In this study, a tailored die quenching experimental method using low closing pressures and an aluminum flat die was developed in order to evaluate the effects of the gap size on the cooling rate in the hot stamping process of a 22MnB5 steel grade. Initially, the necking behavior in hot stamping was investigated by deforming the specimens to different strain levels and subjecting them to quenching in order to assess this effect on the gap profile formed between the die surface and the sample. Next, a controlled gap was promoted in the central region of the aluminum cooler using aluminum spacers (simulating the gap) with different thickness (0.06/0.15/0.40/0.70mm). Then, its effects on the cooling rate and on the hardness after quenching were evaluated. The results showed that the cooling rate is very susceptible to gap size, that the ideal situation occurred when there was no gap, good heat transfer and higher average cooling rates of 120 o C/s were achieved, and that when the gap was wider than 0.20mm the average cooling rates were lower than 20 o C/s, consequently below the critical 22MnB5 steel cooling for quenching, which is 28 o C/s.

In this study a new experimental method using low closing pressure and a flat aluminum die was developed in order to investigate the hot stamping process of a 22MnB5 steel grade. Initially, an experimental set up was developed and validated. Next, experiments were carried out to evaluate the behavior of this steel when subjected to quenching, using this experimental set up and different cooling conditions such as water, oil and air. Results were assessed by cooling curves, as well as by mechanical tests and metallographic analyzes. Cooling rates close to 110 o C/s, hardness up to 480HV and ultimate tensile strength up to 1600 MPa were achieved, which are considered acceptable values for this steel in normal conditions of hot stamping. Keywords: Hot stamping; 22MnB5 steel; Quenching; Cooling rate. UM MÉTODO EXPERIMENTAL PARA SIMULAR O PROCESSO DE ESTAMPAGEM A QUENTE ResumoNesta pesquisa foi desenvolvido um novo método experimental, utilizando baixa pressão de fechamento e uma matriz plana de alumínio, com o objetivo de investigar o processo de estampagem a quente do aço 22MnB5. Inicialmente um aparato experimental foi desenvolvido e validado. A seguir foram realizados experimentos com o objetivo de avaliar o comportamento deste aço quando submetido a diferentes meios de têmpera, usando este método e diferentes condições de resfriamento, tais como água, óleo e ar. Os resultados foram avaliados usando curvas de resfriamento, bem como ensaios mecânicos e análises metalográficas. Foram obtidas taxas de resfriamento próximas de 100 0 C/s, durezas acima de 480HV e limite de resistência acima de 1600 MPa, valores que são considerados aceitáveis para este aço em condições normais de estampagem a quente. Palavras-chave: Estampagem a quente; Aço 22MnB5; Têmpera; Taxa de resfriamento. INTRODUCTIONIn recent years the hot stamping process has been widely studied, generating significant technological advancement and allowing its use in the production of several components with excellent performance due to the combination of high mechanical properties with high dimensional accuracies.An important aspect in the hot stamping process is that sheet conformation occurs at elevated temperatures, where the mechanical strength of the material is significantly reduced. Thus, the load required to deform the sheet is very low, opening up the possibility of the use of less robust and cheaper equipment, which results in lower operating costs and investment. The stamping tools would also be less stiff and cheaper. The use of low stress for deformation also requires the evaluation of the thermal behavior because the material is hot formed and simultaneously quenched to room temperature, in order to obtain a component with good dimensional accuracy and high mechanical resistance [1]. The conditions involving contact between the tool and the blank and the closing pressure have a significant influence on the heat extraction coefficient, on the cooling rate and consequently, on the final properties of the component. In hot stamping the co...