Quick Answer
GG25 is the legacy German DIN 1691 designation for pearlitic gray cast iron, now standardized in Europe as EN-GJL-250 (EN 1561, material number 0.6025), and its closest international equivalents are ASTM A48 Class 35 (USA), JIS G5501 FC250 (Japan), and GB/T 9439 HT250 (China). The number “25” (or “250”) denotes a minimum tensile strength of 250 MPa (36.25 ksi) measured on a separately cast 30 mm test bar, paired with a Brinell hardness of 190–240 HB, a fine pearlitic matrix with Type A flake graphite, superior vibration damping, and excellent CNC machinability.
⚙ Engineering & Foundry Verification — Qingdao Yucheng (YCUMETAL) 34,000㎡ Pingdu Facility
All casting grades on this page are poured and machined in-house at our 34,000㎡ Pingdu foundry & CNC plant (400+ staff, IATF 16949 & ISO 9001 certified). Every heat is verified by Spectro optical emission spectrometry before pouring, with internal soundness and machined datums validated via Nikon XTH 320 industrial CT, Hexagon CMM, and Nikon metallographic microscopy.
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GG25 / EN-GJL-250 International Equivalent Cross-Reference Table
When global OEM buyers source pump housings, gearbox casings, machine tool beds, and agricultural drive housings via resin sand or shell mold casting, drawings from German, American, Japanese, and Chinese engineering teams specify the same pearlitic gray iron under five different standards:
| Standard / Region | Grade Designation | Material Number | Min Tensile Strength (30 mm Test Bar) | Typical Brinell Hardness | Predominant Microstructure |
|---|---|---|---|---|---|
| DIN 1691 (Legacy Germany) | GG25 (GG-25) | 0.6025 | 250 MPa (25 kgf/mm²) | 190–240 HB | ≥90% Fine Pearlite + Type A Flake Graphite |
| EN 1561 (Current EU) | EN-GJL-250 | EN-JL1040 | 250–350 MPa (15 mm wall: ~220 MPa) | 190–240 HB | Pearlitic matrix, inoculated flake graphite |
| ASTM A48 (USA) | Class 35B (or Class 40B) | UNS F12401 / F12801 | 35 ksi (241 MPa) / 40 ksi (276 MPa) | 187–241 HB | Pearlitic; note Class 35 is 241 MPa (Specify Class 40 if strict ≥250 MPa is required) |
| JIS G5501 (Japan) | FC250 | — | ≥250 MPa | 180–240 HB | Pearlitic gray cast iron |
| GB/T 9439 (China) | HT250 | — | ≥250 MPa | 190–240 HB | Pearlitic gray cast iron |
Need to compare GG25 against ductile iron or cast steel? Use our ASTM vs EN/DIN vs JIS vs GB Casting Grade Cross-Reference Calculator or read our Gray Iron vs Ductile Iron Buyer Guide.
Chemical Composition & Carbon Equivalent (CE) Control for GG25 / HT250
Neither EN 1561 nor ASTM A48 mandates a fixed chemical composition because mechanical strength is the governing acceptance criterion. However, achieving a uniform 250 MPa pearlitic structure without chilled white-iron carbides (which destroy CNC tool life in thin ribs) requires tight control of the Carbon Equivalent ( = \%C + \frac{1}{3}(\%Si + \%P)$) between 3.75% and 3.95% and ferrosilicon/strontium inoculation during pouring:
| Element / Parameter | Target Composition Range (wt%) | Metallurgical Role in GG25 / EN-GJL-250 Castings |
|---|---|---|
| Carbon (C) | 3.00% – 3.30% | Controls graphite flake volume; higher C improves fluidity and damping but lowers tensile strength if >3.35%. |
| Silicon (Si) | 1.60% – 2.10% | Promotes graphitization and prevents hard Fe3C chill carbides at thin edges and casting ribs. |
| Manganese (Mn) | 0.65% – 1.00% | Stabilizes pearlite and neutralizes sulfur via MnS (target $\%Mn \ge 1.7 \times \%S + 0.3\%$). |
| Phosphorus (P) | ≤ 0.12% (Pressure parts ≤0.08%) | Excess phosphorus forms brittle steadite networks that cause microporosity leaks in valve bodies and hydraulic manifolds. |
| Sulfur (S) | 0.05% – 0.12% | Controlled trace sulfur aids inoculation nucleation when balanced with Manganese. |
| Cu / Sn / Cr (Optional Pearlizers) | Cu 0.3–0.6% or Sn 0.04–0.08% | Added in heavy sections (>40 mm) to prevent ferrite formation and maintain ≥95% pearlite hardness across thick bosses. |
Wall-Thickness Section Sensitivity: Why a 10 mm Rib and an 80 mm Boss Have Different Strengths
Unlike wrought steel, gray iron strength depends directly on cooling rate. Faster solidification in thin walls refines graphite flakes and raises tensile strength (but risks chill if uninoculated), whereas slow cooling in thick sections coarsens Type A graphite flakes and lowers tensile strength. Per EN 1561 Annex A, buyers should expect the following anticipated properties inside actual casting walls for EN-GJL-250 (GG25):
| Relevant Wall Thickness (mm) | Expected Tensile Strength in Casting (MPa) | 0.1% Proof Stress Rp0.1 (MPa) | Elastic Modulus E (GPa) | Foundry & CNC Engineering Action |
|---|---|---|---|---|
| > 5.0 to 10 mm | ~245 – 270 MPa | ~165 MPa | 103 – 118 GPa | Use potent FeSi inoculation so thin flanges remain below 235 HB for smooth CNC milling & tapping. |
| > 10 to 20 mm | ~220 – 245 MPa | ~145 MPa | 103 – 118 GPa | Optimal design window for pump volutes, gearbox housings, and bearing caps. |
| > 20 to 40 mm | ~195 – 220 MPa | ~130 MPa | 95 – 110 GPa | Standard 30 mm separably cast test bar represents this cooling zone (250 MPa nominal bar). |
| > 40 to 80 mm | ~170 – 195 MPa | ~112 MPa | 90 – 105 GPa | Micro-alloy with 0.4% Cu or 0.05% Sn to prevent soft ferrite halos around mounting bores. |
| > 80 to 150 mm | ~155 – 170 MPa | ~100 MPa | 88 – 100 GPa | Apply stress-relief annealing (530–560°C furnace cool) before finish CNC boring to hold tight geometric flatness. |
When to Choose GG25 (Class 35) vs GGG40 / GGG50 Ductile Iron
- Choose GG25 (EN-GJL-250 / ASTM A48 Class 35) when: Your component requires vibration damping (3–5× higher damping capacity than steel or ductile iron), thermal conductivity (~48 W/m·K for brake discs, exhaust manifolds, and motor frames), lubricant-retaining sliding wear surfaces (machine tool ways, cylinder liners), and low-distortion CNC machining.
- Upgrade to GGG40 (60-40-18) or GGG50 (80-55-06) Ductile Iron when: The part faces tensile shock loads, high internal hydraulic spikes (>16 bar), or bending fatigue where GG25’s 0.3–0.8% fracture elongation is insufficient.
Frequently Asked Questions (FAQ)
Is ASTM A48 Class 35 or Class 40 the exact equivalent of GG25 (EN-GJL-250)?
GG25 (EN-GJL-250) specifies 250 MPa (36,259 psi) minimum tensile strength in a 30 mm cast test bar. ASTM A48 Class 35 specifies 35,000 psi (241 MPa), while Class 40 specifies 40,000 psi (276 MPa). In 90% of commercial RFQs, Class 35B is accepted as the standard US equivalent, while Class 40B is specified if the engineering drawing strictly requires ≥250 MPa tensile strength.
Should GG25 castings be stress-relieved before precision CNC machining?
Yes, for complex housings, machine frames, or parts with uneven wall thickness that require tight flatness and bore concentricity (±0.025 mm). A sub-critical stress-relief heat treatment at 530–560°C for 2–4 hours followed by slow furnace cooling to 200°C eliminates up to 85% of residual casting stresses without softening the pearlitic matrix.
What casting processes does YCUMETAL use for GG25 / HT250 parts?
At our 34,000㎡ Pingdu foundry, we produce GG25 / EN-GJL-250 / ASTM A48 Class 35 components via furan resin sand casting (for medium-to-large housings and beds) and coated-sand shell molding (for tighter CT6–CT8 dimensional tolerances and cleaner internal fluid passages), followed by in-house 3/4/5-axis CNC machining and CMM verification.