Microstructure and mechanical properties of FGBA/BG air cooling bainitic steels containing niobium

The effect of different Nb additions on the mechanical properties and microstructure evolution of grain boundary allotriomorphic ferrite(F_(GBA)) / granular bainite(B_G) air cooling bainitic steels was investigated.The results indicate that the tensile strength and yield strength increase by 157 and 97 MPa,respectively with the addition of 0.02wt%Nb.The steel acquires superior strength and toughness with the addition of 0.06wt%Nb.The results of scanning electron microscopy and transmission electron micro...     

空冷高硅中碳低合金钢的组织与性能

研究了高硅中碳低合金钢空冷态和空冷＋回火态的显微组织和力学性能.试验钢在860℃保温0.5 h奥氏体化后空冷处理,随后分别在250℃和400℃保温1 h回火.结果表明：试验钢空冷后组织为贝氏体/马氏体和残余奥氏体的混合组织,硬度约为41 HRC;而250℃回火后组织变化不大,硬度明显升高,约为49 HRC,韧性明显增加,由44 J/cm2增加到66 J/cm2,抗拉强度、屈服强度和延伸率明显下降.回火温度进一步增加对力学性能影响不大.     

C—Si—Mn系热轧双相钢显微组织与力学性能之间的关系

通过对热轧试样的组织性能测试,研究了热轧双相钢显微组织与力学性能之间的关系。研究发现,铁素体和马氏体强度是影响力学性能的主要因素。建立了C-Si—Mn系热轧双相钢力学性能的数学模型,可以作为热轧双相钢基本力学性能参数预测的理论依据。     

CSP工艺条件下低碳钢板带材力学性能研究

热轧板带材成品因其内在组织形态及成分不同而呈现较明显的力学性能差异.就包钢薄板坯连续连轧CSP工艺条件下,低碳典型钢种Q235B和SS400显微组织及轧制工艺对材料力学性能的影响进行了实验研究.用数理统计方法建立了工艺参数与产品性能回归数值模型,模型拟合效果较好.     

Microstructure and mechanical properties of rapidly solidified Al-Cr alloys

The microstructure and mechanical properties of rapidly solidified Al-Cr alloys were investigated by XRD, TEM and microhardness testing instrument. The results indicate that the matrix of rapidly solidified Al-Cr alloys is α-Al solid solution when the Cr content is lower than 4 wt%. However, when the Cr content is above 4 wt%, the microstructures of rapidly solidified Al-Cr alloys are different along cross section. The microstructure of alloy contacting copper roller consists of α-Al and a few intermetallic compounds. With the increase of distance from copper roller, the matrix consists of α-Al and spherical intermetallic compounds which conglomerate in α-Al matrix. These intermetallic compounds are Al₇Cr, Al₁₁Cr and Al₄Cr. The tensile strength has the maximal value when the Cr content is about 8 wt%. The annealed microstructures show that supersaturated α-Al solid solution dissolved with increasing anneal temperature. The starting temperature of the second phase precipitated from the supersaturated α-Al solid solution desponds on the supersaturation. Meanwhile, the microhardness of rapidly solidified Al-Cr alloy reaches maximal value after annealing at 300 °C. Funded by the Innovation Fund for Outstanding Scholar of Henan Province (No. 0621000700)     

转炉-CSP工艺SS400热轧板带组织与力学性能分析

对包钢CSP工艺生产的SS400低碳热轧板卷进行了组织、力学性能测定分析.结果表明,成品薄板显微组织为大量的多边形铁素体和少量珠光体,晶粒细小、均匀,晶粒平均尺寸约为12 μm,中心区域比表面区域晶粒稍粗大,但差别不大.力学性能较国标的Q235B高,屈强比也较高.     

Microstructure and mechanical properties of Al_3Ti-based alloys in Al-Ti-Mo-X quaternary systems

A part of Al-Ti-Mo-Cr quaternary phase diagram is constructed for the microstructure control of D022-Al3Ti or its derivative, L12-(Al,Cr)3Ti, -based alloys. It was found that quaternary bcc phase equilibrates with either D022-Al3Ti or L12-(Al,Cr)3Ti, or both, exist in large compositional areas. The mechanical properties is strongly affected by precipitates appearing, and presumably alloy microstructures.     

High-temperature mechanical properties of near-eutectoid steel

The high-temperature mechanical properties of near-eutectoid steel were studied with a Cleeble-1500 simu- lation machine. Zero strength temperature （ZST）, zero ductility temperature （ZDT）, hot ductility curves, and strength curves were measured. Two brittle zones and one plastic zone were found in the temperature range from the melting point to 600℃. Embrittlement in zone I is caused by the existence of liquid film along dendritic interfaces. Ductility loss in zone Ⅲ mainly results from precipitates and inclusions as well as S segregation along grain boundaries. Pearlite transformation also accounts for ductility deterioration in the temperature range of 700-600℃. Moreover, the straightening temperature of the test steel should be higher than 925℃ for avoiding the initiation and propagation of surface cracks in billets.     

Effect of tempering temperature on the mechanical properties and microstructure of an copper-bearing low carbon bainitic steel

The effect of tempering temperature on the microstructure and mechanical properties of ultra-high strength, copperbearing, low-carbon bainitic steel has been investigated in the experiment. The results showed that the microstructure was mainly the laths of bainite in the as-quenched steel. The bainitic laths were restored and combined after the steel tempered at various tempera- tures. There were rnartensite/austenite （M/A） islands and numerous dislocations within and between the bainitic laths, while very t-me precipitates of ε-Cu were also observed within the laths. With increasing the tempered temperature from 400 to 600℃, the yield strength （YS） increased from 877 to 957 MPa, whereas the ultimate tensile strength （UTS） decreased from 1020 to 985 MPa. The Charpy V-notch （CVN） varied from 68.5 to 42 J, and the value was minimal for the steel tempered at 500℃. 2008 University of Science and Technology Beijing. All rights reserved.     

高扩孔型铁素体/贝氏体双相钢组织性能研究

对540MPa级铁素体/贝氏体双相钢的组织性能进行分析研究。结果表明,试验钢的显微组织为85%左右的铁素体加上15%左右的贝氏体;铁素体晶粒尺寸细小,基体中有较高的位错密度和大量细小弥散的析出物;贝氏体在铁素体基体上分布均匀,以板条状为主,板条间分布有较多碳化物颗粒。通过合适的成分设计和控轧控冷手段获得的铁素体/贝氏体双相钢组织形态,可较好地保证材料所需的强度-拉伸凸缘性能匹配。     

炉卷轧机X70级管线钢组织与性能研究

采用低碳、低硫和微合金化成分设计,在1200-1220℃加热温度、790-830℃终轧温度、500-550℃终冷温度控制工艺下进行热轧处理,对3500 mm炉卷轧机生产的X70管线钢进行组织性能检验。结果表明,所生产的X70管线钢均满足西气东输二线X70级管线钢的技术要求。     

Microstructure and mechanical properties of as-cast Mg-8Sn-1Al-1Zn-xNi alloys

Mg-8Sn-1Al-1Zn-xNi（x=0.5%, 1.0%, 1.5%, 2.0%, mass fraction） alloys were designed and prepared. The microstructures and the mechanical properties were studied by using optical microscope, scanning electronic microscope, energy dispersive X-ray spectroscope, X-ray diffraction and a standard universal testing machine. The results show that the microstructure of Ni-containing alloys consist of α-Mg, Mg2 Sn, β-Mg-Ni-Al and γ-AlNi phases. No β-Mg-Ni-Al phase was observed in TAZ811-2.0Ni alloy due to its 1：1 atomic ratio of Ni/Al. The addition of Ni refines the α-Mg dendrites and suppresses the formation of coarse Mg2 Sn phase. The tensile properties results show that the TAZ811-0.5Ni alloy presented the best mechanical properties, which is due to the rod-like β-Mg-Ni-Al phase, refined α-Mg dendrites and Mg2 Sn phase, as well as γ-AlNi phase. The tensile fracture mechanism transits from cleavage to quasi-cleavage fracture with the increasing Ni addition.     

Microstructure and mechanical properties of automobile beam steels produced by EAF-CSP process

The microstructure, mechanical properties, and misorientation of automobile beam steels produced by EAF-CSP process were studied using optical microscopy （OM） and electron back-scattered diffraction （EBSD）. It is shown that the microstructure of strips is mainly polygonal ferrite, and the average grain size is about 5-8 μm. The electron back-scattered diffraction results show that grain boundaries in ferrite are basically high-angle grain boundaries without remarkable preferred orientation. Hot strips of automobile beam steels possess a good combination of strength and plasticity because of their fine microstructures and low quantity of impurities.     

Microstructure and mechanical properties of AZ91 magnesium alloy subject to deep cryogenic treatments

AZ91 magnesium alloy was subjected to a deep cryogenic treatment. X-ray diffraction （XRD）, scanning electronic microscopy （SEM）, and transmission electronic microscopy （TEM） methods were utilized to characterize the composition and microstructure of the treated samples. The results show that after two cryogenic treatments, the quantity of the precipitate hardening β phase increases, and the sizes of the precipitates are refined from 8-10μm to 2-4μm. This is expected to be due to the decreased solubility of aluminum in the matrix at low temperature and the significant plastic deformation owing to internal differences in thermal contraction between phases and grains. The polycrystalline matrix is also noticeably refined, with the sizes of the subsequent nanocrystalline grains in the range of 50-100 nm. High density dislocations are observed to pile up at the grain boundaries, inducing the dynamic recrystallization of the microstructure, leading to the generation of a nanocrystalline grain structure. After two deep cryogenic treatments, the tensile strength and elongation are found to be substantially increased, rising from 243 MPa and 4.4% of as-cast state to 299 MPa and 5.1%.     

Effect of fast cooling rate on the microstructure and mechanical properties of low-carbon high-strength steel annealed in the intercritical region

The effect of fast cooling rate on the microstructure and mechanical properties of low-carbon high-strength steel annealed in the intercritical region was investigated using a Gleeble 1500 thermomechanical simulator and a continuous annealing thermomechanical simulator. The results showed that the microstructure consisted of ferrite and bainite as the main phases with a small amount of retained austenite and martensite islands at cooling rate of 5 and 50 ℃/s, respectively. Fast cooling after continuous annealing affected all constituents of the microstructure. The mechanical properties were improved considerably. Ultimate tensile strength(UTS) increased and total elongation(TEL) decreased with increasing cooling rate in all specimens. The specimen 1 at a cooling rate of 5 ℃/s exhibited the maximum TEL and UTS×TEL(20% and 27 200 MPa%, respectively) because of the competition between weakening by presence of the retained austenite plus the carbon indigence by carbide precipitation, and strengthening by martensitic islands and precipitation. The maximum UTS and YS(1 450 and 951 MPa, respectively) were obtained for specimen 2 at a cooling rate of 50 ℃/s. This is attributed to the effect of dispersion strengthening of fi ner martensite islands and the effect of precipitation strengthening of carbide precipitates.     

Evolution of carbides and carbon content in matrix of an ultra-high carbon sintered steel during heat treatment process

DTA, thermal expansion, XRD, and SEM were used to evaluate the effect of quenching temperature on the mechanical properties and microstructure of a novel sintered steel Fe-6Co-1Ni-5Cr-5Mo-1C. Lattice parameters and the mass fraction of carbon dissolved in the matrix of the steel quenched were investigated. It is discovered that the hardness of the steel increases with quench-ing temperature in the range of 840-900℃ and remains constant in the range of 900 to 1100℃. It decreases rapidly when the tem-perature is higher than 1100℃. The mass fraction of carbon dissolved in the matrix of the steel quenched at 840℃ is 0.38, but when the quenching temperature is increased to 1150℃, it increases to 0.98. The carbides formed during sintering are still present at grain boundaries and in the matrix of the steel quenched at low quenching temperatures, such as 840℃. When the quenching temperature is increased to 1150℃, most of the carbides at grain boundaries are dissolved with just a small amount of spherical M23C6 existing in the matrix of the quenched steel.     

Microstructure and mechanical properties of AZ31 alloy ingot fabricated by semi-continuous casting

The AZ31 alloy ingot with diameter of 110 mm and length of 3500 mm was fabricated successfully. The compositions and microstructure morphologies of the ingot at different locations were performed, which indicated that the chemical composition distributed homogeneously through the whole alloy ingot and the average grain size increased from the surface to the center. The results of the EDS and element face-scanning illustrated that the eutectic compounds mainly consisted of fl-Mg17Al12 and a small amount of fl-Mgl7（AlZn）12. Furthermore, slight improvements of the strength and ductility were observed from the center to the surface along the axial direction of the alloy ingot, while both the strength and elongation to failure of the samples along the radial direction are higher than that along the axial direction. The fine grain strengthening was the main contributors to the strength of the as-casted AZ31 alloy.     

高碳低合金钢低温贝氏体组织及其耐磨性研究

设计了一种新的低温等温转变无碳化物贝氏体高碳低合金钢。对该钢低温等温淬火组织和干滑动摩擦磨损耐磨性及磨损机理进行研究,并与淬火＋低温回火处理试样进行比较。结果表明,经1 000℃奥氏体化后在220℃盐浴中进行等温120 h的等温淬火处理,得到了由平均厚度约为120 nm的板条状贝氏体铁素体和薄膜状的残留奥氏体组成的无碳化物贝氏体组织,干滑动摩擦磨损相对耐磨性比回火马氏体组织提高19%,磨损机理为粘着磨损。     

Effect of cooling parameters on the microstructure and properties of Mobearing and Cr-bearing steels

To develop low-cost low carbon bainitic steel,Mo-bearing and Cr-bearing steels were melted in a vacuum induction furnace and were researched by thermal simulation and hot rolling at the laboratory.As the cooling rate increases from 0.2 to 50℃/s,the transformation temperatures of two steels lie between 650 and 400℃,and the final microstructures of them change from quasi-polygonal ferrite and granular bainite to lath bainite.Compared with cooling in air or by interrupted cooling,Mo-bearing and Cr-bearing steel plates cooled by sprayed water boast higher strength and superior toughness,for large-size islands are responsible for the poor mechanical properties.Compared to Mo,Cr is effective to isolate the bainitic reaction in low carbon steel,and the bainitic microstructure can also be obtained in Cr-bearing steel cooled at a wide range of cooling rate.