1018 vs 1020 Carbon Steel: Key Differences Compared

Buyers comparing 1018 vs 1020 carbon steel are usually choosing between two very similar low-carbon grades and trying to understand whether the difference justifies a different price, a different lead time, or a different sourcing strategy. Both grades sit at the lower end of the SAE-AISI carbon steel family, both machine well, both weld without drama, and both are stocked widely across Asia, Europe and North America. Yet the two are not identical, and the gaps in chemistry and supply form show up in real purchase orders, especially when the part is cold drawn, carburized, or destined for high-volume CNC production.

This guide compares 1018 and 1020 side by side on chemistry, mechanical properties, machinability, weldability, formability and cost, then gives a clear selection table you can apply to quotes. It is written for procurement engineers and sourcing managers who need to defend a grade choice on a drawing, not for metallurgists. All figures quoted are typical mill values under SAE J403 and ASTM A29/A510 practice; always confirm the actual heat analysis on the mill test certificate before release.

Chemistry: The Real Difference Between 1018 and 1020

The two grades differ mainly in carbon and manganese targets. AISI 1018 carries a carbon range of 0.15–0.20% with manganese 0.60–0.90%, while AISI 1020 runs slightly higher at 0.18–0.23% carbon with manganese 0.30–0.60%. In plain language, 1018 trades a little carbon for more manganese; 1020 does the opposite. Both keep phosphorus and sulfur below 0.040% in standard quality, and both are produced as fully killed, fine-grained steel when the order specifies it.

In practice this chemistry shift is small. A difference of 0.03% carbon and 0.3% manganese moves tensile strength by only a few percent and barely changes hardness. That is why many buyers treat the grades as interchangeable for generic parts. The distinction starts to matter when a drawing is written to one grade and the supplier offers the other as a substitution: the mechanical property band, the carburizing response and the machinability rating are not perfectly aligned, and an unapproved substitution can void a specification.

Element	AISI 1018	AISI 1020
Carbon (C)	0.15–0.20%	0.18–0.23%
Manganese (Mn)	0.60–0.90%	0.30–0.60%
Phosphorus (P)	0.040% max	0.040% max
Sulfur (S)	0.050% max	0.050% max
Standard	SAE J403 / ASTM A29	SAE J403 / ASTM A29
Delivery form	Cold drawn bar common	Hot rolled bar & plate common

Mechanical Properties Compared

In the hot rolled condition the two grades are nearly twins: tensile strength around 400–450 MPa, yield around 220–250 MPa, and elongation in the 25% range. Cold drawing changes the picture. 1018 is the default cold drawn bar grade in most mills, and cold drawing lifts its yield to roughly 370–450 MPa with a bright surface and tight tolerance. 1020 cold drawn stock exists but is less universal, so buyers who specify 1020 cold drawn often wait longer or pay a premium.

The higher manganese in 1018 gives it a modest edge in hardenability, which matters if the part is carburized or induction hardened after machining. For core strength after case hardening, 1018 typically reaches a slightly higher core hardness than 1020 at the same cycle. Neither grade is intended for through hardening in thick sections — both are low-carbon steels meant to be used as-rolled, cold drawn, or case hardened, not quenched and tempered for high core strength.

Property	1018 hot rolled	1018 cold drawn	1020 hot rolled
Tensile strength	400 MPa typ.	440 MPa typ.	420 MPa typ.
Yield strength	220 MPa typ.	370 MPa typ.	230 MPa typ.
Elongation (50 mm)	25%	15–20%	25%
Hardness (HB)	≤126	126–160	≤131
Machinability rating	78%	78% (drawn)	70%

Machinability: Where 1018 Usually Wins

On the shop floor the choice is decided by chips per hour more than by tensile curves. 1018 has a reputation as one of the friendliest low-carbon steels to machine: the carbon-manganese balance, combined with how the grade is supplied (cold drawn, sometimes with a lightly spheroidized structure), gives clean chip breaking and stable tool life in drilling, turning and threading. Its machinability rating is commonly listed at about 78% of B1112 reference steel.

1020 machines acceptably but runs a few points lower, around 70%, because the standard hot rolled supply form has a coarser ferrite-pearlite banding. In high-volume Swiss turning or multi-spindle work, that difference translates into shorter tool change intervals and slightly more scrapped inserts per thousand parts. Shops that run mixed-grade stock often standardize on 1018 cold drawn precisely to hold one proven cutting recipe across many part numbers.

Weldability: Both Are Excellent

Both grades weld beautifully by every common process — SMAW, GMAW, GTAW and even spot welding in sheet form. With carbon below 0.23% and low alloy content, neither grade needs preheat for sections up to roughly 25 mm, and both tolerate high heat input without cold cracking. For structural weldments in plate or bar, either grade is a safe choice when matched with a standard E7018 or ER70S-6 filler.

The only practical cautions are the same for both grades: thick sections still benefit from a modest preheat of 50–100°C in cold workshops, and carburized or heavily cold-worked surfaces should be ground back to sound metal before welding. For 1018 specifically, the higher manganese slightly raises hardness in the HAZ, but at these low carbon levels the effect is negligible and post-weld heat treatment is rarely specified.

Formability and Case Hardening

Both grades cold form well: brackets, clips, bushings and rolled threads are routine. 1020, with a touch more carbon, has a marginally higher yield in the as-rolled state, so it resists springback slightly more in deep drawing. 1018, especially in the cold drawn condition, is the more common choice for parts that need tight as-drawn dimensions straight off the bar without a sizing pass.

For case hardening, both respond predictably. A standard gas carburizing cycle at 900–925°C with an oil quench and temper produces a hard wear-resistant case over a tough low-carbon core. The case hardness lands in the 55–62 HRC band for either grade. 1018 again has the mild edge because its manganese supports a slightly deeper hardening response in thin cases, which is why it remains the workhorse for small pins, gears and shafts that see wear but not shock.

Availability, Supply Form and Lead Time

This is often the deciding factor for international buyers. 1018 dominates the cold drawn bar market in Asia: Chinese, Indian and Korean mills routinely produce it, so stock sizes from 6 mm to 150 mm diameter ship in days and unusual sizes are drawn to order in two to three weeks. 1020 is widely stocked as hot rolled bar and plate, but cold drawn 1020 is a thinner market — several mills simply quote 1018 as the nearest equivalent.

If your drawing says 1020 and the part is a machined round bar, expect most Asian suppliers to offer a 1018 substitution with an equivalence note. If the drawing says 1018, substitutions flow the other way only for plate products. Writing the grade and the supply form explicitly on the purchase order — for example “1018 cold drawn bar, ASTM A108” — avoids the classic mismatch where a buyer expects bright bar and receives black hot rolled stock.

Cost Comparison in Real Quotes

As a rule of thumb, hot rolled 1020 is the cheapest of the pair, cold drawn 1018 sits 8–15% above hot rolled 1020 for the same nominal size, and cold drawn 1020 (when it must be specially drawn) can cost 20–30% more than standard 1018 bright bar. Freight and MOQ shift these numbers, but the ordering usually holds: if your part tolerates either grade, buying 1018 cold drawn is normally the lower total cost once machining time is counted.

Buyers should also weigh scrap and rework. A grade that machines 10% faster and holds tolerance more predictably often pays back its nominal price premium through insert life and first-pass yield. That is why procurement teams who evaluate cost per finished part, rather than cost per kilogram, frequently land on 1018 cold drawn even when a cheaper 1020 quote is on the table.

Selection Table: Which Grade for Which Part

Application	Better choice	Reason
High-volume CNC turned parts	1018 cold drawn	Best machinability, tight as-drawn tolerance
Carburized pins, gears, cams	1018	Higher Mn gives better case response
Structural weldments in plate	1020	Plate stock widely available, welds equally well
General hot rolled bar stock	1020	Lowest cost per kg in common sizes
Cold formed brackets and clips	Either	Both form well; pick on availability
Threaded fasteners and studs	1018	Cleaner thread rolling, fewer splits

Procurement Checklist Before You Order

1. Confirm the drawing grade and whether the supplier substitution policy allows the other grade.
2. Specify the supply form: hot rolled, cold drawn (ASTM A108), or bright bar.
3. State the size tolerance standard (e.g. cold drawn bar tolerance class) on the PO.
4. Require an EN 10204 3.1 mill test certificate with actual heat chemistry.
5. Agree cut lengths and chamfer requirements before quoting to avoid resheeting costs.
6. For export orders, confirm packing (bundled, oiled, ISPM 15 crates) and inspection scope.

How to Handle Substitution Requests

When a supplier proposes 1018 in place of 1020 (or the reverse), evaluate three points: the mechanical property band against the drawing, the heat treatment or case hardening route, and the machining process already validated. If the part is a simple welded bracket, substitution is almost always safe. If the part is a carburized gear validated with 1020 chemistry, a 1018 substitution should trigger a small engineering review, because case depth and core hardness will shift slightly even though both grades are nominally “the same class” of steel.

Document the decision on a deviation note with the actual heat analysis attached. This keeps the supplier accountable to the substitution and protects you in any later quality dispute. Factories that manage grade substitutions this way avoid the two classic traps: silent substitutions discovered at incoming inspection, and spec drift where successive lots creep away from the original design intent.

Frequently Asked Questions

Is 1020 stronger than 1018?

Marginally, in the as-rolled condition, because 1020 carries slightly more carbon. The difference is a few percent in tensile strength and is rarely decisive. In cold drawn bar, 1018 often delivers equal or higher yield because it is the grade mills routinely draw.

Can I weld 1018 and 1020 to each other?

Yes. Dissimilar low-carbon grades weld freely with standard E7018 or ER70S-6 filler and no preheat for normal section sizes. Match the filler strength to the lower-grade member and clean mill scale from the weld zone first.

Which grade is better for carburizing?

1018 is the conventional choice because its higher manganese content deepens the hardening response for a given case depth. 1020 carburizes perfectly well too, but 1018 is the standard stock item for case hardened small parts.

Are 1018 and 1020 equivalent to S20C or C22?

Broadly yes at the carbon band level: JIS S20C and DIN C22/CK22 bracket the same 0.18–0.23% carbon region as 1020, while 1018 sits a touch lower. They are treated as near-equivalents for most applications, but manganese ranges and testing requirements differ, so confirm against the governing specification.

Cold Working, Residual Stress and Dimensional Stability

Cold drawn bar of either grade carries residual stress from the drawing pass. For most machined parts this is irrelevant, but for long slender parts — shafts above roughly 20 times diameter, precision rollers, screw stock — the stored stress releases as material is removed, and the part bows. The standard remedy is a stress relief at 550–650°C before finish machining, and it applies equally to 1018 and 1020. Buyers ordering long bright bar for precision shafting should discuss straightness after machining with the supplier up front, not discover the bow at final inspection.

1020’s slightly lower manganese gives it a marginally lower as-drawn residual stress in some mills’ practice, but the effect is within lot-to-lot variation and should not drive grade selection. What does matter is consistency: buying both grades from one mill keeps the drawing schedule, grain size and residual stress profile uniform across your part range, which stabilizes your machining process more than any grade-level decision.

Inventory Strategy: Carrying Both Grades or Standardizing

Distributors and captive shops face a stocking decision: carry both 1018 and 1020, or standardize on one. Standardizing on 1018 cold drawn covers machined bar demand with the best machining economics; a small hot rolled 1020 plate position covers weldment and bracket work. That two-line strategy covers the real demand of most job shops with minimal working capital tied up in slow-moving sizes.

Standardizing also simplifies quality. One incoming inspection procedure, one set of supplier qualifications, one material database mapping heat numbers to part numbers. Multi-grade inventories invite mix-ups at the saw — and a 1020 blank ground into a 1018 part is invisible until the certificate audit, by which time the error has already shipped to your customer.

Quality Documents and Incoming Inspection

Whichever grade you buy, demand an EN 10204 3.1 certificate showing heat chemistry and mechanical results, and tie the heat number on the certificate to the tag on the bundle at receiving. A five-minute receiving check — chemistry inside the 1018 or 1020 band, yield and tensile above minimum, heat number match — catches the two most common supplier errors: mixed heats bundled under one tag, and certificates issued to the wrong standard edition.

For cold drawn bar specifically, add dimensional verification of diameter and straightness on a sample per bundle, and a surface check for die marks and draw cracks. Both grades draw cleanly, but die wear at the mill occasionally scores the surface; catching scored bar at receiving converts a rejection into a replacement shipment instead of a machining-floor dispute three weeks later.

Cost of Ownership Beyond the Price per Kilogram

The cheapest quote per tonne is rarely the cheapest per finished part. Machining time dominates the cost of high-volume low-carbon steel components, and 1018’s documented machining advantage — faster speeds, longer insert life, better chip control in small-diameter work — typically saves 5–10% of cycle time against hot rolled 1020. On a part machined in seconds that saving is trivial; on a part machined in minutes across a million-piece program it outweighs any material premium several times over.

Add the softer costs: fewer tool changes, less inspection sampling from stable tolerance, fewer rejections from surface defects, and simpler substitution management. Procurement teams who model cost per part rather than cost per kilogram consistently justify the bright-bar premium — and their machining departments, who feel the difference every shift, will defend the choice for them.

Reading the Certificate: 1018 or 1020 in Disguise

Because the chemistry bands are close, a careless mill or an optimistic trader sometimes ships one grade under the other’s name. The certificate exposes it immediately: check that the actual carbon and manganese fall inside the band for the grade you ordered, not merely inside the SAE J403 family. A heat reading 0.21% carbon with 0.45% manganese is 1020, no matter what the invoice says — and if your drawing required 1018 for its machining behaviour, that discrepancy is worth a deviation note rather than a shrug.

Buyers running supplier scorecards should track grade conformity as its own line. Suppliers who ship the right grade, right form and right certificate the first time are measurably cheaper to work with even at a nominally higher price, because every substitution quietly costs engineering review time, incoming inspection friction and sometimes a scrapped machining program validated for different chips.