Does stress relieving reduce hardness
Does stress relieving reduce hardness
(OP)
We have 4140 forging. Approximate dia 12" and ID 8". This forging is at 28/32 Rc. Would the stress relieving reduce its hardness? How much temperature and what soaking time is applicable for such a section? I would appreciate information on this .





RE: Does stress relieving reduce hardness
Normalize
Austenitize
Oil Quench
Temper around 1050 degrees F holding for 1 hour per inch of controlling section thickness
Stress relieve 50 - 100 degrees F below the tempering temperature for 1/2 hour per inch of controlling section thickness.
The stress relief cycle should produce no detectable effect on the hardness measured after tempering.
RE: Does stress relieving reduce hardness
Does it look OK or am I missing something?
RE: Does stress relieving reduce hardness
RE: Does stress relieving reduce hardness
The stress relieving is required as the part is going to be nitrided at around the same temperature after finish gear shaping. If the stress are not relieved before the finish shaping they would get relieved during nitriding and that would cause the part to distort.
To avoid this, we have to stress relieve the part at the nitriding temperature.
RE: Does stress relieving reduce hardness
4140 isn't a real deep hardening steel, depending on the actual comp. One heat will harden much deeper than another one.
If you can post the actual comp. we can figure it out for you.
RE: Does stress relieving reduce hardness
RE: Does stress relieving reduce hardness
RE: Does stress relieving reduce hardness
RE: Does stress relieving reduce hardness
RE: Does stress relieving reduce hardness
RE: Does stress relieving reduce hardness
RE: Does stress relieving reduce hardness
We also made it a practice to never single temper any material. Even with advent of Cryogenic treatment we still required a double temper.
RE: Does stress relieving reduce hardness
RE: Does stress relieving reduce hardness
RE: Does stress relieving reduce hardness
RE: Does stress relieving reduce hardness
If you want to stress relieve to assure machine stability, shape stabilization, or to reduce premature fatigue then I suggest that you could use sub-harmonic stress relief on your 4140 tubes. The nice part about this process is that it does not change "hardness" at all nor does it cause treatment distortion.
A program that occurred a few years ago involved 4135 forged tubes about 7"OD, 6"ID x 72". Tolerances for the inside full cut bore was extremely tight. Before sub-harmonic stress relief was used the scrap rate was 65%. After sub-harmonic was used 0% scrap and remained at 0% for four years!
My suggestion - get your hardness where you need it, then apply sub-harmonic stress relief between rough and finish machining.
BTI Guy
RE: Does stress relieving reduce hardness
In response to your question about hardness change below the lower critical temperature (phase change). Quenched steel does not require a phase change to change hardness. As you have already esperienced, tempering is done below the lower critical temperature and this reduces hardness.
Jesus is THE life,
Leonard