Bohler-Uddeholm,BÖHLER M268 VMR® Plastic Mold Steel Rod/Bar

Bohler-Uddeholm BÖHLER M268 VMR® Plastic Mold Steel Rod Product Information -:- For detailed product information, please contact sales. -: Bohler-Uddeholm BÖHLER M268 VMR® Plastic Mold Steel Rod Synonyms -:- For detailed product information, please contact sales. -:

Bohler-Uddeholm BÖHLER M268 VMR® Plastic Mold Steel Product Information -:- For detailed product information, please contact sales. -: # **Böhler-Uddeholm BÖHLER M268 VMR® Plastic Mold Steel** ## **Product Overview** **BÖHLER M268 VMR®** is a premium **chromium-nickel-molybdenum alloyed plastic mold steel** manufactured using Böhler-Uddeholm's proprietary **VMR® (Vacuum Melted and Remelted)** technology. This advanced dual vacuum melting process ensures **exceptional internal cleanliness, superior microstructural homogeneity, and minimal anisotropy**. Designed as a high-performance, through-hardening mold steel, M268 VMR® delivers an **excellent balance of toughness, wear resistance, polishability, and dimensional stability**, making it ideally suited for demanding plastic injection molds requiring high precision, complex geometries, and superior surface finishes. --- ## **1. Key Characteristics & Advantages** * **Exceptional Toughness:** Offers high impact strength and resistance to cracking, particularly valuable for molds with thin ribs, delicate cores, and high-aspect-ratio features prone to mechanical stress. * **Superior Internal Cleanliness:** The VMR® process (Vacuum Induction Melting + Vacuum Arc Remelting) drastically reduces non-metallic inclusions and gases (O, H, N), resulting in flawless polishability and enhanced fatigue resistance. * **Excellent Polishability:** Capable of achieving high-grade mirror finishes (up to SPI A-2 / B-1) due to its homogeneous, inclusion-free microstructure. * **Good Wear Resistance:** Provides adequate resistance to abrasion from standard and moderately filled engineering plastics. * **High Dimensional Stability:** Exhibits predictable and minimal distortion during heat treatment, crucial for maintaining tight tolerances in precision molds. * **Good Machinability:** In the annealed state, offers favorable machining characteristics for efficient mold manufacturing. * **Good Nitriding Response:** Readily accepts nitriding surface treatments to significantly enhance surface hardness and wear resistance without compromising core toughness. * **Isotropic Properties:** The VMR® process ensures uniform mechanical behavior in all directions (longitudinal and transverse). --- ## **2. Typical Chemical Composition (Weight %)** | Element | Carbon (C) | Chromium (Cr) | Nickel (Ni) | Molybdenum (Mo) | Manganese (Mn) | Silicon (Si) | | :--- | :---: | :---: | :---: | :---: | :---: | :---: | | **Content** | **0.15 - 0.20** | **1.40 - 1.70** | **3.80 - 4.30** | **0.15 - 0.25** | **1.30 - 1.60** | **0.15 - 0.35** | **Alloying Rationale:** * **Nickel (4.0%):** The key alloying element. Significantly increases toughness and hardenability, promotes a fine-grained microstructure, and improves impact strength at low temperatures. * **Chromium (1.55%) & Molybdenum (0.2%):** Provide hardenability and contribute to strength. Molybdenum also enhances toughness and refines the grain structure. * **Low Carbon (0.18%):** Optimized to prioritize toughness and weldability while providing sufficient hardness after heat treatment. This minimizes the risk of stress cracking in complex molds. * **Manganese (1.45%):** Enhances hardenability and works as a deoxidizer. * **VMR® Process Impact:** This dual vacuum melting is critical. It removes impurities and gases that could act as initiation sites for polish lines, pits, or cracks, guaranteeing the steel's performance in high-quality surface applications. --- ## **3. Physical & Mechanical Properties** ### **Physical Properties:** * **Density:** ~7.85 g/cm³ * **Thermal Conductivity:** ~36 W/(m·K) at 20°C * **Modulus of Elasticity:** ~205 GPa * **Coefficient of Thermal Expansion:** ~12.5 x 10⁻⁶/K (20-100°C) ### **Heat Treatment & Mechanical Data:** * **Annealed Hardness:** ~210 HBW * **Austenitizing Temperature:** 840 - 870°C (1545 - 1600°F) * **Quenching Medium:** Oil or air. For optimal properties and minimal distortion, oil quenching is often preferred. * **Tempering Temperature Range:** 300 - 550°C (570 - 1020°F). **Double tempering is recommended.** * **Typical Working Hardness:** **38 - 44 HRC** * A common specification is **40-42 HRC** (tempered at ~400-450°C), providing an optimal balance of toughness, strength, and polishability for most demanding mold applications. * **Impact Toughness (Charpy V):** Exceptionally high, typically >50 J at 40 HRC. * **Core Strength:** High yield strength supports the hard nitrided surface in treated applications. --- ## **4. Primary Applications** M268 VMR® is engineered for high-performance, precision plastic injection molds where reliability, surface finish, and toughness are critical. * **Large, Complex Injection Molds:** Automotive components (bumpers, dashboards, door panels), appliance housings, and technical parts requiring high dimensional stability. * **Molds with Delicate Features:** Thin-walled components, high-aspect-ratio ribs, and intricate cores where resistance to bending and breakage is paramount. * **High-Gloss Surface Molds:** Consumer electronics, automotive interior trim, and appliance parts requiring very good surface finishes. * **Engineering Plastic Molds:** For polymers like PA (Nylon), PBT, PC, POM, and PPS, where good wear resistance and toughness are needed. * **Mold Bases and Support Plates:** For large mold systems where high strength and toughness of the backing structure are essential. * **General Precision Tooling:** Components requiring a combination of good machinability, toughness, and consistent heat treatment response. --- ## **5. Relevant International Standards & Comparable Grades** M268 VMR® is a proprietary Böhler-Uddeholm grade. Its chemistry places it in the family of nickel-alloyed mold steels, with the VMR® quality being a key differentiator. | Standard | Grade / Designation | Country/Region | Similarity / Key Difference | | :--- | :--- | :--- | :--- | | **Proprietary (Böhler-Uddeholm)** | **M268 VMR®** | International | The reference premium Ni-alloyed mold steel with VMR® quality. | | **AISI / ASTM** | **P20+Ni Modified / 6F7** | USA | Similar nickel-containing mold steel classification. M268 defines a specific, high-quality composition. | | **DIN / Werkstoff** | **1.2738 (≈35CrNiMo6)** | Germany/EU | The common pre-hardened mold steel with nickel. M268 VMR® is supplied annealed, allowing for custom through-hardening, and offers superior cleanliness. | | **JIS** | **SNCM8 / equivalent** | Japan | Japanese Ni-Cr-Mo alloy steel. M268 is optimized specifically for mold performance. | | **Other Premium Grades** | **IMPAX® SUPREME (Hardened)** | Uddeholm | A pre-hardened Ni-alloyed steel. M268 VMR® offers the flexibility of custom through-hardening from an annealed state with guaranteed VMR® cleanliness. | | **Quality Benchmark** | **VMR®** | N/A | This designation, not a chemistry, is crucial. It guarantees a level of internal purity and homogeneity beyond standard air-melted or single vacuum-melted steels. | **Important:** Specifying **"M268 VMR®"** ensures receipt of material with the guaranteed internal cleanliness and consistency required for high-performance, high-finish molds. --- ## **6. Processing & Fabrication Guidelines** * **Machining:** **Excellent machinability** in the soft-annealed condition. Use sharp carbide tools. The VMR® structure provides predictable tool wear and good surface finish from machining. * **Heat Treatment:** For optimal properties, through-harden after machining. 1. Austenitize in a controlled atmosphere or vacuum furnace to prevent decarburization. 2. Quench in well-agitated oil. 3. **Temper immediately and double temper** for best toughness and dimensional stability. * **Stress Relieving:** A stress relief at 600-650°C after rough machining is highly recommended for complex molds. * **Grinding & Polishing:** Grinds and polishes well. The clean VMR® structure allows for high-quality surface finishes without "pulling out" inclusions. * **Welding:** **Good weldability** due to low carbon content. Use appropriate pre-heat (200-300°C) and post-weld heat treatment (tempering) for critical areas. Use a soft, crack-resistant filler metal. * **Surface Treatment (Highly Recommended):** * **Nitriding (Gas or Plasma):** The most common enhancement. Produces a hard, wear-resistant surface layer (up to 700-900 HV) with excellent anti-sticking properties, while the tough M268 core provides support. Ideal for gates, runners, and ejector areas. * **EDM:** Suitable. A low-temperature stress relief after EDM is advisable. --- ## **7. Conclusion** **BÖHLER M268 VMR®** is a **high-reliability, high-performance mold steel** that expertly balances the often-conflicting demands of **toughness, polishability, and manufacturability**. Its nickel-alloyed chemistry provides the backbone for exceptional impact resistance, making it a safe choice for complex, fragile mold designs. The **VMR® manufacturing process** elevates it from a standard material to a premium one, ensuring that the inherent benefits of the alloy design are fully realized through exceptional internal purity. This directly translates to better polishability, more predictable heat treatment, and reduced risk of defects in the final mold. For mold makers designing tools for large, complex parts, engineering plastics, or applications where mold breakage is a significant concern, M268 VMR® offers a robust and proven solution. It provides the safety margin of high toughness without sacrificing the ability to achieve excellent surface finishes or to be easily enhanced with nitriding for demanding production runs. -:- For detailed product information, please contact sales. -: Bohler-Uddeholm BÖHLER M268 VMR® Plastic Mold Steel Specification Dimensions Size： Diameter 20-1000 mm Length <6909 mm Size:We can customized as required Standard： Per your request or drawing We can customized as required Properties（Theoretical） Chemical Composition -:- For detailed product information, please contact sales. -: Bohler-Uddeholm BÖHLER M268 VMR® Plastic Mold Steel Properties -:- For detailed product information, please contact sales. -:

Applications of Bohler-Uddeholm BÖHLER M268 VMR® Plastic Mold Steel Rod -:- For detailed product information, please contact sales. -: Chemical Identifiers Bohler-Uddeholm BÖHLER M268 VMR® Plastic Mold Steel Rod -:- For detailed product information, please contact sales. -:

Packing of Bohler-Uddeholm BÖHLER M268 VMR® Plastic Mold Steel Rod -:- For detailed product information, please contact sales. -: Standard Packing: -:- For detailed product information, please contact sales. -: Typical bulk packaging includes palletized plastic 5 gallon/25 kg. pails, fiber and Steel Rod drums to 1 ton super sacks in full container (FCL) or truck load (T/L) quantities. Research and sample quantities and hygroscopic, oxidizing or other air sensitive materials may be packaged under argon or vacuum. Solutions are packaged in polypropylene, plastic or glass jars up to palletized 3380 gallon liquid totes Special package is available on request. E FORUs’ is carefully handled to minimize damage during storage and transportation and to preserve the quality of our products in their original condition