I don't have any experience with "unalloyed" steels, but it looks like it would be alright to work with.
Probably a brine quench.
Then play with tempering temps until it no longer chips.
They must call it C70 as the "C" content is .70%.
Chemical Composition (in weight %)
C Si Mn Cr Mo Ni
0.70 0.20 0.25 - - -
V W Others
- - -
Description
Unalloyed carbon steel.
Applications
Quenched and tempered steel for heavy duty parts in machines, vechicles.
Physical properties (avarage values) at ambient temperature
Modulus of elasticity [103 x N/mm2]: 210
Density [g/cm3]: 7.85
Soft Annealing
Heat to 680-710oC, cool slowly. This will produce a maximum Brinell hardness of 183.
Hardening
Harden from a temperature of 790-820oC followed by water. Hardness after quenching is 63-64 HRC.
Tempering
Tempering temperature: 180-300oC.
Forging
Hot forming temperature: 1100-850oC.