Microstructure formation is also strongly influenced by the amount of energy required to create new interfaces. Appropriate heat-treatments (quenching, annealing) produce a great variety of microstructures. Frequently, these have an inhomogeneous composition and are almost always metastable at the service temperature.
Full Answer
How do heat treatment conditions affect the microstructure and mechanical properties of ODS?
Various heat treatment conditions including temperature and cooling rate usually affect the microstructure and mechanical properties of ODS steels. In this study, 10Cr and 12Cr dual phase ODS steels mainly underwent three kinds of heat treatment.
What are the microstructures formed after quenching process?
The resultant microstructures after quenching process are observed as martensite with small amount of retained austainite. After the tempering process, the resulting optimum mechanical properties are found at bainitic structure. In the hardening process, selective alloy was heated up to its austenitizing temperature, 870°C, and quenched in oil.
What are the microstructures of iron and steel?
The microstructures of iron and steels is complicated and diverse which is influenced by composition, homogeneity, heat treatment, processing and section size. Microstructure of castings looks different than those of the wrought products even if the composition is same and even if the same heat treatment is given. Pure iron is polymorphic.
What is the microstructure of castings?
Microstructure of castings looks different than those of the wrought products even if the composition is same and even if the same heat treatment is given. Pure iron is polymorphic. Two allotropic phases exist for pure iron in solid state depending on the temperature.
How does heat treatment affect microstructure?
The heating and cooling treatment of the steel specimens have a great effect on the phase of the microstructure of the steel specimen. The addition of alloys or coarsening of the austenitic grain structure increase the hardenability of steel.
Why microstructures are different for different metals?
The crystalline structure of metals further changes as the metal is worked ( forged, hammered, rolled, extruded,etc) with the crystals being elongated, bent, fractured, and generally deformed plastically.
What does microstructure depend on?
The microstructures formed in materials depend not only on the chemical composition and structure but also on the atomic mobility and on the presence of concentration gradients during processing. Microstructure formation is also strongly influenced by the amount of energy required to create new interfaces.
What affects microstructure?
The arrangement of microstructure mostly depends on the grain size, composition of the alloys, porosity, dendritic arm spacing, amount and distribution of the eutectic phase, Inter lamellar eutectic spacing and cooling rate.
How are the properties of materials affected by microstructure?
The microstructure of a material (such as metals, polymers, ceramics or composites) can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance, high/low temperature behaviour or wear resistance.
What are the differenT microstructures?
Modern materials can be divided into four categories: metals, polymers, ceramics and composite materials. Despite the rapid development of macromolecule materials, steel is still the most widely used and most important material in the current engineering technology.
What does the microstructure tell us?
Microstructure measures describe the amount of each phase, its distribution, and its composition using descriptors of size, shape, and relations between the phases. Liquid phase sintering is a normalization process.
How are microstructures formed?
Microstructures are almost always generated when a material undergoes a phase transformation brought about by changing temperature and/or pressure (e.g. a melt crystallising to a solid on cooling). Microstructures can be created through deformation or processing of the material (e.g. rolling, pressing, welding).
Why do we study the crystal structure and microstructure in engineering materials?
Crystalline structure is important because it contributes to the properties of a material. For example, it is easier for planes of atoms to slide by each other if those planes are closely packed.
How does microstructure affect mechanical properties?
By eliminating the columnar microstructure, hardness becomes more uniform and is reduced. There is also a reduction in strength by increasing interpass temperature however toughness at low temperatures increases.
What parameters influence the microstructure of an alloy?
The microstructure, texture and mechanical properties of Mg alloy are significantly affected by extrusion parameters, especially by extrusion temperature and speed.
How does microstructure affect hardness?
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Abstract
This research study investigates the influence of heat treatment on the thermal conductivities of three different tool steels at room temperature.
Introduction
Tool steels with a microstructure of tempered α′-martensite are used in a variety of applications, for instance hot extrusion, polymer processing, press hardening, and die casting [ 1 – 4 ].
Experimental
Three different heat-treatable steels provided by WST Center GmbH & Co KG were investigated in this study: nonalloyed steel C45, low-alloyed steel 40CrMnMo7, and high-alloyed steel X42C13. Their chemical compositions were determined by optical spark emission spectrometry, and the results are listed in Table 1.
Results and discussion
The calculated phase diagrams of the three steels investigated in this study are shown in Fig. 1. Austenitizing temperatures are denoted by a dot that indicates the fully austenitic equilibrium state for the chosen temperatures of 850 and 1120 °C, respectively.
Summary and outlook
Room-temperature thermal conductivities λ of three martensitic steels were measured after quenching and tempering at 200, 400/450, or 600 °C. Values of λ are the lowest in the fully martensitic condition and increase on tempering.
Acknowledgement
The authors gratefully acknowledge the financial support from the Deutsche Forschungsgemeinschaft (DFG) under support code TH531/13-1.
Rights and permissions
Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author (s) and the source are credited.
What cooling media affects tensile strength?
Based on the experiments that have been conducted, the use of post-welding cooling media affects the tensile strength of medium carbon steel with the highest effect on the water cooling media, then the coolant media, and the lowest is the air cooling media.
What is heat treated AISI 1020?
The present work deals with assessment of heat treated AISI 1020, a low carbon steel (0.2%-C), on the basis of various destructive testing and microstructural behaviour. The steels samples were heated above the lower critical temperature range, i.e. up to 750°C. The cooling rate of all the samples was different. Mainly, three different cooling medium were taken. They are: water, air and sand. These three heat treated samples were compared with as received sample. Hence the final condition of all the four samples is: as received; normalised; sand cooled; water quenched. After a proper preparation, samples were undergone through various mechanical tests, such as, tension test, shear test, hardness test, and impact test. In addition, the microstructural images, captured by an optical microscope, of all the samples were observed and analysed. The mechanical properties and microstructural attributes obtained in ‘heat treated’ samples were compared with those results of ‘as received’ samples. From the present experimental analysis, it was found that heat treatment processes significantly changed/improved the desired properties of the AISI 1020 steel samples.
How does coolant affect heat transfer?
The use of additives as a coolant enhances the heat transfer rate as it alters the thermo physical properties of the fluid in the favourable direction of heat transfer. Although the aforesaid technology mitigate the requirements depicted in Time Temperature Transformation diagram; however, the quenching from high temperature, which may lead to a reaction with coolant, deposition and modification of surface morphology has not been addressed in the open literature. Therefore, in the current work, the interaction of coolant with the surface has been tried to disclose in terms of surface reaction, deposition or physical changes leading to variation in morphology. In the current work, AISI 304 steel plates are quenched by water with varied concentration of SDS to mitigate the cooling requirement and by using EDS, XRD and SEM analysis, the surface interaction is revealed. The elemental analysis by EDS and XRD clearly indicate the formation of new compounds resulted from the reaction between hot steel and the coolant. Based on the identified compounds formed on the surface, the possible reactions on the surface due to interaction among the hot surface, water, oxygen and adsorbed SDS are proposed and also validated .
What is oil quench and temper?
The material used in this study was a commercial grade of heavy duty spring steel. Quench and temper process were used as a major heat treatment method . The resultant microstructures after quenching process are observed as martensite with small amount of retained austainite. After the tempering process, the resulting optimum mechanical properties are found at bainitic structure. In the hardening process, selective alloy was heated up to its austenitizing temperature, 870°C, and quenched in oil. After that, tempering was done at 450°C increased by 50°C to 550°C for each tempering time (1 hr, 2 hr, and 3 hr) interval. In this research work, microstructural examination, hardness, tensile and fatigue tests were done before and after tempering condition at room temperature. The experimental results revealed that mechanical properties of selective alloy were significantly changed by temper treatment. By increasing the tempering time and temperature, hardness and ultimate tensile strength are gradually decreased and ductility was improved. Moreover, rather interesting condition is observed in elastic properties and endurance limit at 450°C and one hour tempering condition, and this state is the optimum condition for spring production.
What are the thermal properties of H13 steel?
The parameters that relate the interfacial heat transfer and interface temperature are thermal conductivity and thermal contact conductance (TCC) of the materials in contact. Thermal properties are affected by the heat treatment processes which are mainly employed for the formation of tools and dies. Hence in his work, different heat treatment processes have been performed on the selected materials, viz. Tool steel (H13) and Mild steel. These materials have been chosen for their extensive use in making tools, dies and other instruments. Microhardness of the materials has been compared with and without heat treatments. Further, heat transfer studies have been performed in order to evaluate the thermal properties mainly thermal conductivity and thermal contact conductance. Standard ASTM test methods have been employed for the estimation of thermal conductivity and TCC of the specimens. Experiments have been conducted for varying degree of loading and heat flux in order to observe the effect of contact pressure and mean interface temperatures. Effect of heat treatment has been observed on thermal conductivity of mild steel and tool steel and thermal contact conductance of the tool steel-mild steel contacts. Moreover, the results have been presented in normalized form and suitably compared with the existing literatures.
Why is hot stamping important?
Hot stamped high strength steel components for car bodies become increasingly important due to the need to save weight for multiple reasons like e.g. fuel conservation regulations. Tribological systems in tools for hot stamping depend on process parameters and may include e.g. mechanical and thermal load as well as adhesive and abrasive wear. Furthermore, the process cycle time should be as short as possible due to economic reasons. Commonly used hot work tool steels mainly suffer from rather low wear resistance, while in terms of process cycle time a high thermal conductivity is desired. Thus, solutions showing optimized combination of key properties for application in hot stamping like wear resistance, high thermal conductivity, toughness, and hardening behavior need to be found. In this contribution, novel high thermal conductivity hot work tool steels especially designed for application in hot stamping, are presented and some key properties are compared e.g. to those of conventional hot work tool steels like 1.2367, which is commonly used in this application. Furthermore, tribological investigations are performed in laboratory tests according to ASTM G65 and G75 as well as a flat strip‐drawing test setup using sheets of 22MnB5 under hot stamping conditions. This article is protected by copyright. All rights reserved.
What is thermal contact conductance?
Thermal contact conductance (TCC) is the parameter which relates the interfacial heat transfer and interface temperature. Heat treatment is the process commonly employed to improve the thermo-mechanical properties of a material. Thus, the effect of heat treatment on the tool-sample contacts is the main objective of this work. Here, experiments are performed to investigate the thermal properties at the tool steel–mild steel contacts with and without heat treatments. Experiments have been performed on a simple experimental setup which is based on axial heat flow method. The experiments have been conducted under atmospheric environment and varying loading and heat flux conditions so as to study the contact heat transfer for a range of contact pressure and interface temperatures. Steady-state methodology is employed for estimating thermal contact conductance at the joint of two specimens. Heat treatment of tool steel and mild steel specimens has been carried out using normalizing process. Eventually, the combined effect of hardness and thermal conductivity of the tool steel and mild steel on thermal contact conductance has been presented with varying contact pressure and temperature conditions. Moreover, results of TCC have been presented in normalized form to study the combined effect of different parameters and comparing with the pertinent literatures.
Is steel hardened or elastohydrodynamic?
However, steel in elastohydrodynamic lubricated contacts is usually hardened. It has been known for more than a century now (not within the Tribology community though) that the thermal conductivity of steel could be reduced by a factor of more than two when it is hardened. Only recently did the Tribology community realize this “mistake”, of which the impact on friction predictions is investigated in this work. The mistake is found to lead to significant overestimations of friction in the thermo-viscous regime.
What is the microstructure of iron?
The microstructures of iron and steels is complicated and diverse which is influenced by composition, homogeneity, heat treatment, processing and section size . Microstructure of castings looks different than those of the wrought products even if the composition is same and even if the same heat treatment is given. Pure iron is polymorphic.
Why is martensite formed in steel?
Martensite is formed in steel because the solute atoms of carbon occupy the interstitial sites of iron atoms. This produces substantial hardenability and a highly stained brittle condition. In carbon containing steels the appearance of the martensite changes with carbon in the interstitial sites.
How is martensite formed?
Martensite is formed if the cooling rate from the austenitizing temperature is rapid enough (a function of section size, hardenability and quench medium). Martensite is a generic term for the body centered tetragonal (bct) phase which is formed by the diffusionless transformation. The parent and product phases has the same composition and a specific crystallographic relationship. Martensite is formed in steel because the solute atoms of carbon occupy the interstitial sites of iron atoms. This produces substantial hardenability and a highly stained brittle condition. In carbon containing steels the appearance of the martensite changes with carbon in the interstitial sites. Low carbon steel produce ‘lath’ martensites while high carbon steels produce ‘plate martensite, often called ‘acicular’ martensite, when all the carbon is dissolved into the austenite.
What is the parent phase of steel?
For heat treatment of steels, austenite is the parent phase for all transformation products that make steels so versatile and useful commercially. Austenite is a soft, ductile phase that can be work hardened to high strength levels. Austenite is non magnetic.
What is the degree of change in steel?
The degree of change is a function of the carbon content of the steel. Pearlite increases the strength of carbon steels. Mechanically, pearlite has properties intermediate to soft, ductile ferrite and hard, brittle cementite. Refining of the interlamellar spacing also increases the strength and the toughness.
Is iron a polymorphic substance?
Pure iron is polymorphic. Two allotropic phases exist for pure iron in solid state depending on the temperature. One is bcc (body centered cubic) and the other is fcc (face centered cubic). The bcc crystalline form (?-iron) is stable until a temperature of 912 deg C when it is transformed to fcc (?-iron).
Is delta ferrite a hardened steel?
Delta ferrite is usually considered detrimental to transverse toughness when it is present in a hardened structure. Delta ferrite is not always detrimental.
How does heat treatment change mechanical properties?
During the whole process, the mechanical properties get changed due to changes in microstructure. All metallic metals have grains which are nothing but microstructures of crystals. The nature of those grains determines the behavior of the mechanical properties of a metal. Heat treatment changes that mechanical structure by controlling the rate ...
How does heat treatment help metals?
Heat treatment assist in improving the ductility of metal in the annealing process. Heat treatment helps in hardening metals. Case hardening helps in hardening only the outer surface of the metal piece keeping the rest of the portion soft and ductile. Machinability of metals gets improved.
How is annealing done?
Annealing is done by heating the metals at the above critical temperature , hold them there for some time and then cool it at a very slow rate in the furnace itself. Annealing is usually done on ferrous and non-ferrous metals to reduce hardness after the cold working process.
What is the process of increasing the hardness of a metal?
Curborization. In carburization, the hardness of the metal piece is increased by increasing the carbon content. The metal piece is heated below the melting point with high carbon materials such as charcoal. The heated metal piece then absorbs carbons to make it more hard and brittle.
How does tampering work?
Tampering is a very common process for machine tools, knives, etc. Tampering is usually done by heating the metal at a relatively low temperature. The temperature depends on the required mechanical properties of metals.
What is differential hardening?
Differential hardening is kind of a hardening process in which different area of the metal piece gets a different heat-treatment process. This is a very popular hardening process for high-end cutting tools.
What is case hardening?
Case hardening or surface hardening is a hardening heat-treatment process. In the case of hardening, the complete metal piece is heated. But in the case of case hardening, only the outer surface is heat-treated to make it hardened. The inner metal is still soft and ductile.