1018 Carbon Steel Tensile Test

[Jacob Noble]

I did a tensile test on 2 samples of 1018 carbon steel not heat treated. The samples were from the same order, tested one after the other, no machine settings changed (only re balanced), yet the samples have completely different results from the test.

Densities were also later calculated with both samples having similar densities, within error.

Attached is the graph of both samples (stress vs strain) and some calculations from it.

I would like help in determining how the results are so different when they are supposed to be the same material.

 

[EdStainless]

What is the product form and size?
What is the thermo-mechanical history?
And by the way, they have to have the same modulus.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[bobjustbob]

What does the fracture surface look like?

Bob

 

And by the way, they have to have the same modulus.

And density. Unless one sample was full of holes before the test. (We know both samples were full of holes after the test, if fracture was by microvoid coalescence.)

I would comment that one has very high strength and the other very low elongation, but then I rarely deal with SAE low carbon steels so I don't know what is 'normal'.

p.s., some human needs to intervene in the testing and override the 'smart' device spewing out nine (9) significant figures of strain.

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

 

[weldstan]

Tensile properties in the as rolled condition can vary dramatically based on hot forming temps, reduction especially at the final rolling sttion and cooling rates.

 

[btrueblood]

The orange curve kinda looks like a bent or misaligned sample, with the elbow in the initial part of the curve. You get weird strain data as the sample straightens out under load.

 

[MagBen]

Something must be messed up! E modulus was only 10 GPa vs normal 200Gpa for real. Blue curve shows no hardening, while orange does. Also, as "btrueblood" pointed out orange curve shows no linear portion even under low loads, it seemed the grip was not stable/slipped. I would first question the test itself, not the material.

 

[IFRs]

was one test with the grain and one against the grain ?