1045 steel is a low-hardenability steel, which is a significant weakness.
The low alloy element content of 1045 steel results in a high critical cooling rate during quenching and a limited hardenability depth (water quenching: approximately 20–30mm, oil quenching: only 10–15mm).
Therefore, 1045 steel is ideal for small-to-medium parts (shafts, gears, bolts) with low overall hardenability needs or only surface hardening requirements. For large cross-section parts or those needing high core strength, alloy steels(4140 steel) with better hardenability are preferred.