外文翻译---离子渗氮对马氏体时效钢微观结构和性能的影响
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附录一英文翻译原文
EFFECT of ION NITRIDING ON the MICROSTRUCTURE AND
PROPERTIES of MARAGING STEEL (250 GRADE)
Kishora ShettyS. Kumarb,P. Raghothama Rao;Regional
Centre for Military Airworthiness (Foundry and Forge), CEMILAC, DRDO,
Bangalore-560 037, India
Department of Materials Engineering, Indian Institute of Science, Bangalore-560 012,
India
Received 25 June 2008. Accepted 28 November 2008. Available online 10 December
2008
Abstract
In the present investigation, ion nitriding of Maraging steel (250 grade) has
been carried out at three different temperatures i.e., at 435℃, 450℃ and 465℃ for
10 h duration in order to achieve good wear resistance along with high strength
required for the slat track component of aircraft. The microstructure of the base
material and the nitrided layer was examined by optical and scanning electron
microscope, and various phases present were determined by X-ray diffraction.
Various properties, such as, hardness, case depth, tensile, impact, fatigue properties
and corrosion resistance were investigated for both un-nitrided and ion-nitrided
materials. It is observed that the microstructure of the core material remains unaltered
and Fe4N is formed in the hardened surface layer after ion nitriding at all the three
temperatures employed. Surface hardness increases substantially after ion nitriding.
Surface hardness remains almost the same but case depth increases with the increase
in ion nitriding temperature due to greater diffusivity at higher temperatures. Tensile
strength, fatigue strength and corrosion resistance are improved but ductility and
energy absorbed in impact test decrease on ion nitriding. These results are explained
on the basis of microstructural observations. The properties obtained after ion nitriding at 450 °C for 10 h are found to be optimum when compared to the other two
ion nitriding temperatures.
Keywords：Ionnitriding;Maragingsteel;Microstructure;Casedepth;
Tensileproperties;Fatigue properties
1. Introduction
Surface engineering means ‘engineering the surface’ of a material or
component to confer surface properties, which are different from the bulk properties
of the base material[1]. The purpose may be to reduce wear, minimize corrosion,
increase fatigue resistance, reduce frictional energy losses, act as a diffusion barrier,
provide thermal insulation, exclude certain wave lengths of radiation, promote
radiation, electronic interactions, electrically insulate or simply improve the aesthetic
appearance of the surface. Surface engineering processes may broadly be grouped in
three categories as (a) modifying surfaces without altering the substrate's chemical
composition; these types of processes include transformation hardening, cold
deformation, machining and peening, (b) changing the chemistry of the surface region;
these types of processes include carburizing, nitriding, anodizing and ion implanting,
and (c) adding a layer of material to the surface; these types of processes include weld
overlay, painting, metal spraying, plasma spraying, electroplating, bonding, physical
vapor deposition and chemical vapor deposition. Nitriding is a surface-hardening
process by the introduction of nitrogen into the surface of steel[2]. Process methods
for nitriding include gas nitriding, liquid or salt bath nitriding and plasma or ion
nitriding. In gas nitriding this is done using a mixture of ammonia gas and dissociated
ammonia in suitable proportions. In plasma or ion nitriding a glow discharge
technology is used to introduce nascent (elemental) nitrogen to the surface of a metal
part for subsequent diffusion into the material[3],[4]and[5]. The plasma assisted
surface modification techniques offer a great flexibility and are capable of tailoring
desirable chemical and structural surface properties independent of the bulk
properties[3]. It has other advantages, such as, no or very thin white layer forms after
nitriding and there is no machining or grinding involved after the process, which is particularly beneficial for complex parts. The hardened surface layer becomes an
integral part of the base material and there is no significant reduction in properties of
the base material. It is also known to provide the modified surface without
dimensional change and distortion of the component. Ion nitriding provides better
control of case chemistry and uniformity[3],[6]and[7].
Maraging steels belong to a new class of high strength steels with the
combination of strength and toughness that are among the highest attainable in
general engineering alloys[8]. The term maraging is derived from martensite age
