UK low alloy steel stress relief - effect on props? 2

[RPstress]

We have a supplier who wants to stress relieve a machined component made of UK low alloy steel 817M40 (see BS 970-3).

They want to do so at 570 deg C (1060 deg F) for 5 hours. (This is to keep dimensional control tight, as they feel it will move a bit when they machine it.)

The material's minimum tempering temperature is 600 deg C (1110 deg F) and it's not supposed to be tempered above 660 deg C (1220 deg F).

a) would this change the mechanical properties much?

b) what sort of time is 817M40 (and/or similar alloys) usually tempered for?

Alloy composition (from the mill assay):

C: 0.38.
Mn: 0.55.
Cr: 1.03.
Ni: 1.4.
Mo: 0.26.
Si: 0.28.
S: 0.008.
P: 0.009.
Cu: 0.08.

Here's the nominal (if it helps):

C: 0.36 to 0.44.
Mn: 0.45 to 0.70.
Cr: 1.00 to 1.40.
Ni: 1.30 to 1.70.
Mo: 0.20 to 0.35.
Si: 0.10 to 0.40.
S: 0.040 max.
P: 0.035 max.

 

[unclesyd]

As long as you are below the temperature that you steel was actually tempered there will be no measurable change in properties. The norm is to stay at least 20F, better 50F, below the actual tempering temperature.

Unless this component has a very thick cross section your time seems to be a little long as something like 90% of the stress relief for a specific temperature is accomplished in the first few minutes when the part is at that temperature.

One approach to a problem like yours is to double or triple temper, rough machine, stress relieve and finish machine.

 

[CoryPad]

Syd answered a). Here is the answer to b):

Alloy steels like these typically are temepered for around 1 to 2 hours.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[RPstress]

Many thanks to both unclesyd and corypad.

Unclesyd: these are quite thick parts, at least by my standards; the original billet could be up to 8" thick and the part to be stress relieved could have a maximum effective thickness of about 4".