POSCO’s steel technologies for vehicle plates stand at the forefront of the automotive industry. POSCO manufactures several steel solutions that have tensile strengths rated at more than 1GPa (Gigapascal), and its groundbreaking POSCO GIGA STEEL offers numerous benefits in its strength, safety, lightness, and sustainability.
In this article, The Steel Wire takes a closer look at five of POSCO’s unique steel solutions for the automotive industry.
Twinning-Induced Plasticity (TWIP)
POSCO’s Twinning-Induced Plasticity (TWIP) steel was the world’s first mass-produced giga steel. It was dubbed a “dream steel” upon its release due to its high strength and formability properties. It is a multi-phase steel composed of a ferrite matrix, bainite with a retained austenite phases, and a small portion of martensite. TWIP has a formability that is 2-9 times higher than other mass produced steel products and is mainly used for the front and back bumpers of cars as it can withstand up to 100 kilograms per square millimeter of pressure.
Because of its high formability, TWIP is often used in complex parts in order to reduce the stamping steps. Also, because of its superior absorption qualities, it is useful in materials that are more frequently subject to impacts, such as the bumper beam and wheel housing.
PosM-XF (Extra Formability)
In 2016, POSCO released PosM-XF (Extra Formability), a next generation TWIP with improved strength and forming traits. PosM-XF is designed to have 2-3x more elongation properties compared to other steels of the same strength. Due to its high yield strength and formability, car makers typically use it in the structural parts of vehicles that are both complex to manufacture and critical in keeping passengers safe.
Dual Phase (DP) Steel
POSCO’s Dual Phase (DP) steel can easily be deformed since it has a low yield ratio of around 0.50-0.60. It features good bake hardenability as it is cooled rapidly after annealing and is processed in an Over Aging Section below martensite start (Ms) temperature. It also features a high level of total elongation close to that of TRIP. For this reason, it is mainly used for structural parts such as sill side members, seat rails, and stiffeners.
Complex Phase (CP) Steel
POSCO produces Complex Phase (CP) steel at a 1,180MPa tensile strength grade. CP steel is based on ferrite, where bainite and martensite co-exist together with Ti and/or Nb precipitates. According to its microstructural features, CP steel is characterized by its high yield value and good bendability. Therefore, it is often used to make reinforced auto parts that require high crashworthiness ratings, such as sill side panels, bumper rails, and door impact bars.
Hot Press Forming (HPF) Steel
Hot Press Forming (HPF) steel is hard to process when the intensity level exceeds 1.5GPa (Gigapascal). To counteract this disadvantage, HPF has increased its machinability through heat treatment. Through the HPF process, also known as hot stamping, press hardening and die quenching, the steel is heated before press forming. At high deformation temperatures, steel sheets are very soft so that difficult shapes can be obtained easily. During forming, the heated steel sheet cools down rapidly in the die block, so that resulting pressed parts have a very high strength level. Boron is commonly added to increase the hardenability of the steel sheet.
HPF is often used for parts that require high crashworthiness and impact resistance such as door impact beams, stabilizers, and the center pillars of vehicles, which protect passengers from external shocks in broadside collisions and rollover accidents.
In 2014, POSCO became the first steelmaker in the world to manufacture a steel product with a tensile strength over 2GPa. It was later introduced in Renault’s 1 L concept car EOLAB at the Paris Motor Show in 2014 receiving high marks for its strength and lightweight properties.
With these five different types of POSCO GIGA STEEL products, auto manufacturers are able to build stronger, lighter, and safer cars. Keep an eye on how POSCO GIGA STEEL will drive the future of automotive steel.
Throughout April & May, The Steel Wire will explore the uses and benefits of POSCO GIGA STEEL and what POSCO is doing to lead the industry with new automotive steel solutions. Subscribe here to be sure you don’t miss any of our upcoming stories.