1018 Steel vs 1045 Steel: Which Should You Use
MetalNow ยท August 25, 2026
Grab the wrong one of these two and you'll find out fast, either the part won't hold up under load, or you'll spend twice as long machining something that didn't need to be that tough to begin with. 1018 and 1045 get confused for each other more than almost any other pair of steel grades, mostly because they look similar on a shelf and both show up constantly in general fabrication. They're not interchangeable, though. Here's the real difference and how to know which one your job actually calls for.
Quick answer: 1018 is a low carbon steel valued for easy machining, clean welding, and consistent dimensions, best for pins, dowels, brackets, and low-stress machined parts. 1045 is a medium carbon steel with meaningfully higher strength and the ability to be heat treated for hardness, best for shafts, axles, gears, and anything under real mechanical load. If the part just needs to be machined to shape and hold together, 1018 is usually the more economical choice. If the part needs to survive real stress, wear, or repeated load cycles, 1045 is usually the right call.
What's actually different between them
The core difference comes down to carbon content, and that one number drives almost everything else about how these two grades behave.
1018 is a low carbon steel, typically around 0.15 to 0.20 percent carbon. Low carbon content means it's soft, ductile, and forgiving to work with. It machines cleanly, welds without much fuss, and holds tight tolerances well when supplied cold rolled, which is how it's most commonly sold.
1045 is a medium carbon steel, typically around 0.43 to 0.50 percent carbon. That higher carbon content is what unlocks its biggest advantage: 1045 can be heat treated, meaning it can be hardened through quenching and tempering to reach strength and wear resistance far beyond what 1018 will ever achieve. The tradeoff is that it's tougher on tooling, less forgiving to weld, and typically costs more.
Same base steel family, different carbon percentage, and that percentage changes what each grade is actually good for.
Key properties at a glance
When 1018 is the right call
You're machining a low-stress part. Pins, dowels, spacers, brackets, and general fixturing components that don't carry serious load are a natural fit. 1018's machinability means less tool wear and faster cycle times compared to tougher grades.
You need to weld it into an assembly. 1018's low carbon content makes it one of the more forgiving grades to weld without special preheat or post-weld treatment, which matters if the part is going into a larger welded structure.
Dimensional consistency out of the raw stock matters. Since 1018 is most commonly supplied cold rolled, it starts with tighter tolerances and a cleaner surface finish than a hot rolled equivalent, useful when you're trying to minimize machining time.
Budget is a factor. 1018 is generally the more affordable of the two, and for parts that don't need the extra strength, paying more for 1045 doesn't buy you anything useful.
When 1045 is the right call
The part needs real strength. Shafts, axles, gears, bolts, and anything transmitting torque or carrying significant mechanical load benefit from 1045's higher yield and tensile strength compared to 1018.
Wear resistance matters. Because 1045 can be heat treated, it can reach hardness levels that resist wear far better than 1018 ever will, important for components that see repeated friction or impact.
You're building something that needs to survive fatigue. Parts under cyclical stress, like rotating shafts, hold up better in 1045 thanks to its higher inherent strength and its ability to be further hardened if the application calls for it.
You can accommodate the welding tradeoff. If welding is involved, 1045 typically needs preheat and more careful technique to avoid cracking, so it's a better fit when the part is primarily machined rather than welded, or when your shop already has a solid welding procedure for medium carbon steel.
How to tell them apart without a spec sheet
Machining feel: 1018 cuts smoothly and produces long, curling chips. 1045 machines with more resistance and tends to produce shorter, harder chips, especially if it's been heat treated.
Weight and density: Not a reliable differentiator, since both are close in density. Skip this test.
Surface and stock form: 1018 is almost always cold rolled with a smooth finish. 1045 shows up in both hot rolled and cold rolled/turned-and-ground forms, so surface alone isn't a guarantee, but a rough, scaled surface points toward hot rolled 1045 rather than 1018.
Spark test, if you're equipped for it: 1045 throws a noticeably more energetic, branching spark pattern under a grinder than 1018, due to the higher carbon content. This is the most reliable shop-floor test if the material isn't tagged.
1018 and 1045 vs other common grades
1018 vs A36: A36 is a structural hot rolled grade with looser tolerance, generally used for beams, angle, and plate rather than machined components. 1018 is the better choice when you need a cleaner finish and tighter tolerance for machining.
1045 vs 4140: 4140 is a chromium-molybdenum alloy steel that outperforms 1045 in strength and toughness after heat treatment, particularly for demanding applications like high-load shafts or tooling. 1045 is often the more economical middle ground when full 4140-level performance isn't required.
1018 vs 1045, cost difference: 1045 typically costs more per pound than 1018, reflecting the added processing and higher raw material demands of medium carbon steel. For parts where 1018's strength is sufficient, there's no performance reason to pay the 1045 premium.
Buying 1018 or 1045 as remnants
Both grades show up regularly in remnant inventory, and the same general logic applies to both: a remnant piece carries the same chemistry and mechanical properties as a fresh-cut piece from the same grade, just in a leftover size.
For 1018 remnants, the main thing worth checking is whether the piece is long enough and has enough clean surface for your machining setup, since 1018's main value is ease of machining and dimensional consistency.
For 1045 remnants, it's worth asking whether the piece has already been heat treated or is still in its as-rolled condition, since that affects both machinability and whether it's suitable for your application without further processing. A remnant supplier who can tell you the condition, not just the grade, is worth prioritizing here.
The mistake we see most often
Shops sometimes default to 1045 out of an instinct that "stronger is safer," even for parts that never see meaningful load. That means paying a real premium and fighting tougher machining for strength the part doesn't need. The opposite mistake also happens: using 1018 for a shaft or gear that ends up failing under cyclical load because it needed 1045's strength and hardening capability from the start.
The fix is the same one that applies across grade selection generally: match the material to the actual mechanical demands of the part, not to habit or whatever's closest on the shelf.
A quick gut-check before you order
Does this part carry real mechanical load, torque, or repeated stress? If yes, lean 1045.
Does it need to be welded into an assembly? If yes, lean 1018 unless you have a solid procedure for welding medium carbon steel.
Is wear resistance or hardness a requirement? If yes, 1045 gives you the option to heat treat, 1018 does not.
Is this a low-stress machined component where cost and machinability matter most? If yes, 1018 is usually the more efficient choice.