17-4PH末级长叶片叶根的疲劳强度与缺口效应

采用成组法和升降法开展了室温某17-4PH末级长叶片叶根纵、横方向光滑与缺口试样的疲劳试验,获得了两个方向上材料的S-N曲线,并对典型疲劳断裂试样进行了断口宏微观形貌观察。结果表明:叶片叶根纵、横方向的疲劳强度基本一致,在长寿命区,纵向疲劳强度略高于横向;光滑试样的疲劳断裂主要呈现单裂纹源特征,而缺口试样呈现多裂纹源汇聚的断裂形貌。结合试样缺口根部的弹塑性应变分析,进一步讨论了叶片叶根纵、横方向的疲劳缺口效应。     

A Microstructural and Fractographic Study on the Failure of a Drive Shaft

The automotive industry is one of the most dynamic and competitive segments of the international economy and it has invested considerable resources into the research and development of new components and the improvement of existent pieces. Nonetheless, failures continue to occur, often because of defects in a component. Failure analysis uses several techniques to investigate causes of the defect which led to the failure of a component, equipment, or structure. Usually, these causes are related to the use of inadequate materials, the presence of defects which appear during fabrication or design errors, or improper assembly, maintenance and use. Knowledge about these causes and the correction of such anomalies allow the improvement of the performance of components regarding both efficiency and safety. In this study, the results of the failure analysis of the drive bar of a police car are presented and light optical microscopy and scanning electron microscopy (SEM) results are used to show that the presence of an already existent defect and an unfavorable microstructure led to the occurrence of brittle fracture which caused the premature and catastrophic failure of this component.     

Effect of strain rate on high-temperature low-cycle fatigue of 17-4 PH stainless steels

The effect of strain rate (10⁻², 10⁻³ and 10⁻⁴ s⁻¹) on the low-cycle fatigue (LCF) behavior was investigated for 17-4 PH stainless steels in three different conditions at temperatures of 300–500 °C. The cyclic stress response (CSR) for Condition A tested at 300 and 400 °C showed cyclic hardening due to an influence of dynamic strain aging (DSA). An in situ precipitation-hardening effect was found to be partially responsible for the cyclic hardening in Condition A at 400 °C. For H900 and H1150 conditions tested at 300 and 400 °C, the CSR exhibited a stable stress level before a fast drop in load indicating no cyclic hardening or softening. At 500 °C, cyclic softening was observed for all given material conditions because of a thermal dislocation recovery mechanism. The cyclic softening behavior in Conditions A and H900 tested at 500 °C is attributed partially to coarsening of the Cu-rich precipitates. The LCF life for each material condition, tested at a given temperature, decreased with decreasing strain rate as a result of an enhanced DSA effect. At all given testing conditions, transgranular cracking was the common fatigue fracture mode.     

The effects of fabrication atmosphere condition on the microstructural and mechanical properties of laser direct manufactured stainless steel 17-4 PH

The effects of atmosphere conditions on microstructural and mechanical properties of stainless steel 17-4PH components fabricated by laser direct manufacturing (LDM) were investigated through measurements on phase constitution, porosity, tensile strength, fracture morphology, hardness and evolution of substrate temperature. Results showed that the samples produced in air atmosphere condition possessed higher tensile strength and hardness for both as-deposited and heat-treated states than that in Ar chamber condition, due to dispersion strengthening effect of amorphous oxide particles and nitrogen solution strengthening as a result of higher content of oxygen and nitrogen. The temperature of substrate heat accumulation was higher in Ar chamber condition, leading to dramatically lower porosity and more reverse austenite, which also contributed to the lower strength and hardness.     

On Applicability of Multilayer Coated Tool in Dry Machining of Aerospace Grade Stainless Steel

The present research work has been undertaken with a view to investigate the influence of CVD multilayer coated (TiN/TiCN/Al₂O₃/ZrCN) and cutting speed on various machining characteristics such as chip morphology, tool wear, cutting temperature, and machined surface roughness during dry turning of 17-4 PH stainless steel. In order to understand the effectiveness of CVD multilayer coated tool a comparison has been carried out with that of uncoated carbide insert. The surface roughness and cutting temperature obtained during machining with chemical vapor deposition (CVD) multilayer coated tool was higher than that of uncoated carbide insert at all cutting velocity. However, the results clearly indicated that CVD multilayer coated tool played a significant role in restricting various modes of tool failure and reducing chip deformation compared to its uncoated counterpart. Adhesion and abrasion were found to be dominating wear mechanism with flank wear, plastic deformation, and catastrophic failure being major tool wear modes.     

热处理对选区激光熔化17-4PH不锈钢力学性能的影响

对选区激光熔化成形的17-4PH不锈钢分别进行真空热处理、热等静压高压淬火处理和组合热处理(热等静压固溶后快淬和马弗炉时效后水冷),在1040℃固溶处理2 h和在480℃时效4 h,观察其显微组织并研究了热处理对其力学性能的影响。结果表明,17-4PH不锈钢由回火马氏体和淬火马氏体组成,热处理后沉淀相弥散分布于晶粒内部,其颗粒尺寸为100~150 nm。真空热处理使合金内部孔隙的尺寸减小到3~7 μm,而热等静压使内部孔隙几乎完全闭合,使钢的密度基本上达到理论值。真空热处理+水淬使沉积态17-4PH不锈钢的抗拉强度和硬度都显著提高(分别提高到1300 MPa和448.5HV);热等静压在提高沉积态17-4PH不锈钢抗拉强度的同时使其延伸率显著提高到22.4%。断口分析结果表明,沉积态和热等静压样品的断口形貌为典型的韧性断裂,热等静压样品的韧窝更深、尺寸更大。真空热处理和组合热处理样品的断口形貌具有部分脆性断裂的特征且出现裂纹,与沉积态相比塑性略有降低。     

TiB2含量对17-4PH钢熔覆层组织及性能的影响

目的 选择合适的TiB2添加量以提高17-4PH钢熔覆层的综合性能.方法 采用金属粉末注射成形技术制备17-4PH基体,在基体上通过激光熔覆含有不同质量分数TiB2(0.5％,1％,2％,3％,4％)的混合粉末制备样品,分析其物相及组织,测试材料显微硬度,并进行摩擦磨损与电化学腐蚀实验.通过对样品进行耐磨性与耐腐蚀性的...     

Failure Analysis of Stainless Steel Pipeline Used in Propulsion Engine Test Facility

Austenitic stainless steel pipelines are used as a conduit for gaseous nitrogen to ejector flow lines of propulsion engine test facility. Leakage was noticed near a welded T-joint of such a pipeline system that was in service for years. Detailed metallurgical investigations were carried out to understand the cause of failure. Synergistic effect of chloride ions, thermal stresses from welding, and the presence of sensitized grains of the material led to stress-corrosion cracking of the steel. This paper highlights details of investigation.     

Sintering of 17-4PH stainless steel feedstock for metal injection molding

The sintering behavior of 17-4PH stainless steel feedstock for metal injection molding was investigated in the temperature range of 650-1050 °C. Effects of sintering conditions, such as sintering temperature and sintering atmosphere, were examined. Results showed that when sintered in the hydrogen/nitrogen atmosphere, the 17-4PH feedstock was oxidized over the temperature range of investigation. The degree of oxidization increased with the sintering temperature. The main oxidization product was Cr₂O₃ as revealed by X-ray diffraction and composition analysis. The oxidation can be avoided by sintering in vacuum or argon atmosphere.     

热处理工艺对黏结剂喷射3D打印17−4PH不锈钢微观组织与性能的影响

目的 探究热处理工艺对黏结剂喷射3D打印17?4PH不锈钢样品微观组织、力学性能及电化学腐蚀性能的影响规律,为BJ3DP技术制备综合性能良好的17?4PH不锈钢零件提供参考。方法 基于黏结剂喷射3D打印技术制备17?4PH不锈钢生坯,并将其固化、脱脂、烧结,得到烧结态样品,然后对烧结态样品进行热处理,热处理工艺为在1 040 ℃固溶热处理2 h,随后分别在410、480、550 ℃下热处理3 h后空冷至室温。对烧结态和热处理态样品进行金相试验、单向拉伸试验以及电化学腐蚀试验。 结果 经热处理后,试样在480 ℃时效热处理3 h时力学性能提升最为显著,其屈服强度由608 MPa提升至806 MPa,抗拉强度由1 159 MPa提升至1 245 MPa,伸长率由3.6%提升至13.6%。当时效热处理温度提升至550 ℃时,由于沉淀相的粗化,其力学性能有所下降;同时,电化学腐蚀性能中腐蚀电流密度(Jcorr)减小,腐蚀电位(Ecorr)增大,电荷转移电阻(Rct)增大,出现明显的钝化区。结论 黏结剂喷射3D打印17?4PH不锈钢经热处理后力学性能得到提升,试样在480 ℃时效热处理3 h时力学性能提升最为显著,优于商用热轧17?4PH不锈钢,电化学腐蚀性能与商用热轧17?4PH不锈钢电化学腐蚀性能水平相当。     

Investigation of the Microstructure of Rolled Semi—Solid Steel

In this paper,spring steel-60Si2Mn and stainless steel-1Cr18Ni9Ti were rolled one pass in semi-solid state.The microstructural evolution during rolling of the steels with different solid fraction was investigated.The experimental results showed that the manner of liquid and solid phases flowing and deforming was different.During rolling,most of solid phases remained in the center of the rolled specimens,while liquid phase flowed to the edge,which resulted in the macrosegregation of liquid and solid phases.Only the amount of solid fraction reached a certain value,were the solid phases deformed and flattened.     

Failure Analysis of a High-Pressure Component

Martensitic stainless steel nuts were received for failure analysis. A few of these nuts cracked at the immediate stress loading while the others fractured after 2 years of service. These nuts were subjected to different metallurgical tests such as visual examination, optical microscopy, chemical analysis, hardness testing, and fractography. It was concluded that improper heat treatment weakened the structure and subsequently fractured on the application of load.     

摩托车离合器主轴断裂失效分析及其机理

本文分析了摩托车离合器主轴用材、金相组织、显微硬度以及断口扫描电镜(SEM)宏观、微观形貌,结果表明,该摩托车离合器主轴断裂主要原因是轴颈突变截面尖角顶端曲率半径ρ值太小,形成很大的应力集中从而形成裂纹源,然后裂纹逐步扩展造成的。     

Wear behavior of laser metal deposited 17-4 PH SS-W composite at varied tungsten powder flow rate

This research studies the wear behavior of laser metal deposition of 17-4 PH SS-W composite using a 6 mm alumina-stainless steel ball under a load of 10 N, for 16 minutes, 40 seconds and with acquisition rate of 100 Hz conducted at 25 °C. The effect of laser power of between 2600 W and 1500 W; and powder flow rate of between 0.5 min⁻¹ and 2.0 min⁻¹ on wear resistance is investigated. Other processing parameters are constant throughout the experiments. The results show that the 17-4 PH SS-W composite produced at a high laser power of 2600 W exhibits a higher wear resistance as compared to the 17-4 PH SS-W composite samples produced at low laser power of 1500 W. The 17-4 PH SS-W composite sample produced at high laser power of 2600 W with tungsten powder flow rate of 2.0 min⁻¹ has the highest wear resistance with wear volume of 0.0276 mm³ and wear rate of 8.8 ⋅ 10⁻⁵ mm³/N m while the 17-4 PH SS-W composite sample produced at a low laser power of 1500 W with tungsten powder flow rate of 1.0 min⁻¹ has the wear volume of 0.02834 mm³ and wear rate of 9.0 ⋅ 10⁻⁵ mm³/N m.     

Investigation of the effects of plasma arc parameters on the structure variation of AISI 304 and St 52 steels

In this study, AISI 304 stainless steel and St 52 carbon steel have been cut by plasma arc and the variations of structural specifications occurred after cutting has been investigated. According to the experimental results, it has been seen that burning of particulars and distribution amount were increased when the cutting was performed using the speeds which are upper or lower limits of the ideal cutting speeds proposed by the manufacturer of the machine tool. Moreover, it was determined that the hardness from the outer surface to the core decreased, while the hardness near to the outer surface which affected by the high temperature occurred during cutting increased.     

40Cr钢合闸支撑轴弯曲失效分析

采用化学成分分析、金相检验、硬度测试以及拉伸试验等方法,对某40Cr钢二级合闸支撑轴的弯曲失效原因进行了分析。结果表明:由于该支撑轴设计图纸标注的硬度范围太宽,使加工者无法明确确定的热处理工艺,导致所制造支撑轴的硬度和抗拉强度偏低,从而在磨合试验过程中发生弯曲失效。通过适当降低支撑轴回火温度,提高其硬度和抗拉强度,较好地解决了支撑轴磨合试验过程中弯曲失效问题。     

Microstructural banding of directed energy deposition-additively manufactured 316L stainless steel

The microstructures of 316L stainless steel created by rapid solidification are investigated by comparing the similar microstructures of individual hatches of directed energy deposition additive manufacturing(DED-AM) and those of single, laser surface-melted tracks formed on a solid plate. High recoil pressure,which is exponentially dependent on the laser beam power density, induces convection of the melt pool,which causes formation of microstructural bands in the as-solidified microstructure. The microstructural bands are associated with changes in the chromium concentration and are a significant component of the inhomogeneous microstructure of DED-AM.     

Influence of cryogenic coolant on turning performance characteristics: A comparison with wet machining

Machining of 17-4 Precipitation Hardenable Stainless Steel (PH SS) is one of the difficult tasks because of its high cutting temperatures. Conventional cutting fluids are used to overcome the high cutting temperatures, but these are not acceptable from the health and environmental sustainable points of view. Cryogenic cooling is one of the potential techniques to overcome such problems. In the current work, comparison is made of cryogenic turning results, such as tool flank wear, cutting forces (feed force, main cutting force), cutting temperature, chip morphology and surface integrity characteristics with wet machining during machining of heat-treated 17-4 PH SS. The result showed that in cryogenic machining, a maximum of 53%, 78%, 35% and 16% reductions was observed in tool flank wear, cutting temperature, surface roughness and cutting force, respectively, when compared with wet machining. It was also evident from the experimental results that cryogenic machining significantly improved the machining performance and product quality even at high feed rates.