QT700-2 ductile cast iron represents a high-strength grade of nodular graphite cast iron classified under the Chinese national standard GB/T 1348. The standard numerical designation indicates a minimum tensile strength requirement of 700 MPa, positioning the material as a high-performance ferrous alloy designed for structural components that experience heavy physical stress. The material is produced by introducing specific nodulizers, such as magnesium or rare earth elements, into the liquid iron melt before pouring. The chemical treatment causes the carbon to precipitate as spherical graphite nodules rather than the elongated flakes found in standard gray iron.
The spherical shape of the graphite eliminates the sharp internal stress concentration points within the metallic matrix, providing a distinct balance of high tensile strength, hardness, and wear resistance. Because the underlying microstructure consists primarily of a pearlitic matrix, the material exhibits rigid mechanical behaviors and low elongation characteristics under load. This alloy replaces forged steel, cast steel, or low-alloy carbon steels in heavy industrial machinery, hydraulic systems, and automotive drivetrains. The combination of high mechanical performance and standard casting efficiency allows factories to manufacture complex, near-net-shape components that would require extensive machining if produced from solid steel blocks.
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Chemical Composition of QT700-2 Ductile Cast Iron
QT700-2 is a type of high strength ductile cast iron. The chemical composition of QT700-2 ductile cast iron focuses on balancing carbon and silicon levels to encourage proper graphite nodularization while managing manganese and alloy additions to form a pearlitic matrix. Standard material specifications dictate the allowable ranges for each elemental component, though specific values are often adjusted based on casting thickness and cooling conditions to meet the required mechanical targets. Carbon typically ranges between 3.2% and 3.7%, providing the source material for the graphite spheres. Silicon acts as a graphitizer, encouraging the carbon to precipitate correctly, and is maintained between 2.3% and 2.6%.
Manganese levels are held between 0.5% and 0.7% to assist in stabilizing the pearlite structure, which gives the material its high tensile strength. Phosphorus and sulfur represent trace impurities and are kept as low as possible to prevent embrittlement. Small fractions of magnesium and rare earth elements are introduced during the ladling stage to force the graphite into its distinct nodular shape.
Copper may also be added in small percentages to promote pearlite formation without increasing the risk of cracking. The typical chemical composition range for this grade includes the following elemental proportions:
| Element | Weight Percentage Range (%) |
| Carbon (C) | 3.20 – 3.70 |
| Silicon (Si) | 2.30 – 2.60 |
| Manganese (Mn) | 0.50 – 0.70 |
| Phosphorus (P) | Less than or equal to 0.07 |
| Sulfur (S) | Less than or equal to 0.03 |
| Magnesium (Mg) | 0.025 – 0.060 |
| Rare Earths (Re) | 0.020 – 0.040 |
| Copper (Cu) | 0.20 – 0.40 |
QT700-2 Ductile Cast Iron Mechanical Properties
The mechanical properties of QT700-2 ductile cast iron define its performance under high structural loads and severe mechanical wear. The alloy exhibits a highly developed pearlitic matrix containing spherical graphite nodules, which provides high yield strength and notable fatigue resistance. Testing procedures evaluate these attributes using standard separate cast test bars to confirm compliance with industrial production requirements. A minimum tensile strength of 700 MPa allows components to withstand intense pulling forces without experiencing structural separation, making the metal competitive with structural steel grades.
The material balances this high tensile capacity with a yield strength minimum of 420 MPa, which marks the point where permanent deformation begins under tension. Due to the high pearlite ratio in the microstructural background, the elongation value is relatively low, typically showing a minimum measurement of 2%. The low elongation means the material behaves rigidly and will not bend significantly before fracturing.
Hardness values remain high, ranging from 225 to 305 HBW on the Brinell scale, providing the surface durability needed to resist localized abrasion, scratching, and surface deformation during prolonged machine use. The primary mechanical specifications for this ductile iron grade include the following parameters:
| Mechanical Property | Minimum Specification Value |
| Tensile Strength | 700 MPa |
| Yield Strength | 420 MPa |
| Elongation Percentage | 2% |
| Brinell Hardness Range | 225 – 305 HBW |
Casting Processes for QT700-2 Ductile Iron
The manufacturing of QT700-2 ductile cast iron components requires controlled mold cooling rates and precise metallurgical handling to achieve the desired pearlitic microstructure. Distinct casting methods are deployed depending on the part geometry, production volume, surface finish requirements, and dimensional tolerances specified by the engineering designs.
Sand Casting
Sand casting represents a widespread method used to produce small, medium, and large QT700-2 components. Workers pack a mixture of silica sand, clay, and water around a reusable pattern to form the cope and drag mold halves. The high thermal mass of the sand mold allows for a steady cooling rate, which helps manage internal stresses in thick-walled parts like heavy brackets and transmission housings. We often use green sand casting method for high-volume automated production, while resin sand casting process is used when parts demand greater mold stability and cleaner surface details. Because sand molds expand slightly under heat, parts made through this method usually require extra machining allowances on functional surfaces to achieve final dimensions.
Shell Mold Casting
Shell mold casting provides a higher level of dimensional accuracy and smoother surface finishes than standard sand casting. The process uses a heated metal pattern coated with a resin-coated sand mixture to form a hardened, thin shell mold half. Two matching shells are bonded together to receive the liquid ductile iron. The rigid nature of the shell mold minimizes mold wall movement during the iron solidification stage, helping to maintain strict dimensional tolerances. This method fits medium-sized QT700-2 parts well, such as camshafts and small crankshafts, where reducing post-casting machining saves production time and lowers tool wear.
Investment Casting
Investment casting, also referred to as the lost wax process, is used when QT700-2 components feature intricate shapes, thin walls, or complex internal passages. Operators inject wax into a metal die to create a pattern, which is then dipped into a ceramic slurry repeatedly to build a hard outer shell. The wax is melted out in an autoclave, leaving a precise ceramic cavity that receives the molten iron.
This method minimizes material waste because the resulting castings closely match net-shape specifications, making it a viable option for high-stress hydraulic valve blocks and custom mechanical linkages. Controlling the cooling rate inside the insulating ceramic shell is necessary to make sure the pearlite matrix develops fully without forming hard, brittle iron carbides.
Lost Foam Casting
Lost foam casting uses a polystyrene foam pattern that possesses the exact geometry of the desired component. Workers pack unbonded sand around the foam pattern inside a casting flask, using vibration to compact the sand into all the complex pockets. When the molten iron is poured into the mold, the intense heat vaporizes the foam instantly, and the liquid metal fills the exact space previously occupied by the pattern.
This process eliminates the need for draft angles or core assemblies, allowing engineers to design complex QT700-2 components with internal oil lines or hollow structural sections. The unbonded sand also permits easy shakeout after cooling, though the carbon vapors from the burning foam must be managed to prevent surface defects in the ductile iron.
Key Advantages of QT700-2 Ductile Iron Castings
Selecting QT700-2 ductile iron for industrial components provides several manufacturing and operational benefits due to its unique pearlitic microstructure and nodular graphite formation. The material bridges the gap between the castability of traditional iron and the mechanical performance of structural steel, offering engineers a reliable alternative for high-stress applications. This grade is utilized to achieve a combination of physical durability and cost-effective production.
High Tensile and Yield Strength
The primary benefit of QT700-2 ductile iron is its ability to withstand heavy mechanical loads without structural failure. The minimum tensile strength of 700 MPa paired with a yield strength of 420 MPa allows components to endure extreme pulling, bending, and compressive forces. This high load capacity enables engineers to design thinner, lighter parts that possess the same structural integrity as heavier components made from lower grades of cast iron. The strength profile of the material makes it a viable substitute for carbon steel forgings and fabrications in many structural applications.
Excellent Wear Resistance
The pearlitic matrix of QT700-2 gives the material a high surface hardness, ranging from 225 to 305 HBW. This hardness, combined with the self-lubricating properties of the embedded graphite nodules, results in superior wear resistance under friction. Components subject to continuous sliding contact or abrasive conditions resist surface deformation and scratching over long operational periods. This characteristic extends the service life of mating parts in machinery, reducing the need for frequent replacements or specialized surface hardening treatments.
Superior Vibration Damping and Fatigue Strength
The spherical graphite nodules within the iron matrix assist in absorbing mechanical vibrations and dampening resonance generated by rotating machinery. This capability minimizes cyclic stress accumulation, which lowers the risk of fatigue cracking over millions of operational cycles. Compared to cast steel, QT700-2 handles cyclic loading more effectively by dispersing internal stresses around the rounded nodules rather than allowing cracks to propagate. This makes the alloy well-suited for high-vibration environments like engine compartments and heavy manufacturing floors.
Good Machinability and Casting Efficiency
Despite its high hardness and strength, QT700-2 retains favorable machinability compared to steels of similar tensile capacity. The graphite nodules act as natural chip-breakers during drilling, milling, and turning operations, which reduces friction at the cutting tool interface and extends tool life. Furthermore, the material retains the low melting point and fluid flowing characteristics inherent to ductile iron. The casting efficiency allows the pouring of complex, near-net-shape geometries that reduce the volume of raw material that must be removed through post-casting machining.
Primary Industrial Applications of QT700-2 Ductile Iron Castings
The combination of 700 MPa tensile strength, wear resistance, and high fatigue limits makes QT700-2 ductile iron a common choice across heavy industries. Components cast from this grade perform reliably under continuous cyclical loads, high pressures, and abrasive environmental conditions.
Automotive
In the automotive sector, factories use QT700-2 to manufacture high-stress drivetrain and engine parts that must withstand constant rotational forces. Common automotive castings include heavy-duty crankshafts, camshafts, gearbox housings, transmission gears, and steering knuckles. The pearlite matrix provides the necessary fatigue strength to handle rapid engine cycles, while the nodular graphite assists in dampening engine vibrations, leading to smoother powertrain operation.
Industrial Machinery
General machinery manufacturing relies on this high-strength grade for structural components that encounter severe torque and mechanical stress. Heavy gear wheels, flywheels, transmission housings, electric motor enclosures and large roller bearings are typically cast from the material. The high yield strength prevents structural twisting or deformation when industrial machines experience sudden stops, high-load startups, or continuous continuous operations on factory floors.
Oil and Gas
The oil and gas industry uses QT700-2 castings for surface and downhole equipment exposed to high mechanical loads. The material is used to produce high-pressure manifold joints, mud pump components, and structural connectors for drilling rigs. Its ability to resist cracking under high stress helps maintain structural integrity in pressurized environments, offering a cost-effective alternative to forged steel components.
Pump and Valve
High-pressure fluid handling systems utilize this grade for enclosures and internal components that must resist deformation under constant internal pressure. Pump and valve castings include high-capacity pump casings, heavy-duty valve bodies, regulators, and wear rings. The surface hardness of the pearlitic structure protects internal fluid pathways from localized erosion caused by turbulent flow or minor particulate matter suspended in liquid streams.
Mining and Construction Machinery
Heavy earthmoving and mining equipment operates under severe impact and abrasion, making the durability of QT700-2 highly useful. Mining and construction machinery casting components like excavator track links, conveyor drive pulleys, crusher frames, and structural brackets for bulldozers are frequently poured from this alloy. The high Brinell hardness resists surface gouging from rocks and debris, while the interior matrix prevents structural fracturing during heavy shock impacts.
Agriculture
Agricultural equipment faces diverse load demands and constant exposure to outdoor elements, requiring tough, rigid components. Agricultural machinery castings like tractor axle housings, plow shares, harvester gearbox housings, and hitch assemblies are commonly cast from QT700-2 ductile iron. The casting efficiency of the ductile iron allows for the production of complex, single-piece structural frames that reduce total vehicle weight without sacrificing pulling capacity.
Railway and Transit
The railway sector utilizes QT700-2 for track and rolling stock components that bear high axle loads and constant vibration. Railway castings such as rail clips, brake discs, bogie brackets, and suspension linkages are frequently made from this grade of cast iron. The superior vibration damping qualities of the spherical graphite nodules help dissipate track resonance, reducing mechanical fatigue accumulation and extending the operational lifespan of the transit components.
Common Surface Treatment for QT700-2 Ductile Iron Castings
While QT700-2 ductile iron possesses high baseline hardness and wear resistance due to its pearlitic matrix, surface treatments are frequently applied to modify the exterior layer for specific working conditions. These processes enhance corrosion protection, further increase surface hardness, or improve friction characteristics without altering the tough core properties of the casting.
Shot Peening
Shot peening is a mechanical surface treatment used to improve the fatigue life of QT700-2 components subjected to high cyclic stresses, such as crankshafts and transmission gears. The process involves blasting the casting surface with round metal or ceramic shot at high velocities. This impact creates localized plastic deformation, inducing a layer of compressive residual stress on the exterior. The compressive layer counteracts tensile stresses during machinery operation, preventing microcracks from forming and propagating from the surface.
Nitriding and Nitrocarburizing
Thermochemical treatments like gas nitriding or ferritic nitrocarburizing introduce nitrogen and carbon into the surface layer of the ductile iron at sub-critical temperatures, typically between 500 and 580 degrees Celsius. This creates a hard compound zone and a diffusion layer on the casting exterior. For QT700-2, nitriding significantly boosts surface hardness well beyond the base Brinell rating, dramatically increasing resistance to adhesive wear and scuffing in sliding contact applications like camshafts and valve guides.
Induction Hardening
Induction hardening is used when a localized area of a QT700-2 casting requires maximum wear resistance while the rest of the part needs to retain its standard machinability or toughness. Electromagnetic induction coils rapidly heat specific zones, such as gear teeth or bearing journals, into the austenitic temperature range, followed by a rapid water or polymer quench. This transforms the surface pearlite into a hard martensitic structure, increasing localized hardness up to 50 HRC or higher.
Hot Dip Galvanizing
Hot dip galvanizing provides robust, long-term metallurgical protection for QT700-2 ductile iron castings against severe outdoor and industrial corrosion. The process involves dipping the thoroughly cleaned iron casting into a bath of molten zinc at temperatures around 450 degrees Celsius. The zinc reacts with the iron matrix to form a series of zinc-iron alloy layers topped with a pure zinc outer shell. This coating provides sacrificial protection, meaning the zinc corrodes preferentially to shield the underlying iron if the surface gets scratched. Because the high temperature can cause a slight reduction in the impact toughness of high-strength pearlitic iron, cooling rates and processing times are carefully managed during the galvanizing cycle.
Phosphating
Phosphating, or phosphate conversion coating, involves immersing the cleaned iron casting in a diluted phosphoric acid solution containing zinc, iron, or manganese salts. A chemical reaction takes place, forming an insoluble crystalline phosphate layer on the surface. This porous coating acts as an excellent base for subsequent painting or rust-preventative oils, providing a baseline layer of atmospheric corrosion resistance for industrial components during storage, shipping, and assembly.
Powder Coating and Epoxies
For long-term protection against harsh environmental exposure, chemicals, and moisture, QT700-2 castings often receive a liquid epoxy or thermosetting powder coat. The surface undergoes grit blasting to remove casting skin and scale, ensuring strong mechanical adhesion. The protective coating forms a dense, non-porous barrier that shields the underlying ferrous structure from oxidation, which is useful for components deployed in agricultural machinery, mining equipment, and outdoor industrial environments.
Conclusion
QT700-2 ductile cast iron provides an effective balance of high tensile strength, wear resistance, and casting versatility for modern industrial manufacturing. By utilizing a controlled pearlitic matrix and spherical graphite nodules, this grade achieves mechanical properties that rival many structural steels while maintaining the fluid castability and vibration damping traits inherent to ductile iron. The material allows for the efficient production of complex, near-net-shape components across multiple demanding sectors, including automotive drivetrains, high-pressure fluid systems, and heavy mining machinery.
Implementing proper casting methodologies, such as sand, shell mold, investment, or lost foam casting, allows the manufacturing process to be tailored to exact component designs and production volumes. When paired with targeted surface treatments like induction hardening or nitriding, the performance of the metal can be further optimized to withstand specific environmental and physical operational demands. Ultimately, QT700-2 serves as a reliable, cost-effective engineering alloy that supports the continuous operation and structural integrity of heavy-duty machinery world-wide.
SIMIS is a leading foundry in China, offering high quality iron casting services for QT700-2 and other advanced material grades. We provide complete post-casting value-added services, including precision CNC machining, heat treatments, and specialized surface coatings to deliver ready-to-install components that match exact engineering specifications.
