多向锻造对超高强度不锈钢组织及力学性能的影响

通过光学显微镜(OM)、扫描电子显微镜(SEM)、背散射电子衍射(EBSD)、透射电子显微镜(TEM)对多向锻造淬火后的马氏体超高强度不锈钢的显微组织进行定量表征,分析多向锻造对试验钢显微组织的影响;同时进行力学性能测试,分析多向锻造对试验钢力学性能的影响,讨论不同强化机制对试验钢强度的贡献。结果表明,随着锻造道次的增加,试验钢的原奥氏体晶粒、马氏体板条束(Packet)、板条块(Block)尺寸均逐渐细化,5个道次后原奥氏体晶粒从226.1细化到3.2 μm,Packet尺寸从106.1细化到2.9 μm,Block尺寸从2.3细化到1.5 μm;试验钢的力学性能显著提升,屈服强度由1 030增加至1 175 MPa,冲击功吸收功由140增加至194 J,伸长率也从9.3%增加到了11.6%;试验钢强度的提升主要归功于位错强化与细晶强化并以位错强化为主,且位错强化与细晶强化并不遵从线性叠加强化机制,而更接近均方根叠加机制。     

Effect of equal channel angular pressing on structure and mechanical properties of a low carbon steel

Experiments were conducted on a plain low carbon steel with an initial grain size of ~ 30μm to investigate the changes of microstructure and mechanical properties by repetitive equal channel angular pressings. Under the pressing conditions of giving a strain of ~ 1 and rotating samples 180° between each pass, the yield strength significantly increases from 310 to 750 MPa after single pass, and it reaches 1050 MPa after 12 passes. The increment of yield strength gradually decreases as the number of passes increases. The examination of microstructure by transmission electron microscopy shows that ferrite consists of parallel bands of elongated subgrains having a width of 0.3 μm and a length of 2 μm after a single pass. The subgrains are further divided by boundaries with low angle misorientation on subsequent passages. Low angle boundaries turn to high angle boundaries without noticeable grain refinement as the number of pass increases. In addition, lamellar cementites in pearlite are broken up into fragments within a pearlite colony. Analyses of structural and mechanical changes in a plain low carbon steel by equal channel angular pressing indicate that the strength enhancement is mainly due to the grain refinement of ferrite.     

Intercritical Rolling Induced Ultrafine Lamellar Structure and Enhanced Mechanical Properties ofMedium-Mn Steel

The medium-Mn steel with ferrite and austenite structure was rolled in the intercritical region down to dif- ferent rolling reduction. The microstructure and mechanical properties of the rolled steels were investigated by scan- ning electron microscopy, transmission electron microscopy, X-ray diffraction and tensile tests. It was found that the ferrite and austenite structure gradually evolved into an ultrafine structure from the random directional lath structure to lamellar structure with lath longitudinal direction parallel to the rolling direction with increasing rolling strain. It was found that the thickness of the laths was gradually refined with increasing rolling strain. The lath thickness is about 0. 15 9m stored with high density dislocations and the austenite volume fraction of the steel is about 24% after 80% rolling reduction. Furthermore, it was interesting to find that yield strength, tensile strength and total elongation of the 80% rolled medium-Mn steel are about 1000 MPa, 1250 MPa and 24%, respectively, demonstrating an excellent combination of the strength and ductility. Based on the microstructure examination, it was proposed that the grain refinement of the medium-Mn steels could be attributed to the duplex structure and the low rolling temperature. Analysis of the relationship between the microstructure and the mechanical properties indicated that the high yield strength mainly resulted from the ultrafine grain size and the high density dislocation, but the improved ductili- ty may be attributed to the large fractions of austenite retained after intercritical rolling.     

Effect of Annealing Time on Microstructure and Mechanical Properties of Cold-Rolled Niobium and Titanium Bearing Micro-alloyed Steel Strips

Effects of annealing time on microstructure of cold-rolled niobium-titanium bearing micro-alloyed steel strips were investigated by optical microscopy, scanning electron microscopy, electron back-scatter diffraction (EBSD) and transmission electron microscopy. The complete recrystallization annealing temperature of 670 °C and complete annealing time of 9 min were determined using Vickers-hardness testing and EBSD analysis. The ferrite microstructure with spheric cementite particles and nano-scale precipitates of Nb(C, N) in matrix was obtained. The kinetics of the ferrite grain growth is lowered due to ferrite grain boundaries pinned by the cementite particles, so the ferrite grain size of 5. 5 μm remains unchanged among the annealing time ranging from 9 to 30 min. In addition, the strength of tested steel also keeps unchanged with the increase of annealing time. The higher yield strength of approximately 420 MPa can be obtained by grain refinement and precipitation hardening and the higher elongation of approximately 40% and work-hardening exponent of approximately 0. 2 can be gained due to grain refinement and presence of cementite particles, indicating that the balance of strength, ductility and forming property is realized.     

Control of UFG Microstructure in Welded Carbon Steel Tubes by Cold Drawing and Annealing

The present study is made to develop ultra fine grained microstructure in welded steel tubes, through multiple cold drawing passes followed by an annealing treatment. The average ferrite grain size is reduced from 16 to 1.9 μm. SAE 1019M steel grade used for a typical automotive driveline component is studied. Strains between 0.3 and 1.4 followed by annealing at 400, 450 and 500 °C are considered to optimize the combination of cold drawing strain and temperature required to produce ultra fine grained microstructure in steel tubes. At a strain value of 1.4 and annealing temperature, 500 °C, polygonal ferrite grains and fine carbide particles are obtained. This microstructure is found to be suitable owing to its combination of high strength and good ductility in steel tubes. Tensile strength as high as 1,061 MPa and 9 % elongation is obtained due to microstructural refinement. The strength is increased by 350 MPa compared to the strength of conventional cold-drawn welded tubes.     

热挤压和旋锻粉末冶金纯钛的组织和力学性能

采用粉末冶金技术结合热挤压和旋锻工艺制备纯钛棒,利用万能试验机、维氏显微硬度仪、金相显微镜、高精度多功能密度计等设备测试纯钛棒的屈服强度、维氏硬度、显微组织和相对密度,研究了纯钛棒的制备工艺及其微观组织结构对材料力学性能的影响。研究表明,利用粉末冶金技术结合热挤压和旋锻工艺制备的纯钛棒屈服强度是880 MPa,均匀延伸率是4.06%,在拉伸变形过程中发生韧性断裂。纯钛棒显微组织为等轴状的细晶粒组织,平均晶粒尺寸约1μm,组织分布均匀,无明显裂纹和缺陷,有较高的相对密度。     

轧制变形对 F-M 双相钢 0.05C-2.8Mn-4.2Ni-2Al- 1.2Mo-1.9Cu晶粒细化的影响

借助EBSD场发射扫描电子显微镜,研究了轧制变形及热处理后的铁素体/马氏体双相钢0.05C-2.8Mn4.2Ni-2Al-1.2Mo-1.9Cu显微组织演变及力学性能。结果表明,经900℃30%+780℃75%变形,500℃退火的F-M钢晶粒尺寸0.97μm,屈服、抗拉强度和延伸率分别为876 MPa,976 MPa和15.2%,经900℃30%+780℃50%变形,500℃退火的F-M钢晶粒尺寸1.54μm,屈服、抗拉强度和延伸率分别为801 MPa,895 MPa和19.4%。由轧制变形导致的晶粒细化、小角度晶界增多,是提高实验钢强度的主要原因。然而,较大的轧制变形量也使过多的小角度晶界阻碍位错运动,从而导致实验钢在塑性变形过程中,延展性略差。     

基于退火路径的中锰钢组织转变与力学性能

为了更好地指导中锰钢工业试制,利用扫描电镜、电子背散射衍射、透射电镜和拉伸试验机等研究了不同退火路径下低碳中锰钢的组织转变及合金元素配分行为,并评价了其对力学性能的影响.结果表明,热轧中锰钢的显微组织主要由铁素体、板条马氏体、粒状贝氏体和残余奥氏体构成.经冷轧变形后,原组织中的铁素体和马氏体晶粒破碎,残余奥氏体和M/A...     

C和N含量及终锻温度对38MnVS6性能和组织的影响

摘要：通过显微组织定量统计、高分辨透射电镜及热力学计算等手段,研究了成分微调及终锻温度对38MnVS6非调质钢力学性能和显微组织的影响。结果表明,通过降C增N处理和降低终锻温度,实验钢屈服强度得到一定提高,塑韧性得到明显改善,室温冲击功由52J增加至83J。其作用机制为降C使铁素体体积分数增加,塑韧性得到改善;而增N后提高了钢的析出强化作用,弥补降C带来的强度损失;随着终锻温度的降低,铁素体数量增加且尺寸减小,细晶强化及韧化作用得到进一步提高。两方面综合作用使得实验钢强度保持稳定,而冲击韧性提高。     

980MPa级冷轧双相钢组织性能研究

为研究980 MPa级C-Si-Mn-Nb系冷轧双相钢组织性能,在试验室冶炼该钢并采用临界区保温+两段式冷却+过时效处理的工艺进行热处理。研究表明,试验钢的屈服强度为476 MPa,抗拉强度为1 021 MPa,伸长率为15%,n值为0.29;试验钢热轧组织为(F+P),铁素体晶粒尺寸约为3.3μm;退火组织为(F+M),马氏体体积分数约为63%。微合金元素Nb的添加,起到细晶强化和析出强化的作用。与热轧组织相比,连续退火板带状组织得到明显改善,试验钢表现出良好的强韧性匹配。     

Multi Directional Forging of 2024 Al Alloy After Different Heat Treatments: Microstructural and Mechanical Behavior

Improvement of mechanical properties and microstructure of 2024 aluminum alloy by performing a severe plastic deformation method, called multidirectional forging (MDF), and heat treatment was the aim of this research. In this work, the effects of different heat treatments such as annealing, solid solution, peak ageing and over ageing before MDF on mechanical properties and microstructure of the alloy were studied. Microstructure evolution during severe plastic deformation was considerably affected by the precipitates and non-shearable particles. On the other hand, the severe plastic deformation had different effects on precipitates in the microstructure. Fragmentation, scattering and dissolution of precipitates were the examples of these effects. The study of X-ray diffraction patterns of 8 passes MDFed annealed samples showed that the cell size was decreased to 310 nm while this value was 270 nm for 8 passes MDFed overaged samples. Also, SEM images showed that fragmentation and scattering of precipitates occurred in widespread. The results of hardness and shear punch tests illustrated that the hardness and shear strength of samples were heavily increased by MDF. The increased values were 55 % for 8 passes MDFed annealed samples and 40 % for 8 passes MDFed overaged samples. Applying 2 passes of MDF on super saturated samples resulted in dynamic precipitation and consequently shear strength was increased up to 70 %.     

Cu-P-Cr-Ni-Mo耐候钢双相区多道次轧制模拟的组织演变

 为了实现Cu-P-Cr-Ni-Mo耐候钢的铁素体晶粒细化从而充分提高其强塑性,通过热模拟压缩试验,利用金相、SEM、EBSD等微观组织分析方法研究了其在双相区的多道次压缩变形过程中的组织演变。结果表明,试验钢在变形过程中,第二相（马氏体、贝氏体）呈条带状分布于铁素体基体上,随着道次增加,铁素体晶粒逐步细化,第5道次变形后得到1.8 μm左右的超细晶铁素体。前期铁素体晶粒细化的主要机制是形变强化铁素体相变,即多道次的累积大变形使组织内畸变能增大,铁素体形核点增多,促进铁素体快速析出,形成细小铁素体晶粒;后面几道次变形中,随着应变量继续增大,在铁素体晶粒内形成大量亚晶界,且亚晶界逐步累积扭转成大角度晶界,分割原来的粗大晶粒,发生铁素体连续动态再结晶细化。     

钽合金零件冷摆碾成形组织性能研究

通过合理控制冷摆碾成形工艺参数,成功制备出形状尺寸满足要求、表面质量良好的钽合金薄壁回转体零件,研究了冷变形后钽合金的再结晶退火工艺,检测了退火后钽合金零件的力学性能和硬度分布,观察了径向不同位置的显微组织。结果表明,经过1 350℃×60 min真空退火,钽合金发生了完全再结晶,平均晶粒尺寸50μm左右,零件不同位置的组织均匀性较好,抗拉强度达到360 MPa,延伸率45.5%。     

冷轧压下率对TRIP钢组织与力学性能的影响

研究了含铝TRIP钢在相同的热处理条件和不同冷轧压下率时的组织和力学性能。结果表明,随着冷轧压下率增加,材料组织细化,屈服强度连续升高;而抗拉强度和伸长率则由于晶粒细化以及TRIP效应,先升高后降低。冷轧压下率74%时材料的综合性能最佳,此时带状组织的危害也有所减轻或消失。     

Microstructure and Mechanical Properties of Nb-Microalloyed X100 High Deformability Pipeline Steel

A low carbon Nb-microalloyed high deformability pipeline steel with X100 grade has been processed by TMCP and followed two-stage cooling process.The microstructure is characterized by ferrite/bainite multiphase.The effective grain size is 1.85μm in average.The volume of ferrite is about 10-15% and the grains sizes are mostly less than 5μm.The bainite consists of granular-bainite and lath-bainite,with M/A islands finely dispersed.The longitudinal tensile yield strength,uniform elongation,yield ratio are 647MPa,7.6% and 0.78,respectively.Ferrite/bainite multiphase have large strain hardenability that resulting high strength and high deformability combination.Precipitation of Nb also improves the strength and uniform deformability by precipitation strengthening and grain refinement.     

Controlled Forging of a Nb Containing Microalloyed Steel for Automotive Applications

Controlled forging of microalloyed steels is a viable economical process for the manufacture of automotive parts. Ferrite grain refinement and precipitation hardening are the major microstructural parameters to enhance the mechanical properties of the forged components. In the current study, a modified thermomechanical treatment for additional ferrite grain refinement is developed by exploiting the effect of Nb in increasing the T _NR (no recrystallization temperature) and via phase transformation from a pancaked austenite. This is accomplished by performing the final passes of forging below the T _NR temperature followed by a controlled cooling stage to produce a mixture of fine grained ferrite, small scaled acicular ferrite as well as a limited amount of martensite. The effect of processing parameters in terms of forging strain, cooling rate and aging condition on the microstructure and mechanical properties of a medium carbon, Nb containing microalloyed steel is investigated. An attempt is made to identify a suitable microstructure that provides a proper combination of high strength and good impact toughness. The processing-microstructure relationships for the proposed novel forging procedure are discussed, and directions for further improvements are outlined.     

淬火温度对780 MPa级Ti-Nb-B微合金化水电用钢组织和力学性能的影响

研究了淬火温度对780 MPa级水电用钢(/%:0.09C,0.10Si,1.50Mn,0.009P,0.002S,0.90Cr,0.20Ni,0.023Ti,0.004Nb,0.001 0B)组织和力学性能的影响。结果表明,试验钢不同温度淬火后均得到了板条贝氏体组织,随着淬火温度910℃升高至950℃,奥氏体平均晶粒从9.1μm长大到16.6μm,试验钢回火后基本保持了淬火态的板条结构。淬火温度在910～950℃试验钢的强度随着淬火温度的升高先增大后减小,并在930℃时达到最大,试验钢冲击韧性和断后延伸率与强度有着相同的变化规律。在930℃淬火,610℃回火的工艺参数条件下,获得最佳的力学性能:屈服强度为802 MPa,抗拉强度为858 MPa,伸长率为19%,-40℃冲击功为238 J。     

晶粒细化对奥氏体不锈钢高温力学性能的影响

摘要：对粗晶201LN奥氏体不锈钢采用60%冷变形结合700℃退火120s工艺制备超细晶奥氏体不锈钢,研究晶粒细化对奥氏体不锈钢高温力学性能的影响。利用光学显微镜、扫描电子显微镜、透射电子显微镜、电子背散射衍射技术对粗晶和超细晶奥氏体钢进行了组织表征,并使用万能试验机测试20和650℃环境下力学性能。结果显示粗晶奥氏体不锈钢经过冷变形结合退火工艺处理,平均晶粒尺寸由18μm细化为0.9μm,屈服强度由383MPa提高到704MPa,而伸长率由63.8%下降到46.3%,表明晶粒细化能有效提高奥氏体不锈钢屈服强度的同时较小损害塑性,TEM证实其形变机制均为形变诱导马氏体和孪生协同作用。当温度由20℃提高到650℃时,粗晶奥氏体不锈钢屈服强度和伸长率分别下降到180MPa和28.1%,超细晶奥氏体不锈钢屈服强度和伸长率分别为384MPa和24.2%。这表明在650℃高温环境下细晶强化作用仍然有效,粗晶和超细晶奥氏体不锈钢也有较好的塑性,其形变机制分别变为位错滑移和位错滑移+层错+孪生。     

多向锻造法细化钛及钛合金晶粒的研究现状

多向锻造技术是一种制备超细晶结构材料的重要方法,能够有效改善材料的各项性能,因此近年来越来越受到人们的广泛关注。综述了多向锻造技术细化钛合金晶粒的研究现状,介绍了多向锻造技术的工艺过程和晶粒细化机制,分析了当前研究中存在的主要问题,并展望了多向锻造技术在钛合金加工中的应用前景。     

Effect of hot working on structure and strength of type 304L austenitic stainless steel

The development of microstructure and strength during forging in a single-phase austenitic stainless steel, 304L, was investigated by means of forward extrusion of cylindrical specimens. The temperature, strain, and strain rate of deformation were varied. A low strain rate was imparted by press forging (PF), and a high strain rate by high-energy-rate forging (HERF). Low forging temperatures produced dynamically recovered microstructures and monotonic increases in strength with increasing strain for low and high strain rates. At higher forging temperatures, the high-energy-rate-forged material exhibited softening, after the application of a critical amount of strain, as a result of static recrystallization which occurred within a few seconds after cessation of deformation. Analysis of isothermal compression test data, specifically the strain-to-peak stress associated with the onset of dynamic recrystallization, confirmed that dynamic recrystallization would not be expected for the deformation conditions imposed during forward extrusion in this study. Recrystallized grain size was found to vary uniquely with strain, initial grain size, and the Zener-Hollomon parameter. Recrystallization was much less prevalent in press-forged material and may have been affected by die chilling as well as the predominance of dynamic recovery. The variation of strength, recrystallized grain size, and extent of recrystallization with the deformation parameters, temperature and strain, are presented as a set of processing-property maps for each forging technique (έ). The findings are discussed in the context of developing process design criteria for forging alloy 304L.