Author: Site Editor Publish Time: 2026-10-07 Origin: Site
1020, 1045 and 1050 are three grades from the same AISI/ASTM A29 plain carbon family. Their chemistry differs by less than half a percent of carbon — 0.20%, 0.45% and 0.50% respectively — yet those few hundredths of a percent change everything that matters in procurement: strength, weldability, machinability, hardenability and the applications the steel is fit for. This article walks the carbon-content ladder from low to medium-high and explains, in engineering terms, why each step changes the recommended use.
The three grades share the same AISI 10xx plain carbon family and the same nominal manganese and silicon ranges. The variable is carbon, and it does most of the work.
| Grade | Carbon range (%) | Mn (%) | Category | Typical hardness, hot-rolled (HB) |
|---|---|---|---|---|
| 1020 | 0.18–0.23 | 0.30–0.60 | Low-carbon (mild) | 111–156 |
| 1045 | 0.43–0.50 | 0.60–0.90 | Medium-carbon | 163–192 |
| 1050 | 0.48–0.55 | 0.60–0.90 | Medium-carbon (upper) | 170–210 |
The category label is loose — metallurgists sometimes call 1050 "high carbon," though steels above 0.60% C are more properly named that way. In procurement language: 1020 is the structural and welded grade, 1045 is the general-purpose medium-strength grade, and 1050 is the wear-and-spring grade. Reading down the table, carbon climbs, hardness climbs, and the things you can do with the steel change.
| Element (%) | 1020 | 1045 | 1050 |
|---|---|---|---|
| Carbon (C) | 0.18–0.23 | 0.43–0.50 | 0.48–0.55 |
| Manganese (Mn) | 0.30–0.60 | 0.60–0.90 | 0.60–0.90 |
| Silicon (Si) | 0.15–0.35 | 0.15–0.35 | 0.15–0.35 |
| Phosphorus (P), max | 0.040 | 0.040 | 0.040 |
| Sulfur (S), max | 0.050 | 0.050 | 0.050 |
Nothing else is alloyed in. These are true plain carbon steels — no chromium, no molybdenum, no nickel. That means they are cheap, magnetic, forgeable and weldable, but their hardenability is low and their maximum useful section for through-hardening is small. Where through-hardened medium-strength bar is required, the upgrade path is to alloy grades like AISI 4140 Cr-Mo steel bar, which carries 0.80–1.10% chromium and 0.15–0.25% molybdenum and through-hardens in oil to ~50 mm.
The numbers below are typical for hot-rolled round bar in the 25–50 mm range, as-supplied (no heat treatment).
| Property | 1020 (HR) | 1045 (HR) | 1050 (HR) |
|---|---|---|---|
| Tensile strength, MPa | 410–430 | 565–625 | 580–640 |
| Yield strength (0.2%), MPa | 245–295 | 310–370 | 325–385 |
| Elongation in 2 in., % | 15–20 | 12–16 | 10–12 |
| Reduction of area, % | 40–55 | 30–40 | 25–35 |
| Hardness, Brinell | 111–156 | 163–192 | 170–210 |
| Machinability rating (% of B1112) | ~65 (cold-drawn) / ~50 (HR) | ~57 | ~55 |
| Weldability rating | Excellent | Moderate (preheat 150 °C) | Limited (preheat 200 °C + PWHT) |
Three patterns are worth reading carefully:
Strength scales with carbon — but only up to a point. The jump from 1020 to 1045 is large (roughly 40% higher tensile); the jump from 1045 to 1050 is small. Above 0.50% carbon, each incremental tenth of a percent buys less and less strength while costing more and more toughness.
Ductility falls faster than strength rises. Elongation drops from 15–20% in 1020 to 10–12% in 1050. Reduction of area falls by roughly 30 percentage points across the three grades. For any part that must deform before failing, that trend matters.
Weldability falls off a cliff at 0.30% carbon. Below that line (1020), the steel welds like structural steel. Above it (1045, 1050), preheat and post-weld heat treatment become mandatory, and the weld metal itself is at risk of hydrogen-induced cracking.
1020 is the lowest-carbon grade in this comparison and the one most specified for welded structures, sheet and plate fabrication, carburized parts, and formed sections. With carbon at 0.20%, its as-rolled strength is modest (around 410 MPa UTS), but it pays you back in three ways:
Weldability. No preheat required for thin to medium sections. MIG, TIG, stick and submerged arc all run cleanly. The carbon equivalent (CE) sits around 0.30–0.35, well below the threshold where hydrogen cracking becomes a concern.
Formability. 1020 bends, deep-draws and rolls without cracking. The 15–20% elongation in hot-rolled bar becomes 25–30% in cold-drawn stock, which is why 1020 cold-drawn seamless tube and 1020 sheet are the standard materials for stampings, brackets and drawn cups.
Carburizing response. 1020 is the textbook carburizing grade: pack, gas or vacuum carburize at 900–925 °C, oil quench, temper at 150–200 °C, and you get a 58–62 HRC case over a 25 HRC tough core. This is the standard route for low-cost wear parts: gear teeth, cam surfaces, bushings, pins.
The limits of 1020 are equally clear. It cannot through-harden — carbon is too low to form enough martensite — so it is unsuitable for any part that needs through-section strength above ~300 MPa yield. It machines poorly in the hot-rolled condition (soft, gummy chips), but improves markedly in cold-drawn stock where the work-hardened surface gives cleaner turning.
1045 is the workhorse of the medium-carbon family. With carbon at 0.43–0.50%, it sits in the middle of the band that gives a useful combination of strength, machinability and modest hardenability. It is the grade most commonly specified for:
Machined shafts and pins in the 20–50 mm range, where strength of 600 MPa UTS is enough but through-hardening is not required.
Induction- and flame-hardened wear surfaces — gear teeth, spline shafts, hydraulic rod surfaces. The carbon content is high enough to form 55–60 HRC martensite in the induction-heated surface, while the core stays at 25–30 HRC and tough.
Bolts, keys, ratchets, hand tools where a wear-resistant surface and reasonable core strength are both wanted, but the loading is not severe enough to justify alloy steel.
Wear plates, low-stress dies, guide rails — parts where surface hardness matters more than through-section strength.
Heat treatment of 1045 is straightforward. Austenitize at 815–845 °C, water or brine quench for thin sections (oil for parts up to ~12 mm to avoid cracking), and temper at 150–200 °C for maximum hardness or 425–540 °C for toughness. The grade is sensitive to quench cracking above 25 mm section in water; for larger shafts that have to carry fatigue, the right answer is to step up to AISI 4130 Cr-Mo steel or 4140, both of which through-harden in oil to larger sections.
Weldability of 1045 is moderate. With CE around 0.55–0.65, preheat to 150–200 °C and low-hydrogen consumables (E7018, ER70S-6) are needed. Post-weld stress relief at 550–650 °C is recommended for restrained joints. 1045 should not be specified for welded structural assemblies where PWHT is impractical; 1020 (or a structural grade like A36) is the better call.
1050 sits one notch above 1045 in carbon, and that notch matters more than it might seem. The 0.05% extra carbon pushes the as-rolled hardness up to 170–210 HB and, more importantly, the as-quenched hardness to 60–63 HRC — the practical ceiling for plain carbon steels before excessive brittleness sets in.
1050 is specified for:
Flat springs and leaf springs for low-stress applications. The temper window of 400–500 °C gives a useful combination of elasticity and toughness (≈45–50 HRC).
Hand tools — hammers, chisels, punches, shear blades. The wear surface is induction- or flame-hardened to 55–60 HRC over a tempered core.
Wear plates, scraper blades, agricultural implement edges where abrasion is moderate and impact is low.
Lock washers, retaining rings, spring clips in the cold-rolled and tempered condition.
The trade-off is brittleness. 1050 in the as-quenched condition has impact toughness below 10 J at room temperature, which is unacceptable for any part that sees shock loading. Tempering is mandatory, and even after tempering at 425 °C, Charpy values stay around 15–20 J. For parts that combine wear with impact, the right answer is an alloy grade such as 4140 or 4150, or a tool steel — not 1050.
Welding 1050 is a special case. With CE above 0.75, the grade requires preheat to 200–250 °C, low-hydrogen consumables matching the carbon (E8018 or ER80S-D2), and immediate post-weld stress relief. In practice, 1050 is rarely welded; parts are designed as one-piece forgings or machined from solid.
To make the relationship explicit, here is how the three properties change with the carbon ladder:
| Property trend (as carbon rises 0.20 → 0.45 → 0.50) | Direction | Practical consequence |
|---|---|---|
| Tensile and yield strength | ↑ | 1045/1050 carry roughly 40–55% higher strength than 1020 |
| Elongation and reduction of area | ↓ | 1050 has half the ductility of 1020 |
| Hardness (hot-rolled) | ↑ | 1020 ~130 HB, 1045 ~180 HB, 1050 ~190 HB |
| Through-hardenability | (slight ↑) | All three still low — carbon alone does not deepen hardening |
| Surface hardenability (case) | ↑ | 1020 carburizes well; 1045/1050 induction-harden to 55–63 HRC |
| Machinability (hot-rolled) | ↓ | 1020 chips are gummy; 1045 and 1050 cut cleaner once hardened |
| Weldability | ↓ sharply | 1020 welds freely; 1045 needs preheat; 1050 rarely welded |
| Quench-crack risk | ↑ | Water quenching 1050 in section >12 mm is risky |
| Cost (per kg, common sizes) | ~ flat | 1020 cheapest; 1045 and 1050 within 10–15% of each other |
| Application | Loads | Recommended grade | Reasoning |
|---|---|---|---|
| Welded brackets, frames, structural tubes | Static, welded | 1020 | Welds without preheat; cheap; formable |
| Carburized gears, bushings, pins (low load) | Surface wear only | 1020 (carburized) | Cheap core + 58–62 HRC case |
| Stamped and drawn parts, sheet fabrication | Forming | 1020 (cold-drawn) | Best ductility of the three |
| General-purpose machined shafts, 20–50 mm | Bending + torsion | 1045 | Good strength-to-cost; machines well |
| Induction-hardened gear teeth, splines | Surface wear + moderate core load | 1045 (induction hardened) | 55–60 HRC case over 25 HRC core |
| Keys, ratchets, hand tools (medium wear) | Wear + moderate impact | 1045 or 1050 | Hardenable to 55–58 HRC |
| Flat springs, leaf springs (low stress) | Repeated elastic bending | 1050 (tempered 45–50 HRC) | High elastic limit |
| Hammers, chisels, shear blades | Impact + wear | 1050 (surface hardened) | 60+ HRC surface; cheap |
| Wear plates, scraper blades | Abrasion | 1050 | Best plain-carbon wear resistance |
| Hydraulic cylinder rods (medium duty) | Surface wear + tensile | 1045 (chrome plated) | Standard industry choice |
| Shafts over 75 mm, fatigue-critical | Bending + fatigue | None of these — go to 4140 | 1045/1050 will not through-harden |
| Springs with impact or repeated shock | Cyclic + impact | None of these — go to 5160 / 6150 | 1050 lacks the alloy toughness for cyclic loads |
Will the part be welded in service? Yes → 1020. Above 0.30% carbon, welding becomes a defect risk.
Is the loading primarily surface wear, with a soft or low-stress core? Yes → 1020 carburized, or 1045/1050 induction hardened depending on core load.
Is the loading moderate tensile and bending, with no through-hardness requirement? Yes → 1045. The general-purpose answer.
Is the part a wear edge, spring, or hand tool taking abrasion but little shock? Yes → 1050. Hardenable to 60+ HRC; cheap.
Does the part see cyclic impact, fatigue, or large section that must through-harden? Yes → none of these three. Step up to AISI 4140 alloy steel for shafting, or 5160 / 6150 for springs.
Q: Can I use 1045 instead of 1050 for springs?
For low-stress flat springs, yes — 1045 tempered at 425–500 °C reaches 45–50 HRC and works. For higher elastic limits or repeated cycling, 1050 is the better choice, and for impact-loaded springs both grades are inadequate — specify an alloy spring steel (5160, 6150, 9260).
Q: Why is 1020 so much weaker than 1045?
Carbon at 0.20% forms less martensite on quenching and a softer pearlite-ferrite microstructure in the hot-rolled condition. The difference is metallurgical and fundamental — strength in plain carbon steel tracks carbon content closely.
Q: Is 1050 a "high-carbon" steel?
By the AISI convention, steels above 0.60% C are high-carbon. 1050 sits at the top of the medium-carbon range (0.48–0.55%), though it is sometimes informally called high-carbon. The behavior is closer to medium-carbon than to true tool steels.
Q: Which grade is best for threading and spline cutting?
Cold-drawn 1045 cuts the cleanest threads of the three. Hot-rolled 1020 produces gummy chips that tear threads; 1050 in the hardened condition is too abrasive on tooling.
Q: Can I induction-harden 1020?
Not usefully. With 0.20% carbon, induction hardening produces only about 40–45 HRC — barely higher than the cold-drawn core. For an induction-hardened wear surface, you need at least 0.40% carbon, which is the floor of 1045.
If you are sizing a part and want a second opinion on whether 1020 will hold, 1045 is the right call, or 1050 earns its place, send the drawing and the load case. Qilu Metal supplies hot-rolled, cold-drawn, peeled, Q&T and induction-hardened bars in all three grades to ASTM A29, EN 10083-2 and JIS standards, with mill test reports and full traceability. Email enquiry@qilumetal.com and our metallurgy team will come back with a quotation and a heat-treatment recommendation matched to your section size and load.
