Silicon steel is a ferritic Fe-Si alloy carrying 1–3.5% Si in commercial grades (up to 6.5% in laboratory alloys), and is split into two distinct categories: non-oriented isotropic electrical steel and grain-oriented anisotropic electrical steel, which together account for roughly 40% and 25% respectively of the global soft magnetic materials market [S1].
Selection is driven by core loss in watts/lb, stamped as AISI M-numbers (M15, M19, M22, M27, M36, M43, M45, M47) where higher M values mean higher allowable loss and lower unit cost, and M19 is the most common grade specified for motion-control laminations [S3].
Two Principal Families: Grain-Oriented vs Non-Oriented
Non-oriented silicon steel (NGO, also called CRNGO) is processed without controlled crystal alignment, typically contains 2–3.5% Si plus up to 0.5% Mn or Al for workability, and is isotropic in the rolling plane, which makes it the default material for rotating machines where flux direction is not fixed [S2][S5].
Grain-oriented silicon steel (GO, or CRGO) is heavily textured to a sharp {110}〈001〉 Goss orientation, with commercial grades held near 3.25% Si to suppress the austenite (γ) loop in the Fe-Si phase diagram, allowing high-temperature anneal without a destructive bcc-fcc phase change [S1][S4]. GO is reserved for wound-core and stacked-core transformers where flux follows the rolling direction, and it carries the lower-loss half of the soft-magnetic market by value [S1].
Why Silicon: The 1–3.5% Band Explained
Adding Si to iron raises electrical resistivity by a factor of about 5 (4.72×10⁻⁷ Ω·m at 3% Si versus 9.61×10⁻⁸ Ω·m for pure iron), which suppresses eddy currents and trims the hysteresis loop to roughly one-third the loss of plain carbon steel [S2].
Si also drops the magnetocrystalline anisotropy constant K₁ and pushes magnetostriction toward zero near 6% Si, both of which help domain-wall motion, but the trade-off is severe embrittlement: above ~2 wt% Si the alloy becomes hard to roll, above ~3 wt% it is hard to produce, and Si in the 5–6% range triggers the brittle DO₃ ordered α₁ phase, so practically all commercial grades stay below 3.5% Si [S1][S7]. Carbon is held below 0.005–0.01% to avoid magnetic aging and to keep the γ-loop suppressed during decarburizing anneal in hydrogen or endothermic atmospheres at 1350–1450 °F [S2][S3].
Grade Cross-Reference: AISI, EN, IEC, JIS, GOST, ASTM
Designations are equivalent across major standards, so a single grade can be ordered under several specifications. The cross-reference for fully-processed 0.35 mm and 0.50 mm NGO laminations includes: 250-35-A5 / M250-35A / M-15 / 36F145 / 35A250 / 2413; 270-35-A5 / M270-35A / M-19 / 36F158 / 35A270 / 2412; 300-35-A5 / M300-35A / M-22 / 36F168 / 35A300 / 2411; 330-35-A5 / M330-35A / M-36 / 36F190 [S4].
For 0.50 mm gauge the chain reads 290-50-A5 / M290-50A / M-15 / 47F168 / 50A290 / 2413, 310-50-A5 / M310-50A / M-19 / 47F174 / 50A310 / 2412, 330-50-A5 / M330-50A / M-27 / 47F190, 350-50-A5 / M350-50A / M-36 / 47F205 / 50A350 / 2411, 400-50-A5 / M400-50A / M-43 / 47F230 / 50A400 / 2312, and 470-50-A5 through 800-50-A5 for the heavier-loss M45 and M47 grades [S4]. The governing standards families are IEC 60404-8-4 (cold-rolled grain-oriented), EN 10106, JIS C2552, ASTM A677 for high-permeability NGO, and GOST 21427 [S2][S4].
Thickness, Processing State, and Stamping Decisions
Standard NGO lamination thicknesses are 0.014 in. (29 gauge, 0.35 mm), 0.0185 in. (26 gauge, 0.47 mm), and 0.025 in. (24 gauge, 0.65 mm); thinner 0.002, 0.004, and 0.007 in. electrical steels are re-rolled from M19-equivalent stock for high-frequency or high-performance stacks, at a material cost premium [S3].
Fully-processed material arrives annealed to optimum magnetic properties, while semi-processed stock is available only in M43 and worse grades and must be decarburization-annealed after stamping, otherwise excess carbon and punching stress leave a degraded edge zone that increases loss, particularly in narrow tooth sections [S3]. A 1350–1450 °F soak in a non-oxidizing, non-carburizing atmosphere (endothermic, nitrogen, or vacuum) is the standard stress-relief cycle, and one tachometer builder reportedly cut stack height 10% by adding this step [S3].
Physical and Mechanical Reference Numbers
At roughly 3% Si the reference numbers are: density 7,650 kg/m³, resistivity 4.72×10⁻⁷ Ω·m, melting point about 1,500 °C, tensile strength 300–450 MPa, fatigue strength 250–350 MPa, and elongation 2–4%, with the higher Si pushing resistivity up further at the cost of ductility [S2].
Specifying silicon steel is therefore a multi-axis decision: Si content sets resistivity and embrittlement, grain orientation sets directional permeability, AISI M-number sets the watts-per-pound ceiling, and gauge/anneal state sets the high-frequency loss penalty, all of which interact with the lamination insulation coating (C-oxide, C-5, inorganic, or organic) chosen to limit interlaminar eddy currents [S3][S6].
Application Routing: Where Each Family Lands
Higher-loss NGO grades feed small motors, generators, relays, and small power transformers where efficiency is secondary to cost; the lowest-loss NGO and GO grades feed large generators, distribution transformers, and power transformers where mass and watts-per-kilogram dominate the specification [S1][S4].
For the wider product chain, silicon steel laminations are a key sub-assembly inside electricity meter current coils and into the stator stacks of the lighting equipment and electric lamps drivers and ballasts covered in spec-driven lighting builds, which is why grain texturing matters at the material level rather than at the assembly level [S4].
Limits, Failure Modes, and Substitution Rules
Three practical failure modes drive every deviation from the default M19 / 0.014 in. lamination: magnetic aging when carbon leaves solid solution as carbides, contamination-driven hysteresis loss from carbides/sulfides/oxides/nitrides as small as 1 µm, and edge-zone damage from punching that demands a post-stamp stress-relief anneal on narrow or high-flux parts [S2][S3].
Substitution moves one direction only: a lower M-number can replace a higher M-number (M19 for M36) but not the reverse, and designers weighing semi-processed M43 should benchmark against low-carbon steel, which often matches the loss at lower cost once the post-stamp anneal is priced in [S3]. When the alloying is pushed past 3.5% Si to chase the zero-magnetostriction point near 6% Si, the material leaves the cold-rollable window and is no longer stocked in standard AISI M designations [S1].
For cross-material sourcing context that affects the same Fe-Si supply chain, the molybdenum demand 2026-2030 outlook tracks steel-sector alloy consumption, and a related tungsten producer map is the parallel reference for the refractory-alloy side of the same electrical-steel specification chain. Track the next node: IEC 60404-8-7 reduced-coercivity CRGO revisions and the next-generation high-induction low-loss GO grades built on sharper {110}〈001〉 texture, both of which are the active front for transformer-core loss reduction beyond the existing M-grade ceiling [S1][S2].