JIS 3131 SPHC Standard material composition limits

[skhots]

I'm trying to get a second opinion on the material composition limits within the JIS steel standards, specifically 3131 and 3141 for hot rolled and cold rolled sheet.

The standard states MAXIMUM limits for C, Mn, S, P for the different quality such as commercial, drawing, and deep drawing. The limits decrease as you go towards the more malleable drawing quality grade.
Now when you specify SPHC which is considered commercial quality hot rolled steel, you have a higher limit on composition. If you receive steel that meets the deep drawing quality(SPHE), is it considered acceptable that you got SPHC because it falls under the limit of SPHC? Or would you say that the range of acceptance is the max of one grade to the max of the next grade?
For instance:
Carbon % max - commercial is 0.15%, drawing is 0.12%.
Ignoring all the other elements for discussion's sake.

If you get material that is 0.125%, it exceeds the max of drawing quality so it is commercial quality. Right?
But if you get material that is 0.11% C, you have drawing quality but could it also be sold as commercial quality? I think not.
If this isn't the case, shouldn't the standard list a minimum or range for the composition percentage allowed?

The problem here would be that if you specified SPHC for the less malleable material and got drawing quality, supplier could say you got material that was within print specs, yet the yield strength is not as expected.

Or am I thinking of this the wrong way in that just because it's drawing quality doesn't directly mean that it's yield strength is lower?

For background information and this might help frame your response: we specified SPHC on our prints, a specific batch of material failed under testing conditions whereas the previous batch of parts passed the same testing.
Reviewing the material cert, it says SPHC but the material composition meets that of deep drawing quality -- more malleable, less hardness.

 

[EdStainless]

When they are only max that is exactly what it means. If the mill wanted to they could make the most restricted chemistry and sell it for all of the grades.
As long as it still met the minimum strength for each grade.
Did your material fail the tensile test or a functional test? If it was a functional test then you need a higher strength than you have required. Never rely on a mill to give you higher strength material just because they have in the past.

An example of this is CP Ti Gr1, 2, and 3. Gr1 is the lowest Oxygen and lowest strength. What people do is make one grade that is right at the max oxygen for Gr1, and then sell it as Gr1 and Gr2. And then they make one at the max oxygen for Gr2 and sell it as 'strong' Gr2 and Gr3.
This tactic is common in may alloys, steels included.

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P.E. Metallurgy, consulting work welcomed

 

[mfgenggear]

"3131 and 3141 for hot rolled and cold rolled sheet.
malleable drawing quality grade."
on the engineering or/and the P.O.
it needs to specify the minimum tensile requirements
that would solve the issues.

engineering took for grant all grades met the tensile,
it needs to be spelled out so the correct material is purchased.
talk to the supplier and ask them if they can do this.