Hypereutectoid Structural Steel: Sifat, Penggunaan, Wawasan Pakar

If your project needs steel that balances high hardness, Pakai rintangan, and strength—like industrial gears, railway tracks, or mining equipment—hypereutectoid structural steel is a specialized solution worth considering. Its defining trait (carbon content above 0.83%) gives it unique mechanical properties, Tetapi bagaimana ia melaksanakan tugas-tugas dunia nyata? Panduan ini memecah sifat utamanya, aplikasi, dan perbandingan dengan bahan lain, so you can choose the right steel for wear-prone, Projek tekanan tinggi.

1. Material Properties of Hypereutectoid Structural Steel

Hypereutectoid steel’s performance stems from its high carbon content and carefully balanced alloying elements, which create a structure ideal for wear resistance. Let’s explore its defining properties.

1.1 Komposisi kimia

The Komposisi kimia of hypereutectoid steel is marked by carbon content above the eutectoid point (0.83%), plus alloys to refine strength and toughness (setiap piawaian industri):

1.2 Sifat fizikal

Ini sifat fizikal make hypereutectoid steel suitable for high-wear environments:

• Ketumpatan: 7.85 g/cm³ (selaras dengan keluli struktur yang paling banyak)
• Titik lebur: 1400 - 1450 ° C. (slightly lower than low-carbon steel due to high carbon)
• Kekonduksian terma: 42 W/(m · k) pada 20 ° C. (Pemindahan haba yang lebih perlahan, ideal for parts needing heat retention)
• Kapasiti haba tertentu: 450 J/(kg · k)
• Pekali pengembangan haba: 12.8 × 10⁻⁶/° C. (20 - 100 ° C., minimal warping during heat treatment)

1.3 Sifat mekanikal

Hypereutectoid steel’s mechanical traits are tailored for wear and strength:

• Kekuatan tegangan: 800 - 1100 MPA (higher than low-carbon steel, thanks to high carbon)
• Kekuatan hasil: ≥ 550 MPA
• Pemanjangan: 8 - 12% (lower than low-carbon steel—trades ductility for hardness)
• Kekerasan: 280 - 350 Hb (Skala Brinell; hingga 60 HRC after quenching and tempering—excellent for wear)
• Rintangan kesan: 20 - 40 J pada 20 ° C. (sederhana; better with nickel alloying—avoids brittle fracture)
• Rintangan Keletihan: 350 - 450 MPA (good for parts under repeated wear, Mis., gear)
• Pakai rintangan: Cemerlang (cementite phase resists abrasion—outperforms low-carbon steel by 2–3x)

1.4 Sifat lain

• Rintangan kakisan: Sederhana (Memerlukan salutan seperti penyaduran krom atau minyak untuk kegunaan luaran; high carbon increases rust risk slightly)
• Kebolehkalasan: Poor to fair (memerlukan pemanasan 250 – 300°C and post-weld heat treatment to avoid cracking)
• Kebolehkerjaan: Adil (harder than low-carbon steel; best when annealed to reduce hardness—uses carbide tools)
• Sifat magnet: Ferromagnet (berfungsi dengan alat pemeriksaan magnetik)
• Kemuluran: Rendah (limited bending; better for parts with simple shapes like gears or shafts)
• Ketangguhan: Sederhana (alloying with nickel/tungsten prevents brittleness—suitable for non-extreme impact)
• Hardenability: Baik (responds well to quenching and tempering—hardens deeply for thick parts)

2. Applications of Hypereutectoid Structural Steel

Hypereutectoid steel shines in projects where wear resistance is non-negotiable. Berikut adalah kegunaan utamanya, dengan contoh sebenar:

• Pembinaan umum:
• Rangka kerja struktur: Heavy-duty crane hooks (resist wear from lifting cables). A Chinese port used hypereutectoid steel for its crane hooks—last 5 tahun vs. 2 years for low-carbon steel.
• Rasuk dan lajur: Wear-resistant supports for industrial warehouses (handle forklift impacts).
• Kejuruteraan Mekanikal:
• Bahagian mesin: High-wear gears for industrial mixers (abrasive materials like cement). A German factory’s hypereutectoid gears last 4 tahun vs. 1 year for standard alloy steel.
• Aci dan gandar: Grinding machine shafts (resist wear from abrasive dust).
• Industri automotif:
• Komponen enjin: Batang injap dan camshafts (high wear from friction). A Japanese carmaker uses hypereutectoid steel for its diesel engine camshafts—reduces warranty claims by 35%.
• Bahagian penghantaran: Gigi gear tugas berat (Tolak haus dari meshing berterusan).
• Jentera Perindustrian:
• Gear: Mining conveyor gears (abrasive coal/dust). An Australian mine’s hypereutectoid gears need replacement every 3 tahun vs. 1 year for carbon steel.
• Galas: High-load bearing races (resist wear from rotating shafts).
• Industri Keretapi:
• Komponen lokomotif: Brake discs (high wear from friction). Indian Railways used hypereutectoid steel for its freight train brake discs—last 80,000 km vs. 40,000 km for standard steel.
• Trek keretapi: Sendi kereta api (resist wear from train wheels). A European railway’s hypereutectoid rail joints reduced maintenance by 40%.
• Perlombongan dan peralatan berat:
• Bahagian penggali: Bucket teeth (abrasive rock/soil). A South African mining firm uses hypereutectoid steel for its excavator bucket teeth—last 2x longer than alloy steel.
• Komponen penghancur: Plat rahang untuk penghancur batu (Pakaian melampau). A Brazilian quarry’s hypereutectoid jaw plates last 6 Bulan vs. 2 Bulan untuk keluli karbon.

3. Manufacturing Techniques for Hypereutectoid Structural Steel

Producing hypereutectoid steel requires careful processing to balance hardness and toughness:

3.1 Proses rolling

• Rolling panas: Primary method—steel heated to 1150 - 1250 ° C., pressed into bars, plat, or gear blanks. Hot rolling refines the grain structure and distributes cementite evenly.
• Rolling sejuk: Jarang berlaku (used only for thin sheets like bearing races)—done at room temperature for tight tolerances and smoother surface finish.

3.2 Rawatan haba

Heat treatment is critical to unlock hypereutectoid steel’s wear resistance:

• Penyepuhlindapan: Dipanaskan ke 750 - 800 ° C., penyejukan perlahan. Melembutkan keluli untuk pemesinan (mengurangkan kekerasan 200 - 250 Hb) without losing core strength.
• Menormalkan: Dipanaskan ke 850 - 900 ° C., penyejukan udara. Improves uniformity for large parts (Mis., railway tracks) to avoid wear hotspots.
• Pelindapkejutan dan pembajaan: Dipanaskan ke 820 - 850 ° C. (dipadamkan dalam minyak), tempered at 500 - 600 ° C.. Creates a hard surface (50 - 60 HRC) with a tough core—ideal for wear-prone parts like gears.
• Karburisasi: Pilihan (for parts needing extra surface wear resistance)—adds carbon to the surface, then quenched/tempered. Used for high-load gears or bearings.
• Nitriding: Dipanaskan ke 500 - 550 ° C dalam suasana nitrogen. Mencipta nipis, ultra-hard surface layer (60 - 65 HRC) for parts like camshafts.

3.3 Kaedah fabrikasi

• Memotong: Pemotongan plasma (Cepat untuk plat tebal) atau Pemotongan laser (precision for gear blanks). Uses high-speed, low-heat tools to avoid hardening the cut edge.
• Teknik kimpalan: Kimpalan arka (on-site repairs) atau kimpalan laser (bahagian ketepatan). Preheating and post-weld annealing are mandatory to prevent cracking.
• Membongkok dan membentuk: Selesai semasa anil (dilembutkan). Limited to simple shapes (Mis., 90-degree angles)—avoid complex curves to prevent cracking.

3.4 Kawalan kualiti

• Kaedah pemeriksaan:
• Ujian ultrasonik: Pemeriksaan untuk kecacatan dalaman (Mis., lubang) di bahagian tebal seperti rahang penghancur.
• Pemeriksaan zarah magnet: Mencari keretakan permukaan (Mis., welded gear blanks).
• Ujian kekerasan: Verifies surface hardness meets specs (Mis., 55 HRC untuk gear) using a Rockwell tester.
• Piawaian pensijilan: Meets ISO 683-1 (Keluli struktur) dan ASTM A681 (high-carbon steel for mechanical parts) untuk memastikan kualiti.

4. Kajian kes: Hypereutectoid Steel in Action

4.1 Perlombongan: Gigi baldi penggali (South Africa)

A South African mining firm switched to hypereutectoid steel for its excavator bucket teeth. Sebelum ini, they used EN19 alloy steel, which wore out after 1 month in iron ore mines. Hypereutectoid teeth—heat-treated to 58 HRC—last 2 bulan, memotong kos penggantian oleh 50%. The Pakai rintangan of the cementite phase handled abrasive ore, while nickel alloying prevented brittle fracture during impacts.

4.2 Keretapi: Freight Train Brake Discs (India)

Indian Railways upgraded its freight train brake discs to hypereutectoid steel. Standard steel discs needed replacement every 40,000 km due to friction wear; hypereutectoid discs (quenched/tempered to 55 HRC) terakhir 80,000 km. The rintangan haba of hypereutectoid steel also reduced brake fade (terlalu panas) in hot climates, improving safety. The upgrade saved $2 million annually in maintenance.

5. Analisis perbandingan: Hypereutectoid Steel vs. Bahan lain

How does hypereutectoid steel stack up to alternatives? Mari kita bandingkan:

5.1 vs. Jenis keluli lain

5.2 vs. Bahan bukan logam

• Konkrit: Hypereutectoid steel is 10x stronger in tension and 3x lighter. Concrete is cheaper for foundations but can’t match steel’s wear resistance—e.g., a crusher uses concrete for its base and hypereutectoid steel for its jaw plates.
• Bahan Komposit (Mis., ceramic-reinforced plastic): Composites resist wear but cost 3x more and are brittle. Hypereutectoid steel is better for high-impact wear (Mis., excavator bucket teeth).

5.3 vs. Bahan logam lain

• Aloi aluminium: Aluminum is lighter but has lower hardness (15 - 30 HRC) dan memakai rintangan. Hypereutectoid steel is better for wear-prone parts like gears.
• Keluli tahan karat: Stainless steel resists corrosion but has lower hardness (20 - 35 HRC) dan kos 2x lebih banyak. Hypereutectoid steel is better for indoor, bahagian yang dipakai tinggi (Mis., machine bearings).

5.4 Kos & Kesan alam sekitar

• Analisis kos: Hypereutectoid steel costs more upfront than carbon/alloy steel but saves money long-term. A mine using it for bucket teeth saved $120,000 annually in replacements.
• Kesan alam sekitar: 100% boleh dikitar semula (menyelamatkan 75% Tenaga vs. Membuat keluli baru). Production uses more energy than low-carbon steel but less than composites—eco-friendly for long-lifespan wear parts.

6. Yigu Technology’s View on Hypereutectoid Structural Steel

Di Yigu Technology, we recommend hypereutectoid steel for high-wear, medium-impact projects like mining gears, railway brake discs, and excavator parts. Itu Rintangan haus yang sangat baik dan good hardenability make it a top choice for reducing maintenance costs. Kami membantu pelanggan mengoptimumkan rawatan haba (quenching/tempering for gears, nitriding for bearings) and select coatings to boost corrosion resistance. While it’s less ductile than low-carbon steel, its ability to extend part life by 2–3x makes it a smart investment for wear-prone applications.

FAQ About Hypereutectoid Structural Steel

1. Can hypereutectoid steel be used for outdoor applications?

Ya, Tetapi ia memerlukan perlindungan kakisan. Its high carbon content increases rust risk, so apply coatings like chrome plating, Cat epoksi, or oiling. For coastal/marine use, pair it with a zinc-nickel coating to extend lifespan to 5+ tahun.

2. Is hypereutectoid steel difficult to machine?

It’s harder than low-carbon steel but manageable with proper tools. Anneal it first to reduce hardness (ke 200 - 250 Hb), then use carbide drills/mills—this cuts tool wear by 30%. Avoid machining unannealed hypereutectoid steel (kekerasan >300 Hb) Untuk mengelakkan kerosakan alat.

3. When should I choose hypereutectoid steel over alloy steel (Mis., EN19)?

Choose hypereutectoid steel if your part faces extreme wear (Mis., perlombongan, rock crushing) and needs hardness >50 HRC. EN19 is better for parts needing a balance of strength and ductility (Mis., shafts with moderate wear)—it’s cheaper and easier to weld.