1. The Five Factors, in Order
Every fine blanking part can be reduced to five questions. Answer them in this order and the grade largely selects itself; skip one and the part will find the mistake for you — usually at the press, or worse, at hardness testing after heat treatment.
1.1 Carbon: what the part must finally be
Start with the finished part, not the blank. If the part is used as-blanked and needs to stay soft and formable, you are in low-carbon territory. If it must be hardened to 40–55 HRC, you need medium carbon. If it must reach 50 HRC and above — springs, blades, clutch plates — you need high carbon. If the requirement is a hard, wear-resistant surface with a tough core, the carburizing grades are the answer, whatever their base carbon.
1.2 Delivered hardness: the spheroidized band
Once the grade family is fixed, the delivered condition decides whether the blanking works at all. Fine blanking strip is supplied spheroidized with a controlled hardness band. The band matters twice: a band that is too hard overloads the die and tears the shear surface; a band that is too soft can fold or gall. For a given grade the difference between a good heat and a bad one is usually visible on the hardness certificate before the coil is ever loaded.
1.3 Thickness: tonnage and flow
Blanking force scales with shear perimeter × thickness × shear strength. Thick parts need a bigger press and, more subtly, the material must flow plastically across a longer shear zone — which raises the bar on spheroidization quality. A 6 mm blank runs at roughly half again the force of a 4 mm blank of the same perimeter; at some point the choice is not just grade but press class.
1.4 Part complexity: geometry that punishes
Fine blanking handles tight contours well, but spline profiles, thin walls and features with sharp corners concentrate stress in the die and demand material that flows rather than fractures. Splines are the classic example: involute teeth impose such tight profile tolerances and surface finish requirements that the established route is fine blanking the contour and cutting the splines by broaching or machining — a process choice that changes what you ask of the strip, even if the grade stays the same.
1.5 Post-blanking heat treatment
Finally, look downstream. A part that will be carburized and quenched needs the carbon and alloy content for a case — 20MnCr5 and 16MnCr5 are the familiar fine blanking examples, supplied annealed. A part that will be quenched-and-tempered to a specified core hardness needs enough carbon in the base grade, with the blank made in the soft condition first. A part used as-blanked needs no hardenability at all, and paying for high carbon buys nothing but trouble in the press.
2. The Carbon–Formability–Hardness Table
The table below is the practical map for fine blanking grades stocked and supplied by HS-FINEB. Hardness figures are indicative — confirm against the governing standard and the delivered inspection report.
| Carbon family | Typical grades | Fine blanking formability (spheroidized) | Hardenability after quench | Typical finished hardness | Typical parts |
|---|---|---|---|---|---|
| Low carbon (<0.15% C) | SPCC, DC01, SAE1010 | Excellent — forms easily | Poor without carburizing | — (used soft) | Brackets, levers, non-wear parts |
| Medium carbon (0.30–0.55% C) | SAE1035, SAE1050, C45E, S45C | Good — needs full spheroidization | Good — quench & temper | 40 – 55 HRC | Seat adjusters, pawls, gears |
| High carbon (0.60–0.85% C) | SAE1078, C67S, C75S, 65Mn | Requires full spheroidization | Excellent — quench & temper | 50 – 60+ HRC | Clutch plates, springs, blades |
| Alloy carburizing (0.17–0.25% C + Cr/Mn) | 20MnCr5, 16MnCr5 | Good — supplied annealed | Excellent case hardness | 58 – 62 HRC case | Synchronizer bodies, cam plates |
Indicative values. Shear strength for press sizing is commonly estimated from annealed tensile strength — for an annealed grade such as 20MnCr5 at ~700 MPa tensile, shear is typically taken around 80% of that for fine blanking force calculations.
3. Spheroidized vs Normalized vs Annealed
Three delivery conditions get confused in RFQs, and the difference is not cosmetic.
- Normalized: fine pearlitic structure, higher hardness, good for bending and machining, wrong for fine blanking — the material tears and wears tools.
- Spheroidized: globular carbides, low hardness, the standard fine blanking condition. This is what the die design and tonnage calculations assume.
- Annealed (generic): an ambiguous term. It may be a full anneal, a process anneal or a spheroidizing cycle. Always confirm the microstructure and hardness band rather than accepting the word "annealed".
The detail of what the cycle does to the steel — and the three defects to watch for — is covered in our spheroidizing annealing guide.
4. The Decision Flow, Step by Step
- Define the finished part. Hardness? Wear? Toughness? Load? →
- Lock the final heat treatment. None / quench-temper / carburize. →
- Set the carbon family. Low / medium / high / carburizing alloy. →
- Check the geometry. Splines or tight contours? If yes, plan secondary machining now. →
- Size the press. Force ≈ perimeter × thickness × shear strength × 1.5–1.7 for V-ring and counter pressure. →
- Specify the strip condition. Spheroidized, with a hardness band, and a decarb limit if hardening without machining. →
- Verify on the first article. Shear quality, burr, hardness, then the full dimensional report. →
5. Three Real Selection Cases
5.1 Seat adjuster sector
The part: a stamped sector gear in a vehicle seat adjuster, blanked at about 2.5 mm and hardened so the teeth wear well. The reasoning: the teeth need 40–48 HRC, so the grade must be hardenable; the contour is open and forgiving, so a medium carbon is enough. The choice: SAE1035–SAE1050 spheroidized, blanked, then induction or furnace hardened. Low carbon would leave the teeth soft; high carbon would add cost and press load without benefit.
5.2 Door lock ratchet
The part: a lock ratchet with fine tooth profiles, around 3 mm thick, needing a hard wear surface and a tough body. The reasoning: the tooth profile is tight enough that fine blanking the full tooth form risks tearing and short die life — the proven route is fine blanking the contour and finishing the teeth, with the strip supplied to hold consistent blanking quality. The choice: a high-carbon or medium-carbon hardenable grade such as SAE1050–SAE1078 in the spheroidized condition, hardened after blanking. If the design demands a case-hardened surface instead, 20MnCr5 is the alternative.
5.3 Clutch plate
The part: a clutch separator or pressure plate, thin gauge, blanked in high volume and hardened and tempered to a stable spring-like response. The reasoning: final hardness and fatigue strength require high carbon; the thin section blanks cleanly only from a fully spheroidized coil; consistency of the hardness band is what keeps the heat treat result repeatable. The choice: SAE1078 or C67S/C75S, spheroidized, slit to progressive-die width. This is the case where our SAE1078 strip is routinely specified.
6. The Mistakes Buyers Make
- Choosing carbon for the blank instead of the finished part. The blank only needs to blank; the finished part defines the grade.
- Buying "annealed" without a hardness band. A certificate without numbers is not a specification.
- Ignoring press capacity until the first tryout. Size the press from the annealed shear strength before ordering material or tooling.
- Fine blanking splines into the part by default. Splines are usually cheaper and more accurate by broaching or machining; confirm the process route before finalizing the strip specification.
- Switching suppliers and assuming the same grade behaves the same. Same grade, different spheroidization, different band — verify the delivered hardness on the first coil.
7. Frequently Asked Questions
Short answers here; the full FAQ with schema follows below.
- Can one grade cover all my fine blanking parts? Only if all parts share the same final hardness requirement and thickness range — uncommon. Splitting between a medium-carbon and a high-carbon family usually pays for itself.
- Does grade choice change the burr specification? Indirectly. Harder, less spheroidized strip produces higher burr and faster die wear, so a tight burr spec argues for a well-spheroidized coil.
- What do I send with an RFQ? Finished-part hardness, thickness, annual volume, geometry notes (splines?), and the post-blanking heat treatment. That is enough for a grade match.