Is boron steel or carbon steel a harder metal? Which one is more flexible?
The only thing that affects the hardness of steel is the carbon content. But there are many elements that can make it easier for a steel to achieve its maximum hardness. And Boron is an extremely effective element that increases the hardenability of steel. Adding as little as 0.002% Boron can have a big impact upon quenching of a steel. Boron is usually added when you need the hardness of a heat treated steel part to extend deep below the surface. For example, lets say you had a two identical plain carbon steel parts, but one had boron and the other didnt, and you wanted to heat treat them both After quenching, the surface should be the same on both, and lets say its 55 Rockwell C. In the plain carbon one, the hardness might drop down to 50 at 2mm under the surface, but the boron treated one might not drop to 50 until 4mm under the surface. Now, these numbers were completely made up, and it would depend on the specifics as to what the difference might be.
Boron is classified as a Metalloid element and is located in Groups 13, 14,15, 16 and 17 of the Periodic Table. An element classified as a Metalloid has properties of both metals and non-metals. Some are semi-conductors and can carry an electrical charge making them useful in calculators and computers.
There is really no simple answer to this question. Boron is usually used for a handful of reasons, but most center on high volume low cost production of durable hardened steel. Boron is a very cheap way to get very durable parts with very minimal alloying of expensive materials. It was born of necessity during WW2 and is currently in WIDE use in bulldozer undercarriage. Probably in place of what would otherwise be 4140. Boron steel is quite a bit more difficult to properly heat treat. Better suited to mass production facilities with tight controls, but when done properly provides material just as durable as higher alloys. Not a backyard endeavor such as ht/tempering carbon steel or tool steels without appropriate homework and treatment controls.
