Influence of Lamellar Direction in Pearlitic Steel Wire on Mechanical Properties and Microstructure Evolution

During cold drawing of pearlitic steel wire,the lamellar structure becomes gradually aligned with the draw-ing axis,which contributes to the ultra-high strength.A direct simulation about the mechanical behaviors and micro-structural evolution of pearlitic lamellae was presented.A representative volume element (RVE)containing one pearlitic colony was established based on the real transmission electron microscope (TEM)observation.The deform-ation of pearlitic colony during tension,shear and wire drawing were successfully simulated.The numerical results show that this metallographic texture leads to a strong anisotropy.The colony has higher yielding stress when the la-mellar direction is parallel and perpendicular to the tensile direction.The lamellar evolution is strongly dependent on the initial direction and deformation mode.The formation of typical period shear bands is analyzed.In the wire draw-ing,the pearlitic colony at the sub-surface experiences a complex strain path:rotation,stretching along the die sur-face,and rotation back.     

Microstructures and Mechanical Properties of as-Drawn and Laboratory Annealed Pearlitic Steel Wires

Near eutectoid fully pearlitic wire rod (5.5 mm diameter) was taken through six stages of wire drawing (drawing strains of 0 to 2.47). The as-drawn (AD) wires were further laboratory annealed (LA) to re-austenitize and reform the pearlite. AD and LA grades, for respective wire diameters, had similar pearlite microstructure: interlamellar spacing (λ) and pearlite alignment with the wire axis. However, LA grade had lower hardness (for both phases) and slightly lower fiber texture and residual stresses in ferrite. Surprisingly, essentially identical tensile yield strengths in AD and LA wires, measured at equivalent spacing, were found. The work hardened AD had, as expected, higher torsional yield strengths and lower tensile and torsional ductilities than LA. In both wires, stronger pearlite alignment gave significantly increased torsional ductility.     

铝对喷射成形超高碳钢组织与性能的影响

在喷射成形快速凝固条件下,含铝超高碳钢会发生铝在渗碳体中的非平衡固溶.由于这种含铝渗碳体的不稳定性,在随后的加热中会迅速由喷射态的晶界网络形态或珠光体片层状转化为分散而细小的颗粒,从而使该材料具有很好的高温塑性和热加工性能.加铝的喷射成形超高碳钢可把碳的质量分数提高到1.8%,经一道次70%热轧后形成致密、无碳化物网络、均匀细化的组织,使屈服强度和抗拉强度分别提高到1 088 MPa和1 419MPa,并仍有一定的塑性.     

Influence of Mo Content on Microstructure and Mechanical Properties of Fire-Resistant Construction Steel

In order to ensure fire-resistant property of the steel under the condition of the least molybdenum content,effects of molybdenum on microstructure and properties of the fire-resistant construction steel,specially on high temperature strength were investigated.The results show that the room temperature and high temperature strength of the steel is enhanced due to increased Mo content but the impact toughness deteriorates at the same time.The fraction of bainite in the microstructure increases with increasing Mo content while the fractions of polygonal ferrite and pearlite decrease.Comparing with the steel of adding Nb alone,it was obvious that combined addition of Mo and Nb could provide better effect in high temperature strengthening.Addition of 0.25mass% Mo in the steel containing Nb could meet fire-resistant requirements of the construction steel and provide better economical effectiveness.     

Nb对OCrll铁素体不锈钢组织和性能的影响

铁素体不锈钢与奥氏体不锈钢相比具有成本低、热膨胀系数低和耐应力腐蚀等优点,所以被广泛应用到汽车排气系统、家用电器和建筑等领域.研究了不同的Nb含量对铁素体不锈钢显微组织和力学性能的影响.研究结果表明:Nb有细化晶粒的作用,随着Nb含量的增加,晶粒的平均尺寸减小;由于合金元素Nb和Ti的加入,形成了TiN、NbC和FezNb析出相,其透射电镜观察结果与Thermal-eale计算结果一致;材料的抗拉强度和显微硬度随着Nb含量的增加而增加,这是由于Nb的固溶强化和析出强化共同作用的结果.     

Microstructure and Mechanical Properties of NANOBAIN Steel

The microstructure and mechanical properties of NANOBAIN steel treated at different isothermal temperatures were investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),uniaxial tensile tests and X-ray diffraction(XRD).It was found that bainitic ferrite(BF)plate was made of basic shear transformation units arranged in the same direction of subunits.The existence of defects,such as nanoscale twinning and dislocation,suggested that the growth of transformation units was controlled by the surrounding defect plane with dislocation,which was consistent with the moving direction of BF/austenite interface parallel to the twinning plane.The behavior of work hardening indicated that mechanical stability of microstructures obtained at 250 ℃ and 300 ℃ was much more stable than that obtained at 210℃.The evolution of carbon partitioning in retained austenite and bainitic ferrite also indicated that austenite was enriched in carbon at the initial stage step by step;after the formation of BF,the austenite did not seem to be greatly enriched in carbon and the carbon content showed a little decrease instead;subsequently,aphenomenon of little decarburization of supersaturated bainitic ferrite has also been found.     

Influence of Ni Addition on the Microstructure and Mechanical Properties of 3.5Mn Medium-Mn Steel

Metallurgical and Materials Transactions A - The influence of Ni addition on the microstructure evolution and mechanical properties of Fe–0.2C–3.5Mn medium Mn steel after intercritical...     

Improving the Mechanical Properties and Wear Resistance of a Commercial Pearlitic Rail Steel Using a Two-Step Heat Treatment

Metallurgical and Materials Transactions A - The possibility of improving the mechanical and wear performance of steel rails with conventional compositions, near-eutectoid and without special...     

Influence of Austempering Temperature on Microstructure and Mechanical Properties of High-Silicon Carbide-Free Bainitic Steel

The microstructural evolution of a novel high-silicon carbide-free bainitic steel at different austempering temperatures is investigated. The microstructure is evaluated by means of optical and electron microscopy, X-ray diffraction, microhardness, and nanohardness. Results show a variation in the amount of stabilized retained austenite changing the temperature of the isothermal treatment. In particular, it is observed an increase in the retained austenite volume fraction increasing the temperature up to 350 °C, while further increase leads to a reduction. Moreover, increasing the isothermal holding temperature from 250 °C, through 300, 350, and 370 °C, a progressive bainite coarsening and an increase in the amount of stabilized carbon-enriched retained austenite are observed. Tensile tests reveal an excellent combination of mechanical properties: mechanical strength in the range 1276–1988 MPa and total elongation 0.18–0.44.     

等温淬火温度对C-Si-Mn系TRIP钢组织和力学性能的影响

利用金相显微镜和X射线衍射方法研究了0.11C-1.23Si-1.65Mn冷轧TRIP钢等温淬火温度对组织和力学性能的影响.结果表明,实验钢在840℃×180 s退火 420℃× 240 s等温处理后可得到6.55%的残余奥氏体,此时可获得较佳的相变诱发塑性和较好的强韧性配合,其强塑积可达到2.28×104MPa·%,提高或降低等温温度都会降低强塑积.在840℃退火,适当延长退火时间,可提高残余奥氏体体积分数及碳含量,有助于提高材料的综合性能.     

Effect of Macrosegregation on the Microstructure and Mechanical Properties of a Pressure-Vessel Steel

Macrosegregation refers to the chemical segregation, which occurs quite commonly in the large forgings such as nuclear reactor pressure vessel. This work assesses the effect of macrosegregation and homogenization treatment on the mechanical properties of a pressure-vessel steel (SA508 Gr.3). It was found that the primary reason for the inhomogeneity of the microstructure was the segregation of Mn, Mo, and Ni. Martensite, and coarse upper bainite with M-A (martensite-austenite) islands have been obtained, respectively, in the positive and negative segregation zone during a simulated quenching process. During tempering, the carbon-rich M-A islands decomposed into a mixture of ferrite and numerous carbides which deteriorated the toughness of the material. The segregation has been substantially minimized by a homogenizing treatment. The results indicate that the material homogenized has a higher impact toughness than the material with segregation, due to the reduction in M-A island in the negative segregation zone. It can be concluded that the microstructure and mechanical properties have been improved remarkably by means of homogenization treatment.

     

Microstructure and Mechanical Properties of a Low Carbon Bainitic Steel

A low carbon bainitic steel with microstructure of granular bainite (GB), acicular ferrite (AF), and bainitic ferrite (BF) is obtained under different deformation and cooling rate. The effect of deformation and cooling rate on microstructural characteristics such as the type of the matrix, the size, and area fraction of the martensite–austenite (M–A) constituents is investigated. In addition, the nanohardness of these three kinds of matrix as well as that of the M–A constituents in them is characterized. Further, the effect of matrix and M–A constituents on strength–toughness balance is studied. Results indicate that deformation expands the transformation region. The size as well as the area fraction of the M–A constituent decreases with the increasing of the cooling rate. After deformation, the area fraction of the M–A constituents increases. Nanohardness of GB, AF, and BF increases orderly, but that of the M–A constituents in them decreases accordingly. The nanohardness of the M–A constituent is significantly affected by its carbon concentration. AF is the optimum microstructure having superior strength–toughness balance.     

Influence of Tempering Time on the Microstructure and Mechanical Properties of AISI M42 High-Speed Steel

AISI M42 high-speed steel is prone to fracture as a result of its brittle martensitic microstructure together with abundant carbides located at the grain boundaries. In this study, a series of property tests including hardness, impact toughness, and wear loss were performed to study the effect of tempering conditions on the mechanical properties of AISI M42 high-speed steel over holding time ranging from 1 to 20 hours. The effects of the tempering time on the characteristics and growth of carbides were also investigated. The results indicated that carbides in the experimental steels were obviously coarsened when the tempering time exceeded 4 hours. The dimension of the carbides increased, while the volume fraction decreased with the increasing tempering time, and the grain sizes were significantly augmented due to the reducing of small carbides. Moreover, the dislocation density decreased with the increasing tempering time, which led to the reducing of the yield stress of high-speed steel. An appropriate holding time (4 hours) resulted in fine-scale secondary carbides and a smaller grain size, which efficiently improved the impact toughness and wear resistance simultaneously. Nevertheless, a prolonged tempering time (>?4 hours) promoted the coarsening and coalescence of carbides, which were detrimental to the impact toughness and wear resistance. Consequently, the formation of fine-scale secondary carbides is the major influential factor to improve both the wear resistance and impact toughness.     

轧制工艺参数对高级别管线钢组织及性能的影响

试验研究了在贝氏体基体中形成针状铁素体,来改善高强度管线钢的综合机械性能,特别是低温韧性.为了研究轧制工艺参数对组织的影响,以及获得合适的轧钢条件,以保证强度和韧性的最佳结合,达到X80和X120的性能要求.首先运用Gleeble进行了热模拟,然后,根据热模拟的试验结果,进行了试验轧制.根据组织观察和性能分析,阐述了微观结构和力学性能的关系.结果表明:随着冷却速度的提高,上贝氏体的体积比增加,并且,通过控制冷却速度和终止冷却温度,可以控制各构成相的体积比,从而获得不同的强度级别;由于针状铁素体的有效晶粒尺寸小,贝氏体基体中针状铁素体的含量越多,上架能量(IJSE)越大,并且针状铁素体能降低韧脆转变温度(JDBTF);初轧阶段采用大的压下率对组织细化有很大影响.     

控轧直接淬火钢的微观组织与力学性能

分析了22SiMn2TiB钢再结晶控轧直接淬火(RCR&DQ)、未再结晶控轧直接淬火(CR&DQ)以及两者重新调质后(CR&DQQ、RCR&DQQ)的微观组织和力学性能。同时,与传统再加热淬火处理(RA&Q)的组织和性能进行了对比,结果表明:试验钢直接淬火后强硬度明显高于再加热淬火钢,塑性基本相当,而韧性也得到了较大幅度的提升。     

时效温度对S32101双相不锈钢组织和力学性能的影响

利用光学显微镜、铁素体仪进行了硬度和拉伸实验,研究了S32101双相不锈钢不同时效态下组织与力学性能之间的关系。研究结果表明,随着时效温度的升高,S32101双相不锈钢的屈服强度、抗拉强度和硬度减小,延伸率增大;析出相的产生是造成力学性能变化的主要原因,700℃为最敏感析出温度,900℃时析出相开始逐渐消失。     

Microstructure and Mechanical Properties of TWIP Steel Joints

As a new type of high manganese steel, the twinning induced plasticity （TWIP） steels have attracted a growing interest in the automotive industry due to their good performance. Thin plates of TWIP steel were welded by laser beam welding （LBW） and gas tungsten arc welding （GTAW）. The microstructure result shows that GTAW joint has obvious heat-affected zone （HAZ）, while the HAZ of LBW joint is almost invisible. The X-ray diffraction result shows that the phase compositions of both joints are austenitic and no phase transition occurs. Energy disper- sive spectrometry result shows that there is violent evaporation of Mn element in LBW joint, while the proportion of Mn element in GTAW joint is almost unchanged. Tensile tests and micro-hardness measurements were performed to take into account the mechanical properties of joints manufactured by the two different processes. The micro-hard- ness profiles of both joints present a typical saddle distribution, and the hardness of GTAW seam is lower than that of LBW seam. The failure positions of LBW joints are all located in base metal while the GTAW joints are all at the weld toe due to the softening of HAZ. By means of scanning electron microscopy, a typical ductile fracture is observed in LBW joint, while a brittle fracture with quasi-cleavage fracture characteristic is observed in GTAW joint.     

Nb对0Cr11铁素体不锈钢组织和性能的影响

 铁素体不锈钢与奥氏体不锈钢相比具有成本低、热膨胀系数低和耐应力腐蚀等优点,所以被广泛应用到汽车排气系统、家用电器和建筑等领域。研究了不同的Nb含量对铁素体不锈钢显微组织和力学性能的影响。研究结果表明：Nb有细化晶粒的作用,随着Nb含量的增加,晶粒的平均尺寸减小;由于合金元素Nb和Ti的加入,形成了TiN、NbC 和 Fe2Nb析出相,其透射电镜观察结果与Thermal calc计算结果一致;材料的抗拉强度和显微硬度随着Nb含量的增加而增加,这是由于Nb的固溶强化和析出强化共同作用的结果。     

Influence of Rare Earth Elements on Microstructure and Mechanical Properties of Cast High-Speed Steel Rolls

The influence of rare earth （RE） elements on the solidification process and eutectic transformation and mechanical properties of the high-V type cast, high-speed steel roll was studied. Test materials with different RE additions were prepared on a horizontal centrifugal casting machine. The solidification process, eutectic structure transformation, carbide morphology, and the elements present, were all investigated by means of differential scanning calorimetry （DSC） and scanning electron microscopy energy dispersive spectrometry （SEM-EDS）. The energy produced by crack initiation and crack extension was analyzed using a digital impact test machine. It was found that rare earth elements increased the tensile strength of the steel by inducing crystallization of earlier eutectic γ-Fe during the solidification process, which in turn increased the solidification temperature and thinned the dendritic grains. Rare earth elements with large atomic radius changed the lattice parameters of the MC carbide by forming rare earth carbides. This had the effect of dispersing longpole M C carbides to provide carbide grains, thereby, reducing the formation of the gross carbide and making more V available, to increase the secondary hardening process and improve the hardness level. The presence of rare earth elements in the steel raised the impact toughness by changing the mechanism of MC carbide formation, thereby increasing the crack initiation energy.