Steel M-3
M-3 is a high-permeability (Hi-B) grain-oriented silicon steel to ASTM A876, produced with a sharper Goss texture and a phosphate–magnesium silicate tension coating that together give the lowest core loss in the M-series.
Reference datasheet — M-3 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
M-3 tempers and conditions
M-3 is supplied in 2 conditions, soft to hard.
Compare all 2 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Stress-relief annealed after shearing/forming | Apply this ≈800–840 °C protective-atmosphere anneal to wound or punched and bent cores to recover core loss raised by processing stress; yield falls to 295 MPa, elongation rises to 12%. | 295 | 340 | 12 | 150 HB | 3.6 % IACS |
Domain refined (laser/mechanically scribed) Hi-B strip | Use laser- or mechanically scribed domain-refined Hi-B strip for large transformer stacked cores needing the lowest core loss with no stress-relief anneal; mechanical properties are unchanged. | 315 | 360 | 7 | 163 HB | 3.6 % IACS |
Supply forms, finishes and certifications
Ways M-3 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
FP-C2 | Fully processed with thin inorganic (glass film + phosphate) coating | Surface finish |
FP-C5Default | Fully processed, C-5 tension-coated | Coating |
What is M-3?
M-3 is a high-permeability (Hi-B) grain-oriented silicon steel to ASTM A876, produced with a sharper Goss texture and a phosphate–magnesium silicate tension coating that together give the lowest core loss in the M-series. It is supplied as slit coil and mitre-cut laminations in C-5 or C-2 coated, domain-refined and stress-relief annealed conditions for large, high-efficiency transformer cores where capitalised no-load loss outweighs material cost. The sheet is hard, brittle and strongly anisotropic (8 % elongation, 84 HRB), limited to about 200 °C, and needs an anneal after cold work; M-6 is the lower-cost alternative. M-3 has a density of 7.65 g/cm³ (0.276 lb/in³), lighter than 97% of steel grades. It melts at 1,470°C (2,678 °F). M-3 has a yield strength of 315 MPa (45.7 ksi) and a tensile strength of 360 MPa (52.2 ksi) — weaker than 82% of steel grades. Elongation at break is 8% and the elastic modulus is 120 GPa (17.4 Msi).
What is M-3 used for?
- Large power transformer cores
- High-efficiency distribution transformer cores
- Generator step-up transformer cores
- Mitre-cut stacked core laminations
- Wound C-cores and toroidal cores
- Shunt reactor cores
Limitations
- Low stiffness — 120 GPa (17.4 Msi), worse than 99% of steel grades
- Limited ductility — 8%, worse than 95% of steel grades
- Poor heat conductor — 21 W/m·K (12.1 BTU/hr·ft·°F), worse than 95% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- High embodied carbon — 2.6 kg CO₂/kg, worse than 87% of steel grades
M-3 properties
Typical room-temperature values; bars are the position among steel grades.
Physical3
M-3 has a density of 7.65 g/cm³ (0.276 lb/in³), lighter than 97% of steel grades. It melts at 1,470°C (2,678 °F).
Mechanical11
M-3 has a yield strength of 315 MPa (45.7 ksi) and a tensile strength of 360 MPa (52.2 ksi) — weaker than 82% of steel grades. Elongation at break is 8% and the elastic modulus is 120 GPa (17.4 Msi).
Thermal6
M-3 is rated for continuous service to 200°C (392 °F). It conducts heat at 21 W/m·K (12.1 BTU/hr·ft·°F), worse than 95% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
M-3 conducts electricity at 3.6 % IACS, worse than 85% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of M-3 takes about 35 MJ of energy and emits 2.6 kg of CO₂ — more than 87% of steel grades. Typical recycled content is 15%.
Manufacturability6
M-3's machinability is fair (35/100, worse than 84% of steel grades); weldability fair (40/100); formability poor (30/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. M-3 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with M-3
Is M-3 easy to machine?
Work mainly by precision shearing, blanking and laser or waterjet cutting. The high silicon content wears dies quickly, so use carbide cutting edges and closely controlled die clearance to limit burrs and edge stress.
Can M-3 be welded?
Avoid welding between laminations — welds short the interlaminar insulation and raise core loss in the heat-affected zone. Where tacking is unavoidable, use low-heat-input TIG or laser spot welds followed by a stress-relief anneal.
Can M-3 be formed, bent or molded?
The material is hard, brittle and strongly anisotropic, so restrict work to shearing, slight bending or core winding. Anneal at 800–840 °C in a protective atmosphere after any cold work to restore magnetic properties.
M-3 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 |
|---|---|---|
| Sicore alloying element; raises resistivity, lowers eddy-current loss | 2.9 – 3.4 | 3.15 |
| Cdecarburization annealed; very low C avoids magnetic aging | ≤ 0.01 | 0 |
| Mn | 0.03 – 0.2 | 0.1 |
| AlAlN inhibitor for the Hi-B process | 0.02 – 0.04 | 0.03 |
| Nforms AlN inhibitor with Al | ≤ 0.01 | 0.01 |
| SMnS inhibitor residue; low in finished product | ≤ 0.01 | 0.01 |
| P | ≤ 0.03 | 0.01 |
| Cuused as auxiliary inhibitor in some process routes | ≤ 0.3 | 0.1 |
| Fe | balance |
What surface finishes work on M-3?
Supplied with a phosphate–magnesium silicate tension coating and needs no plating. For painting or bonding, remove the coating locally or use a compatible primer; varnish sheared edges for rust protection.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
How much does M-3 cost?
M-3 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
M-3 — frequently asked
What is M-3 used for?
M-3 is typically used for large power transformer cores, high-efficiency distribution transformer cores, generator step-up transformer cores, mitre-cut stacked core laminations, wound C-cores and toroidal cores and shunt reactor cores. In short: lowest-loss grain-oriented grade; hi-B high-permeability steel; highest cost per kilogram.
What is the yield strength of M-3?
M-3 has a typical yield strength of 315 MPa (45.7 ksi) and a tensile strength of 360 MPa (52.2 ksi) — weaker than 82% of steel grades. Strength varies by condition: see the 2 listed tempers.
Is M-3 easy to machine?
Not especially — machinability is rated fair (35/100, worse than 84% of steel grades). Work mainly by precision shearing, blanking and laser or waterjet cutting. The high silicon content wears dies quickly, so use carbide cutting edges and closely controlled die clearance to limit burrs and edge stress.
Can M-3 be welded?
With care — weldability is rated fair (40/100). Avoid welding between laminations — welds short the interlaminar insulation and raise core loss in the heat-affected zone. Where tacking is unavoidable, use low-heat-input TIG or laser spot welds followed by a stress-relief anneal.
What surface finishes work on M-3?
Supplied with a phosphate–magnesium silicate tension coating and needs no plating. For painting or bonding, remove the coating locally or use a compatible primer; varnish sheared edges for rust protection.
Can M-3 be formed, bent or molded?
The material is hard, brittle and strongly anisotropic, so restrict work to shearing, slight bending or core winding. Anneal at 800–840 °C in a protective atmosphere after any cold work to restore magnetic properties.
What is the maximum service temperature of M-3?
M-3 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.
How much does M-3 cost?
M-3 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM A876/A876M — Flat-Rolled, Grain-Oriented, Silicon-Iron, Electrical Steel, Fully Processed Types — ASTM International (2020)
- ASTM A34/A34M — Practice for Sampling and Procurement Testing of Magnetic Materials — ASTM International (2021)
- Grain-Oriented Electrical Steels Product Data Bulletin — AK Steel / Cleveland-Cliffs (2019)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (magnetically soft materials) — ASM International (1990)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.