Overview
1018 is the workhorse machine shop bar — the default cold-finished carbon steel for general machined parts. The selection logic is straightforward:
- Better surface and tolerance than A36 — cold drawing produces
smooth finish (
32 Ra mill) and tight dimensional control (±0.001″) - Moderate strength — 38 ksi yield in cold-drawn condition, adequate for most general-purpose parts
- Excellent weldability — slightly more carbon than A36 but still in the routine-weld range
- Cheap — ~$0.75/lb in bar form, modest premium over A36
The position in the carbon steel landscape:
| Need | Choose |
|---|---|
| Hot-rolled structural shapes | A36 |
| Machined general-purpose bar | 1018 |
| Maximum machinability (production) | 12L14 |
| Through-hardenable medium-carbon | 1045 |
| Tool blade / spring | 1095 |
| Heat-treatable alloy steel | 4140 / 4340 |
| Case-hardening (gears, bearings) | 8620 |
1018 cannot be through-hardened — the 0.18% carbon is too low for meaningful quench response. For hardened parts, either carburize 1018 for surface hardness, or specify 1045 (medium carbon, through-hardenable to ~58 HRC) or 4140 (alloy steel, deeper hardenability).
Machining notes
1018 is forgiving and predictable:
- HSS adequate for low-volume; carbide for production
- Speed: 100–250 SFM (HSS) or 200–500 SFM (carbide)
- Feed: 0.005–0.020 in/rev
- Cutting fluid: water-soluble emulsion or straight oil
- Tool life: excellent
The cold-drawn structure breaks chips somewhat better than fully annealed mild steel. For high-volume turned parts where chip control is critical, free-machining 12L14 (leaded) cuts 2–3× faster but is unweldable. For everyday machining where the part might be welded or stressed, 1018 is the better all-around choice.
Surface finish on 1018 is achievable to 16 Ra readily; 8 Ra requires careful sharp-tool finishing. For mirror surface, the limitation is the steel itself (carbide cluster size), not the operation — for true polished surfaces, switch to 416 stainless or specialized alloys.
Heat treatment options
1018 is fundamentally a low-carbon non-hardenable steel. The practical heat treatments are:
- Stress relief (550–650°C) — relieves cold-work and welding residual stress without changing properties significantly
- Normalize (870–925°C, air cool) — improves uniformity after forging or heavy fabrication; eliminates cold-work strengthening
- Anneal (760–800°C, slow cool) — softens for severe forming; rarely needed on cold-drawn bar
- Carburize + quench + temper — case hardening for wear surfaces
Through-hardening by quench: 1018 won’t respond meaningfully. The ~0.18% carbon doesn’t form enough martensite to harden the matrix. For through-hardened parts, use 1045 or higher carbon.
Carburizing 1018 is the standard surface-hardening approach:
- Pack, gas, or salt carburize at 900–925°C
- Quench (water or oil)
- Temper at 150–200°C
- Result: 58–62 HRC surface, soft ductile core
Case depth typically 0.5–1.5 mm. For premium case hardening, 8620 alloy steel gives better core toughness; 1018 is the budget carburizing grade.
Welding considerations
1018 is highly weldable — slightly more carbon than A36 but still routine. All common processes work:
- Stick (SMAW) with E7018 for structural welds
- MIG (GMAW) with ER70S-6 wire
- TIG (GTAW) with ER70S-2 filler
- Oxy-acetylene for thin sections
The cold-work residual stress in CRS bar can release during welding and cause slight warpage on thin sections. Anticipate this — tack- weld in pattern, use fixturing for tight tolerances, and consider stress relief after heavy welding for precision parts.
For welded carburized 1018 parts, weld before carburizing — the HAZ of welds in case-hardened material is unpredictable and can create crack initiation sites.
Corrosion considerations
Same baseline as A36 — none. 1018 rusts in any moist environment. The cold-rolled finish develops rust faster than A36 hot-rolled mill scale in some atmospheres (no protective oxide layer to start). Protection options:
- Oil — simplest, used during storage and inter-process handling
- Black oxide + oil — cosmetic + minor corrosion protection
- Zinc plating — sacrificial corrosion barrier, 5–15 μm typical
- Electroless nickel — better corrosion + wear barrier
- Hard chrome — wear + corrosion for cylinder rods, bearings
- Paint — for outdoor service
- Phosphate + paint — improved adhesion
For applications requiring corrosion resistance without protection, stainless steel is the right material — typical choices are 304 (general purpose) or 17-4 PH (high-strength stainless).
Applications by industry
- Machine shops (general manufacturing) — the dominant industry. Custom shafts, pins, bushings, prototype hardware, fixturing components, drill jigs, test stands.
- Industrial equipment — hardware brackets, lightly stressed shafts, machine-key stock, bushings.
- Automotive — hardware fasteners, brackets, low-stress components.
- Agriculture / construction equipment — lightly stressed pins, hardware, fixturing.
- Cold-headed fasteners — low-strength fasteners (Grade 2 bolts often 1018 cold-headed).
- Prototype and R&D — first-article machined parts where cost and machinability matter more than performance.
- Case-hardened components — gears, cams, sliding components needing wear-resistant surface with ductile core. The budget alternative to 8620.
Failure modes worth designing around
Atmospheric corrosion is the #1 in-service issue. 1018 in any moist environment rusts; protective coating from day one is the design decision, not the field-repair decision.
Specifying 1018 for through-hardening is a common designer error caught at heat treatment. The low carbon won’t respond to quench. For hardened parts, specify 1045 or 4140 from the start.
Galvanic corrosion with stainless or copper in mixed-metal assemblies in moist service — 1018 corrodes preferentially. Use isolation washers, sealants, or matched-potential fasteners.
Decarburization during heat treatment without protective atmosphere — surface carbon depletion reduces case-hardening response and surface fatigue strength. Use protective atmosphere or salt bath for carburizing; leave grinding stock for parts requiring controlled surface composition.
Distortion during welding of thin sections — cold-work stress release plus welding shrinkage. Tack-weld pattern, use clamping fixtures, and consider stress relief after heavy welding for precision-tolerance parts.
Fatigue at machined fillets and sharp transitions — 1018 is fatigue-sensitive at stress concentrations. Polish fatigue-critical surfaces, use generous fillet radii, and consider shot peening for high-cycle parts.
Low-temperature brittleness below -30°C. Not suitable for cryogenic service. For sub-zero applications, use a steel with controlled impact toughness (A516, A537) or stainless.