Fatigue strength of 304, cold worked versus annealed
Fatigue strength of 304, cold worked versus annealed
(OP)
This web page:
http://www.hghouston.com/ss_cwp.html
states:
304 annealed = 35 ksi
304 3/4 hard = 92 ksi
I'm in the process of designing something that will be subject to fatigue. Cycles will quickly exceed 10^6 cycles, and even 10^8 cycles will come along all to quickly.
The part is in axial tension/compression. It will have stress concentrations of about 2 or 3. But the statement made makes me wonder...
Which material would be best, annealed or cold worked? How can this be quantified?
http://www.hghouston.com/ss_cwp.html
states:
The web page also shows that fatigue strength can be improved dramatically by cold working. Endurance limit is listed as:Quote:
Cold working increases the fatigue strength of the austenitic stainless steels. However, the fatigue strength of these cold worked alloys is reduced by notches, as compared to notched fatigue strength in the annealed condition.
304 annealed = 35 ksi
304 3/4 hard = 92 ksi
I'm in the process of designing something that will be subject to fatigue. Cycles will quickly exceed 10^6 cycles, and even 10^8 cycles will come along all to quickly.
The part is in axial tension/compression. It will have stress concentrations of about 2 or 3. But the statement made makes me wonder...
Which material would be best, annealed or cold worked? How can this be quantified?





RE: Fatigue strength of 304, cold worked versus annealed
As long as you select a stress amplitude that is safely below the endurance limit of 304 stainless steel, you can accommodate an infinite number of cycles. The reported endurance limit (in bending) for annealed 304 is 35 Ksi**. The endurance limit will increase with cold work**.
**Handbook of Stainless Steels by
RE: Fatigue strength of 304, cold worked versus annealed
RE: Fatigue strength of 304, cold worked versus annealed
This makes it sound as if a stress concentration for a cold worked bar will somehow be higher than for an annealed bar. What do they mean by that statement?
RE: Fatigue strength of 304, cold worked versus annealed
Basically, annealed material like 304 stainless has significant capacity to absorb cold work or local tensile strain accumulation at notches with no adverse effects on fatigue life.
When you cold work material you have less capacity to absorb additional cold work and local tensile strain and as such, this could reduce fatigue life at areas of stress concentration.
As you can see you have options with using a higher strength material condition to take advantage of high strength. However, you need to understand that what comes along with this is lower capacity to absorb additional tensile strain around regions of stress concentration if not accounted for in the design of the component.
By the way you never mentioned the type of component your designing and selection of material and strength condition requires more that just fatigue strength. Also, material supplied in a cold worked condition has limitation in terms of size versus annealed material. Give careful consideration to this and other service conditions like corrosion resistance (if applicable).
RE: Fatigue strength of 304, cold worked versus annealed
Given the stress is going to be X, I'll have a stress concentration of Y, is it safe to say that ultimately, the cold worked material will have better fatigue strength? In other words, comparing an annealed bar and cold worked bar without notches, the cold worked bar has higher fatigue strength. Putting a notch in the bars makes things worse in both cases. Does a notch (or stress concentration) somehow affect the cold worked bar so severely, that the annealed bar will have a higher fatigue strength?
RE: Fatigue strength of 304, cold worked versus annealed
Not unless the increase in tensile stress (aka stress intensification) at the base of the notch exceeds the stress amplitude reported for the endurance limit.
It can. However, this is not an easy question to answer because you need to evaluate the notch sensitivity characteristics of this material under fatigue loading to determine if the fatigue strength is reduced.
RE: Fatigue strength of 304, cold worked versus annealed
RE: Fatigue strength of 304, cold worked versus annealed
I'll have to sharpen the pencil and see if the 304 annealed is suitable.
RE: Fatigue strength of 304, cold worked versus annealed
How long a piece o 3.25" round bar do you require?
Using 304 SS or 316 SS a 1.25 " dia is about as large round bar that cold working is effective.