Difference between 10.9 and SAE grade 8

[Gorpomon]

Hi, I am evaluating the differences between the two mentioned grades of materials. While comparing the specifications I am noticing small discrepancies, but no major differences. I'm soon to conclude that they are very similar, and thus interchangeable. Is there some big difference (chemical, mechanical etc) I am missing? Would assuming they're interchangeable be an issue?

FYI, this is not for any sort of safety critical application.

Thanks for any feedback!

 

[CoryPad]

They are essentially interchangeable.

 

[drawoh]

Gorpomon,

The material for 12.9 screws have ultimate stresses approximately equivalent to SAE grade[ ]8 screws. 10.9 screws are closer to SAE grade[ ]5. I have an old Machinery's Handbook which explains that the ultimate stress of a 12.9 screw is 120kg/mm². The 26th edtion claims that 12 is approximately one hundredth the minimum tensile stress in megapascals. English conversions I have seen, are closer to the kilogram values. The 0.9 value is the ratio of yield stress to ulitimate stress.

You realize of course that 10.9 and 12.9 screws are metric and the SAE screws are Unified National. Screws in tapped holes are not interchangeable. Nuts and bolts have slightly different tensile stresses, and different stress areas.

JHG

 

[CoryPad]

Ignore drawoh's material information, it is not correct. Grade 8 according to SAE J429 has a minimum ultimate tensile strength of 150 ksi, which is equivalent to 1040 MPa, which is the minimum ultimate tensile strength of 10.9 fasteners according to ISO 898-1.

He is correct regarding the threads, one is inch-based, the other is metric, so you will need to choose one or the other.

 

[swall]

CoryPad got it right.

 

[Gorpomon]

Yeah, I've seen the mistake of equating 10.9 to grade 5 before. I am only wondering from a material point of view, not from a geometrical one.

For instance could I expect different behaviors in cold service, corrosive environments or some other uncommon service conditions?

Has anyone ever seen a situation where they are different?

I was also told one of them (I think grade 5) goes through a double heat treat, does anyone know how that differentiates the two materials?

 

[swall]

Both Metric class 10.9 and U.S. spec grade 5 are quenched and tempered for the heat treatment. The 10.9 class will utilize a low alloy steel (with some exceptions) ; the grade 5 is carbon steel. Take a look at SAE J429 and 1199 sometime--this will explain it all.

 

[CoryPad]

There should be little to no difference between the two with respect to temperature, corrosion, etc.

Fasteners with property class 10.9 do not have to use an alloy steel. Common alloys are 10B21, 19 MnB 4, 1541, 4037, and 32 CrB 4.