T: +86-0731-85185770
E: enquiry@qilumetal.com
E: enquiry@qilumetal.com
No. 18 Xiangfu Middle Road,Yuhua District, Changsha City
 |
| Quantity: | |
|---|---|
1.2738
Qilu
DIN 1.2738 steel is a Cr-Ni-Mo alloyed plastic mould steel supplied in the pre-hardened and tempered condition. It is the nickel-modified evolution of 1.2311 (P20), engineered specifically for large-section moulds where through-hardness uniformity is critical. The 1% nickel addition improves hardenability, ensuring consistent mechanical properties from surface to core even in blocks exceeding 400 mm thickness.
Unlike through-hardening grades that require post-machining quenching, 1.2738 arrives ready to machine at 280–325 HB (approximately 30–34 HRC), eliminating distortion risk and shortening mould build cycles. It is not a tool steel for cutting applications—it is a mould base and cavity material optimized for polishability, texturing response, and dimensional stability under injection pressure.
Country | China | Germany | USA |
Standard | GB/T 1299 | DIN 17350 | ASTM A681 |
Grade | 3Cr2MnNiMo | 40CrMnNiMo8-6-4/1.2738 | P20+Ni/718 |
Grade | C | Si | Mn | Cr | Mo | P | S | Ni |
| 40CrMnNiMo8-6-4/1.2738 | 0.35-0.45 | 0.20-0.40 | 1.30-1.60 | 1.80-2.10 | 0.15-0.25 | 0.030Max | 0.030Max | 0.90-1.20 |
| 3Cr2MnNiMo | 0.32-0.40 | 0.20-0.40 | 1.10-1.50 | 1.70-2.00 | 0.25-0.40 | 0.030Max | 0.030Max | 0.85-1.15 |
Pre-hardened and tempered, tested 12.5 mm below the surface in line with EN ISO 4957 sampling.
| Size range | Hardness | Tensile strength | Yield strength | Alongation | Impact value At RT/J |
| d≤100 | 30-34 HRC | 1050-1150 MPa | 900 MPa min | 12% min | 25 J min |
| 100＜d≤300 | 28-32 HRC | 980-1080 MPa | 800 MPa min | 13% min | 25 J min |
| 300＜d≤500 | 27-31 HRC | 900-1000 MPa | 700 MPa min | 14% min | 20 J min |
| 500＜d≤800 | 26-30 HRC | 850-950 MPa | 650 MPa min | 14% min | 20 J min |
Strength falls as section size grows, and the drop is not noise. On a 600 mm block the 12.5 mm sub-surface reading can sit 2 to 4 HRC above the centre. A single hardness figure quoted for every thickness applies to the surface only.
| Condition | Hardness |
| Pre-hardened, as delivered | 28-32 HRC, 290-325 HB |
| Soft annealed | 235 HB max |
| Oil quenched 860 °C, tempered 550 °C | 38-42 HRC |
| Oil quenched 860 °C, tempered 600 °C | 32-36 HRC |
| Oil quenched 860 °C, tempered 650 °C | 28-31 HRC |
| Nitrided 510 °C for 20 h | 650-750 HV0.5 at surface |
Hardenability in oil reaches roughly 400 mm of round section. Beyond that the core will not follow the surface, which is why 1.2738 is normally bought pre-hardened. Re-hardening a 600 mm block in-house usually makes the core worse.
Billets are heated to 1150-1200 °C and finish forged above 850 °C. Plastic mold blocks are upset and drawn to a forging ratio of at least 3:1, and 4:1 where the cavity will be polished or textured. The post-forge step is where suppliers lose blocks: 1.2738 is air hardening, so a 20 tonne block left to cool in still air will develop cracks before it reaches the annealing furnace. It goes straight from the press to a furnace at 600 °C, holds, then cools at 20 °C per hour. Thick sections are vacuum degassed, and hydrogen is held to 2 ppm or below, because flakes in a mold block only show up after the cavity is finished.
Ultrasonic testing follows EN 10228-3, class 3 for general blocks and class 4 for mirror-polished surfaces. Test after pre-hardening, not before: a block that passes as forged can fail once the hardness rise exposes internal stress.
| Process | Temperature | Cooling |
| Soft annealing | 710-740 °C, 2 h per 25 mm of section | furnace, 20 °C/h to 500 °C, then air |
| Stress relieving | 550-600 °C, 2 h, after rough machining | furnace |
| Austenitizing | 840-870 °C, 1 h per 25 mm | oil, air for sections under 50 mm |
| Tempering | 550-650 °C, 2 h per 25 mm | air |
Temper twice for sections above 200 mm, cooling to room temperature between cycles. A single temper leaves retained austenite in the core that moves later, usually after the cavity is cut.
Product type | Size range | Length |
Hot rolled bar | Φ10-Φ190mm | 2000-5800mm |
Hot forged bar | Φ200-Φ600mm | 2000-5800mm |
Hot rolled plate/sheet | T:10-60mm; W:310-810mm | 2000-5800mm |
Hot forged plate | T:70-250mm; W:310-810mm | 2000-5800mm |
Hot Forged block | T: 260-500mm; W: 300-1000mm | 2000-5800mm |
Surface Finish | Turned | Milled | Grinding(Best) | Polished(Best) | Peeled(Best) | Black Forged | Black Rolled |
Tolerance | +0/+3mm | +0/+3mm | +0/+0.05mm | +0/+0.05mm | +0/+0.1mm | +0/+5mm | +0/+1mm |
Straighness | 1mm/1000mm max. | 3mm/1000mm max. | |||||
Automotive interior and exterior molds: bumpers, instrument panels, door panels, grilles and lamp housings. Large, deep cavities where through-hardness decides whether the mold holds shape after 200,000 shots.
Home appliance molds: washing machine drums, refrigerator liners, air conditioner shells, television back covers. High polish requirements, often textured, which punishes any hardness variation.
Large packaging molds: pallets, crates, totes and containers. Thick walls, long flow paths, and a mold that has to survive abuse.
SMC and BMC compression molds: automotive structural panels and electrical housings, where the steel must hold hardness at 150-180 °C.
Rubber and tyre molds: tread and sidewall sectors, where the block is thick and the cavity is cut deep.
Mold bases, die holders and bolster plates: where 1.2738 in forged bar replaces assembled plates and removes a stack of bolted joints.
| Aspect | AISI P20 | 1.2738 / P20+Ni |
| Nickel (Ni) | ≤ 0.30 %, effectively none | 0.90 – 1.20 % |
| Through-hardening depth | Best in thinner sections | Uniform in heavy blocks (> 300 mm) |
| Sulfur / cleanliness | Standard melt, higher S typical | Vacuum degassed, S ≤ 0.005 % |
| Polishability | Good, production-grade | Excellent, mirror/optical grade |
| Typical delivery hardness | ~280–320 HBW | 280–325 HBW |
| Best for | Small-to-medium commodity molds | Large, high-finish, textured molds |
A1: 718H is a trade name, not a standard grade. It refers to a 1.2738-type steel supplied pre-hardened, commonly at 290-330 HB. The chemistry is essentially the same, but the hardness range and the inspection certificate are brand-specific. Specify 1.2738 to EN ISO 4957 with a hardness range for a defensible purchase order.
A2: No, and the difference is nickel. 1.2311 (P20) has no deliberate nickel addition and hardens through only to about 300 mm, which is fine for small and medium molds. 1.2738 adds 0.90 to 1.20 percent nickel and reaches roughly 400 mm. Using P20 for a 500 mm block gives a soft core and a mold that moves under injection pressure.
A3: Yes, and it is common on plastic mold slide faces and gate areas. Nitride at 500-540 °C for 15 to 25 hours to reach 650-750 HV0.5 at the surface. Temper the block above the nitriding temperature first, otherwise the base hardness drops during the cycle and the case has nothing to support it.
A4: No. Expect the core 2 to 4 HRC below the 12.5 mm sub-surface reading. If the cavity sits near the centre of a thick block, ask for a core hardness test and design to that number.
A5: Only with preheat at 300-350 °C, a matched low-hydrogen filler and immediate tempering at 550-600 °C. At CEV 1.14 an uncontrolled repair will crack; for cosmetic surfaces use a welded insert.
A6: Choose 1.2738 for strength and through-hardness on large molds running standard resins. Choose 1.2316 when the resin is corrosive, such as PVC, or when the mold sits idle in humid conditions, because 1.2316 carries about 16 percent chromium.
Contact us for quotation, stock, sample cut or a custom block size. Send the drawing and hardness range, and we will confirm the forging route and UT class before quoting.
