Steel Heat Treating Fundamentals And Processes Pdf

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In metallurgy and materials science , annealing is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness , making it more workable. It involves heating a material above its recrystallization temperature, maintaining a suitable temperature for an appropriate amount of time and then cooling. In annealing, atoms migrate in the crystal lattice and the number of dislocations decreases, leading to a change in ductility and hardness.

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Heat Treatment Books

To browse Academia. Skip to main content. By using our site, you agree to our collection of information through the use of cookies. To learn more, view our Privacy Policy. Log In Sign Up. Download Free PDF. Fundamentals of the Heat Treating of Steel.

Batuhan Turkselci. Download PDF. A short summary of this paper. All Rights Reserved. In carbon steel and low-alloy steel, the maximum carbon is about 2. Fundamentally, all steels are mixtures, or more properly, alloys of iron and carbon. The carbon content of plain-carbon steels may be as high as 2. Carbon content of commercial steels usually ranges from 0. The alloying mechanism for iron and carbon is different from the more common and numerous other alloy systems in that the alloying of iron and carbon occurs as a two-step process.

In the initial step, iron combines with 6. Thus, at room temperature, conventional steels consist of a mixture of cementite and ferrite essentially iron. Note that phases of steel should not be confused with structures. There are only three phases involved in any steel—ferrite, carbide cementite , and aus- tenite, whereas there are several structures or mixtures of structures. Details of this designation system can be found in Ref 2.

For example, with- out aluminum and titanium alloys, current airplanes and space vechicles could not have been developed. Neither of these is necessarily correct; iron is by no means the most abundant ele- ment, and it is not the easiest metal to produce from ore. Copper, for example, exists as nearly pure metal in certain parts of the world. These phenomena are thus the underlying principles that permit the achievements that are possible through heat treatment.

In entering the following discussion of constitution, however, it must be emphasized that a maximum of technical description is unavoidable. This portion of the subject is inherently technical. To avoid that would result in the discussion becoming uninformative and generally useless.

The purpose of this chapter is, therefore, to reduce the prominent technical features toward their broadest generalizations and to present those gen- eralizations and underlying principles in a manner that should instruct the reader interested in the metallurgical principles of steel.

The objective of this section is to begin with a generalized discussion of the constitution of commercially pure iron, subsequently leading to discussion of the iron- carbon alloy system that is the basis for all steels and their heat treatment. All pure metals, as well as alloys, have individual constitutional or phase diagrams.

However, the constitutional diagram of a pure metal is a simple vertical line. The constitutional diagram for commer- cially pure iron is presented in Fig. As pure iron, in this case, cools, it changes from one phase to another at constant temperature. No attempt is made, however, to quan- tify time, but merely to indicate as a matter of interest that as temperature increases, reaction time decreases, which is true in almost any solid- solution reaction.

A crystalline structure, known as ferrite, or delta iron, is formed point a, Fig. This structure, in terms of atom arrangement, is known as a body-centered cubic lattice bcc , shown in Fig. This lattice has nine atoms—one at each corner and one in the center. As cooling proceeds further and point b Fig. The lattice now has an atom at each corner and one at the center of each face. This is known as a face-centered cubic lattice fcc , and this structure is called gamma iron.

The change at point d on Fig. The ferrite forming above the temperature range of austenite is often referred to as delta ferrite; that forming below A3 as alpha ferrite, though both are structurally similar. In this Greek-letter sequence, austenite is gamma iron, and the inter- changeability of these terms should not confuse the fact that only two structurally distinct forms of iron exist.

Figures 1 and 2 thus illustrate the allotropy of iron. In the following sections of this chapter, the mechanism of allotropy as the all-important phenomenon relating to the heat treatment of iron-carbon alloys is dis- cussed.

Alloying Mechanisms Metal alloys are usually formed by mixing together two or more metals in their molten state. The two most common methods of alloying are by atom exchange and by the interstitial mechanism. The exchange mechanism simply involves trading of atoms from one lat- tice system to another. An example of alloying by exchange is the copper- nickel system wherein atoms are exchanged back and forth.

Under certain conditions, the tiny carbon atoms enter the lattice the interstices of the iron crystal Fig. A description of this basic mechanism follows. Effect of Carbon on the Constitution of Iron As an elemental metal, pure iron has only limited engineering useful- ness despite its allotropy.

Carbon is the main alloying addition that capi- talizes on the allotropic phenomenon and lifts iron from mediocrity into the position of a unique structural material, broadly known as steel.

Even in the highly alloyed stainless steels, it is the quite minor constituent carbon that virtually controls the engineering properties. Furthermore, due to the manufacturing processes, carbon in effective quantities persists in all irons and steels unless special methods are used to minimize it. However, it is quite soluble in gamma iron. Carbon actually dissolves; that is, the individual atoms of carbon lose themselves in the interstices among the iron atoms. Certain interstices within the fcc structure austenite are considerably more accommodating to carbon than are those of ferrite, the other allotrope.

This preference exists not only on the mechanical basis of size of opening, however, for it is also a funda- mental matter involving electron bonding and the balance of those attrac- tive and repulsive forces that underlie the allotrope phenomenon. The effects of carbon on certain characteristics of pure iron are shown in Fig. In Fig. Thus, each vertical dashed line, like the solid line in Fig. Note that carbon lowers the freezing point of iron and that it broadens the tempera- ture range of austenite by raising the temperature A4 at which delta ferrite changes to austenite and by lowering the temperature A3 at which the austenite reverts to alpha ferrite.

Hence, carbon is said to be an austenitizing element. In a practical approach, however, it should be emphasized that Fig. Furthermore, in slow heating of iron, these transformations take place in a reverse manner. Transformations of this type occur not only in pure iron but also in many of its alloys; each alloy composition transforms at its own characteristic temperature. It is this transformation that makes possible the variety of properties that can be achieved to a high degree of reproduci- bility through use of carefully selected heat treatments.

First, transformation temperatures are lowered, and second, transformation takes place over a range of temperatures rather than at a single tempera- Fig. These data are shown in the well-known iron-cementite phase dia- gram Fig. However, a word of explanation is offered to clarify the distinction between phases and phase diagrams.

A phase is a portion of an alloy, physically, chemically, or crystallo- graphically homogeneous throughout, which is separated from the rest of the alloy by distinct bounding surfaces. Phases that occur in iron-carbon alloys are molten alloy, austenite gamma phase , ferrite alpha phase , cementite, and graphite.

These phases are also called constituents. Not all constituents such as pearlite or bainite are phases—these are microstruc- tures. In the iron-cementite system, temperature is plotted verti- cally, and composition is plotted horizontally. The iron-cementite diagram Fig. In metal systems, pressure is usu- ally considered as constant. Frequent reference is made to the iron-cementite diagram Fig. Consequently, understanding of this concept and diagram is essential to further discussion.

The iron-cementite diagram is frequently referred to incorrectly as the iron-carbon equilibrium diagram. Solubility of Carbon in Iron In Fig. In fact, most heat treating opera- tions notably annealing, normalizing, and heating for hardening begin with heating the alloy into the austenitic range to dissolve the carbide in the iron. At no time during such heating operations are the iron, carbon, or austenite in the molten state.

A solid solution of carbon in iron can be visualized as a pyramidal stack of basketballs with golf balls between the spaces in the pile. In this analogy, the basketballs would be the iron atoms, while the golf balls interspersed between would be the smaller carbon atoms.

As indicated by the austenite area in Fig. Under normal conditions, austenite cannot exist at room temperature in plain carbon steels; it can exist only at elevated temperatures bounded by the lines AGFED in Fig. The solubility limit for carbon in the bcc structure of iron-carbon alloys is shown by the line ABC in Fig.

The maximum solubility of carbon in alpha iron ferrite is 0. At room temperature, ferrite can dissolve only 0. This is the narrow area at the extreme left of Fig. For all practical purposes, this area has no effect on heat treatment and shall not be discussed further. Further discussion of Fig. The line BGH is known as the lower transformation temperature A1. The line AGH is the upper transformation temperature A3. The triangular area ABG is also a two-phase area, but the phases are alpha and gamma, or ferrite plus austenite.

A1 and A3 intersect and remain as one line to point H as in- dicated.

Fundamentals of the Heat Treating of Steel

This volume includes 50 articles that address the physical metallurgy of steel heat treatment and thoroughly cover the many steel heat treating processes. Fundamentals of hardness and the use of hardenability as a selection factor are discussed as are the fundamentals of quenching and quenching processes. The volume also discusses annealing, tempering, austempering, and martempering as well as cleaning, subcritical annealing, austenitizing, and quench partitioning. It also presents practical information on surface hardening by applied energy, carburizing, carbonitriding, nitriding, and diffusion coatings. Dossett, George E. Sign In or Create an Account. User Tools.

This volume includes 50 articles that address the physical metallurgy of steel heat treatment and thoroughly cover the many steel heat treating processes. Fundamentals of hardness and the use of hardenability as a selection factor are discussed as are the fundamentals of quenching and quenching processes. The volume also discusses annealing, tempering, austempering, and martempering as well as cleaning, subcritical annealing, austenitizing, and quench partitioning. It also presents practical information on surface hardening by applied energy, carburizing, carbonitriding, nitriding, and diffusion coatings. Dossett, George E. Sign In or Create an Account. User Tools.

Allow Bodycote to provide a deeper understanding of your options. Heat treatment is a critical and complex element in the manufacturing of gears that greatly impacts how each will perform in transmitting power or carrying motion to other components in an assembly. Heat treatments optimize the performance and extend the life of gears in service by altering their chemical, metallurgical, and physical properties. Heat treatments improve physical properties such as surface hardness, which imparts wear resistance to prevent tooth and bearing surfaces from simply wearing out. These same compressive stresses prevent fatigue failures in gear roots from cyclic tooth bending. Physical properties such as surface hardness, core hardness, case depth, ductility, strength, wear resistance and compressive stress profiles can vary greatly depending on the type of heat treatment applied.

Heat Treatment Books

The "quenching and partitioning" process: background and recent progress. John G. Speer I ; Fernando C.

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Fundamentals of the Heat Treating of Steel

Annealing (metallurgy)

While some heat treatments are used to soften the material or improve its machinability, most are processed to obtain strengthened or hardened properties. The majority of heat treatments apply to metallic materials and, typically, the techniques include annealing, normalizing, quenching, tempering, precipitation strengthening, surface hardening, and case hardening. Heat treatment is so critically important that we can safely say a part undergoing extensive manufacturing processes such as melting, rolling, forging, and other related machining is of little or no value without the necessary and appropriate heat treatment. Carburizing is one of the most widely used case hardening treatments.

Volume 4A introduces the basics of steel heat treating and provides in-depth coverage of the many steel heat treating processes. Coverage includes:. New articles on cleaning, subcritical annealing, austenitizing, and quench partitioning of steel heat treatment. Significant expansion on the fundamental and applied aspects of surface hardening by applied energy, carburizing, carbonitriding, nitriding, and diffusion coatings.

Steel heat treating fundamentals and processes

Citations per year

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To browse Academia. Skip to main content. By using our site, you agree to our collection of information through the use of cookies. To learn more, view our Privacy Policy. Log In Sign Up. Download Free PDF.

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