Showing items 1 - 10 of 10

Your selections:

An evaluation of strain rate sensitivity of selected stainless steels at different temperatures

  • Authors: Marques, Sérgio
  • Date: 2012-09-12
  • Subjects: Stainless steel , Metals - Mechanical properties , Strains and stresses
  • Type: Thesis
  • Identifier: uj:10242 , http://hdl.handle.net/10210/7613
  • Description: M.Ing. , In the design and analysis of components and structures, detailed information on the material behaviour and its properties is required. When a material is loaded dynamically, such as in metal punching, the material properties may not be the same as when loaded statically. This is known as the strain rate sensitivity of a material, which implies that properties such as the yield strength, tensile strength and ductility may vary with the rate at which the material is loaded. South Africa is one of the large stainless steel producing countries. Seventy percent of the known chromium ore reserves are found in the Bushveld Igneous Complex in the Northern Province and Mpumalanga. To compete on the global stainless steel market it is essential that the South African producers have all the relevant product information directly available. Considerable research has been performed on mild steel at different strain rates and temperatures[1]. Work has also been done on some austenitic stainless steels. Very little, or no work has been done in this regard on ferritic and martensitic stainless steels and on the proprietary alloy 3CR12[2]. The aim of this thesis is to investigate the strain rate sensitivity of Types 304, 430 and 316 stainless steel, 3CR12 corrosion resistant steel and mild steel at different temperatures. To achieve this, tensile tests are performed. at strain rates between 10's -1 to approximately 100s -1 and at temperatures ranging from -40°C to 140°C. Shear tests are also performed at various strain rates, to investigate the effect that material behaviour has on a typical metal working process. The results obtained show that all the materials tested are strain rate sensitive. The strain rate sensitivity varies as a function of the material tested and the testing temperature. Constitutive models which take into account the strain rate sensitivity at room temperature for all the materials are also presented. These models describe the behaviour of the material fairly accurately. Three dimensional plots are also presented which depict how the yield strength, tensile strength and elongation vary as a function of both strain rate and temperature. These plots clearly show material trends for the strain rates and temperatures tested.
  • Full Text:

Characterization of laser metal deposited 17-4 PH stainless steel and tungsten composite for surface engineering applications

  • Authors: Adeyemi, A.A.
  • Date: 2018
  • Subjects: Pulsed laser deposition , Metal coating , Metals - Mechanical properties , Lasers - Industrial applications , Stainless steel
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/284734 , uj:30767
  • Description: Abstract: 17-4 PH Stainless steel is a martensitic characterized precipitation hardened stainless steel with excellent mechanical properties that has been tailored to industrial applications such as aerospace, automobile, marine, food processing equipment, oil and gas industries and chemical processing industries. Despite the growth experienced in the use of this material, 17-4 PH stainless steels are prone to degradation due to long service use in applications that required extreme hardness and wear resistance. This limitation led to the research of property enhancement of the material using modern fabrication technique called laser metal deposition additive manufacturing technology. Laser metal deposition is a modern additive manufacturing technique used in fabricating physical components from the configuration of a 3D CAD data model using a high intensity laser beam while depositing metallic powder on a substrate one layer at a time. This process is flexible in its use as it allows addition of reinforcing particles to improve surface properties of a metallic material such as hardness and wear amongst others. This research study presents the use of laser metal deposition process to investigate the property enhancement of 17-4 PH stainless steel through various characterization process such as microstructural evaluation, microhardness and wear test. The deposition process was carried out using Rofin Sinar Ytterbium fibre laser system of laser capacity of 3.0 kW. The reinforcement material was 17-4 PH stainless steel and tungsten metallic powder deposited on 316 stainless steel substrate. The deposition process commenced firstly with a trial-run deposition of 5 samples with multiple-track of 17-4 PH stainless steel at 50% overlapping percentage on 316 stainless steel substrate to establish process window. The reason for the trial-run was to achieve a deposition with no defects such as pores and cracks. After this was achieved, 17-4 PH stainless steel metallic powder and tungsten metallic powder were now deposited in form of multiple track at 50% overlapping percentage at high laser power and low laser power of 2600 W and 1500 W at varied tungsten powder flow rate on 316 stainless steel substrate. The microstructural evaluation, geometrical analysis, microhardness profiling and wear resistance characteristics of the deposited composites were investigated. The microstructural evolution investigation was carried out using optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD). Geometrical analysis was carried out on the deposited composite samples both at high and low laser power to investigate the extent of laser... , M.Ing. (Mechanical Engineering)
  • Full Text:

Characterization of laser metal deposited 316L stainless steel

  • Authors: Bayode, A. , Akinlabi, Esther Titilayo , Pityana, S.
  • Date: 2016
  • Subjects: Laser metal deposition , Microhardnes , Stainless steel
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/92382 , uj:20223 , Citation: Bayode, A., Akinlabi, E.T. & Pityana, S. 2016. Characterization of laser metal deposited 316L stainless steel.
  • Description: Abstract: Laser metal deposition (LMD) is an innovative manufacturing technique that uses laser to melt powders to fabricate fully dense components layer by layer. It is capable of processing different metallic powders and can also be used for consolidating different powder to produce custom alloys or functionally graded materials (FGM). The properties of laser processed materials is dependent on the final microstructure of the parts which in turn is dependent on the LMD processing parameters. This study investigates the effects of laser power on the structural integrity, microstructure and microhardness of laser deposited 316L stainless steel. The result showed that the laser power has much influence on the evolving microstructure and microhardness of the components. The average microhardness of the samples were observed to decrease as the laser power increased due to grain coarsening.
  • Full Text:

Cleanability of certain stainless steel surface finishes in the brewing process

  • Authors: Cluet, John David
  • Date: 2008-11-18T09:07:18Z
  • Subjects: Stainless steel , Stainless steel surfaces , Stainless steel cleaning
  • Type: Thesis
  • Identifier: uj:14727 , http://hdl.handle.net/10210/1731
  • Description: M.Phil. , Stainless steel is considered to be the most appropriate material for the fabrication of plant and equipment in the food and beverage industry. The apparent ease by which the surface finish of the material can be kept hygienically clean is a key factor in favour of stainless steel over other materials and those with applied surfaces, as is its resistance to corrosion. The manufacture of stainless steel and subsequent processes to fabricate the finished product into plant or equipment are well researched and documented. The relevance of a so called clean surface during manufacture and fabrication is documented in international standards to ensure that the material is protected against corrosion to prevent failures during the life cyle of the product. The importance of cleanability of specific surface finishes on stainless steel and comparative materials has been researched in small scale experimental set-ups. The results indicate that the rougher surfaces make cleaning more difficult and that the cleaning processes have a significant impact on the final cleanliness of the surface. No research has been documented on the effect of the operational environment in a brewery on the passive oxide layer of the stainless steel equipment surface. The possible breakdown of the passive layer on the surface is generally known to cause corrosion, that in turn causes failures in the fabricated equipment. The critical importance of maintaining strict hygienic standards in food processing plants has been the focus of international standard bodies to reduce the incidents of foodborne diseases. It has therefore become critical to understand how clean is the surface, and how the surface can be measured in an operational environment by using effective and reliable non-destructive testing procedures. A brewery operational environment review of stainless steel equipment was carried out to assess the impact on the surface of the equipment after 10 years. The results obtained from this review were used to design the experimental set-up. The test vessel is a fermenter that forms part of a training brewery that produces beer using standard processes. The internal surfaces of the fermenter were prepared with 4 different finishes (2B milled, 120 and 240 mechanically polished and electropolished). These are finishes that are used in the food and beverage industry. The fermentation process carried out in the vessel created a standard soil that was then cleaned off by the standard Cleaning-In-Place (CIP) process using caustic, acid and sterilant regimes. The experiments were repeated to assess the results of the comparative cleanability on the different surfaces and the possible changes occuring on the surfaces during the fermentation and cleaning cycles. The method used to check for cleanability is based on ATP Bioluminescence that detects minute traces of organic material that indicate the level of hygiene in the vessel. The methods used to check the surface roughness include standard Two-Dimensional Profilometry directly on the metal surfaces and Three-Dimensional Microscopy on replicated samples. Visual appraisal of cleanability was also done at each step of the process. All these tests were carried out on the surfaces before use and after each fermentation and CIP cycle. The results indicate that all surfaces are equally clean in areas where the CIP chemicals impinge directly on the surface at the top of the vessel. As the chemicals flow down the side of the vessel and reach the bottom cone, the levels of hygiene reduce. The surface that achieved the best level of hygiene is the electropolished surface finish, even at the lower section of the vessel. The mechanically polished surface (240 Grit) started to pit after the second cycle. Both the lower cleanability of surfaces at the bottom of vessel, and the roughening caused by pitting, have been observed during the operational review. The results also indicate that further work can be done to optimize the CIP processes to achieve effective cleaning at the lowest cost, and that the surface breakdown can be assessed and analysed using the replicating sample method with microscopy to determine the extent of change over the life cycle of the equiment.
  • Full Text:

Effect of crystallographic orientation on the pitting corrosion resistance of laser surface melted AISI 304L austenitic stainless steel

  • Authors: Krishnan, S. , Dumbre, J. , Bhatt, S. , Akinlabi, Esther Titilayo , Ramalingam, R.
  • Date: 2013
  • Subjects: Laser melting , Stainless steel , Austenitic stainless steel , Corrosion resistance
  • Type: Article
  • Identifier: uj:4846 , http://hdl.handle.net/10210/12513
  • Description: The localized corrosion behavior of laser surface melted 304L austenitic stainless steel was studied by potentiodynamic polarization test. The extent of improvement in corrosion resistance was governed by the preferred orientation and the percentage of delta ferrite present on the surface of the laser melted sample. It was established by orientation imaging microscopy that the highest pitting potential value was obtained when grains were oriented in the most close- packed [101] direction compared to the random distribution of the base metal and other laser surface melted samples oriented in [001] direction. The sample with lower percentage of ferrite had good pitting resistance.
  • Full Text:

Evolution of stress–strain models of stainless steel in structural engineering applications

  • Authors: Dundu, Morgan
  • Date: 2018
  • Subjects: Stainless steel , Stress–strain , Non-linear
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/270603 , uj:28766 , Citation: Dundu, M. 2018. Evolution of stress–strain models of stainless steel in structural engineering applications.
  • Description: Abstract: Stainless steel is a family of steel alloys with a minimum of approximately 10.5% mass of chromium. Unlike carbon steel, it has high corrosion and heat resistant properties. Stainless steel does not easily corrode because it forms an invisible thin passive film of about 5x10-6mm of chromium oxide (Cr2O3), which is impervious to water and air. If this film is damaged by scratching, it repairs itself as chromium in the steel reacts rapidly with oxygen and moisture in the environment to re-form the oxide layer. Since the early 20th century a lot of research work has been performed to understand the stress-strain response and mechanical properties of materials which exhibit non-linear behaviour over the complete shape of the stress-strain curve. Significant progress was achieved when the Ramberg– Osgood model was developed, however, there is consensus amongst researchers that this model is only accurate up to the 0.2% proof stress. As designs become more complicated and refined, it is clear that the behaviour of non-linear materials cannot be fully described by the Ramberg–Osgood model. Advanced numerical analysis and design requires knowledge of the stress-strain relationship of the alloys over a full range of the stress-strain curves. This paper provides a detailed review of the evolution of the stress-strain models of stainless steel, in literature.
  • Full Text:

Finite element analysis of distortional buckling of cold-formed stainless steel columns

  • Authors: Aihua, Liang
  • Date: 2012-01-24
  • Subjects: Stainless steel , Stainless steel cold working , Buckling (Mechanics) , Strength of materials
  • Type: Thesis
  • Identifier: uj:1943 , http://hdl.handle.net/10210/4302
  • Description: M.Ing. , Because cold-formed stainless steel is a new type of light steel material and dose not have a long history of utilisation in structures, there are many issues that need to be researched and discussed. Making a more thorough investigation and study of cold-formed stainless steels is essential. As a numerical analysis tool, the finite element method proves to be useful in structural analysis. The buckling modes of cold-formed stainless steel members, such as local, flexural, torsional and torsional-flexural buckling, are well known and well documented in design specifications. Distortional buckling is a special kind of buckling mode, which is less well known. Researchers have recently paid more attention to this problem. For stainless steel structures, it is necessary to investigate their behaviour when distortional buckling occurs. In this project, the distortional buckling of cold-formed stainless steel columns under axial compression is investigated. The finite element method is used to analyse and calculate different buckling modes, especially distortional buckling. This is compared to experimental results and other theoretical predictions. The ABAQUS finite element code is used throughout. Finite element modelling is very important prior to processing and analysis. ABAQUS models are created to study distortional buckling. The initial imperfection of structural members is taken into account with these models, using specific sine wave descriptions with respect to different structural parameters. A dynamic processing approach is chosen in the finite element analysis. The effectiveness and accuracy of these models have been verified by both experimental tests and theoretical calculations. Buckling mode and behaviour are predicted and analysed in terms of the finite element models and processes. Suggestions are made for buckling analysis and design based on the research results.
  • Full Text:

Investigation on dry machining of stainless steel 316 using textured tungsten carbide tools

  • Authors: Mashinini, P. M. , Soni, Hargovind , Gupta, Kapil
  • Date: 2020
  • Subjects: Machinability , MRR , Stainless steel
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/411192 , uj:34544 , Citation: P M Mashinini et al 2020 Mater. Res. Express 7 016502 , DOI: https://doi.org/10.1088/2053-1591/ab5630
  • Description: Abstract: In this research, austenitic stainless steel SS316 material has been machined using textured carbide cutting tools under dry conditions. Micro-textures were made on tool rake face using wire spark erosion machining technology. Effects of three important machining process parameters i.e. cutting speed, depth of cut and feed rate on machinability (MRR, average roughness, and tool wear) of SS316 have been investigated. Taguchi L27 orthogonal array based twenty seven experiments have been carried out by varying machining parameters at three levels. Feed rate has been identified as the most important parameter. Machining parameters have been optimized by grey entropy method to enhance the machinability. Optimal combination of machining parameters i.e. 170 m min−1 cutting speed, 0.5 mm/rev feed rate and 1.5 mm depth of cut produced the best machinability with 3.436 μm average roughness, 105187 mm3 min−1 . MRR, and tool wear 234.63 μm. Lastly, a tool wear and chip morphology study have been done where textured tools have been found outperformed plain (Non-textured) tools.
  • Full Text:

Machinability analysis and hybrid optimization during wet turning of SS304 using coated tools

The punching shear capacity of concrete slabs reinforced with 3CR12 corrosion resistant stainless steel and carbon steel

  • Authors: Fourie, Johan Becker
  • Date: 2011-12-06
  • Subjects: Concrete slabs , Shear (Mechanics) , Stainless steel , Carbon steel
  • Type: Thesis
  • Identifier: uj:1839 , http://hdl.handle.net/10210/4199
  • Description: M.Ing. , In this study a comparison is made between the punching shear capacities of square slabs reinforced with 3CR 12 corrosion resisting stainless steel and high tensile strength carbon steel. A square column 11 0 mm x 11 0 mm is used to simulate the point load on the slab. Three different slab depths were chosen for the experimental procedure. The South African concrete design specification SABS 0 I 00, the Eurocode concrete design specification and Menetrey's design model are used to determine the theoretical punching shear capacities of the slabs. It is concluded in this study that the procedures described in the concrete design codes and by Menetrey to determine the punching shear stress of concrete slabs reinforced with high strength carbon steel reinforcing bar compare well with the experimental results when 3CR I 2 corrosion resisting steel is used as reinforcing bar in concrete. The experimental results do not compare well with the theoretical results when the new Eurocode is used.
  • Full Text:
  • 1
  • Disclaimer
  • Privacy
  • Copyright
  • Contact