Heat treatment of SAE 440B steel
Heat treatment of SAE 440B steel
(OP)
We've had a few problems with some pins in 440B steel failing due to corrosion.
According to a consultants report --
.. evidence of grossly intercrystalline corrosion pits and some associated intercrystalline branched cracks that appeared characteristic of stress corrosion cracking.
.. significant grain boundary carbide precipitation was evident and most likely originated from the heat treatment process due to tempering within the 425-565 deg C range. Tempering within the range 150-370 deg C prevents reduced impact values and poor corrosion resistance.
The presence of the grain boundary carbides has significantly reduced the corrosion resistance of the material making the pins more susceptable to corrosion in service.
If the pins were re heat treated and tempered at the lower temperature (say 200 deg C) would the carbides be eliminated leading to improved corrosion resistance.
Any comments would be appreciated.
According to a consultants report --
.. evidence of grossly intercrystalline corrosion pits and some associated intercrystalline branched cracks that appeared characteristic of stress corrosion cracking.
.. significant grain boundary carbide precipitation was evident and most likely originated from the heat treatment process due to tempering within the 425-565 deg C range. Tempering within the range 150-370 deg C prevents reduced impact values and poor corrosion resistance.
The presence of the grain boundary carbides has significantly reduced the corrosion resistance of the material making the pins more susceptable to corrosion in service.
If the pins were re heat treated and tempered at the lower temperature (say 200 deg C) would the carbides be eliminated leading to improved corrosion resistance.
Any comments would be appreciated.





RE: Heat treatment of SAE 440B steel
RE: Heat treatment of SAE 440B steel
This should be as good as you can do.
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Plymouth Tube
RE: Heat treatment of SAE 440B steel
The pins are typically 25mm dia and traditionally the heat treatment was oil quench from 1050 deg C, followed by tempering at 100-150 deg C as per manufacturers data sheet.
Due to some confusion a new subcontractor has been tempering at a higher temperature to give Rc57, I believe in the 400-450 deg C range.
The manufacturers tempering data (from some years ago) suggests-
100 C - 730 Hv
200 C - 650 Hv
300 C - 610 Hv
400 C - 650 Hv
500 C - 650 Hv
550 C - 520 Hv
600 C - 400 Hv
There was no comment about any adverse problems with high tempering temperatures.
EdStainless,
We are currently getting some samples re-treated to see if we can get rid of the grain boundary carbides.
I just thought I'd canvass other opinions on the problem. Also it's being said that 420 steel would not have this problem due to the lower carbon content, true??
RE: Heat treatment of SAE 440B steel
RE: Heat treatment of SAE 440B steel
Many thanks for your comments on 420. I've just increased my knowledge significantly.
RE: Heat treatment of SAE 440B steel
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Plymouth Tube
RE: Heat treatment of SAE 440B steel
RE: Heat treatment of SAE 440B steel
RE: Heat treatment of SAE 440B steel
RE: Heat treatment of SAE 440B steel