Non-metallic inclusions in steel

In metallurgical engineering,non-metallic inclusions in steel are an important research topic.These inclusions not only affect the quality of steel,but also have a significant impact on its mechanical,physical and chemical properties.This article will take an in-depth look at the sources,types,effects,and methods of reducing their content of non-metallic inclusions in steel.

I.The definition and origin of non-metallic inclusions

Non-metallic inclusions in steel refer to various non-metallic material particles entrained in steel.These inclusions are mainly composed of compounds of elements such as oxygen,nitrogen,and sulfur in steel,as well as foreign substances such as slag,refractory materials,and sediment.During the steelmaking process,because the solubility of these elements in steel is higher at high temperatures and significantly reduced at room temperature,when the steel cools and solidifies,these elements will precipitate and combine with iron and other metals to form various Compounds,called non-metallic inclusions.

The sources of non-metallic inclusions can be divided into two categories:endogenous inclusions and exogenous inclusions.Endogenous inclusions are compounds such as oxides and silicates formed during the steelmaking process due to the addition of deoxidizers.For example,deoxidizing elements react chemically with oxygen to form oxides that are insoluble in steel.Some of these oxides may float up into the slag in the molten steel,but some will remain in the steel as inclusions.Exogenous inclusions are caused by slag,refractory materials or other inclusions that do not float out in time during the solidification of the molten steel and remain in the steel.

II.Types of Non-Metallic Inclusions

There are many types of non-metallic inclusions,which can be divided into the following categories according to their composition and morphology:

Oxide inclusions:Oxides are the most common inclusions,mainly including simple oxides(such as FeO,Fe₃O₄,Fe₂O₃,MnO,SiO₂,Al₂O₃,Cr₂O₃,etc.),silicates,spinel inclusions and calcium aluminates.Among them,alumina(Al₂O₃)is a common inclusion in aluminum-deoxidized steel.It has high hardness and is easily broken into small angular particles during steel rolling,which damages the mechanical properties of the steel.

Sulfide inclusions:Sulfide inclusions are mainly composed of sulfur and metal elements,such as MnS.These inclusions are usually plastic and extend and thin as the metal deforms.

Nitride inclusions:Nitride inclusions are formed by the combination of nitrogen and metal elements,such as TiN,etc.These inclusions usually have a high softening point and hardness,and do not deform or break during hot working,maintaining their original shape.

Silicate inclusions:There are many types of silicate inclusions,including single-phase silicates(such as iron silicate,manganese silicate)and complex silicates.Single-phase silicates are usually glassy and appear as small spheres;complex silicates may become glassy or combined crystals.

Composite inclusions:Composite inclusions are complex inclusions composed of multiple elements and compounds,and their properties and morphology depend on their composition.

III.Effect of non-metallic inclusions on steel properties

The existence of non-metallic inclusions has a significant impact on the properties of steel,mainly in the following aspects:

Destruction of the continuity of the metal matrix:Non-metallic inclusions destroy the continuity of the metal matrix,resulting in reduced plasticity,toughness and fatigue properties of the material.These inclusions can easily become sources of cracks under stress,leading to a decrease in the mechanical properties of the steel.

Impact on hot and cold processing properties:The presence of non-metallic inclusions will affect the hot and cold processing properties of steel.For example,during the rolling process,inclusions are likely to cause microcracks and stress concentration in the metal matrix,resulting in a decrease in the surface quality of the steel.

Reduce the corrosion resistance of steel:Non-metallic inclusions may also reduce the corrosion resistance of steel.For example,aluminum oxide inclusions tend to form a hard and brittle oxide film on the surface of steel,affecting the corrosion resistance of steel.

Impact on the cutting performance of steel:Although some inclusions may be beneficial to the cutting performance of steel under special conditions,in most cases,non-metallic inclusions will reduce the cutting performance of steel.

IV.Methods to reduce the content of non-metallic inclusions

In order to reduce the content of non-metallic inclusions in steel and improve the quality of steel,the following methods can be adopted:

Optimize the deoxidation process:By optimizing the deoxidation process and selecting the appropriate deoxidizer and deoxidation temperature,the formation of endogenous inclusions can be reduced.For example,when using aluminum deoxidation,the amount of aluminum added should be controlled to avoid the formation of excessive aluminum oxide inclusions.

Strengthen slag control:Slag is one of the important sources of non-metallic inclusions.Therefore,slag control should be strengthened,and appropriate slag-making materials and slag-making systems should be selected to reduce the contamination of slag to molten steel.

Improving refining effect:By improving the refining effect,the content of non-metallic inclusions in steel can be further reduced.For example,vacuum refining technology can remove gas and inclusions in molten steel;argon blowing and stirring technology can promote the floating and separation of inclusions.

Strictly control the quality of refractory materials:Refractory materials are another important source of non-metallic inclusions.Therefore,the quality of refractory materials should be strictly controlled,high-quality refractory materials should be selected,and the maintenance and management of refractory materials should be strengthened.

Using advanced detection technology:With the advancement of microanalysis instruments,the analysis and identification technology of non-metallic inclusions in steel is also developing.The use of advanced detection technology can accurately determine the type,quantity,size and distribution of inclusions,providing strong support for optimizing production processes and improving steel quality.

V.Research significance of non-metallic inclusions

The study of non-metallic inclusions is of great significance for improving the quality of steel.First,by studying the sources and types of non-metallic inclusions,we can gain a deep understanding of their formation mechanism and influencing factors,and provide a theoretical basis for optimizing the production process.Secondly,by studying the effects of non-metallic inclusions on steel properties,we can formulate effective measures to reduce their content and improve the mechanical,physical and chemical properties of steel.Finally,by studying the detection technology and evaluation methods of non-metallic inclusions,we can establish a scientific evaluation system to provide strong support for the quality control of steel.

VI.Conclusion

In summary,non-metallic inclusions in steel are one of the important factors affecting the quality of steel.By optimizing the deoxidation process,strengthening slag control,improving the refining effect,strictly controlling the quality of refractory materials and adopting advanced detection technology,the content of non-metallic inclusions in steel can be effectively reduced and the quality of steel can be improved.At the same time,the study of non-metallic inclusions is of great significance to promoting the development of metallurgical engineering and improving the competitiveness of steel.

In future research,we should continue to explore the formation mechanism and influencing factors of non-metallic inclusions,develop more effective technologies and methods to reduce the inclusion content,and make a greater contribution to the development of the steel industry.