20钢热轧卷板的球化退火工艺

通过扫描电镜分析和拉伸试验研究20钢双相区和亚温区的球化退火行为和力学性能。结果表明,与双相区球化退火相比,亚温区球化退火时碳化物球化效果明显,具有良好的力学性能,球化退火时间明显缩短。     

65Mn宽钢带冷轧边裂原因分析及预防

利用金相观察、硬度检测等手段对65Mn宽钢带冷轧过程出现的边裂问题进行了原因分析和研究。结果表明:65Mn钢热轧原料组织为铁素体+珠光体,但由于在热轧水冷过程中边部冷却速度比中间快,珠光体组织片层相对更细。在两相区球化退火过程中,边部较细的珠光体组织更容易被脆性较大的粗珠光体组织所取代。在相对较大的冷轧压下率条件下,造成边部出现裂口。将一次退火工艺由两相区球化退火优化调整为亚温球化退火后,65Mn钢带边部组织球化率显著提高,基本避免了边裂情况的产生,并为实际工业生产提供了积极的指导作用。     

轧制工艺对GCr-15球化退火的影响

通过热模拟的方法研究轧制工艺对GCr15球化退火的影响。结果表明，轧制工艺对GCr15轴承钢组织有显著影响。相对于常规轧制（CR）试样，控轧控冷（CRC）试样珠光体发生退化且片层细小．渗碳体呈短棒状或颗粒状，部分渗碳体片产生扭折甚至断裂。亚温球化退火中，CRC试样可获得细小均匀的球化组织，其球化效果明显优于CR试样，且显著地缩短球化退火时间。     

TEM STUDY OF AUSTENITE FORMATION IN A LOW CARBON STEEL

<正> 低碳铁素体加马氏体双相钢的强度和塑性取决于马氏体的数量和分布,这与亚温区加热过程中奥氏体形成的特点有关。由于奥氏体的形成是在高温下进行,速度快,难于直接获得有关形核的信息。本文研究低碳钢中奥氏体形成的部位,以及预先冷轧的影响。 试验用低碳1.5Mn钢,其化学成分为(wt-％):C 0.08,Mn 1.45,si 0.21,Al 0.045,N 0.005。经高频感应电炉熔炼成45kg的钢锭后,热轧成2.5mm厚的板材。在真空炉中经过1200℃均匀化退火24h。然后,在盐炉中900℃加热15min后空冷,获得铁素体加珠光体型的正火原始组织。另将一部分正火的坯料进行厚度压下量     

7CrMn2Mo钢球化退火行为和碳化物类型

采用常规的退火工艺和空淬＋退火工艺研究了7CrMn2Mo钢的球化退火行为。结果表明：预先进行空淬处理是改善该钢球化组织的重要环节;与连续退火、等温退火相比,7CrMn2Mo钢亚温退火时碳化物球化速度较快,效果较好;钢中锰元素含量高,成分接近共析成分,主要碳化物类型为M23C6是导致7CrMn2Mo钢球化退火工艺性能差的三个主要原因。     

退火软化对高强度钢300M组织及硬度的影响

为提高300M钢的后续切削性能,拓宽300M钢的应用领域,研究了退火软化工艺对300M高强度钢显微组织及硬度的影响。结果表明,300M钢在Ac₁以下(730 ℃)退火,显微组织由马氏体转变为回火索氏体,碳化物呈球状或颗粒状;在两相区(780 ℃)退火,显微组织为珠光体+先共析铁素体,碳化物呈球状或短棒状;在Ac₃以上(860 ℃)退火,显微组织转变为珠光体+先共析铁素体,碳化物呈长薄片状。退火冷速对300M钢软化影响显著,冷速缓慢才能使碳化物充分析出并球化,硬度显著降低。300M钢两相区等温+缓慢冷却退火工艺下有更显著的软化效应,硬度可控制在240 HBW以下。     

Subcritical Spheroidization of Medium-Carbon 50CrV4 Steel

An investigation on subcritical spheroidization anneal of the cold-rolled 50CrV4 steel at 720?°C has been carried out. During spheroidization anneal, the lamellar cementite was gradually broken down and changed to spherical shape. With prolonging of soaking time, the amount of lamellar cementite decreases gradually, and that of the spheroidized cementite particle increases gradually. The relationship of the spheroidization ratio versus soaking time for the steel can be described by a typically sigmoid curve. Additionally, the cold rolling deformation accelerates the breakup of lamellar cementite and the formation of spheroidal cementite particles during spheroidization anneal of the steel. The more severe the deformation is, the more rapidly the spheroidization occurs. From the results of tensile and hardness test, the yield strength, ultimate tensile strength, and hardness decrease and the percentage elongation to failure increases rapidly during the first 2?h of spheroidization. Between 2 and 8 h, the yield strength, ultimate tensile strength, hardness nearly keep a constant, which are independent of the soaking time, whereas the percentage elongation to failure firstly increases and then decreases with prolonging of soaking time.     

厚大断面RE-Mg球铁喷粉净化及球化效果的研究

利用自行研制的喷粉装置，首先探讨了厚大断面RE-Mg球铁喷粉脱硫净化的效果，然后研究了稀土镁球化剂在喷粉处理时的净化及球化效果，进而对喷粉脱硫、球化、孕育综合处理工艺进行了试验研究。结果表明：喷粉处理时活性CaO的脱硫率与CaC2的脱硫率相近，使得CaO取代CaC2成为可能，喷粉处理具有突出的净化作用，在脱硫的同时，使氧含量显著降低，同时使硫趋于均匀分布；喷粉球化是一种有效的新球化方法，可获得低硫、低氧、石墨圆整而细小的铸态铁素体球墨铸铁；综合喷粉球化工艺可将脱硫剂、球化剂、孕育剂同时喷入铁液，完成脱硫、球化、孕育过程，获得的球铁在强度较高的同时，使伸长率和冲击值也增大。     

铸态高强度、高韧性球铁的生产

通过选用合适的原材料及配比,选择合理的化学成分；采用电炉熔炼,进行高温过热处理获得洁净铁液；使用喂丝球化处理工艺,以获得较高的球化率；选用低稀土球化处理丝,以获得恰当的珠光体和铁素体比例.生产实践表明,可使球铁铸态性能达到高强度、高韧性的要求.     

Study on behaviors of tungsten powders in radio frequency thermal plasma

This paper describes an investigational study of the spheroidization of refractory metal tungsten powders by radio frequency thermal plasma, with emphasis on the melting, solidification and growth behavior of the tungsten powder particles during the spheroidization process. The flight time and melting time of tungsten powder particles in the plasma were estimated, and the growth behavior of the tungsten powder particles was analyzed in detail by investigating the change in the average particle size before and after plasma spheroidization. The morphology and spheroidization rate were analyzed using field emission scanning electron microscopy. The flight time and melting time for tungsten powder particles with radius of 7.8 μm were calculated to be 9.3 ms and 2.9 ms, respectively. The change in powder particle size during the process showed that the growth of tungsten powder particles was mainly caused by the coalescence of droplets in the thermal plasma system. The experimental results demonstrated that the spheroidization rate can reach up to 95% under the operating conditions used in this work.     

Preparation of spherical silica powder by oxygen–acetylene flame spheroidization process

A novel economic oxygen–acetylene flame spheroidization process and special equipments to prepare spherical silica powders are presented. Before spheroidization treatment, the raw silica is purified by mixed acids. In this spheroidization process, oxygen is used both as the carrier gas to transport the purified silica powders to the flame region, and as the combustion-supporting gas. The crystallized silica powders are melted and then transformed to amorphous silica after oxygen–acetylene flame spheroidization treatment. The powder size analysis indicates that the powder size increases and the size distribution become narrower after spheroidization treatment. By optimizing the process parameters, spherical silica powders were obtained. A scanning electron microscope (SEM) investigation reveals that the spheroidization efficiency of the 5 μm diameter powder is more than 95% at feeding rates below 60 g/min. The closer the length–diameter ratio of raw silica powder is to 1, the higher the spheroidization efficiency of the sample is. The fluidity value and apparent density of the powder with the spheroidization efficiency 95% is 70 s/50 g and 0.88 g/cm³, respectively. Oxygen–acetylene flame spheroidization process is a promising low-cost alternative for large-scale production of spherical silica powder.     

Spheroidization of a granulated molybdenum powder by radio frequency inductively coupled plasma

To reduce mass loss and improve spheroidization efficiency during the spheroidization process, a granulated molybdenum powder was spheroidized by radio frequency induction plasma. The influences of plasma power and addition of hydrogen in the sheath gas on spheroidization were investigated. Results show that spheroidization is improved with the increase of plasma power. The best spheroidization can be achieved when the plasma power is 43 kW. Spheroidization percentage, Hall flow time and apparent density of powders spheroidized at 43 kW are 99.8%, 12.5 s/50 g and 5.52 g/cm³, respectively. The addition of hydrogen in the sheath gas can also improve spheroidization. Moreover, investigation of typical morphologies during spheroidization of the individual granulates indicates that the spheroidization process is a combination of melting, sintering and solidification.     

Precipitation of carbonitrides and high-temperature strength in heat-affected zone of high-Nb containing fire-resistant steel

The morphology and structure of precipitates in the heat-affected zone (HAZ) of fire-resistant steel were studied by transmission electron microscopy, while the simulated elevated temperature strength studies were carried out to elucidate the effect of precipitation state on strength at high temperature. The precipitates were identified as (Nb,Ti)(C,N) with FCC structure. A high density of fine (Nb,Ti)(C,N) precipitated in subcritical HAZ. As the peak temperature of thermal cycle was increased, the density and size of particles were observed to decrease. During austenisation, precipitates were dissolved mostly in the coarse-grained heat-affected zone and dissolved totally in the fusion line. The higher strength at 600?°C was present in coarse-grained heat-affected zone and lower in intercritical heat-affected zone. The different precipitate condition in sub-HAZs led to the different evolution behaviour of carbonitrides on heating and thus high-temperature strength.     

X80管线钢埋弧焊接头性能分析

从焊接性和焊接接头使用性能两个方面入手，结合焊接接头的硬度、拉伸和冲击韧度的测试，对X80管线钢的焊接性能进行了试验分析：结果表明，焊接热影响区的性能发生了较大变化，其中粗晶区出现硬化脆化现象，并导致韧度下降，而不完全重结晶区和回火区则存在一个软化区。通过组织分析，对焊接热影响区的组织状态对焊接接头力学性能的影响进行了讨论。     

Effects of isothermal heat treatment on microstructural evolution of semisolid Al-4Cu-Mg alloy

The authors investigated the effects of the isothermal heat-treatment conditions on the microstructural evolution and composition distribution of semisolid Al-4Cu-Mg alloy during isothermal heat treatment. The experimental results show that the microstructural evolution and composition distribution of semisolid Al-4Cu-Mg alloy are controlled by atom diffusion during the isothermal heat treatment process. Grain growth and spheroidization were promoted with the increase of the isothermal temperature and/or the holding time. Moreover, the higher the isothermal temperature, or the longer the holding time, the more segregation constituent elements occurred to the grain boundaries. The low melting structure at grain boundary is greatly affected by Cu. The microstructural evolution in the isothermal heat-treatment process is as follows: recovery, recrystallization, fragmentation, spheroidization, and coarsening. Such fragmentation, spheroidization, and grain growth of coalescence and Ostwald ripening are involved as main mechanisms in the isothermal heat-treatment process.     

临界退火冷却方式对含铌中锰钢奥氏体稳定性和力学性能的影响

针对含铌中锰钢进行了不同退火温度(700、750和800 ℃)和不同冷却方式(空冷、水冷)下的临界退火试验。结果表明,随着临界退火温度的升高,强塑积和残留奥氏体含量呈现先升高再降低的趋势。在750 ℃临界退火水冷后,试验钢的力学性能最佳,屈服强度达到750 MPa,抗拉强度为1820 MPa,断后伸长率为13.9%。随着临界退火温度升高,试验钢中渗碳体逐渐溶解,基体中C和Mn含量增多,在保温过程中配分进入奥氏体的C和Mn含量增多,导致奥氏体更稳定,残留奥氏体含量增多。当临界退火温度进一步升高,保温时奥氏体含量的增多导致配分进入奥氏体的C和Mn浓度降低,导致奥氏体稳定性降低,在冷却过程中形成大量马氏体。马氏体的增多和大尺寸团簇状(Nb,Mo)C的析出导致800 ℃临界退火后试验钢的高强度和低塑性。在相同临界退火温度下,水冷和空冷后试验钢的相组成相同。在800 ℃临界退火时,两种冷却方式对残留奥氏体含量和力学性能引起的差异最为明显,这与空冷过程中C和Mn向奥氏体配分更充分有关。     

采用新型差温轧制工艺生产Q690级特厚钢板

为了实现在厚度方向上具有优异强度均匀性的Q690级特厚钢板的研发,采用一种新型的差温轧制工艺进行了实验室轧制,并研究了差温轧制工艺对钢板显微组织、厚度方向上强度均匀性和力学性能的影响。结果表明:差温轧制工艺能够显著细化钢板芯部和1/4厚度处的原始奥氏体组织,增加芯部和1/4厚度处淬火组织中的两相区铁素体体积分数。通过差温轧制工艺生产的Q690级钢板具有优异的力学性能,钢板的伸长率和-40℃冲击功分别大于16%和60J,从表面到芯部,钢板屈服强度差异小于10 MPa。     

Properties evolution of additive manufacture used tungsten powders prepared by radio frequency induction plasma

In this study, radio frequency induction plasma was adopted to improve tungsten powder properties to meet the requirements of additive manufacturing process. After plasma spheroidization process operated, tungsten particles changed from irregular shape to uniform spherical shape. The average size and oxygen content of raw tungsten powders were both decreased, meanwhile, the laser absorption coefficient was increased by plasma spheroidization process. Furthermore, a series of tests were carried out for raw and spherical tungsten powders to investigate the influence of plasma spheroidization process on powder flowability evolution. The results displayed that, plasma spheroidized powders had a better comprehensive flowability, such as basic flow property, aerated flow property, compressibility, permeability and shear property, comparing to raw tungsten powders. In conclusion, plasma spheroidized tungsten powders met demands of additive manufacturing process very well.     

12Cr1MoVG钢硬度与球化关系研究及其寿命评估

采用高温加速时效的方法模拟12Cr1MoVG钢管珠光体(贝氏体)组织球化的演变过程并测试不同球化程度下的布氏硬度,结合现场检测对电站锅炉12Cr1MoVG钢管进行硬度和球化程度分析.基于Matlab软件模拟建立硬度与珠光体(贝氏体)球化之间的关系模型,提出12Cr1MoVG珠光体(贝氏体)组织的球化与温度和时间之间的关系公式,进而提出该钢管寿命评估的新方法.