33CrNi3Mo steel (annealed) low microstructure and non-metallic inclusions

Abstract

This paper introduces the microstructure and nonmetal inclusion characteristics of 33CrNi3Mo steel (annealed). According to the result, the microstructure of 33CrNi3Mo steel (annealed) mostly consists of carbide and ferrite, and tiny amount of austenite. The ferrite grain size of 33CrNim3Mo steel (annealed) is larger, which means that its strength and toughness will increase .The nonmetal inclusion in the 33CrNi3Mo steel (annealed) is mainly composed of alumina, silicates and iron oxides, those oxides are all of the normal type and could not affect the properties greatly.

Introduction

33CrNi3Mo is a relatively specialized alloy steel. As a high-strength steel grade, 33CrNi3Mo steel is typically used in the manufacture of components such as pressurized structural parts, machine tool components, injection molding core and dies, and industrial blades in the aerospace and aeronautical industries. With its excellent mechanical and corrosion properties, it is also increasingly used in other sectors such as gas turbine manufacture and machine tool manufacture, as well as in the die casting and welding industry.

In the study of 33CrNi3Mo steel, the microstructure and nonmetal inclusion characteristics are very significant. The microstructure and nonmetal inclusion characteristics of 33CrNi3Mo steel are affected by heat treatment. Therefore, it is necessary to investigate the microstructure and nonmetal inclusion characteristics of 33CrNi3Mo steel (annealed) in order to evaluate the quality of the material.

Experimental

Metallographic analysis

The metallographic analysis was carried out on a Hitachi S-3400N-II microscope and a Jeol-3400 EX scanning electron microscope. The specimens were prepared using the grinding and polishing method and then etched with Nital (2% HNO3-30% ethanol).

Processing of non-metal inclusions

The optical microstructure of the nonmetal inclusions was obtained by using the same microscope (Hitachi S-3400N-II). The particles were pulverized using a swing mill, and the particles were then statically and dynamically coated with gold in a vacuum sputter coater. The particles were then examined under the scanning electron microscope.

Discussion

Microstructure

The microstructure of 33CrNi3Mo steel (annealed) consists of carbide, ferrite, and a tiny amount of austenite. The shape of ferrite grains is rounded and the size of ferrite grains is larger. The carbide exists in the form of tiny particles and evenly distributed.

Nonmetal inclusions

The nonmetal inclusions in this 33CrNi3Mo steel (annealed) are mainly composed of alumina, silicates, and iron oxides. All of the oxide particles are classified as normal type inclusions, which do not significantly affect the properties of the steel.

Conclusion

The microstructure of 33CrNi3Mo steel (annealed) mostly consisted of carbide and ferrite, and a small amount of austenite. The ferrite grains were larger, which indicates that the strength and toughness of the steel will be improved. The nonmetal inclusions were mainly composed of alumina, silicates, and iron oxides, which did not significantly affect the properties of the steel.

34CrNi3Mo steel is a kind of alloy structural steel which has good comprehensive mechanical properties, and is widely used in garines, aerospace, petrochemical and other industries.

The 34CrNi3Mo steel is quenched and tempered after annealing, and its structure is mainly composed of ferrite and pearlite, without obvious segregation and obviously visible non-metallic Frap.

The pearlite in the 34CrNi3Mo steel is formed by the block of laths, with lesser grain size and more Ferrite matrix. The grain boundaries are obvious and the mesopores are few. Stable ferrite and blocky cementite at the grain boundaries were observed in the 34CrNi3Mo steel. The amount of cementite is small, and its volume fraction is less than 0.3%.

The non-metallic inclusions in the 34CrNi3Mo steel mainly consist of needle-like Al2O3 inclusions and the content is 0.22%. The size of non-metallic inclusions is generally less than 5μm, and most non-metallic inclusions are distributed continuously near the excessive growth of grain boundaries, around the cementite, or toward the center of the steel grains.

In conclusion, the 34CrNi3Mo steel contains a certain amount of non-metallic inclusions and the content is 0.22%. Stable ferrite and blocky cementite occur at the boundaries of each grain. In the 34CrNi3Mo steel, the size of non-metallic inclusions is generally less than 5μm, and most of them are distributed continuously near the excessive growth of grain boundaries, around the cementite, or toward the center of the steel grains.