The only way to take temper out of steel is to heat it. Sandblasting would not do this unless you hold the blast in one place long enough for it to get hot. Sweeping motion when blasting dosen't get that hot but I have seen people hold it on a stubborn spot of rust til it will eat thru the metal. Biggest thing to remember is to keep it moving and come back to those stubborn spots maybe 2,3,or 4 times but never just hold it there for any lenght of time. You should make this clear to whoever does it if you don't do it yourself and maybe stay with your pieces if need be.