Creep characterization of type 316LN and HT-9 stainless steels by the K-R creep damage model

The Kachanov and Rabotnov (K-R) creep damage model was interpreted and applied to type 316LN and HT-9 stainless steels. Seven creep constants of the model,A, B. k, m, λ, γ, andq were determined for type 316LN stainless steel. In order to quantify a damage parameter, the cavity was interruptedly traced during creep for measuring cavity area to be reflected into the damage equation. For type 316LN stainless steel, λ=ε _R /ε* and λ _f =ε/ε _R were 3.1 and increased with creep strain. The creep curve with λ=3.1 depicted well the experimental data to the full lifetime and its damage curve showed a good agreement whenr=24. However for the HT-9 stainless steel, the values of A and A/ were different as λ=6.2 and λ _f =8.5, and their K-R creep curves did not agree with the experimental data. This mismatch in the HT-9 steel was due to the ductile fracture by softening of materials rather than the brittle fracture by cavity growth. The differences of the values in the above steels were attributed to creep ductilities at the secondary and the tertiary creep stages.     

Elevated temperature deformation behavior in an AZ31 magnesium alloy

An AZ31 magnesium alloy was tested at constant temperatures ranging from 423 to 473 K (0.46 to 0.51T _m ) under constant stresses. All of the creep curves exhibited two types depending on stress levels. At low stress (σ/G<4×10⁻³), the creep curve was typical of class A (Alloy type) behavior. However, at high stresses (σ/G>4×10⁻³), the creep curve was typical of class M (Metal type) behavior. At low stress level, the stress exponent for the steady-state creep rate was of 3.5 and the true activation energy for creep was 101 kJ/mole which is close to that for solute diffusion. It indicates that the dominant deformation mechanism was glide-controlled dislocation creep. At low stress level wheren=3.5, the present results are in good agreement with the prediction of Fridel model.     

An examination of the electrochemical characteristics of two stainless steels (UNS S32654 and UNS S31603) under liquid-solid impingement

The erosion-corrosion resistance of high alloy stainless steel UNS S32654 and standard stainless steel UNS S31603 has been assessed under liquid-solid impingement conditions. The electrochemical characteristics of the two stainless steels have been examined via free corrosion potential measurements, anodic polarisation, linear polarisation and potentiostatic control in erosion-corrosion.It has been shown in this paper that high alloy stainless steel UNS S32654 exhibits better corrosion and erosion-corrosion performance than lower grade alloy UNS S31603. A general linear relationship between two electrochemical parameters (E_corr and R_p) has been shown in this study. A critical solid loading between 60 and 100 mg/l, at which there is a transition from corrosion to erosion-corrosion for the two stainless steels under different conditions, has been determined.     

Atom probe,AFM, and STM studies on vacuum-fired stainless steels

The surface morphology of grades 304L and 316LN stainless steels, after low-temperature bake-out process and vacuum annealing, has been studied by atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). The local elemental composition on the surface before and after thermal treatment has been investigated by atom probe (AP) depth profiling measurements. After vacuum annealing, AFM and STM show significant changes in the surface structure and topology. Recrystallization and surface reconstruction is less pronounced on the 316LN stainless steel. AP depth profiling analyses result in noticeable nickel enrichment on the surface of grade 304L samples. Since hydrogen recombination is almost controlled by surface structure and composition, a strong influence on the outgassing behaviour by the particular surface microstructure can be deduced.     

High-temperature low cycle fatigue, creep–fatigue and thermomechanical fatigue of steels and their welds

High-temperature low cycle fatigue (LCF) is influenced by various time-dependent processes such as creep, oxidation, phase transformations and dynamic strain ageing (DSA) depending on test conditions of strain rate and temperature. In this paper, the detrimental effects of DSA and oxidation in high-temperature LCF are discussed with reference to extensive studies on 316L(N) stainless steel and modified 9Cr–1Mo steel. DSA has been found to enhance the stress response and reduce ductility. It localizes fatigue deformation, enhances fatigue cracking and reduces fatigue life. High-temperature oxidation accelerates transgranular and intergranular fatigue cracking in modified 9Cr–1Mo steel and during long hold time tests in austenitic stainless steel. In welds, microstructural features such as presence of course grains in the HAZ and formation of brittle phases due to transformation of δ ferrite during testing influence crack initiation and propagation and fatigue life. Thermomechanical fatigue (TMF) studies are suggested as more closer to the actual service conditions. In 316L(N) stainless steel, TMF lives under out-of-phase cycling are found to be lower than those under in-phase conditions in the low-temperature regimes, while the converse holds good when the upper temperature encompassed the creep-dominant regime.     

The effect of fretting on the fatigue behaviour of plasma nitrided stainless steels

The plain fatigue and fretting fatigue behaviour of a plasma nitrided dual phase stainless steel known as 3CR12 and an AISI 316 austentic stainless steel have been studied in the present work, using a modified Wohler rotating-bending configuration. Test specimens were produced at two nitriding temperatures, namely 400 and 520 °C, representing low temperature and conventional nitriding temperature, respectively. The test results demonstrate that both nitriding processes can enhance the plain fatigue limit of these steels by approximately 10-25%, with the high temperature process being slightly more effective. Under fretting fatigue conditions, the beneficial effect of plasma nitriding is even more significant and the fretting fatigue limit is increased between 50 and 100% for 3CR12 and at least 50-150% for the AISI steel as the nitriding temperature is raised from 400 to 520 °C.     

Tribological behaviour of AISI 316L stainless steel for biomedical applications

Abstract

The aim of this research is to study the tribological behaviour of AISI 316L stainless steel for surgical implants (total hip prosthesis). The tribological behaviour is evaluated by wear tests, using tribometers ball on disc and sphere on plane. These tests consisted of measuring the weight loss and the friction coefficient of stainless steel (SS) AISI 316L. The oscillating friction and wear tests have been carried out in ambient air with an oscillating tribotester in accord with standards ISO 7148, ASTM G99-95a and ASTM G133-95 under different conditions of normal applied load (3, 6 and 10 N) and sliding speed (1, 15 and 25 mm s^?1). A ball of 100Cr 6, 10 mm in diameter, is used as counter pairs. These tribological results are compared with those carried out with a tribometer type pin on disc under different conditions of normal load applied P (19·43, 28 and 44 N) and sliding speed (600 and 1020 rev min^?1). The behaviour observed for both samples suggests that the wear and friction mechanism during the tests is the same, and to increase the resistance to wear and friction of biomedical SS AISI 316L alloy used in total hip prosthesis (femoral stems), surface coating and treatment are necessary.     

A comparison of residual stresses in built-up steel beams using hole-drilling method

Residual stresses have a significant effect on the stability resistance of metal building systems. An experimental program was conducted to measure these stresses in built-up steel beams using incremental hole-drilling method. The experimental results reveal that the predicted residual stress type of pattern for built-up I-sections with fillet welds on one side of the web is not the same as the pattern of residual stresses in built-up I-sections with fillet welds on both sides of the web. This paper was recommended for publication in revised form by Associate Editor Youngseog Lee Mohammed Al-Nawafleh received his B.S. and M.S degrees in Mechanical Engineering from Leningrad Institute of Textile and Light Industry, in 1989. He then received his Ph.D. degree from Sankt-Petersburg State University of Technology and Design, Russia in 1993. Dr. Nawafleh (1997–2005) was a Professor at the Department of Mechanical Engineering at Al-Balqa’ Applied University in Jordan. From 2005 to 2008 he was a Professor at the Department of Mechanical Engineering at Tafila Technical University, and currently he is a Professor at the Department of Civil Engineering at Al-Hussein Bin Talal University, Jordan.     

Study on the oxidation of stainless steels 304 and 304L in humid air and the friction during hot rolling

In rolling process, the contact friction is of crucial importance for accurate modeling, optimum design and control of industrial rolling processes. It is important to characterize the features of the oxide scale of stainless steel in hot strip rolling because the scale on the strip surface affects friction coefficient and thermal conductivity coefficient. To some extent, the rolling force and friction condition depend on the thickness and the microstructure of the oxide scale. Oxidation tests of stainless steels 304 and 304L were carried out in a high temperature electric resistance furnace. The humid air in which the water vapour content can be controlled was generated and remained to flow into the chamber of the furnace in 2.5 × 10⁻⁴ m³/s to study the effect of humidity on the oxidation of stainless steels. The microstructure and thickness of oxide scale layer of stainless steels were obtained and two or three oxide layers can be found. The humid air has a significant effect on the growth of oxide scale. Hot rolling tests were carried out on Hille 100 rolling mill. The friction condition at the roll–strip interface during hot rolling of stainless steel was determined and the transfer of surface roughness was discussed.     

Hygrothermal behavior of electro-active paper actuator

Mechanical properties of the electro-active paper (EAPap) actuator were tested to investigate its hygrothermal behavior. Tensile creep behavior was studied with constant load at 30–70% relative humidity ranges and 25–40°C temperature. Creep deformation showed typical trend of abrupt strain increase in a short period followed by steady increase of strain, which resulted from the breakdown of cellulose microfibrils. Dependence on the material orientation of EAPap was observed in the creep tests. As changing the orientation of EAPap samples, the creep resistances were varied. Creep strains and creep strain rates were increased as increasing the relative humidity level at 25°C. However, at the elevated temperature of 40°C, the creep strain rate at secondary creep was not significantly raised under increased relative humidity level from 30% to 50%. The hygrothermal effect by increasing the relative humidity level and temperature on the creep rate was reduced due to the saturated moisture at a higher temperature even with lower humidity level. The activation energy levels for creep were around 607–658 kJ/mol for 30% relative humidity level and 623–671 kJ/mol for 50% relative humidity level depending on the material orientation. Understanding of hygrothermal effect in conjunction with the humidity and temperature provides useful information for the potential nano-bio applications of the EAPap actuator. This paper was recommended for publication in revised form by Associate Editor Chongdu Cho Heung Soo Kim received his B.S. and M.S. degrees in the Department of Aerospace Engineering from Inha University, Korea in 1997 and 1999, respectively. He got his Ph. D degree in the Department of Mechanical and Aerospace Engineering from Arizona State University in 2003. He is now working as an assistant professor in the School of Mechanical and Automotive Engineering, Catholic University of Daegu. His main research interests are in biomimetic actuators and sensors, structural health monitoring, smart materials and structures as applied to aerospace structures and vehicles. Chulho Yang received his B.S. and M.S. degree in Mechanical Engineering from Inha University in 1991 and 1993, respectively. He also obtained M.S. and Ph. D degree in Mechanical Engineering from University of Florida in 1995, and 1997, respectively. In March 2003, he joined the School of Mechanical Engineering at Andong National University, Korea, where he is now an Associate Professor. His main research interests are mechanical behavior of materials including smart materials both experimentally and computationally. Jaehwan Kim received his B.S. degree in Mechanical Engineering from Inha University, in 1985. He received his M.S. degree from KAIST in 1987 and his Ph.D. degree from The Pennsylvania State University in 1995. Dr. Kim is currently a Professor of Dept. of Mechanical Engineering at Inha University, Inchoen, Korea. He serves as an Associate Editor of Smart Materials and Structures. He is the director of Creative Research Center for EAPap Actuator supported by KOSEF. Dr. Kim’s research interests are smart materials such as piezoelectric materials, electro-active polymers and their applications including sensors, actuators, motors and MEMS devices.     

Characterization of the Q* parameter for evaluating creep crack growth rate for type 316LN stainless steel

In this study, the Q* parameter was characterized to evaluate the Creep crack growth rate (CCGR) of type 316LN stainless steel. Creep crack growth (CCG) data were obtained by CCG tests under different applied loads at 600°C. An additional CCG test was conducted at 550°C to investigate the possible temperature dependence of the stress intensity factor. An equation using the Q* parameter for evaluating CCGR was proposed, and this parameter was characterized and compared with the typical C* fracture parameter, which is commonly used. The Q* parameter exhibited good linearity of the data, exhibiting no nonlinearity-induced dual value at the early stage. The Q* parameter was suitable for characterizing the CCGR regardless of different applied loads and types of steels. In addition, fracture microstructures near the crack revealed a typical intergranular fracture mode, and this fracture was dominantly propagated along the grain boundary. The cracks were developed by the growth and interlinking of cavities, which were attributed to the precipitates forming along the grain boundary.

     

Relation between surface hardening and roughness induced by ultrasonic shot peening

This paper is focused on the identification of a relation between surface hardening and roughness induced by ultrasonic shot peening. A method that dissociates the influence of roughness from the value of the true macroscopic hardness is applied to AISI 316L stainless steel specimens treated using different processing conditions. The true macroscopic hardness is identified and used to determine the surface roughness parameter and scale that give the best relation between hardness and roughness. A relation is identified between the five point pit height S_5V roughness parameter (local depth of roughness) and hardness using a high-pass filter with a cut-off of 100 µm. This power function was identified at a scale that corresponds to the size of the shot impacts.     

Strengthening caused by power law creep deformation of dispersed particles in an elastic matrix

The interaction energy is approximated between an edge dislocation and a particle deformable by power law creep in an elastic matrix. The stress required to overcome the interaction energy barrier is found to be greater than the Orowan stress, and the dislocation bulges to escape the particle. If the ratio of the shear modulus of the matrix to the viscosity of the particle (μt^m/σ₀) is large, the stress required to climb over the particle is larger than the Orowan stress and the dilocation bulges before it climbs. It is concluded that even if the particle is soft enough to exhibit creep, the strengthening of alloys can be achieved by an Orowan mechanism. The critical resolved shear stress (CRSS) of Cu-B₂O₃, obtained experimentally by Onaka et al. [11], agrees closely with that obtained in our analysis. This supports our analysis that the strength of Cu-B₂O₃ alloy at high temperature may be accounted for by the Orowan mechanism and the attraction between a dislocation and viscous particles. The energy and the force to overcome the energy barrier increases significantly with decrease of m, the strain rate exponent associated with the power law creep particle. It is found through analysis that for m < 1.0 and for certain values of μt^m/σ₀ > 1, the particle repulses the dislocation, while for m = 1.0 and for all values of μt^m/σ₀ > 1, the particle attracts the dislocation, which is the expected interaction between an elastic particle and a dislocation in an elastic matrix.     

Delamination wear of metal injection moulded 316L stainless steel

The wear behavior of metal injection moulded (MIM) stainless steels was studied using a pin-on-disc apparatus under dry sliding conditions. Pin specimens were MIM 316L stainless steel, while disc specimens were wrought 316L stainless steel. At low sliding speeds (0.2–0.6 m/s), the wear rates gradually decreased with increasing sliding speed, but then increased at high sliding speeds (0.6–2 m/s). The adhesive-induced delamination wear dominated at low sliding speeds, while abrasive-induced delamination wear dominated at high sliding speeds. At low sliding speeds, the surface densification occurred on the worn surface of pin specimens, hence no difference was found between the wear resistances of MIM pins containing 2% and 6% porosity. In contrast, the abrasive-induced delamination wear at high sliding speeds was enhanced by porosity; therefore the wear rates of MIM pins containing 6% porosity were higher than those of MIM pins containing 2% porosity.     

An Investigation of the High Speed Machining Process Using a Variable Flow Stress Machining Theory

Abstract

This article investigates the application of the Oxley modeling approach to high speed machining (HSM) process for gaining a fundamental understanding and performance prediction of this process which is gaining increased popularity due to its many economic and technological advantages such as faster metal removal rates, efficient use of machine tools and, improved surface finish and lower cutting forces. Oxley's theory has so far mainly been applied for making machining predictions for plain carbon steels in the conventional speed range. In the present work, this theory has been applied for two plain carbon steels and a low alloy steel under HSM conditions. The predicted cutting forces, chip thicknesses, and secondary deformation zone thicknesses are then compared with the experimental results obtained under identical conditions. Good agreement has been shown between measured and predicted results. In addition, the possibility of applying the theory to predict the tool life and tool deformation conditions is also explored. An ability to predict these process parameters is of paramount importance since catastrophic tool failure under HSM conditions can be extremely costly and dangerous.     

内压圆筒中表面裂纹蠕变扩展的数值分析

金属蠕变的研究逐渐趋向对含缺陷材料与结构进行探讨,但针对金属构件表面裂纹蠕变扩展特性的研究仍然有限。基于三维有限元方法,对高温内压下含轴向表面裂纹的低合金Cr-Mo钢圆筒进行研究。有限元计算得到的应力强度因子K和蠕变裂纹驱动力参量C*积分与前人的研究进行比较,提出一种基于软件ABAQUS的步步分析方法来描述蠕变裂纹的扩展行为。最后,通过对若干不同初始形状裂纹的研究,得到四种不同初始形状的表面裂纹的形貌变化特性,以及裂纹深度、裂纹长度、C*积分和剩余寿命的变化规律。     

Behaviour of ferritic–martensitic steel and aluminium base coatings under demanding elevated temperature conditions

Abstract

Ferritic–martensitic steels are found in many elevated temperature applications due to their excellent strength properties and thermal conductivity. However, their resistance to elevated temperature corrosion, wear and combination of these is typically not at a desired level. One solution is to improve the surface properties by the application of a coating. In this study, aluminium diffusion coatings were deposited on 9Cr–1Mo steel and characterised in terms of microstructure and elevated temperature corrosion and erosion–corrosion behaviours. The two behaviours are then compared to those of an uncoated steel. The results from the tests indicate that aluminising shows great potential under the studied demanding elevated temperature conditions. The benefits and challenges of the deposition and use of aluminised coatings are discussed in this paper.     

Influence of microstructure on erosion resistance of steels

Erosive wear due to solid particle impingement is a very intensive degradation process of surface layers of metallic materials. Erosion resistance is influenced by the working conditions (impact angle, impact velocity of solid particles, size, shape, hardness and amount of impinging particles) and the parameters of the worn material like hardness and microstructure. In our experiments some structural and tool steels were tested by slurry with SiO₂ particles at a flow velocity of 20 m/s. The microstructures of the tested steels were modified in a broad range by changing the conditions of their heat treatment. Increasing pearlite share in the structure of annealed carbon and low-alloyed steels has a positive effect on their erosion resistance. The growing carbon content in the tested hardened steels increases their erosion resistance. Maximum erosion resistance was found in hardened chromium ledeburite steel. Hardened high-speed steel HS 11-0-4 in spite of its high hardness has lower erosion resistance than ledeburitic chomium steels. An increasing amount of retained austenite and decreasing carbide and martensite shares with growing quenching temperature of the tested ledeburitic chromium steels leads to the reduction of their erosion resistance.     

Influence of structural features of welded joints of low-alloy steels on magnetic and micromagnetic properties

Variations of magnetic (coercive force H _c , residual induction B _r , maximum magnetic permeability μ_max, maximum magnetic-permeability field H _μmax, saturation magnetization J _max) and micromagnetic (number of pulses N and RMS Barkhausen-noise amplitude U) characteristics along the parent metal-welded joint direction were studied for welds of steels 10XCHД, 15XCHД, 09Γ2C, and X70.     

Fracture strength evaluation of welded steel joint by means of small punch test

It has been well known that the ductile-brittle transition temperature (DBTT) of each weld structure or its shift (ΔDBTT) from parent material is one of the very useful measures of the fracture characteristics in steel weldment. In order to present an applicability of small punch (SP) test technique to weldments, in this study, a fracture strength of microstructure at any localized region of interest on HAZ, weld metal and parent material in two steels was evaluated by using DBTT or ΔDBTT obtained from the SP test in relation to the data obtained from the COD test. The empirical correlation, (ΔDBTT) _SP ⋟0.55 (ΔDBTT) _COD , was obtained from the SP and COD test. In addition, the effects of test materials, that is the microstructures of welded region and the orientations of specimens etc, did not appear at the empirical correlation.