Reducing the sintering time/temperature has been long desired. A so-called "non-firing sintering" was previously introduced by authors, without using thermal energy. This method involves the chemical activation of powder surface via ball milling, however, the mechanical strength of solidified bodies by non-firing sintering method is still low. In this study, an optimized non-firing process will be proposed in order to achieve high-strength materials comparable to the high-temperature sintered counterparts. Results showed that by optimizing the process, mechanical strength of 270 MPa and Vickers hardness of 2.1 GPa (214 Hv) were successfully achieved. It is also shown that the particle-particle bridge strength determines the bulk strength. (c) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).