Conversations involving Endurance limit (fatigue strength) are generally concerned with discovering the life-expectancy of a part. “If I use steel type “A” instead of steel type “B”, how much longer may I expect the part to last?
A normal concern for sure, however, there is no test or formula for arriving at an even remotely accurate answer, based solely on the chemical and physical properties of a type of steel. Data posted showing “Endurance Limit” relative to standard SAE grade steels, is intended for general guidance. In order to obtain any meaningful data, relative to endurance limits, the finished part must be tested under conditions that simulate actual service conditions. You want to know about your part? You got to run tests on your part. There are tests that will provide relatively accurate estimates of predictable service life, when the actual part is in simulated service conditions.
The R.R. Moor Endurance Test, is an example of a test that utilizes bending and rolling contact to test torsional fatigue. [Variables introduced may be; vibration, compression, bending, twisting, rolling, etc.]. This test is expensive and the evaluation period is lengthy. Results may be expressed in “Cycles to failure” as opposed to “PSI.”
Specialty alloys and stainless shafts furnished by Associated Steel are made to requirements
intended to extend service-life over what is typically experienced with their commercial equivalent alloy. General metallurgical data available for public reference is typical to standard grade SAE steels and is at best general in nature. It is not intended to be an accurate reflection of the potential extended service life of refined or modified material.
Endurance limit relates to “Toughness.” Toughness in metals considers the durability (Ductility) of the metal at elevated strength levels. You can enhance “toughness” by modifying the metals chemistry, minimizing defects, refining grain and improving thermal conditioning during manufacturing production.
Associated Steel is a supplier of value added materials intended for critical service and intended to extend service-life.
-Howard Thomas, December 8th, 2022