Heat treatment in any of its forms is used to achieve a desirable improvement in the characteristics of material or to regain those characteristics which may have been adversely affected by production processes such as welding/bending/forming etc.
What are the benefits of heat treatment?
This process allows us to achieve the majority of heat treatments, such as quenching and annealing. This low-pressure treatment is suitable for alloys that are heat-resistant, including nickel-based ones, and helps parts to better withstand high heat environments and other stresses.
What is heat treatment process?
Heat treatment is a process of heating the metal to a certain temperature, keeping it there for some time, and then cool it down. During the whole process, grain crystallization happens, which helps alter the mechanical, chemical, and electric properties of metals. What are the different types of heat treatment?
What is the most common application of heat treatment?
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 a desired result such as hardening or softening of a material.
How to improve the performance of heat treated materials?
Uniform material organization and composition, improve material properties or prepare for subsequent heat treatment processes. Heat the metal parts to a certain high temperature for a period of time, then let them cool in the air by water spraying, mist spraying, blowing, etc.
Where is heat treatment required?
Some notable industries in which heat treatment plays an important role include aircraft, automobiles, hardware–such as saws and axes, computers, spacecraft, military, and the oil and gas industry.
What is purpose object of heat treatment?
The main objectives of heat treatment as follows: to increase strength, hardness and wear resistance (bulk hardening, surface hardening) to increase ductility and softness (tempering, re-crystallization annealing) to increase toughness (tempering, re-crystallization annealing)
Why heat treatment of steel is required?
Heat Treatment Does a Lot for Steel The softening of steel allows for metal working operations such as deep drawing, cold forging and machining. Thus, steel also increases its strength, making the material ductile or more flexible, while also introducing wear-resistance characteristics, making the material tougher.
Why hardening is done?
Metal Hardening Hardened materials are usually tempered or stress relieved to improve their dimensional stability and toughness. Steel parts often require a heat treatment to obtain improved mechanical properties, such as increasing increase hardness or strength.
What are the principles of heat treatment?
Heat treating changes metal properties by heating the metal to a specific temperature, holding it at that temperature for a certain length of time, and then using one of several methods to control the cooling of the metal. A metal's properties are determined by the shape and alignment of its atoms.
What is critical temperature in heat treatment?
Critical temperature of steel defines phase transition between two phases of steel. As the steel is heated above the critical temperature, about 1335°F (724°C), it undergoes a phase change, recrystallizing as austenite.
Overview
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 th…
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 sim…
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 hystere…
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 operation…
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 i…
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 hea…
See also
• Carbon steel
• Carbonizing
• Diffusion hardening
• Induction hardening
• Retrogression heat treatment