A 5-step decision framework for picking the right steel grade — from part function to post-blanking heat treat — with a carbon–blankability–hardness table, a spheroidized-vs-normalized decision tree, and three worked production cases.
Work through these in order. Each step narrows the field. Skip one and you will either over-specify the material (and pay too much) or under-specify it (and scrap parts at the press).
Define what the part does. Is it a structural bracket that stays soft? A wear surface that needs hardness? A safety component with certified strength? The function sets the final-property target.
Fine blanking force = shear perimeter × thickness × shear strength × process factor (≈1.6). Check that your press has the tonnage. Thicker parts need softer material and more press capacity.
Carbon sets the achievable hardness after heat treat — and the blanking difficulty. Pick the lowest carbon that meets the final hardness target. Low = easiest to blank, high = hardest edge.
For fine blanking, spheroidized (soft-annealed) is the standard. Normalized is only for simple bending. If you skip in-house heat treat, ask for hardened-and-tempered strip.
Through-hardening (quench + temper), case hardening (carburizing), or no heat treat at all. This decides whether you need a medium-carbon through-hardening grade or a low-carbon carburizing grade.
The single most important table in this guide. Carbon content drives both the final hardness and the blanking difficulty — the art is picking the lowest carbon that still meets your part's hardness requirement.
| Category | Typical grades | C (%) | Annealed hardness | Final hardness (Q&T) | Fine blanking suitability | Typical parts |
|---|---|---|---|---|---|---|
| Low carbon | SAE1010, SPCC, DC01 | ≤ 0.12 | 120 – 160 HB | n/a (not hardenable) | Excellent — cleanest shear face, lowest die wear | Door lock ratchets, brackets, housings, clips |
| Medium carbon | SAE1035, SAE1045, S35C–S50C, C45–C60 | 0.30 – 0.50 | 160 – 200 HB (spheroidized) | 40 – 50 HRC | Good when fully spheroidized; requires controlled die clearance | Seat recliner sectors, transmission plates, gears |
| High carbon | SAE1078, C67S, C75S, 65Mn | 0.70 – 0.85 | 160 – 200 HB (spheroidized) | 50 – 60 HRC | Fair — requires full spheroidizing; higher press load, more die wear | Clutch plates, saw blade bodies, spring-loaded parts |
| Alloy / carburizing | 20MnCr5, 16MnCr5, 20CrMnTi | 0.15 – 0.25 | 140 – 180 HB | 58 – 62 HRC (case) | Good — low core carbon blanks well; hard case after carburizing | Gears, shafts, synchronizer components |
Hardness values are indicative. Annealed hardness assumes a fully spheroidized condition for medium- and high-carbon grades. Final hardness depends on section size, quench medium and tempering temperature. Confirm with the MTC and a trial heat treat for your section.
The delivery condition is where most fine blanking problems start. A supplier who ships "annealed" strip without specifying the microstructure is shipping a gamble. Use this tree to specify exactly what you need.
Yes → Require spheroidized (soft-annealed) strip with a documented hardness band and microstructure. This is non-negotiable for a clean shear face.
No (simple bending / forming only) → Normalized or cold-rolled strip may be acceptable and cheaper.
≤ 0.12% C → Spheroidizing has limited effect; cold-rolled or normalized strip is usually fine. 0.30–0.85% C → Full spheroidizing is essential. Lamellar pearlite will tear in the die and wear the punch.
Specify a target range, not a maximum. For SAE1078 fine blanking, 160–200 HB is typical. Too soft → poor shear surface and dimensional drift. Too hard → excessive press load and die wear. We document the band on the MTC.
Yes → Buy spheroidized strip, blank, then quench-and-temper. No → Buy hardened-and-tempered strip and blank or form to final shape — but note that blanking hardened strip increases die wear and may not be feasible above ~45 HRC.
Each case follows the 5-step framework. The grade is not chosen first — it is the output of working through the constraints.
Step 1 — Function: The sector carries the seat recliner load and must engage a pawl tooth-on-tooth. It needs hardness at the tooth profile for wear resistance, plus toughness in the body. Through-hardening to 42–48 HRC is the target.
Step 2 — Thickness: 3.0 mm with a shear perimeter of roughly 280 mm. At ~560 MPa shear strength and a 1.6 process factor, the blanking force is approximately 750 kN (≈76 tons) — well within a 300-ton press with margin for the V-ring and counterpressure.
Step 3 — Carbon: 42–48 HRC requires medium carbon. SAE1035 (0.32–0.38% C) reaches this range after quench-and-temper. SAE1045 would also work but is harder to blank and offers no benefit at this hardness target. SAE1010 cannot harden above ~30 HRC — insufficient.
Step 4 — Condition: Spheroidized to 160–190 HB. Normalized SAE1035 would be ~220 HB and cause excessive roll-over on the tooth profile. The spheroidized structure gives a clean shear face with minimal roll-over — critical for tooth engagement.
Step 5 — Heat treat: Blanked parts are quenched (850–880°C, oil) and tempered (350–450°C) to 42–48 HRC. The lower temper gives higher hardness at the tooth; the higher temper gives more toughness in the body. The exact temper is set by the seat strength test (FMVSS 207 / ECE R17).
Result: SAE1035 spheroidized strip, 3.0 mm × coil width, MTC per coil. Trial coil from one ton to confirm shear quality and hardenability before production volume.
Step 1 — Function: The ratchet pawl engages the striker and holds the door closed. It is not a wear surface in the same way as a gear — the load is impact and fatigue, not sliding wear. The part is zinc-plated after blanking for corrosion protection. No heat treatment is specified.
Step 2 — Thickness: 2.5 mm, shear perimeter ~200 mm. Blanking force approximately 450 kN (≈46 tons) — a 160-ton press has ample margin. The part has complex internal and external contours, so shear-face quality matters for fit with the striker.
Step 3 — Carbon: Since there is no post-blanking heat treatment, carbon content is irrelevant to final hardness. Low-carbon SAE1010 (≤0.12% C) is the easiest to blank, gives the cleanest shear face, and is the lowest-cost option. Medium carbon would add cost with no functional benefit.
Step 4 — Condition: Cold-rolled and annealed to ≤160 HB. Full spheroidizing is unnecessary at this carbon level — the microstructure is primarily ferrite with small pearlite islands. A standard box anneal is sufficient.
Step 5 — Heat treat: None. The part is fine blanked, deburred, zinc-plated, and assembled. The as-blanked hardness (~120–150 HB) is adequate for the latch duty cycle.
Result: SAE1010 annealed strip, 2.5 mm, slit to progressive-die width. Lowest material cost in the range, highest blanking yield, no heat treat step — the right choice for a non-hardened structural latch part.
Step 1 — Function: The diaphragm spring is the load-bearing element of the clutch cover assembly. It must maintain spring force under repeated cycling at elevated temperature (up to ~150°C under hard driving). It requires high hardness (44–50 HRC) and high yield strength after quenching and tempering.
Step 2 — Thickness: 2.0 mm, but the shear perimeter is very large — the part is a ring with multiple finger slots, total perimeter ~600 mm. Blanking force approximately 1,075 kN (≈110 tons) at 560 MPa shear. A 400-ton press is needed for the V-ring force and counterpressure on this large perimeter.
Step 3 — Carbon: 44–50 HRC with spring properties requires high carbon. SAE1078 (0.72–0.85% C) is the standard clutch plate grade. Medium-carbon SAE1045 would top out around 45 HRC with lower yield strength — insufficient for the spring load. SAE1078 is the minimum carbon that reliably delivers the required spring properties.
Step 4 — Condition: Fully spheroidized to 160–200 HB. This is the most critical step for high-carbon fine blanking. As-rolled SAE1078 has a lamellar pearlite structure at ~250 HB — it will tear in the die and wear the punch within a few thousand strokes. Full spheroidizing rounds the carbides and drops the hardness to a blankable range.
Step 5 — Heat treat: Blanked plates are quenched (800–830°C, oil) and tempered (350–420°C) to 44–50 HRC. The temper is carefully controlled to avoid the temper brittleness range and to set the spring load characteristic. Flatness after heat treat is critical — the plate must stay flat to apply even pressure across the clutch disc.
Result: SAE1078 fully spheroidized strip, 2.0 mm, with documented hardness and decarburization depth on the MTC. Decarburization control is critical — a decarburized surface will not harden fully and will soften the spring finger tips.
These grade families share material, processing or application territory with the topic on this page.
SAE1078 / 65Mn / SK5 grades for hardened parts, springs and cutting edges.
SAE1045 / C45 grades balancing strength and formability for induction-hardened parts.
65Mn / 50CrV4 / 60Si2Mn grades with high elastic limit and fatigue resistance.
Include material target, thickness × width, annual volume and heat treat route. Our engineers reply within one working day.