As a follow-up to the SAE specifications to identify the different types of shot peening media types, there are also specifications that specify the hardness of the Steel Shot or Steel Grit. Hardness is reported in the Rockwell ‘C’ range and is stated as Rc or HRC with higher numbers indicating a harder grade. SAE specifies that “ninety percent of random hardness checks performed on a representative sample shall fall within the ranges” and that the standard deviation allowed is +/- 3 HRC.
The typical ranges are as follows:
40 to 51 HRC (KGP)
47 to 56 HRC (KGB)
54 to 61 HRC (KGL)
61+ HRC (KGH)
Generally, the softer grades will round over more quickly making it better for removal of oxides and cleaning. Harder grades will maintain the angular shape (with Steel Grit) and are best for stripping and etching applications.