BENTELER Automotive Vigo

Fracture toughness assessment of TRIP800 coils to rationalise edge-cracking

BENTELER is a global company specializing in metal processing. It works closely with customers and partners in the automotive industry to create lighter, safer, and more sustainable mobility solutions. With 92 locations in 27 countries, Benteler is a tier 1 supplier in various markets. They are renowned for their crash management systems and axle suspensions, found in almost every car worldwide.

BENTELER Vigo, part of the Benteler Automotive division, has acted as beneficiary of ToughSteel Open Call.  It focuses on developing lightweight construction products and enhancing manufacturing processes, materials, and technologies. The Vigo plant engages in the production, assembly, and marketing of metal parts for the automotive and similar industries, employing technologies such as cold and hot forming, laser cutting, welding, cataphoresis painting, machining, and assembling.

Motivation

Investigation of a component made of TRIP800 with problems of edge-cracking in some coils. Previously, different tests on mechanical properties and chemical composition did not reveal any significant deviation that can justify the behaviour in specific coils compared to others.

The aim was to correlate fracture toughness properties with the cracking sensitivity of the different coils and establish an additional material parameter allowing to predict in advance the fracture of the part during forming. Eurecat performed fracture toughness measurements through the Essential Work of Fracture (EWF) methodology.

ToughSteel Open Call was an opportunity for us to try new tests and understand better the behaviour of the materials and their performance

Miguel Dourado, Production Unit Leader, Hot & Cold Stamping Department, BENTELER

Case study results

The fracture toughness of three TRIP800 steels has been characterized by means of the EWF methodology. The EWF methodology has been successfully used to evaluate the fracture toughness of the steels from different OK (without defects during forming) and NO OK (with fractures)batches, as it helped to describe properly the effects of fracture performance of the materials studied.

Out of the three coils analysed, the two OK coils, used as a reference,  showed the highest cracking resistance, as measured through the EWF method. On the other hand, the NO OK coil showed much lower crack propagation resistance, which explained the poorer formability and the higher cracking susceptibility of the batch during forming. Additionally, the fracture tests revealed some fracture instabilities during crack propagation, which suggests the presence of microstructural heterogeneities that may cause a loss of ductility in very localized areas. Thickness reduction measurements on pre-craked DENT specimens showed a good correlation with fracture toughness values, being also a suitable parameter to understand the cracking susceptibility of high-strength steels.

Results of BENTELER case study