Kas yra pilka geležis?

1. Įvadas

Grey Iron, or Grey cast iron—distinguished by its flaky graphite microstructure—combines cost‑effectiveness, Vibracijos slopinimas, ir puikus apdirbamumas.

Originating in the early 19th century for steam‑engine cylinders, grey cast iron has since powered applications from automotive brake drums to industrial machine bases.

Šiandien, it remains a foundational material across Automobiliai, Sunkiosios mašinos, vamzdynai, ir domestic sectors thanks to its unique blend of properties.

2. Kas yra pilkasis ketus?

Grey cast iron is a type of cast iron that is easily recognizable by the grey color of its fractured surface, which results from the presence of graphite flakes in its microstructure.

These graphite flakes give grey iron its characteristic properties, including excellent damping capacity, geras apdirbamumas, ir palyginti maža kaina.

It is the most commonly used form of cast iron and plays a foundational role in both traditional and modern manufacturing industries.

Classification and Grades of Grey Cast Iron

ASTM A48 Classification (JAV. Standartas)

The ASTM A48 standard classifies grey cast iron into grades by minimum tensile strength, measured in ksi (1 ksi = 6.89 MPA).

ASTM Grade	Minimum Tensile Strength (MPA)	Typical Microstructure	Bendros programos
Klasė 20	138 MPA	Predominantly ferritic	Atsvarai, decorative castings
Klasė 30	207 MPA	Feritinis-perlitinis	Variklio blokai, siurblių korpusai
Klasė 40	276 MPA	Mostly pearlitic	Brake drums, smagračiai, Mašinų lovos
Klasė 50	345 MPA	Puikus perlitinis, low ferrite	Cilindrų įdėklai, high-load brackets

Į 1561 Klasifikacija (European Standard)

Europos standartas EN 1561 uses the “EN-GJL” prefix (GJL = Graphit Gusseisen mit Lamellenstruktur, or “lamellar graphite cast iron”) followed by the tensile strength in MPa.

EN Grade	Min. Tempimo stiprumas (MPA)	Kietumas (BHN)	Tipiškas taikymas
EN-GJL-150	150	~150	Ornamental parts, light covers
LT-GJL-200	200	~160–170	Pavarų korpusai, perdavimo atvejai
LT-GJL-250	250	~180–200	Cylinder blocks, dideli liejiniai
LT-GJL-300	300	~220–240	Brake rotors, didelio našumo korpusai

Typical Chemical Composition Range (% pagal svorį)

Elementas	Tipiškas diapazonas (%)	Function in Grey Iron
Anglies (C)	2.5 - 4.0	Promotes graphite flake formation; increases castability
Silicis (Ir)	1.8 - 3.0	Graphitizer; aids carbon precipitation and improves fluidity
Manganas (Mn)	0.2 - 1.0	Strengthens matrix; promotes pearlite formation
Fosforas (P)	≤ 0.12 (Maks 0.5)	Improves fluidity; excessive amounts cause brittleness (steadite)
Sieros (S)	≤ 0.12	Generally undesirable; forms iron sulfide inclusions
Lygintuvas (Fe)	Pusiausvyra	Matrix base metal

4. Fizinis & Mechaninės savybės

Grey cast iron exhibits a distinctive combination of physical and mechanical properties due to its graphite flake microstructure embedded in a ferrous matrix.

These properties make it highly suitable for a wide range of structural and thermal applications, particularly where vibration damping, Šilumos laidumas, and castability are essential.

Mechaninės savybės

The mechanical behavior of grey cast iron is heavily influenced by the graphite flake morphology, matrix type (feritas, Perlitas, arba mišrus), and section thickness.

Nuosavybė	Typical Value Range	Pastabos
Tempimo stiprumas	150– 350 MPa	Varies by grade (Pvz., ASTM A48 Class 20 į Klasę 50)
Suspaudimo stiprumas	3–4× tensile strength	High due to graphite flake orientation
Kietumas	130–250 BHN	Increases with pearlite content
Pailgėjimas	~0.5–1%	Very low due to stress concentrations at flake tips
Elastiškumo modulis	70–100 GPa	Lower than steel due to graphite flakes disrupting stress transfer

PASTABA: Unlike steel, grey iron exhibits virtually no ductility and fails in a brittle manner under tensile loading.

Fizinės savybės

Nuosavybė	Tipinė vertė	Reikšmė
Tankis	6.9–7.2 g/cm³	Slightly lower than steel (~7.85 g/cm³)
Šilumos laidumas	35–55 W/m·K	Much higher than ductile or malleable iron; ideal for heat dissipation
Savitoji šilumos talpa	~460 J/kg·K	Comparable to other ferrous metals
Coefficient of Expansion	~10.5–11.5 × 10⁻⁶ /K	Vidutinis; important for dimension-critical thermal applications
Slopinimo pajėgumas	10× that of steel	Excellent vibration and noise absorption
Lydymosi taškas	1140–1200°C	Lower than steel; enhances castability

Unique Functional Advantages

• Superior Damping Capacity: Thanks to the internal friction created by graphite flakes, grey iron absorbs vibration far better than steel or ductile iron.
  This makes it ideal for engine blocks, machine tool beds, ir stabdžių komponentus.
• Geras šilumos laidumas: Its ability to transfer heat efficiently makes grey cast iron a preferred material for cookware, radiator components, and brake discs.
• Puikus apdirbamumas: The presence of graphite acts as a built-in lubricant, reducing tool wear and enabling higher cutting speeds.
  Pearlitic grades are harder but still more machinable than many steels.

5. Casting Suitability for Grey Iron

Grey cast iron is one of the most castable metals in the foundry industry, renowned for its excellent fluidity, low melting temperature, and minimal shrinkage.

These characteristics make it ideal for producing complex geometries, dideli liejiniai, and high-volume parts with reliable dimensional accuracy and surface finish.

Excellent Fluidity

Grey cast iron exhibits exceptional molten flow characteristics due to its relatively low pouring temperature (typically between 1,150–1,250°C) and graphite content.

This fluidity allows it to easily fill intricate molds and thin-walled sections (as thin as 3–5 mm), reducing the risk of cold shuts or misruns.

Low Shrinkage Rate

With a linear solidification shrinkage typically in the range of 0.8–1.0%, grey cast iron maintains superior dimensional stability.

This predictable shrinkage can be accurately compensated for in pattern design, minimizing defects and machining allowances.

Graphite Flake Structure Enhances Castability

The flake graphite in grey iron not only contributes to its mechanical damping and machinability but also assists in feeding during solidification, reducing the likelihood of internal shrinkage porosity.

It acts as a natural micro-riser, improving overall casting soundness.

Aukštas šilumos laidumas

The high thermal conductivity (typically 50–60 W/m·K) promotes rapid heat dissipation during solidification, helping to control microstructure and reduce thermal cracking risk.

This is particularly advantageous in large castings or high-speed production environments.

Excellent Machinability Post-Casting

Due to the lubricating effect of graphite flakes and relatively low hardness (Brinell 150–250 HB), it can be easily machined without requiring extensive finishing processes.

This lowers post-processing costs and enhances production throughput.

Suitable Casting Methods for Grey Iron

6. Terminis apdorojimas & Apdirbimas

Grey iron rarely undergoes quench‑and‑temper cycles; vietoj to, foundries apply:

• Annealing/Stress Relief: 650–700 °C for 1–2 hours reduces residual stresses and improves machinability.
• Normalizavimas: Fine‑tunes matrix (feritas vs. Perlitas) for targeted hardness.

Apdirbimo metu, engineers favor:

• Carbide tooling vidutiniu greičiu (50–80 m/min).
• Rigid workholding to offset low tensile strength.
• Coolant use to avoid built‑up edge; graphite flakes facilitate chip breaking.

Post‑machining, grey cast iron achieves paviršiaus apdaila as low as Ra 1.6 µm with minimal secondary operations.

7. Privalumai ir trūkumai

Privalumai:

• Vibracijos slopinimas: Iki 90 % better than steel, reducing noise and fatigue.
• Aparatas: Graphite flakes act as chip breakers, lowering tool wear.
• Ekonominis efektyvumas: > 80 % recycled content and lower melting energy than steel.

Trūkumai:

• Low Tensile Ductility: < 2 % elongation limits shock‑loading use.
• Anizotropija: Flake orientation creates directional strength variations (~ 20 %).
• Trapumas: Lower impact resistance compared to ductile iron.

8. Paraiškos & Spektaklis

Grey cast iron’s property synergy drives its use in:

• Automobiliai: Variklio blokai, cilindro galvutės, brake drums—leveraging thermal conductivity (~ 45 W/m · k) for heat dissipation.
• Sunkiosios mašinos: Pavarų korpusai, machine tool bases—utilizing vibration damping to extend bearing life.
• Statyba & Vamzdynas: Šulinio dangteliai, valve bodies—benefiting from corrosion resistance in neutral waters and low cost.
• Domestic Goods: Virtuvės indai, radiators—ensuring even heat distribution and durability.

9. Palyginimas su alternatyviomis medžiagomis

Grey cast iron has long served as a foundational material in engineering and manufacturing, but it often competes with alternatives like ductile iron, plienas, aliuminio lydiniai, ir kompozitai.

Each of these materials brings distinct benefits and trade-offs, making material selection highly application-dependent.

Below is a comparative overview that highlights where grey iron stands about its common substitutes.

Lyginamoji lentelė: Grey Cast Iron vs. Alternatyvios medžiagos

Kario geležies vs. Pilkas ketaus

• Kariuomenė geležis offers much higher ductility and strength, making it suitable for pressure-containing or dynamic load applications.
  Tačiau, grey cast iron still outperforms it in damping and cost-efficiency, especially in static structural parts.

Anglies plienas vs. Pilkas ketaus

• Steel provides superior tensile properties and ductility, but is more expensive and harder to machine.
  Grey iron is preferred for parts requiring vibration control (Pvz., mašinų bazės, korpusai).

Aluminum Alloys vs. Pilkas ketaus

• Aliuminis is significantly lighter and offers excellent corrosion resistance, making it ideal for transport and heat-sensitive components.
  Grey iron, kita vertus, excels in applications needing rigidity and vibration absorption.

Composites vs. Pilkas ketaus

• While advanced composites can surpass grey iron in strength-to-weight ratio and corrosion resistance, they are far more costly and difficult to manufacture at scale.

10. Išvada

Grey iron endures as a kertinio akmens medžiaga dėl jos economic production, built‑in damping, ir apdirbimo paprastumas.

By mastering its eutectic graphite formation, casting practices, ir projektavimo gairės, engineers can continue leveraging grey cast iron for reliable, cost‑effective solutions across industries—from the heart of an engine to the base of heavy machinery.

As emerging alloy modifications and hybrid manufacturing techniques evolve, grey cast iron will maintain its role in shaping tomorrow’s engineered components.

Tai yra puikus pasirinkimas jūsų gamybos poreikiams, jei jums reikia aukštos kokybės Grey Iron castings.

Susisiekite su mumis šiandien!