用超声波试验评价铸铁

铸铁的机械性能和显微组织可以用超声波测量和图象分析仪测定。超声速度随着石墨从球状演变到片状而降低。区分高强度铸铁(如球铁、具有球墨的蠕铁)与灰铁以及典型蠕铁的速度值约为5300米/秒,在声速≥5300米/秒,石墨形状系数K≥35%的情况下,声速与石墨形状系数之间存在着线性关系,如基体中珠光体数量不变,机械性能与超声速度之间也存在着精确的线性关系。具有相同石墨形状的铸铁,其基体中的珠光体数量可以通过硬度试验来检查。超声速度测量和硬度试验结合对间接测量不同石墨和基体结构的高强度铸铁的抗拉强度来说是最满意的方法。     

球墨铸铁QT800-6正火处理工艺研究

利用光学显微镜、硬度试验机、拉伸试验机以及箱式电阻炉设备,研究了不同正火处理工艺对球墨铸铁QT800-6力学性能的影响。结果表明:正火工艺处理后,球铁基体组织中的铁素体向珠光体转变后组织为少量铁素体基体+珠光体+球状石墨。大多数的铁素体转变为珠光体,珠光体数量在基体组织中大大增加,正火温度860℃保温1 h风冷获得的球墨铸铁具有良好的综合力学性能。     

关于提高球墨铸铁焊缝强度问题的探讨

本文通过试验和分析,探讨了球墨铸铁正火焊缝强度较低的原因。指出,焊缝快速冷却的固有特征,使焊缝中存在大量、细小的石墨球,为基体中的碳在正火冷却时向石墨球表面扩散沉淀,创造了极好的条件,使焊缝基体中的碳含量降低,促使奥氏体向铁素体转变。文中还指出,在焊缝中加入适当的Cu、Mo、Mn、Ni、Sn等元素使基体合金化,是增加正火焊缝中的珠光体含量和提高强度的有效方法,并可达到与珠光体球墨铸铁(如QT60-2)等强度的要求。     

激光表面淬火对铬钼铸铁组织和硬度的影响

采用TH-3DC3000型激光加工系统对铬钼铸铁进行了激光表面淬火处理,研究了不同激光功率和扫描速度对铬钼铸铁显微组织、表面硬度及硬化层深度的影响。结果表明,经激光表面淬火后,铬钼铸铁的组织由硬化区、过渡区和基体3个区域组成,硬化区组织为隐晶马氏体、残留奥氏体和球状石墨,过渡区组织为隐晶马氏体、珠光体和球状石墨,基体组织为铁素体、珠光体和球状石墨。在激光表面淬火未对试件产生过热影响时,激光功率的增大和扫描速度的降低均会提升铬钼铸铁的表面硬度和硬化层深度。在5 mm×20 mm的矩形激光光斑下,确定最优的参数组合为激光功率2300 W、扫描速度0.003 m/s,采用该参数组合对铬钼铸铁进行激光淬火处理时,表面硬度为760 HV0.3,硬化层平均硬度为724 HV0.3,硬化层深度可达1.4 mm以上。     

大断(丆口)球铁铸件

一、大断(丆口)球铁件的显微组织通常薄壁铸件中球状石墨形成很好,石墨分布于珠光体,铁素体或者混合体(珠光体+铁素体)基体中。增加铸件壁厚,不仅在凝固期间,而且在γ—α转变期间都会降低冷却速度。这样便导致石墨形状与尺寸的变化,同时也必然影响金属基体和机械性能的变化。     

低温正火工艺对球墨铸铁显微组织的影响

对球墨铸铁进行低温正火,研究了保温时间对球铁中石墨及基体组织的影响。结果表明,随着保温时间的延长,球状石墨的圆整度提高,保温2 h后,点状石墨基本全部溶解。基体中铁素体的破碎程度随着保温时间的延长而提高,珠光体数量增多,但保温时间超过2 h后,基体组织没有明显变化。     

球墨铸铁低温冲击韧性的研究

研究了球墨铸铁基体组织中珠光体率和石墨数量对其硬度以及低温 (-20℃) 冲击韧性的影响.研究结果表明,随着珠光体率的增加,球墨铸铁硬度增加,但低温冲击韧性下降;对于铸态和正火态球铁,石墨数量对基体硬度和U形缺口低温 (-20℃) 冲击韧性几乎没有影响.对于退火态球铁,随着石墨数量的增加,-20℃冲击韧性值显著增加;当石墨数量达到400个/mm~2时,其U形缺口冲击韧性达29.0 J/cm~2,是铸态的3倍.     

铸铁的机械性能和声速的关系

一、绪言铸铁的机械性能随着其显微组织中的石墨量及形状、基体组织中的珠光体及铁素体量而变化。近来,随着无损检测的应用,尤其是声速(超声波)测定探头和超声波接收放大器等的推广,应用于衰减显著的材质成为可能,已经在铸铁中广为采用。     

热处理对高镍铬离心复合铸造球墨铸铁轧辊组织与性能的影响

采用热膨胀法测定了高镍铬离心复合铸造球磨铸铁轧辊的相变点,根据其临界转变温度,进行正火和回火试验,研究了热处理工艺对轧辊工作层性能的影响。结果表明,860℃和890℃正火时,轧辊工作层硬度值较高;正火温度为920℃时,冷却后残留奥氏体(Ar)量增多,硬度明显下降;正火温度为830℃时,出现硬度较低的珠光体组织。860℃正火冷却后,在400℃回火时应力消除比较完全,碳化物尚未长大,细小且均匀弥散的分布在针状马氏体基体上,轧辊工作层硬度较高,有利于阻止裂纹的扩展。     

中国蠕墨铸铁40年(三)

(接上期)5蠕铁的热处理灰铸铁的性能主要取决于其片状石墨,热处理不能显著改变石墨形态,因而热处理对于改变灰铸铁材质性能(除硬度外)潜力不大;球化良好的球铁之性能主要取决于基体组织。热处理可改变其基体组织,因而热处理使球铁的用途大大扩展了。然而球铁不具备灰铸铁的许多优点。蠕铁具有灰铸铁的一些特点,是否也具有像球铁那样可通过热处理大幅度改变其材质性能的优点呢?犤58,155—159犦犤160—168犦的研究表明,蠕铁通过淬火、淬火-回火、等温淬火和正火处理,分别可获得淬火马氏体、回火马氏体、下贝氏体、索氏体和珠光体基体组织,从而…     

30CrMnSiA钢回火组织对超声信号影响的试验研究

30CrMnSiA钢具有较高的强度和良好的韧性，是重要的飞机结构受力部件，常在淬火后不同温度回火处理状态下使用。本研究取淬火态的30CrMnSiA钢在200~700 ℃进行回火，观察其金相组织，并使用超声检测方法对不同回火组织进行检测，分析超声波传播特征（纵波声速、声衰减系数、底波频移）与回火温度、组织变化之间的关系。结果表明:随回火温度提高，30CrMnSiA组织依次为回火马氏体、回火屈氏体、回火索氏体、铁素体+珠光体，硬度逐渐降低；受回火脆性的影响，在540~620 ℃回火得到的回火屈氏体超声检测特征参数值呈大幅度波动；其他回火组织进行超声检测时，随回火温度的升高，超声声速呈增大趋势，底波频移呈下降趋势。     

超声波检测球铁球化率方法的研究与应用

介绍了超声波检测球化率的基本原理以及超声波声速与石墨形态关系,分析出球墨铸铁声速的影响因素是球化率、石墨大小和基体组织,通过数据统计以及回归分析得出球化等级与声速之间的关系:1级声速5 680~5 820 m/s、2级声速5 620~5 680 m/s、3级声速5 560~5 620 m/s、4级声速5 500~5 560 m/s、5级声速5 440~5 500 m/s、6级声速小于5 440 m/s。在不同时间分别对其中15个铸件进行了3次检测,结果显示,声速法测定球化率与金相法测定的球化率相吻合。     

超声波检测球化率的研究与应用

采用超声波穿透法对铸件进行检测,耦合方法为液浸法,并适当提高探测灵敏度以补偿零件与耦合液之间的衰减。选用压电晶片较大、频率为5MHz的纵波直探头来检测零件的球化率。金相组织分析表明:石墨的球状越好,超声波的传播速度越快。     

Relationship between ultrasonic characteristics and mechanical properties of tempered martensitic stainless steel

This research studied the relationship between the ultrasonic characteristics and the mechanical properties of tempered CA-15 martensitic stainless steel (MSS). The results show that, for as-quenched specimens, a chromium carbide film at the martensitic boundary of the as-cast specimen will disappear causing a change in the mechanical properties (e.g., the tensile strength is decreased or the hardness and the toughness are increased). For the tempered MSS, the correlation of the ultrasonic velocity and the tensile strength, hardness, and toughness is not obvious. However, there is a highly positive correlation with the elastic modulus (E) of the material. For the ultrasonic attenuation evaluation, the attenuation coefficient (α) has a positive correlation with the tensile strength and the hardness, while there is a negative correlation with the toughness and the elongation. Also, a higher-frequency probe would cause the better sensitivity, but the data are relatively dispersed.     

铸铁件的超声波检测

介绍了超声波探伤原理及铸铁件超声波探伤特点,常见缺陷波形以及超声波传播速度与球化率,力学性能的关系。     

Evaluation of mean grain size using the multi-scale ultrasonic attenuation coefficient

An evaluation model based on the multi-scale ultrasonic attenuation coefficient was developed to control both systematic error and random error. AISI 304 stainless steel was used to validate the presented model. Wavelet transformation was used to obtain the variation of ultrasonic signal over time and scale. Particle swarm optimization was utilized to correlate the coefficient with grain sizes. The model shows the attenuation of all scales increased with the grain size, and ultrasound attenuates faster on smaller scales. Compared with the ultrasonic velocity method and the traditional attenuation method, the proposed method has less systematic error and random error.     

Evaluation of material properties of 3Cr-1Mo-0.25V steel by magnetic, electrical and elastic properties

The magnetic, electrical and elastic properties of 3Cr-1Mo-0.25 V steel were investigated using heat treatment procedures (as-quenched→tempered→PWHT). The mechanical properties were determined for the respective specimens with three types of heat histories. The mechanical properties (yield stress, hardness) and magnetic properties (permeability, coercive force, remanence) were inversely proportional to the heat treatment procedures. The permeability decreased linearly with an increase in the grain size; however, the yield stress, hardness, coercive force and remanence did not vary greatly with grain size. The electrical resistivity and ultrasonic velocity of the as-quenched material differed from those of the tempered/PWHT material. This trend was due to the defects, precipitates and carbides in the grain and at the grain boundary caused by the heat treatment procedures. However, the electrical resistivity and ultrasonic velocity did not vary greatly with grain size.     

Characterization of the sensitization degree in the AISI 304 stainless steel using spectral analysis and conventional ultrasonic techniques

Specimens of AISI 304 stainless steels exposed to sensitization and carbide solution heat treatment employing ultrasonic testing have been evaluated. The study involved measurements of the longitudinal wave velocity, attenuation and spectral analysis. Despite the large size difference between the ultrasonic wave length and the precipitated carbides, the results showed a clear attenuating effect in the sensitized specimens. This effect suggests a relation between carbide precipitation in the material and the attenuation coefficient of the ultrasonic wave. The attenuation increase is mainly attributed to the continuous distribution and possible coalescence of the carbide along the grain boundaries. Power spectra exhibit an increase of the amplitude at specific frequencies in specimens with the longest sensitization times. Ultrasonic velocity measurements did not provide significant information in order to predict any sensitization grade of the evaluated materials. The combined assessment by spectral analysis and attenuation measurements is discussed.     

颗粒增强铝基复合材料的超声表征

用粉末冶金方法制备了两种碳化硅增强铝基复合材料,其中制备两种复合材料所用的碳化硅颗粒和铝合金粉末的粒度比不同。分析了两种复合材料热压态和挤压态在径向和轴向的声速、衰减和草状回波的异同。结果表明,利用超声波的声速、衰减和草状回波,对粉末冶金方法制备的复合材料的微观组织进行无损表征是可行的。复合材料声速和草状回波可以用来反映复合材料各向异性,其中草状回波还可以反映复合材料碳化硅颗粒的分布均匀性,而超声波的衰减则对热挤压工艺比较敏感。     

Role of spheroidized carbides on the fatigue life of bearing steel

The fatigue characteristics of bearing steel in ultrasonic fatigue tests are investigated with regard to the role of spheroidized carbides. The results show that, despite a similar hardness level, the bearing steel with spheroidized carbide has a much longer fatigue life than steel without, and that the failure mechanism differs in each case. All the samples of SAQT-processed steel examined using ultrasonic fatigue tests were characterized by a conventional fish-eye structure, which implies they went through subsurface-originated or interior inclusion-induced failure. On the contrary, it was shown that surface-induced failure prevailed in the QT-processed steel without spheroidized carbide. The results suggest spheroidized carbide may strengthen the tempered martensitic matrix of the bearing steel and concentrate the stress around an inclusion rather than at the surface, allowing for prolonged fatigue life over the steel without spheroidized carbide.