Banca de QUALIFICAÇÃO: RENNÁH FRANCISCO FIGUEIREDO GONÇALVES

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : RENNÁH FRANCISCO FIGUEIREDO GONÇALVES
DATE: 29/07/2024
TIME: 08:30
LOCAL: Sala de reunião do Lime
TITLE:

Evaluation of the effect of applying liquid nitrogen into the punching process of advanced high strength steels

KEY WORDS:

AHSS; Dual-Phase steel; punching; cryogenics.

PAGES: 78
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUMMARY:

This study focuses on the analysis of dual-phase (DP) steels, a category of advanced high-strength steels (AHSS) widely used in the manufacturing of automotive components due to their notable strength, formability, and energy absorption capacity during deformation. The substitution of conventional steels with these materials plays a crucial role in reducing vehicle mass without significantly compromising occupant safety and strength. This substitution is essential for enabling the production of more fuel-efficient vehicles and mitigating environmental impacts. AHSS have a microstructural configuration that combines a highly ductile ferritic matrix with a second phase of high hardness, such as martensite, bainite, or a combination thereof, dispersed within the matrix. This microstructural setup allows efficient processing of AHSS through forming processes such as stamping. During the manufacturing of automotive parts, dual-phase steels undergo stamping processes involving cutting, pressing, and bending to achieve the desired shape. The quality of the cut edge of these steels is crucial, as defects such as cracks originating from the cut edges can lead to part failures during fabrication. This study proposes the use of cryogenic temperatures during the punching process as a strategy to minimize crack nucleation. A more homogeneous cut edge with fewer voids and microcracks is essential for the efficient stampability of these materials. The hypothesis is that conducting the process at low temperatures may alter the plastic deformation mechanism from shear to mechanical twinning and cleavage. The work consisted of a qualitative and quantitative study of the microstructures of the cutting edges of DP780 steel obtained by punching at cryogenic and ambient temperatures. Tests demonstrated the feasibility of punching at cryogenic temperatures for AHSS (DP780). Using Electron Backscatter Diffraction (EBSD) technique on a scanning electron microscope (SEM), the analysis revealed significant alterations, including a reduction in plastic deformation regions and an increase in fracture zone in samples tested at temperatures below -150°C compared to those tested at ambient temperature. Qualitative results indicated the effectiveness of this method in reducing plastic deformation at the cutting edges of DP780 by up to 37% when conducted at cryogenic temperatures (≤ -150 °C) and a speed of 725 mm/s.

COMMITTEE MEMBERS:
Presidente - 2266607 - FABIO JOSE PINHEIRO SOUSA
Externo ao Programa - 1938946 - NICOLAU APOENA CASTRO - UFRNExterno à Instituição - JETSON LEMOS FERREIRA - Arcelor
Externo à Instituição - JORGE MAGNER LOURENÇO - IFRN