33CrNi3Mo steel (high temperature dehydrogenation annealing) low-magnification structure and non-metallic inclusions

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Abstract

A study of the fine structure, non-metallic inclusions, and other microstructural features of 33CrNi3Mo steel (hydrogen quenching tempering) was conducted. The results were compared to those of the tempering-only treatment. The main conclusion from this study is that the steel at the lower tempering temperature (℃), when quenched to below 1030℃, showed better microstructural features than the tempering-only treatment.

This study started with a base material of 33CrNi3Mo steel supplied in a bar form of 150 mm in diameter. The material was divided into two parts, one of which was tempered at 600℃ (remaining at 425℃) and the other at 475℃ (remaining at 320℃). The samples were then subjected to a hydrogen quenching process.

Microstructural analysis revealed that the finer tempered steel contains larger numbers of spheroidized MnS inclusions compared to the conventional tempering-only treatment. The microstructure of the steel quenched and tempered at 475℃ is mainly composed of bainite and ferrite. The amount of lamellar pearlite also increases due to the presence of more grain boundaries in the lower temper treatment. The presence of more grain boundaries is likely due to the increased initiation of bainite at the early stages of tempering.

Due to the higher amount of inclusions present in 33CrNi3Mo steel at lower temperatures, nonmetallic inclusions analysis was also made. The content of C and Si are higher in lower temperatures. The amount of Al2O3 and MnS is also slightly higher in the lower temperature range.

Micro-brinell hardness measurements were also made on the two materials in order to compare the hardness values. The hardness of the steel at 475℃ is higher than the one at 600℃ due to more microstructural features present at higher temperatures.

It is concluded from this study that 33CrNi3Mo steel is better at the lower tempering temperature range as quenched to below 1030℃ and has better microstructural features such as fewer inclusions, larger numbers of spheroidized MnS, and higher hardness.

In summary, 33CrNi3Mo steel, when quenched and tempered at temperatures below 1030℃, shows better microstructural features than the tempering-only treatment. The lower tempering temperature causes grain refinement and increased presence of non-metallic inclusions. The microstructure consists of bainite and ferrite, with a small amount of lamellar pearlite. Hardness is also higher in this condition compared to the conventional tempering treatment.

33CrNi3Mo steel is a high temperature steel composed of Cr-Ni-Mo series alloy elements. It is produced with the advanced process to obtain a good microstructure and property for performance engineering and structural metal materials.

The low-temperature de-hydrogenation annealing process of 33CrNi3Mo steel can obtain excellent properties. This process can reduce the hardness and quencher from the austenite structure and significantly improve the mechanical properties and toughness. After tempering and quenching, 33CrNi3Mo steel has even higher strength, hardenability and fatigue strength.

33CrNi3Mo steel also has good resistances to fire and oxidation as well as excellent anti-corrosive properties due to its high concentration of chromium. The carbon content of 33CrNi3Mo steel is very low, and the added alloys can reduce carbide contact, which can increase its corrosion resistance.

Due to the high temperature annealing process, the metallographic structure of 33CrNi3Mo steel is relatively homogeneous and tough. The content of non-metallic inclusions is low, which can ensure the material quality and help improve its tensile strength, ductility and plasticity.

In conclusion, 33CrNi3Mo steel is an excellent high-temperature steel, which offers excellent mechanical properties and corrosion resistance due to its special de-hydrogenation annealing process. Its low-temperature mechanical properties and properties are also better than other alloys. 33CrNi3Mo steel has uniform metallographic structure, low non-metallic inclusion content and high hardness, plasticity and strength.