Air Hardening Steel is a type of alloy steel that does not require quenching to harden. Instead, it is hardened by cooling in air from above its critical temperature range.

Annealing is a heat treatment process used to soften metals by changing their microstructure. It involves heating and cooling the metal in the solid state, usually with relatively slow cooling in carbon and alloy steels. Annealing is used to remove stresses, induce softness, alter physical and mechanical properties, change the crystalline structure, and produce a definite microstructure.

Austempering is a method of hardening steel by quenching it from the austenitizing temperature into a heat extracting medium and holding it until austenite is transformed to bainite. This process is limited to sections less than 1/2 inch in diameter and results in increased ductility and toughness at a hardness of RC 45-55.

Austeitic is the solid solution of iron and carbon achieved by heating to high temperatures above the upper critical temperature. The austenitizing  temperature varies for different grades of carbon, alloy, and tool steels and must be achieved to obtain the proper microstructure and full hardness of stainless steel pipe during heat treating.

Bainite is a type of microconstituent or structure in steel that results from the decomposition or transformation of austenite. Metallurgists use this term to describe a particular structure of steel when it is polished, etched, and examined with a microscope.

Brinell Hardness is a measure of a material's hardness determined by applying a 3000-kilogram load to the surface of the material through a hardened steel ball of 10mm. The diameter of the resulting depression is measured, and the hardness is calculated as the ratio of load to spherical area.

Carburizing involves adding carbon to the surface of steel by heating it below its melting point in contact with carbonaceous solids, liquids, or gases.

Case Hardening is a surface hardening heat treatment that involves changing the composition of the outer layer of an iron-base alloy by inward diffusion of a gas or liquid followed by appropriate thermal treatment. Typical hardening processes include carburizing, cyaniding, carbo-nitriding, and nitriding.

Cyaniding is a surface hardening process that involves carbon and nitrogen absorption of a steel article or portion of it by heating it at a suitable temperature in contact with cyanide salt, followed by quenching.

Decarburization is the loss of carbon at the surface of steel when it is subjected to high temperatures in media containing air, oxygen, or hydrogen. This chemistry change reduces the strength of the part by reducing its size and produces a softer surface hardness than the core.

Flame Hardening is a heat treatment method used to harden the surface of some parts where only a small portion of the surface is hardened or where the part might distort in regular carburizing or heat treating operations. The operation involves heating the surface to be hardened by an acetylene torch to the proper quenching temperature followed immediately by water quenching and proper tempering. Wrought or cast steels with carbon contents of .30 to .40%, low alloy steels, and ductile and malleable cast irons are suitable for flame hardening.

Hardenability refers to the ability of steel to harden deeply upon quenching and takes into consideration the size of the part and the method of quenching. The Jominy Test is used to determine the hardenability of any grade of steel.

Hardening is the heating and quenching of certain iron-base alloys from a temperature above the critical temperature range for the purpose of producing a hardness superior to that obtained when the alloy is not quenched. This term usually refers to the formation of martensite.

Hardness refers to a metal's ability to resist penetration. The principle methods for determining steel hardness are the Rockwell, Brinell, and Scleroscope Tests.

Heat Treatment involves heating and cooling a metal or alloy in the solid state to obtain certain desirable conditions or properties.

Martempering or Marquenching is a method of hardening steel by quenching it from the austenitizing temperature into some heat extracting medium that is maintained at some constant temperature level above the point at which martensite starts to form. The advantages of this method are minimum distortion and residual strains, and larger parts can be treated than with austempering.

Martenisitic refers to a microconstituent or structure in quenched steel that has the maximum hardness among all other stainless steel structures resulting from the transformation of austenite stainless steel tubes.

Nitriding is another term for case hardening.

Normalizing involves heating steels to approximately 100 F above the critical temperature range followed by cooling to below that range in still air at ordinary temperatures. This heat treat operation is used to erase previous heat treating results in carbon steels up to .40% carbon, low alloy steels, and to produce a uniform grain structure in forged and cold-worked steel parts.

Oil Hardening is a process of hardening a ferrous alloy of suitable composition by heating within or above the transformation range and quenching in oil.

Pearlite is another microscopic structure of steel that results from slow cooling or air cooling low to medium carbon and low alloy steels from the austenitic state.

Quenching and Tempering involves heating material to the proper austenitizing temperature, holding at that temperature for sufficient time to effect desired changes in crystalline structure, and then quenching in a suitable medium such as water, oil, or air depending on chemical composition. After quenching, material is reheated to predetermined temperature below critical range and then cooled under suitable temperatures (tempering).

Rockwell Hardness is determined by performing a hardness test on a Rockwell hardness testing machine. The hardness is determined by measuring the depth of penetration of a steel ball for softer steels and a diamond cone for heat-treated and harder steels when a load is applied.

Scleroscope or Shore Hardness is another type of hardness test performed on a Shore Scleroscope Hardness Tester. The hardness is determined by measuring the rebound of a diamond-pointed hammer when it strikes the surface of a specimen. This type of hardness testing is generally used on large parts that cannot be tested using Rockwell or Brinell machines.

Sub-Critical Annealing or Stress Relief Annealing is used to relieve or dissipate stresses in weldments, heavily machined parts, castings, and forgings. The parts are heated to 1150 F., uniformly heated through, and then either air-cooled from temperature or slow-cooled from temperature depending on the type of part and subsequent finishing or heat treating operations.

Tempering, also known as drawing, involves reheating usually quenched hardened steel to some temperature below the lower critical temperature followed by any desired rate of cooling after thoroughly soaking at temperature. Usual tempering temperatures are 300 F to 1100 F.

Water Hardening involves hardening high-carbon grades of tool steel, straight  carbon steels, and low alloy steels by quenching them in water during heat treating operations.

Heat Treatment:

Avoid PWHT Post Weld Heat Treatment

Heat Treatment of Stainless Steel for Spring Application

Stainless Steel for Spring Application

Heat Treatment of Metals

Heat treatment Stainless Steel

The Heat Treatment of Steel

Heat Treating Terms and Definitions

Steel Metal Glossary

Metals - Material Definitions and Terms

Technic of Metals Heat Treatment

Heat Treatable Aluminium Alloys

Elements in the annealed state

Passivation of Stainless Steels

Stainless Steel Tube Bright Annealing


Martempering Marquenching




Annealing of Aluminum and Aluminum Alloys


Flame Hardening

Induction Hardening

Stress Relieving

Stress Relieving Heat Treatment for Austenitic Stainless Steel


Normalizing Normalising of Gray iron

304 Heat Treatment

304L Heat Treatment

304H Heat Treatment

321 Heat Treatment

316L Heat Treatment

317L Heat Treatment

309S Heat Treatment / Annealing

310S Heat Treatment

347 Heat Treatment

410 Heat Treatment

410S Heat Treatment

430 Heat Treatment

ASTM A380 - Practice for Cleaning, Descaling and Passivating of Stainless Steel Parts, Equipment and Systems

ASTM A967 - Specification for Chemical Passivation Treatment for Stainless Steel Parts

EN 2516 - Aerospace series - Passivation of corrosion resisting steels and decontamination of nickel base alloys

Heat temper colours on stainless steel surfaces heated in air

Chemical Composition of ACI Heat Resisting Stainless Steel