Steel metallographic inspection and main inspection items

Metallographic Examination of Carbon Steel and its Main Inspection Item

Introduction

Metallography is a type of materials science that studies the structure and microstructure of metals. Through the observation and analysis of the microstructure of metals, the formation and internal qualities of the metal can be revealed. The summary of these characteristics mainly includes grain structure, surface defects, segregation, inclusions and mechanical properties. The knowledge and understanding of the microstructure of metals is also an important step for making correct engineering decisions. Due to its improved surface finish and mechanical properties, carbon steel has long been used for industrial applications. Metallographic examination provides useful information about the quality and capability of carbon steel.

Microstructure Characterization of Carbon Steel

Carbon steels are much stronger and harder than ordinary steels. As carbon steels contain carbon, their microstructures are mainly composed of ferrite and pearlite. Ferrite is a pure iron phase and accounts for 75%-90% of the microstructure. Pearlite is an intermetallic compound, generally a mixture of ferrite and cementite. It is harder than ferrite and gives carbon steels their increased strength and hardness. The carbon content in the microstructure of a carbon steel is also an important indicator of its capabilities. High Carbon Steels usually have a carbon content between 0.60%-2.0%, while low carbon steels have a carbon content below 0.30%.

Metallurgical Examination of Carbon Steel

The metallurgical examination of carbon steel mainly involves three aspects: grain size, surface defects and segregation. Firstly, the grain size of the carbon steel is investigated. The size of the grain affects the mechanical properties of the steel. Generally, smaller grain sizes give the steel higher strength and higher ductility. Secondly, the surface defects of the carbon steel are examined. Defects on the surface can affect the wear resistance and corrosion resistance of the steel. Lastly, segregation in the microstructure is determined. Segregation of material in the microstructure can impair the mechanical properties of the steel.

Inspection Tool and Processing Procedure

The metallurgical examination of carbon steels is mainly carried out by optical microscopes. A grinding machine is used for specimen preparation. The specimen is firstly sliced and then polished to remove mechanical deformation and surface abrasions. Once the specimen is prepared and cleaned, it is ready for the inspection of grain sizing and surface defects. The size of the grains is determined by the transmission electron microscopy and the surface defects are examined by a stereomicroscope. When examining the microstructure of a carbon steel, several magnifications should be used to better identify any possible segregation.

Conclusion

Metallographic examination of carbon steel is a useful and reliable technique to analyze the material and microstructure of the steel, which in turn can help make more informed decisions in engineering. By employing the right tool and processing procedure, the accuracy of the examination can be increased. The microstructure of the carbon steel should be carefully examined in order to ensure the quality and capability of the steel.

Metallographic examination of stainless steel

Metallographic examination of stainless steel is an essential part of quality control. Stainless steel is a type of steel alloy which contains more than 10.5% chromium, providing superior corrosion and high temperature resistance. In addition to chromium, stainless steel may also contain other alloying metals such as nickel, molybdenum, and nitrogen to name a few.

Metallographic examination is a process of observing the microstructural details of a metal specimen. It can reveal information about the materials chemical composition, as well as its mechanical properties. Common analysis methods includes optical microscopy, scanning electron microscopy, energy dispersive spectroscopy etc.

Common testing items for stainless steel metallographic examination incluude hardness, microstructure, grain size, and their distribution, inclusion evaluation, oxidation and decarburization layer analysis, mechanical property analysis etc. Hardness assessment is done using microhardness tester. Common tests include Vickers hardness, Knoop hardness etc. Microstructure observations are done using optical microscopy and scanning electron microscopy. It is used to determine the level of homogeneity of the material, and the distribution pattern of inclusions, particles and other flaws. Grain size is measured by standard grain size measurement method. And inclusion evaluation is carried out by microscopical examination. Oxidation and decarburization layer analysis is done by chemical analysis and optical observation. Mechanical properties are tested by tensile strength testing.

Metallographic examination is the key to quality assurance of stainless steel. It helps the quality control personnel to ensure uniformity of the material and to detect the presence of any undesirable flaws which might adversely affect the performance of the component or component part.