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《International Heat Treatment & Surface Engineering》2013,7(2):69-72
AbstractCurrent practice when nitriding high speed steel (HSS) cutting tools is to avoid embrittlement of the cutting edge by limiting the depth of the diffusion zone. This is accomplished by reducing the nitriding time and temperature and eliminating any compound layer formation. However, in many applications there is an argument for generating a compound layer with beneficial tribological properties. In this investigation, results are presented of a metallographic, X-ray diffraction and X-ray photoelectron spectroscopy analysis of nitrided HSS surface layers generated using active screen plasma nitriding and reactive vapour deposition using cathodic arc. These results are discussed in the context HSS cutting tool performance when machining under built-up edge conditions. 相似文献
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We have studied the effect of nitrogen on the cold forging properties of a low carbon steel as a function of temperature. Five AISI 1020 steels with nitrogen contents from 12 to 180 ppm were examined by tensile testing from 25 to 371 °C. Yield strength, tensile elongation (ductility), ultimate tensile strength (UTS), strain hardening exponents and strength coefficients were determined. The influence of nitrogen on the mechanical property behavior of this low carbon steel exhibits trends as expected—when nitrogen content increases, the strength of the steel increases and the ductility decreases. Likewise, as the temperature increases, the strength of the steel generally decreases; however, the ductility initially decreases, then exhibits an increasing trend. Additionally, there is an intermediate temperature range for these alloys where anomalous behavior is observed. Serrated stress–strain curves seen in this temperature range are indicative of dynamic strain aging. It is probable that this anomalous mechanical property trend is due to dynamic strain aging. 相似文献
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P. Bala Srinivasan C. V. Krishnakumar N. Krishnaraj 《Journal of Materials Engineering and Performance》2002,11(5):509-515
Salt bath nitrocarburizing is a well-known thermochemical diffusion process for enhancing the tribological and corrosion properties
of ferrous components. The current work describes the role of a compound layer developed during nitrocarburizing, both in
the ferritic and austenitic regimes of Fe-N-C system, on the sliding wear behavior of a medium carbon steel. The wear behavior
of the nitrocarburized steel discs was assessed by the pin-on-disc tests (ASTM G 99-99) under different normal loads running
against a hardened SAE52100 pin. It was observed that the compound layer on the surface not only controlled the wear rate
but also resisted the adhesive wear/transfer of material from pin to disc, aside from providing low-friction coefficients. 相似文献
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使用优化工艺对冷作模具钢SDC99进行TD法盐浴渗钒,获得了厚度约13 μm的VC渗层,并对其截面形貌、物相、结合力、显微硬度梯度和摩擦磨损性能进行了研究。结果表明,渗后截面由表及里为渗钒层、过渡层、基体;渗钒层主要由VC相组成,同时还有一些VCx(x=0.65~0.90) 相;渗层到基体的硬度呈下降趋势;渗层与基体结合强度约为72 N;经过TD处理的试样比未经处理的试样磨损体积减少70%,VC渗层的磨损机理为试样表面初期产生犁沟,随磨损试验的进行逐渐产生微裂纹并不断扩展,最终导致渗层呈薄片状剥落,表现为疲劳磨损的特征。 相似文献
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MM Ghoneim 《Journal of Materials Engineering and Performance》1997,6(4):511-516
MANET II, a modified 12% Cr steel with the German designation DIN 1.4914, is a candidate structural material for the first
wall and blanket in fusion reactors. In the present study, the tensile properties of this steel were investigated in the temperature
range of 25 to 350 °C at strain rates of 5 x 10-5 ,1.2 x 10-4, and 1.2 x 10-3s-1, Both microstructure and fracture surfaces were examined using optical and scanning electron microscopic (SEM) techniques.
The results showed that the steel suffers dynamic strain aging, although no serrated flow was observed. Yield strength, ultimate
strength, and elongation showed negative strain rate sensitivity. Dynamic strain aging also affected the strain hardening
rate. Results are discussed with regard to the chemical composition and fracture surface morphology. 相似文献
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304奥氏体不锈钢低温盐浴渗氮处理 总被引:4,自引:0,他引:4
采用430℃低温盐浴对304奥氏体不锈钢进行渗氮处理,研究了渗氮时间对渗氮层组织和性能的影响。利用XRD衍射仪、光学显微镜、表面显微硬度计和带能谱仪(EDS)的扫描电镜(SEM)分别分析渗氮层的相组成、厚度、表面硬度和显微组织。结果表明:304奥氏体不锈钢在430℃渗氮不同时间后,渗氮层厚度和表面硬度都随着时间的延长而增加。渗氮时间为1 h时,渗氮层仅为单一的S相,随着渗氮时间的增加,渗氮8 h时开始有少量CrN生成,渗氮16 h时,渗氮层由大量CrN+S相两相混合。用电化学极化的方法评价耐蚀性能的结果表明:盐浴渗氮处理后耐Cl-点蚀性能得到了一定的改善,在430℃渗氮4 h,其耐蚀性能是最好的,优于没经过渗氮的试样,而在所有的渗氮试样中,渗氮8 h、16 h的试样耐点蚀性能较差。 相似文献
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通过在盐浴渗氮中施加7.5 V的直流电场,在不同外热温度(545~575℃),不同保温时间(60~120 min)下对35钢进行盐浴渗氮,研究了直流电场对35钢盐浴渗氮动力学的影响。利用光学显微镜、X射线衍射仪对渗层的显微组织、厚度及物相进行了测试和分析。结果表明:直流电场对活性氮原子在基体内部的扩散有显著促进作用,提高渗氮速度,降低盐浴渗氮温度或缩短保温时间;直流电场盐浴渗氮的扩散系数都比常规盐浴渗氮提高约2倍,扩散激活能从常规盐浴渗氮的220 k J/mol降低到181 k J/mol,从而达到增加渗层厚度的显著效果。有无直流电场条件下盐浴渗氮,35钢渗层主要物相均为ε-Fe3N及少量γ'-Fe4N。 相似文献
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采用FLiNaK氟化盐对3Cr13不锈钢表面分别进行不同时间的热反应沉积(TD),利用X射线衍射仪(XRD)、电子探针(EPMA)、扫描电镜(SEM)、显微维氏硬度计研究了VC涂层的形貌、成分特征、表面硬度及其生长动力学。结果发现,3Cr13不锈钢的表面形成了3~5μm厚的均匀致密的VC涂层,表面呈花瓣状,VC相中含少量的Si和Fe元素。VC涂层的平均(HV)硬度高达32 220 MPa,其厚度与保温时间满足抛物线关系。VC涂层表面几百纳米厚度存在不均匀分布的SiO_2,表面呈龟裂状。主要是因为SiO_2的热膨胀系数大于VC涂层,使得SiO_2在冷却过程中受到拉应力而发生龟裂。本研究首次表明低熔点高活性的氟化盐可以用于TD法制备VC涂层。 相似文献
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Various amounts of FeSiRe23, which were used as reducing agents, were added into typical borax salt bath used in thermal diffusion (TD) process to explore the effects of rare earths on borax salt bath vanadizing process and microstructure and properties of vanadium carbide coating. The effect results of rare earths on coating thicknesses at different process conditions showed that the right amount of rare earths could greatly accelerate vanadizing rate and that the accelerating effect worked mainly at the initial stage of TD process and decreased with increasing thickness of vanadium carbide layer. Moreover, the comparison of diffusion activation energies at various temperatures revealed that rare earths have optimal accelerating effect at 950 °C or so. The effect results of rare earths on coating microstructure and properties showed that the addition of rare earths into the borax salt bath can decrease grain size and improve fragility of vanadium carbide coating but decrease coating microhardness. And the electron probe microanalysis (EPMA) revealed that the addition of rare earths could decrease carbon concentration in the coating. 相似文献
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An /γ′-iron nitride compound layer grown on α-Fe at 823 K by gas nitriding shows a nitrogen redistribution upon annealing at 630 K: an until now not observed “backwards growth” of the γ′-sublayer occurs, accompanied by a nitrogen enrichment of the remaining -sublayer. The observed thickness changes can be explained theoretically. 相似文献
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针对高级管线钢应变时效问题,对X90级直缝埋弧焊管管体不同预应变及时效前后的组织和力学性能进行了对比,研究了应变时效对X90级管线钢组织和力学性能的影响。结果表明:不同应变时效前后X90级管线钢的显微组织和冲击韧性变化不明显;应变时效后拉伸曲线由拱顶型连续曲线转变为吕德斯型屈服曲线,屈服强度增加,屈强比升高;预应变量越大,屈服强度和屈强比升高越显著,且横向性能受到预应变量的影响比纵向要大,而200~250 ℃温度区间时效对屈服强度和屈强比影响较小。 相似文献
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Kinetics of strain aging in bake hardening ultra low carbon steel—a comparison with low carbon steel 总被引:1,自引:0,他引:1
A. K. De B. C. De Cooman S. Vandeputte 《Journal of Materials Engineering and Performance》2001,10(5):567-575
The kinetics of the static strain aging process have been analyzed in a vacuum-degassed ultra low carbon bake hardenable (ULC
BH) steel with a total carbon content of 20 wt.ppm through measurement of the strength properties. The influence of prestrain
and free interstitial carbon content has been studied. The kinetic results were compared with those of a BH low carbon (LC)
steel. In the derivation of the time exponent and the activation energy, only the first stage of aging was considered. It
was observed that, at all prestrain levels and matrix solute carbon contents, the initial aging process in the ULC steel obeyed
the t
2/3 kinetic law and the kinetics were not influenced by the changes in dislocation structure due to prestrain and the dissolved
carbon content. In comparison, the aging process and the kinetics in the LC steel were found to be significantly influenced
by the amount of prestrain. The presence of carbide particles in LC steels can modify the aging kinetics. 相似文献
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Influence of time on the microstructure of AISI 321 austenitic stainless steel in salt bath nitriding 总被引:1,自引:0,他引:1
Jun Wang Yuanhua Lin Jing Yan Dezhi Zen Qiang Zhang Runbo Huang Hongyuan Fan 《Surface & coatings technology》2012
Influence of nitriding time on the microstructure and microhardness of AISI 321 austenite stainless steel was investigated, using a complex salt bath heat-treatment at low temperature, 430 °C. Experimental results revealed that after salt bath nitriding, a modified layer was formed on the surface of substrate with the thickness ranging from 2 μm to 30 μm with changing treating time. The nitrided layer depth thickened extensively with increasing nitriding time. The growth of the nitrided layer takes place mainly by nitrogen diffusion according to the expected parabolic rate law. Scanning electron microscopy and X-ray diffraction showed that in 321 stainless steel subjected to complex salt bathing nitrided at such temperature for less than 8 hours, the main phase of the nitrided layer was expanded austenite (S phase) by large. When the treatment time is prolonged up to 8 hours and more, S phase is formed and subsequently transforms partially into CrN, and then the secondary CrN phase precipitated. With treating time prolonged, more CrN precipitates formed along the grain boundaries in the outer part. In the inside part between the some CrN and the substrate, there is still a broad single S phase layer. All treatments can effectively improve the surface hardness. 相似文献