Steel SPFC780-SK
Supply condition
SK = skin-passed / temper-rolled, high surface quality
Order skin-passed (temper-rolled) material to remove the yield-point elongation and improve flatness and surface for appearance panels or tight springback control; yield rises to 510 MPa, elongation 15 %.
Values for the SK condition
Other SPFC780 tempers and conditions
SPFC780 is listed in 4 conditions; see the grade overview at SPFC780.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Low-yield-ratio (dual-phase) type per JIS G 3135 | Specify the JIS G 3135 low-yield-ratio dual-phase type at 470 MPa yield and 820 MPa tensile for the best stamping formability and dent resistance; it is the variant normally purchased. | 470 | 820 | 17 | 21 HRC | 8.6 % IACS |
CRDefault Cold rolled | Take the bare cold-rolled, continuously annealed dual-phase coil as the default for body inner structural parts that are stamped then phosphated and e-coated; rust protection comes only from paint. | 480 | 820 | 16 | 22 HRC | 8.6 % IACS |
SKThis page Skin-passed / temper-rolled, high surface quality | Order skin-passed (temper-rolled) material to remove the yield-point elongation and improve flatness and surface for appearance panels or tight springback control; yield rises to 510 MPa, elongation 15 %. | 510 | 830 | 15 | 23 HRC | 8.6 % IACS |
2 % prestrain + 170 °C/20 min paint-bake | Use the 2 % prestrain plus 170 °C/20 min paint-bake state for CAE and crash assessment: bake hardening raises yield to 570 MPa while elongation drops to 12 %. | 570 | 850 | 12 | 25 HRC | 8.6 % IACS |
What is SPFC780-SK?
SPFC780-SK is SPFC780 supplied in the SK condition — order skin-passed (temper-rolled) material to remove the yield-point elongation and improve flatness and surface for appearance panels or tight springback control; yield rises to 510 MPa, elongation 15 %. SPFC780-SK has a yield strength of 510 MPa (74 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 65% of steel grades. Elongation at break is 15% and the elastic modulus is 207 GPa (30 Msi). SPFC780-SK has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,490°C (2,714 °F). CR is the default condition FabDigit quotes; SK is available on request or by drawing note.
Limitations
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Difficult to machine — 34/100, worse than 86% of steel grades
SPFC780-SK properties
Typical room-temperature values for SPFC780-SK; 23 are specific to this condition. Other listed values are SPFC780 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SPFC780-SK has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,490°C (2,714 °F).
Mechanical16
SPFC780-SK has a yield strength of 510 MPa (74 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 65% of steel grades. Elongation at break is 15% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
SPFC780-SK is rated for continuous service to 200°C (392 °F). It conducts heat at 45 W/m·K (26 BTU/hr·ft·°F), better than 66% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
SPFC780-SK conducts electricity at 8.6 % IACS, better than 66% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of SPFC780-SK takes about 26 MJ of energy and emits 2.3 kg of CO₂ — less than 64% of steel grades. Typical recycled content is 20%.
Manufacturability7
SPFC780-SK's machinability is poor (34/100, worse than 86% of steel grades); weldability good (60/100); formability fair (44/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SPFC780-SK
Is SPFC780 easy to machine?
Very little machining is done; blanking and laser cutting dominate. Use a punching clearance of 10–14 % of sheet thickness with powder-metallurgy or coated (TiCN/CrN) tool steels for wear resistance, since burred cut edges markedly reduce flanging and fatigue performance.
Can SPFC780 be welded?
Resistance spot welding is the main process, with a narrower current window than mild steel; pulsed current plus a tempering pulse is recommended to reduce nugget martensite brittleness. Laser and MAG welding are feasible, but the softened HAZ band becomes the tensile failure site, so avoid prolonged local high heat input.
Can SPFC780 be formed, bent or molded?
Cold stamped with n ≈ 0.16 and r ≈ 0.9; springback and sidewall curl are pronounced, so use CAE springback compensation, higher blank-holder force or a stepped/variable-radius punch. Bend radius should be ≥3 t, and because sheared-edge flangeability is low, laser trim or stress-relieve after trimming.
What surface finishes work on SPFC780?
Bare sheet must be protected: phosphate plus cathodic e-coat, or order EG, GI or GA coated condition. Avoid strong acid pickling and high-hydrogen plating processes to prevent hydrogen-induced delayed cracking; powder coating and structural adhesive bonding are compatible.
SPFC780 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CJIS G 3135 limit ≤0.18; DP780 typically 0.09–0.15 | 0.07 – 0.18 | 0.12 |
| Sisuppresses cementite, stabilizes retained austenite | 0.1 – 0.8 | 0.35 |
| Mnmain hardenability element | 1.3 – 2.5 | 1.9 |
| P | ≤ 0.04 | 0.02 |
| Slow S improves bending and flanging | ≤ 0.02 | 0 |
| Aldeoxidizer | 0.02 – 0.08 | 0.04 |
| CrCr/Mo optional to raise martensite fraction | ≤ 0.6 | 0.25 |
| Mooptional | ≤ 0.35 | 0.1 |
| Nbmicroalloying for grain refinement (optional) | ≤ 0.06 | 0.02 |
| Tioptional | ≤ 0.06 | 0.02 |
| Boptional, increases hardenability | ≤ 0.01 | 0 |
| N | ≤ 0.01 | 0 |
| Fe | balance | — |
SPFC780-SK — frequently asked
What is SPFC780-SK used for?
SPFC780-SK is typically used for door rings, cross members and seat structures. In short: 780 MPa cold-stamping grade; between DP590 and DP980; springback-sensitive in dies.
What is the yield strength of SPFC780-SK?
SPFC780-SK has a typical yield strength of 510 MPa (74 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 65% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is SPFC780-SK easy to machine?
Not especially — machinability is rated poor (34/100, worse than 86% of steel grades). Very little machining is done; blanking and laser cutting dominate. Use a punching clearance of 10–14 % of sheet thickness with powder-metallurgy or coated (TiCN/CrN) tool steels for wear resistance, since burred cut edges markedly reduce flanging and fatigue performance.
Can SPFC780-SK be welded?
Yes — weldability is rated good (60/100). Resistance spot welding is the main process, with a narrower current window than mild steel; pulsed current plus a tempering pulse is recommended to reduce nugget martensite brittleness. Laser and MAG welding are feasible, but the softened HAZ band becomes the tensile failure site, so avoid prolonged local high heat input.
What surface finishes work on SPFC780-SK?
Bare sheet must be protected: phosphate plus cathodic e-coat, or order EG, GI or GA coated condition. Avoid strong acid pickling and high-hydrogen plating processes to prevent hydrogen-induced delayed cracking; powder coating and structural adhesive bonding are compatible.
Can SPFC780-SK be formed, bent or molded?
Cold stamped with n ≈ 0.16 and r ≈ 0.9; springback and sidewall curl are pronounced, so use CAE springback compensation, higher blank-holder force or a stepped/variable-radius punch. Bend radius should be ≥3 t, and because sheared-edge flangeability is low, laser trim or stress-relieve after trimming.
What is the maximum service temperature of SPFC780-SK?
SPFC780-SK is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SPFC780-CR and SPFC780-SK?
CR is the default condition — take the bare cold-rolled, continuously annealed dual-phase coil as the default for body inner structural parts that are stamped then phosphated and e-coated; rust protection comes only from paint. SK: order skin-passed (temper-rolled) material to remove the yield-point elongation and improve flatness and surface for appearance panels or tight springback control; yield rises to 510 MPa, elongation 15 %. Yield strength is 480 MPa in CR versus 510 MPa in SK.
Sources
- JIS G 3135 — Cold-reduced high strength steel sheet and strip for automobile structural uses — JISC (2018)
- Advanced High-Strength Steels Application Guidelines V7 — WorldAutoSteel (2021)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- Cold-rolled dual phase steel (DP780) product data — Nippon Steel / JFE Steel (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.