February 2025 Volume 7

EQUIPMENT & TECHNOLOGY

Case Study Highlights The chemical compositions of the steel grades studied (AISI 4140 & AISI 4130) are presented in Table 1 below. Before quenching test, the cylindrical sample was normalized at 925°C for 1h inside a carbon-containing box (to avoid decarburi zation) and cooled on air to eliminate any possible microstructural variations induced by preceding hot working.

The study’s methodology and findings underscore its practical applicability: 1. Jominy Test Simulation: The FEM model accurately simulated cooling rates, phase transformations, and hardness distributions along the length of Jominy specimens. Figure 1 (a & b) illustrates the comparison between experimental and simulated hardness profiles for AISI 4130 and AISI 4140 steels. 2. Industrial-Scale Application: The methodology was extended to a 7-inch diameter bar, with simulations predicting martensite content and hardness gradients from surface to core. Figure 2 showcases the micro structural distribution of martensite in the industrial-scale bar. 3. Microstructure Evolution: Detailed analysis of phase transformations revealed a seamless transition from martensite at the quenched end to ferrite and pearlite at the opposite end. Figure 3 highlights the microstruc tural evolution in AISI 4140 steel at various positions. 4. Correlation Insights: A strong correla tion was established between Jominy test results and industrial-scale quenching, as shown in Figure 4. This correlation validates the scalability and reliability of the FEM approach. 5. Process Optimization: The ability to model varying parameters, such as water flow rate and temperature, allows manufacturers to fine-tune the

quenching process for different steel grades and geometries, ensuring optimal results every time.

Table 1:Chemical composition of materials, wt.%

Table 2 presents the hardnesses HRC as received and after normalizing. The approach used to model rapid quench involves breaking down the isothermal process into elementary stages. This approach allows us to obtain anisothermal kinetics from isothermal data based on the isothermal JMAK equation and Scheil’s additivity rule. In the generalized form, we have the Avrami equation described the evolution of the phase (y), as follows

Fig3.Microstructural evolution of AISI 4140 steel at various Jominy positions

Fig2.Microstructural distribution of martensite in a AISI 4140 7-inch diameter industrial scale bar

FIA MAGAZINE | FEBRUARY 2025 22