When manufacturers ask me which mold steel offers stable hardness, reliable corrosion resistance, and high polishability for chemically aggressive plastics, 1.2316 tool steel is always on the shortlist. As an engineer who has worked with hot-work and plastic-mold tool steels for more than 15 years, I’ve seen 1.2316 steel become a global favorite—especially in PVC mold making—because it sits in a unique sweet spot: part stainless steel, part tool steel, part precision engineering material.
This article consolidates verified data from reputable databases, combined with field experience from industrial mold workshops. If you are sourcing, designing, machining, or heat-treating 1.2316 steel, this guide gives you the complete perspective.
Overview of 1.2316 Tool Steel
1.2316 is a martensitic stainless tool steel (DIN designation X38CrMo16) with a high chromium content of 15.5–17.5%, which places it in the same chemical family as AISI 420 but with improved hardenability and more stable heat-treat performance thanks to its molybdenum (Mo ≈1.0–1.3%).
Industry synonyms:
| Standard | Designation |
|---|---|
| DIN / EN | 1.2316, X38CrMo16 |
| AISI | 420 mod. (not identical to regular 420) |
| JIS | SUS420J2 equivalent range |
| China GB | Sometimes sold as 4Cr13 (Mo content differs) |
Chemical Composition
| Element | Composition (%) |
|---|---|
| Carbon (C) | 0.33 – 0.45 |
| Chromium (Cr) | 15.50 – 17.50 |
| Molybdenum (Mo) | 1.00 – 1.30 |
| Manganese (Mn) | 1.00 – 1.30 |
| Silicon (Si) | 0.30 – 0.50 |
| Phosphorus (P) | ≤ 0.030 |
| Sulfur (S) | ≤ 0.030 |
Key Properties of 1.2361 Tool Steel
1. Corrosion Resistance
Compared to the 1.2083 grade, 1.2316 delivers superior corrosion resistance thanks to its higher molybdenum content. This extra molybdenum creates a more stable passive layer on the surface, extending protection even in harsher industrial conditions. It’s more obvious during PVC processing, where hydrochloric acid release during molding would normally damage standard steels. 1.2316 stands up to this acidic environment without breaking down.
2. Polishability
1.2316 tool steel achieves mirror-quality surface finishes that other steels can’t match. The fine grain structure allows polishing to an exceptional shine.For plastic molds requiring SPI A-1 standards—the highest grade for mold surfaces—1.2316 delivers consistently. Clear plastic parts with zero visible defects depend on this level of finish. Medical device casings, automotive light covers, and cosmetic packaging all demand this precision. Optical lens molds push polishing requirements even further. Tiny scratches or bumps that barely register to the naked eye will ruin a precision lens. 1.2316 handles the ultra-fine polishing steps needed for optical-grade tools without losing sharp edges or fine details.
3. Machinability
1.2316 tool steel machines more easily than most hardened steels, saving you time and reducing tool wear. The hardness stays uniform throughout the material, so cutting tools bite consistently across the entire workpiece. You won’t encounter soft spots that cause chatter or hard zones that prematurely dull your bits.Most suppliers ship this material pre-hardened to 280–325 HB (approximately 30 HRC). This delivery state eliminates the entire heat treatment cycle from your workflow. You can start cutting immediately and use the parts straight from the machine.The fine carbide distribution prevents tool edges from chipping during cuts, while chips form cleanly and evacuate without building up on the cutting tool. Threading and EDM operations proceed without complications, and the stable structure maintains dimensional accuracy throughout machining.
4. Toughness and Ductility
1.2316 tool steel absorbs impact without cracking, bending slightly before breaking. This balance between strength and flexibility comes from controlled tempering after hardening, giving you a material that performs reliably under real-world production stresses.Drop a heavy workpiece on a 1.2316 mold, and the steel handles it. Sharp corners stay intact. No chips break off.
5. Wear Resistance
Hard carbide particles embedded in 1.2316’s matrix act like microscopic armor plates, protecting the surface during extended molding cycles. These carbides give the steel exceptional resistance to abrasive wear.The chromium carbides resist scratching better than softer tool steels, keeping mold cavities at their original dimensions far longer than conventional materials would allow. The steel’s hardness range (30-52 HRC) creates a durable working surface where sharp edges on cavity details stay crisp instead of slowly dulling and compromising part quality.
6. Heat Resistance
1.2316 tool steel maintains dimensional stability as temperatures rise during production. The chromium-molybdenum composition resists heat softening up to 400°C (752°F), providing the stability needed for continuous molding operations where friction and plastic flow generate constant heat, allowing you to process demanding plastics at elevated temperatures while maintaining part accuracy. Even when cavity surfaces reach 300-350°C during rapid injection cycles, the material keeps its hardness and dimensional precision..
Hardness Specifications
1.2316 tool steel is available in different hardness levels depending on heat treatment. Suppliers measure hardness using two scales: Brinell (HB) and Rockwell C (HRC), giving you flexibility to choose the right condition for your specific application.
| Condition | Hardness (HB) | Hardness (HRC) | Best For |
|---|---|---|---|
| Pre-Hardened | 280–325 | 29–33 | Most plastic molding applications; ready to machine |
| Annealed | Max 235 | N/A | Heavy machining and complex cavity shapes |
| After Quenching | N/A | 48–52 | Maximum hardness (requires tempering) |
| Post-Tempering | N/A | 32–49 | Balance of hardness and toughness |
Most suppliers deliver the steel pre-hardened to 280–325 HB after quenching and tempering. This condition allows immediate machining without additional heat treatment, making it ideal for most plastic mold applications. For projects requiring deep cuts or complex cavity shapes, the annealed condition (maximum 235 HB) offers easier machining.
After quenching, the steel reaches 48–52 HRC—its peak hardness and strength. However, you must temper it to prevent brittleness. The tempering temperature controls final hardness: lower temperatures around 480°C maintain hardness near 49 HRC, while higher temperatures up to 650°C reduce it to 32 HRC. This flexibility lets you balance hardness against toughness based on your specific requirements. Higher hardness provides better wear resistance, while lower hardness offers superior impact and heat stress resistance.
Physical Properties
| Property | Value | Practical Effect / Advantage |
|---|---|---|
| Density | 7.71–7.80 g/cm³ | Provides a solid, heavy base for molds and dies |
| Elastic Modulus | ~241,000 N/mm² | High stiffness resists deformation, maintaining precise mold shapes |
| Thermal Expansion (20–200°C) | 11.2 ×10⁻⁶ K⁻¹ | maintain tight tolerances in hot-working applications. |
| Thermal Expansion (20–400°C) | 11.5 ×10⁻⁶ K⁻¹ | Stable thermal behavior minimizes distortion |
Mechanical Properties
1.2316 tool steel holds up well in demanding production environments. After hardening and tempering to 32-34 HRC, the material shows reliable performance across multiple mechanical parameters that matter for toolmaking applications.
| Property | Value / Range | Benefits / Notes |
|---|---|---|
| Hardness (HRC) | 32–34 | Provides a durable surface that resists wear; ensures mold longevity in high-volume production. |
| Yield Strength (Rp0.2) | 855 MPa (124 ksi) | High resistance to permanent deformation; prevents mold bases from warping under clamp pressure. |
| Tensile Strength (Rm) | 1020 MPa (148 ksi) | Handles substantial loads without fracture; ejector pins and other components resist snapping. |
| Elongation (A%) | 13% | Offers sufficient ductility; material shows visible warning before failure rather than shattering. |
| Reduction of Area (Z%) | 38% | Confirms toughness; cross-section shrinks gradually under stress, giving safety margin. |
| Elastic Modulus (E) | 205 GPa (29,733 ksi) | Ensures stiffness; large mold plates maintain flatness under injection pressure spikes. |
| Impact Strength (KCV) | 35 J | Absorbs shocks and protects tools from accidental drops or sudden thermal stress. |
Primary Applications
Plastic injection molding uses most 1.2316 tool steel. This steel resists corrosion and polishes to a mirror finish. That makes it great for tough polymer processing jobs.
| Application Category | Specific Use Case |
|---|---|
| Chemical-Aggressive Materials | PVC Processing |
| Abrasive-Filled Plastics (Glass Fiber, Ceramic Filled) | |
| High-Finish Applications | Super-Mirror Molds (SPI A-1 Finish) |
| Optical Components | |
| Medical & Consumer Products | Cosmetic Containers / Medical Housings / Pharma Packaging |
| Light Guide Plates (LCD Displays) | |
| Bottle Caps & High-Cycle Consumer Parts |
Supply Specifications
| Stock Type | Dimensions / Range | Typical Uses |
|---|---|---|
| Round Bar Stock | Diameter: 16–500 mm | Small diameters (16–100 mm): ejector pins, cores, insertsLarge diameters (200–500 mm): full mold bases, heavy-duty die blocks |
| Flat Plate Stock | Thickness: 16–120 mmWidth: 200–610 mm | Cavity blocks, backing plates, structural mold parts |
| Module Stock | Thickness: 120 mm and above | Oversized tooling projects, large injection molds, heavy-duty stamping dies |
Conclusion
1.2316 (X38CrMo16 / AISI 420 Modified) is one of the most reliable stainless tool steels for PVC molds, corrosive plastic tooling, medical packaging, and precision transparent components. With ~16% chromium, molybdenum reinforcement, and excellent polishability, it provides a combination of benefits unmatched by most general-purpose mold steels.
By understanding its composition, properties, heat treatment, and supply variations, engineers and buyers can choose the right grade, optimize performance, and control procurement cost. When sourced from reputable suppliers and treated properly, 1.2316 delivers high productivity, long service life, and premium surface finish quality.