ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Heat Treatment in Metals

Updated on July 16, 2013

Heat treatment is the name given to the process of heating metal above the critical temperature, at which internal changes occur, and then cooling the metal slowly or rapidly to give it more desirable physical and mechanical properties.

The heat treatment process are normalizing, annealing, hardening and tempering.


Steel is normalized by heating it slowly to just above the temperature at which the changes in the internal structure takes place; it is then soaked at this temperature. After the soaking period, the steel is slowly cooled in air. Air cooling is referred to as medium cooling.

Normalizing refines the grain structure of the steel.


Annealing is similar to normalizing. Different rates of cooling are required for different materials. Steel is annealed by heating to required temperature at which its internal structure changes, and then soaking at this temperature. After soaking, the steel is cooled slowly in a furnace. Furnace cooling is referred to as slow cooling.

  • Annealing refines the grain structure, reduces hardness, and increases ductility.


Steel is hardened by heating to a specified temperature followed by rapid cooling. The cooling may be in the air, or by quenching in oil or water: the method used depends on the type of steel and the properties required. A gain in hardness is accompanied by a loss in ductility. In the fully hardened state steel is brittle. Steels containing very small amounts of carbon cannot be hardened.


Steel is tempered by heating hardened steel and then cooling it by air or quenching. The temperature to which it is heated and he quenching rate control the degree of hardness, strength and ducility.

Steel is tempered to obtain special mechanical or physical properties. Important engine parts such as coupling bolts, bearing bolts, and parts subjected to alternating stress, are tempered to increase their strength and resistance to fatigue failure.

Surface Hardening

Surface hardening is a process by which the structure of the surface of a material is changed to give it better wearing properties. The process may increase the carbon content of the steel by caburization or, in the case of steels with higher carbon content, by heat treating the surface concerned.

The names of various surface hardening processes are as follows.

Carburizing Process

  • Cyaniding - Pack Method
  • Nitriding - Gas Method

Heat Treatment Process

  • Flame Hardening
  • Induction Hardening


    0 of 8192 characters used
    Post Comment
    • profile image


      6 years ago

      careful heat treatment prolong useful material life...improper treatment leads to immature corrosion.


    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

    Show Details
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
    ClickscoThis is a data management platform studying reader behavior (Privacy Policy)