Steel 42CrMo4 stress relieve, time temperature diagram question

Hi, could anyone help me to find the diagram t/T for the 42CrMo4 steel stress relieve? There is the dispute between the client and the factory. In certificate there is the mark +QT but stress relieve is not pointed separately. Factory claims that the stress relieve is done trough the tempering (T from +QT mark) and they sent a diagram. Since the quality control of the client is not very familiar with this matter , they claim that they supposed to put the separate mark for the stress relief.
Now to solve that dispute I have to find from independent source t/T diagram with short explanation. This I can use as the proof. I couldn't find it.
I'm mechanical engineer and they simply do not accept my explanation as the proof