What if Luders Bands do NOT show up as expected?

[Lorenzo]

Hello,

Luders Bars are expected to show up when testing at room temperature tensile specimens made of low alloy steel. The tensile graph will therefore CLEARLY show an Upper Yield Point and a Yield Point Elongation between the elastic and the elastoplastic phases.

But what if this doesn't happen, and the graphs only shows elastic and plastic phases, one after the other?
This is currently happening in numerous occasions
Which are the possible interpretations or reasons?
Should the test be invalidated?
Should the material be considered NOT suitable?

Please note that NOT ALL the samples coming from the same block of steel and extracted one near the others show this behaviour. Nevertheless, in some cases it happened.
It is likely that proximity has a role then, therefore there might be something locally in the material which can justify this behaviour. But What exactly?

Last information: yield and ultimate strength values don't show any significant difference in respect of the presence or not of the Luders Bands

thanks in advance for your help

 

[Tom.G]

A google search turned up https://www.princeton.edu/~maelabs/mae324/glos324/ludersbands.htm
The article starts out with: "In a well annealed low carbon steel alloy..."
I actually know nothing about this, but hopefully this will give you a lead.