Effect of Cooling Process on Microstructure and Properties of Low Alloy Wear-resistant Steel NM400
Introduction
The wear-resistant steel NM400 has been widely used in a variety of industries due to its excellent mechanical properties and great hardness. This low alloy steel has high strength and toughness, excellent wear resistance and uniform microstructure. Additionally, it has high strain hardening capacity and a good resistance to abrasion. The NM400 also has an excellent balance of strength, ductility and weldability, properties that are essential for its applications. In order to optimize the performance of NM400 and further enhance its properties, a cooling process has been used to influence its microstructure and wear properties.
Overview of NM400
NM400 wear-resistant steel is a typical low alloy steel, which is characterised by high wear resistance, excellent engineers and good welding performance. Its strength and ductility, meanwhile, provide excellent impact wear resistance. The NM400 steel possesses good formability and is capable of being easily welded. This property increases its versatility in applications, as it is suitable to be machined, cut or formed into different desired shapes. In terms of its hardness level, NM400 can reach up to 400HBW(Brinell Hardness) with a thickness of 6mm or more and a Vickers hardness of 370HV. This high hardness is combined with a uniform microstructure which gives it exceptional wear-resistance, even in applications where impact wear is a factor.
Overview of Cooling Process
When considering the cooling process of NM400, a post production heat treatment may be used to further improve its properties by changing its microstructure. This can be achieved by subjecting the steel to a cooling process, whereby it is heated during fabrication then cooled in either an aqueous solution or in air. Both processes will produce different microstructures, as well as influencing the hardness, toughness and wear-resistance of the steel.
Impact of Cooling Process on Microstructure
The cooling process of NM400 steel can have a significant influence on its microstructure. The microstructure of NM400 steel can be manipulated by changing the cooling rate and heat treatment process. The microstructure of NM400 produced by air cooling is typically formed of a ferrite/pearlite matrix which exhibits a relatively low hardness and toughness, making it suitable for applications with mild wear. On the other hand, the microstructure of NM400 produced by aqueous solution cooling will display a martensitic matrix which is characterised by a higher hardness and improved toughness. This increased hardness and toughness makes the steel more suitable for applications with severe wear.
Impact of Cooling Process on Properties
The cooling process can also have a major influence on the properties of NM400 steel. The properties of NM400 produced by air cooling will typically be lower compared to NM400 produced by aqueous solution cooling. The air cooling process produces a ferrite/pearlite matrix which will result in lower hardness, strength and wear resistance compared to steel produced by aqueous solution cooling. In contrast, the martensitic matrix produced by the aqueous solution cooling results in higher hardness, strength and wear resistance.
The change in the source of cooling will also have an influence on the mechanical properties of the steel. The air cooling process typically results in a reduction of the yield strength, ultimate tensile strength and hardness. The impact wear resistance, on the other hand, is usually improved with the aqueous cooling process due to the formation of a martensitic matrix.
Conclusion
In conclusion, the cooling process has a significant influence on the microstructure and properties of NM400 wear-resistant steel. By controlling the cooling rate and process, the microstructure and properties of the steel can be changed to better suit the particular application. The air cooling process results in the formation of a ferrite/pearlite matrix which produces lower hardness and strength compared to the martensitic matrix produced by aqueous solution cooling. This increases the hardness, strength and wear resistance of the steel, making it more suitable for applications with a severe wear.
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