1 Introduction to S136 Mold Steel
S136, also known as DIN 1.2083 or ASSAB STAVAX ESR, is a premium martensitic high-chromium stainless mold steel. Manufactured via Electro-Slag Remelting (ESR) technology, this material eliminates most internal non-metallic impurities, achieving extremely high purity and uniform microstructure. Compared with conventional EAF-smelted mold steel, ESR-grade S136 delivers superior surface finish, dimensional stability, and corrosion resistance, making it a preferred option for high-precision, high-gloss, and hygiene-critical injection molds.
In industrial molding production, S136 exhibits 2 to 3 times longer service life than ordinary pre-hardened mold steels. In corrosive molding environments involving PVC, POM, and flame-retardant plastics, its lifespan can reach 5 to 10 times that of traditional mold materials. Currently, S136 is widely adopted in 40%–50% of medical disposable molds, 60% of food-safe packaging molds, and 30% of high-end cosmetic transparent molds.
2 Core Performance Advantages of S136
S136’s comprehensive performance advantages distinguish it from common mold steels, covering surface quality, anti-corrosion capability, mechanical stability, and machining precision.
2.1 Premium SPI A-1 Mirror Polishing Performance
The refined grain structure of ESR-grade S136 supports ultra-fine surface polishing, reaching a maximum roughness of Ra 0.012μm and meeting the strict SPI A-1 mirror grade standard. This capability enables the production of flawless high-gloss parts, including optical lenses, transparent cosmetic shells, and clear medical plastic components. While NAK80 can achieve similar gloss levels, it lacks reliable corrosion resistance, and P20 and 718H cannot reach ultra-mirror surface quality.
2.2 Excellent Long-Term Corrosion Resistance
With a chromium content ranging from 12.5% to 14.0%, S136 forms a dense, stable passive oxide film on its surface. This protective layer effectively resists acidic gas erosion generated by molten PVC and POM plastics. It also withstands repeated alcohol disinfection and high-temperature steam sterilization, which are essential for medical and food-grade mold production. Molds made of S136 require minimal daily anti-rust maintenance, greatly reducing long-term mold upkeep costs.
2.3 Stable Hardness and Uniform Mechanical Texture
After vacuum quenching and double tempering, S136 achieves a stable hardness of 48–52 HRC with balanced hardness and toughness. Even for large-sized mold blanks, the material maintains consistent hardness throughout the entire cross-section, avoiding partial wear, deformation, or cracking during long-term mass production.
2.4 Ultra-Low Machining Deformation
S136 features a controllable thermal expansion rate and uniform internal structure, which effectively reduces thermal deformation after heat treatment. It stably maintains a precision tolerance of ±0.05 mm, fully satisfying the dimensional accuracy requirements of micro-structured parts and high-precision IVD medical components.
3 S136 Material Technical Specifications
3.1 Chemical Composition and Functional Analysis
| Element | Typical Content | Content Range | Core Function |
| C | 0.38% | 0.36–0.42% | Determines mold steel hardness and surface wear resistance |
| Si | 0.90% | 0.60–1.00% | Deoxidizes molten steel and improves mirror polishing smoothness |
| Mn | 0.50% | 0.30–0.80% | Enhances material hardenability and overall structural strength |
| Cr | 13.60% | 12.50–14.00% | Forms anti-corrosion passive film, core element for rust resistance |
| V | 0.30% | 0.20–0.50% | Refines internal grain structure and improves low-temperature toughness |
| P | ＜0.025% | ≤0.030% | Restrict harmful impurities to prevent surface defects during polishing |
| S | ＜0.001% | ≤0.003% | Excessive sulfur generates surface streaks and degrades mirror surface quality |
3.2 Physical and Mechanical Properties (20°C)
| Performance Item | Standard Parameter | Practical Machining Significance |
| Density | 7.85 g/cm³ | Supports accurate blank weight calculation and clamping design |
| Elastic Modulus | 215 GPa | High structural rigidity reduces cutting vibration during processing |
| Thermal Conductivity | 25.0 W/m·K | Low heat dissipation requires high-pressure full coolant during milling |
| Annealed Hardness | ≤235 HB | Allows direct rough milling without pre-heat treatment |
| Quenched Hardness | 50–55 HRC (Recommended 50–52 HRC) | Balances hardness, toughness, polishing and anti-corrosion performance |
| Tensile Strength | 1750–1900 MPa | Resists repeated injection pressure deformation in mass production |
| Magnetism | Magnetic | Martensitic structure, not applicable for non-magnetic mold requirements |
3.3 S136 VS Common Mold Steels Comprehensive Comparison
| Steel Grade | Corrosion Resistance | Max Polishing Grade | Mold Shot Lifespan | Relative Cost | Best Application Scenarios |
| S136 ESR | Excellent | SPI A-1 (Ra0.012μm) | 500,000–1,000,000+ | +60%~90% vs P20 | Medical molds, food containers, PVC flame-retardant plastic, optical lenses |
| P20 (1.2311) | Poor | Ordinary gloss only | 50,000–300,000 | Baseline 1.0x | Trial molds, mold bases, low-precision non-corrosive plastic parts |
| 718H | Fair | Medium gloss | 300,000–800,000 | +35% vs P20 | Automotive and home appliance mass production molds |
| NAK80 | Moderate | Ultra-high mirror | 500,000–900,000 | +45% vs P20 | Transparent optical parts without corrosive plastic molding |
4 Professional CNC Machining Guide for S136
S136 has low thermal conductivity and high hardness, making it more difficult to machine than ordinary mold steels. Cutting heat easily accumulates on tool edges, causing rapid tool wear, surface ripples, and dimensional errors. Standardized parameters and scientific tool selection are essential for stable machining quality.
4.1 Recommended Rough Milling Parameters
Optimized for Ø125 face mill cutter and large S136 mold blanks:
• Spindle Speed: 1200–1500 rpm
• Feed Rate: 1200–1500 mm/min
• Axial Cut Depth (Ap): 1.5–2 mm
• Radial Cut Width (Ae): 80–100 mm
• Coolant Pressure: ≥70 bar full flood cooling to eliminate concentrated cutting heat
4.2 Tiered Tool Selection Standard
Tool selection directly determines surface finish and processing efficiency for hard and corrosion-resistant S136 steel. Ultra-fine grain carbide tools with professional coatings are required for different processing stages.
| Processing Stage | Preferred Tool Type | Optimal Coating | Processing Tips |
| Rough Milling | Ultra-fine WC-Co carbide end mill | AlCrN priority, TiAlN alternative | 8–12% cobalt substrate for enhanced impact resistance; avoid HSS tools |
| Semi-Finishing | Solid carbide ball nose end millSolid carbide ball nose end mill | TiAlN | 30–45° helix angle to reduce cutting vibration and tool load |
| Mirror Finishing | CBN precision tools | TiSiN or uncoated sharp edge | 12–15° edge relief angle to remove micro tool marks for mirror surface |
| Deep Cavity Machining | Long-neck reinforced carbide end mill | TiAlN | Control L/D ratio within 10:1 to prevent tool chatter and deformation |
4.3 EDM Processing Key Points
S136 contains high chromium content, which easily forms a thick and brittle Cr₂O₃ white layer during EDM processing. This oxide layer is three times thicker than that of ordinary carbon steel, resulting in tiny surface pits and reduced polishing quality if not handled properly.
To optimize EDM quality, reduce peak current and extend pulse interval to lower oxide deposition. After EDM processing, remove the residual white layer through acid pickling or electro-polishing to ensure a flawless mirror polishing foundation.
5 Typical Application Scenarios & Usage Restrictions
5.1 Recommended Applications
Medical Injection Molds
S136 meets ISO 13485 hygiene standards, suitable for disposable syringes, infusion connectors, nebulizer shells, blood glucose detector housings and surgical instrument accessories. It withstands repeated high-temperature sterilization and alcohol disinfection without rust or surface contamination.
Food-Grade Packaging Molds
Ideal for food storage containers, baby bottle caps and kitchenware plastic molds. Its stable corrosion resistance prevents chemical erosion from food residues and ensures long-term food safety compliance.
High-Gloss Cosmetic & Optical Molds
Capable of SPI A-1 mirror finish, perfectly applicable for transparent cosmetic bottles, cream shells, optical lenses, light guide plates and high-transparency plastic parts with strict surface and light transmittance requirements.
Corrosive Resin Molding
Suitable for PVC, POM and flame-retardant modified plastic products. It resists acidic corrosive gas generated during high-temperature melting, effectively avoiding mold rust and surface failure during mass production.
5.2 Non-Recommended Application Scenarios
High-Impact Heavy Load Molds
S136 has balanced but not ultra-high toughness. Long-term strong impact load will cause cavity cracking and fatigue damage.
30%+ Glass Fiber Reinforced Plastics
Low wear resistance cannot resist continuous scratching from glass fiber, leading to rapid cavity surface wear and reduced product uniformity.
Continuous Working Temperature Above 200°C
Long-term high-temperature environment will degrade hardness, toughness and anti-corrosion performance, causing unstable mold accuracy.
High-Chlorine Plastic Molding
Chloride ions will destroy the chromium passive film on the steel surface and cause irreversible pitting corrosion.
Low-Precision & Small-Batch Products
High material cost and long processing cycle lead to unnecessary cost waste for ordinary low-demand molds.
Frequent Welding Repair Scenarios
High carbon and chromium composition results in high welding crack sensitivity, easily causing surface cracking after repair.
6 Common Defects & Professional Solutions
6.1 Surface Rusting After Machining
S136’s chromium passive film will be damaged during milling, grinding and EDM processing. Chloride-containing cutting fluid and humid workshop air accelerate local pitting corrosion.
Solution: Use chloride-free coolant throughout processing; complete professional passivation treatment after polishing; clean and fully dry mold surfaces before storage.
6.2 Rapid Tool Wear During Cutting
S136 thermal conductivity is only one-third of 45# steel. Cutting heat cannot dissipate timely and accumulates on tool edges, causing rapid coating ablation and tool wear.
Solution: Adopt ultra-fine grain carbide coated tools; reduce spindle speed by 20% compared with ordinary mold steel processing; maintain continuous high-pressure coolant cooling.
6.3 Large Deformation After Quenching
Poor thermal conductivity causes internal temperature difference over 300°C during vacuum quenching, coupled with 3% martensitic volume expansion, resulting in uneven shrinkage and mold deformation.
Solution: Conduct stress relief annealing before rough processing; adopt step heating quenching process; reserve 0.3–0.5mm finishing allowance for post-heat treatment correction.
6.4 Welding Cracking Failure
High carbon and chromium content produces high residual stress after heat treatment. Rapid temperature change during welding easily induces cold cracks on mold surfaces.
Solution: Preheat the workpiece to 300°C before welding; adopt low-current segmented welding; perform integral tempering immediately after welding to eliminate residual stress.
6.5 Dimensional Instability Over Time
Trace vanadium and molybdenum elements in S136 cause aging hardening and carbide precipitation, leading to subtle dimensional changes after long-term placement.
Solution: Conduct 180°C × 8 hours aging treatment after finishing; keep 7-day constant temperature stabilization at 40°C before final delivery.
7 FAQ
Q1 What is the difference between S136 and 1.2083 steel?
1.2083 is the unified DIN standard grade name, while S136 STAVAX ESR is the high-end commercial version. Ordinary 1.2083 adopts conventional EAF smelting with more internal impurities, while ESR-grade S136 uses electro-slag remelting technology to minimize inclusions, achieving ultra-high mirror polishing performance and more stable corrosion resistance for high-end precision molds.
Q2 Is S136 cost-effective compared with P20 and 718H?
Although S136 has higher material costs, its mold service life is 5–10 times longer in corrosive molding environments. It greatly reduces mold replacement frequency, maintenance costs and defective product rates, bringing significant comprehensive cost advantages for long-term mass production of medical, food and corrosive plastic products.
Q3 Can ordinary smelted S136 achieve SPI A-1 mirror surface?
No. Ordinary EAF-smelted S136 contains large-sized non-metallic inclusions. These impurities will fall off during polishing, forming tiny pits on the cavity surface. Only ESR ultra-pure S136 with inclusion size controlled below 10μm can achieve Ra 0.012μm flawless SPI A-1 mirror finish.
8 Conclusion
S136 ESR stainless mold steel stands out in high-end mold manufacturing industry for its ultra-high mirror polishing performance, excellent corrosion resistance and stable mechanical properties. It perfectly solves common pain points of ordinary mold steels such as easy rust, poor surface finish and short service life. With standardized CNC machining, EDM processing and heat treatment processes, S136 can maintain long-term dimensional stability and surface quality, becoming the most ideal material for medical hygiene, food safety, optical transparency and corrosive plastic molding projects.