Without heat treatment, many of the products we use daily, and take for granted, would need to be designed differently or would not function as effectively. One of these is the automotive seat-belt clasp. Before getting into some specifics of this part, however, let’s look at the history and benefits of these restraints.

Seat belts were invented by George Cayley in the late 1800s. They did not become common in aircraft until the 1930s, although they were introduced sometime earlier. In the 1920s and 1930s, a group of physicians equipped their own cars with lap belts and began urging manufacturers to install them in all new cars. For 20 or 30 years, this warning went unheeded until 1954 when the Sports Car Club of America began requiring competing drivers to wear lap belts. Ford and Chrysler offered lap belts as optional equipment in the front seats of the 1956 models. In 1958, however, it was Saab that was the first manufacturer to introduce seat belts as standard equipment.

In 1963, Volvo was the first to introduce the three-point harness for the front seat as standard.  It was not until 1965 that all U.S. manufacturers were installing lap belts in the front seats, and it was 1968 before rear lap belts became standard equipment. The first child car seats – very different from today’s – were invented in 1921 following the introduction of the Model T. In 1978, Tennessee became the first state to require child safety seat use.

The benefits of seat belts as a lifesaver are indisputable. Using 1966 as the baseline, the death rate from automobile accidents was 5.5 per 100 million miles driven. Thirty-five years later, the death rate had dropped to 1.5. In that same time period, traffic fatalities declined 18% while the number of vehicles on the road more than doubled and the number of drivers nearly doubled. The NHTSA estimated that front seat belts saved 11,900 lives in 2000, and the use of these restraints improves your chance of survival by 50%. One of the reasons for the drop in the fatality rate is the increase in seat-belt usage over time. In 1994, average usage across the U.S. was 58%. This has increased to 81% by 2005.

Like many components in the automotive industry, seat-belt hardware is manufactured by a contractor to the OEM that typically sends the metal parts requiring heat treatment to a commercial heat treater. A photo of the buckle hardware is shown on this page. This hardware is made from 1050 carbon steel, and the parts are through hardened, quenched and tempered to the ideal hardness. This operation is performed in continuous atmosphere furnaces, and an endothermic atmosphere is generated that is neutral to the carbon in the buckle material. The post-hardening oil quench is followed by a wash, and the part is subsequently plated with a nickel-chrome coating. Portions of these parts are also coated with plastic depending on the application.

It is often surprising to consider the quantities of items such as this. At a single commercial heat treater in Ohio, approximately 100,000 of these “buckles” are heat treated each month. That’s over one million parts a year. It is believed that this specific application is limited primarily to child car seats and built-ins for minivans and similar usages. If one considers all of the like hardware heat treated throughout the world for all auto manufacturers, many heat treaters would be similarly involved.

Hopefully, this column has shown one more way that heat treatment makes the things we use in our day-to-day lives better and keeps us safer. Our hope is also that you have been presented with sobering statistics that encourage you to buckle up – your life may depend on it. IH