科研人员开发出新型“超强钢” 有望提升合金的强度和韧性

正中国香港大学和美国劳伦斯伯克利国家实验室合作研制出一种"超级钢",该材料的抗变形屈服强度约为2GPa,断裂韧性为102MPa·m~(1/2),均匀伸长率为19%,其比Grade 300马氏体时效钢更强、更坚韧,但其制造成本只有Grade 300的20%左右。这种新型超级钢采用了一种新的变形分     

残余奥氏体及其机械稳定性与钢强韧性关系的研究

钢中残余奥氏体发生应变诱发马氏体相变的百分量与拉伸应变量的对数呈线性关系,用直线斜率的倒数Ks值可表示残余奥氏体机械稳定性的大小。提高钢中残余奥氏体量及其机械稳定性是改善钢强韧性的有效途径之一。残余奥氏体发生应变诱发马氏体相变吸收能量是提高钢韧性的主要原因。在低碳贝氏体钢中,以M—A岛形式存在的残余奥氏体因受岛中马氏体的强化作用使屈服强度保持较高水平,而残余奥氏体在拉伸的均匀塑性变形阶段因应变诱发相变形成的马氏体使钢的抗拉强度提高。     

预变形对低碳含铌钢板条马氏体等温时效性能的影响

研究了预变形对含铌低碳钢常规力学性能的影响。试验结果表明，在等温时效过程中预变形使含铌钢析出过程加快，析出的Nb(CN)变小，而且使含铌钢板条马氏体等温时效拉伸强度提高200MPa，其中第二相Nb(CN)粒子的强化效果约为130MPa，位错强化效果约为90MPa。     

用超快速冷却工艺开发热轧高强度带钢的实验研究

在实验室以一种普通含Nb微合金化钢为原料,用超快速冷却工艺开发热轧高强度带钢。采用LEICA图像分析仪观察分析开发的热轧高强度带钢试样的微观组织,采用INSTRON拉伸机检测试样的屈服强度、抗拉强度、断后总延伸率等力学性能。结果表明,采用该工艺获得两种具有良好强塑性能匹配的新钢级:一种为体积分数82%多边形铁素体+体积分数18%岛状马氏体的双相钢,屈服强度为516 MPa,抗拉强度为795 MPa,断后总延伸率为23%;另一种为体积分数95%粒状贝氏体+体积分数5%岛状马氏体的复相钢,屈服强度为538 MPa,抗拉强度为790 MPa,断后总延伸率为25%。     

基于有限元计算的形状记忆合金-金属玻璃复合材料变形行为

利用有限元模拟方法,研究了拉伸-卸载预应变对形状记忆合金-金属玻璃复合材料力学行为的影响及其内在机理.结果表明:预处理应变增加,形状记忆合金-金属玻璃复合材料的屈服强度及弹性应变极限均提高,但拉伸延展性急剧下降.预应变增加导致形状记忆合金颗粒第二次加载时的变形行为由典型的马氏体相变过渡为连续的马氏体相变,甚至表现为纯马氏体相的弹性变形.这一"相变效应"的减弱甚至消失,是形状记忆合金-金属玻璃复合材料经拉伸-卸载预处理后拉伸性能退化的直接原因.     

残余奥氏体的诱发相变对Cr12钢耐磨性的影响

利用金相，Ｘ射线，扫描电子显微镜等手段研究了Ｃｒ１２钢中残余奥氏体的形变诱发马氏体相变对耐磨性能的影响，探讨了强化机制。结果表明，Ｃｒ１２钢经１１５０℃淬火得到大量处于变塑状态的残余奥氏体，并在磨损过程中发生形变诱发马氏体相变，使表面硬度和耐磨性显著提高，超过常规的９８０℃淬火。残余奥氏体对耐磨性强化，为逐层诱发马氏体的循环强化机制。     

应力梯度特征对金属镍变形行为与力学性能的影响

本文针对金属材料镍,利用扭转变形制备了应力/应变梯度分布的特殊结构.结合ABAQUS软件,构建了包含应力梯度特征的有限元模型,系统分析了应力梯度特征在塑性变形过程中的演化规律及其对变形行为与力学性能的影响.结果表明,随着应力梯度的提高,材料的屈服强度从100 MPa提高到240 MPa;应力梯度分布从单一递减分布演化为"V"字型分布特征,屈服行为由连续屈服转化为屈服降;上下屈服点之差从10 MPa增加到60 MPa.     

残余奥氏体的诱发相变对Cr12钢耐磨性的影响

利用金相、Ｘ射线、扫描电子显微镜等手段研究了Ｃｒ１２钢中残余奥氏体的形变诱发马氏体相变对耐磨性能的影响，探讨了强化机制．结果表明，Ｃｒ１２钢经１１５０℃淬火得到大量处于变塑状态的残余奥氏体，并在磨损过程中发生形变诱发马氏体相变，使表面硬度和耐磨性显著提高，超过常规的９８０℃淬火．残余奥氏体对耐磨性的强化，为逐层诱发马氏体的循环强化机制．     

纳米尺度拉伸变形行为的分子动力学模拟

为了研究单晶面心立方材料在纳米尺度下的拉伸变形机理,采用分子动力学方法模拟了单晶Cu的拉伸变形过程,并研究了不同温度、不同应变速率对其拉伸变形行为的影响.结果表明:不同温度对单晶Cu屈服强度影响明显,温度越高,屈服强度越低;不同应变速率对拉伸过程的弹性变形和屈服机理没有影响,但对塑性变形影响大,应变速率越大,屈服强度越大.     

双相2OCr钢冲击载荷应变速率敏感性研究

利用分离式霍普金斯杆技术,在旋转盘击拉伸试验机上测试了双相20Cr钢冲击拉伸应力一应变曲线,研究了应变速率及组织对动态力学性能的影响.结果表明,双相20Cr钢是一种应变速率敏感材料,在相当高应变速率下仍可保持高的初始加工硬化率并具有较大的应变速率敏感系数,正是这种特性维持了双相20Cr钢在冲击戴荷作用下的高强度、塑性水平.马氏体相的加入使体铁素体晶粒明显细化,马氏体对强度的贡献主要通过增加强化相比例和使其体铁素体相强化而获得.     

Microstructures and properties of 550 MPa grade high strength thin-walled H-beam steel

The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.     

Lamella Multiple Grained Structure Making 2205 Duplex Stainless Steel with Superior Strength and Ductility

We demonstrate a 2205 duplex stainless steel (DSS) synthesized by aluminothermic reaction and followed two-step rolling which had a superior yield strength of 863 MPa,ultimate tensile strength of1 103 MPa and an elongation of 21% at room temperature.The phase,grain size and distribution of the steel were characterized by optical microscope,X-ray diffraction,electron back-scatter diffraction and transmission electron microscope.The results show that the steel consists of lamellar ferrite and austenitic phase with multiple grain size distribution from nanoscale to microscale.The high strength is attributed to strengthening of high back stress arising from laminated dual-phase heterogeneous ultrafine grained structure and distribution.The high ductility originates from back-stress hardening and dislocation hardening.     

碱性激发钢渣水化活性的研究

介绍了采用各种碱性激发剂对转炉钢渣水化活性激发情况,用90%钢渣、5%碱性激发剂、5%无水石膏混合配制钢渣水泥时发现:采用含Na2SiO3的固体复合激发剂可以获得和水玻璃相近的激发效果,其中28 d的抗折强度为3.7 MPa,抗压强度为17MPa,采用固体碱性激发剂激发10%熟料、40%高炉矿渣和40%钢矿渣水泥样品的抗折强度和抗压强度可以达到5.2,24 MPa.     

500MPa级钢筋混凝土偏心受压柱受力性能的试验研究

通过对9根350 mm×200 mm×2200 mm 500 MPa级钢筋混凝土偏心受压柱受力性能的试验,分析了偏心受压柱荷载—挠度曲线、荷载—钢筋应变曲线、荷载—混凝土压应变曲线以及破坏形态的特点.试验研究结果表明,500 MPa级钢筋在柱中与混凝土协同工作性能较好,其强度得到了充分发挥.在试验和理论分析的基础上,提出了500 MPa级钢筋在混凝土柱中的强度设计取值fy=450 MPa和受压承载力计算公式的建议.     

HRBF500钢筋混凝土大偏心受压柱承载力的试验研究

通过对7根HRBF500钢筋混凝土偏心受压柱和1根HRB400钢筋混凝土偏心受压柱的试验,对500MPa细晶粒钢筋混凝土偏压柱性能有了初步了解.分析了荷载-钢筋应变、混凝土应变曲线以及破坏形态的特点.试验研究表明：500 MPa细晶粒钢筋和普通的HRB400钢筋一样,当作为受力主筋用于受压构件时,其强度能得到充分的利用.在试验和理论分析的基础上,提出了HRBF500钢筋在混凝土柱中的强度设计取值为450 MPa和受压承载力计算公式的建议.     

钢丝增强AZ91复合材料的力学性能

为了提高AZ91镁合金的力学性能,采用浸入铸造法制备了体积分数为3.3%的不锈钢纤维增强AZ91复合材料,并在相同条件下对AZ91及其复合材料进行了热挤压处理.采用扫描电镜（SEM）和力学性能试验机分别对铸态和挤压态材料的显微组织、断口和拉伸性能进行了研究.结果表明：铸态AZ91及其复合材料的抗拉强度分别为250和240MPa.然而经过挤压后,钢丝增强AZ91镁合金的屈服强度和抗拉强度分别达到了375和428.6MPa,与挤压态AZ91和铸态AZ91复合材料相比,分别提高了50%、20%和57.6%、78.6%.同时挤压态复合材料的塑性变形量也显著提高.     

Effects of Strain Rate on the Mechanic Performance of Lattice Materials

Split Hopkinson pressure bar (SHPB) was utilized to explore the effects of loading strain rate on the dynamic compressing strength of the titanium alloy lattice material.Results reveal that the yield strength of alloy lattice material reaches 342 MPa initially and then drops to 200 MPa before it rebounds to 252 MPa while the loading strain rate correspondingly increases from the static value 1 401/s to 2 084/s.Numerical simulations were then carried out to explore the possible reason underlying.Results show that the lattice structure changed the stress distribution and caused significate stress concentration at finite strain with high strain rate.It is believed that the strain rate strengthening effect and layer-wise failure mode are the main reasons of the above mechanical properties change.     

Effects of annealing temperature on the microstructure and properties of the 25Mn-3Si-3Al TWIP steel

Microstructures and mechanical properties of the 25Mn twinning induced plasticity (TWIP) steel at different annealing temperatures were investigated. The results indicated that when the annealing temperature was 1000°C,the 25Mn steel showed ex-cellent comprehensive mechanical properties,the tensile strength was about 640 MPa,the yield strength was higher than 255 MPa,and the elongation was above 82%. The microstructure was analyzed by optical microscopy (OM),X-ray diffraction (XRD),and transmission electron...     

耐热铸钢GX12的组织与力学性能分析

对耐热铸钢GX12的组织性能进行分析研究,为该材料的推广和应用提供一些基础参数。文中对耐热铸钢C-X12进行热处理、常温拉伸和高温托伸试验,常温下GX12钢的抗拉强度807MPa,在550℃、600℃、650℃、700℃下GX12钢抗托强度分别为565MPa、505MPa、410MPa、315MPa,研究结果表明：经正火＋高温回火获得的组织为吲火板条马氏体组织;通过与不锈钢（ZG0Cr13Ni4Mo）和碳素钢（ZG20MnSi）的对比,GX12耐热铸钢具有良好的高温力学性能,对高温断口扫描分析,GX12钢在高温下的断裂方式为韧性断裂,随温度升高其塑性提高。