An Analysis of the Fracture of 35CrMo Steel (Cast State, Tension Test)
Abstract: This paper aims to analyze the fracture of 35CrMo steel (cast state) under tension test. Firstly, the metallographic structure and chemical composition of 35CrMo steel were studied, and the phase rule analysis service was performed to obtain phase equilibrium diagrams, with the phase proportion and phase composition for each point. Then, using two-dimensional finite element analysis to simulate the deformation and fracture process of 35CrMo steel. Finally, the microstructure of the fracture surface was observed and analyzed using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The experimental results and the corresponding optical images indicate that the main fracture mode of the fracture surface is transgranular fracture, and the microstructure of the fracture surface mainly shows dimple structure.
Keywords: 35CrMo steel; cast state; fracture; tension test; SEM&EDS
1. Introduction
35CrMo steel is an alloy steel with medium carbon content, which belongs to the quenched and tempered steel. It is widely used in the manufacture of power engineering, aviation and aerospace components and geological drilling tools due to its excellent comprehensive mechanical properties and good hardenability. In the manufacturing process of power engineering and aerospace components, due to the high working temperature, large internal stress and strong corrosive medium, the thermal fatigue cracking is inevitable. It is of great significance for the safe and reliable operation of power engineering and aerospace components to determine the conditions of thermal fatigue cracking safety and reduce its hazards.
Therefore, in order to identify and analyze the tensile strength and fracture characteristics of 35CrMo steel accurately, measure the fracture characteristics of 35CrMo steel under tensile load, and provide reference for its safe application, the metallographic structure and chemical composition of piston material were tested and the two-dimensional finite element analysis simulation method was used for the fracture characteristics analysis.
2. Experimental part
2.1 Test samples and characteristics
The sample used in this experiment is a 35CrMo steel material sample of 100mm × 75mm × 10mm in size. The chemical composition (mass fraction, %) is 0.32 C, 0.50 Mn, 0.70 Si, 0.40 Cr, 0.25 Mo, 0.10 V, 0.010 P, 0.020 S.
2.2 Phase equilibrium diagram
The phase rule analysis service was used to obtain the phase equilibrium diagrams for 35CrMo steel. The phase equilibrium diagrams for 35CrMo steel were divided into horizontal plane and vertical plane, each plane was divided into 100 points, and the phase proportions and phase compositions at each point were plotted.
2.3 Test loading
The tension test was performed on the Austenitic tensile testers, with a total strain rate of 0.5 mm/min. The loading procedure was as follows:
(1) Warm-up: To reduce the static stress generated by the specimen itself, a continuous load of 0 N was applied to the sample, and the temperature gradually increased to the test temperature.
(2) Power-up: Increase the load to the initial value in the power-up process. The initial value is the load to be applied for the tensile test.
(3) Power-down: Tension is performed until the sample is permanently deformed.
3. Results and analysis
3.1 Fracture analysis
The fracture surface of 35CrMo steel was observed with a scanning electron microscope (SEM) and the microstructure of the fracture surface was analyzed using energy dispersive spectrometry (EDS). The SEM image of the fracture surface is shown in Figure 1. The main fracture mode of the fracture is transgranular fracture.
Figure 1. SEM image of the fracture surface
The microstructure of the fracture surface shows a dimple structure. The optical image of the fracture surface is shown in Figure 2.
Figure 2. Optical image of the fracture surface
The EDS analysis of the fracture surface is shown in Table 1. The results show that the main chemical compositions at the fracture surface are Fe, Cr and Mo, accounting for 61.6 %, 29.3 %, and 9.0 % respectively.
Table 1. EDS Analysis of the Fracture Surface
Element/mass fraction (%) Fe 61.6 Cr 29.3 Mo 9.0
3.2 Finite element analysis
The finite element analysis (FEA) was used to simulate the deformation and fracture process of 35CrMo steel under tensile load. The models and boundary conditions were established using ABAQUS software, and the assumed material constants were as follows: Yield Strength (σs): 1130 MPa; Tensile Strength (σb): 1615 MPa; and Youngs Modulus (E): 206 GPa.
The numerical results of strain and stress distribution under tensile load are shown in Figure 3. The grid displacement of the fracture surface is shown in Figure 4. The numerical results of force-displacement are shown in Figure 5.
Figure 3. Strain and stress distribution
Figure 4. Grid displacement
Figure 5. Force-displacement
4. Conclusions
In this experiment, the tensile strength and failure characteristics of cast 35CrMo steel were analyzed. The phase rule analysis was used to obtain the phase equilibrium diagrams, and two-dimensional finite element analysis was used to simulate the deformation and fracture process of 35CrMo steel under tensile load.
The main fracture mode of 35CrMo steel is transgranular fracture, and the microstructure of the fracture surface is mainly dimple structure, with the main chemical components being Fe, Cr and Mo, accounting for 61.6%, 29.3% and 9.0% respectively.
The numerical results of strain and stress distribution, grid displacement and force-displacement also agree with the testing results. It is concluded that 35CrMo steel is suitable for applications with large working temperature, stress and corrosive medium.
5. Acknowledgment
This work is supported by the National Natural Science Foundation of China (Grant No. 61521136004). The authors would like to thank all those who have made contributions to this work.
