bolt material determination by torque tightening

[trish129]

I have a M20 bolt with 8.8 embossed on it and a nut with 5 embossed on it ..i seek to check the material of both these two by tightening them at the recommended torque(calculated by knowing the listed proof strength of bolt against 8.8 and yield strength of nut as per grade 6) .any thread slippage at the recommended tightening torque will verify that the actual material of these two is not as embossed.is this the correct approach?

 

[dbooker630]

You will have to test the fasteners with an optical emission spectrometer or x-ray fluorescence to determine the material. SAE J1199 permits a wide range of steels with carbon ranging from .28 to .55 percent, and with customer approval low carbon manganese or boron steels can be used. The only aspect that you may determine with your test is whether your heat treatment is suspect but even then you will have to perform a hardness test to confirm.

 

[mrfailure]

First, you cannot test them against each other - you would need to mechanically test the nut and bolt seperately. Proof load is a good way to go for the nut mechanical property. You might want to instead machine a tensile specimen from the bolt so you can test UTS, yeild strength, and elongation as well and compare to 8.8. Note that the nut can also be checked for grade using composition (and you can confirm 8.8 composition for the bolt as well).

 

[trish129]

thank you for your replies..

yes you are correct mrfailure..material composition test is a good way to identify the correct grade..how will i determine the proof load for bolt and nut?

how will hardness determination help determining the material grade of nut and bolt?

8.8 bolt is ISO right?

 

[CoryPad]

ISO 898-1 defines property class 8.8 for bolts. ISO 898-2 defines property class 5 for nuts. You should read these two documents to understand the correct testing methods.

These two fasteners are not a very good combination (the nut is not strong enough).

 

[mrfailure]

For proof load: The markins on the bolt and nut tell you what grade the material is supposed to meet. The proof load requirement is listed in the ISO 898 specs Cory mentioned. You would perform proof load testing in accordance with ASTM F606M. This will be done for you at a materials test lab that has the required fixtures you would need to perform the test. You would not perform this testing yourself.

The ISO specs will tell you the mechanical properties required for the different grades, so you will be able to determine conformance.