0Cr13Ni4Mo马氏体不锈钢表层的喷丸强化

对经1000℃正火和600℃回火的水轮机过流部件用钢0Cr13Ni4Mo进行喷丸处理,测量了喷丸影响层的显微硬度、X射线衍射线半高宽和屈服强度等参量的沿层深分布,并计算了相应的晶块尺寸、微观应变和位错密度等微观结构参量.结果表明,该影响层以显微硬度和屈服强度表征的组织强化效应显著,显微硬度和屈服强度提高是由于晶块细化、微观应变和位错密度增大造成的.喷丸影响层不同部位的显微硬度与条件屈服点之比约为3.37;半高宽与显微硬度之间存在两段式线性关系:Hw=2.07×10-3 HV-3.47(HV<2835 MPa)和Hw=1.14×10-3 HV-0.81(HV>2835 MPa),条件屈服点与位错密度的平方根之间存在Bailey-Hirsch线性关系: σ0.2S=551+16.2×10-4ρ1/2.

低碳马氏体不锈钢0Cr13Ni4Mo磨削表层屈服强度的研究

借助X射线应力分析技术测量了屈服强度在马氏体不锈钢0Cr13Ni4Mo磨削影响层上的分布,同时测量或计算了残余应力、X射线衍射线半高宽、显微硬度、嵌镶块尺寸、微观应变和位错密度等参量的沿层深分布。结果表明,该影响层的屈服强度大幅度提高了,与用半高宽和显微硬度比较起来,用屈服强度作指标能够更好地反映磨削影响层的强化。磨削表面的条件屈服强度提高了约50%,嵌镶块尺寸从约64nm减小到约28nm,微观应变从约7×10-4增高至约14×10-4。磨削影响层的条件屈服强度σ0.2与位错密度的平方根之间存在线性关系。这些结果说明,磨削表面发生了严重的塑性形变。冷作塑性形变强化是磨削影响层的屈服强度得以提高的根本原因。

HRB400热轧带肋钢筋盘条无屈服现象问题的解决方法

分析了在高速线材生产线上生产HRB400热轧带肋钢筋盘条过程中出现力学检验时应力-应变曲线无明显屈服现象问题的原因,据此调整生产工艺后,成功解决了这一问题的方法。

Research and modeling on correlation among microstructure,yield strength and process of bainite/martensite steel

The contributions of different strengthening mechanisms to yield strength of bainite/martensite multiphase rail steel with different finish cooling temperatures in the controlled cooling process were quantitatively investigated.Dislocation density and substructure size of the rail steel were measured by scanning electron microscopy,electron backscatter diffraction and X-ray diffraction.The results show that the dislocation density increases with the decrease in block width in rail steel.Based on the correlation among dislocation density,block width and yield strength,a physical model was proposed to predict the yield strength of rail steel.The variation of block width and dislocation density in different positions of rail head microstructure was integrated with temperature field simulation.Dislocation density and block width reveal significant correlations with the finish cooling temperature.

针状铁素体对含铌HRB400钢筋屈服行为的影响

对比研究成分为20MnSiV和16MnVNb的HRB400钢筋的屈服行为,在同一轧制工艺条件下,与含钒钢筋相比,含铌钢筋应力-应变曲线没有明显的屈服平台。对试验钢的化学成分、显微硬度进行测试分析,利用光学显微镜、扫描电镜和透射电镜对试验钢的微观组织进行观察。结果表明,20MnSiV试验钢组织主要为铁素体+珠光体组织,16MnVNb的组织为等轴状铁素体+珠光体+针状铁素体,其中针状铁素体周围珠光体退化明显。针状铁素体的显微硬度介于珠光体与铁素体之间,其内部存在高密度位错。针状铁素体组织的大量存在是导致含铌HRB400钢筋无屈服平台的原因。

终轧后冷待对高层建筑用钢板屈强比的影响

通过透射电镜、扫描电镜和电子背散射衍射(EBSD)等分析方法和力学性能测试,研究了终轧后冷待对Nb微合金试验钢屈强比的影响。结果表明,终轧后冷待可以增大铁素体晶粒尺寸,减少铁素体晶粒内位错密度,影响珠光体球团片层的分布,增大碳化物片层的厚度,降低屈强比。当冷待至770℃时,试验钢屈强比由未冷待的0.765降低至0.739;当冷待至730℃时,屈强比降低至0.724。考虑到强度的综合要求,确定试验钢的最佳冷待温度为(770±10)℃。

Tensile deformation behavior of high strength anti-seismic steel with multi-phase microstructure

To investigate the tensile deformation behavior of high strength anti-seismic steel with multi-phase microstructure,tensile tests with strains of 0.05,0.12 and 0.22 were performed at room temperature.Microstructure of tested steels was observed by means of optical microscopy（OM）,transmission electron microscopy（TEM）and scanning electron microscopy（SEM）.Tensile mechanical properties of tested steels were obtained,and the influence of bainite content on deformation behavior was also discussed.Meanwhile,the deformation mechanism of steel with three kinds of microstructures of bainite,pearlite and ferrite was analyzed.Results show that tested steel with high volume fraction of bainite exhibits a continuous deformation behavior,and this may be attributed to a higher bainite volume fraction and a lower mobile dislocation density.The morphology of microstructure will influence the mechanical properties of tested steels.An increasing content of bainite can improve the tensile strength,but reduce the plasticity and toughness of the tested steels.In the deformation process of 0.039 Nb steel,the ferrite and bainite have priorities to deform,and the deformation exhibits co-deformation of all microstructures in the later stage of deformation.In the deformation process of 0.024Nb-0.032 Vsteel,the ferrite and pearlite have priorities to deform,and the deformation exhibits co-deformation of all microstructures in the later stage of deformation.

Creep deformation and strength evolution mechanisms of a Ti-6Al-4V alloy during stress relaxation at elevated temperatures from elastic to plastic loading

In this study, the stress relaxation(SR) behaviors of a Ti-6Al-4V alloy pre-loaded from elastic to plastic regions and corresponding strength evolution mechanisms at different temperatures were systematically studied. In order to quantitatively analyze the detailed deformation and strength evolution mechanisms during the whole SR tests, which is composed of the loading stage and subsequent SR stage, the evolutions of α/β structures and dislocations have been identified by a series of microstructural observations,i.e., scanning electron microscopy(SEM), electron backscatter diffraction(EBSD), high resolution transmission electron microscopy(HRTEM), energy dispersive spectroscopy(EDS). A great quantity of entangled dislocations in α phase introduced by the plastic loading at temperatures below 800 °C promotes the emergence of SR behavior with a higher creep rate, leading to the much higher SR level with larger pre-load levels. Diffusion is significantly enhanced by dislocations accumulated at interfaces with higher temperatures(> 800 ℃), contributing to a similar SR phenomenon under different initial strain levels.Apparent strength loss has been observed after SR with high temperatures or pre-loaded to the plastic region, e.g., 94 MPa loss for 800 °C, pre-loaded with a stain of 10% and SR for 2400 s. The strength loss mainly comes from the loading stage where distorted and fragmented β layers occur. The subsequent SR stage facilitates interfacial diffusion and results in a higher fraction of granular β phases, leading to a further decrease in yield strength(YS). This study enhances the understanding on the deformation and strength evolution mechanisms of titanium alloys with lamellar structures in the whole SR process, providing a physical foundation for optimizing the processing parameters for manufacturing titanium alloy components with high accuracy and performance.

两相区QT工艺对低屈强比890 MPa级高强钢组织与性能的影响

研究了低屈强比890 MPa级高强钢在两相区QT处理中组织转变及其对力学性能的影响。通过扫描电镜对热处理态组织进行观察,并结合力学性能与XRD位错密度计算分析回火温度对组织性能的影响,进一步通过Gleeble热模拟试验结果分析淬火温度对组织性能的影响。结果表明,两相区QT处理态组织为铁素体+回火板条状组织。随回火温度升高,板条形态逐渐分解,位错强化增量降低,使得抗拉强度降低;软硬相间的协调变形作用使得屈服强度先升高,后随整体位错密度降低而降低,整体波动不大,从而屈强比升高。随淬火温度升高,位错强化增量升高,抗拉强度升高;相变过程中的膨胀量变化升高,软相铁素体占比降低,使得屈服强度升高,屈强比升高;硬相回火板条状组织占比增加,低温韧性降低。