New generation of cold rolled manganese boron steels now available for advanced automotive applications

02.06.2021 | Article of Salzgitter Flachstahl GmbH


The new cold-rolled grade 34MnB5 has been developed in close cooperation between Salzgitter Mannesmann Forschung GmbH (SZMF) and Salzgitter Flachstahl (SZFG). This grade is a manganese-boron (MnB) alloyed heat-treatable steel. 
 
Our extensive, in-depth know-how based on over 40 different products involving manganese-boron alloyed heat-treatable steels entered into the development. Comprehensive characteristic values (according to SEP 1240 and SEP 1220, among others) as well as material data for numerical simulation are available and can be accessed at all times via the COMDaS material online portal. Work on the parameterization of a material model mapping the press hardening process harnessing the LS-DYNA software is currently being ongoing. 
 
Manganese-boron alloyed, cold-rolled heat-treatable steels for press hardening have been specially developed for the automotive industry. The use of these steels enables advances in lightweight design and construction, while increasing occupant protection and also protecting the battery in the case of BEVs (Battery Electric Vehicles). 
 
To date, 22MnB5 has featured as the standard grade, and finds use in many areas of car body construction. The new 34MnB5 grade will now supplement or substitute 22MnB5 in many areas and applications. 
 
In its as-delivered condition, 34MnB5 exhibits very good formability and is consequently also suitable for the cold forming of complex components. Manganese-boron steels only attain their final strength during hot forming and the associated controlled cooling in the die (press hardening). In hot forming, the microstructure of the initial blank is converted to the austenitic range under an inert gas atmosphere at around 950°C, after which the blank is formed directly. During cooling in the tool to temperatures between 100°C and 200°C, the material thereby acquires a martensitic microstructure, which greatly increases the tensile strength. 
 
Thanks to the combination of formability and hardenability, this grade is particularly suitable for load-bearing and safety-relevant components such as A-pillar reinforcements, B-pillar reinforcements, sill reinforcements, floor cross members in BEVs, bumper cross members, roof cross members, etc.

 

Customers and users have already developed advanced technologies and applications for and with the 22MnB5, most of which can also be applied to the 34MnB5. At Salzgitter AG, various Group companies are joining forces in supporting customers in their respective implementation and development activities (Initiative Automotive). Salzgitter Europlatinen GmbH (SZEP) is the contact for Tailored Welded Blanks (TWB). 
The new product has already been included in the draft standard VDA239-500 (May 2021).

C Mn Si Al Ti Cr B N
34MnB5
SZFG
0.31 - 0.39 1.10 - 1.50 0.15 - 0.35 0.020 - 0.045 0.020 - 0.055 0.05 - 0.25 0.0010 - 0.0050 < 0.007
Cr1900T-MB-DS* 0.30 - 0.38 ≤ 2.0 ≤ 0.8 0.010 - 0.080 Ti+Nb ≤ 0.2 ≤ 0.50 0.0010 - 0.0050 ≤ 0.010
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Does all this sound interesting? Our sales and technical customer service department would be more than happy to assist you in selecting the appropriate material for your applications as well as providing the respective prototype material.