What is the tensile strength of industrial 1.2312 steel plate?

The tensile strength of an industrial 1.2312 steel plate typically falls within the range of 800 to 1,000 MPa (megapascals) in the hardened and tempered condition, but this is not a fixed number. It depends heavily on the specific heat treatment applied, the plate thickness, and the exact chemical composition of the batch. For a direct answer: if you are looking at a standard 1.2312 plate in the quenched and tempered state (commonly to a hardness of 30-34 HRC), you can expect a tensile strength around 850-950 MPa. However, if the plate is supplied in the annealed condition (soft), the tensile strength drops significantly to about 650-750 MPa. This variability is why you need to check the mill certificate or test report for your specific industrial 1.2312 steel plate.

Let's break down the material itself. 1.2312 is a German standard designation (DIN 1.2312) for a pre-hardened plastic mold steel. It is essentially a variant of 1.2311 (40CrMnMoS8-6) but with added sulfur to improve machinability. The chemical composition is tightly controlled. Typical ranges are: Carbon (C) 0.35-0.45%, Silicon (Si) 0.20-0.40%, Manganese (Mn) 1.30-1.60%, Phosphorus (P) max 0.030%, Sulfur (S) 0.05-0.10%, Chromium (Cr) 1.80-2.10%, Molybdenum (Mo) 0.15-0.25%. The sulfur content is the key differentiator. It forms manganese sulfide inclusions, which act as chip breakers during machining. This makes the steel much easier to cut, drill, and mill compared to a non-sulfurized grade like 1.2311. But the trade-off is a slight reduction in transverse toughness and polishability. The tensile strength is directly influenced by the martensitic structure after hardening. When you quench from the austenitizing temperature (around 850-880°C) and then temper, the steel transforms into tempered martensite. The higher the tempering temperature, the lower the tensile strength but the higher the toughness.

For a deeper dive into the data, here is a typical tensile strength range for 1.2312 based on common heat treatment conditions. This is not from a single source but compiled from multiple European steel supplier datasheets (e.g., ThyssenKrupp, Bohler, Saarstahl) and standard references (DIN EN ISO 4957).

Table 1: Typical Tensile Strength of 1.2312 Steel Plate vs. Heat Treatment Condition

Notice the inverse relationship between tensile strength and elongation. As you push the tensile strength higher, the material becomes less ductile. This is critical for mold making. You don't just want brute strength; you need a balance to avoid cracking under stress concentration. The yield strength is also a crucial parameter. It tells you the stress level at which the steel will start to permanently deform. For a 1.2312 plate at 30-34 HRC, the yield strength is typically 75-80% of the tensile strength. So, if tensile is 900 MPa, yield is around 675-720 MPa. This is more than enough for most plastic injection mold applications, where the clamping forces are high but the stress is distributed across the plate area.

Now, let's talk about the factors that can cause real-world variation. Plate thickness matters. A 200 mm thick plate will not have the same tensile strength as a 20 mm thick plate after the same heat treatment. The reason is mass effect. Thicker sections cool slower during quenching. This results in a less complete martensitic transformation in the center of the plate. The core of a thick plate might have a mixed microstructure of bainite and martensite, which lowers the overall tensile strength. For a 200 mm thick plate, you might only achieve 800-850 MPa in the center, even if the surface is at 950 MPa. Steel suppliers often specify a "through-hardening" depth. For 1.2312, you can typically achieve a uniform hardness (and thus tensile strength) up to about 100-150 mm thickness. Beyond that, you need to adjust your expectations. The chemical composition also plays a role. A batch with carbon on the lower end (0.35%) will have a slightly lower tensile strength than one with carbon on the high end (0.45%). The same goes for chromium and molybdenum. These elements increase hardenability and strength. Molybdenum, in particular, also helps prevent temper embrittlement, which is a phenomenon where the steel becomes brittle if tempered in a certain temperature range (around 250-400°C).

Let's look at a specific example from a real-world supplier. One major European steelmaker lists the following for 1.2312 in the quenched and tempered condition to 30-34 HRC for a plate thickness of 100-200 mm: Tensile strength Rm = 880-980 MPa, Yield strength Rp0.2 = 680-780 MPa, Elongation A5 = 12-16%. Notice the range. This is typical. They don't give a single number because they can't guarantee it for every single plate. They guarantee a minimum. For a 20 mm thick plate, the same supplier might list Rm = 920-1,020 MPa. So, the thickness effect is real. If you are designing a critical mold component, you should always use the minimum guaranteed value from the supplier, not the average. The standard for these steels is often DIN EN ISO 4957, which specifies the chemical composition and hardness ranges but not a specific tensile strength. The tensile strength is derived from the hardness. There is a general correlation: for steel, tensile strength (MPa) is approximately 3.2 x Brinell hardness (HB). For 1.2312 at 30 HRC (which is about 290 HB), the calculated tensile strength would be 3.2 x 290 = 928 MPa. This matches the datasheet values. At 34 HRC (about 320 HB), it would be 3.2 x 320 = 1,024 MPa. This is a useful rule of thumb, but it is not perfectly accurate for all conditions. It is based on the assumption of a fully martensitic structure. If the structure contains bainite or ferrite, the correlation weakens.

Another angle to consider is the anisotropy of the tensile strength. Because 1.2312 has added sulfur, it forms elongated manganese sulfide inclusions during rolling. These inclusions act like weak points in the transverse direction (perpendicular to the rolling direction). The tensile strength in the longitudinal direction (parallel to rolling) is typically 5-10% higher than in the transverse direction. For a 1.2312 plate, the longitudinal tensile strength might be 920 MPa, while the transverse could be 860 MPa. This is a critical detail for mold designers. If you are applying a high stress in a direction that is perpendicular to the rolling direction, you need to account for this lower strength. The sulfur content also affects the impact toughness. The Charpy V-notch impact energy for 1.2312 at room temperature is typically around 15-25 Joules in the longitudinal direction, but only 8-15 Joules in the transverse direction. This is significantly lower than a non-sulfurized grade like 1.2311, which can have impact values of 30-40 Joules. So, the trade-off for better machinability is a reduction in toughness and a more pronounced anisotropy in mechanical properties.

Let's get into the nitty-gritty of the heat treatment process. To achieve a tensile strength of 900 MPa, you would typically austenitize at 850-880°C for 30-60 minutes per 25 mm of thickness. Then you quench in oil or a polymer solution. The cooling rate must be fast enough to avoid pearlite or bainite formation. Then you temper immediately. For a target of 30-34 HRC (which corresponds to 850-950 MPa tensile), the tempering temperature is usually around 550-600°C. The tempering time is typically 2 hours per 25 mm of thickness. A double temper is often recommended to stabilize the structure and relieve residual stresses. The first temper might be at 550°C, and the second at 570°C. This process reduces the tensile strength from the as-quenched value (which could be over 1,500 MPa) down to the desired range. If you temper at a lower temperature, say 400°C, you will get a higher tensile strength (1,000-1,100 MPa) but lower toughness. If you temper at a higher temperature, say 650°C, you will get a lower tensile strength (700-800 MPa) but higher toughness. This is a classic strength-toughness trade-off.

For practical applications, here is a table of typical tensile strength values for 1.2312 plate in different hardness ranges, based on standard tempering curves from multiple sources.

Table 2: Tempering Temperature vs. Tensile Strength for 1.2312 (Quenched from 860°C, Oil Quenched)

One more thing: the tensile strength of 1.2312 is also affected by the testing temperature. At elevated temperatures, the strength drops. For example, at 200°C, the tensile strength might be 10-15% lower than at room temperature. At 400°C, it could be 30-40% lower. This is important if the mold is used for hot runner systems or if the plastic melt temperature is high. The steel is not designed for high-temperature service. It is a pre-hardened plastic mold steel, not a hot-work tool steel like H13. So, if your application involves prolonged exposure to temperatures above 300°C, you should consider a different grade. The modulus of elasticity (Young's modulus) for 1.2312 is about 210 GPa, which is standard for all steels. This does not change significantly with heat treatment. The hardness and tensile strength are the primary variables.

Finally, a word on standards and testing. The tensile test is usually done according to ASTM E8 or ISO 6892. The test piece is typically a round bar with a gauge diameter of 10 mm or a flat strip. The strain rate is controlled. The results are reported as the maximum stress before fracture (tensile strength) and the stress at 0.2% plastic strain (yield strength). For a 1.2312 plate, the supplier will provide a mill test certificate with the actual values for that specific heat. You should always request this if you are doing critical design work. The certificate will also list the chemical composition and hardness. The hardness is often checked on the surface of the plate using a Rockwell C tester. The tensile strength can be estimated from the hardness, but the direct tensile test is more accurate. For a 1.2312 plate, the typical hardness range in the pre-hardened condition is 30-34 HRC. This is the standard delivery condition. If you need a different hardness, you can order it, but it will be a special order. The tensile strength of 1.2312 is a reliable and well-documented property, but it is not a single number. It is a range that depends on the specific processing and geometry of the plate. Use the data from the supplier, not from a generic table, for your final design calculations.