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Effects of Surface Hardening and Residual Stress on the Fatigue Characteristics of Nitrided SACM 645 Steel

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International Journal of Modern Physics B
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Byung Won Hwang
Byung Won Hwang
Byung Won Hwang
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Chang Min Suh at Kyungpook National University
Chang Min Suh
Ho Kyung Jang
Ho Kyung Jang
Ho Kyung Jang
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Abstract

To analyze the effect of the surface hardening and residual stress on the fatigue strength and behavior of crack nucleation, fatigue test were performed on SACM 645 steels nitrided using the Nitemper method. The gas nitriding was performed for 9 hours at 540°C and 8 hours at 570°C to obtain different depths of hardening, and some of the specimens were subjected to stress relief (SR) treatment to clarify effect of residual stress on the fatigue characteristics. After nitriding, the fatigue strength of specimens was 40% higher than that of base materials. It was also found that the increment in the fatigue characteristics was due to the compressive residual stresses that formed on the surface of specimens and produced subsurface crack nucleation during fatigue.
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International Journal of Modern Physics B
Vol. 17, Nos. 8 & 9 (2003) 1633-1639
© World Scientific Publishing Company
EFFECTS OF SURFACE HARDENING AND RESIDUAL STRESS ON THE
FATIGUE CHARACTERISTICS OF NITRIDED SACM 645 STEEL
BYUNG WON HWANG
Dept. of Mechanical Engineering, Kyungpook National Univ.,Sankeugdong, Pukgu,
Taegii,
702-701, Korea
bwhwang@kebi.com
CHANG MIN SUH'and HO KYUNG JANGb
"Dept. of Mechanical Engineering, Kyungpook National Univ.,Sankeugdong, Pukgu,
Taegii,
702-701, Korea
bGraduate School of Mechanical Engineering, Kyungpook National Univ.,Sankeugdong, Pukgu,
Taegu, 702-701, Korea
Received 12 September 2002
Revised 28 November 2002
To analyze the effect of the surface hardening and residual stress on the fatigue strength and
behavior of crack nucleation, fatigue tests were performed on SACM 645 steels nitrided using the
Nitemper method. The gas nitriding was performed for 9 hours at 540°C and 8 hours at 570°C to
obtain different depths of hardening, and some of the specimens were subjected to stress relief (SR)
treatment to clarify effect of residual stress on the fatigue characteristics. After nitriding, the fatigue
strength of specimens was 40% higher than that of base materials. It was also found that the
increment in the fatigue characteristics was due to the compressive residual stresses that formed on
the surface of specimens and produced subsurface crack nucleation during fatigue.
1.
Introduction
Machine elements and components, such as shafts, bearings, and gears, are subjected to
continuous fatigue and wear loading during working. Generally, the surfaces of these
components are required to resistance against wear, and the inner sides need a high
toughness. For this purpose, the surface hardening method on the plain carbon or alloy
steels has been used to improve two characteristics at the same time
[1-4].
Several methods had been developed to harden the surface of materials. Among
them, Nitriding is commonly used to improve the mechanical properties of metallic
materials. When compared with cementation based on the diffusion of carbon into
austenite, nitriding has the advantage that it can be performed within a temperature
range of 500-600°C, blow the austenite transformation temperature. Accordingly, since
it only involves a minimal dimension change, nitriding is commonly used in the
manufacture of die and precision parts
[5-7].
w
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1633
... Para aumentar o limite de fadiga de qualquer material é necessário a introdução de tensões residuais na sua superfície. Essas tensões residuais podem ser introduzidas utilizando processos tais como, jateamaneto com granalhas, roleteamento superficial, deformação a frio em furos de prendedores, tratamentos térmicos e tratamentos termoquímicos (nitretação a plasma) [10,13,14]. A camada de nitretos formada durante o tratamento possui uma influência positiva na vida em fadiga de um componente, graças a dois motivos principais [14]. ...
... Essas tensões residuais podem ser introduzidas utilizando processos tais como, jateamaneto com granalhas, roleteamento superficial, deformação a frio em furos de prendedores, tratamentos térmicos e tratamentos termoquímicos (nitretação a plasma) [10,13,14]. A camada de nitretos formada durante o tratamento possui uma influência positiva na vida em fadiga de um componente, graças a dois motivos principais [14]. O ...
... Com a ionização do gás, uma corrente elétrica é gerada, e sua sustentação dependerá da variação da diferença de potencial entre os eletrodos, dada pela curva da FIGURA 1 [3,14]. Figura 1 -Curva característica da densidade de corrente-voltagem aplicada entre dois eletrodos [3]. ...
Plasma nitriding influence in the fatigue behavior of austenitic stainless steels AISI 304 and 316
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The austenitic stainless steels are attractive materials to many industrial sectors which work on corrosive environments, as chemical industry alcohol, petrochemical, cellulose industries, in the petroleum prospection and pharmaceutical and textiles industries. However, they present poor tribological properties. In order to improve these properties, like increasing superficial hardness, wear and fatigue resistance superficial heat treatment methods have being used. The most efficient is the plasma nitriding process which occurs in a vacuum container under hydrogen and nitrogen gas mixture. A potential difference is applied between the cathode (samples receptor) and the anode (container walls), accelerating the ions against the piece, heating it and removing electron from the surface of material. These atoms react with the surface plasma species, producing unstable compounds like FeN, which recombine producing stable nitrides. The success of this treatment is due to the low temperature operation, the short effective time of treatment and to the uniformity control of the layer’s thickness. The nitrides layer produced during the treatment have a positive influence in the fatigue life of a component, thanks to two main reasons. The first is the retardation in crack nucleation due to increasing of superficial mechanical strength. The second reason is due to introduction of compressive residual stress during the surface hardening process, which retards de crack initiation process. The specimens were nitriding at 400°C during 6 hours, at a 4,5mbar pressure and using a gas mixture of 80% vol. H2 and 20% vol. N2. The surface mechanical strength increased, due to the nitrides layer, which was evident with the sensitive increase in the fatigue limit of the nitriding specimens, comparing to the untreated ones. The fatigue limit of the AlSl 316 steel in untreated condition was 400 MPa and in nitriding condition was 510 MPa, whereas AlSl 304 steel, the fatigue limit of the untreated condition was 480 MPa and the fatigue limit for the nitrided condition was 560 MPa
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... These residual stresses can be introduced through processes such as blasting with abrasive grains, surface rolling, cold deformation in fastener holes, heat treatment, and thermochemical treatment (plasma nitriding). [3,8,9] The layer of nitrides formed during the treatment has a positive influence on the fatigue life of a component for two main reasons. [9] The first is the delay in fatigue crack nucleation due to the increase in surface mechanical strength. ...
... [3,8,9] The layer of nitrides formed during the treatment has a positive influence on the fatigue life of a component for two main reasons. [9] The first is the delay in fatigue crack nucleation due to the increase in surface mechanical strength. The second reason has to do with the introduction of residual compressive stresses during the process of surface hardening, which retards the onset of cracks, reducing the stress intensity factor. ...
... The second reason has to do with the introduction of residual compressive stresses during the process of surface hardening, which retards the onset of cracks, reducing the stress intensity factor. [3,9,10] Thus, the objective of this work was to study the composition of the nitride layer and the influence of this layer on the high-cycle fatigue properties of AISI 304 and 316 austenitic stainless steels with similar composition and microstructure. ...
The influence of plasma nitriding on the fatigue behavior of austenitic stainless steel types AISI 316 and AISI 304
Article
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The plasma nitriding process has been used as an efficient method to optimize the surface properties of steel and alloy in order to increase their wear, fatigue and corrosion resistance. This paper reports on a study of the composition and influence of the nitrided layer on the high-cycle fatigue properties of the AISI 316 and 304 type austenitic stainless steels. Test specimens of AISI 316 and 304 steel were nitrided at 400°C for 6 hours under a pressure of 4.5 mbar, using a gas mixture of 80% volume of H2 and 20% volume of N2. The rotary fatigue limit of both nitrided and non-nitrided steels was determined, and the effect of the treatment on the fatigue limit of the two steels was evaluated. The mechanical properties of the materials were evaluated based on tensile tests, and the nitrided layer was characterized by microhardness tests, scanning electron microscopy and X-ray diffraction. The resulting nitride layer showed high hardness and mechanical strength, increasing the fatigue limit of the nitrided material in comparison with the non-nitrided one. The fatigue limit of the 316 steel increased from 400 MPa to 510 MPa in response to nitriding, while that of the 304 steel increased from 380 MPa to 560 MPa. One of the contributing factors of this increase was the introduction of residual compressive stresses during the surface hardening process, which reduce the onset of crack formation underneath the nitride layer. Copyright © (2010) by Associação Brasileira de Metalurgia Materiais e Mineração (ABM).
View
... It is possible to observe that the hardness decreases indepth with the nitrided layer due to nitrogen percentage reduction. The highest hardness was observed in point 1, with 550HV, proving the increase in the surface hardness of the material due to the plasma nitriding, which forms iron nitride as Fe 4 N and Fe 2-3 N, with presents ceramic characteristics and compressive tensions that increase the material hardness [20]. ...
Plasma Nitriding Effect on Tribological Behavior of AISI D2 tool steel: Understanding of Wear Rate
Article
Full-text available
  • Nov 2022
Plasma nitriding increases tool steels life. In the Steady-State of wear (SSW) the wear coefficient (k-wear rate) as a function of the sliding distance and applied load does not change and allows the development of mathematical models to predict the wear behavior of the material under the test conditions. The AISI D2 steel was plasma nitrided at 480°C (80%N2/20%H2) for 4h. The nitrided layer has a thickness of 80μm and a composite layer of 2.46μm. The increase in hardness in the nitrided sample improved the wear resistance of the material studied. In addition, it was possible to obtain the SSW of the material and determine the constant k through mathematical models that allow the prediction of wear behavior. Thus, plasma nitriding treatment was effective to improve the wear resistance of AISI D2, and SSW is an important parameter to predict the wear behavior of materials.
View
... Николетто, Р. Конечка, В. Мажерова, Н. Ванг, Дж. Лю, З. Уанг и другие [2][3][4][5][6][7][8]. Первые трое анализировали воздействия светлых областей на усталостное разрушение в высокопрочных чугунах с шаровидным графитом (ШГ) после процесса азотирования. ...
View
... Consequently, the structural steel of those components should be always surface modified to provide these needed properties. The surfaces of these components are required to attain high hardness values to resist wear, and the inner cores still need to have high toughness strength [1,2]. Therefore, various methods, such as nitriding, carburizing, ceramic coating and thermal chemical treatments, have been devised to improve the surface mechanical properties of the components [3][4][5]. ...
Effects of Gas Nitriding on the Mechanical and Corrosion Properties of SACM 645 Steel
Article
Full-text available
  • Jan 2011
The effects of the nitrided case produced by gas nitriding processes on the mechanical and corrosion resis-tance properties of the JIS SACM 645 steel were studied in this paper. JIS SACM 645 steel specimens with different substrate hardness were gas nitrided at 530˚C for various nitriding durations. Nitrided specimens were characterized by means of optical and scanning electron microscopy, X-ray diffraction, glow discharge optical spectrometry, microhardness profiling, wear test, torsion mode fatigue test as well as electrochemical corrosion test in an aerated 3.5% NaCl solution. The surface hardness values of the nitrided specimens with Fe 3 N and Fe 4 N phases precipitated in the case layer were observed higher than 1000 HV 0.1 . Mass loss meas-urement of the wear test showed increases of wear resistance of the nitrided specimens, and the mass losses of the specimens were strongly influenced by nitriding durations. Electrochemical measurements showed that corrosion current density of the specimens was significantly decreased after nitriding and the corrosion potential was shifted to the noble direction as the increase of the nitriding durations. The fatigue limit of the specimen nitrided for 96 h rose 44% to 600 MPa in exceeding the untreated specimen in this study.
View
... Consequently, the structural steel of those components should be always surface modified to provide these needed properties. The surfaces of these components are required to attain high hardness values to resist wear, and the inner cores still need to have high toughness strength [1,2]. Therefore, various methods, such as nitriding, carburizing, ceramic coating and thermal chemical treatments, have been devised to improve the surface mechanical properties of the components [3][4][5]. ...
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In this project, the alternating torsion fatigue test was carried out to investigate the effect of the nitrided case produced by gas and plasma nitriding processes on the fatigue endurance of the JIS SACM 645 steel. The surface layers of the nitrided specimens exhibited hardness profiles in the range between 1000–1100HV0.1, and the white layer of the nitrided specimen was consisted of Fe3N and Fe4N. Wear test result indicated that the mass loss of JIS SACM 645 steel was greatly improved by nitriding processes. From the mass loss data, the wear resistance of the steel was significantly influenced by nitriding time. The fatigue strength of the 35C-GN48 nitrided specimen rose 51.9% to 632 MPa, which was the maximum fatigue strength in this study.
View
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