Key Specifications for a Custom 1.2311 Round Bar
When you’re sourcing a custom 1.2311 round bar, the key specs boil down to its chemical composition, hardness range, dimensional tolerances, and heat treatment response. This tool steel, also known as 40CrMnMoS8-6 under DIN 1.2311, is a pre-hardened plastic mold steel. It’s delivered in a quenched and tempered condition, typically hitting a hardness of 280 to 325 HB (Brinell). That’s not a random range—it’s engineered to balance machinability with wear resistance for injection molding and extrusion dies. The sulfur content, around 0.05% to 0.10%, is what gives it improved machinability compared to its sibling 1.2312, which has higher sulfur for even easier cutting but lower toughness. For a custom 1.2311 round bar, you’re looking at a diameter range from 20 mm to 600 mm, with lengths up to 6 meters standard, though custom cuts are common. The material’s density sits at 7.85 g/cm³, and its thermal conductivity is about 34 W/m·K at 20°C, which matters for cooling channel design in molds. Let’s break down the specifics so you know exactly what you’re ordering.
The chemical makeup of 1.2311 is precise. Carbon content runs 0.35% to 0.45%, which gives it that through-hardening capability. Manganese is 1.30% to 1.60%, chromium is 1.80% to 2.10%, molybdenum is 0.15% to 0.25%, and sulfur is 0.05% to 0.10%. Silicon stays under 0.40%, and phosphorus is max 0.025%. This composition is what makes it a pre-hardened steel—you don’t need to heat treat it after machining for most applications. The delivery condition is already hardened and tempered to 280-325 HB, which translates to a tensile strength of roughly 900-1100 MPa. If you’re after a custom 1.2311 round bar with a tighter hardness window, say 290-310 HB, that’s doable but requires careful control during the tempering process. The steel’s microstructure is a mix of tempered martensite and bainite, which gives it good dimensional stability. For comparison, 1.2343 (H11) hot work steel has higher chromium and vanadium for hot strength, but 1.2311 is your go-to for cold and warm work plastic molds where you need consistent polishability and low distortion.
Dimensional tolerances are a big deal when you’re ordering custom. For a custom 1.2311 round bar, the standard tolerance for diameter is h11 to h9, depending on the mill. That means for a 100 mm bar, h11 gives you a range of 99.78 mm to 100.00 mm, while h9 tightens it to 99.87 mm to 100.00 mm. Length tolerances are typically +10 mm to +50 mm for standard bars, but custom lengths can be held to +/- 5 mm if you specify. Straightness is usually within 1 mm per meter for rolled bars, but for ground bars, you can get 0.5 mm per meter. Surface finish matters too—black bars come with a mill scale finish, while peeled or turned bars have a roughness of Ra 3.2 µm or better. If you’re using it for a mold cavity, you’ll want a ground finish with Ra 0.8 µm to minimize post-machining work. The steel’s machinability rating is about 70% of AISI 4140, which is decent for a pre-hardened tool steel. You can cut it with carbide tools at speeds of 80-120 m/min, but that sulfur content helps chip breakage, so you’ll get better surface finishes than with 1.2379 (D2).
Heat treatment isn’t usually needed for 1.2311 since it’s pre-hardened, but if you’re doing a custom 1.2311 round bar for a specific application that requires higher hardness, you can re-austenitize it. The hardening temperature is 840°C to 870°C, followed by oil or polymer quenching. Tempering is done at 540°C to 660°C to achieve a hardness of 300-350 HB. But here’s the catch—re-heat treating can cause distortion and scale loss, so you’ll need to account for that in your machining allowance. The steel’s hardenability is good, with a critical diameter of about 100 mm in oil, meaning sections up to that size can be fully hardened. For larger bars, you might see a hardness drop in the core, so if you need uniform properties across a 300 mm diameter, you’ll want to specify a through-hardened condition. The steel’s tempering resistance is solid—it retains hardness up to 500°C, which is why it’s used in plastic molds that run at 100-200°C. For higher temperature applications, like 300°C, you’d look at 1.2343 or 1.2344.
Mechanical properties vary by hardness. At 280 HB, the yield strength is around 700 MPa, ultimate tensile strength is 900 MPa, and elongation is 14% in 50 mm. At 325 HB, those numbers jump to 800 MPa yield, 1100 MPa UTS, and 10% elongation. Impact toughness, measured by Charpy V-notch, is about 20 J at 280 HB and drops to 15 J at 325 HB. That’s decent for a mold steel, but if you’re doing high-stress applications like die casting inserts, you might want a tougher grade like 1.2738 (which has nickel for improved toughness). The steel’s polishability is rated as good to very good, with a surface finish down to Ra 0.05 µm achievable with proper grinding and polishing techniques. That’s because the sulfur inclusions are fine and evenly distributed, unlike some free-machining steels that leave pits. For optical mold applications, you’ll need to specify a sulfur content on the lower end, around 0.05%, to minimize inclusions that could affect clarity.
Weldability is another factor. 1.2311 can be welded with preheating to 200-300°C, using filler metals like 1.2311 matching wire or a low-alloy steel like 1.6580. Post-weld stress relief at 550-600°C is recommended to avoid cracking. But if you’re doing a custom 1.2311 round bar for a welded assembly, you’ll want to specify a low-sulfur variant, as high sulfur can cause hot cracking in the weld zone. The steel’s thermal expansion coefficient is 11.5 x 10⁻⁶ /°C from 20°C to 200°C, which is typical for tool steels. That’s important for designing cooling channels in molds—you need to account for expansion to avoid warping during operation. For electrical discharge machining (EDM), the steel’s conductivity is about 4.5% IACS, which is low, so you’ll need to adjust your EDM parameters to avoid recast layers. The recast layer thickness can be controlled to under 10 µm with proper settings, but you’ll want to specify a post-EDM tempering to relieve stress if you’re doing critical surfaces.
When you order a custom 1.2311 round bar, the supplier should provide a mill certificate with the actual chemical analysis and mechanical test results. For example, a typical certificate from a European mill like ThyssenKrupp or Böhler will show carbon at 0.38%, manganese at 1.45%, chromium at 1.95%, molybdenum at 0.20%, sulfur at 0.07%, and hardness at 295 HB. You should also get ultrasonic testing for internal soundness, especially for bars over 200 mm diameter. The standard is SEP 1921, class 3, which allows for small inclusions up to 3 mm in diameter. For critical applications, you can specify class 1, which limits inclusions to 1 mm. The steel’s cleanliness is rated by the ASTM E45 method, with typical values of A1, B1, C0, D1 for sulfur-based inclusions. That’s good for most mold work, but if you’re doing mirror polishing, you’ll want a cleaner grade like 1.2311 ESR (electroslag remelted), which reduces inclusion sizes to under 5 µm.
Cost is a factor. A custom 1.2311 round bar in standard sizes runs $2.50 to $4.00 per kg, depending on the mill and quantity. For a 300 mm diameter bar, 3 meters long, that’s about 550 kg, so $1,375 to $2,200. If you need it ground and polished, add $0.50 to $1.00 per kg. For small quantities, like a 50 mm bar, 1 meter long, you’re looking at $50 to $100, but you’ll pay a premium for cutting and handling. Lead times vary—standard sizes are usually in stock, but custom diameters or lengths can take 4 to 6 weeks from European mills. Chinese mills like Dongbei or Fushun can do it in 2 to 3 weeks, but you’ll need to verify their quality control. The steel’s machinability is good enough that you can run it on CNC lathes with standard inserts, but you’ll want to use a coolant with high lubricity to avoid built-up edge. For drilling, use cobalt or carbide drills with a 118-degree point angle, and run at 30-40 m/min with a feed of 0.1-0.2 mm/rev.
Surface treatments are common. If you’re using a custom 1.2311 round bar for a mold that needs corrosion resistance, you can nitride it at 520°C for 10 hours to get a case depth of 0.2 mm and a surface hardness of 900 HV. That’s useful for molds processing PVC or other corrosive plastics. But nitriding can cause dimensional growth of about 0.01 mm, so you’ll need to account for that in your final machining. For wear resistance, you can do a TiN coating via PVD, which gives a hardness of 2300 HV and a coefficient of friction of 0.4. That’s common for high-cavity molds where you need to reduce sticking. The steel’s tempering temperature of 540-660°C limits the PVD process to around 500°C, so you can’t do high-temperature coatings like CVD. For polishing, you’ll want to use a sequence of 120, 240, 400, 600, 800, and 1200 grit diamond paste, followed by a final polish with 3 µm diamond suspension. The sulfur content helps with chip removal during polishing, but you’ll need to avoid heavy pressure to prevent smearing.
Industry standards are key. 1.2311 is covered by DIN 1.2311, and it’s equivalent to AISI P20 modified, but with higher sulfur. The ASTM A681 standard covers P20, but 1.2311 has tighter tolerances on sulfur. For a custom 1.2311 round bar, you’ll want to specify that it meets the SEP 1921 ultrasonic test and the DIN 1.2311 chemical limits. Some suppliers offer a “premium” grade with stricter sulfur control at 0.05% to 0.08% for better polishability. The steel’s annealed condition is at 200-220 HB, but that’s rare for custom orders—most people want it pre-hardened. If you’re doing a large project, like a mold for automotive bumpers, you’ll need to order a custom 1.2311 round bar with a diameter of 400 mm and a length of 4 meters, which weighs about 1,000 kg. The supplier will need to do a forging operation to get that size, which adds 2 to 3 weeks to the lead time. Forging reduces the grain size and improves toughness, but you’ll need to specify a forging ratio of at least 3:1 for uniform properties.
Testing is non-negotiable. Every batch should come with a certificate of analysis showing the actual chemistry and a hardness test report. For a custom 1.2311 round bar, you can request a tensile test, impact test, and microstructural analysis. The microstructure should show tempered martensite with no retained austenite, which can cause dimensional instability. The grain size should be ASTM 7 or finer, which gives better toughness. For ultrasonic testing, the standard is to scan the entire bar with a 2 MHz probe, looking for any defects larger than 2 mm. If you find a defect, the supplier should mark it and allow you to cut it out. The steel’s cleanliness is also checked by the JIS G0555 method, with a typical rating of 0.10% for oxide inclusions. That’s fine for most applications, but if you’re doing a mold for medical devices, you’ll want a rating of 0.05% or less, which means you’ll need to specify a vacuum-arc remelted (VAR) grade. That adds cost, but it’s worth it for critical parts.
Handling and storage matter. A custom 1.2311 round bar should be stored in a dry environment to prevent rust, especially if it’s in a black finish. The steel’s corrosion resistance is poor, so you’ll want to apply a rust preventive oil if it’s going to sit for more than a week. For bars over 200 mm diameter, you’ll need to store them on wooden blocks to avoid moisture contact. If you’re cutting the bar, use a band saw with a blade speed of 30-40 m/min and a feed rate of 0.1 mm per tooth. For flame cutting, preheat to 200°C to avoid cracking, and use a cutting speed of 200-300 mm/min for a 100 mm thick section. The heat-affected zone will be about 5 mm deep, and you’ll need to grind that off before machining. For laser cutting, the steel’s reflectivity is low, so you can cut it with a 2 kW laser at 10 mm/min for a 10 mm thickness. But for thicker sections, plasma cutting is more economical.
Applications are broad. A custom 1.2311 round bar is used for injection molds for ABS, polycarbonate, and nylon, where the mold temperature is 80-120°C. It’s also used for extrusion dies for PVC profiles, where the die temperature is 160-180°C. For blow molds, it’s used for the neck ring and base, where you need good wear resistance. The steel’s toughness is enough for small to medium-sized molds, but for large molds over 500 kg, you might want 1.2738 for better through-hardness. In the automotive industry, it’s used for fender molds and bumper molds, where the production runs are 100,000 to 500,000 parts. The steel’s polishability is key for class A surfaces, which require a surface finish of Ra 0.1 µm or better. For that, you’ll need to specify a custom 1.2311 round bar with a sulfur content of 0.05% and a fine grain size of ASTM 8. The supplier should also provide a micrograph showing the inclusion distribution to ensure no clusters are present.
Quality control is a must. When you receive a custom 1.2311 round bar, check the hardness with a portable tester. The reading should be within 5 HB of the certificate. Also, check the diameter with a micrometer at three points along the length—the variation should be within 0.1 mm for a ground bar. For length, measure from the end face, which should be square within 0.5 mm. If the bar has a center hole, check that it’s centered within 1 mm. For ultrasonic testing, you can do a spot check with a 5 MHz probe on the end face to look for any internal defects. The steel’s density is uniform, so any voids will show up as a loss of backwall echo. If you find a defect, reject the bar and ask for a replacement. The supplier should have a return policy for defective material, typically within 30 days of receipt.
Cost optimization is possible. If you’re ordering a custom 1.2311 round bar in large quantities, say 10 tons, you can negotiate a price of $2.00 per kg for a standard size. But for custom diameters, you’ll pay a premium of 10% to 20%. You can also save by ordering a black bar and machining it yourself, rather than paying for a ground finish. The steel’s machinability is good enough that you can do the finishing in-house, as long as you have the right tooling. For small shops, it’s often cheaper to buy a pre-ground bar to avoid the cost of grinding equipment. The lead time for a ground bar is about 2 weeks longer than a black bar, so plan accordingly. If you’re in a hurry, some suppliers offer expedited shipping for an extra 10% fee.
Environmental factors are worth noting. 1.2311 is fully recyclable, and the scrap value is about $0.30 per kg. The steel’s production has a carbon footprint of about 2.5 tons of CO2 per ton of steel, which is typical for tool steels. If you’re concerned about sustainability, look for suppliers that use electric arc furnaces with recycled scrap, which can reduce the footprint by 50%. The steel’s life cycle is long—a mold made from 1.2311 can last 500,000 cycles before needing repair, so the environmental impact per part is low. For a custom 1.2311 round bar, you can also specify a “green” grade with a lower carbon content, but that’s rare and usually only available from a few mills.
Safety is a consideration. When machining a custom 1.2311 round bar, the chips are sharp and can cause cuts, so use gloves and a chip guard. The steel’s dust from grinding can contain chromium and molybdenum, which are hazardous if inhaled, so use a dust collector and a respirator. For heat treatment, the fumes from quenching oil are