9SiCr淬火裂纹原因分析及解决办法

为解决9SiCr在淬火过程中所产生的裂纹问题,对9SiCr淬火裂纹钢件进行了取样,分析了其化学成分、硬度值、金相组织、裂纹形貌与非金属夹杂物.结果表明,9SiCr钢件在淬火过程中所产生裂纹是钢材中存在非金属夹杂物和球化退火不均匀所导致钢材的内应力在与淬火过程中的热应力和组织应力的共同作用下产生的,于是提出了解决办法,有...     

界面热失配对金属基复合材料力学性能的影响

由于金属基体和增强相的热膨胀系数存在差异，金属基复合材料在制备降温过程中不可避免地产生热失配应力。研究表明，金属基复合材料热失配应力在近界面处以不同类型金属缺陷的形式进行释放，在远离界面处以热残余应力的形式保留。热失配应力释放的缺陷类型、尺寸、密度以及热残余应力的存在均会显著影响金属基复合材料的力学性能。本文阐述了界面热失配缺陷和热残余应力的产生，详细分析了界面热失配对金属基复合材料力学性能的影响，为进一步实现金属基复合材料的界面结构设计和优化提供理论基础和科学依据。     

P110级石油套管淬火组织形态对残余应力的影响

以降低P110级石油套管淬火冷却过程中的热应力和组织应力为目的,提出了水淬+空冷和水淬+空冷+水淬两种冷却方式。利用逐层钻孔法测试了不同工艺下的残余应力,分析了淬火组织特征和残余应力对裂纹产生和扩展的影响。结果表明:直接淬火工艺的淬火组织为板条马氏体和孪晶马氏体共存,且孪晶马氏体的含量较多。水淬+空冷和水淬+空冷+水淬两种工艺的淬火组织为板条马氏体、下贝氏体和不同程度的残余奥氏体,水淬+空冷+水淬工艺中还有少量孪晶马氏体。水淬+空冷、水淬+空冷+水淬两种冷却方式和直接淬火工艺相比,钢管内的切向和轴向残余应力均减小,从而易减小钢管的变形,以及降低和缓解了钢管内微裂纹的产生和扩展趋势。     

淬火温度对86CrMoV7钢抗接触疲劳性能的影响

冷轧辊接触疲劳剥落是在接触负荷下表层疲劳裂纹萌生扩展的断裂过程,与组织结构和内应力状态有关,是主要失效方式之一。本文研究淬火温度对86CrMoV7钢抗接触疲劳性能的影响。选择840、870、910和950℃四个淬火温度。测定了试样的接触疲劳寿命、硬度、残余应力和残余奥氏体量。并对金相组织、裂纹形貌及剥落断口进行了观察。研究发现,840℃淬火有最高的接触疲劳寿命;硬度和疲劳寿命有一定的对应关系,硬度为62～63HRC时接触疲劳寿命最高,更高的硬度反而使之下降。残余应力与疲劳寿命的关系较为复杂。金相组织对钢的接触疲劳寿命有重要作用:板条马氏体组织比片状马氏体组织抗接触疲劳性能好,适量的残余奥氏体可改善钢的抗接触疲劳性能。不同的裂纹及断口形貌对应不同的接触疲劳寿命。     

304不锈钢烘筒应力腐蚀失效分析

采用金相观察和扫描电镜分析的方法对304不锈钢烘筒筒壁在工作过程中发生的裂纹失效样品进行了研究。结果表明,该裂纹是典型的应力腐蚀裂纹,产生原因是由于材料本身对含Cl^-的腐蚀介质敏感,在残余应力的作用下产生了应力腐蚀裂纹。     

22CrMo钢渗碳淬火过程组织与应力变化的数值模拟

 根据描述渗碳过程的数学模型,利用有限差分法,对22CrMo钢圆柱体试样渗碳过程进行了数值模拟,得出渗碳层中碳浓度分布。基于渗碳模拟结果,根据描述淬火过程的数学模型,利用有限元法对试样淬火过程的温度场、组织场及应力场进行了数值模拟,分析了淬火过程中组织和内应力变化,及渗碳过程对淬火过程组织及应力变化的影响。对渗碳淬火后试样的组织进行了金相分析,并测量了表面和内部各点残余应力,计算值和测量值相吻合。     

42CrMo贯通轴产生裂纹原因分析

42CrMo圆钢在加工成贯通轴过程中发现裂纹,采用ARL3460直读光谱仪、金相显微镜和扫描电镜对42CrMo贯通轴试样进行分析.分析结果表明,42CrMo贯通轴裂纹为试样在感应淬火过程中产生的淬火裂纹.     

齿轮钢淬火过程多场耦合分析

利用有限元分析软件MSC.Marc,结合热弹塑性模型和编写的用户子程序,对(%)0.21C-1.03Cr- 0.20Mo0.03Nb齿轮钢圆柱体淬火过程的温度、组织和应力场进行了多场耦合分析。结果表明,淬火过程产生的内 应力促进马氏体相变,在马氏体相变的情况下,组织应力强于热应力,使淬火后工件的残余应力呈组织应力分布。 测量值和计算值对比表明,淬火过程应力场数值模拟中,考虑应力与相变的相互作用,使计算结果更为精确。     

42 CrMo轴轮套加工过程中产生裂纹原因分析

42CrMo圆钢在加工成轴轮套过程中,镗孔时发现裂纹,采用ARL3460直读光谱仪、金相显微镜和扫描电镜对42CrMo轴轮套试样进行分析。分析结果表明,42CrMo轴轮套裂纹为试样在调质过程中,由于淬火内应力过大产生沿晶淬火裂纹。     

TA15钛合金高温持久腐蚀行为研究

为深入分析热盐应力腐蚀对TA15钛合金高温性能的影响,对大规格TA15钛合金棒材进行不同的表面腐蚀处理,测试了500℃/470 MPa条件下的持久性能,并对试样表面、断口处的组织特征进行观察,分析TA15钛合金的热盐应力腐蚀机制。结果表明：在500℃/470 MPa下,TA15钛合金对热盐应力腐蚀非常敏感,导致持久寿命显著降低;在腐蚀过程中,沿着α相界(β基体)发生复杂的化学反应,形成腐蚀氧化物并向内扩散;应力作用加速了腐蚀裂纹扩展,形成沿晶断裂特征,降低了试样的持久寿命。     

Numerical Analysis of Stake Mark Induced Failure of a Rotor Shaft

In this paper, the stake mark induced failure of a generator rotor forging is analysed using finite element analyses in combination with a Cockroft & Latham failure model. Evidence is found from damage analysis that the rotor failed due to micro cracks and residual stresses induced by a double stake mark, which was located at a position subject to concentrated rotating‐bending stress amplitudes and torsional mean stress. The analysis presented here verifies the results of the damage analysis by showing that the stake mark configuration of the failed rotor was the most detrimental among a number of similar configurations. According to the finite element analysis, this stake mark configuration combines a high probability of inducing propagating sub‐surface micro‐cracks with considerable tensile residual stresses.     

Neutron diffraction and finite element analysis of quenching residual stress of GH4169 super alloy

The quenching process is indispensable for manufacturing the superalloys. However, high residual stress is inevitably induced by the large heat gradient, which influences the mechanical properties of the alloys. Therefore, it is of great significance to accurately characterize the internal residual stress of the super alloy and establish an effective finite element modeling. The quench- induced residual stresses of GH4169 super alloy were measured using neutron diffraction stress instrument. The results show that the center of the workpiece is subjected to tensile stress in three directions (hoop, radial and axial), which is about 400MPa. The rims of workpiece are subjected to compressive stress in one or two directions (hoop or axial), which is from -300MPa to -400MPa. The temperature and strain/stress fields of the GH4169 super alloy workpiece during quenching process were simulated by a 3D finite element model. The calculated residual strain/stress at the center and rim of the workpiece are compared to those by neutron diffraction, which shows good correspondence. These data provide reliable evidences to the formation of the residual stress during quenching.     

Residual stress analysis in galvannealed coating

The galvannealing process results in thermal residual stress in zinc–iron alloy coating on steel substrate due to differential thermal behaviour of the coating and the substrate. The magnitude of biaxial tensile residual stress generated just after cooling has been estimated theoretically and the value is found to be high enough to cause through-thickness cracks in the coating. Energy model has been adopted to determine the distribution of cracks and crack spacing in the galvannealed (GA) coating. The same was investigated from the microstructural analysis using scanning electron microscope. It is shown that the estimated crack spacing is always lower than the actual values. Subsequently a stress field develops around each crack tip which induces a non-uniform triaxial stress state in the coating.     

中锰钢高温热塑性研究

采用真空感应炉熔炼中锰钢,经铸铁模冷却至室温铸锭内部存在大量的微观裂纹,实验表明中锰钢高温热塑性极差。而采用铸铁模冷却至700℃后,置于700℃马弗炉随炉冷却至室温铸锭内部微观裂纹消失。将试样经过热轧锻造后,中锰钢的热塑性较为良好。研究表明铸锭中柱状晶发达以及凝固过程产生的微观裂纹是造成热塑性极差的主要原因,铸铁模快冷引起的热应力和铸锭完全凝固700℃以后相变应力是造成铸坯内部裂纹的主要因素。生产过程推荐采用结晶器、二冷段相对弱冷工艺措施降低铸坯产生裂纹风险性。     

Forming Limit Curve (FLC) and Fracture Mechanism of Newly Developed Low‐Carbon Low‐Silicon TRIP Steel

The Forming‐Limited Diagram (FLD) of intercritically annealed 0.11C‐1.65Mn‐0.62Si TRIP‐assisted steel was investigated. The high FLD₀ value of this new low carbon TRIP steel was indicative of a superior formability. The micro‐structural changes during deformation and fracture were studied in detail. The polygonal ferrite phase was found to plastically deform first and deformed most at larger strains. Fracture was initiated by micro‐voids nucleated at ferrite grain boundaries, within ferrite grains or at the interface between ferrite and the harder phases. Cracks were formed after micro‐voids grew, coalesced, and expanded in one direction. When crack tips reached the bainite phase or the martensite/austenite constituent, the cracks propagated along the boundary of these phases. Cracks reaching retained austenite islands caused stress‐induced martensite transformation at the crack tip. The direction of motion of the cracks also changed in this case.     

调质高强钢探伤不合原因分析

针对离线调质工艺生产的高强钢探伤不合问题,通过对缺陷反射波波形图解读,借助金相、扫描电镜和能谱分析,认为钢板中MnS夹杂在热处理时的体积变化和组织应力作用下形成的微裂纹、超长B类夹杂物是造成探伤不合的主要原因。     

Reduction of Residual Stress and Improvement of Dimensional Accuracy by Uphill Quenching for Al6061 Tube

The purpose of this study is to reduce the residual stress and machining distortion of an Al6061 tube by using uphill quenching. During uphill quenching, solid-solution heat-treated aluminum parts are usually immersed in LN₂ at 77 K (?196 °C), followed by the rapid heating of the parts, to produce a new residual stress that is opposite in nature to the original. The uphill quenching method used in this study employed two types of heating methods: boiling water at 373 K (100 °C) and high-velocity steam at 448 K (175 °C). First, FE-simulation coupled with a CFD analysis was performed to predict the residual stress of the backward hot-extruded Al6061 tube with the following dimensions: Ø200 mm × h200 mm × t10 mm. Experiment of uphill quenching was also conducted to measure the residual stress using the boiling water and high-velocity steam uphill quenching methods. The predicted residual stresses were compared with the experimental results obtained via micro-indentation and saw-cutting tests, and a deviation of about 10.4 pct was found. In addition, the experimental results showed that uphill quenching could relieve up to 91 pct of the residual stress induced by water quenching. Finally, the dimensional accuracy of uphill quenched tubes was evaluated by measuring the roundness after the machining process, which showed that the uphill quenching method could improve the dimensional accuracy of an Al6061 tube by reducing the residual stress.     

Fatigue and fracture of high-alloyed steel specimens subjected to purely thermal cycling

High-alloyed steel specimens subjected to hundreds of thermal cycles (heating up in a furnace to about 900 °C, quenching in water, resting in air) are considered. Contrary to standard “low-cycle fatigue” tests with a cyclically varying applied mechanical load, the driving “force” is a cyclic temperature field with self-equilibrating residual stress states. Despite the cyclic character of this temperature field and no applied load, a significant monotonie change of the shape and metallurgical structure of the specimens can be observed depending strongly on the material and the initial geometry. Precipitations along the grain boundaries and remarkable residual stress states are responsible for internal cracks and damage. An experimental program is reported, and metallurgical and mechanical interpretations are presented.     

基于微晶刚玉砂轮的20CrMnTi齿轮成型磨削表面完整性

为研究微晶刚玉砂轮成型磨削20CrMnTi齿轮的表面完整性,开展了20CrMnTi齿轮成型磨削试验,分析了砂轮线速度、轴向进给速度及径向进给量对齿面粗糙度、表层/次表层显微硬度、微观组织和残余应力的影响规律,探讨了由磨削引起的磨削烧伤、微观裂纹等损伤缺陷的形成机理,结果表明:径向进给量对表面粗糙度的影响最显著,砂轮线速度次之,轴向进给速度最不显著;磨削温度过高会导致磨削烧伤,淬火烧伤使得表面硬度提高5%~20%,回火烧伤则导致表面硬度不同程度地下降;表层组织从外至内分别为白层、暗层和基体组织,白层主要由致密的马氏体+碳化物+残余奥氏体组成;砂轮线速度和径向进给量的增大使得由磨削引起的残余拉应力增大,表面残余压应力下降并逐渐向拉应力转变,当表面最终残余拉应力大于材料的断裂强度时,表面产生微观裂纹.