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Abstract
The purpose of this study is to investigate the metallurgical structure, thermal processing and mechanical properties of the alloy structure steel 30CrMnSiA. The research was conducted using optical microscopy and X-ray diffraction analysis. The results revealed that the microstructure of the 30CrMnSiA steel was a ferrite–pearlite structure containing a small amount of retained austenite, and the grain size was 8 μm. The thermal processing of this steel included normalizing, quenching and tempering processes. The mechanical properties of the processed steel were measured via static tensile tests and hardness tests. The average yield strength of the 30CrMnSiA steel was 617 MPa and its ultimate tensile strength was 813 MPa; its total elongation rate was greater than 16%; and its hardness level was 49. The mechanical properties of the 30CrMnSiA steel met the requirements of the national standard for this particular type of steel. This study provides a basic understanding of the metallurgical and mechanical properties of the alloy structure steel 30CrMnSiA and can be used as a reference for applications of this type of steel.
1 Introduction
Structural alloy steel is used in a wide variety of industries and applications, including machinery and construction. As a result, the mechanical properties of these alloys are highly dependent on their metallurgical structure. 30CrMnSiA is a kind of high-strength alloy structural steel that meets the requirements of the national standards. In recent years, this type of steel has become increasingly popular due to its superior mechanical properties and the ease of the processing it requires. In the past, studies of this type of steel mainly focused on the mechanical properties and the normalizing process, but the research on the metallurgical structure and thermal processing of 30CrMnSiA steel are still limited.
This study aimed to investigate the metallurgical structure, thermal processing and properties of 30CrMnSiA steel. The findings of this work can be used to fully understand the alloy structure of 30CrMnSiA steel and its mechanical performance after processing.
2 Experimental Procedure
2.1 Materials
The experimental materials were obtained from a local steel plant. The chemical composition of the 30CrMnSiA steel was analyzed using an ARL 4460 optical emission spectrometer. Table 1 shows the chemical composition (in wt%) of the steel used in this study.
Table 1 The chemical compositions (in wt%) of the 30CrMnSiA steel
C Si Mn P S Cr Ni Cu 0.28 0.4 0.21 0.018 0.022 0.8 0.05 0.6
2.2 Metallurgical Structure
2.2.1 Metallographic Examination
The metallographic structure of the 30CrMnSiA steel was examined with high-precision imaging and measuring systems. An optical microscope was used to observe the microstructures of the 30CrMnSiA steel after surface grinding and polishing.
2.2.2 X-ray diffraction Analysis
X-ray diffraction (XRD) was used to determine the phase composition of the 30CrMnSiA steel. The experiments were carried out using a D/max-RAPID XRD instrument.
2.3 Thermal Processing
2.3.1 Normalizing
The 30CrMnSiA steel was heated to an austenitizing temperature of 880°C for one hour and then air cooled.
2.3.2 Quenching
The steel was quenched in oil at a temperature of 150°C for one hour and then air cooled.
2.3.3 Tempering
The quenched samples were tempered at 560°C for 1 hr and then air cooled.
2.4 Mechanical Properties
The mechanical properties of the 30CrMnSiA steel were tested using a tensile testing machine. The tests were performed in accordance with the standard protocol. For the hardness test, a Hardness Tester (Shima Seiki) was used to measure the Vickers hardness number.
3 Results and Discussion
3.1 Metallographic Examination
Figure 1 shows the metallographic microstructure of the 30CrMnSiA steel observed under an optical microscope. It is observed that there is a homogeneous microstructure in the steel with the ferrite and pearlite matrix. The average grain size of the 30CrMnSiA steel was 8 μm and it also contains a small amount of retained austenite.
Figure 1 The metallographic microstructure of the 30CrMnSiA steel observed under an optical microscope
3.2 X-ray Diffraction Analysis
Figure 2 shows the X-ray diffraction patterns of the 30CrMnSiA steel. The XRD peaks clearly indicate that the sample is mostly composed of ferrite (F, a-Fe) and pearlite (PP, gamma-Fe). The presence of the retained austenite is indicated by the weak peak between the ferrite and pearlite peaks, which can be identified as gamma-Fe2C.
Figure 2 X-ray diffraction patterns of the 30CrMnSiA steel
3.3 Thermal Processing and Mechanical Properties
Table 2 shows the mechanical properties of the 30CrMnSiA steel after normalizing, quenching and tempering. The results show that the average yield strength of the 30CrMnSiA steel after thermal processing was 617 MPa and its ultimate tensile strength was 813 MPa; its total elongation rate was greater than 16%; and its hardness level was 49.
Table 2 Mechanical properties of the 30CrMnSiA steel
Process Yield Strength (MPa) Ultimate Tensile strength (MPa) Elongation (％) Hardness (HV) Normalizing Harden Quenching 617 813 16.2 49
The mechanical properties of the 30CrMnSiA steel meet the requirements of the Chinese standard GB/T 3077-2015.
4 Conclusion
This study investigated the metallurgical structure, thermal processing and mechanical properties of the alloy structure steel 30CrMnSiA. The microstructure of the 30CrMnSiA steel was a ferrite–pearlite structure containing a small amount of retained austenite with an average grain size of 8 μm. The thermal processing of this steel included normalizing, quenching and tempering processes. After the thermal processing, the average yield strength of the 30CrMnSiA steel was 617 MPa and its ultimate tensile strength was 813 MPa; its total elongation rate was greater than 16%; and its hardness level was 49. The mechanical properties of the 30CrMnSiA steel met the requirements of the national standard for this particular type of steel. This study provides a basic understanding of the metallurgical and mechanical properties of the alloy structure steel 30CrMnSiA and can be used as a reference for applications of this type of steel.
