Identify the governing material standard
China's official standards portal lists GB/T 699-2015 for quality carbon structural steels and GB/T 3077-2015 for alloy structural steels as current. 45 steel is normally discussed under the former, while 40Cr is discussed under the latter.
State standard, grade, product form and substitution rule instead of only “medium-carbon” or “alloy steel.” Similar-looking grades from different systems are not automatically equivalent.
Grade, supply condition and Q&T are separate layers
Grade identifies the material system; supply condition describes the delivered process state; quenching and tempering is a heat-treatment route. The same grade can produce different hardness and microstructure with section and heat-treatment changes.
A 45 steel Q&T ground bar should therefore identify diameter, length, hardness range, test location, final ground size and report requirements.
Do not mix core, case and chrome hardness
Q&T substrate hardness, induction-hardened case and hard-chrome hardness come from different process regions. Express each with the relevant method and unit. An HV or HRC value cannot be applied to the whole shaft without load, location and condition.
Section effects, core/surface differences, sample direction and decarburization should be addressed through drawing, process agreement or inspection plan when functionally relevant.
Purchasing checklist
Record standard/edition, grade, material/product form, delivery or heat-treatment condition, dimensions and allowance, hardness method/location, material/heat-treatment documents, batch sampling and substitution authority. Stock, price and lead time remain order-specific.