The effect of processing parameters on the properties of multi-phase advanced high strength steel grades

Tomorrow's car must be safe, environmentally friendly, durable and cheap. As a result, the requirement of steel for these cars is to be:
. High-strength steel to limit weight and preserve safety
. Galvanised for durability
. Produced with reduced operational costs
Production of new steel grades for the automotive industry through robust industrial process in-order to ensure consistently identical mechanical properties is, in itself a challenge to steel producers.
Over years, strip processing line technologies have evolved to match the new requirements of steel grades. Subsequently, new steel grades demanded more sophisticated thermal cycles and thermal technologies. Today, we can identify three major milestones:

. 2000: Dual Phase (DP)-grades requesting rapid cooling stages
. 2007: New grades, such as TRIP (Transformation Induced Plasticity), must be processed on the same continuous galvanising line (CGL) that processes DP grade steels.
. 2012: Higher mechanical properties (TS greater than 1000 MPa) using multi-phase steel grades, such as Quenching & Partitioning, require additional after-soaking heat-treatment together with a higher annealing temperature.

Each stage of the thermal cycle will influence the mechanical properties of the steel. Processing of new AHSS (Advanced High strength Steel) grades increases in complexity after the soaking stage of the process as the requirements of the thermal cycle are different for every family of AHSS. Therefore, a continuous galvanising line (CGL) needs to have enough flexibility to process all these grades.
Since SUK-PT is preparing for an investment in its existing CAPL for making it a "swing-line" to combine CGL and CAL capabilities, detailed knowledge on the processing of new AHSS grades for Automotive is a must for a robust industrial process.