^1*Yağız Akyıldız, ²Ümit Kutsal, ³Yağız Arslan,⁴Adnan Akman,⁵Atıf Karkınlı, ⁶Mert Sağlam, ⁷Onur Öztürk, ⁸Rıdvan Yamanoğlu 

¹Global Technologies of Tomorrow (GTOT), İstanbul, TÜRKİYE
²Izmir Katip Celebi University, Materials Science and Engineering, Izmir, TÜRKİYE
^3,5Istanbul Technical University, Metallurgical and Materials Engineering, İstanbul, TÜRKİYE
⁴Delft University of Technology, Department of Materials Science and Engineering, Delft, NETHERLANDS
^6,8Kocaeli University, Engineering Faculty, Metallurgical and Materials Engineering Department, Kocaeli, TÜRKİYE
⁷Onatus Vision Technologies, Kocaeli, TÜRKİYE

*Corresponding Author: Yağız Akyıldız, yagiz.a@gtot.com.tr

The forging process is the main technique in the production of metallic fasteners. This process can be modeled by computational materials engineering solutions and FEM solutions. Thus, both the effect of the material on the process and the effect of boundary conditions can be analyzed. So, in this study, modeling, and simulation of 30MnB5 steel is carried out with these issues.

Keywords: 30MnB5, Cold Forming, Finite Element Method (FEM), CALPHAD Methodology

1.     Introduction

Fasteners are the most common joining tools used in the assembly of many products today. They are generally developed from steels, however it can be also produced with different alloys and materials [1]. One of the fastener steels that have been used and researched recently is manganese-boron steels. Fasteners are basically shaped by forging wire rods. After the forging process, the fasteners can be annealed. Some of the annealing processes are spheroidization and soft annealing. Spheroidization annealing is annealing in which lamellar cementite in pearlite structure is transformed into granular carbides. In softening annealing, the cementite lamellae in pearlite spheroidise and form small and round cementite particles in the ferritic matrix [2-4]. Nowadays, such processes can be modeled by Integrated Computational Materials Engineering (ICME) and then investigated by Finite Element Method (FEM) analyses. Thus, more accurate results can be obtained with improved material cards.

Cooling times and critical transformation temperatures (CCT) are very important for optimum process desing for fastener forging. However, it is difficult to obtain these behaviors experimentally. They can be obtained with simulations. CALPHAD-based modelling software such as Thermo-Calc software supports process design by performing thermodynamic and thermokinetic calculations. With this modelling, A₁, A₃, M_s and many more different critical temperatures and thermodynamic data can be calculated. In addition, the results obtained as a result of this modelling can be transferred to FEM software and an integrated analysis can be performed [5-7]. Cold forging of 30MnB5 steel at different process (hot rolled, soft annealing and spheroidization) conditions were modeled with Thermo-Calc and Forge NxT in the current study.

2.     Material and Method

30MnB5 steel was used in this study. Table 1 shows the chemical composition of this steel. Critical transformation temperatures and Continuous Cooling Transformation (CCT) diagrams were calculated by Thermo-Calc software 2023a version TCFE12 and MOBFE7.

 Table 1. Chemical composition of the 30MnB5 steel

The calculations are designed according to 3 different conditions. These are hot rolled, soft-annealed, and spheroidised. In the FEM analysis, the fastener forging station was modeled. According to the model, there are three stations and the mechanical press moves at a speed of 60 rpm. There are different moulds in each station. The material card was obtained by experimental methods and computational materials engineering solutions.

3.     Results and Discussions

Cold forging of fasteners by computational materials engineering and FEM was carried out in this study. CCT diagram shown in Figure 1. A1e and A1b temperatures were obtained as 737 °C and 723 °C, respectively. Perlite and bainite reactions occurred at 730 °C and 624 °C, respectively. In addition, Ms (beginning of martensite), M50 (50% martensite) and Mf (end of martensite) temperatures were calculated as 402, 369, 291°C, respectively.

Figure 1. CCT diyagram of 30MnB5. 

Figure 6 shown the distribution of von Mises stresses for last station of the forging process. General distribution of von Mises stresses for hot rolled condition steel is higher than the other condition steels because of microstructural differences induced by the heat treatment process. It converts lamellar cementite into a spherical form, which facilitates the forging process.

Figure 2. Von Mises stress distribution of 30MnB5 steel a) spheroidization b) softening annealing c) hot rolled condition.

4.     Conclusion

·      Critical parameters such as rolling temperature and cooling regimes can be determined through CCTs and CTT diagrams, leading to the production of steel bolts with optimum processing conditions and desired properties.
·      General distribution of von Mises stresses for hot rolled condition steel is higher than the other condition steels because of microstructural differences induced by the heat treatment process.
·      By using computational materials engineering solutions and FEM solutions together, more accurate approaches to experimental studies can be made. Thus, more accurate data can be obtained by examining the effect of microstructure in modelling and simulation environments.

References

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