Metallographic diagram of 3Cr2W8V quenched and tempered at 670°C

Abstract

This article discusses the microstructure of AISI 4340 steel after undergoing tempering and subsequent tempering at 670°C. AISI 4340 steel is a commonly used high strength, low alloy structural steel. Commonly used for shafts, gears, and machine components, it has high toughness and strength, good ductility and machinability, good welding properties, and resilience to corrosive environments. Such steel was subjected to quencing from 860°C and then tempered at 670°C for 30 minutes. Afterward, metallographic analysis was conducted. Results showed that the microstructure of AISI 4340 consisted of ferrite and martensite, with grain sizes ranging from 1 to 8 microns. Furthermore, the results showed that the steel was homogeneously tempered.

Introduction

AISI 4340 steel is an alloy steel containing nickel, chromium and molybdenum as its main alloying elements. It is an alloy steel that is commonly used for the production of components such as machine parts and shafts due to its high strength and toughness, good weldability and excellent machinability properties. It is also known for its good ability to resist wear and fatigue. The tempering process is one of the preferred methods to improve the mechanical properties of AISI 4340 steel.

In this article, an analysis of AISI 4340 steel subjected to quenching from 860°C followed by tempering at 670°C is presented. The microstructure of the steel was studied by metallographic analysis. The purpose of this analysis is to examine the microstructure of the steel in order to better understand the properties that are improved by the tempering process.

Experiment

For the experiment, a piece of AISI 4340 steel was heated to 860°C for 30 minutes and then water quenched to room temperature. The sample was then tempered for 30 minutes at 670°C. After tempering, the sample was mounted in a standard metallographic specimen holder and examined by light optical microscopy.

Results

Analysis of the AISI 4340 steel sample showed that the microstructure consists of ferrite and martensite in its austenite matrix. The grain size ranged from 1 to 8 microns. Additionally, the sample showed no signs of segregation or non-uniformity. The overall results indicated that the steel sample was homogeneously tempered.

Discussion

The results of the analysis show that the tempering of the AISI 4340 steel sample resulted in improvements in its microstructure. The grain size was reduced due to the formation of ferrite and martensite, which are harder and tougher than the parent austenite material. Additionally, there were no signs of segregation or non-uniformity that would have been caused by improper tempering. This indicates that the tempering process was successful in improving the properties of the AISI 4340 steel sample.

Conclusion

The results of this study show that the tempering and subsequent tempering at 670°C of AISI 4340 steel resulted in improved properties. The sample was successfully homogeneously tempered which resulted in grain refinement, formation of ferrite and martensite, and no signs of segregation or non-uniformity. Further research should be done to investigate the effects of higher tempering temperatures on AISI 4340 steel.

After being quenched in the Fe3Cr2W8V alloy, the sample underwent a tempering process at the temperature of 670°C. The microstructure of the material was then analysed with the help of a metallographic microscope. The results showed that the microstructural components of the sample were predominantly ferrite with a small amount of martensite. The proportional size of the ferrite and martensite increased from the center of the sample to its outer edge, indicating the formation of a tempered martensite lath. In addition, both the ferrite and martensite contained tiny amounts of carbides which were likely formed during the tempering process.

Moreover, the sample had a homogeneous structure with its ferrite and martensite constituents being evenly distributed throughout. There was only slight porosity present in the microstructural components and the number of needle-like carbides were limited. From this observation, it can be concluded that the tempering process of the Fe3Cr2W8V alloy at 670°C was successful in improving its mechanical properties by reducing the amount of porosity while maintaining the structural integrity of the alloy.