Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Higher tensile strength for alloy steel 4340 screw

Higher tensile strength for alloy steel 4340 screw

Higher tensile strength for alloy steel 4340 screw

May be someone can help me in this:
I have a screw :#10-32 (diameter .19", length 1")hex head, full thread, alloy steel (4340), that according to NAS1801 it has 160 KSI tensile strenght.
Can I heat treating it, to get 300 KSI tensile strenght, if the case what would be the treatments, temperatures and times.
thanks in advance  

RE: Higher tensile strength for alloy steel 4340 screw

The specs for this particular screw says: heat treat: 160 to 180 KSI tensile strength.
I just want to know if this material can get better tensile strength and what are the steps in heat treating to get that.

RE: Higher tensile strength for alloy steel 4340 screw

You can get ultimate tensile strength between 250 ksi and 300 ksi using this process:

austenitize at 800 °C
oil quench
temper at 225 °C

You must be careful with material in this condition.  Low elongation, low fracture toughness, low impact resistance, and low resistance to hydrogen assisted cracking and stress corrosion cracking are all strong probabilities.

RE: Higher tensile strength for alloy steel 4340 screw

The screw will be use inside of the cockpit(airplane), for some attaching device.
can you be more specific about the process
austenitize at 800c but what time?
oil quench  what Temperature of the oil?
temper how long?
Mater if the screw already has a treating process,
(as specs indicated)
do I need to do a previo process?

Thanks in advance!!

RE: Higher tensile strength for alloy steel 4340 screw

The hold time at 800 C is 15 minutes for each 25 mm of section/thickness, or a minimum of 15 minutes.  Quench in warm oil at 25-60 C.  Since the part is already threaded you will want to use as high a temperature as possible.  Temper at least 2 hours.

As CoryPad mentioned, this will result in a very brittle microstructure, with low fracture toughness.  And since you will be eliminating the residual compressive stresses in the shank-to-head transition that were introduced by fillet rolling, this fastener will be very susceptible to SCC and fatigue failures in this area.  Do you intend to have this part electroplated after heat treating?  If the answer is yes, you will now have a very brittle fastener that has been exposed to hydrogen, and therefore hydrogen embrittlement and delayed fracture are a signficant concern.

Based on all of this information, you would be well advised to find a proper aerospace-quality fastener rather than re-work an existing part.

RE: Higher tensile strength for alloy steel 4340 screw

Possible but not advisable.  Airplanes vibrate and the temperatures can be very cold at altitude.  As mentioned previously at 300 ksi the frax toughness, fatigue properties, etc. would be pitifully low.  Cold temperatures will make these even worse.  Also the thread is spec'ed at class 3(close tolerance).  They will have to be cleaned up after any re-heat treatment.  Best approach would be to use another type of material for the screws or more of them.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close