Tempering influence on residual stresses and mechanical properties of AISI 4340 steel

Marcel Freitas De Souza,Sérgio Souto Maior Tavares,Luana Ferreira Serrão,Juan Manuel Pardal,Maria Cindra Fonseca

doi:10.1007/s00170-022-08880-3

Marcel Freitas De Souza, Sérgio Souto Maior Tavares + Show 3 more

Open Access

https://doi.org/10.1007/s00170-022-08880-3

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Abstract

The present work evaluated the tempering temperature influence on microstructure, mechanical properties, and residual stresses of AISI 4340 steel. The residual stresses were measured by X-ray diffraction (XRD) by the sin2ψ method and compared to magnetic Barkhausen noise (MBN). The residual stresses exhibited high tensile values after quenching, but a small relief was observed in tempering treatments at 300 °C and 400 °C, which also presented a hardness decrease compared to the as-quenched condition. XRD and MBN analyses indicated that residual stresses became compressive in tempering performed between 500 and 650 °C. Therefore, compressive residual stresses combined with appropriate hardness and toughness values (35 HRC and 33 J) obtained from 500 °C tempering temperature can be used to improve the mechanical properties of AISI 4340 steel components. Additionally, a mathematical model was established to estimate the tempered martensite hardness for different tempering temperature conditions. This model showed high accuracy (R2 = 0.99) for a holding time of 90 min.

Highlights

IntroductionThe AISI 4340 steel is employed in quenched and tempered conditions, is susceptible to embrittlement phenomena when tempered between 300 and 400oC
The AISI 4340 steel is employed in quenched and tempered conditions, is susceptible to embrittlement phenomena when tempered between 300 and 400oC. This problem has been investigated by several researchers, who have evaluated changes in microstructure and mechanical properties at different tempering temperatures [1,2,3]
Tempering can be used as a stress relief process, ensuring reduction or even absence of tensile residual stresses, which have a deleterious effect on fatigue life

Summary

Introduction

The AISI 4340 steel is employed in quenched and tempered conditions, is susceptible to embrittlement phenomena when tempered between 300 and 400oC This problem has been investigated by several researchers, who have evaluated changes in microstructure and mechanical properties at different tempering temperatures [1,2,3]. The present work evaluated changes in mechanical properties, microstructure, residual stresses and MBN for AISI 4340 steel at different tempering temperatures. A quenched sample of each type was selected for tempering, which was carried out using five different temperatures, 300°C, 400°C, 500°C, 600°C and 650°C, for 90 min and later air-cooled. Rockwell C hardness test was performed in as-received condition and after tempering treatment.

Results and Discussions

Findings

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