Influence of Strain and Stress Triaxiality on the Fracture Behavior of GB 35CrMo Steel during Hot Tensile Testing

Zheng Li,Sanxing Wang,Yajun Zhou

doi:10.1155/2018/5124524

Zheng Li, Sanxing Wang + Show 1 more

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https://doi.org/10.1155/2018/5124524

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Abstract

To better understand cavitation nucleation and crack initiation in 35CrMo steel during high-temperature tensile processing and the effect of stress triaxiality on its fracture behaviors, uniaxial and notch high-temperature tensile tests were performed. The microstructure, fracture morphology, fracture strain, and stress triaxiality of the tested 35CrMo steel were then characterized and discussed. The results showed that crack formation in 35CrMo steel included stages of nucleation, growth, and microcavity aggregation. Scanning electron microscopy and energy-dispersive X-ray spectroscopy demonstrated that crack formation was closely related to the presence of steel inclusions. High-temperature tensile testing of samples with different notch radii showed that the fracture strain of 35CrMo steel was decreased with increasing stress triaxiality, that is, increased stress levels corresponded to decreased material plasticity. In addition, the recrystallization degree was decreased with increased stress triaxiality, and the grain size growth was slowed. The failure of 35CrMo steel occurred via ductile fracture, and low stress triaxiality, and high temperature conditions induced large and deep dimples on the fracture surface.

Highlights

Because it offers excellent comprehensive mechanical properties, 35CrMo steel is often used to manufacture important structural parts, such as the rotors of turbo generators, spindles, transmission shafts with heavy loads, and largesection parts [1,2,3,4]
E study of the effects of crack initiation and stress state on ductile fractures began with Ludwik and Scheu [7], who assumed that ductile metal fracture was controlled by the stress-strain curve
Pardoen and Hutchinson [9], Benzerga [11], and Gao and Kim [12] demonstrated that the Gologanu–Leblond–Devaux model showed significantly improved accuracy in its description of void growth and the corresponding material behavior during ductile fracture

Summary

Introduction

Because it offers excellent comprehensive mechanical properties, 35CrMo steel is often used to manufacture important structural parts, such as the rotors of turbo generators, spindles, transmission shafts with heavy loads, and largesection parts [1,2,3,4]. Recent experimental and numerical studies by Mirza et al [23] on pure Fe, mild steel, and the BS1474 Al alloy in a wide range of strain rates, and by Bao and Wierzbicki [24, 25] and Bao [26, 27] on 2024 Al alloy during quasistatic loading reaffirmed the strong relationship among equivalent strain, stress triaxiality, and crack formation. In these studies, stress triaxiality was used to define the failure function of the material. In this paper, the effects of strain, temperature, and stress triaxiality on the fracture behavior of 35CrMo steel were investigated by uniaxial and notched hightemperature tensile testing. e microstructure evolution and fracture behavior of 35CrMo steel under different tensile conditions were studied after stretching by means of metallographic structure and fracture scanning analysis

Experimental Materials and Procedures

Results and Discussion

C Atomic percentage

Conclusions