Since the early 20th century, car manufacturers have realized the importance of using specific steel for specific purposes. Henry Souther of the New York Times reported in 1909, “The secret of the use of steel is to put the right steel in the right place.” Until fairly recently, automotive steel mostly consisted of weaker mild steels that were affordable and easy to form into parts, but innovations in advanced high-strength steels (AHSS) have given automakers more options when designing vehicles.

Today’s automakers and parts manufacturers must consider several properties of the steel they are using: formability, crashworthiness, and durability. Each plays an important role in how the car is made and how the car performs over time and during impact. Below we take a look at these criteria and why each is important for manufacturers when designing a car and its parts.

Formability in Manufacturing

Formability is a key aspect to any automotive material. If a part cannot be made, it cannot be used. Typically, to make steel stronger, automakers had to make sacrifices in weight and formability, and if manufacturers needed a material with more ductility they were forced to give up strength.

The first generation of advanced high-strength steels (AHSS) increased strength while decreasing weight, giving automakers the opportunity to use thinner steel sheets. However, as the steel became stronger it lost formability, making it difficult to mold into parts.

POSCO GIGA STEEL is formable so that it can be shaped into complex parts.

Development of the second generation of AHSS focused on improving formability and elongation; however, its commercial use was limited due to its high cost and tendency to produce delayed cracking at room temperature.

With the new third-generation AHSS, like POSCO GIGA STEEL, steel producers have been able to bridge those gaps by producing steel that is formable, strong, and durable.  

While the average car built in 1975 utilized just 3.6% medium and high strength steels, by 2007 that percentage had increased by more than 230% in large part because the practical uses of AHSS have expanded.

Crashworthiness is Key for Safety

Crashworthiness is one of the most important elements to consider when designing automobiles because it is directly linked to the safety of passengers. The crashworthiness of a car is affected by many things including its structural build, safety devices, and materials.

While crash tests of full vehicles are often performed when developing a new car, crash tests of automotive parts are not carried out as often. To bridge this gap, POSCO developed its own crash test simulation for auto parts using high-speed compression and bending.

Crashworthiness criteria such as energy absorption & fracture, collapse mode, reaction force, and mean load is evaluated to provide reference data for car design. With these tests, POSCO is able to provide dynamic material data to its customers in order to propose the most appropriate steel solutions that maximize safety for passengers.

SsangYong Motor designed the new G4 Rexton SUV with a body frame that contains 63% POSCO GIGA STEEL. This is the highest ratio ever achieved in a body frame design and helps ensure significant levels of strength and safety for consumers. In the video below, watch as the SUV goes through various safety tests showing its crashworthiness and durability.

Durability to Prevent Fatigue Failure

The durability of parts is a critical factor to consider in vehicle design as their complicated components are subject to a wide array of complex stresses. In cars, material fatigue due to repeated mechanical loading can lead to the damage of critical components. Also, as vehicles are mobile machines, they are subject to even more unpredictable degrees of loading that can amplify the effects of fatigue on their parts. Moreover, because fatigue failure is often abrupt and difficult to detect, material providers must work to improve durability and ensure longer fatigue life.

“90% of the failures which occur in engineering components can be attributed to fatigue.”
– TR Gurney, Fatigue of Welded Structures

POSCO works with customers to provide accurate durability analysis for each of its products. Through extensive testing with various steel types, specimen shapes, and welding conditions, POSCO is able to provide in-depth testing results requested by customers.

POSCO also works with customers through its Solution Marketing 2.0 program that helps optimize the design and production process of each part – helping ensure that durability performance meets the customer’s needs.

POSCO GIGA STEEL provides automakers with durability to protect against fatigue failure.

Parts that require higher durability such as the CTBA (Coupled Torsion Beam Axle), wheel, engine cradle, lower control arm and stabilizer bar are interlinked with the fatigue data of POSCO steel. This provides the results of the durability analysis in order to suggest the most appropriate steel type for the manufacturer. Furthermore, POSCO supports joint research with customers for the design, manufacturing, and durability evaluations of its parts. POSCO also analyzes the causes of fatigue failure through SEM imaging of fatigue fracture surfaces, measurements of surface roughness, and measurements of strain rate and residual stress.

Today’s automakers must consider these properties during the design and manufacturing stages in order to find the right steel for each component. POSCO is committed to working with its automotive customers to ensure that the right steel solution is used for the right part – helping to find the right balance between formability, crashworthiness, and fatigue life.

Increasing Safety Requirements Demand Stronger Steel

With an increasing awareness about car safety – governments and regulatory agencies have been passing stricter safety regulations for autos. At the same time, consumers began demanding better protections, and car makers began building safer vehicles. While there are many factors to consider in building a safer car – airbags, seatbelts, glass type – the crashworthiness, or structural integrity, of the car’s body frame is one of the most critical.

In 1975 the average vehicle was manufactured with 55.9% mild steel and just 3.6% medium and high strength steels. By 2007, the percentage of medium and high strength steels used in an average car had increased by more than 230%. In the seventies, steel companies simply did not have the technology to make the steel that they can produce today because while it was strong, it was brittle and difficult to work with. Today, innovations in steel technology have given car makers the ability to use a variety of advanced high-strength steels (AHSS) that exceed 1,000MPa – meaning it can withstand more than 100 kilograms-force per square millimeter – because they are both strong and formable.

To demonstrate how far we come in terms of building stronger, safer vehicles, watch this crash test performed by the IIHS for their 50th anniversary with a 1959 Chevrolet Bel Air and a 2009 Chevrolet Malibu.

POSCO GIGA STEEL, the Industry’s New Standard for Strength and Formability

With a tensile strength of more than 1,000MPa, POSCO GIGA STEEL falls in the strongest categories of steel available to auto manufacturers today. In addition to providing the strength needed to meet safety regulations, POSCO GIGA STEEL is also ideal because of its formability and processability.

While recent years have seen ultra strength steels come on to the market with tensile ratings above 1,000MPa, these have often been rigid and brittle, making them difficult to process and mold into workable parts. POSCO GIGA STEEL bridges that gap by offering an automotive steel solution with high ductility and high tensile strength. This unique technology makes POSCO GIGA STEEL a unique fit for automakers seeking materials that can be processed into complex parts while also offering the highest levels of strength and safety for consumers.

Because of the combination of both strength and formability, SsangYong Motor unveiled their new G4 Rexton SUV with a body frame that contains 63% POSCO GIGA STEEL – the highest ratio ever achieved in a body frame design. Manufacturers like SsangYong Motor can use such high ratios of AHSS because of the technological advancements that have improved its formability in line with its improvements in strength.

The body frame of SsangYong Motor’s new G4 Rexton is manufactured with 63% POSCO GIGA STEEL.

Testing the Strength of POSCO GIGA STEEL and Aluminum

As lightweighting has become a priority for car makers seeking to build more fuel efficient cars, many have been looking toward alternative materials to step in as a substitute for steel. However, while offering certain benefits in weight, these alternative materials offer tradeoffs in strength and formability. On the other hand, POSCO GIGA STEEL offers an ideal solution in terms of strength, weight, and formability for auto manufacturers that must adhere to safety and environmental regulations along with consumer demand.

To compare the strength and impact energy absorption of POSCO GIGA STEEL (CR1180TRIP) and aluminum (Al5083), researchers at the KAIST National Center for Standard Reference Data performed an experiment in which a projectile was fired at three equidistantly spaced pieces of POSCO GIGA STEEL and aluminum.

Traveling at 185 meters per second, researcher Park Myung-joon noted that “the projectile ripped through all three pieces of aluminum while not even breaking one sheet of the POSCO GIGA STEEL.” Saying, “This experiment helped demonstrate how POSCO GIGA STEEL is more than three times stronger than aluminum making it ideal for automotive applications.”

Watch the video below to see how the experiment was designed, set up, and carried out.

POSCO GIGA STEEL is seeing increasing demand with car makers as they realize the dual benefits of strength and formability. At the Seoul Motor Show last month, Renault Samsung Motors and Chevrolet both unveiled new vehicles that were made using POSCO GIGA STEEL instead of aluminum – boosting the car body’s strength and safety for passengers.

Due to POSCO GIGA STEEL’s increased strength and high formability, the new Renault Samsung QM6 was able to maintain excellent safety standards with easy integration into its production process.

POSCO GIGA STEEL is unique because it combines both strength and formability. With strength more than three times stronger than aluminum and with formability properties that allow it to be made into complex auto parts – POSCO GIGA STEEL is the most ideal solution for car makers today.

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.

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