Metallographic diagram of 16Mn (normalized at 910°C)

Metallography of 16Mn Hot Rolled Steel

Metallography is defined as the study and analysis of the internal structure of a metal or alloy. It involves the use of microscopes and other optical instruments to closely inspect the microstructure of metals and alloys. Metallography-based analysis is used to help the characterization of materials in order to make an appropriate choice for different engineering applications. One of the primary uses of metallography is in the study of the effects of hot-rolling processes on the microstructures of steels.

This paper is a study of the metallography of hot-rolled 16Mn steel. 16Mn steel is an alloy of manganese and carbon with a nominal composition of 0.13%-0.18% C and 1.60%-2.00% Mn. It is commonly used in the manufacture ofstructural steel, and is also well suited for sheet metal work. The microstructure of the 16Mn steel was hot rolled in a furnace at approximately 910°C.

A sample of 16Mn steel was taken from the hot rolled material and cut into thin slices using a diamond impregnated cutting wheel. The cut slices were then mounted on the metallographic specimen holder for optical examination. The slices were then polished using metallographic polishing up to a surface finish of 0.25 microns. Once the sample was prepared, it was then projected onto a low magnification microscope for observation.

Under the microscope, the 16Mn steel was observed to have a ferritic structure as indicated by a relative lack of bright eta-carbides and the presence of grain boundaries. The 16Mn steel also showed a high degree of uniform ferritic grain structure, with grain boundaries evenly spread out. The ferritic grains were uniform in size and shape with an almost equally distributed grain size and shape.

The Etchants used were a 2% Nital etchant solution and a 5% Acetic acid etchant. The Nital etch revealed that the ferrite grains were uniform and had a higher degree of crystallinity with small visible inter-planar holes. The Acetic Acid etch revealed that the ferrite grains had a more uniform shape and appearance with fewer visible grain boundaries than the Nital etch.

The metallographic analysis revealed that the 16Mn steel hot-rolled sample had a high degree of crystallinity, with a uniform ferritic grain structure. The uniform grain structure, evenly distributed grain size, and the lack of eta-carbides indicated that the hot-rolling process had an effective annealing effect on the steel.

The results of the metallographic study provide useful insights into the behavior of 16Mn hot rolled steels. The material exhibited a high degree of crystallinity, uniform grain structure, and a lack of eta-carbides indicative of a successful hot-rolling operation. The results confirm that 16Mn steel is well suited for hot rolling and should be a viable option for use in structural steel applications.

The microstructure of 16Mn is a tempered lath type, which is observed by bright field observation. Its width is between 0.2~2.0mm and it is distributed in the shape of nets. Most of the morphology of 16Mn is large and small pearlite and small hard mearite. There are trace ferrite, carbides and retained austenite. The tempered lath type 16Mn has good comprehensive mechanical properties.

The pearlite zone shows a light gray crust-like band boundary between pearlite and ferrite. The quenched austenite is retained or turned into fine granular pearlite or tiny mearite depending on the tempering temperature. The carbide particles are very fine, round, and evenly distributed. The fishbone structure of the mearite is obvious. The pearlite, mearite and a small amount of ferrite all undergo uniform and dense dispersion,which is beneficial to the improvement of the strength and toughness of the steel.

Carbide particles are more evenly distributed, fine and round in size. The distribution of retained austenite is mainly in the insert layer, the austenite grain size is fine, and small amounts are distributed in the matrix, which can prevent and reduce the occurrence of crack.

In conclusion, the bright field observation of 16Mn has the typical morphological characteristics of pearlite and mearite, and there are also a small amount of ferrite, austenite and carbides. The uniform dispersion of pearlite, mearite and a small amount of ferrite can improve the tensile and impact properties of the steel.