Process Optimization and Microstructure-Property Regulation of P20 Plastic Mold Steels

Improving the mechanical and surface properties of mold steels is a long-standing challenge in industrial manufacturing. Current methods often struggle to balance hardness, toughness, and polishing performance. Prior research has shown that heat treatment significantly influences the microstructure of mold steels. However, the specific effects of air-cooled and oil-quenched processes on P20 steel remain unclear. This gap motivated a detailed investigation into how different heat treatments affect microstructure and performance. No prior work had resolved the impact of austenitizing temperature on carbide distribution and polishing behavior. Existing studies often focus on single-phase steels or lack process-specific comparisons. This study aims to address these limitations by comparing two common quenching methods. Understanding these effects can guide process optimization in mold steel production.

The goal was to evaluate how air-cooled and oil-quenched processes influence the microstructure and mechanical properties of P20 plastic mold steel. The study focused on the role of austenitizing temperature in determining carbide distribution and polishing performance. Researchers aimed to identify the optimal heat treatment for balancing hardness and toughness. They also sought to determine the impact of grain coarsening on impact toughness. The motivation was to provide a practical framework for process optimization in mold steel manufacturing. This work addresses a specific need for improved polishing performance in mold applications. The study's findings could help reduce production costs and improve product quality. The research builds on prior knowledge of heat treatment effects on steel properties.

The study compared air-cooled and oil-quenched processes for P20 steel. Austenitizing temperatures ranged from 820 °C to 940 °C. After quenching, samples were tempered at 550 °C or 650 °C. Microstructure was analyzed using optical and scanning electron microscopy. Mechanical properties were measured through hardness and impact toughness tests. Polishing performance was evaluated using surface roughness measurements. Elemental segregation was assessed through microchemical analysis. The experimental design allowed for direct comparison of process outcomes. This approach enabled researchers to isolate the effects of each treatment step.

At 940 °C, both processes produced more uniform carbide distributions. Air-cooled samples showed carbides aligned along bainite laths after tempering at 650 °C. Oil-quenched samples had equiaxed carbides due to matrix recovery. Hardness increased slightly with higher austenitizing temperatures. Impact toughness dropped from 157.6 J to 111.7 J at 940 °C due to grain coarsening. Tempering at 550 °C after air cooling provided the best balance of properties. Polishing performance improved with higher austenitizing temperatures. Elemental segregation remained a limiting factor in polishing quality. These results highlight the trade-offs between hardness and toughness.

The study shows that air cooling after high-temperature austenitizing offers the best compromise between hardness, toughness, and polishing performance. Carbide alignment in air-cooled samples suggests a directional microstructure. Oil quenching leads to more uniform carbide distribution but lower impact toughness. Grain coarsening at 940 °C reduces impact resistance despite improved hardness. Tempering at 550 °C after air cooling enhances overall performance. Mitigating elemental segregation is crucial for further polishing improvements. The findings support the use of air-cooled pre-hardening for P20 mold steel. These results align with the authors' hypothesis about process effects on microstructure.