Full Answer
What factors affect the outcome of heat treating?
Other factors affecting the final outcome are oil films on the surface and the type of heat source used. Many heat treating methods have been developed to alter the properties of only a portion of an object.
What is the importance of heat treatment?
The importance of heat treatment is evident in many products in the automotive, aerospace, construction, agriculture, mining, and consumer goods industries, all using heat treatment to improve the properties of materials, especially steel [2].
What are the methods of heat treatment?
The material can be cooled rapidly, slowly (in the furnace), or can be quenched (using water, brine, oils, polymer solutions, salts, or gases). Heat treatment generally consists of controlled heating, soaking and cooling steps. There are five techniques used for the heat treatment of materials.
How long has heat treatment been around?
Most metals and alloys are heat treated in one way or another, and the understanding and science of heat treatment have been developed over the past 100 to 125 years.
What are the effects of heat treatment?
The heat treatment develops hardness, softness, and improves the mechanical properties such as tensile strength, yield strength, ductility, corrosion resistance and creep rupture. These processes also help to improve machining effect, and make them versatile.
What happens after heat treatment?
Stress is relieved by heating metal to a temperature lower than that required for transformation. After this process, the metal is then slowly cooled. Normalizing is a form of heat treatment that eliminates impurities and improves strength and hardness by altering the grain size to be more uniform throughout the metal.
What is the main purpose of heat treatment?
Heat treating can soften metal, to improve formability. It can make parts harder, to improve strength. It can put a hard surface on relatively soft components, to increase abrasion resistance. It can create a corrosion-resistant skin, to protect parts that would otherwise corrode.
What is the effect of heat treatment on a metal?
Heat Treating of steel and other metals can lead to: Improved wear resistance. Increased resistance to deformation and warpage and. Increased strength or toughness.
Which of the following property is affected by heat treatment?
Which of the following property is affected by heat treatment? Explanation: Heat treatment involves changes in the micro structure and hence all the internal properties are effected.
How does heat treatment affect hardness?
Hence, it will increase the hardness of the steel. When the cooling rate is very high, it will increase the strength of the steel but it will reduce the toughness and the ductility of the steel. Higher cooling rate tends to make the steel become less flexible and more brittle.
What are the advantages and disadvantages of heat treatment?
Heat treatment helps to get desired mechanical and chemical properties, to reduce stresses, prevent stress relief and distortion when put to service. Whilst the disadvantages include distortion, surface oxidation or other contamination, added cost, etc.
How does heat affect the material?
High temperature reduces material stiffness and strength, while low temperature increases material stiffness and strength.
What is the effect of heat treatment on the mechanical properties of the materials?
During the heat treatment process, the material usually undergoes phase microstructural and crystallographic changes [14]. The purpose of heat treating carbon steel is to change the mechanical properties of steel, usually ductility, hardness, yield strength tensile strength and impact resistance.
How does heat treatment affect a steel grain structure?
Annealing changes a metal's properties by altering and realigning the grain structure using heat, making the metal softer and more ductile. In this process, the steel is heated to just above its re-crystallization point, allowing it to cool slowly.
What are the 3 stages of heat treatment process?
Stages of Heat TreatmentThe Heating Stage.The Soaking Stage.The Cooling Stage.
Which is the stage of heat treatment process?
Three stages of heat treatment The stages of the heat treatment process include heating, soaking, and cooling.
What is the effect of tempering after quenching?
After being quenched, the metal is in a very hard state, but it's brittle. The steel is tempered to reduce some of the hardness and increase ductility. It's heated for a set period of time at a temperature that falls between 400° F and 1,105° F.
What are the three stages of annealing heat treatment process?
There are three main stages to an annealing process.Recovery stage.Recrystallization stage.Grain growth stage.
Overview
Heat treating (or heat treatment) is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve the desired result such as hardening or softening of a materi…
Physical processes
Metallic materials consist of a microstructure of small crystals called "grains" or crystallites. The nature of the grains (i.e. grain size and composition) is one of the most effective factors that can determine the overall mechanical behavior of the metal. Heat treatment provides an efficient way to manipulate the properties of the metal by controlling the rate of diffusion and the rate of cooling within the microstructure. Heat treating is often used to alter the mechanical pr…
Effects of composition
The specific composition of an alloy system will usually have a great effect on the results of heat treating. If the percentage of each constituent is just right, the alloy will form a single, continuous microstructure upon cooling. Such a mixture is said to be eutectoid. However, If the percentage of the solutes varies from the eutectoid mixture, two or more different microstructures will usually form simultaneously. A hypo eutectoid solution contains less of th…
Effects of time and temperature
Proper heat treating requires precise control over temperature, time held at a certain temperature and cooling rate.
With the exception of stress-relieving, tempering, and aging, most heat treatments begin by heating an alloy beyond a certain transformation, or arrest (A), temperature. This temperature is referred to as an "arrest" because at the A temperature the metal experiences a period of hysteresis. At this point, all of the heat energy is used to cause the crystal change, so the temperature stops rising for a short time (arrests) and then continues climbing …
Techniques
Complex heat treating schedules, or "cycles", are often devised by metallurgists to optimize an alloy's mechanical properties. In the aerospace industry, a superalloy may undergo five or more different heat treating operations to develop the desired properties. This can lead to quality problems depending on the accuracy of the furnace's temperature controls and timer. These operations can usually be divided into several basic techniques.
Specification of heat treatment
Usually the end condition is specified instead of the process used in heat treatment.
Case hardening is specified by hardness and case depth. The case depth can be specified in two ways: total case depth or effective case depth. The total case depth is the true depth of the case. For most alloys, the effective case depth is the depth of the case that has a hardness equivalent of HRC50; however, some alloys specify a different hardness (40-60 HRC) at effecti…
Furnace types
Furnaces used for heat treatment can be split into two broad categories: batch furnaces and continuous furnaces. Batch furnaces are usually manually loaded and unloaded, whereas continuous furnaces have an automatic conveying system to provide a constant load into the furnace chamber.
Batch systems usually consist of an insulated chamber with a steel shell, a heating system, an…
See also
• Carbon steel
• Carbonizing
• Diffusion hardening
• Induction hardening
• Retrogression heat treatment