1. What is GGG-40?

GGG-40 is a widely used grade of ductile iron (also called ductile cast iron or spheroidal graphite cast iron). Its designation comes from the European standard EN 1563 (latest edition EN 1563:2018 “Foundations – Ductile cast iron”).

• GGG: Abbreviation of the German phrase “Gusseisen mit Globularem Graphit,” meaning cast iron with spheroidal graphite — i.e., ductile iron.

• 40: Indicates the minimum tensile strength at room temperature in kgf/mm² (equivalent numerically to MPa). Thus, GGG-40 denotes a minimum tensile strength of 400 MPa (N/mm²).

• In the latest EN 1563:2018, it is more precisely designated as EN-GJS-400-15, where 400 represents the minimum tensile strength (MPa) and 15 the minimum elongation (%).

2. Core Feature: Graphite Morphology

The superior performance of ductile iron lies in the morphology of its graphite:

(1)Melting and Treatment: Prior to casting, the molten iron undergoes special spheroidizing treatment (usually with magnesium or cerium additions) and inoculation.

(2)Graphite Shape: After treatment, the graphite precipitates during solidification are no longer flake-like (as in gray cast iron) but form spherical or nodular shapes.

(3)Performance Enhancement: This spherical graphite greatly reduces cleavage effects on the metallic matrix, significantly improving strength, ductility, and toughness. The material behaves closer to steel while retaining cast iron’s excellent castability, vibration damping, wear resistance, and machinability.

3. Key Mechanical Properties of GGG-40 (EN-GJS-400-15)

The standard focuses on mechanical properties:

(1)Tensile Strength: Minimum ≥ 400 MPa (40 kgf/mm²). Typical range 400–550 MPa depending on casting thickness, cooling rate, microstructure, etc.

(2)Yield Strength: Minimum ≥ 250 MPa (25 kgf/mm²). Important as the stress at which noticeable plastic deformation begins.

(3)Elongation: Minimum ≥ 15% (for specimens with gauge length Lo = 5d). A key indicator of ductility and impact resistance. Typical elongation ranges from 15% to 25% or higher.

(4)Hardness: Typically 130–210 HBW (Brinell hardness), varying with matrix composition (ferrite/pearlite ratio). GGG-40 usually has a ferritic matrix to maximize ductility and toughness, placing hardness near the lower or middle range. Note: hardness is generally referenced, not strictly specified in the standard, and varies within different casting sections.

4. Metallographic Structure (Microstructure)

(1)Graphite: Spheroidal or nodular graphite with spheroidizing levels meeting standards (generally grade 1–3).

(2)Matrix: Predominantly ferritic (usually >85–90%) to achieve GGG-40’s performance, especially high elongation. Small amounts of pearlite (<10–15%) may be present.

(3)Achieving Ferritic Matrix:

• As-cast: Controlled chemistry (low manganese, limited pearlite-promoting elements), rapid cooling (thin sections), or strong inoculation (challenging to stabilize).

• Heat Treatment: More reliable and common method—annealing heat treatment above austenitizing temperature (900°C–950°C), holding to dissolve carbon, then slow cooling (furnace cooling) or prolonged holding just below eutectoid temperature (~720°C), decomposing austenite into ferrite and graphite, yielding a near-fully ferritic matrix.

5. Chemical Composition

Carbon: 3.5–3.8% (high carbon ensures good casting fluidity and graphite formation).

Silicon: 2.3–2.8% (promotes graphite and ferrite formation; excessive amounts reduce toughness).

Manganese: < 0.2% (critical! High Mn stabilizes pearlite, harming ductility and toughness; GGG-40 requires low Mn).

Phosphorus: < 0.05% (lower is better; high P causes brittle phosphide formation, reducing toughness).

Sulfur: < 0.015% (very low; sulfur consumes spheroidizers and interferes with nodularity).

Magnesium: 0.03–0.06% (residual, ensures spheroidization).

Others: Trace amounts of copper, tin, antimony may be present but strictly controlled to avoid promoting pearlite or harmful phases.

6. Main Advantages

High strength combined with good ductility: 400 MPa tensile strength and ≥15% elongation allow it to bear high loads and absorb impacts without fracturing.

Excellent toughness: Far superior to gray cast iron, also with good low-temperature impact resistance (though low-temperature toughness decreases).

Good castability: Excellent fluidity and lower shrinkage than cast steel, enabling complex and thin-walled castings.

Superior vibration damping: Better than cast steel, reducing noise and vibration.

Good wear resistance: While not as hard as some materials, ferritic matrix provides toughness support for many working conditions.

Excellent machinability: Easier to machine than steel.

Cost-effective: Balances performance and manufacturing costs between gray cast iron and cast steel, offering great value.

7. Limitations and Considerations

• Sensitive to cooling rates: thick casting sections may develop coarse graphite nodules and increased pearlite, reducing performance. Good casting design and heat treatment are needed to ensure uniformity.

• Requires strict control of chemical composition and production processes: improper spheroidizing, inoculation, or melting purity can cause defects such as graphite degeneration, floating graphite, flake-like graphite, or carbides, leading to poor performance.

• Low-temperature brittleness: Toughness decreases sharply below about -20°C; specialized low-temp grades (e.g., EN-GJS-400-18U-LT) are needed for colder environments.

• Relatively low hardness: Ferritic matrix results in lower hardness, potentially insufficient for severe abrasive wear without further heat treatment (e.g., austempered ductile iron).

8. Application Fields

GGG-40’s excellent strength and ductility make it widely used in components subject to load, impact, or vibration:

• Automotive: chassis parts (knuckles, control arms, brackets), differential housings, clutch housings, brake calipers, turbocharger housings.

• Construction machinery: drive axle housings, gearbox casings, hydraulic valve blocks, pump bodies, wheel hubs, suspension parts.

• General machinery: gearboxes, pump casings, valve bodies, compressor housings, flywheels, pulleys, couplings, machine tool parts.

• Pipeline systems: pipes, fittings (elbows, tees, flanges), valves.

• Energy and wind power: wind turbine hubs (large models use higher grades, but some parts use GGG-40), gearbox housings (external).

• Agricultural machinery: gearbox housings, rear axle housings, drive hubs.

• Railways: brake system parts, suspension components, couplers and buffers.

• Architectural hardware and fixtures: brackets and connectors requiring strength and toughness.

9. Comparison with Other Grades

• ISO 1083: GGG-40 corresponds to 400-15 (Rm ≥ 400 MPa, A ≥ 15%).

• China GB/T 1348: closest is QT400-18 (Rm ≥ 400 MPa, A ≥ 18%) with slightly higher elongation.

• ASTM A536 (USA): closest is 60-40-18 (Rm ≥ 414 MPa / 60 ksi, Rp0.2 ≥ 276 MPa / 40 ksi, A ≥ 18%) with slightly higher yield strength.

• JIS G5502 (Japan): equivalent to FCD400 (Rm ≥ 400 MPa, A ≥ 18%).

• Gray cast iron (EN-GJL-250 / GG-25): lower strength (~250 MPa), poor ductility (<1%), brittle but better vibration damping and lower cost.

• Higher-strength ductile irons: GGG-50 / 500-7, GGG-60 / 600-3 offer higher strength but lower ductility (7% or 3% elongation), often with more pearlite or special treatments.

• Cast steel (EN 10293 G20Mn5): similar or higher strength (400–500 MPa), better ductility (20–25%+), weldability, but poorer castability, higher shrinkage, and higher cost, with poorer vibration damping.

10. Summary

GGG-40 (EN-GJS-400-15) is a ferritic-matrix ductile iron grade featuring a unique combination of moderate strength (≥400 MPa) and excellent ductility/toughness (elongation ≥15%). This balance, together with good castability and machinability, makes it an ideal choice for complex parts under dynamic loads, impact, or vibration across various engineering sectors. Representing a major advancement in cast iron strength and toughness, its successful application relies on strict chemical control (especially low manganese), precise spheroidizing and inoculation, and typically annealing heat treatment to ensure the required ferritic matrix and spherical graphite morphology.

11. About Suzhou Bolaibao Metal

Suzhou Bolaibao Metal specializes in the development and production of high-quality ductile iron materials, including GGG-40, equipped with advanced melting, spheroidizing, and heat treatment technologies to ensure stable microstructure and mechanical properties that meet international standards such as EN 1563 and ASTM A536. We provide customized solutions for automotive, heavy industry, infrastructure, and energy sectors, committed to delivering castings that combine strength, toughness, and cost efficiency.

Choose Bolaibao for more reliable equipment and superior performance.
Phone: +86 15366282159
Email: sale@bolaibao1.com
Website: www.blbszmetal.com