Що таке сірий залізо?

1. Вступ

Grey Iron, or Grey cast iron—distinguished by its flaky graphite microstructure—combines cost‑effectiveness, Вібраційне демпфірування, і відмінна оброблюваність.

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.

Сьогодні, it remains a foundational material across автомобільний, важка техніка, трубопровід, і domestic sectors thanks to its unique blend of properties.

2. Що таке сірий чавун?

Сірий чавун 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, Хороша обробка, і відносно низька вартість.

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 (США. Стандартний)

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	Загальні програми
Клас 20	138 MPA	Predominantly ferritic	Противаги, decorative castings
Клас 30	207 MPA	Феритно-перлітний	Блоки двигуна, насосні корпуси
Клас 40	276 MPA	Mostly pearlitic	Brake drums, маховики, ліжка машини
Клас 50	345 MPA	Дрібний перліт, low ferrite	Гільзи циліндрів, high-load brackets

У 1561 Класифікація (European Standard)

Європейський стандарт 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. Сила на розрив (MPA)	Твердість (BHN)	Типове застосування
EN-GJL-150	150	~150	Ornamental parts, light covers
EN-GJL-200	200	~160–170	Корпуси передач, випадки передачі
EN-GJL-250	250	~180–200	Cylinder blocks, large castings
EN-GJL-300	300	~220–240	Brake rotors, надміцні корпуси

Typical Chemical Composition Range (% за вагою)

Елемент	Типовий діапазон (%)	Function in Grey Iron
Вуглець (C)	2.5 - 4.0	Promotes graphite flake formation; increases castability
Кремнію (І)	1.8 - 3.0	Graphitizer; aids carbon precipitation and improves fluidity
Марганець (Мн)	0.2 - 1.0	Strengthens matrix; promotes pearlite formation
Фосфор (С)	≤ 0.12 (макс 0.5)	Improves fluidity; excessive amounts cause brittleness (steadite)
Сірка (S)	≤ 0.12	Generally undesirable; forms iron sulfide inclusions
Прасувати (Феод)	Балансувати	Matrix base metal

4. Фізичний & Механічні властивості

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, Теплопровідність, and castability are essential.

Механічні властивості

The mechanical behavior of grey cast iron is heavily influenced by the graphite flake morphology, matrix type (феррит, перлітний, або змішані), and section thickness.

Майно	Typical Value Range	Нотатки
Сила на розрив	150–350 МПа	Varies by grade (Напр., ASTM A48 Class 20 до класу 50)
Міцність на стиск	3–4× tensile strength	High due to graphite flake orientation
Твердість	130–250 BHN	Increases with pearlite content
Подовження	~0.5–1%	Very low due to stress concentrations at flake tips
Модуль еластичності	70–100 GPa	Lower than steel due to graphite flakes disrupting stress transfer

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

Фізичні властивості

Майно	Типове значення	Значимість
Щільність	6.9–7.2 g/cm³	Slightly lower than steel (~7.85 g/cm³)
Теплопровідність	35–55 W/m·K	Much higher than ductile or malleable iron; ideal for heat dissipation
Конкретна теплоємність	~460 Дж/кг·К	Comparable to other ferrous metals
Coefficient of Expansion	~10.5–11.5 × 10⁻⁶ /K	Помірний; important for dimension-critical thermal applications
Демпфірування	10× that of steel	Excellent vibration and noise absorption
Точка плавлення	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, і компоненти гальма.
• Good Thermal Conductivity: Its ability to transfer heat efficiently makes grey cast iron a preferred material for cookware, radiator components, and brake discs.
• Excellent Machinability: 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, large castings, 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.

Висока теплопровідність

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. Термічна обробка & Обробка

Grey iron rarely undergoes quench‑and‑temper cycles; замість цього, foundries apply:

• Annealing/Stress Relief: 650–700 °C for 1–2 hours reduces residual stresses and improves machinability.
• Нормалізація: Fine‑tunes matrix (ферит проти. перліт) for targeted hardness.

During machining, engineers favor:

• Carbide tooling at moderate speeds (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 поверхнева обробка as low as Ra 1.6 µm with minimal secondary operations.

7. Переваги та недоліки

Переваги:

• Гасіння вібрації: До 90 % better than steel, reducing noise and fatigue.
• Обробка: Graphite flakes act as chip breakers, lowering tool wear.
• Ефективність витрат: > 80 % recycled content and lower melting energy than steel.

Недоліки:

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

8. Заявки & Виконання

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

• Автомобільний: Блоки двигуна, головки циліндрів, brake drums—leveraging thermal conductivity (~ 45 З/м · k) for heat dissipation.
• Важка техніка: Корпуси передач, machine tool bases—utilizing vibration damping to extend bearing life.
• Будівництво & Трубопровід: Кришки люків, valve bodies—benefiting from corrosion resistance in neutral waters and low cost.
• Domestic Goods: Посуд, radiators—ensuring even heat distribution and durability.

9. Порівняння з альтернативними матеріалами

Grey cast iron has long served as a foundational material in engineering and manufacturing, but it often competes with alternatives like ductile iron, сталь, алюмінієві сплави, і композити.

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.

Порівняльна таблиця: Grey Cast Iron vs. Альтернативні матеріали

Ductile Iron vs. Сірий чавун

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

Вуглецева сталь проти. Сірий чавун

• Steel provides superior tensile properties and ductility, but is more expensive and harder to machine.
  Grey iron is preferred for parts requiring vibration control (Напр., машинні бази, корпус).

Aluminum Alloys vs. Сірий чавун

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

Composites vs. Сірий чавун

• 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. Висновок

Grey iron endures as a матеріал наріжного каменю завдяки його economic production, built‑in damping, і легкість обробки.

By mastering its eutectic graphite formation, casting practices, і design guidelines, 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.

Це є ідеальним вибором для ваших виробничих потреб, якщо вам потрібна якісна Grey Iron castings.

Зв’яжіться з нами сьогодні!