Metals/Hardness to tensile conversion
Hello Mr. Fercy,
Everyone knows that a hardness value is like a "poor man's" tensile test.
When looking at any given conversion chart of Brinell to tensile strength the values tend to seem very definitive. Yet, there is a certain amount of variation. A hardness number can only provide an approximation of an expected tensile value.
Do you know a resource that adequately explains this variation between a hardness number and the associated tensile strength? Do you also have a resource that provide a reasonable expected range of tensile values for a given Brinell (or Rockwell, Vickers etc.) hardness value?
As you pointed out, Brinell hardness does seem to have a direct relationship with strength. I am not aware of a definitive 'conversion chart' as such.
The main reason is the strength of steel is determined through chemistry, prior to the quench and tempering process, where the material is hardened. The same steel chemistry can achieve similar tensile strengths, yet wildly different hardness and yield strength values. This is all determined with different temperatures in the tempering process.
Comparing AR400 to A514 steel (most commonly referred to as T-1 from USS)is a good example. The chemistry and tensile strengths are very close to the same between these steels. The main difference is in the hardness values and yield strengths; both determined by the specific tempering point.
A514 is tempered around 900 degrees Fahrenheit. The A514 is used as a structural steel for everything from buildings to heavy duty truck frames. (If you have seen a sticker on a semi frame that says Do Not Weld Or Drill This Frame, you are looking at A514.) The yield strength has a wide margin compared to the tensile strength.
Not so with AR400. AR400 is tempered around 500 degrees Fahrenheit. AR400 is used for wear resistance. The lower tempering point delivers a steel that is very hard, but with a very narrow range between tensile and yield strength. As a result AR400 is not suitable for structural purposes.
There are several different options for wear resistant steel. If you are searching for longer wear plate life, check out www.WearAnswers.com for infomation on longer life.
The bottom line answer for your question - no formula exists because due to the variables in chemistry and the quench and temper process. While this is not the answer you were hoping for, it should provide the reasons you have not seen it previously.
One of the best questions I have had; thank you!
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