Dear Mr Manat
I got the broken parts.
And I compared broken parts and sample parts.
The deformation due to the crack of die may be not related with this problem.
And the color is completely different from sample parts.
(Needless to say the color might change by corrosion.)
Conclusion about comparison.
Heat treatment may be not good.
・Please measure the hardness of broken parts by HV and HRB.
・And please ask the heat treatment supplier his opinions about hardness and color.