AISI/SAE 1045 is a medium-carbon, plain-carbon steel with no significant alloying additions beyond manganese — its properties come almost entirely from carbon content (roughly 0.43–0.50%) rather than from chromium, molybdenum, or nickel. That makes it simpler and generally less expensive than the low-alloy grades in this family, while still offering meaningfully more strength and hardness potential than low-carbon steels.

1045 can be used as-rolled or normalized for moderate-strength applications, or through-hardened and tempered when higher strength and wear resistance are needed, since its carbon content is high enough to respond to conventional heat treatment (unlike case-hardening grades such as 8620). This versatility — decent strength without the cost or complexity of alloy additions — is why 1045 is one of the most common general-purpose engineering steels in machine shops. Typical applications include shafts, spindles, gears, bolts, studs, axles, and structural components where moderate strength and toughness are needed but the extreme hardenability or high-temperature performance of an alloy steel isn't required. It's a practical, economical default grade for parts that need to be stronger than mild steel without moving into alloy-steel territory.

1045 is generally regarded as a good machining benchmark among carbon steels — better than dead-soft low-carbon grades in terms of chip formation and surface finish, but requiring more cutting force and generating more tool wear than lower-carbon grades because of its higher carbon content. There are no chromium or molybdenum carbides to contend with, so abrasive wear is lower than on comparable alloy steels, but the increased carbon still raises hardness and cutting forces relative to low-carbon grades.

Chip formation is typically favorable in the normalized or as-rolled condition, producing well-broken chips with standard chipbreaker geometry rather than the long stringy chips associated with very low-carbon steels. In the hardened and tempered condition, cutting forces and heat generation increase accordingly, and tool selection needs to shift toward more wear-resistant coated grades to hold acceptable tool life.

Work-hardening is a modest concern rather than a dominant one on 1045 — light or interrupted cuts, or dwelling on a workpiece with a dull tool, can locally harden the surface and make the next pass more difficult, but this is far less pronounced than on austenitic stainless or high-manganese materials. Standard positive-rake carbide geometries, moderate cutting speeds, and normal coolant practices are usually sufficient to get consistent finish and reliable tool life on this grade.