature regulation with the exposure time,the width of cross-section or the change of steel ratio.However,great temperature dropping at the concrete adjacent to the contact interface,and gentle temperature increase at steel tube,exist if considering contact thermal resistance.The results of the study are expected to provide theoretical basis for the fire resistance behavior and design of the CFST columns being exposure to fire.

Effect of Rare Earth on Thermal Shock Resistance of Steel 9Cr2Mo

The effect of rare earth elements on thermal shock resistance of cold roller steel 9Cr2Mo was investigated by means of X-ray diffractometry and optical microscopy. Experimental results show that the process of carbide precipitation of heat effect zone is restrained by adding RE elements in steel 9Cr2Mo. Therefore, thermal shock resistance of this steel can be improved.

Effect of retained austenite and nonmetallic inclusions on the thermal/electrical properties and resistance spot welding nuggets of Si-containing TRIP steels

Five advanced high-strength transformation-induced plasticity(TRIP) steels with different chemical compositions were studied to correlate the retained austenite and nonmetallic inclusion content with their physical properties and the characteristics of the resistance spot welding nuggets. Electrical and thermal properties and equilibrium phases of TRIP steels were predicted using the JMatPro? software. Retained austenite and nonmetallic inclusions were quantified by X-ray diffraction and saturation magnetization techniques. The nonmetallic inclusions were characterized by scanning electron microscopy. The results show that the contents of Si, C, Al, and Mn in TRIP steels increase both the retained austenite and the nonmetallic inclusion contents. We found that nonmetallic inclusions affect the thermal and electrical properties of the TRIP steels and that the differences between these properties tend to result in different cooling rates during the welding process. The results are discussed in terms of the electrical and thermal properties determined from the chemical composition and their impact on the resistance spot welding nuggets.

Investigation on the Fire Resistance of Cellular Steel Beam with Sinusoidal Openings

This paper investigated the fire resistance of CSBs with various parameters under high temperature rise due to fire using finite element software ABAQUS. The mechanical parameters of CSBs are analyzed, including load-bearing capacity and the temperature distribution during the heating process. Through structural analysis simulation of the entire heating process, the structural response of the CSBs is divided into five stages: elastic stage, elastic-plastic stage, self-balancing stage, catenary stage and ultimate destruction stage. The results indicate that the opening diameter-to-height ratio, opening spacing-to-height ratio and load ratio significantly affect the structural responses of CSBs in fire, followed by opening shape as secondary effects. In all the numerical analyzes, CSBs are analyzed with a uniformly distributed load and having simply supported boundary conditions.

Development of heat-resistant ferritic stainless steels for exhaust lines at Nisshin Steel

Exhaust emission regulations of the automotive are enforced in each country to prevent air pollution and global warming,and the restriction standard tends to become severer.Various techniques such as the combustion improvement of gasoline,upgrades of the catalyst,and the thermal capacity decreases in the exhaust lines are adopted to suit the regulations,and these lead to an increase of the maximum temperature of the exhaust gas. Recently,ferritic stainless steels are mainly used to parts of exhaust lines,as their thermal expansion coefficient is small,and the cyclic oxidation resistance and the thermal fatigue property are better than austenitic stainless steels. This paper presents newly developed heat-resistant stainless steels from Nisshin Steel for exhaust lines usage,and describes the currents of the steel development that could be envisaged in the future.With regard to improving the high-temperature strength of ferritic stainless steels,the addition of Nb,Mo and Cu is effective in solution hardening and precipitation hardening at 700℃,while the addition of Nb,Mo and W is effective in mainly solution hardening at 900℃.The addition of Cr,Si and Mn suppress the breakaway oxidation in air at 950℃up to 200 h of ferritic stainless steels containing 14%Cr.Especially,the addition of 0.8%or higher Mn would effectively improve the adherence of oxide scale.It is confirmed that ferritic stainless steels,NSSHR-1(14Cr-lMn-0.9Si-Nb) and NSSHR-2(10Cr-0.9Si-Nb-Ti ),is having a superior heat resistance,formability and cost performance compared to conventional Type441 and Type439 respectively.

High-resolution Transmission Electron Microscopy Characterization of the Structure of Cu Precipitate in a Thermal-aged Multicomponent Steel

High-dispersed nanoscale Cu precipitates often contribute to extremely high strength due to precipitation hardening,and whereas usually lead to degraded toughness for especially ferritic steels.Hence,it is important to understand the formation behaviors of the Cu precipitates.High-resolution transmission electron microscopy(TEM)is utilized to investigate the structure of Cu precipitates thermally formed in a high-strength low-alloy(HSLA)steel.The Cu precipitates were generally formed from solid solution and at the crystallographic defects such as martensite lath boundaries and dislocations.The Cu precipitates in the same aging condition have various structure of BCC,9 R and FCC,and the structural evolution does not greatly correlate with the actual sizes.The presence of different structures in an individual Cu precipitate is observed,which reflects the structural transformation occurring locally to relax the strain energy.The multiply additions in the steel possibly make the Cu precipitation more complex compared to the binary or the ternary Fe-Cu alloys with Ni or Mn additions.This research gives constructive suggestions on alloying design of Cu-bearing alloy steels.

Dynamic simulation of resistance spot welding of zinc-coated steels

A model was developed to simulate the temperature distribution and nugget formation during resistance spot welding （ RS1V） of zinc-coated steels. It employs a coupled thermal-electrical-mechanical analysis simulating the dynamic RSW process. Temperature-dependent thermal-electrical-mechanical material properties were considered including contact-resistance. The contact area was determined from a coupled thermal-mechanical analysis. A layer of transition elements was used to represent the change of contact area by killing or activating elements. The heat generation and temperature field were computed in a coupled thermal-electrical model. All these analyses were solved using the commercial finite element method （FEM） based on ANSYS code, and some advanced functions were used by writing a paragraph of codes by the authors. Compared with the results from only coupled thermal-electrical model in which contact area was uniform during the whole process, the result matches better to the experimental results.

Thermal aging effect on 2205 duplex stainless steel

： The effect of isothermal aging treatment on the mechanical and corrosion properties of 2205 duplex stainless steel was investigated by means of impact toughness test and micro-hardness measurement in combination with the critical pitting temperature （CPT） technique. The corresponding fractography of the steel was then observed after the impact toughness test. The results demonstrated that, at the critical temperature for precipitation of the sigma （σ） phase, e. g., 850 ℃, the impact toughness decreased rapidly and the micro-hardness increased gradually with increasing aging time. The CPT decreased from 61 to 15 ℃ as the aging time increased from 4 rain to 8 h. In addition, optical microscopy, transmission electron microscope （TEM） and X-ray diffraction studies showed that the ferrite in the steel transformed into secondary austenite and σ phase.

钢渣热阻沥青路面的抗车辙性能研究

为了研究钢渣替代天然集料对沥青混合料高温抗车辙性能的影响,首先,用钢渣等体积替代玄武岩粗集料制备了不同钢渣掺量沥青混合料,对其热物性参数进行了测试,并通过室内等效热辐射试验对钢渣沥青混合料降温效果进行评价;其次,采用数值模拟方法分析了不同钢渣掺量沥青路面面层对温度场分布的影响,并利用单轴静载蠕变试验获取沥青混合料蠕变参数,建立基于上述温度场的车辙分析模型,对钢渣沥青路面的抗车辙性能进行评价。结果表明,钢渣的掺入使沥青混合料的导热系数降低,比热容增大,变化幅度最大可以达到40%以上;随着钢渣掺量增大,路表温度小幅度上升,而中下面层温度逐渐降低,其中4 cm深度处降温效果最为明显;当钢渣掺量为100%时,温度相较于纯玄武岩沥青路面降低了3.4℃,而75%掺量沥青混合料钢渣的车辙变形量最小,相较于玄武岩沥青混合料下降幅度达到43%,可有效提高路面抗车辙性能。

4Cr5MoSiV1热作模具钢循环渗氮及热疲劳行为研究

针对4Cr5MoSiV1热作模具钢在使用过程中经受熔融铝液及冷却液的循环冲击,在热应力作用下容易产生热疲劳失效的问题。采用可控循环气体渗氮的方法分别在回火态和热疲劳态模具钢表面制备无铁氮化合物和有化合物的渗层,进行热疲劳性能测试。结果表明:循环渗氮制备的无化合物的渗层可以有效延缓热疲劳裂纹的萌生,抗热疲劳性能优于有化合物的渗层。同时,在裂纹产生前进行二次渗氮可以补充氮原子,重置压应力并增加硬度,进一步提升热疲劳抗性。

航空超高强度钢表面防护技术的研究进展

超高强度钢同时具有高强度和高韧性,是航空航天领域的重要承载构件,在飞机起落架、主梁、传动件、承力螺栓等领域有着广泛的应用。由于其使用时经常暴露在海洋大气环境下,腐蚀现象比较严重,通过对其进行表面保护,可以有效地改善其耐蚀、耐磨等性能,延长相关零件的使用寿命。针对目前常用的几种表面防护技术(热喷涂、真空镀、电镀、化学镀、表面组织转化、激光熔覆、离子注入等),综述了这些表面防护方法对不同超高强度钢耐磨、耐蚀、氢脆、疲劳等方面的影响,分析了这些防护方法的优缺点,并对其今后的发展方向进行了展望。

膨胀型防火涂层“新-老”涂层体系的热阻

在既有老化涂层上涂覆新涂层形成“新-老”复合涂层体系,复合涂层的热阻并非既有涂层热阻与补涂涂层热阻的简单叠加.基于隔热性能试验的温度测量结果,计算复合涂层体系的等效热阻常数,通过对不同试件等效热阻常数的对比分析,考察补涂涂层对既有涂层和复合涂层热阻的影响规律.结果表明:既有涂层热阻随补涂涂层厚度增加而降低,当补涂涂层厚度大于1.0 mm时,既有涂层热阻的贡献率不超过20%,计算复合涂层热阻时可忽略不计;当补涂涂层厚度较薄(0.5 mm)且既有涂层老化时间较短(≤21循环),或既有涂层有面漆时,建议考虑既有涂层热阻的贡献(贡献率>20%).当补涂涂层与既有涂层类型不同时,复合涂层体系的热阻更大,隔热性能更好.

轻钢龙骨复合墙板研究进展

装配式钢结构建筑具有抗震性能好、自重轻、施工速度快等优点,但因与其配套的围护外墙板较少,制约了装配式钢结构的发展。近年来结构轻便、保温性能好、抗震性能优良的轻钢龙骨复合墙板被逐渐应用到装配式钢结构建筑当中。对现有轻钢龙骨复合墙板进行了分类,总结了各类墙板的特点,并介绍了国内外针对墙板的抗弯性能、抗剪性能、抗震性能以及热工性能等方面的研究现状。在此基础上,分析了轻钢龙骨复合墙板存在的问题,提出了一种热工与防火性能好、自重轻、连接安全可靠、管线易于分离且可工业化生产的新型轻钢龙骨复合墙板。

Changes in microstructure and properties of weld heat-affected zone of high-strength low-alloy steel

The evolution of the microstructure and toughness of APL5L X80 pipeline steel after thermal welding simulation was investigated by X-ray diffraction,electron backscatter diffraction,and transmission electron microscopy.The results indicated that primary heat-affected zones can be divided into weld,coarse-grained,fine-grained,intercritical,and sub-critical zones.The microstructure of the weld zone is mainly composed of bainitic ferrite and a small amount of granular bainite;however,the original austenite grains are distributed in the columnar grains.The structure of the coarse-grained zone is similar to that of the weld zone,but the original austenite grains are equiaxed.In contrast,the microstructure in the fine-grained zone is dominated by fine granular bainite,and the effective grain size is only 8.15μm,thus providing the highest toughness in the entire heat-affected zone.The intercritical and subcritical zones were brittle valley regions,and the microstructure was dominated by granular bainite.However,the martensite-austenite(M/A)constituents are present in island chains along the grain boundaries,and the coarse size of the M/A constituents seriously reduces the toughness.The results of the crack propagation analyzes revealed that high-angle grain boundaries can significantly slow down crack growth and change the crack direction,thereby increasing the material toughness.The impact toughness of the low-temperature tempering zone was equivalent to that of the columnar grain zone,and the impact toughness was between those of the critical and fine-grained zones.

铝包殷钢芯耐热铝合金绞线的应用探讨

铝包殷钢芯耐热铝合金绞线在云南电网中的应用较多,在设计评审工程中发现部分设计人员对其特性理解不足,存在弧垂计算错误及工程量估算偏差等问题。本文利用斜抛物线公式结合拐点温度计算方法,搭建了适用于铝包殷钢芯导线的张力弧垂计算模型,编制了计算程序;理论分析了铝包殷钢芯绞线的弧垂特性、拐点温度随档距变化特点等,分析了该类导线的应用场景,并提出了相应的意见和建议。

汽轮机用叶片0Cr17Ni4Cu4Nb钢的组织和性能的研究

通过对0Cr17Ni4Cu4Nb钢进行1040℃固溶和620℃时效热处理,检测该状态下材料的缺口敏感系数、650℃抗高温氧化性、磁导率、热导率、微观组织等相关理化检验,以期达到对该钢更多深层次的了解,掌握该钢的相关物理参数,利于发挥材料特有的物理属性,以期拓展材料的使用范围。

Effect of trace boron on corrosion resistance of rust layer of high-strength low-alloy steel in 3.5 wt.% NaCl solution

The influence mechanism of trace boron on the corrosion resistance of high-strength low-alloy(HSLA)steel in a simulated marine environment was studied by combining first-principles calculation with experiment.The effect of boron on the corrosion properties and corrosion morphology of the rust layer formed on the surface of HSLA steel was studied by means of corrosion weightlessness method,polarization curve,scanning electron microscopy(SEM)and X-ray diffraction(XRD)technique.The mass loss measurements and polarization curves revealed that the corrosion resistance of HSLA steel is improved by adding trace boron.XRD and SEM results show that the rust layer is produced byα-FeOOH(the main protective phase),Fe_(3)O_(4) andγ-FeOOH,and boron contributes to stability ofα-FeOOH.Based on the first-principles calculation,the solid solution of B atom in the corrosion product is beneficial to the fixation of Cl atom and to the reduction of the corrosion of Cl atom to the steel matrix.

浅析双相钢硬密封耐磨球阀的质量控制管理

煤化工装置中,黑水、灰水的介质中固体颗粒浓度较高、介质的流速较快、介质腐蚀性强的特点,使得一般耐磨球阀容易出现密封副寿命低、交变载荷疲劳断裂、阀门使用周期短的情况,影响到阀门的正常使用,从而影响到装置的稳定运行。为了能够较好地克服上述不利因素,近年来陆续投用的硬密封耐磨球阀是选择之一,其可以在较为苛刻的工况下,能够较为长期的稳定使用。本文从采购方的质量控制角度,对国产双相钢硬密封耐磨球阀物资的重要质量控制点进行了较为深入的研究和分析,强化阀门的质量过程控制管理,从而使得国产双相钢硬密封耐磨球阀接近或达到进口阀门的出厂质量。

Bonding characteristics of the Al_2O_3-metal composite coating fabricated onto carbon steel by combustion synthesis

The fabrication of an alumina-metal composite coating onto a carbon steel substrate by using a self-propagating high-temperature synthesis technique was demonstrated. The effects of the type and thickness of the pre-coated layer on the binding structure and surface qual- ity of the coating were systematically investigated. The macrostructure, phase composition, and bonding interface between the coating and the substrate were investigated by scanning electronic microscopy （SEM）, X-ray diffraction （XRD）, and energy-dispersive X-ray spectrometry （EDS）. The diffraction patterns indicated that the coating essentially consisted of α-Al2O3, Fe（Cr）, and FeO-Al2O3. With an increase in the thickness of the pre-coated working layer, the coating became more smooth and compact. The transition layer played an important role in enhancing the binding between the coating and the substmte. When the pre-coated working layer was 10 mm and the pre-coated transition layer was 1 ram, a compact structure and metallurgical bonding with the substrate were obtained. Thermal shock test results indicated that the ceramic coating exhibited good thermal shock resistance when the sample was rapidly quenched from 800℃ to room temperature by plunging into water.