Steel M15-SP (Semi-processed, as-shipped)
Finish state
AISI/SAE M15 · UNS T11315
Choose when the laminator will stress-relief/quality anneal punched parts to develop grain size and final core loss.
Values for the SP condition
Other M15 tempers and conditions
M15 is listed in 2 conditions; see the grade overview at M15.
- SP-ANN
- SP
Compare all 2 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Semi-processed after customer quality anneal | Condition of finished laminations after the user's decarburizing/grain-growth anneal; softest state, lowest core loss. | 295 | 430 | 25 | 140 HB | 3.4 % IACS |
SPThis page Semi-processed, as-shipped | Choose when the laminator will stress-relief/quality anneal punched parts to develop grain size and final core loss. | 400 | 510 | 9 | 185 HB | 3.3 % IACS |
What is M15-SP?
M15-SP is M15 supplied in the SP condition — choose when the laminator will stress-relief/quality anneal punched parts to develop grain size and final core loss. M15-SP has a yield strength of 400 MPa (58 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 60% of steel grades. Elongation at break is 9% and the elastic modulus is 200 GPa (29 Msi). M15-SP has a density of 7.65 g/cm³ (0.276 lb/in³), lighter than 97% of steel grades. It melts at 1,500°C (2,732 °F).
Limitations
- Limited ductility — 9%, worse than 93% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Poor heat conductor — 22 W/m·K (12.7 BTU/hr·ft·°F), worse than 93% of steel grades
- Low electrical conductivity — 3.3 % IACS, worse than 86% of steel grades
- Difficult to machine — 40/100, worse than 77% of steel grades
M15-SP properties
Typical room-temperature values for M15-SP; 21 are specific to this condition. Other listed values are M15 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
M15-SP has a density of 7.65 g/cm³ (0.276 lb/in³), lighter than 97% of steel grades. It melts at 1,500°C (2,732 °F).
Mechanical12
M15-SP has a yield strength of 400 MPa (58 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 60% of steel grades. Elongation at break is 9% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
M15-SP is rated for continuous service to 200°C (392 °F). It conducts heat at 22 W/m·K (12.7 BTU/hr·ft·°F), worse than 93% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
M15-SP conducts electricity at 3.3 % IACS, worse than 86% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (15/100), better than 75% of steel grades.
Sustainability4
Producing a kilogram of M15-SP takes about 34 MJ of energy and emits 2.4 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 25%.
Manufacturability7
M15-SP's machinability is fair (40/100, worse than 77% of steel grades); weldability fair (48/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with M15-SP
Is M15 easy to machine?
Rarely machined; silicon makes it abrasive and gummy — use carbide tooling, and grind/EDM only with a follow-up stress-relief anneal to restore magnetics.
Can M15 be welded?
Lamination stacks are TIG/laser welded only in short skip beads — weld metal shorts laminations and locally destroys permeability; prefer interlocking or bonding.
Can M15 be formed, bent or molded?
Punches cleanly with sharp (<25 µm burr) dies and tight clearance (~5 % of thickness); limited bendability, avoid tight radii transverse to rolling direction.
What surface finishes work on M15?
Supplied pre-insulated with C-3 or C-5 core-plate; bare edges rust, so varnish-impregnate or encapsulate finished stacks and avoid pickling that removes the coating.
M15 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 |
|---|---|---|
| Cfully processed, decarburized | ≤ 0.01 | 0 |
| Simain resistivity former | 2.7 – 3.3 | 3 |
| AlSi+Al total ≈3.3–3.6 % | 0.2 – 0.9 | 0.5 |
| Mn | 0.1 – 0.45 | 0.25 |
| P | ≤ 0.05 | 0.02 |
| Skept low for grain growth | ≤ 0.01 | 0 |
| N | ≤ 0 | 0 |
| Fe | balance | — |
M15-SP — frequently asked
What is M15-SP used for?
M15-SP is typically used for high-efficiency motors, generators and small transformers. In short: lower core loss than M19; high-efficiency lamination grade; pre-insulated core-plate stock.
What is the yield strength of M15-SP?
M15-SP has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 2 listed tempers.
Is M15-SP easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% of steel grades). Rarely machined; silicon makes it abrasive and gummy — use carbide tooling, and grind/EDM only with a follow-up stress-relief anneal to restore magnetics.
Can M15-SP be welded?
With care — weldability is rated fair (48/100). Lamination stacks are TIG/laser welded only in short skip beads — weld metal shorts laminations and locally destroys permeability; prefer interlocking or bonding.
What surface finishes work on M15-SP?
Supplied pre-insulated with C-3 or C-5 core-plate; bare edges rust, so varnish-impregnate or encapsulate finished stacks and avoid pickling that removes the coating.
Can M15-SP be formed, bent or molded?
Punches cleanly with sharp (<25 µm burr) dies and tight clearance (~5 % of thickness); limited bendability, avoid tight radii transverse to rolling direction.
What is the maximum service temperature of M15-SP?
M15-SP 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.
Sources
- ASTM A677 – Nonoriented Electrical Steel Fully Processed Types — ASTM International (2020)
- ASTM A683 – Nonoriented Electrical Steel, Semiprocessed Types — ASTM International (2019)
- Non-oriented electrical steel product data (M-grades, C-5 coating) — Cleveland-Cliffs / AK Steel (2021)
- ASM Handbook Vol. 1 – Properties of Magnetically Soft Materials — ASM International (1990)
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.