The main defects produced during hardening are: 1. Mechanical Properties not up to the Specifications. 2. Soft Spots. 3. Quench Cracks. Defect # 1. Mechanical Properties not up to the Specifications: Hardness is the most common test used for checking hardened tools and components, but other tests are also done on machine components to check the other mechanical properties to [...]
In this article we will discuss about:- 1. Meaning of Hardening 2. Objectives of Hardening 3. Austenitising Temperature for Different Classes of Steels 4. Heating Time 5. Components 6.Internal Stresses during Quenching. Contents: Meaning of Hardening Objectives of Hardening Austenitising Temperature for Different Classes of Steels Heating Time for Hardening Components for Hardening Internal Stresses during Quenching 1. Meaning of [...]
Tempering of steels takes place in four distinct but overlapping stages: 1. First Stage of Tempering: (Though mild steels as a rule are not hardened and tempered in industry, it is of academic interest to see the changes occurring in such steels during tempering after hardening). The tempering reactions in steels, containing carbon less than 0.2%, differ somewhat from the [...]
In this article we will discuss about:- 1. Introduction to Tempering 2. Aim of Tempering 3. Stages 4. Classification 5. Effects 6. Time and Temperature Relationship 7. Calculation of Hardness of Tempered Steels Based on Composition 8. Industrial Practice. Contents: Introduction to Tempering Aim of Tempering Stages of Tempering Classification of Tempering Effects of Tempering Time and Temperature Relationship in [...]
The presence of alloying elements effects substantially, the tempering behaviour of the steels depending on the nature, amount and simultaneous presence of number of alloying elements. Most common elements (except cobalt) shift the CCT curve to longer times, which essentially result in the increase of hardenability of the steels, so that pearlitic transformation can be avoided easily to obtain martensitic [...]
In this article we will discuss about:- 1. Introduction to Age-Hardening Treatment 2. Requirements of Age-Hardening Treatment 3. Steps 4. Classification of Precipitates 5. Duplex Ageing 6. Barriers. Contents: Introduction to Age-Hardening Treatment of Metals Requirements of Age-Hardening Treatment of Metals Steps in Age-Hardening Treatment of Metals Classification of Precipitates in Age-Hardening Treatment of Metals Duplex Ageing Treatment of Metals [...]
Many problems occurs during carburising of steels. Some of these are: 1. Low Surface Hardness 2. Low Case Depth 3. Non-Uniform Case Depth 4. Soft Spots 5. Sooting 6. Distortion. Problem # 1. Low Surface Hardness: There are two main reasons of low surface hardness of a carburised component- Presence of large amount of retained austenite or decarburisation. There is [...]
Depending on the nature of carbonaceous atmosphere, carburising is called pack, or solid carburising, liquid carburising, or, gas carburising. But, whatever may be the method used, carburisation always takes place via a gaseous phase. Method # 1. Pack or Solid Carburising: In this method, the carburising compound is a solid carburiser, usually charcoal of 3 to 10 mm size (fines [...]
In this article we will discuss about:- 1. Introduction to Flame-Hardening 2. Methods of Flame-Hardening 3. Operating Variables 4. Gases Used 5. Steels for Flame-Hardening 6. Applications 7. Advantages and Disadvantages. Contents: Introduction to Flame-Hardening Methods of Flame-Hardening Operating Variables for Flame-Hardening Gases Used for Flame-Hardening Steels for Flame-Hardening Applications of Flame-Hardening Advantages and Disadvantages of Flame-Hardening 1. Introduction to [...]
Carbon potential may be defined as that carbon content which a specimen of a carbon-steel foil acquires when equilibrium conditions have been achieved between the carbon potential of the carburising medium and the carbon content of the foil. Fig. 8.4 illustrates that surface carbon content may be less than the carbon potential of the atmosphere. The activity of carbon in [...]