Microstructural examination of steel

Microstructure of Low Carbon Steel

Low carbon steel (LCS) is one of the most commonly used materials in industry due to its numerous beneficial characteristics, such as outstanding mechanical properties, excellent thermal and electrical conductivity, high wear resistance, and low price. Along with these properties, the microstructure of LCS is great for processing, forming and cutting. The microstructure of low carbon steel is composed of ferrite and pearlite, which are formed when the steel is heat treated.

When cooled, ferrite forms a large, plate-like grain and pearlite forms small, rod-like grain. The formation of ferrite and pearlite is directly related to the carbon content and cooling rate. The microstructure of LCS consists primarily of ferrite, which accounts for over 80% of the microstructure. Pearlite generally accounts for between 15% and 20% of the microstructure and the remainder is retained austenite.

When microstructurally examined, ferrite typically appears as a mixture of non-uniformly-shaped grains bounded by continuous boundaries. The range of grain size tends to be wide with varying grain population distribution. Pearlite typically appears as a combination of fine ferrite laths and cementite lamellae. The ferrite laths are usually small, approximately 0.005mm in size, while the cementite lamellae are usually much thinner, approximately 0.001mm in size.

The microstructure of LCS is important due to its effects on the mechanical properties of the material. The ferrite grains are much softer than the pearlite and contribute to the materials ductility and toughness. The pearlite, on the other hand, is much harder and contributes to the materials strength and wear resistance. The size and distribution of ferrite and pearlite in the microstructure can also affect other material properties, such as fatigue strength, creep strength and fatigue cracking resistance.

Given its wide variety of beneficial properties and its microstructure, LCS is an ideal material for many industrial applications. It is often found in construction and automotive applications. It is also a common choice for machinery parts, fasteners, and lubrication components.

In conclusion, LCS is a popular and versatile material that is used in numerous industrial applications. Its microstructure is composed primarily of ferrite and pearlite, with ferrite accounting for more than 80% of the microstructure. The size and distribution of the ferrite and pearlite in the microstructure directly affect the mechanical properties of the material, such as its strength, ductility, toughness, and wear resistance. LCS is an extremely useful material due to its beneficial properties and its microstructure, and it is a popular choice in many industries.

Microstructure inspection of stainless steel

Stainless steel is a kind of metallic materials, and its use and production have a long history. With the development of metallurgy technology, the kinds of stainless steel are also increasing. Microstructure inspection technology is an important testing method of stainless steel, which can help to understand the form, size, location and quantity of base phase. To inspect the microstructure of stainless steel, the specimens are usually grinded and polished, then observed by optical microscope or scanning electron microscope.

Usually, the typical cross-sectional, longitudinal and end-face surface of stainless steel specimen are equally polished, and then their microstructure is test. After grinding, specimens should be acid-washed for 1 to 2 hours, and then degrease. During the polishing operation, the specimens should be placed in transverse, longitudinal and end-face, respectively, and use fine emery cloth to polish until the surface roughness is minimised, then use the successively polishing fluid mixed with common alumina powder. The final polishing should use a polishing fluid mixed with diamond. During the process, the specimen should be washed in both the polishing liquid and in each alcohol rinse.

After the specimens are well polished, it can be observed and test directly. Under the optical microscope, the specimens are generally observed at the magnification of 40 to 400 times, and it is better to observe the cross section and longitudinal oblique section along the rolling direction. If the microstructure needs further investigation, the scanning electron microscope can be used for further analysis of the size, shape and distribution state of metallographic substructure.

Inspection of the microstructure and texture of stainless steel can provide a scientific grasp of the performance and quality of the material and provide basis information for the selection of materials and the application of product process. Therefore, the microstructure inspection should be paid enough attention to ensure the quality assurance of stainless steel materials.