Conventional grain-oriented electrical steel — quick answer
Quick answer: 27Q120 / B27G120 is a conventional grain-oriented electrical steel (CRGO) of 0.27 mm nominal thickness from Baosteel. The number 120 is the nominal no-load loss grade: maximum 1.15 W/kg at 1.7 T / 50 Hz (P1.7/50) with minimum polarization J800 = 1.85 T. It is the workhorse core material for distribution transformers (pole-mounted, pad-mounted, small oil-immersed) and for power transformer cores where high-efficiency (domain-refined) grades are not required by the design.
How to read the grade designations
Chinese GO grades encode thickness and loss. In 27Q120: 27 = 0.27 mm nominal thickness, Q = 取向 (grain-oriented), 120 = nominal specific total loss 1.20 W/kg at 1.7 T / 50 Hz. The B-grade form B27G120 is Baosteel's Q/BQB 485-2023 designation (B = Baosteel, G = GO steel). In the IEC 60404-8-7 style used for export, this loss class is written around 120-27 (P1.7 nominal 1.20 W/kg, 27 = 0.27 mm). Nominal and maximum values differ: the standard guarantees the max value, e.g. B27G120 max 1.15 W/kg vs nominal 1.20 W/kg.
Magnetic properties (per Baosteel Q/BQB 485-2023)
| Grade | Nominal thickness (mm) | Max core loss P1.7/50 (W/kg) | Min polarization J800 (T) | Min stacking factor |
|---|---|---|---|---|
| B23G110 / 23Q110 | 0.23 | 1.08 | 1.85 | 0.95 |
| B27G120 / 27Q120 | 0.27 | 1.15 | 1.85 | 0.96 |
| B30G120 / 30Q120 | 0.30 | 1.15 | 1.86 | 0.96 |
| B30G130 / 30Q130 | 0.30 | 1.20 | 1.85 | 0.96 |
| B35G135 / 35Q135 | 0.35 | 1.35 | 1.88 | 0.96 |
Typical (non-guaranteed) values for B27G120: P1.7/50 ≈ 1.12 W/kg, J800 ≈ 1.86 T. GO grades are measured at 1.7 T (not 1.5 T as for NGO grades) because transformer cores operate near saturation. Every quotation includes the full guaranteed values per heat number.
International grade correspondence
| China Q/BQB 485-2023 | IEC 60404-8-7 style (class) | Typical JIS class (class) |
|---|---|---|
| B23G110 / 23Q110 | 110-23 | 23ZDKH / 23ZH class |
| B27G120 / 27Q120 | 120-27 | 27ZDKH / 27ZH class |
| B30G120 / 30Q120 | 120-30 | 30ZDKH / 30ZH class |
| B30G130 / 30Q130 | 130-30 | 30ZDKH class |
Class correspondence for reference only — test conditions and guaranteed values differ between standards. Confirm the exact grade on the mill test certificate before ordering. See our full steel grade equivalent charts.
Typical applications
0.27 mm conventional GO steel is the standard core material for distribution transformers worldwide: 10 kV/11 kV pole-mounted transformers, pad-mounted units, small oil-immersed transformers, dry-type transformers up to a few MVA, and reactor/instrument transformer cores. In power transformers it serves as the material of choice for return limbs and yokes and for utility specifications where DOE/IEC efficiency tiers are met without domain-refined material. Transformer OEMs and rewind shops in Latin America, Africa, the Middle East and Southeast Asia buy 27Q120-class material as their default grade — it balances core loss, price and availability better than any other GO class.
Supply form, coating and packaging
Supplied as slit coils for step-lap or conventional stacking: typical coil weight 2–6 t, inside diameter 508/510 mm, slit to your lamination width. Two insulation coatings per Q/BQB 485-2023: coating S (tension inorganic coating, withstands stress-relief annealing at 850 °C) and coating H (environmental chrome-free coating); both give inter-laminar resistance and withstand transformer winding stress. Export packaging: rust-proof paper + steel strapping, desiccant, eye-to-wall container loading. Every coil ships with the original Baosteel mill test certificate (loss and polarization values per heat number).
Why Baosteel, why Baohui
Baosteel operates the world's most advanced GO steel lines and supplies conventional grades like 27Q120 at scale with tight magnetic scatter — critical for transformer builders who design core loss margins per stack. As a Baosteel channel partner, Baohui Steel quotes GO material ex-mill or ex-warehouse with the original MTC, arranges slitting to your stacking width, and consolidates mixed-thickness orders (0.23/0.27/0.30 mm) into one container. Send your grade, thickness, width and quantity for a firm FOB Shanghai quotation within 24 hours.
