Creep of metals
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Creep is the time-dependent deformation of a material under stresses below its yield strength and at elevated temperatures. It occurs as the applied load causes the gradual distortion of the material's internal structure over time. Creep is an important consideration for components that operate at high temperatures, such as those found in oil refineries and steam turbines, as excessive creep deformation can lead to failure if adjacent parts come into contact. The temperature at which different metals will experience creep depends on their melting points, with creep typically occurring above 0.5 times the absolute melting temperature of the metal. The creep rate of a material is characterized by an initial rapid decrease in strain rate, followed by a steady minimum rate, and then an acceleration until failure.
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heat treatment
The document discusses various heat treatment processes used to alter the properties of metals and alloys. It describes processes like annealing, normalizing, hardening, and tempering. Annealing is used to relieve stress, soften metals, and refine grain size. Normalizing produces a uniform structure and relieves stresses. Hardening involves heating metal and rapidly cooling to produce martensite for hardness. Tempering is then used to reduce brittleness caused by hardening. The document also discusses diagrams like TTT and CCT that are used to determine the effects of different cooling rates on microstructure formation.
Heat Treatment
The document discusses various heat treatment processes used to alter the properties of metals and alloys. It describes processes like annealing, normalizing, hardening, and tempering. Annealing is used to relieve stress and induce softness. Normalizing increases strength and achieves a uniform structure. Hardening through quenching improves hardness but causes brittleness, which tempering relieves by controlled reheating. The Jominy end quench test measures a steel's hardenability or ability to harden uniformly during quenching.
Materials creep
This document discusses creep deformation in materials. It defines creep as time-dependent deformation under an applied load, typically occurring at high temperatures. The main mechanisms of creep are described as bulk diffusion, grain boundary diffusion, and dislocation climb. Classical creep curves consist of primary, secondary, and tertiary creep stages. Factors that influence creep include temperature, stress, grain size, and dislocation movement. Common tests to characterize creep properties are described, such as constant-load tests and stress rupture tests. Design considerations to minimize creep include reducing grain boundaries, using high melting temperature materials, and employing creep data for material selection and inspection intervals.
Hardening process
The document discusses the hardening process used to increase the hardness of metals. Hardening involves heating metals to their hardening temperature, holding at that temperature, and then rapidly cooling via quenching. This rapid cooling results in the formation of martensite, giving the metal a high hardness. The main purposes of hardening are to improve wear resistance, tensile strength, and yield strength. Factors like chemical composition, size and shape of the metal, and the quenching medium used affect how effective the hardening process is. Various hardening methods are discussed, like conventional quenching, quenching in stages, spray quenching, and quenching with self-tempering. Hardened metals find
Fabrication of metals
This document discusses various metal fabrication processes and heat treatments. The main metal fabrication processes covered are cutting, folding, punching, shearing, welding, forging, rolling, extrusion and drawing. Common raw materials used include plate metal, tube stock, welding wire, castings and fittings. Annealing heat treatments are also summarized, which involve heating metal to high temperatures to relieve stresses, increase softness and ductility, and produce desired microstructures, followed by controlled cooling. The stages of annealing and different types of annealing like normalizing and full annealing are defined.
Module 2.ppt
Cold working involves plastically deforming ductile metals at temperatures below their recrystallization temperature to strengthen them. This increases dislocation density and stored strain energy, improving strength but reducing ductility. Heating allows recovery, recrystallization and grain growth processes to remove strain. Recovery occurs at low temperatures through dislocation motion. Recrystallization forms new strain-free grains between 0.3-0.5Tm. Grain growth enlarges grains, decreasing boundary energy. Phase diagrams depict equilibrium phases present at different temperatures and compositions.
1632790339123_14-Physical-Vapor-Deposition.pdf
The document discusses various physical vapor deposition (PVD) techniques for depositing thin films, including thermal evaporation, electron beam evaporation, and sputter deposition. Thermal evaporation uses resistive heating to melt and evaporate a source material, while electron beam evaporation uses an electron beam to heat the source. Sputter deposition creates an argon plasma that bombards a source target, ejecting atoms to deposit on a substrate. All techniques require high vacuum and precise thickness monitoring to control the deposition process.
Industrial Materials Lectures.pptx
Heat treatment processes involve heating and cooling metals to change their mechanical properties. There are several types of heat treatment processes, including softening processes like annealing which involves slowly cooling metals, hardening processes like quenching which rapidly cool metals, and tempering which heats quenched metals to reduce brittleness. Other processes include case hardening to harden surfaces, austempering to improve properties without distortion, and martempering to reduce cracking during hardening. Each process produces different microstructures and properties in metals to make them suitable for various applications.
Heat treatment process
This document summarizes a presentation on heat treatment processes. It defines heat treatment as heating a material to a particular temperature, holding it for a period of time, and cooling it to achieve desired properties. The document then classifies and describes common heat treatment processes like annealing, normalizing, hardening, and tempering. It explains how each process affects the microstructure and properties of metals. The document also discusses principles of heat treatment, factors that influence hardness, and surface hardening techniques like induction hardening and flame hardening.
Solo swiss heat treatment glossary
The document defines various heat treatment terms and processes. It provides multiple definitions for some terms to highlight subtle differences. Key terms defined include annealing, austempering, austenite, bainite, hardening, and aging. Annealing involves heating and cooling to soften metals and modify properties or microstructure. Austempering and hardening involve controlled cooling after heating to achieve specific microstructures like bainite that impart strength.
impact test 10-4
This document discusses impact testing techniques used to evaluate the fracture behavior of materials. It provides background on impact testing and describes the Charpy and Izod impact tests. These tests involve fracturing a notched specimen using a swinging pendulum. The absorbed energy is measured and used to determine the ductile to brittle transition temperature (DBTT) of the material. The DBTT curve shows how absorbed energy and fracture surface morphology change with temperature. Factors that influence the DBTT, such as chemical composition, grain size, and heat treatment are also reviewed. Experimental procedures for conducting impact tests at different temperatures are outlined.
Heat treatment basics
This will explain the basics of material crystal structures,Iron Carbon diagram,TTT diagram and various heat treatment process.
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Creep of metals
- 2. Creep • Materials in service are often exposed to elevated temperatures or static loads for long duration of time. • Deformation under such circumstances may be termed as creep. • Time-dependent deformation of a material while under an applied load that is below its yield strength. • Mostly occurs at elevated temperature though some materials creep at room temperature. • Creep is a deformation mechanism that may or may not constitute a failure mode.
- 3. High Temperature Applications Components exposed to high temperature. Oil Refinery Steam turbine used in power plant Sagging of the filament coil increases with time due to creep deformation caused by the weight of the filament. Too much deformation--the adjacent turns of the coil touch one another--causing an electrical short and local overheating, which quickly leads to failure of the filament
- 4. Creep • Metals/alloys do not exhibit time dependent deformation under normal service condition. • Metals subjected to a constant load at elevated temperatures will undergo a time dependent increase in length. At what temperature the material will creep? • Different metals have different melting temperatures. e.g. Pb 327°C, W 3407°C. • Material will creep when the temperature will be ˃ 0.5Tm (Tm = absolute melting temperature). Metal Melting temp. 0.5xMelting Temp Lead 327oC 600oK 327oK 27oC W 3407 3680 1840 1567
- 5. Creep Curve
- 6. Creep Curve • In the initial or primary stage, strain occurs at a relatively rapid rate but the rate gradually decreases (creep resistance increases). • In the secondary stage, the creep rate is minimum and constant. • This creep in this stage may be termed as steady-state creep. • In the third stage, the strain rate increases until failure occurs. The rate of deformation of a sample is known as the creep rate. It is found by measuring the slope of the strain v time curve.