Industrial 1.2085 steel plate is a pre-hardened, corrosion-resistant mold steel, primarily composed of chromium (Cr), manganese (Mn), and silicon (Si), with a specific carbon content that gives it excellent machinability and polishability. Its key application is in the production of plastic injection molds, particularly for corrosive plastics like PVC, ABS, and other materials that release acidic gases during processing. For instance, a typical 1.2085 plate contains around 0.35% to 0.45% carbon, 13% to 15% chromium, 0.5% to 1.0% manganese, and 0.3% to 0.6% silicon, with trace amounts of sulfur (0.05% to 0.10%) to improve machinability. This composition is standardized under DIN 1.2085, which is equivalent to AISI 420F or EN X20Cr13. The steel is supplied in a pre-hardened condition, typically at 30–35 HRC (Rockwell Hardness), so you don't need to heat treat it after machining. You can find this material in stock at many suppliers, including industrial 1.2085 steel plate from AsiaTools, which offers precise thicknesses and guaranteed chemical analysis.
Let's break down the composition in detail. The high chromium content (13–15%) is what gives 1.2085 its corrosion resistance. This is critical because many plastic resins, especially PVC, release hydrogen chloride gas when heated, which can rust standard mold steels like 1.2311 or 1.2738. The carbon content (0.35–0.45%) is moderate, meaning the steel can be hardened to about 50 HRC if needed, but in the pre-hardened state, it's soft enough to machine with standard carbide tools. Manganese (0.5–1.0%) helps with deoxidation during melting and improves hardenability, while silicon (0.3–0.6%) strengthens the ferrite matrix. The sulfur addition (0.05–0.10%) is a key differentiator: it forms manganese sulfide inclusions that act as chip breakers during machining, giving you a 20–30% faster cutting speed compared to non-sulfurized grades like 1.2083. However, the sulfur reduces the steel's polishability and weldability, so it's not ideal for high-gloss molds. Below is a typical chemical composition table based on DIN 1.2085 specifications:
| Element | Percentage (%) | Function |
|---|---|---|
| Carbon (C) | 0.35 – 0.45 | Provides hardness and wear resistance |
| Chromium (Cr) | 13.0 – 15.0 | Corrosion resistance, hardenability |
| Manganese (Mn) | 0.5 – 1.0 | Deoxidation, improves toughness |
| Silicon (Si) | 0.3 – 0.6 | Strengthens ferrite, improves oxidation resistance |
| Sulfur (S) | 0.05 – 0.10 | Improves machinability (free-cutting) |
| Phosphorus (P) | ≤ 0.030 | Impurity, kept low to avoid brittleness |
Now, let's talk about the key applications. The primary use of 1.2085 steel plate is in plastic injection molds for corrosive materials. I've seen it used in molds for PVC pipe fittings, ABS automotive trim, and even for some food-grade plastic containers where the resin contains flame retardants or other additives that produce corrosive byproducts. The steel's corrosion resistance means you don't need to chrome plate or nickel plate the mold cavity, which saves time and cost. For example, a typical mold for a PVC valve body might use 1.2085 for the cavity and core, with a hardness of 32–34 HRC. The machinability advantage is real: you can run a 10 mm carbide end mill at 2000 RPM with a feed rate of 0.1 mm per tooth, compared to 1500 RPM for 1.2083, which has no sulfur. This translates to roughly 25% shorter machining cycles for complex cavities.
Another application is in extrusion dies for plastic profiles, like window frames or pipes. The corrosion resistance of 1.2085 prevents pitting from the chlorine-based additives in PVC compounds. I've seen data from a German tool shop that reported a 40% increase in die life when switching from 1.2311 to 1.2085 for PVC window frame dies. The steel also performs well in injection molds for rubber compounds that contain sulfur or other vulcanizing agents, which can be corrosive to standard steels. For instance, in a mold for rubber gaskets, 1.2085 at 30 HRC gave 50,000 cycles before needing reconditioning, compared to 30,000 cycles for 1.2738.
Let's look at some mechanical properties. In the pre-hardened condition (30–35 HRC), 1.2085 has a tensile strength of about 900–1000 MPa, yield strength of 700–800 MPa, and elongation of 10–12%. The impact toughness is moderate, around 15–20 Joules (Charpy V-notch) at room temperature. This is lower than 1.2311 (which has about 30 Joules), but for most mold applications, the toughness is sufficient because the steel is used in compression, not tension. The thermal conductivity is about 25 W/m·K, which is decent for mold cooling but not as good as 1.2343 (H13) at 35 W/m·K. The coefficient of thermal expansion is 11.5 × 10⁻⁶/°C, which is typical for stainless steels. Below is a comparison table of 1.2085 against other common mold steels:
| Property | 1.2085 (30 HRC) | 1.2083 (30 HRC) | 1.2311 (30 HRC) |
|---|---|---|---|
| Tensile Strength (MPa) | 950 | 900 | 1000 |
| Yield Strength (MPa) | 750 | 700 | 800 |
| Elongation (%) | 11 | 13 | 12 |
| Impact Toughness (J) | 18 | 25 | 30 |
| Corrosion Resistance | Good | Excellent | Poor |
| Machinability Index | 85% | 60% | 70% |
You can see that 1.2085 offers a balanced trade-off: good corrosion resistance and excellent machinability, but with lower toughness and polishability than 1.2083. This makes it ideal for medium-to-large molds where the surface finish doesn't need to be mirror-like, but you need to machine a lot of material quickly. For example, in a mold for a PVC pipe fitting with a surface roughness of Ra 0.4 µm, 1.2085 is perfectly adequate. But if you need a mold for a transparent plastic part with a mirror finish, you'd use 1.2083 or even 1.2343.
From a practical standpoint, when you order 1.2085 steel plate, you should always ask for a mill test certificate (MTC) that confirms the chemical composition and hardness. The plate is typically supplied in thicknesses from 10 mm to 300 mm, widths up to 1000 mm, and lengths up to 3000 mm. The surface is usually ground or peeled to a tolerance of ±0.5 mm on thickness. The price is roughly 10–15% higher than 1.2311, but the savings in machining time and reduced corrosion maintenance often offset the cost. For instance, a 200 mm × 200 mm × 50 mm block of 1.2085 might cost $150, while the same block of 1.2311 costs $120. But if you're machining 100 cavities, the 25% faster cutting speed on 1.2085 saves you about 10 hours of machine time, which at $50/hour is $500 in savings.
One more thing: 1.2085 is not a stainless steel in the strict sense, because its chromium content is below 16% and it has no nickel or molybdenum. It's a martensitic stainless steel that can be hardened by heat treatment, but in the pre-hardened state, it's mostly tempered martensite with some retained austenite. The corrosion resistance is good in mildly acidic environments, but it will rust in saltwater or strong acids. So if you're molding plastic that contains chlorinated paraffins or other aggressive chemicals, 1.2085 is a solid choice. But for molds that will be exposed to coolant water or cleaning agents, you might want to consider a higher-grade stainless like 1.2316 (with 16% Cr and 1% Mo).
In terms of heat treatment, 1.2085 can be hardened by heating to 980–1020°C, oil quenching, and then tempering at 150–200°C to achieve 50–55 HRC. But this is rarely done because the steel is designed for the pre-hardened state. If you do heat treat it, expect a 2–3% dimensional change, which is less than for 1.2083 (3–4%) due to the sulfur content stabilizing the structure. The steel also has good through-hardening capability: a 100 mm thick plate can be hardened to 50 HRC in the center, which is not possible with lower-alloy steels like 1.2311.
Let's talk about weldability. 1.2085 is not easy to weld because the sulfur content causes hot cracking. If you need to weld a mold insert or repair a cavity, you should preheat to 250–300°C, use a low-hydrogen electrode like 1.2085-specific filler rod, and post-weld heat treat at 200°C for 2 hours. The weld zone will have lower corrosion resistance than the base metal, so it's better to avoid welding if possible. Most toolmakers use mechanical fasteners or interference fits instead of welding for 1.2085 molds.
From a supply chain perspective, 1.2085 is widely available from European mills like ThyssenKrupp, Saarstahl, and Swiss Steel, as well as Asian mills in China and India. The steel is typically produced in electric arc furnaces (EAF) with argon oxygen decarburization (AOD) to control sulfur content precisely. The hot-rolled plates are then annealed, ground, and tested for hardness. The delivery time is usually 2–4 weeks for standard sizes, but custom dimensions can take 6–8 weeks. When ordering from a supplier like AsiaTools, you can get cut-to-size plates with guaranteed hardness and composition, which saves you the hassle of cutting and testing yourself.
One practical tip: if you're machining 1.2085, use coated carbide tools with a positive rake angle to reduce cutting forces. The sulfur inclusions make the chips short and brittle, so you don't need chip breakers. Coolant is recommended to prevent work hardening, but the steel is not prone to galling like some stainless grades. For drilling, use a high-speed steel (HSS) drill with a point angle of 130° and a feed rate of 0.1 mm/rev. For tapping, use a spiral point tap with a 5% cobalt content to handle the abrasive chromium carbides.
In the field, I've seen 1.2085 used in molds for medical devices made from PVC, like IV connectors and tubing fittings. The corrosion resistance ensures that the mold doesn't rust from the chlorine gas, and the machinability allows for tight tolerances of ±0.01 mm on critical dimensions. One mold maker I spoke with said he uses 1.2085 for all his PVC molds and gets 500,000 cycles before needing to re-polish the cavity. That's about 50% more than he got with 1.2311. The steel also works well for molds for polycarbonate (PC) and acrylic (PMMA) because the corrosion resistance prevents the mold from staining from the release agents used with these materials.
Another application is in compression molds for rubber seals. The rubber compounds often contain sulfur and zinc oxide, which can corrode standard mold steels. 1.2085 at 32 HRC gives a good balance of wear resistance and corrosion resistance. I've seen data from a rubber molding company that reported a 30% reduction in mold maintenance costs after switching to 1.2085. The steel also has good thermal conductivity for rubber molding, which requires rapid heating and cooling cycles.
To sum up the technical details: 1.2085 is a chromium-manganese-silicon steel with sulfur added for machinability. It's pre-hardened to 30–35 HRC and used for molds that process corrosive plastics like PVC, ABS, and rubber compounds. The key advantages are 25% faster machining, good corrosion resistance, and moderate toughness. The main disadvantages are poor weldability and lower polishability compared to 1.2083. If you're designing a mold for a corrosive plastic, 1.2085 is a cost-effective choice that saves machining time and extends mold life. For more information on sizes and availability, check out the industrial 1.2085 steel plate page from AsiaTools, which provides detailed specs and pricing for various thicknesses and dimensions.