Trouble with Heat Treatment of 1022 steel Fasteners 1

[J G]

I am making special fasteners from 1022 steel.

The screw needs a high surface hardness (58-60 HRc) but should be able to bend also (5-7 degrees).

In my heat treatment process I get the hardness but the screw does not pass the bend test. It is brittle and breaks.

HELP !

 

[TugboatEng]

Being able to bend is a very unusual requirement for a screw. Can you give more information about the application? It seems the best approach would be to eliminate the need to bend.

 

[weldstan]

That's the maximum hardness that you can achieve with this material and of course it is brittle. Have you thought of nitriding or carburizing the surface to meet surface hardness requirements. Then the underlying material's ductility will achieve your ductility requirements. One must question why you need to use 1022 for this purpose.

 

[EdStainless]

I don't believe that as quenched 1022 will make 58HRC.
The answer is surface hardening, either nitride or carburize. The process temp will temper your steel so that it is ductile and the surface will be hard.
1022 does seem an odd choice

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P.E. Metallurgy, consulting work welcomed

 

[Martinos]

Carburizing or carbonitriding. That is the purpose of this grade.

 

[blacksmith37]

Maximum possible hardness with 0.22 C is about HRC 45 , depending on thickness , austneitizing temp, quench severity, etc, etc. Gas carburizing is the standard process for ordinary steel screws. It seems like you are carburizing to get above C 45.

 

[J G]

The screw I am making is a Self Drilling Screw. 1022 is the standard material.

The screw has to be hard enough to cause the drilling (in 6mm steel plate), then the threads have to tap the steel plate until the flange touches. It should NOT break during the process.

I am doing Carbonitriding, Quenching and Tempering. I am able to achieve a surface hardness of 60 HRc (case is 0.2 mm so the entire thread thickness is kind of through hardened). I then bring the hardness down to about 56 HRc in tempering, but the screw still breaks while tapping. The break is about 3-5mm below the head.

Is the tempering faulty ? What can I do to increase toughness ?

 

[blacksmith37]

A case of 0.2 mm is not thick enough to get a HRc test at 60. The surface hardness should be tested with Rockwell Superficial like 15 N or Vickers with a light load. I think the actual surface hardness is higher than HRC 60. I would gas carburize at a carbon potential of about 0.4 % , then the lower carbon in the surface would not be so hard and untough.

 

[Tmoose]

"but the screw still breaks while tapping"

Is this a bending failure, or twisting?

Please show detailed drawings of the screw and some pictures of the failures.
Does the screw cut the threads, or roll-form the threads ?

If the tapping geometry of the screw is incorrect the torque to tap will be excessive.
Ditto if the size of the resulting drilled hole is too small.

 

[J G]

 

[J G]

This is the screw.
The drill size is pre matched in the front tip.
I think the picture will answer most questions.

 

[J G]

To answer “blacksmith”, we are testing on HV1 scale.
The HRc is only conversion.

 

[mrfailure]

HV1 (i.e. 1 kg load) seems pretty high. Using Vickers, it should be more like 100 g (HV0.1) or, as blacksmith suggested, use the superficial tester.

 

[mfgenggear]

the size and length of this screw is in adequate to drill and tap .236 thick plate. it's going to break., or fail.
need a bigger fastener. and it may need to use a stiff carbide drill. then tap.

 

[WKTaylor]

J-G...

Part of the problem with Your design is that it needs-to-be 'self-drilling-and-thread-tapping'... Yet the screw appears to be ordinary 'self-drilling' for soft-metal/wood installation.

WHAT are You intending to install this fastener into: hard wood??? soft aluminum or low strength carbon steel??? or nickel alloys and titanium??? Etc?? The intended material to be fastened is a very IMPORTANT FACET OF THIS DISCUSSION.

In my humble opinion the drill-tip must be capable of drilling the 'starter/pilot hole' and clearing-away those 'chips'... and then...

The lead-in threads will be required to begin the process of tapping the hole... and then...

The remaining threads MUST be capable of clearing-away new-chips as tapping/insertion progresses.

Sooo…

The lead-in threads should probably 'look like' a hole-thread-tap... and the remaining thread should probably have a way of passing-out [or otherwise absorbing] the chips... possibly with spiral grooves cut thru the thread flanks [lengthwise] or some-other process. Without being abrasively destroyed in the process. My head hurts.

High strength low allow steels [almost tool-steel because of possible friction heating] are probably necessary... with either nitriding or a very hard surface coating such as IVD titanium Nitride to provide high temp friction/wear resistance.

Hmmmmmm… A high strength CRES with nitrogen-surface hardening + wear/abrasion coating... might also be suitable candidate material.

One last possibility is a fastener with fine/hardened threads that is installed in a conventionally drilled-hole that 'cold-works the based-metal hole-wall into a matching female thread-pattern'. This would require a fastener capable of sustained high torque loading during installation. My head still hurts.



Regards, Wil Taylor
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[Tmoose]

Did I miss what size the fastener is? Thread size and length?

" the threads have to tap the steel plate until the flange touches... but the screw still breaks while tapping. The break is about 3-5mm below the head."
Have the first few "tapping thread" passed completely thru the plate when the screw breaks? Does the screw break more-or-less at the surface of the part?

 

[EdStainless]

If the size is right, and if the design is right, then the C control must be at fault.
Have you ended up with the material too hard too deep? Or is it too weak?
You need cross sections and microhardness traverse along with some analysis of the fractures.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

Looking at information for these types of screws, generally the screws are limited to a maximum plate thickness equal to their diameter. It seems this is simply the wrong application for the screw. You may also have problems if the threads engage before the drilling tip has passed through the material.

 

[SwinnyGG]

If the length of the drilling tip of the screw (not including the taper on the nose) is less than the thickness of the plate being drilled, your self tapping screw will never tap a hole through the plate without breaking - it's impossible.

When you're drilling, you're creating chips. As soon as the thread touches the top surface of the plate, the hole is closed. The chips have nowhere to go; they will jam the drilling operation and the shaft of the screw will fail. This will happen pretty much every single time unless the bit driving the screw becomes disengaged.

This seems to me to be an application of the wrong screw to the wrong plate, not a problem with the design or heat treatment of the screw itself.

 

You'll first need to clarify what you mean by '1022' steel, because the first thing that comes to mind is SAE 1022, which in no way can approach 58-62 HRC, and isn't used for screws AFAIK.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."