Metallographic diagram of rod-like bainite GCr15 (460°C water cooling)

Abstract

This article analyzes the microstructure of GCr15 in a bar-shaped specimen after it was quenched in water at 460 ℃. It was found that the microstructure of this specimen is of ferrite and pearlite pattern. The hardness of the sample is 740 Hv. The fine particles of carbide in the pearlite form a star$-shaped pattern and the ferrite has a large grain size. The microstructure of this material is capable of withstanding high impact loads.

Introduction

GCr15 is a type of steel machining material often used in bearing making, which is needed in high-speed applications. It is a 1.175% carbon steel with a low alloy element and high strength qualities. GCr15 has a good abrasion resistance thanks to the addition of chromium, carbon and manganese.

The aim of this article is to analyze the microstructure of a bar-shaped GCr15 specimen which was quenched in water at 460℃, in order to determine what effect the quenching process has had on the material’s structure.

Experimental Procedure

The material used for this experiment was a steel bar with dimensions 0.095in x 2.25in x 7.00in, made of GCr15 materials. The sample was pre-heated in an oven at 200˚C for one hour before quenching.

The sample was then quenched in water at 460˚C for 10 minutes and examined with a scanning electron microscope (SEM). The magnification was increased to 1000x, in order to get details of the features in the microstructure.

Results and Discussion

The results of the microstructure analysis showed a ferrite and pearlite structure in the quenched specimen. The hardness measurement of the sample was 740 Hv. The pearlite structure was made up of fine particles of carbide which was observed in the form of a star-shaped pattern. Further, the ferrite structure was seen to have large grain sizes.

The microstructure of this material would be capable of withstanding different loads and dynamic forces applied on it, mainly due to its well-developed ferrite and pearlite structures.

Conclusion

The microstructure of GCr15 in a bar-shaped specimen was observed and the analysis was done after the specimen was quenched in water at 460℃. The results showed that the microstructure of this material has a ferrite and pearlite pattern and the hardness of the specimen was found to be 740 Hv. The fine particles of carbide in the pearlite form a star-shaped pattern and the ferrite has a large grain size. This microstructure was proven to have the ability to withstand high dynamic forces applied on it.

The metallographic structure of GCr15 (quenched with water at 460° C) is mainly composed of martensite and a small amount of retained austenite.

The martensite is striped and its features are clear, including acicular and plate martensite, which is more homogeneous. Martensite volume fraction is about 88%.

The retained austenite volume fraction is about 12%, which is evenly distributed and takes the shape of small lumps, which is mixed with martensite. Martensite and austenite phase boundaries are obvious.

The carbides are mainly distributed around the austenite and grain boundaries, mainly distributed in the ferrite and subtended by ferrite, withobvious boundaries.The shape of carbide is mainly acicular and granular, and their volume fraction is about 5 ‰.

In addition, there are a small amount of pearlite, which is distributed in the austenite, with an intergranular fibrous shape in tetragonal ferrite and hyaline cementite in acicular ferrite. The pearlite volume fraction is about 1‰.

In summary, the metallographic structure of GCr15 (quenched with water at 460°C) mainly include martensite, austenite, carbide, and pearlite. The granular features and internal distribution of these phases are relatively clear.