Rapid hardness drop when tempering martensitic SS
Rapid hardness drop when tempering martensitic SS
(OP)
I find that Rc hardness drops rapidly when tempering 400 series SS between 950-1000 deg f.Why does this happen and how can it be avoided?A typical example is 416ss oil hardened from 1750f .15%C atmosphere requiring 37-41 Rc.1st temper @ 600f results in high hardness.2nd temper 2 hr @ 960f high results again(42-45Rc).Then a 3rd temper @970 2hr ,same furnace,results are 34-40Rc.Similar results happen with 410,420,431,440,and some tool steels when tempered about 975f.Preferably ,I'd like to get the required hardness by tempering lower or higher where it does'nt drop so fast.





RE: Rapid hardness drop when tempering martensitic SS
Your post is confusing because you have packed a lot of information into it.
What size is the 4xx series stainless steel piece?
Are you sequentially tempering the same piece or are the tempering times and temperatures you referenced above based on separate test pieces? It was not clear to me.
RE: Rapid hardness drop when tempering martensitic SS
RE: Rapid hardness drop when tempering martensitic SS
This really sounds to me like you have a serious process problem. Either you are not achieving an adequate quench after austenitizing, or your hardness measuring technique is incorrect, and last, you should not be performing sequential tempering on the same piece to optimize hardness. You only need to perform the following for 416 ss;
1. Austenitize at 1700-1850 deg F
2. Quench in oil (process check for as-quenched hardness)
3. Temper at 550-600 deg F for 1 hour per inch of thickness at temperature to achieve a hardness HRc of ~ 40.
RE: Rapid hardness drop when tempering martensitic SS
RE: Rapid hardness drop when tempering martensitic SS