There are a few universal truths in life: death, taxes, distortion in heat treating—and for years, it was believed that any factor that improves manufacturability invariably compromises heat treatment. In many cases this still holds true, until you throw boron into the mix.
Since the Bronze Age, humans have developed countless metal alloys to advance our material capabilities and create products that last longer and perform better. Steel alloys have been some of the most critical developments in constructing stronger buildings, safer cars, and beyond.
There are many elements that can make up steel, the four most common ones are: iron, manganese, carbon, and sometimes chromium.
- Iron is the main component of steel and the primary building block for every steel alloy.
- Manganese helps remove oxygen and sulfur when iron ore is converted into iron and decreases the brittleness of steel.
- Carbon is responsible for giving steel strength. Carbon content in steel can range between 0.10-1.00%, depending on the grade required for your application.
- Chromium is the most common alloying element added to steel to supply improved hardenability.
The inclusion of boron in steel alloys is a relatively recent innovation that has revolutionized the materials industry. Adding a small amount of boron (a few parts per million) and a small amount of manganese creates steel that’s highly machinable, weldable, and able to achieve a higher strength with less distortion during heat treatment. And because a little boron goes a long way, this alloy is also an affordable option compared to most other alloys.
Because of their weldability and high hardenability, boron steels have been widely adopted by the automotive industry. The Society of Automotive Engineers (SAE) J403 standard categorizes these boron steel grades for use in automotive components. Boron additions, according to this standard, are precisely controlled to enhance the desired properties in the steel. This standard is critical in maintaining consistency and quality across various applications.
BORON––– Standard killed carbon steel, which are fine grain, may be produced with a boron addition to improve hardenability. Such steels are produced to a range of 0.0005 to 0.003% boron. These steels are identified by inserting the letter “B” between the second and third numerals of the grade number, for example, 10B46. The UNS designation is also modified by changing the last digit to “1” to indicate boron, for example, G10461.
15B24 and 10B21 Specifications
There are two primary boron steel alloys that are widely used in automotive: 15B24 and 10B21. Both of these alloys are weldable, formable, exhibiting an excellent response to heat treatment, and are capable of reaching strengths up to 210 ksi (1450 Mpa).
This alloy contains 0.18–0.23% carbon, 0.60–0.90% manganese, and 0.0005–0.003% boron. Its composition makes it particularly suitable for applications where increased strength and toughness are required. This alloy is also a common choice in parts that will undergo carburizing and carbonitriding processes.
Slightly richer in carbon (0.19 – 0.25%), manganese (1.35 – 1.65%), and boron (0.0005 – 0.003%), 15B24 is known for achieving higher strength and wear resistance in thicker components.
|0.18 – 0.23%
|0.60 – 0.90%
|0.0005 – 0.003%
|0.19 – 0.25%
|1.35 – 1.65%
|0.0005 – 0.003%
Applications in Automotive Seating
A common application for boron steel is in automotive is seating components.
Structural Seating Elements
Seat frames and brackets are often made from 15B24 or 10B21. The components are stamped and formed and then must undergo a through hardening process. This three-step process involves heating the part to alter its physical properties, rapid quenching (in oil, salt, or caustic solution), and then reheating to eliminate excess brittleness. Heat treating is a critical step in ensuring the part can sustain heavy loads throughout their service life.
In the case of guides, gear rims, locks, and cams, manufacturers typically lean towards 10B21, 1018, 1020, 8620, or 4130 alloys. 10B21 is the standard choice for improved strength due to its cost effectiveness. Mechanism components made from 10B21 are typically case hardened, a process that increases the wear resistance of the surface (and the teeth in gears) while maintaining the strength of the core.
Deeper Dive into Seating Components:
If you want to learn about more materials and heat treating methods used for safety-critical seating components, check out our in-depth seating component guide.
Learn more about:
- Thermal processes used for seating components
- Key materials used for recliners, latches, frames and brackets
- Harnessing heat treating data for high-precision parts
- Finding a heat treating partner with automotive experience that can be the vital link in your supply chain
Download the Essential Guide:Thermal Processing for Automotive Seating Components