After steel has been designed for a specific application, the designer, or the purchaser has to select the specific steel from those available in the market. The steels are sold with standard specifications and associated notations. Some knowledge of the specifications is thus, essential. The specifications and the notations used for the steels vary from country to country, but each [...]
In this article we will discuss about:- 1. Introduction of Austenitic Grain-Size of Steels 2. Actual Austenitic Grain Size of Steels 3. Importance 3. Effects 4. Austenitic Grain-Size Growth of Heating 5. Methods of Revealing. Contents: Introduction of Austenitic Grain-Size of Steels Actual Austenitic Grain Size of Steels Importance of Austenitic Grain-Size of Steels Effects of Austenitic Grain-Size of Steels [...]
When a steel part is heated to high temperatures for heat treatment, its surface reacts chemically with the surrounding medium in the furnace. The furnace atmosphere may consists of various gases depending on the conditions of combustion and the temperature The common furnace gases are O2, CO2, CO, H2, H2O (water vapour), N2, CH4, etc. As a result, two undesirable [...]
The first step in the true heat treatment cycle of steel is the austenitisation, i.e. to get a homogeneous austenite by heating it to a predetermined temperature in the austenite stability range. Normally, the initial structure of carbon steels, before this heat treatment, is ferrite + pearlite (in hypo-eutectoid steels), pearlite (eutectoid steel), or cementite + pearlite (hyper eutectoid steels). [...]
Unless special precautions are taken, heating the steel results usually in certain amounts of oxidation or scaling and may also result in decarburisation. Both are usually undesirable. To prevent oxidation and decarburisation of steels, various methods from the simplest, but not completely reliable, to complex and expensive but almost full proof, are used depending on the criticality of the part, [...]
The control of ferrite grain size in ferrite-pearlitic steels, or of pearlite colony size in eutectoid steels, is obtained by controlling the austenite grain size. This can be achieved during following stages of processing steels: 1. During solidification 2. During mechanical working 3. During heat treatment. 1. During Solidification: Types of steels based on deoxidation practice- Plain carbon steel ingots [...]
Once the original austenite grain boundaries are revealed, the austenite grain size may be determined by one of the following methods suitable for the purpose. The name of the method used is always mentioned with the grain size specification. 1. ASTM Standard Grain Size Number: This is the most common method of measuring grain size, where the grain size is [...]
In this article we will discuss about:- 1. Causes of Overheated and Burnt Steels 2. Detection of Overheated and Burnt Steels 3. Reclamation. Causes of Overheated and Burnt Steels: When steels are heated above the upper critical temperatures, austenite grains coarsen. If the coarsening is not excessive, normalising, or annealing can refine the grains to normal size. If the heating [...]
In this article we will discuss abour the formation of widmanstatten structure of steels. Also learn about the factors controlling its formation. Formation of Widmanstatten Structure of Steels: If a coarse-austenite grained steel is cooled fast but less than its critical cooling rate, then a typical micro-structure develop called widmanstatten structure. (See Fig. 2.38, a typical micrograph illustrating this structure, [...]
In this article we will discuss about:- 1. Introduction to Martensitic Transformation in Steels 2. Characteristics of Martensitic Transformation in Steels 3. Crystal Structure of Martensite 4. Crystallography 5. Thermodynamics 6. Reversibility. Contents: Introduction to Martensitic Transformation in Steels Characteristics of Martensitic Transformation in Steels Crystal Structure of Martensite Crystallography of Martensitic Transformation in Steels Thermodynamics of Martensitic Transformation in [...]