喷丸强化对OCr13Ni8Mo2Al钢疲劳性能的影响

研究了表面喷丸强化后表面残余应力、表面粗糙度和表面层残余压应力场对0Cr13Ni8Mo2Al钢疲劳性能的影响.结果表明:0Cr13Ni8Mo2Al钢经喷丸强化后,在表面层残余压应力场的作用下疲劳裂纹源由表面被"驱赶"到表面强化层下,疲劳寿命得到显著提高.     

喷丸强化对0Cr13Ni8Mo2Al钢疲劳性能的影响

研究了表面喷丸强化后表面残余应力,表面粗糙度和表面层残余应力场对0Cr13Ni8Mo2Al钢疲劳性能的影响,结果表明：0Cr13Ni8Mo2Al钢经喷丸强化后,在表面层残余应力场的作用下疲劳裂纹源由表面被“驱赶”到表面强化层下,疲劳寿命得到显著提高。     

热处理制度对OCr13Ni8Mo2Al钢组织和性能的影响

研究了热处理制度对OCr13Ni8Mo2Al钢微观组织性能的影响。结果表明，含有高密度位错的板条马氏体及与基体共格的细小弥散分布的β-NiAl沉淀析出是该钢具有高强度的主要原因。530℃左右时效强度达到峰值，510℃左右时效冲击韧性处于谷值。时效过程中合金的脆性与残余奥氏体的分解无关。     

热处理制度对0Cr13Ni8Mo2Al钢组织和性能的影响

研究了热处理制度对0Cr13Ni8Mo2Al钢微观组织和性能的影响.结果表明,含有高密度位错的板条马氏体及与基体共格的细小弥散分布的β-NiAl沉淀析出是该钢具有高强度的主要原因.530℃左右时效强度达到峰值,510℃左右时效冲击韧性处于谷值.时效过程中合金的脆性与残余奥氏体的分解无关.     

Effects of shot peening on bending fatigue strength of spring steel SS 2090

Abstract

The influence of prior surface condition and of a shot peening treatment on the bending fatigue strength of a standard Si–Cr spring steel (SS 2090) has been investigated. This steel was initially hardened and tempered to a hardness of 52–54 HRC. After shot peening, compressive residual stresses had been introduced into a surface layer of depth ~0·3 mm, with the maximum value of ~1000 MN m^?2 being found close to the surface. The effect of this treatment was to increase the fatigue limit by ~40% to 890 MN m^?2. Coincident with this increase was a change in the site of fatigue initiation from a surface to a subsurface location beneath the compressive residual stress layer. The initiating inclusions, which were 20–40 μm in size, were analysed and found to be Al₂O₃. At stress amplitudes greater than the fatigue limit, initiation was invariably found to occur at the surface and was not always due to inclusions. Inclusion initiated failure has been modelled using the size and spatial distribution of inclusions in the test bars in addition to the variation of applied and residual stresses through the section. A crack propagation criterion based on linear elastic fracture mechanics is used, assuming that propagation is controlled by stress intensity threshold value. It is assumed that small cracks exist at oxide inclusions from the beginning of the fatigue life and that failure is associated with the propagation of one of these cracks.

MST/1392     

Evaluating surface deformation and near surface strain hardening resulting from shot peening a tempered martensitic steel and application to low cycle fatigue

The plastic deformation resulting from shot peening treatments applied to the ferritic heat resistant steel FV448 has been investigated. Two important effects have been quantified: surface roughness and strain hardening. 2D and 3D tactile and optical techniques for determining surface roughness amplitude parameters have been investigated; it was found that whilst R_a and S_a were consistent, S_z was generally higher than R_z due to the increased probability of finding the worst case surface feature. Three different methods for evaluating the plastic strain profile have been evaluated with a view to establishing the variation in yield strength near the surface of a shot peened component. Microhardness, X-ray diffraction (XRD) line broadening and electron backscatter diffraction (EBSD) local misorientation techniques were applied to both uniaxially deformed calibration samples of known plastic strain and samples shot peened at intensities varying from 4A to 18A to establish the variation in plastic strain and hence the variation in yield strength. The results from the three methods were compared; XRD and EBSD profiles were found to be the most similar with microhardness profiles extending much deeper into the sample. Changes in the measured plastic strain profile after exposure to low cycle fatigue and the correlation of these changes with the cyclic stress–strain behaviour of the material are also discussed with a view to assessing the importance of the dislocation profile in component life assessment procedures.     

Hot workability of 00Cr13Ni5Mo2 supermartensitic stainless steel

The hot workability of 00Cr13Ni5Mo2 supermartensitic stainless steel was investigated by hot compression and hot tension tests conducted over the temperature range of 950–1200 °C and strain rates varying between 0.1 and 50 s^?1. The processing map technique was applied on the basis of dynamic materials model and Prasad instability criterion. Microstructure evolutions, Zener–Hollomon parameter as well as hot tensile ductility were examined. The results show that, as for the hot working of 00Cr13Ni5Mo2 supermartensitic stainless steel in the industrial production, the large strain deformation should be carried out in the temperature range 1140–1200 °C and strain rate range 0.1–50 s^?1, where the corresponding Zener–Hollomon parameters exhibit low values. Moreover, when deformed under high strain rate range (above 15 s^?1), the deformation temperature can be reduced reasonably.     

Effects of electroless deposition and shot peening on fatigue strength of 30CrMo4 steel

Abstract

Electroless nickel coatings cause a marked decrease in the fatigue strength of the base steel. For the 30CrMo4 steel used in the present work, the fatigue limit is reduced by electroless deposition by 39, 52, and 55% for heat treatment conditions of 200°C for 1 h, 400°C for 1 h, and 600°C for 3 h, respectively. Shot peening before deposition can increase the fatigue strength for material heat treated at 200 and 400°C, but reduces the fatigue strength for material heat treated at 600°C. Under all conditions, the loss of fatigue strength is primarily due to the poor fatigue properties of the coating and the weak interface between the coating and the substrate. The main factors which affect the fatigue properties of coated samples are the coating ductility, the interface bonding, and the residual stress within the coating.

MST/3123     

Effect of severe shot peening on ultra-high-cycle fatigue of a low-alloy steel

It is well known that shot peening is able to increase the fatigue strength and endurance of metal parts, especially with a steep stress gradient due to a notch. This positive effect is mainly put into relation with the ability of this treatment to induce a compressive residual stress state in the surface layer of material and to cause surface work hardening. Recently the application of severe shot peening (shot peening performed with severe treatment parameters) showed the ability to obtain more a remarkable improvement of the high cycle fatigue strength of steels. In this paper severe shot peening is applied to the steel 50CrMo4 and its effect in the ultra-high cycle fatigue regime is investigated. Roughness, microhardness, X-ray diffraction residual stress analysis and crystallite size measurement as well as scanning electron microscopy (SEM) observations were used for characterizing the severely deformed layer. Tension–compression high frequency fatigue tests were carried out to evaluate the effect of the applied treatment on fatigue life in the ultra-high cycle region. Fracture surface analysis by using SEM was performed with aim to investigate the mechanism of fatigue crack initiation and propagation. Results show an unexpected significant fatigue strength increase in the ultra-high cycle region after SSP surface treatment and are discussed in the light of the residual stress profile and crystallite size.     

0Cr13Ni5Mo不锈钢电火花强化表面耐腐蚀性能研究

针对我国水轮机过流部件长时间运行后表面腐蚀严重这一问题,选用YG8电极材料对水轮机叶片用0Cr13Ni5Mo不锈钢进行电火花表面强化处理,基于电化学测试技术和交流阻抗测试方法,对强化层的电化学腐蚀性能进行了深入研究.结果表明,强化过程中电极材料与基体材料元素相互熔渗和扩散,强化层内有新的相结构生成,且强化层为冶金结合.与基体材料相比,在腐蚀溶液中电火花强化后试件的自腐蚀电位增大,自腐蚀电流密度减小,试件腐蚀速度变慢,耐腐蚀性能明显提高.     

0Cr15Ni5Cu2Ti不锈钢表面TiN膜层制备

0Cr15Ni5Cu2Ti不锈钢基材表面多弧离子镀方法制备TiN硬质涂层.工件表面镀膜处理技术的关键是膜/基结合强度.分析预热温度和工作偏压对膜层的膜/基结合强度、膜层结构及表面硬度的影响,优化制备工艺,满足使用要求.结果显示预热温度和工作偏压对膜/基结合效果影响显著.镀膜处理后,工件表面硬度大于1200HV0.05,膜/基结合力最小临界载荷高于60N.     

Influence of shot peening on notched fatigue properties of magnesium alloy ZK60

Abstract

The influence of shot peening on high cycle fatigue performance of notched specimen was investigated for ZK60 and ZK60-T5 magnesium alloys. The results show that the notched fatigue strengths (at 10⁷ cycles) for ZK60 and ZK60-T5 alloys increase from 150 and 155 MPa to 220 and 240 MPa at the optimum Almen intensity of 0·30 and 0·40 mmN respectively. In comparison to ZK60 alloy in extruded condition, higher notched fatigue performances of both unpeened and peened specimens were observed for ZK60-T5 alloy.     

Improvement of fatigue properties by shot peening for Mg-10Gd-3Y alloys under different conditions

In the present study we investigated the influence of shot peening on the high cycle fatigue (HCF) performance of the Mg-10Gd-3Y magnesium alloys in four different conditions referred to as-cast, cast-T6, as-extruded and extruded-T5, respectively. The results show that shot peening can cause different degree of enhancement of fatigue performance for Mg-10Gd-3Y alloys depending on the Almen peening intensity applied; and that the Almen intensity could always be found that conferred the optimum improvement. The effect of shot peening was quantified, and for the as-extruded and extruded-T5 alloys it was found to be superior to that for the as-cast and cast-T6 alloys. The peened extruded-T5 Mg-10Gd-3Y alloy showed the highest fatigue strength at 10⁷ cycles of 240 MPa. The results of the analyses established a connection between the grain size, ductility and precipitates within the studied alloys. Microstructure affected the magnitude of the surface roughness induced by shot peening and also the maximum compressive residual stress and its relaxation during fatigue, and then determine the beneficial effect of shot peening.     

0Cr12Mn5Ni4Mo3Al钢制弹簧断裂分析

某型0Cr12Mn5Ni4Mo3Al钢制弹簧在进行低温试验过程中发生断裂。通过断口分析、金相检验和能谱分析进行了综合评定。结果表明:弹簧的断裂性质为脆性过载断裂;弹簧断裂的直接原因是弹簧材料中含有较多的脆性夹杂物。     

High temperature mechanical properties and surface fatigue behavior improving of steel alloy via laser shock peening

Laser shock peening was carried out to reveal the effects on ASTM: 410L 00C_r12 microstructures and fatigue resistance in the temperature range 25–600 °C. The new conception of pinning effect was proposed to explain the improvements at the high temperature. Residual stress was measured by X-ray diffraction with sin²ψ method, a high temperature extensometer was utilized to measure the strain and control the strain signal. The grain and precipitated phase evolutionary process were observed by scanning electron microscopy. These results show that a deep layer of compressive residual stress is developed by laser shock peening, and ultimately the isothermal stress-controlled fatigue behavior is enhanced significantly. The formation of high density dislocation structure and the pinning effect at the high temperature, which induces a stronger surface, lower residual stress relaxation and more stable dislocation arrangement. The results have profound guiding significance for fatigue strengthening mechanism of components at the elevated temperature.     

Mo对TiC/Al复合材料组织和性能的影响

为了细化TiC/Al基复合材料中的增强颗粒,进一步提高TiC颗粒对基体的强化效果,在锻铝6A02基体中加入适量Mo元素,用原位合成的方法制备TiC/Al基复合材料.对制备得到的铸态和轧制态材料进行了显微组织观察、拉伸和磨损实验.结果表明,TiC颗粒可以作为异质形核核心起到细化基体组织的作用.TiC颗粒的引入提高了材料在室温和高温的抗拉强度和屈服强度,同时改善了材料的耐磨损性能,且随着载荷的增加,耐磨性能的提高越明显.当加入质量分数1.0%的Mo时,可改善基体对TiC颗粒的润湿性,细化TiC颗粒的尺寸(0.5μm),使TiC颗粒分布更为均匀,材料的力学性能和磨损性能得到提高.然而,过高的Mo含量将导致在组织中出现粗大的脆性Al5Mo相,同时使材料的力学性能和磨损性能有所降低.     

喷丸强化对Ti6Al4V半椭圆表面裂纹J积分和裂纹扩展速率的影响

采用修正的J积分计算方法,考虑残余应力、残余应变和残余应变能,定量计算和分析喷丸强化对半椭圆表面裂纹前沿J积分参数的影响规律。对喷丸强化工艺进行有限元建模仿真,通过改变约束条件生成疲劳裂纹并施加远场载荷,计算J积分和裂纹扩展速率。考虑不同深度的半椭圆表面裂纹和不同丸粒速率对断裂参量的影响。结果表明:丸粒速率一定时,与未喷丸相比喷丸后J积分值的降幅随裂纹深度的增加而减小,喷丸强化有益于抑制疲劳浅裂纹的扩展。当裂纹深度为0.3mm时,裂纹最深点的J积分值由4.25N/mm降低到2.99N/mm,降幅约30.1%。裂纹深度一定时,J积分值随丸粒速率的增大而降低,提高丸粒速率对抑制裂纹扩展更有益。     

Effect of surface nanocrystallization on the tribological properties of 1Cr18Ni9Ti stainless steel

Surface nanocrystallization of 1Cr18Ni9Ti austenite stainless steel was conducted by the supersonic fine particles bombarding (SFPB) technique. The friction coefficients and wear losses in air and vacuum were tested to analyse the effect of surface nanocrystallization on the tribological properties of 1Cr18Ni9Ti steel. The results show that the microstructure of the surface layer was refined into nano-grains successfully by SFPB treatment; furthermore, strain-induced martensitic transformation occurred during the treatment. The tribological properties of SFPB treated samples enhanced greatly, The dominant wear mechanism of the original 1Cr18Ni9Ti stainless steel is abrasive wear and adhesive wear, while it transfers to the combined action of fatigue wear, abrasive wear and adhesive wear after surface nanocrystallization by SFPB.     

3Cr2W8V钢形变热处理研究

3Cr2W8V钢广泛应用于有色金属热锻、热挤压和压铸成形.为进一步挖掘3Cr2W8V钢的使用潜力,提高模具材料综合使用性能和使用寿命,本文开展了针对该钢的形变热处理研究,讨论了形变温度、冷却方式及回火温度对试样组织与性能的影响.研究表明高温形变热处理不适宜于3Cr2W8V,形变后水冷优于空冷,并得出组织性能俱佳的优化形...