Interface and Bond Strength of Brazing Cemented Carbide K20 to Alloy Steel AISI 4140 by High-Frequency Induction

High-frequency induction brazing of cemented carbide (WC–Co, K20) and alloy steel (AISI 4140) using Cu–Zn base filler metal was carried out. The relationship between microstructure and performance of the welding joint was investigated. It was found that the filler metal exhibited excellent wettability and metallurgical bond in the welding surface. As the heating rate reduced, welding joint appeared smooth without any visible crack. In the diffusion layer, some intermetallic compounds were observed, which were produced by the reaction of diffusion atoms. The microhardness in the middle of the welding seam was 168 Hv and it increased gradually when approaching to the edge of welding seam. With brazing temperature increased or heating rate decreased, the shear strength of welding joint increased first and then decreased. The machining test clearly revealed that the cutting temperature and the flank wear increased with the cutting speed rose. The welding joint had good shear strength when the temperature was below 500°C and the shear strength decreased seriously when the temperature exceeded 500°C.     

Diffusion kinetics of borided AISI 52100 and AISI 440C steels

In this study, the case properties and diffusion kinetics of AISI 440C and AISI 52100 steels borided in Ekabor-II powder were investigated by conducting a series of experiments at temperatures of 1123, 1173 and 1223 K for 2, 4 and 8 h.The boride layer was characterized by optical microscopy, X-ray diffraction technique and micro-Vickers hardness tester. X-ray diffraction analysis of boride layers on the surface of the steels revealed the existence of FeB, Fe₂B and CrB compounds.The thickness of boride layer increases by increasing boriding time and temperature for all steels. The hardness of the boride compounds formed on the surface of steels AISI 52100 and AISI 440C ranged from 1530 to 2170 HV_0.05 and 1620 to 1989 HV_0.05, respectively whereas Vickers hardness values of untreated steels AISI 440C and AISI 52100 were 400 HV_0.05 and 311 HV_0.05, respectively. The activation energies (Q) of borided steels were 340.426 kJ/mol for AISI 440C and 269.638 kJ/mol for AISI 52100. The growth kinetics of the boride layers forming on the AISI 440C and AISI 52100 steels and thickness of boride layers were also investigated.     

进口E52100轴承钢盐浴热处理、磨削后表面出现凹坑原因分析

由美国进口牌号为E52100、线径为φ1.6mm的轴承钢盘圆,加工成小型精密轴承零件,经中性盐浴热处理并在圆端面磨削到成品要求后,被磨削的表面出现了极细小的黑色凹坑,凹坑数量及位置无规律可循。经光学显微镜和扫描电镜观察及X射线能谱分析后发现,在E52100轴承钢材料基体内部存在着大小不等、形状各异、位置不确定的异常组织颗粒,这些颗粒均含有较高含量的氧元素,为氧化物夹杂;在磨削过程中,这些硬而脆的氧化物颗粒极易从基体中剥落而出现凹坑;这些非金属氧化物夹杂是轴承钢材料中原有的,与盐浴热处理无关。     

Tribological Behavior of AISI52100 Steel After PC/MoS2 Lubricant Surface Modification

Strength of Materials - Bearings, as a key part of a vehicle transmission system, were extensively studied to improve their abrasion resistance and fatigue life. Mixtures of hard ceramic particles,...     

Evolution Behaviors of Oxides in Severely Plastic Deformed Region of AISI 52100 Steel during Dry Sliding Wear

Under dry sliding wear, the evolution of oxides in severely plastic deformed(SPD) regions of metals has a great impact on the wear behaviors. To study the evolution behaviors of oxides in the SPD region, an SPD region was prefabricated on the surface of AISI 52100 steel by supersonic ?ne particle bombarding(SFPB) treatment. Dry sliding wear tests were carried out on both of the SFPB-treated and original samples.Wear volume loss of the SPBF-treated samples were compared with those of the original samples at different loads. Microstructure, element composition and oxides distribution in the SPD region were characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM) and an electron probe microanalysis(EPMA). The results show that the evolution behaviors of the oxides in the SPD region change signi?cantly with the load. Under low loads, oxides are usually formed on the contact surface. It inhibits adhesive wear on the steel. However, under high loads, oxides are apt to distribute along the cracks in the subsurface layer. The internal oxidation along the cracks can accelerate the cracks propagation, resulting in severe delamination wear on the steel.     

Estimation of martensite carbon content in as-quenched AISI 52100 steel by X-ray diffraction

Overlapping martensite doublets have been resolved by approximating each component peak by a Pearson VII function. The Bragg angle difference between the component peaks of the resolved doublet is then used to calculate the carbon content of the martensite based on equations originally proposed by Roberts. The analysis has been applied to both an as-received and thermomechanically processed 52100 steel, heat treated to an as-quenched condition, and the results are in good agreement with hardness and retained austenite data.     

Plasma paste boronizing of AISI 8620, 52100 and 440C steels

In the present study, AISI 8620, 52100 and 440C steels were plasma paste boronized (PPB) by using 100% borax paste. PPB process was carried out in a dc plasma system at temperature of 700 and 800 °C for 3 and 5 h in a gas mixture of 70%H₂–30%Ar under a constant pressure of 4 mbar. The properties of boride layer were evaluated by optical microscopy, X-ray diffraction and Vickers micro-hardness tester. X-ray diffraction analysis of boride layers on the surface of the steels revealed FeB and Fe₂B phases for 52100 and 8620 steels and FeB, Fe₂B, CrB and Cr₂B borides for 440C steel. PPB process showed that since the plasma activated the chemical reaction more, a thicker boride layer was formed than conventional boronizing methods at similar temperatures. It was possible to establish boride layer with the same thickness at lower temperatures in plasma environment by using borax paste.     

Fatigue behaviour of AISI 304 steel to AISI 4340 steel welded by friction welding

In the presented study, The weldability of AISI 304 austenitic stainless steel to AISI 4340 steel joined by friction welding in different rotational speeds and fatigue behaviour of friction-welded samples were investigated. Tension tests were applied to welded parts to obtain the strength of the joints. The welding zones were examined by scanning electron microscopy (SEM) and analyzed by energy dispersive spectroscopy (EDS). The Vıckers microhardness distributions in welding zone were determined. Fatigue tests were performed using a rotational bending fatigue test machine and the fatigue strength has been analysed drawing S-N curves and critically observing fatigue fracture surfaces of the tested samples. The experimental results indicate that mechanical properties and microstructural features are affected significantly by rotation speed and the fatigue strength of friction-welded samples decrease due to chromium carbide precipitation in welding zone with increasing rotation speed in choosen conditions.     

淬火微观组织对重轨钢疲劳裂纹扩展速率的影响

以U75V重轨钢CT(Compaction test)试样为研究对象,分别研究了冷速为3℃/s、5℃/s及空冷轧态的组织对稳定区(疲劳扩展Ⅱ区)疲劳裂纹扩展速率的影响,疲劳试验在高频共振疲劳试验机上进行。研究结果表明:疲劳裂纹扩展速率随着珠光体片层间距的减小而降低,冷速由大到小(5℃/s、3℃/s、空冷)所对应的n值分别为3.603 05、3.631 18和3.885 28;珠光体组织的疲劳裂纹断裂形式主要以穿晶断裂为主,同时伴随部分沿晶断裂;片层间距影响裂纹扩展路径的偏折程度,偏折程度随片层间距的减小而增大,增大的裂纹偏折路径对裂纹扩展的阻碍作用增强,有利于疲劳裂纹扩展速率的降低。     

Sliding wear evaluation of various coating processes on AISI 52100 and M 50 steels

Abstract

Lubricated sliding wear tests were carried out on various surface coatings that were deposited on AISI 52100 and M50 steel substrates. The coatings include titanium nitride (TiN) deposited via an ion plating process, an electroplated chromium termed thin dense chrome (TDC), and a vanadium carbide (VC) deposited via the Toyota diffusion (TD) process. The tests were carried out using a synthetic turbine oil at one sliding speed and stepwise loading until catastrophic failure of the coating occurred. Friction coefficients were measured throughout the test interval, which showed that the vanadium carbide coating produced the lowest values (less than 0·055). Furthermore, this coating process had the greatest load carrying capacity, followed by the ion plated TiN on the M 50 substrate. Optical and scanning electron microscopy revealed that each coating process exhibited a different wear mode. In the TiN and VC coatings, polishing occurred along with the formation of cracks perpendicular to the sliding direction. Portions of the TiN coating spalled off the substrate via a delamination process. The TDC coating exhibited only a polishing wear mode.

MST/1691     

轴承用20CrMoH钢S-N疲劳曲线的拟合

为了合理并高效地设计20CrMoH钢轴类零件的安全服役应力,根据轴类零件使用工况用标准旋转疲劳试样进行了旋转弯曲疲劳试验,并采用Parabola曲线模型拟合了中寿命区到长寿命区的中值S-N曲线以及在0.1%失效概率和95%置信度条件下的P-S-N曲线,最后利用疲劳应用统计学,对线性数学模型和Parabola曲线模型两种拟合方法进行了对比。初步研究发现:无论是在50%失效概率还是在0.1%失效概率、95%置信度条件下,与线性数学模型拟合方法相比,Parabola曲线模型拟合得到的S-N曲线结果均具有较高的相关系数,在中、低应力区有着较为保守的疲劳寿命估计,而在高应力区也更贴近原始数据。     

The Influence of Long Operation on Fatigue Strength of Pipe Steel

The paper presents the results of fatigue tests of specimens cut from 630-mm-diameter 018GS2 steel pipes from the "Druzhba" oil pipeline prior to and after a long period of operation. We have found that the fatigue strength of the base and weld metal decreased upon long operation by 14.9% and 9.5%, respectively. Analysis has demonstrated that in the course of operation of linear sections of oil pipelines the material properties of the inner pipe surface deteriorate steadily and substantially, and it is this deterioration which constrains the operating reliability of the pipeline.     

高强带肋钢筋疲劳寿命置信区间的分析方法比较

本文对比介绍了求解疲劳寿命置信区间的三种方法:数理统计方法、ASTM法以及Bootstrap方法,详细阐述了Bootstrap方法在小子样空间下计算疲劳试验样本参数估计的步骤。以高速铁路用HRB400、HRB500高强带肋钢筋疲劳试验数据为例,采用三种方法来计算高强带肋钢筋的疲劳寿命置信区间,验证了Bootstrap方法在小子样空间下可以较为有效地改善其他计算方法可能存在的危险问题。     

Improvement of Toughness of Ultrahigh Strength Steel Aermet 100

1.IntroductionUp to now,the experimental investigation on the ul-trahigh strength steel has been basically limited to the ex-ploration of increasing strength and there have been fewreports on the breakthrough of combination optimiza-tion between strength and toughness[1~6].Moreover,afundamental understanding on some critical microstruc-tural features and the problem of the stability of AR inthe steel are still not clear[1].Generally speaking,the larger fraction of AR formedat higher temperat…     

几种高强度钢腐蚀疲劳裂纹扩展行为的研究

本文研究了ＧＣ－４，３０ＣｒＭｎＳｉＮｉ２Ａ和３００Ｍ超高强钢的腐蚀疲劳裂纹扩展行为。考虑了环境，热处理制度，应力比和频率对裂纹扩展的影响。研究结果表明：腐蚀环境和热处理制度对疲劳裂纹扩展有显著影响。在侵蚀性环境中随频率降低，裂纹扩展大幅度上升，随应力比提高，环境影响加剧。利用扫描电镜对试样断口形貌进行了分析，并讨论了高强钢的腐蚀疲劳机理。     

Characterization of Grain Size and Yield Strength in AISI 301 Stainless Steel Using Ultrasonic Attenuation Measurements

AISI 301 stainless steel samples were annealed over the temperature range of 800?C1200°C for 60?minutes to produce different grain sizes. These samples were characterized by ultrasonic immersion technique, tensile test, and optical microscopy. The attenuation of ultrasonic waves measured at a frequency of 20?MHz showed a good correlation with average grain size, hardness, and yield strength of AISI 301 stainless steel samples. A?new equation was derived for calculation of yield strength on the basis of ultrasonic wave attenuation and Hall-Petch relation.     

屈服强度对40CrMnSiMoVA超高强度钢腐蚀疲劳裂纹扩展的影响

研究了屈服强度对４０ＣｒＭｎＳｉＭｏＶＡ（ＧＣ－４）超高强度钢腐蚀疲劳（ＣＦ）裂纹扩展行为的影响，结果表明，不同屈服强度时，ＧＣ—４钢在３．５％ＮａＣｌ溶液中的ＣＦ裂纹扩展曲线上，都出现了类似于应力腐蚀的平台区，而且随屈服强度提高，平台区裂纹扩展速度显著增大。研究表明，氢脆在ＧＣ—４钢的腐蚀疲劳中起重要作用，进一步的理论分析与计算表明，屈服强度会影响高强钢氢致开裂的过程和速度．