Steel Suggestion for Non-Heat Treated Fasteners 4

[metalman8357]

Hi all,

I just have a quick question. We have a line of fasteners (0.200" diameter) that are normally made from 10B21 and hardened to 28-34 HRc via heat treatment. We also make the same fasteners from cold worked 316 and are able to achieve the same hardness. The idea came up that we should look at eliminating our heat treatment on 10B21 by selecting a cold worked material that has a hardness of 28-34 HRc as-received. Would there be any negatives to this approach? Other than the fact that rolling threads on a harder material will wear the die out quicker, does this seem like a feasible approach? Or will material cold worked to 28-34 HRc have terrible ductility/impact resistance when compared to a heat treated 10B21? Also what cheap materials should we look into that could satisfy these requirements?

Thanks,
M

 

[swall]

If you are working to SAE fastener specs, such as J429 or J1199, the material and heat treat conditions are part of the spec requirements, so no, you don't have much leeway to do what you are proposing.

 

[arunmrao]

You might want o consider 1025 grade steel to be used without heat treatment. In my experience 1030 and 1040 grades need heat treatment.Higher carbon grades like 1045 are not recommended for fastener applications. Hope it helps.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[metalman8357]

We are not working to any fastener spec at the moment. These are special application fasteners. Arunmrao, to my understanding 1025 is not available cold worked to 28-34 HRc. Also, why are higher carbon grades like 1045 not recommended for fastener application.

We could also look into using an alloy steel if the price was still cheaper than heat treated 10B21.

 

[Screwman1]

The EU fastener mfg. have done extensive work in this area and they have special alloys for reaching PC 8.8 (approx 120 ksi) UTS. The problem with the work hardening material is that it is a beast on header tooling if you have a recess drive and the cost savings from eliminating HT is eaten up in material cost in the small size parts you are talking about. For M10 and bigger parts then the weight leads to some decent heat treat cost savings.
You will not get the degree of work hardening that you need with any straight carbon steel, you will need alloying and a special mill heat treat to give you a unique micro structure that has ductility for heading and also strength.

 

[arunmrao]

Higher carbon steel grades are to recommended because of loss of ductility and susceptibility to Hydrogen embrittlement and stress corrosion cracking.

1025 grades are available in hot rolled condition .

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[EdStainless]

Or look at a micro-alloyed/HSLA grade. These steels are lower carbon.
They are often used in the cold worked stress relieved condition. You are not going to a very high hardness.
These steels may cost more but you would loose the heat treatment.

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Plymouth Tube

 

[TVP]

As Screwman noted, the Europeans have led the development in this area. Below are some links that you can review for more detailed information. Basically the steels that have been developed for non-heat treated high strength steel fasteners consist of mixed microstructures (ferrite + martensite or so called dual phase, ferrite + pearlite, ultra low carbon bainite) that strain harden considerably during cold forming. In North America, there are only a few options to consider for cold heading quality steel wire rod, namely, Charter, ArcelorMittal (former Ispat Inland), Republic, and Nucor. ArcelorMittal used to offer their ultra low carbon bainitic grade called FreeForm, but that appears to have been discarded. I am not familiar with Charter or Nucor offering anything, but both are willing to work on new developments. Republic has produced a ferrite + pearlite steel similar to Saarform 900 (see below) for use in fastener-type applications. They were producing wire rod in larger diameters for automotive applications, but I would expect that they would offer a small diameter Stelmor-cooled product suitable for your use. And take note about the reduced tool life-- the higher flow stress can be especially problematic on old, beat-up headers.


Cold heading quality low-carbon ultra-high- strength bainitic steels (Coheadbain)

http://www.swiss-steel.com/fileadmi...om/documents/dokumente/18_Coheadbain_RFCS.pdf

Micro-alloyed steels for non heat treated ball studs and pins

http://www.swiss-steel.com/fileadmi...ocuments/dokumente/16_Microalloyed_steels.pdf

8MnSi7 - Saarform 800

http://www.saarstahl.com/fileadmin/...dukte/walzstahlsorten/english/5113_8MnSi7.pdf

30MnVS6 (27MnSiVS6) - Saarform 900

http://www.saarstahl.com/fileadmin/.../walzstahlsorten/english/1302_30MnVS6_kss.pdf

Technological Properties of the New High Strength Bainitic Steel 20MnCrMo7

http://www.ezm-mark.de/index.php?id=1103