The material specification framework for heavy-gauge fine blanking — carbon window, spheroidization requirements, thickness tolerance bands, press tonnage relationships, die design implications, typical thick-strip parts, and why no material supplier has published a systematic guide for this range.
Thick-strip fine blanking covers parts produced from strip 8 mm to 15 mm thick — above the conventional 1.5–5 mm production range and below the practical limit of specialized fine blanking presses. It is not simply "thin strip fine blanking with thicker material." The physics changes.
Fine blanking works by creating a hydrostatic stress state in the material through three simultaneous forces: the punch descending, the V-ring indenter pressing into the strip around the punch perimeter, and the ejector (counterpunch) holding the part from below. This triaxial compression suppresses fracture and forces the material to shear plastically through nearly 100% of the thickness, producing a smooth, burnished cut face with no fractured zone.
At 1.5–5 mm, the deformation path through the thickness is short. The material flows a few millimeters under the punch, the V-ring penetrates a fraction of a millimeter, and the hydrostatic state is easy to maintain. At 8–15 mm, the deformation path is 3–5 times longer. The material must flow through 8–15 mm of thickness under compression, and every microstructural defect — lamellar pearlite, inclusions, segregation bands — has more distance over which to initiate and propagate a crack.
Blanking force scales linearly with thickness. The fundamental formula is:
F = L × t × τ
where F is blanking force in newtons, L is the total cut perimeter in mm (outer profile + all internal holes), t is strip thickness in mm, and τ is the material shear strength in MPa (typically 0.7–0.8 × tensile strength for spheroidized steel). For a part with a 200 mm perimeter in SAE1045 (tensile ~550 MPa, shear ~400 MPa), the blanking force at 3 mm is approximately 240 kN (24 tons); at 12 mm it is approximately 960 kN (96 tons) — a fourfold increase. Add V-ring counterpressure (typically 20–30% of blanking force) and ejector force, and the required press tonnage enters the 300–800 ton class.
Above 15 mm, even the largest fine blanking presses (up to ~1,000 tons) struggle to maintain the hydrostatic stress state across the full thickness. The V-ring cannot penetrate deeply enough, the press frame deflects under load, and the shear face develops a fractured zone. For this reason, 15 mm is generally regarded as the upper practical limit for conventional fine blanking, with 8–12 mm being the most common heavy-gauge production range.
For the baseline material requirements that apply to all fine blanking gauges, refer to the companion fine blanking material requirements complete guide. This page specifies how those requirements shift at heavy gauge.
The three-parameter material window — carbon content, hardness, and microstructure — tightens at heavy gauge. The table below compares thin strip and thick strip requirements and explains why each parameter shifts.
| Parameter | Thin strip (1.5–5 mm) | Thick strip (8–15 mm) | Why it changes |
|---|---|---|---|
| Carbon upper limit | ≤ 0.85% C (fully spheroidized high-carbon grades such as SAE1078, C67S) | ≤ 0.65–0.70% C above 10 mm; ≤ 0.75% C at 8–10 mm (industry typical reference) | Longer deformation path amplifies carbide-related cracking. Higher carbide volume increases work hardening mid-stroke, raising press load and tear risk. Medium-carbon grades (SAE1035/1045/C45) dominate. |
| Hardness band (as-delivered) | 160–200 HB (medium/high carbon spheroidized); 120–160 HB (low carbon) | 150–180 HB preferred (medium carbon); lower end of band specified for >10 mm | Longer deformation path generates more work hardening during the stroke, effectively raising resistance mid-stroke. Starting softer compensates. Above 180 HB at 12 mm+ press load and die wear become excessive. |
| Spheroidization ratio | ≥ 90% globular cementite in ferrite matrix | ≥ 92–95% preferred; carbide particle size 0.5–1.5 µm | Lamellar pearlite colonies have more distance over which to initiate and link cracks through the thickness. Tighter spheroidization reduces crack initiation sites. Finer carbide size minimizes local stress concentration. |
| Decarburization limit | Total decarb ≤ 1.5% of thickness per side; max 0.10–0.15 mm absolute | Total decarb ≤ 1.0% of thickness per side; max 0.15 mm absolute (industry typical reference) | At heavy gauge, decarburized surface layer represents a larger absolute depth. For parts that are subsequently induction-hardened or through-hardened, a soft surface layer causes premature wear. Tighter limit compensates. |
| Inclusion rating | ASTM E45 thin-series: A ≤ 2.5, B ≤ 2.0, C ≤ 2.0, D ≤ 2.0 | ASTM E45 thin-series: A ≤ 2.0, B ≤ 1.5, C ≤ 1.5, D ≤ 1.5 (industry typical reference) | Non-metallic inclusions act as crack initiation sites. Over a longer deformation path, a single inclusion is more likely to propagate into a visible tear on the shear face. Tighter inclusion rating reduces this risk. |
| Hardness uniformity (within coil) | ≤ 20 HB difference between hardest and softest readings | ≤ 15 HB difference preferred (industry typical reference) | At heavy gauge, hardness variation causes uneven material flow across the part width, leading to dimensional drift and uneven shear face quality. Tighter uniformity is needed because the press load is higher and less tolerant of variation. |
All values are industry typical reference ranges, not a quality commitment. Actual limits are confirmed per grade standard (ASTM A109, EN 10132, JIS G4051) and per purchase specification. The carbon upper limit for thick strip depends on part geometry — simple parts with low perimeter-to-area ratio may tolerate up to 0.75% C at 12 mm, while complex parts with fine teeth or small holes should stay at or below 0.55% C.
Why medium-carbon grades dominate thick-strip fine blanking. SAE1035–1050 steel strip and C45E medium-carbon steel (0.30–0.50% C) are the workhorse grades for 8–15 mm fine blanking. They offer a favorable balance: enough carbon to through-harden to 40–50 HRC after quenching and tempering for gear and sprocket applications, but low enough carbide volume to blank cleanly at heavy gauge when fully spheroidized. High-carbon grades such as SAE1078 steel strip and 65Mn spring steel strip (0.65–0.85% C) are generally limited to 8 mm or below in fine blanking, unless the part geometry is simple and the press has excess tonnage. Alloy grades such as 42CrMo alloy steel strip are used for high-stress thick-strip parts but require careful spheroidizing and higher press tonnage due to alloy carbides.
Spheroidization is the single most important microstructural parameter for fine blanking. At 8–15 mm, it becomes even more critical because the longer deformation path gives lamellar pearlite more opportunity to initiate and propagate cracks.
Why lamellar pearlite is more dangerous at heavy gauge. Lamellar pearlite consists of alternating plates of ferrite and cementite (Fe3C). The cementite plates are hard and brittle; under the compressive-shear deformation of fine blanking, they fracture at the carbide-matrix interface, creating micro-cracks. In thin strip (2–4 mm), the deformation path is short enough that these micro-cracks may not link up into a visible tear before the part is ejected. In thick strip (8–15 mm), the material must shear through 8–15 mm of thickness — a distance long enough that micro-cracks initiated at lamellar colonies in the upper portion of the strip can propagate downward, link with cracks from other colonies, and produce a visible fractured zone or secondary shear on the cut face. The probability of crack linkage scales with deformation path length, which is why the spheroidization requirement tightens from ≥90% to ≥92–95% at heavy gauge.
Carbide size control. Globular carbide particle size matters at least as much as the spheroidization ratio. For thick-strip fine blanking, the preferred carbide particle size is 0.5–1.5 micrometers, uniformly distributed in the ferrite matrix. Carbides coarser than ~2.5 micrometers act as local stress concentrators — under the high compressive stresses of heavy-gauge blanking, the matrix can debond from a coarse carbide particle, creating a void that grows into a tear. Carbides finer than ~0.3 micrometers may indicate incomplete spheroidization, with lamellar remnants that have not fully globularized. The carbide size distribution should be assessed by metallographic examination at 1000× magnification per ASTM A892 or ISO 16069, with image analysis to quantify the particle size distribution.
Recommended spheroidizing cycles for thick strip (industry typical reference). Thick-strip spheroidizing requires longer hold times and slower cooling than thin strip because the thermal mass of the coil is greater and the carbide dissolution/diffusion kinetics are slower at the strip center. The following cycles are industry typical reference values:
All spheroidizing should be performed in a neutral or slightly carburizing atmosphere (endothermic gas with controlled CO/CO₂ ratio, or nitrogen-hydrogen with controlled dew point) to prevent decarburization. For a detailed treatment of the spheroidizing process — temperature cycles, hold times, cooling rates, furnace atmosphere control, and common defects — refer to the spheroidizing annealing complete guide.
Prohibited phases at heavy gauge. Bainite and martensite are absolutely prohibited in the as-delivered condition for any fine blanking gauge, but at heavy gauge they are even more destructive because the higher press load amplifies the chipping risk to the punch and die edges. If bainite or martensite is found on metallographic examination, the coil has not been properly annealed — it should be rejected or re-annealed. Free ferrite networks (continuous ferrite at grain boundaries) should also be avoided because they create soft planes that can cause uneven material flow and dimensional drift at heavy gauge.
Fine blanking dies are built to a specific strip thickness. At heavy gauge, thickness variation has a magnified effect on press load and part dimensions because the blanking force scales linearly with thickness. The table below lists tolerance bands for the 6–15 mm range.
| Thickness range (mm) | Tolerance grade | Allowable deviation (mm) | Crown limit (mm) | Notes |
|---|---|---|---|---|
| 6 – 8 | IT9 / IT10 | ± 0.040 | ≤ 0.020 | Transition range between conventional and heavy-gauge fine blanking. Medium-carbon grades standard. Press tonnage 200–300 t typical. |
| 8 – 10 | IT10 | ± 0.050 | ≤ 0.025 | Lower end of heavy-gauge range. Carbon upper limit ~0.75%. Spheroidization ≥92%. Press tonnage 300–400 t typical. |
| 10 – 12 | IT10 / IT11 | ± 0.060 | ≤ 0.030 | Mid heavy-gauge range. Carbon upper limit drops to ~0.65–0.70%. Hardness 150–180 HB preferred. Press tonnage 400–500 t typical. |
| 12 – 15 | IT11 | ± 0.075 | ≤ 0.040 | Upper practical limit for fine blanking. Carbon ≤0.60% for complex geometry. Spheroidization ≥95%. Press tonnage 630–800 t typical. Above 15 mm requires specialized presses or alternative processes. |
Tolerance grades are industry typical reference per EN 10140 (cold-rolled strip) and ASTM A568 (carbon and alloy steel sheet), applied to strip thickness. Actual tolerance is confirmed per purchase order. Crown is defined as center thickness minus average edge thickness. Thickness should be measured at five points across the strip width (both edges, two quarter points, center) at head, middle, and tail of each coil.
Why tolerance widens at heavy gauge but must still be controlled. Cold-rolled strip tolerances naturally widen as thickness increases because the rolling mill has less ability to reduce thickness variation in heavier gauge — the roll gap is larger, roll deflection is greater, and the strip's own resistance to reduction is higher. However, fine blanking at heavy gauge is less tolerant of thickness variation, not more. A 0.06 mm variation at 12 mm represents 0.5% of thickness, which translates directly to a 0.5% variation in blanking force — at 500 tons press load, that is a 2.5 ton swing from part to part. This variation changes the V-ring penetration depth, the counterpressure distribution, and ultimately the part dimensions. For this reason, thick-strip fine blanking buyers should specify the tighter end of the standard tolerance band (e.g., ±0.050 mm for 8–10 mm rather than the standard ±0.060 mm) and require the mill to report thickness measurements at five points across the width on the MTC.
Width tolerance and camber at heavy gauge. Strip width is typically held to ±0.15 mm for widths up to 300 mm and ±0.20 mm for widths 300–600 mm when slit to order. At heavy gauge, the slit edges are more likely to have burr because the slitting knives must cut through thicker material — edge burr should be limited to ≤5% of strip thickness with an absolute maximum of 0.10 mm for 10 mm+ strip. Camber (side curvature) should be ≤1.5 mm per 1000 mm for general purpose and ≤1.0 mm per 1000 mm for precision progressive dies. Heavy-gauge strip has more residual stress from rolling and leveling, so camber can be more pronounced — the coil should be tension-leveled after cold rolling to minimize residual stress.
Flatness at heavy gauge. Flatness requirements for thick-strip fine blanking are ≤8 I-units for general parts and ≤5 I-units for precision parts (industry typical reference). Heavy-gauge strip is stiffer and less likely to have severe wave, but residual stresses from rolling and leveling can cause the strip to twist or bow after blanking. The V-ring indenter must contact the strip uniformly across the full width — a wavy strip causes uneven V-ring penetration and uneven counterpressure, leading to dimensional drift. For precision thick-strip parts (gears, sprockets), flatness should be verified at incoming inspection with a flatness table or I-unit meter.
Thick-strip fine blanking requires presses in the 300–800 ton class with rigid frames, modified V-ring geometry, and tighter die clearance. The formula, counterpressure requirements, and design differences are summarized below.
Blanking force formula and worked examples. The blanking force for fine blanking is calculated as:
F = L × t × τ × k
where F is blanking force in N, L is total cut perimeter in mm (outer profile + all internal holes), t is thickness in mm, τ is shear strength in MPa (typically 0.7–0.8 × tensile strength for spheroidized steel), and k is a fine blanking factor (typically 1.1–1.3 to account for the V-ring and counterpressure increasing the effective shear resistance). For a medium-carbon part (SAE1045, tensile ~550 MPa, shear ~400 MPa) with a 200 mm perimeter and k = 1.2:
These are blanking forces only. The fine blanking press must also deliver V-ring counterpressure (typically 20–30% of blanking force, or 20–40 tons in these examples) and ejector force (typically 5–10% of blanking force). The press must also have a safety margin — typically 15–20% above the calculated total load — to account for material hardness variation, die wear, and unexpected load spikes. This is why the industry typical reference press sizes are 300 tons for 10 mm parts, 400–500 tons for 12 mm, and 630–800 tons for 15 mm, even though the raw blanking force is lower. The press frame must be rigid enough to avoid deflection under these loads — typically a C-frame or straight-side frame with a deflection rating of ≤0.05 mm per 100 tons at the slide.
V-ring design differences at heavy gauge. The V-ring (also called the vee-ring or indenter ring) is a raised triangular profile on the pressure plate that penetrates the strip around the punch perimeter, creating the hydrostatic stress state. At thin gauge (1.5–5 mm), the V-ring typically has a height of 0.3–0.8 mm, an angle of 90°, and is positioned 0.5–1.5 mm from the punch edge. At thick gauge (8–15 mm), the V-ring must be larger and more aggressive to penetrate the stiffer material:
Die clearance. Die clearance (the gap between the punch and the die opening) is typically 0.5–1.0% of strip thickness for conventional fine blanking. At heavy gauge, the clearance should be tightened to 0.3–0.5% of thickness to prevent the material from being drawn into the gap and producing a torn or secondary-shear zone. For a 12 mm part, this means a die clearance of 0.036–0.060 mm per side — requiring high-precision die manufacturing and careful alignment. The punch and die materials should be high-speed steel (e.g., ASP2023, ASP2030) or powder metallurgy tool steel with PVD coating (TiN, TiCN, or AlCrN) to withstand the higher abrasive wear at heavy gauge.
Counterpressure requirements. The ejector (counterpunch) force holds the part against the punch during blanking and controls the roll-over at the top of the shear face. At thin gauge, counterpressure is typically 5–10% of blanking force. At heavy gauge, counterpressure should be increased to 10–15% of blanking force to prevent the part from deflecting under the higher blanking load and to control roll-over depth. Excessive counterpressure, however, can cause the part to stick to the punch and increase the stripping force — the optimal value must be determined by trial blanking with the actual material.
The 8–15 mm range is dominated by structural and power-transmission parts that require a clean, near-net-shape cut face to eliminate or reduce secondary machining. The table below lists the most common part types, their typical thickness, material, industry, and key requirements.
| Part type | Typical thickness (mm) | Common material | Industry | Key requirements |
|---|---|---|---|---|
| Transmission gears & gear blanks | 8 – 12 | SAE1035, SAE1045, C45, C45E | Automotive, agricultural machinery, industrial gearboxes | Clean tooth flanks with no fractured zone; minimal post-machining (hobbing or shaving only); flatness ≤0.05 mm; bolt-hole positional accuracy ±0.02 mm; through-hardened to 45–55 HRC after blanking |
| Sprockets & chain wheels | 8 – 12 | SAE1045, 40Cr, 42CrMo | Motorcycles, bicycles, conveyor systems, agricultural machinery | Wear-resistant tooth profile; tooth pitch accuracy ±0.03 mm; induction-hardened tooth tips to 50–55 HRC; hub bore concentricity ≤0.02 mm; clean cut face on tooth flanks |
| Flanges & flange rings | 10 – 15 | SAE1020, SAE1035, Q235 | Automotive, pipeline, industrial machinery | Flatness ≤0.05 mm across full diameter; bolt-hole positional accuracy ±0.05 mm; no warpage after blanking; clean outer and inner diameter cut faces; may be subsequently turned or drilled |
| Brake components (shoe plates, anchor plates, backing plates) | 8 – 12 | SAE1045, 40Cr | Automotive, commercial vehicles, trailers | High structural rigidity; flatness ≤0.08 mm; hole positional accuracy ±0.05 mm; clean cut face with no burr; may be subsequently welded or assembled; safety-critical — 100% dimensional inspection |
| Structural brackets & mounting plates | 10 – 15 | SAE1020, Q235, SAE1035 | Automotive chassis, construction machinery, railway | High load capacity; multiple holes with positional accuracy ±0.10 mm; flatness ≤0.10 mm; clean cut faces; may be subsequently bent, welded, or painted; often replaces cast or forged brackets |
| Clutch plates & clutch hubs | 6 – 10 | SAE1078, 65Mn, C67S | Automotive, motorcycles, agricultural machinery | Spring-back consistency; flatness ≤0.03 mm; clean cut face on friction surfaces; through-hardened to 44–50 HRC; decarburization ≤1.0% of thickness; high-carbon grades limited to ≤10 mm in fine blanking |
All values are industry typical reference ranges. Actual part specifications depend on the OEM drawing and performance requirements. Thick-strip fine blanking is often chosen for these parts because it produces a clean, near-net-shape cut face that eliminates or reduces secondary machining (milling, turning, grinding), reducing per-part cost compared to machining from bar or plate. For application-specific details, see automotive seat recliner fine blanking and automotive chassis and suspension components.
Why these parts are fine blanked at heavy gauge instead of machined or forged. Each of these part types shares a common economic driver: fine blanking produces a near-net-shape part in a single press stroke, with a clean cut face that requires minimal or no secondary machining. For a 12 mm gear blank, machining from bar stock would require turning the outer diameter, drilling the center hole, hobbing the teeth, and deburring — four or five operations with associated setup time, tooling cost, and material waste (typically 30–50% of the starting weight becomes chips). Fine blanking produces the same gear blank in one stroke with a cut face quality that may require only a light honing or shaving operation. The material waste is limited to the skeleton (the strip remaining after the part is blanked), which is typically 20–30% of the starting weight for a well-nested layout. For high-volume parts (100,000+ pieces per year), the per-part cost savings are substantial.
Limitations of thick-strip fine blanking for these parts. Not every heavy-gauge part is a candidate for fine blanking. Parts with very deep draws, sharp internal corners (radius less than 0.5 × thickness), or very small holes (diameter less than thickness) may not be fine blankable because the punch cannot withstand the load or the material cannot flow into the feature. Parts with complex 3D geometry (not flat) require subsequent forming operations. Parts with annual volume below ~10,000 pieces may not justify the tooling cost (a thick-strip fine blanking die can cost $30,000–$80,000 or more). For these cases, conventional stamping, machining, or forging may be more economical. The fine blanking vs conventional stamping guide provides a detailed process selection decision tree.
The table below summarizes the key process differences between conventional thin-strip fine blanking (1.5–5 mm) and thick-strip fine blanking (8–15 mm) across eight dimensions.
| Dimension | Thin strip (1.5–5 mm) | Thick strip (8–15 mm) |
|---|---|---|
| Deformation mode | Short deformation path (2–5 mm). Hydrostatic stress state easy to maintain. Material flows plastically through full thickness with minimal work hardening. | Long deformation path (8–15 mm). Hydrostatic stress state harder to maintain — V-ring must penetrate more deeply. Work hardening accumulates through the stroke, raising effective resistance mid-stroke. |
| Press tonnage | 60–200 tons typical. Small to medium fine blanking presses. C-frame or straight-side. | 300–800 tons typical. Large fine blanking presses with rigid frames. Straight-side preferred for minimal deflection. Safety margin 15–20% above calculated load. |
| Die clearance | 0.5–1.0% of thickness per side. E.g., 0.015–0.030 mm at 3 mm. | 0.3–0.5% of thickness per side. E.g., 0.036–0.060 mm at 12 mm. Tighter clearance prevents material draw-in and secondary shear. |
| V-ring geometry | Height 0.3–0.8 mm, angle 90°, position 0.5–1.5 mm from punch edge. Single V-ring standard. | Height 0.8–2.0 mm, angle 75–90°, position 1.5–3.0 mm from punch edge. Double V-ring for parts >12 mm or high perimeter ratio. |
| Counterpressure (ejector force) | 5–10% of blanking force. Sufficient to control roll-over and hold part against punch. | 10–15% of blanking force. Higher force needed to prevent part deflection under higher blanking load and control roll-over depth. |
| Lubrication | Standard fine blanking oil or emulsion. Applied by roll coater or spray. Film thickness 2–5 g/m². | High-pressure extreme-pressure (EP) lubricant with solid additives (MoS₂, graphite, or polymer). Film thickness 5–10 g/m². May require pre-lubrication or phosphate coating for high-carbon grades. |
| Die life | 500,000–2,000,000 strokes between regrinds for medium-carbon steel. Punch and die made of high-speed steel or PM tool steel. | 100,000–500,000 strokes between regrinds (industry typical reference). Higher abrasive wear due to thicker material and higher contact pressure. PVD coating (AlCrN or TiCN) recommended. More frequent die maintenance. |
| Common defects | Roll-over (if counterpressure too low), die wear (if hardness too high), dimensional drift (if flatness poor), slight shear-face tearing (if spheroidization <90%). | Secondary shear / fractured zone (if V-ring insufficient or clearance too large), internal shear cracking (if lamellar pearlite present), part deflection or bowing (if counterpressure too low), punch chipping (if die clearance too tight or material too hard), die wear acceleration (if lubrication insufficient). |
All values are industry typical reference ranges. Actual process parameters depend on part geometry, material grade and condition, press capability, and die design. Die life figures are for medium-carbon steel (SAE1035/1045) in fully spheroidized condition; high-carbon and alloy grades will have shorter die life.
The most common thick-strip defect: secondary shear. Secondary shear (also called double shear or torn zone) appears as a rough, fractured region on the cut face, typically starting at the mid-thickness or lower portion of the shear face. It occurs when the hydrostatic stress state breaks down during the stroke — the V-ring penetration is insufficient, the counterpressure drops, or the material work-hardens to the point where it fractures rather than flows. At thin gauge, secondary shear is relatively rare because the deformation path is short and the hydrostatic state is easy to maintain. At thick gauge, secondary shear is the most common quality issue and the primary reason why thick-strip fine blanking requires larger presses, more aggressive V-rings, tighter die clearance, and better material quality. If secondary shear appears on trial parts, the corrective actions are: increase V-ring height or switch to double V-ring, increase counterpressure, reduce die clearance, verify spheroidization ratio (reject if <92%), and verify that the press has sufficient tonnage and frame rigidity.
Use this checklist when writing a purchase specification for 8–15 mm fine blanking steel strip. Each item should be specified on the purchase order and verified on the mill test certificate (MTC) and at incoming inspection.
| # | Specification item | Requirement for thick strip (8–15 mm) | Verification method |
|---|---|---|---|
| 1 | Grade and chemical composition | Medium-carbon preferred: SAE1035/1045/C45 (0.30–0.50% C). Carbon ≤0.70% for >10 mm; ≤0.75% for 8–10 mm. S ≤0.015%, P ≤0.020% for precision parts. | MTC chemical analysis per heat. Verify C, Mn, Si, S, P, and any alloying elements against grade standard (ASTM A109, EN 10132, JIS G4051). |
| 2 | Delivery condition | Fully spheroidized annealed. Bright or pickled-and-oiled surface. No cold work after annealing (no skin pass or temper rolling that would raise hardness). | MTC delivery condition statement. Verify hardness and microstructure confirm spheroidized condition. |
| 3 | Hardness band | 150–180 HB preferred for medium carbon at >10 mm; 160–190 HB acceptable for 8–10 mm. Within-coil variation ≤15 HB. | Brinell hardness test at head, middle, tail of coil; center and edge of width. Minimum 6 readings per coil. |
| 4 | Spheroidization ratio | ≥92% for 8–10 mm; ≥95% for 10–15 mm. Carbide particle size 0.5–1.5 µm. No lamellar pearlite above 8%. No bainite or martensite. | Metallographic cross-section mount, polish, etch (2% nital), examine at 500–1000× per ASTM A892 / ISO 16069. Image analysis for spheroidization ratio and carbide size. |
| 5 | Decarburization depth | Total decarb (ferritic + partial) ≤1.0% of thickness per side. Max absolute 0.15 mm. No continuous ferritic decarburization layer. | Cross-section mount, examine at 100–200× per ASTM E1077 / ISO 3887. Measure both surfaces. |
| 6 | Inclusion rating | ASTM E45 Method A (JK chart) thin-series: A (sulfide) ≤2.0, B (alumina) ≤1.5, C (silicate) ≤1.5, D (globular oxide) ≤1.5. | Metallographic examination per ASTM E45. Report on MTC. For safety-critical parts, verify at incoming inspection. |
| 7 | Thickness tolerance | Per tolerance table (Section 04): ±0.050 mm (8–10 mm), ±0.060 mm (10–12 mm), ±0.075 mm (12–15 mm). Crown ≤0.025–0.040 mm. | Micrometer at 5 points across width (both edges, 2 quarter points, center) at head, middle, tail. Verify crown and wedge. |
| 8 | Width tolerance | ±0.15 mm (width ≤300 mm); ±0.20 mm (width 300–600 mm). Slit edges with burr ≤5% thickness (max 0.10 mm). | Caliper or tape measure at 3 positions along coil. Edge burr gauge at head and tail. |
| 9 | Flatness | ≤8 I-units (general); ≤5 I-units (precision). Edge wave / center wave ≤2 mm over 1 m. | Flatness table or I-unit meter. Or straightedge + feeler gauge on unspooled 1 m section. |
| 10 | Camber | ≤1.5 mm / 1000 mm (general); ≤1.0 mm / 1000 mm (precision progressive dies). | Straightedge 1000 mm, feeler gauge at maximum deviation. |
| 11 | Surface quality | No scratches >0.02 mm deep. No oxidation, rust, or scale. No roll marks >0.02 mm. Oil film 0.5–2.0 g/m². Ra 0.4–1.2 µm (pickled) or Ra 0.2–0.8 µm (bright). | Visual inspection under 500 lux. Portable roughness tester. Oil film weight by solvent extraction. |
| 12 | Grain size | ASTM grain size 5–8. No mixed grain (difference >2 ASTM numbers in same field). | Cross-section mount, etch, examine at 100× per ASTM E112. |
| 13 | MTC documentation | Full MTC per coil: heat number, grade, chemistry, mechanicals (tensile, elongation), hardness, microstructure (spheroidization ratio, carbide size), decarburization, inclusion rating, dimensional results (thickness, width, flatness, camber), surface condition, packaging. Signed by mill quality authority. | Document review against purchase order. Verify all 13 items are reported. Reject coils with incomplete MTC. |
| 14 | Packaging | Waterproof wrapping intact. Rust preventive oil present. ID/OD protected. Label shows heat number, grade, dimensions, weight, mill name. Coil weight per purchase spec (typically 2–5 tons for heavy gauge). | Visual check at receiving. Verify label information matches MTC. |
This checklist is an industry typical reference template for thick-strip fine blanking steel procurement. Adjust acceptance limits and inspection frequencies to match your purchase specification, quality agreement, and part criticality. For safety-critical automotive parts (brake components, transmission gears), tighten frequencies to 100% coil inspection for hardness and dimensional checks. For non-critical structural brackets, reduced sampling per ANSI/ASQ Z1.4 may be acceptable. HS-FINEB supplies spheroidized fine blanking strip in fine blanking steel grades including SAE1035, SAE1045, SAE1078, 65Mn, C45E and 42CrMo with full MTC documentation per coil — contact us for a thick-strip material specification tailored to your part.
Why no material supplier has published a systematic guide for the 8–15 mm range. Three structural reasons explain the gap in published technical literature. First, the 8–15 mm range represents a small fraction of total fine blanking production volume — industry estimates suggest less than 10% of fine blanked parts are above 6 mm, and the majority of those are 6–8 mm. Suppliers allocate technical marketing resources to the high-volume 1.5–5 mm range where the customer base is larger. Second, thick-strip fine blanking is highly application-specific: the optimal material condition depends on part geometry (perimeter, aspect ratio, hole density, corner radii), press tonnage and frame rigidity, die design (V-ring geometry, clearance, tool steel), lubrication, and post-heat-treatment route. A single generic guide cannot cover the variation — each application requires trial blanking to optimize the material condition and process parameters. Third, the heavy-gauge range sits at the intersection of three disciplines: steel strip metallurgy (composition, spheroidization, inclusions), press engineering (tonnage, frame rigidity, counterpressure), and die design (V-ring, clearance, tool steel, coating). No single organization — steel mill, press builder, or die maker — owns the full process chain, so none publishes a complete guide. Steel mills publish material data sheets but not process recommendations; press builders publish tonnage tables but not material specifications; die makers share design rules but not material windows. This guide consolidates the available industry typical reference data from all three disciplines into a single specification framework for the 8–15 mm range.
These resources cover the baseline material requirements for all fine blanking gauges, the spheroidizing treatment process, the process selection decision, and the specific steel grades referenced in this thick-strip guide.
The baseline specification for all fine blanking gauges: carbon window, spheroidized microstructure, hardness bands, dimensional tolerances, surface quality, flatness, decarburization limits, and an incoming material acceptance checklist.
Temperature cycles, hold times, cooling rates, furnace atmosphere control, and common spheroidizing defects — the process behind the ≥92% microstructure requirement for thick-strip fine blanking.
Side-by-side comparison of material requirements, die life, cut-face quality and cost structure — with a 5-step process selection decision tree to determine whether a thick-strip part should be fine blanked or conventionally stamped.
HS-FINEB spheroidized fine blanking steel strip in SAE1035, SAE1045, SAE1078, 65Mn, C45E and 42CrMo, with full MTC per coil. Available in thicknesses up to 15 mm for heavy-gauge fine blanking.
Include part function, thickness × width, annual volume, press tonnage, and heat treat route. Our engineers reply within one working day with a full material specification and MTC template for thick-strip fine blanking.