1. Why Three Grades, Not One
A buyer who scans a steel catalogue sees SAE1020, C45E and 51CrV4 listed under "carbon and alloy steel strip" and might assume they are interchangeable options for the same part. They are not. Each grade occupies a distinct rung on the carbon-and-alloy ladder, and moving up one rung changes nearly every property that matters — weldability, formability, hardenability, machinability, fatigue life and cost.
The mistake that causes the most scrap is specifying a grade by habit rather than by requirement. A part designed for SAE1020 that gets quoted in C45E will be harder to blank, impossible to weld without preheat, and more expensive. A part designed for 51CrV4 that gets substituted with C45E will fail in fatigue long before the design life. The right question is never "which is better" — it is "which set of tradeoffs matches this part's loading, processing and budget."
1.1 The carbon and alloy ladder
Carbon is the single most influential element in steel. Every 0.10% increase in carbon raises tensile strength by roughly 70–100 MPa in the normalized condition, but it also reduces ductility, weldability and cold formability. Alloying elements — chromium, vanadium, manganese — shift the curve further by improving hardenability (the depth to which the steel hardens during quenching) and temper resistance (the ability to hold strength at higher tempering temperatures).
SAE1020 sits at the bottom of the ladder: low carbon, no intentional alloying. C45E sits in the middle: medium carbon, enough to through-harden in thin sections, no intentional alloy beyond manganese. 51CrV4 sits at the top: medium carbon plus chromium and vanadium, designed for deep hardening and high-temperature temper resistance in spring applications.
1.2 What each grade was designed for
SAE1020 was designed as a general-purpose low-carbon steel for welded structures, cold-formed brackets, carburized pins and shafts where the surface needs hardness but the core needs toughness. Its defining feature is weldability — with a carbon equivalent typically below 0.35, it can be joined by nearly every welding process without preheat. Its defining limitation is that it cannot be through-hardened; quenching produces at most a thin, shallow-hard case, and the core remains soft and ferritic-pearlitic.
C45E was designed as a medium-carbon engineering steel for machine parts that need a balance of strength and toughness after quenching and tempering. Shafts, gears, spindles, bolts and tool holders are its territory. It can be through-hardened in sections up to roughly 20–30 mm in oil, and it machines reasonably well in the annealed or normalized condition. Its defining limitation is weldability — the carbon equivalent sits around 0.55–0.65, and cold cracking is a real risk without preheat and post-weld heat treatment.
51CrV4 was designed as a spring steel. The chromium improves hardenability so that thick spring sections harden through, and the vanadium forms fine carbides that pin grain boundaries and resist softening during tempering. The result is a steel that can be tempered at 400–500°C to a tensile strength of 1300–1600 MPa while retaining enough toughness for cyclic loading. Its defining limitation is cost — both the raw material premium and the more demanding heat treatment — and its near-unweldability.
2. Chemical Composition Compared
The table below lists the chemical composition ranges for each grade under its governing standard. SAE1020 follows AISI/SAE J403 and ASTM A29 / A108. C45E follows EN 10083-2 (the "E" suffix denotes improved sulfur control for better machinability, with S ≤0.030%). 51CrV4 follows DIN 17221 / EN 10089 for spring steels. Values are typical of the latest revision; always refer to the current edition of the standard and the supplier's mill test certificate for the heat you are buying.
| Element | SAE1020 (AISI/ASTM) | C45E (EN 10083-2) | 51CrV4 (DIN 17221 / EN 10089) |
|---|---|---|---|
| Carbon (C) | 0.18 – 0.23% | 0.42 – 0.50% | 0.47 – 0.55% |
| Manganese (Mn) | 0.30 – 0.60% | 0.50 – 0.80% | 0.70 – 1.10% |
| Chromium (Cr) | ≤ 0.25% (residual) | ≤ 0.40% (residual) | 0.90 – 1.20% |
| Vanadium (V) | — | — | 0.10 – 0.25% |
| Silicon (Si) | ≤ 0.15% | ≤ 0.40% | 0.15 – 0.40% |
| Phosphorus (P) | ≤ 0.040% | ≤ 0.030% | ≤ 0.025% |
| Sulfur (S) | ≤ 0.050% | ≤ 0.030% | ≤ 0.025% |
Composition limits are indicative and based on standard specifications. Actual heat chemistry varies within these windows; confirm against the mill test certificate. SAE1020 may be supplied with lead addition (1020Pb) for improved machinability — confirm at RFQ. 51CrV4 is equivalent to 50CrV4 (GB/T 1222) and closely related to SAE 6150; the chemistry windows overlap but are not identical.
Three observations from the table drive every property difference that follows:
- Carbon doubles from SAE1020 to C45E. Moving from 0.20% to 0.46% carbon is the difference between a steel that cannot through-harden and one that can. It is also the difference between a steel that welds freely and one that needs preheat.
- Chromium and vanadium appear only in 51CrV4. The ~1% chromium raises hardenability dramatically — a 51CrV4 part through-hardens at section thicknesses where C45E would only case-harden. The ~0.15% vanadium forms MC-type carbides that refine grain size and resist over-tempering, which is why 51CrV4 can be tempered to high strength without becoming brittle.
- Phosphorus and sulfur tighten up the ladder. SAE1020 allows up to 0.050% S; 51CrV4 caps both P and S at 0.025%. Lower sulfur improves fatigue life (sulfide inclusions are fatigue crack initiation sites), which matters for a spring steel but is less critical for a welded bracket.
3. Mechanical Properties by Condition
Mechanical properties for these three grades are not single numbers — they depend entirely on the heat-treatment condition. SAE1020 is almost always supplied in the annealed or cold-finished condition because heat treatment does not meaningfully change its strength. C45E and 51CrV4 are typically supplied annealed for machining and forming, then quenched and tempered by the part maker to reach the target strength. The tables below present typical property bands for each condition.
3.1 Annealed and normalized condition
| Grade | Condition | Yield strength (MPa) | Tensile strength (MPa) | Elongation A5 (%) | Hardness |
|---|---|---|---|---|---|
| SAE1020 | Annealed | 290 – 350 | 440 – 520 | 30 – 36 | HB 120 – 140 |
| SAE1020 | Cold drawn / strip | 350 – 450 | 500 – 600 | 15 – 25 | HB 140 – 170 |
| C45E | Annealed | 300 – 380 | 580 – 680 | 16 – 22 | HB 170 – 200 |
| C45E | Normalized | 340 – 420 | 620 – 720 | 14 – 20 | HB 180 – 210 |
| 51CrV4 | Annealed (soft) | ≤ 600 | ≤ 900 | ≥ 12 | HB ≤ 255 |
| 51CrV4 | Spheroidized annealed | 400 – 550 | 650 – 800 | 18 – 25 | HB 190 – 230 |
Typical values for strip and thin-section material. SAE1020 cold-drawn properties depend on reduction ratio. C45E annealed hardness per EN 10083-2 is typically ≤HB 229 (annealed) or ≤HB 255 (normalized). 51CrV4 annealed hardness per EN 10089 is ≤HB 255 for delivery condition; spheroidized annealing is specified for cold heading and fine blanking. Actual values vary by section size and heat-treatment practice — confirm on the mill test certificate.
In the annealed condition, the strength gap is already visible: C45E runs roughly 150 MPa higher tensile than SAE1020, and 51CrV4 (even in the soft spheroidized condition) runs higher still. But the annealed condition is not where these grades earn their keep — C45E and 51CrV4 are meant to be heat treated after forming.
3.2 Quenched and tempered condition
This is the table where the three grades diverge most sharply. SAE1020 does not meaningfully respond to quenching and tempering — it is included for completeness. C45E and 51CrV4 are transformed by the quench-and-temper cycle into high-strength engineering steels.
| Grade | Quench | Temper | Yield (MPa) | Tensile (MPa) | Elong. A5 (%) | Hardness |
|---|---|---|---|---|---|---|
| SAE1020 | Water (no significant harden.) | — | 300 – 400 | 450 – 550 | 20 – 30 | HRC ≤ 25 |
| C45E | Water / oil, 820–860°C | 500–600°C | 450 – 650 | 600 – 800 | 14 – 17 | HRC 20 – 30 |
| C45E | Water, 820–860°C | 300–400°C | 700 – 900 | 850 – 1000 | 8 – 12 | HRC 30 – 40 |
| 51CrV4 | Oil, 830–870°C | 400–500°C | 1100 – 1300 | 1300 – 1600 | 6 – 10 | HRC 43 – 50 |
| 51CrV4 | Oil, 830–870°C | 500–600°C | 900 – 1100 | 1100 – 1300 | 8 – 12 | HRC 35 – 42 |
Properties are typical for section thickness ≤16 mm after quenching and tempering. C45E water-quenched sections above ~20 mm may not through-harden; oil quenching gives a shallower hardening depth. 51CrV4 properties per EN 10089 for strip thickness ≤16 mm: yield ≥1100 MPa, tensile 1300–1600 MPa, elongation ≥6% at the high-strength temper. Fatigue limit (rotating bending, 10^7 cycles) for properly heat-treated 51CrV4 is typically 450–550 MPa; for C45E Q&T it is typically 280–360 MPa. Confirm heat-treatment parameters with your heat treater for the specific section size.
The pattern is clear. C45E in the standard quench-and-temper condition (tempered at 500–600°C for toughness) lands at 600–800 MPa tensile — the sweet spot for shafts, gears and general machinery. If tempered lower for more strength, it can reach 850–1000 MPa but elongation drops to 8–12%, and the part becomes notch-sensitive. 51CrV4, even when tempered at a relatively high 400–500°C, reaches 1300–1600 MPa tensile with 6–10% elongation — a strength-toughness combination that C45E cannot match because C45E lacks the chromium and vanadium to resist temper softening.
4. Application Scenario Decision Table
The table below maps the three grades to the application scenarios where each is the correct specification. Work down the rows; the grade that matches the most rows is the grade your part needs.
| Application scenario | SAE1020 | C45E | 51CrV4 |
|---|---|---|---|
| Welded structural brackets, frames, supports | ✓ Primary grade | △ Needs preheat | ✗ Not recommended |
| Cold-formed clips, housings, simple stampings | ✓ Primary grade | △ Marginal | ✗ Too hard |
| Carburized pins, shafts, gears (hard case, tough core) | ✓ Primary grade | — | — |
| Quenched-and-tempered shafts, spindles, axles | ✗ Insufficient strength | ✓ Primary grade | △ Over-specified |
| Gears, sprockets, tool holders (moderate strength) | ✗ | ✓ Primary grade | △ Over-specified |
| Bolts, studs, fasteners (8.8 / 10.9 class) | ✗ | ✓ Primary grade | △ |
| Leaf springs, coil springs, suspension components | ✗ | ✗ Fatigue insufficient | ✓ Primary grade |
| Clutch discs, diaphragm springs, brake parts | ✗ | ✗ | ✓ Primary grade |
| High-cycle fatigue parts (>10^6 cycles) | ✗ | △ Marginal | ✓ Primary grade |
| Fine blanked parts (spheroidized condition) | △ Low strength | ✓ Common | ✓ Available |
Application mapping is based on typical industry practice. Specific part requirements (load, section size, environment, regulatory standard) may justify a different grade. For fine blanking, both C45E and 51CrV4 are supplied in spheroidized-annealed condition with controlled hardness band — see the fine blanking steel product page for the full grade range.
SAE1020's territory is welded and formed parts where strength is not the governing constraint. If the part is a bracket, a frame, a clip or a carburized pin, SAE1020 is the most economical choice and the easiest to process. C45E's territory is heat-treated machinery parts where moderate strength (600–800 MPa) is needed and the part is not under high cyclic load. 51CrV4's territory is springs and high-cycle fatigue components — the clutch disc spring application page and spring steel strip product page cover this family in detail.
5. Processing Performance Compared
A grade that has the right mechanical properties can still be the wrong choice if it cannot be processed with the equipment and skill available in your shop. The table below compares the three grades across the four processing dimensions that cause the most production problems.
| Processing dimension | SAE1020 | C45E | 51CrV4 |
|---|---|---|---|
| Weldability | Excellent — CE ~0.30, no preheat needed for most thicknesses; all standard processes | Poor — CE ~0.55–0.65; preheat 150–250°C, low-H consumables, PWHT recommended | Very poor — CE >0.75; welding generally discouraged; if unavoidable, preheat 250–350°C, immediate stress relief |
| Machinability | Good in cold-drawn condition; gummy in annealed; leaded variant (1020Pb) available | Good in annealed/normalized (HB 170–210); harder after Q&T requires carbide tools | Fair in spheroidized annealed; poor in hardened condition; requires rigid setup and sharp tooling |
| Hardenability | Very low — cannot through-harden; shallow case only; carburizing required for hard surface | Moderate — through-hardens in water up to ~20 mm section; oil quench for thinner sections | High — through-hardens in oil up to ~40–50 mm section; Cr and V ensure deep hardening |
| Cold formability | Excellent — high ductility (El 30–36% annealed); suitable for deep drawing, bending, cold heading | Fair — moderate ductility (El 16–22% annealed); suitable for simple bending, not deep drawing | Poor in annealed (El ≥12%); good only in spheroidized condition (El 18–25%) for fine blanking |
Carbon equivalent (CE) calculated per IIW formula: CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. Weldability guidance is general — always follow the welding procedure specification (WPS) for your specific joint design and thickness. Machinability ratings are relative; actual cutting speeds and feeds depend on the tool material, coolant and operation. For fine blanking of C45E and 51CrV4, spheroidized annealing is mandatory — see our spheroidizing annealing guide.
Weldability is the dimension where the three grades are most different, and it is the one most often overlooked at the specification stage. SAE1020 can be dropped into a welded assembly with no special handling. C45E requires a welding procedure with preheat — if your shop does not have preheat capability, C45E welds will crack. 51CrV4 should not be welded at all in most designs; if a spring component needs to be attached, use mechanical fastening (bolting, riveting, crimping) rather than welding.
Cold formability follows the reverse pattern. SAE1020 is the grade for deep drawing and cold heading. C45E can be bent and lightly formed in the annealed condition but will crack in severe draws. 51CrV4 is formable only in the spheroidized-annealed condition, and even then it is limited to fine blanking and roll forming — not deep drawing. Our fine blanking grade selection guide covers the spheroidized-condition formability of C45E and 51CrV4 in detail.
6. Cost-Performance Tradeoff
Cost is not just the price per tonne — it is the total cost of getting from coil to finished, heat-treated, inspected part. The table below breaks the cost into raw material, processing and performance dimensions.
| Cost dimension | SAE1020 | C45E | 51CrV4 |
|---|---|---|---|
| Raw material (relative per tonne) | 1.0× (baseline) | 1.15 – 1.30× | 1.50 – 1.80× |
| Heat treatment cost | Minimal (no Q&T needed; carburizing optional) | Moderate (quench + temper, possible straightening) | High (oil quench + temper, strict process control, likely straightening) |
| Machining / blanking cost | Low (soft, easy to cut) | Moderate (annealed condition machines well) | Moderate-high (spheroidized for blanking; hardened condition needs grinding) |
| Welding / joining cost | Low (standard processes, no preheat) | High (preheat, PWHT, qualified procedure) | Very high (welding discouraged; mechanical fastening required) |
| Scrap / rework risk | Low (forgiving material) | Moderate (quench distortion, weld cracking risk) | High (quench cracking risk, distortion, decarburization sensitivity) |
| Service life / performance | Low strength, but adequate for welded/formed parts | Balanced strength-toughness for general machinery | Highest strength and fatigue life; longest service life in cyclic applications |
| Total cost verdict | Lowest total cost for low-strength parts | Best value for moderate-strength heat-treated parts | Highest cost, justified only for fatigue-critical parts |
Relative cost multipliers are indicative and based on typical market pricing for strip in the 1.0–3.0 mm range. Actual costs vary by thickness, width, surface finish, order quantity and market conditions. Heat treatment cost assumes batch furnace processing; continuous-line heat treatment may differ. The total cost verdict assumes the part is correctly matched to the grade — using 51CrV4 for a welded bracket is not "higher performance," it is wasted cost.
7. Grade Selection Summary
Work through these four questions in order. The answers point to the grade.
- Does the part need to be welded? If yes, and the weld is structural, SAE1020 is the default. C45E can be welded only with a qualified preheat procedure. 51CrV4 should not be welded.
- Does the part need through-hardened strength above 500 MPa yield? If no, SAE1020 (or carburized SAE1020 for a hard surface) is sufficient. If yes, move to C45E or 51CrV4.
- Does the part see cyclic loading above 10^5 cycles? If no, C45E gives the best value at 600–800 MPa tensile. If yes, 51CrV4 is the grade — its fatigue limit is roughly 50–80% higher than C45E.
- What is the budget and heat-treatment capability? C45E requires water or oil quenching plus tempering. 51CrV4 requires oil quenching plus tempering with strict process control and likely straightening. If your heat treater cannot handle 51CrV4, either outsource the heat treatment or redesign for C45E.
HS-FINEB stocks all three grades — SAE1020, C45E and 51CrV4 (50CrV4) — in cold rolled strip from 0.30 to 4.00 mm and widths from 20 to 1250 mm, with precision slitting, cut-to-length and spheroidized annealing processed in-house. C45E and 51CrV4 for fine blanking are supplied in spheroidized-annealed condition with a controlled hardness band (typically HB 180–220 for C45E, HB 190–230 for 51CrV4) and decarburization depth reported on the inspection certificate. For the full product range, see the medium carbon steel strip page and the 50CrV4 spring steel strip page.