738 Molde de aço: Propriedades, Usos & Fabricação de moldes versáteis de alta qualidade

If you’re searching for apre-hardened mold steel that balances mirror polishability, estabilidade dimensional, and cost-effectiveness for mid-to-high-end molds—738 mold steel é a solução ideal. Amplamente utilizado no setor automotivo, produto de consumo, e moldes para dispositivos médicos, esta liga resolve pontos problemáticos comuns, como acabamentos de superfície inconsistentes, deformação do molde, ou produção lenta. Neste guia, vamos detalhar suas principais propriedades, aplicações do mundo real, etapas de fabricação, and how it compares to other materials—so you can create reliable, high-quality molds that fit your budget.

1. Material Properties of 738 Molde de aço

738’s appeal lies in its well-rounded composition, which delivers premium performance without the ultra-high cost of top-tier mold steels. Let’s explore its properties in detail:

1.1 Composição Química

The elements in 738 work together to enhance polishability, resistência, and stability—tailored for versatile mold-making. Below is its typical composition (per industry standards):

1.2 Propriedades Físicas

These properties determine how 738 behaves during mold manufacturing and use—such as heat transfer and shape retention. All values are measured at room temperature unless noted:

• Densidade: 7.85 g/cm³ (consistent with most mold steels, making it easy to calculate mold weight).
• Ponto de fusão: 1450 – 1500 °C (high enough to withstand forging and pre-hardening heat treatment).
• Condutividade Térmica: 30 C/(m·K) (good heat transfer, ensuring plastic parts cool evenly in injection molds).
• Coeficiente de Expansão Térmica: 11.8 × 10⁻⁶/°C (de 20 para 600 °C; low expansion reduces mold warping during production).
• Capacidade Específica de Calor: 470 J/(kg·K) (efficient at absorbing and releasing heat, reducing plastic injection cycle times).

1.3 Propriedades Mecânicas

Como umpre-hardened mold steel, 738 is supplied ready for machining—no post-machining heat treatment needed. Below are its typical mechanical properties (in pre-hardened state):

1.4 Outras propriedades

• Resistência à corrosão: Bom. Chromium content protects against rust in workshop environments and mild chemicals (por exemplo, plastic additives or mold release agents).
• Resistência ao desgaste: Moderate to Good. Suitable for most plastic and die casting applications; nitriding can boost wear resistance for high-wear molds.
• Usinabilidade: Excelente. Its pre-hardened hardness (HRC 32–36) and fine grain structure make it easy to mill, furar, and turn—reducing machining time by 20–25% vs. unhardened steels.
• Temperabilidade: Muito bom. It maintains uniform hardness across thick sections (até 100 milímetros), so large molds (por exemplo, automotive molds for door panels) have consistent performance.
• Estabilidade Dimensional: Outstanding. Low thermal expansion and pre-hardened state prevent mold warping—critical for optical molds or precision consumer product molds.
• Mirror Polishability: Muito bom. Fine grain structure and low sulfur content let it achieve mirror finishes (Ra ≤ 0.02 μm)—ideal for consumer product molds (por exemplo, potes de cosméticos) or semi-optical parts.

2. Applications of 738 Molde de aço

738’s versatility makes it suitable for a wide range of mid-to-high-end mold applications. Aqui estão seus usos mais comuns, com exemplos reais:

2.1 Plastic Injection Molds

• Exemplos: Molds for making plastic parts like automotive interior components (por exemplo, center consoles), invólucros de eletrônicos de consumo (por exemplo, tablet shells), ou caixas de dispositivos médicos.
• Why it works: Pre-hardened state speeds up production, while dimensional stability ensures part consistency. A Chinese plastic manufacturer used 738 for tablet casing molds—production time dropped by 30% contra. using unhardened steel.

2.2 Automotive Molds

• Exemplos: Molds for automotive exterior parts (por exemplo, caixas de espelho) or under-hood components (por exemplo, suportes de sensores).
• Why it works: Toughness handles high-volume production stress, and corrosion resistance stands up to workshop chemicals. A German automotive supplier used 738 for sensor bracket molds—mold life increased from 180,000 para 350,000 peças.

2.3 Consumer Product Molds

• Exemplos: Molds for cosmetic containers (por exemplo, frascos de loção), utensílios de cozinha (por exemplo, high-gloss plastic spatulas), or toys (por exemplo, detailed action figures).
• Why it works: Mirror polishability delivers premium aesthetics, while machinability lets you create complex shapes. A French cosmetic brand used 738 for lotion bottle molds—customer complaints about surface flaws fell by 85%.

2.4 Semi-Optical and Medical Molds

• Exemplos: Molds for plastic light covers (por exemplo, LED headlights) or non-critical medical parts (por exemplo, pill bottle caps).
• Why it works: Dimensional stability ensures part accuracy, and corrosion resistance meets basic medical hygiene standards. Um EUA. medical supplier used 738 for pill bottle cap molds—part tolerance accuracy improved by 15%.

3. Manufacturing Techniques for 738 Molde de aço

Virando 738 into high-quality molds is streamlined thanks to its pre-hardened state. Aqui está uma análise passo a passo:

1. Fusão: Matérias-primas (iron, níquel, cromo, etc.) are melted in an electric arc furnace (EAF) at 1550–1650 °C. Strict control ensures uniform element distribution (critical for consistent hardness).
2. Fundição: Molten steel is poured into ingot molds or continuous casters to form slabs. Resfriamento lento (50–100 °C/hour) prevents internal defects and refines grain structure.
3. Forjamento: Slabs are heated to 1100–1200 °C and pressed/hammered into mold blanks (por exemplo, 500x500x200 mm for injection molds). Forging improves toughness and eliminates voids.
4. Pre-hardening Heat Treatment:
   • Recozimento: Heat to 800–850 °C, hold 2–4 hours, cool slowly. Softens steel to HRC 22–25 for initial machining.
   • Têmpera: Heat to 880–920 °C, hold 1–2 hours, tempere em óleo. Hardens steel to HRC 45–48.
   • Temperamento: Reheat to 580–620 °C, hold 2–3 hours, cool. Sets final pre-hardened hardness (HRC 32–36) and relieves internal stress.
5. Usinagem: Mold blanks are milled, drilled, or turned into mold cavities using CNC machines. Carbide tools are recommended for tight tolerances (±0,005mm).
6. Polimento: Molds are polished to the desired finish—from matte (para peças funcionais) to mirror (para produtos de consumo). 738’s fine grain structure lets it achieve Ra ≤ 0.02 μm with diamond paste.
7. Tratamento de superfície (Opcional):
   • Nitretação: Creates a hard surface layer (HRC 60–65) to boost wear resistance for high-cycle molds.
   • Galvanoplastia: Adds a chrome or nickel coating to improve corrosion resistance (ideal for medical or food-contact molds).

4. Estudo de caso: 738 in Automotive Center Console Molds

A Korean automotive parts manufacturer faced a problem: their P20 mold steel center consoles had inconsistent surface finishes and required post-heat treatment, which caused warping. They switched to 738, e aqui está o que aconteceu:

• Processo: Mold blanks (pre-hardened to HRC 34) were CNC-machined to console geometry, polished to Ra 0.4 μm (matte-gloss finish), and treated with a mold release coating.
• Resultados:
  • Surface finish consistency improved—99% of consoles met automotive quality standards (acima de 82% with P20).
  • Production time per mold dropped from 3 semanas para 2 semanas (33% melhoria) — no post-heat treatment needed.
  • Warping eliminated—console fitment issues reduced by 70%.
• Why it works: 738’s pre-hardened state skipped heat treatment, while its nickel and molybdenum content prevented warping. Its fine grain structure also ensured uniform polishing across the console’s complex curves.

5. 738 contra. Other Mold Materials

How does 738 compare to common alternatives for mid-to-high-end molds? Let’s evaluate key properties:

Key takeaway: 738 offers the best cost-performance ratio for mid-to-high-end molds. It’s more polishable and stable than P20, cheaper than 718H or stainless steel, and far more reliable than aluminum for production molds.

Yigu Technology’s View on 738 Molde de aço

Na tecnologia Yigu, 738 is our top recommendation for clients needing versatile, cost-effective mid-to-high-end molds—like automotive parts or consumer products. Its pre-hardened state cuts production time, while its polishability and stability ensure consistent quality. We often use it for complex molds, as its machinability lets us create intricate designs without warping. For clients balancing quality and budget, 738 isn’t just a material—it’s a practical solution that delivers premium results without the premium price tag.

FAQ About 738 Molde de aço

1. Can 738 be used for die casting molds (por exemplo, aluminum or zinc)?

Sim, but we recommend nitriding to boost wear resistance. 738’s toughness handles die casting pressure, and its dimensional stability ensures part consistency—we’ve helped clients use nitrided 738 for aluminum die casting molds with life up to 250,000 ciclos.

2. Is 738 suitable for molds that need ultra-mirror finishes (Ra ≤ 0.01 μm)?

738 can achieve Ra ≤ 0.02 μm, which is suitable for most consumer products. For ultra-mirror finishes (Ra ≤ 0.01 μm) (por exemplo, high-end optical parts), we recommend upgrading to 718H or stainless steel (S136), as their finer grain structure supports even smoother polishing.

3. How does 738’s cost compare to P20, and is it worth the extra expense?

738 costs about 25% more than P20, but it’s worth it for mid-to-high-end molds. It eliminates heat treatment costs, reduces scrap rates (better stability), and lasts 40–60% longer—saving money in the long run, especialmente para produção de alto volume.