Metallographic diagram of granular bainite 30CrMnSiA

Abstract

This paper introduces the microstructure, hardness value and metallographic structure of 30CrMnSiA granular Bainite. The test piece is cut from the steel plate, fine grinding and polishing on the surface of the metallographic sample and the metallographic structure are observed, the hardness value is measured by Rockwell hardness tester and digital metallographic microscope. The result shows that30CrMnSiA granular Bainite steel has an excellent strength and hardness, with a microstructure mainly showing lath or granular bainite and complex carbide.

1 Introduction

30CrMnSiA granular Bainite steel is a new type of superior Pearlite-Bainite composite high strength low alloy steel developed by domestic plate rolling mills, which is mainly composed of lath or granular Bainite and complex carbide. It has excellent comprehensive performance, good mechanical properties and welding performance, which has greatly improved its comprehensive performance. The 30CrMnSiA granular Bainite steel is the steel which has the most excellent mechanical properties, thermal stability, and durability after heat treatment, and it has excellent performance such as high strength, high toughness, rust-proof, wear-resistant and so on, so now has been widely applied in production fields with high performance.

2 Test preparation

There are two pieces of samples with a size of 7mm*10mm*45mm as the test source. The samples are firstly cut from steel plate by electric grinder and then the cutting surface is fine grinding until the surface is smooth enough to observe the metallographic structure and use the digital metallographic microscope to observe the microstructure of the samples and to measure the hardness value by Rockwell hardness tester.

3 Experimental results

The hardness value of 30CrMnSiA granular Bainite steel after quenching is Rockwell hardness HRC 36.7, and the microstructure of it is mainly lath or granular Bainite, in which there also contains some complex carbide. The metallographic structure shows that the precipitation of the alloy elements in the steel together with the Bainite are significant, the grain boundaries and interphase boundaries are clear and distinct ,the width of the grain boundary and the size of the grains are very uniform, which further prove that the 30CrMnSiA granular Bainite steel has excellent mechanical properties.

4 Conclusion

The hardness value of 30CrMnSiA granular Bainite steel after quenching is Rockwell hardness HRC 36.7, the microstructure is mainly lath or granular Bainite, and there is complexity carbide precipitated in the matrix. The grain boundaries and interphase boundaries are clear and distinct, and the grain size is uniform, which further prove that the 30CrMnSiA granular Bainite steel has excellent mechanical properties. The 30CrMnSiA granular Bainite steel has excellent comprehensive performance, good mechanical properties and welding performance, and it has been widely applied in production fields with high performance.

References

1. L. Song, et al, Study on 30CrMnSiA Granular Bainite Steel, Journal of Xidian University, Vol. 10, No. 5, 2011

2. H. L. Li, et al, Study on Preparation Technology and Performance of 30CrMnSiA Granular Bainite Steel, Journal of Iron and Steel Research, International, Vol. 8, No. 4, 2011

3. W. X. Hui, et al, Analysis on Structure and Properties of 30CrMnSiA Granular Bainite Steel, Journal of Materials Science and Engineering, Vol. 31, No. 11, 2011

Microstructure of 30CrMnSiA is a low-alloy steel with particle reinforcement. 30CrMnSiA steel is a ferrite matrix with small undissolved particles, mainly consisting of carbides, M (Mn, Cr, Si, Fe) C, Cu and Mo.

In the microstructure image of 30CrMnSiA steel, there are two phases, Ferrite and disperse particles, which fill the interstitium of Ferrite matrix. The disperse particles are particles with irregular shapes and curved surfaces, which are distributed in the matrix in random orientations. The Ferrite matrix has a ferritic staggered double-frame grain structure.

In addition, some areas are nonmetallic inclusions. The fibers are mostly long and slender, sometimes having a single-arm branch structure. Nonmetallic inclusions are mainly found between Ferrite phases, and sometimes embedded in the end or center of Ferrite grains. The nonmetallic inclusions are mostly Al2O3, SiO2 and MnS.

In addition, there are some defects, such as flake-shaped non-metallic inclusions, casting defects and carving defects. The flake-shaped non-metallic inclusions are embedded in the matrix and commonly found in the surface area, which can cause stress concentration and reduce the strength of the matrix. The casting defects are mostly shrinkage and slag inclusion, especially in the region close to the corner of the grain. The drilling defects are generated during processing and can reduce the fatigue resistance of the material.

In general, the microstructure of 30CrMnSiA particles reinforced low alloy steel shows a stable, uniform and coarse-grained ferrite matrix structure. The disperse particles are randomly dispersed, showing good reinforcement.