Metallurgy/Annealing of 316 SST
We have some .500" diameter bar where the the mechanical properties exceed the desired results. This material's tensile is currently 119KSI and hardness is at 252HB. We need to lower the Tensile to between 70 and 100 KSI and hardness not to exceed 238 HB. Is this achievable through Vacuum solution annealing? Is there a specific method to achieve the results? Time at temp, cooling method and rate, etc.?
The desired properties will be achieved by slight increase of the testing temperature, for instance raising the temperature from room temperature to between 50-100 degrees Celsius. If this is not allowed, you may want to consider buying another charge of the same grade which has a higher amount of alloying elements such as Ni, Mn, Cr, and even C (in spite of the fact that carbon is known as a strengthening alloying element). If this too is not an option, you may want to consider changing the solution annealing temperature to a temperature where a small fraction of delta ferrite forms in the microstructure (if this is allowed by the standards you use). This decreases your elongation but the partitioning of alloying elements such as carbon, Ni, and Mn to the austenite is equivalent to increasing the nominal content of these elements in your alloy.
In short, the temperature and composition dependence of tensile properties and hardness in austenitic stainless such as 316 is controlled by the deformation-induced processes in the microstructure (dislocations glide, deformation-induced twinning, deformation-induced transformation to martensite, etc.). For tensile curves of a typical 316 grade tested at various temperatures (150-400 C), please check the following research article: