We present results for pseudo-critical temperatures of QCD chiral crossovers at zero and non-zero values of baryon (B), strangeness (S), electric charge (Q), and isospin (I) chemical potentials . The results were obtained using lattice QCD calculations carried out with two degenerate up and down dynamical quarks and a dynamical strange quark, with quark masses corresponding to physical values of pion and kaon masses in the continuum limit. By parameterizing pseudo-critical temperatures as , we determined and from Taylor expansions of chiral observables in . We obtained a precise result for MeV. For analogous thermal conditions at the chemical freeze-out of relativistic heavy-ion collisions, i.e., and fixed from strangeness-neutrality and isospin-imbalance, we found and . For MeV, the chemical freeze-out takes place in the vicinity of the QCD phase boundary, which coincides with the lines of constant energy density of and constant entropy density of .