Specifying 4140

[graybeach]

To save time, a fabricator has suggested machining some leaf spring retainers out of AISI 4140 instead of casting in ASTM A27 Grade 70-36. The retainers are part of replacement intake gates at a hydro plant. Cast steel was was used for the retainers on the existing 50 year old gates and has worked fine. The retainers are bolted on to the gates, are 1.25"x6"x5", and have a .75 inch deep recess to hold the spring. The gates are used infrequently.

If 4140 is used, how should it be specified to have the hardness and impact strength of the finished parts close that of cast steel? Annealed only? Should the parts be stress relieved after machining? How should the stress relieving be specified? Should the hardness and impact testing be done after stress relieving?

Many thanks.

 

[swall]

What is the lowest ambient temperature these retainers would be exposed to?

 

[graybeach]

When the gates are being used, the temperature will not be lower than 32 degrees F.

 

[metengr]

graybeach;
You don't need to use 4140 (low alloy steel) in this application. I would look at machining the retainers from ASTM A-36 structural steel plate. The ASTM A-36 has a minimum yield strength of 36 Ksi, which meets your original ASTM A-27 specification (which is cast steel for general application) for yield strength. The ASTM-A27 Grade 70-36 is 70 Ksi ultimate tensile strength and 36 Ksi yield strength. The impact properties of the ASTM A-36 steel plate would be well above 20 ft-lbs at 32 deg F.

 

[graybeach]

metengr;
Your suggestion seems to make sense. I will look into using A36. Thanks.