Every type of metal, including alloy steel, is composed of tiny parts called grains. These grains combine together and make the respective metal. We can quantify the grain size by different testing methods. The boundary of each grain is called grain boundaries where the inclusions accumulate. Dislocations can be caused within the grain, the grain boundary essentially stops the dislocations in their tracks thus stabilising the structure and improving strength. Therefore, if you want to improve the strength of your metal, you’ll want the grain size to be as small as possible because this increases the amount of grain boundary. The larger the size of the grain, the softer the steel becomes and the smaller the grain size, the tougher the steel.
Why Do Smaller Grains Work This Way?
Grains that are small have a bigger surface-area-to-volume ratio hence, the more grain boundaries in any type of metal, the stronger that metal becomes. Small grain sizes improve both the stress relaxation resistance and the yield strength of the final product, resulting in a much stronger metal in the end.
Is This Always Practical?
All of this being said, it is sometimes a challenge to make sure that grain size is very small, but the good news is that there are other ways to strengthen the metal, and a lot of those ways are even better and more effective than trying to manage the metal’s grain size. But grain size is a possibility when your goal is a stronger metal at the end of the process. Therefore after quenching and tempering the grain sizes become smaller making the steel tougher.
Kisco has one of the advanced quenching and tempering facilities which are API 6A / AMS 2750 certified with a capacity of 300 tons/month, ranging from carbon steel, alloy steel, tool steel and die steel (DIN 1.2714). For example, the hardened and triple tempered die blocks have a uniformity of +/-2 HRC from surface to core giving a high die life to our valuable customers for many years.