Metallographic diagram of 50 steel (860°C air cooling)

Metallographic analysis of Fe-50 steel at 860℃

Introduction

Metallography is a method used to study the microstructure and composition of metals. Metallography is useful in understanding how alloys behave differently under different external forces and, as such, is essential in materials science. Sample preparation is critical to the success of the metallography and includes polishing, etching, and examination. An essential element of the preparation process is selecting the appropriate methods of material removal and polishing. One of the more common techniques is mechanical polishing, involving the use of abrasive papers, discs and other tools to achieve a fault-free polished surface. This paper presents a metallographic study of Fe-50 steel as an example of the metallographic approach.

Metallographic Analysis of Fe-50 Steel at 860℃

The metallographic analysis of Fe-50 steel at 860°C was conducted using a manual tool polishing system. The sample was evaluated initially on a prepared semi-fine grind with 400 and 800 grit diamond discs. After a successful polishing process, the sample was evaluated with a combination of light transmittance and quantitative etching techniques. Commonly used etching techniques include nitric acid and aqua regia. In this study, the latter was used to obtain an indication of the composition of the material.

The sample appeared to consist of a homogenous ferritic structure that exhibited little to no difference in appearance or texture between grains. There were no visible inclusions or anomalies in the microstructure. High resolution images revealed that the grain boundary complexes, which is the collection of grains of crystal lined in various directions, were relatively unrestricted and uniform in size.

Analysis

The analysis of Fe-50 steel revealed an austenitic ferritic mixture of iron and chromium. The chromium content in the alloy was 2.5 wt%, with 0.3 wt% of additional material consisting of manganese and silicon. The results of light transmittance yielded a hardness of 140HV1. The higher hardness was attributed to a higher chromium content and considerable residual stresses surrounding the grain boundaries.

Conclusion

The metallographic analysis of Fe-50 steel at 860°C revealed a homogenous ferritic structure with high chromium content of 2.5 wt%. The sample was relatively free of inclusions and contained no anomalies within the microstructure. Results from the light transmittance test yielded a hardness value of 140HV1, which is higher than normal due to the increased chromium content and residual stresses. This study suggests that Fe-50 steel has suitable properties for many applications at high temperatures.

The metallographic structure of 45# steel (air-cooled at 860 ℃) is mainly composed of pearlite, ferrite and a small amount of dispersion carbide. The pearlite structure is mainly fine, mainly the dispersion of tiny point-like cementite, distributed in the body of ferrite. The dispersion of cementite particles in the dendritic ferrite grains is uniform, and the dispersion degree of cementite particles is fine. The high temperature organization has obvious signs of full pearlite, and the mesophase of pearlite is very clear.

The grain size of the metal is fine, among which the grain size of the pearlite is 2-3 mm. The internal structure of ferrite is relatively dense and continuous, and the ferrite grain size is maintained at 0.8-1.2mm, which has good plasticity. There is a small amount of retained austenite in the grain boundary, and small amount of intergranular ferrite which is easy to dissolve and form, and the structure of streptoid is also obvious.

The dispersion of carbide particles in the metal sample is mainly distributed between the dendrite branches of pearlite, at the grain boundary of ferrite and in the ferrite intergrain, and the form of distribution is mainly in the shape of ellipses. Its dispersion form is mainly bloc, with average size of 0.04-0.07 mm. Although it has high hardness, it does not cause brittle fracture, because it is finely dispersed and uniformly distributed.

Overall, the metallographic structure of 45# steel (air cooled at 860 ℃) is fine and dispersive. The grain size of pearlite and ferrite is fine, and they are full and regular. The distribution of carbide particles is uniform and the size is also very small. All these characteristics can meet the requirements of metal plasticity and strength.