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Views: 0 Author: Site Editor Publish Time: 2026-10-22 Origin: Site
An aluminium die casting die takes a thermal shock on every shot. Where liquid metal touches the cavity, the surface climbs toward 500-600 °C in a fraction of a second, then falls back to 250-300 °C when the die opens and the release spray lands. A die running 60 shots an hour passes through that reversal hundreds of thousands of times in a normal campaign. The first sign of trouble is usually a web of fine cracks on the cavity surface, and by the time anyone sees them, the steel grade and the tempering temperature have been fixed for months.
Three hot work tool steels cover most of this work: 1.2344, 1.2343 and 1.2367. On a mill certificate they look close enough to be interchangeable. In a die they are not. The differences below decide whether an insert reaches 80,000 shots or 250,000, and whether the first rework job comes from a hairline crack or from a gate that has washed open.
Thermal fatigue causes most failures in aluminium casting. The cavity surface goes into compression as it heats and into tension as it cools, and it yields in compression a little on every shot. After enough cycles the accumulated strain tears cracks at the surface, usually at 45 degrees to the stress direction and often along the boundaries of the tempered structure. Hardness pushed too high for the section and a single tempering cycle that leaves retained austenite behind both shorten the time to first cracking.
Erosion of the gate is a separate problem. Molten aluminium crosses the gate at 40-70 m/s, and it washes the steel away shot by shot. Gate design and shot speed usually drive this, and a higher working hardness buys time.
Soldering turns up where a core or a thin section runs hot and the protective oxide on the steel has broken down. Aluminium bonds to the surface, tears a little steel away on ejection, and leaves a rough patch that grows. Cores with weak cooling suffer most.
Gross cracking is the failure everyone remembers. It traces back to an insert hardened above 48-50 HRC, a sharp internal corner, or a die started cold with a heavy spray.
1.2344 is the grade most often quoted for aluminium die casting inserts, and the H13 composition behind it is well known. Roughly 5 percent chromium, 1.3 percent molybdenum and 1 percent vanadium. The vanadium drives secondary hardening, which is why the steel keeps useful hardness at 550-600 °C where a plain quenched and tempered alloy steel has already drawn back. On a well-cooled cavity, 1.2344 at 46-48 HRC gives a long and predictable life, and it is the cheapest of the three in small quantities.
The weakness sits in thick sections and in dies with sharp geometry. Above 48 HRC the steel has little tolerance for stress concentration, and the notch at an internal corner becomes the crack initiation site.
1.2343 is the H11 composition. Vanadium drops from about 1 percent to 0.25-0.50 percent and carbon comes down slightly. The steel gives up some wear resistance and temper resistance in exchange for toughness and a little more thermal conductivity.
On a block over roughly 400 mm across, or on a die where the spray pattern leaves one area permanently hot, that trade usually pays. Running 1.2343 at 44-46 HRC on a large insert commonly outlasts 1.2344 at 48 HRC in the same position, because thermal cracking is the dominant failure there.
1.2367 raises molybdenum to about 3 percent and holds vanadium near 0.5 percent. The extra molybdenum lifts the temperature at which the steel softens. Cores, slides and thin walls that run hot benefit most, and the same applies to dies casting at higher melt temperatures.
The grade costs more per kg and is harder to find in small sections, so it rarely makes sense for a standard aluminium insert with good water lines. Where a die runs hot and the life target is set in hundreds of thousands of shots, the premium is repaid.
The ranges below follow EN ISO 4957 for the three hot work grades. Nickel is not specified for them in that standard.
Grade | C | Si | Mn | Cr | Mo | V |
1.2344 (X40CrMoV5-1) | 0.37-0.42 | 0.80-1.20 | 0.25-0.50 | 4.75-5.50 | 1.10-1.75 | 0.80-1.20 |
1.2343 (X37CrMoV5-1) | 0.33-0.41 | 0.80-1.20 | 0.25-0.50 | 4.80-5.50 | 1.10-1.60 | 0.25-0.50 |
1.2367 (X38CrMoV5-3) | 0.35-0.40 | 0.30-0.50 | 0.30-0.60 | 4.80-5.20 | 2.70-3.30 | 0.40-0.60 |
Vanadium and molybdenum define the performance gap across 1.2344, 1.2343 and 1.2367. Higher vanadium gives 1.2344 stronger temper resistance than low‑vanadium 1.2343, which prioritizes toughness instead. 1.2367 features a sharply elevated molybdenum level for outstanding resistance to thermal softening. It is worth noting that the allowable molybdenum span within a single grade is broad under EN ISO 4957. For example, a 1.2344 melt with 1.10% Mo and another with 1.75% Mo both satisfy the standard specification, yet the higher-molybdenum variant produces a more robust die.
Hot work tool steel arrives soft annealed, usually to 229 HB maximum for 1.2344 and 1.2343 and 241 HB maximum for 1.2367. The cavity is then machined and hardened, and the tempering temperature is what fixes the hardness the die runs at.
Tempering temperature, two cycles of 2h | 1.2344 | 1.2343 | 1.2367 |
540 °C | 52-54 HRC | 51-53 HRC | 54-56 HRC |
560 °C | 50-52 HRC | 49-51 HRC | 52-54 HRC |
580 °C | 48-50 HRC | 47-49 HRC | 50-53 HRC |
600 °C | 45-48 HRC | 45-47 HRC | 48-51 HRC |
620 °C | 43-46 HRC | 43-45 HRC | 46-49 HRC |
Austenitizing sits at 1020-1040 °C for 1.2344, 1000-1030 °C for 1.2343 and 1030-1060 °C for 1.2367, followed by vacuum or controlled atmosphere quenching. The figures above are typical bands. Austenitizing temperature, quench medium and section size all move them, so confirm against the steelmaker's chart for the actual heat.
Run two tempers of two hours each. After the first temper the retained austenite is still there. It transforms in service, the cavity grows a few hundredths of a millimetre, and the stress that comes with the transformation opens cracks. A die that shifts dimension after a few thousand shots and then cracks has usually been single tempered.
Working hardness is a choice with two sides. Higher hardness holds the gate longer and keeps a polish on the cavity. It also brings the first heat check network forward.
Application | First choice | Working hardness | Reason |
Small and medium aluminium inserts with good cooling | 1.2344 | 46-48 HRC | Balance of wear and thermal fatigue resistance |
Large inserts, over roughly 400 mm, uneven spray | 1.2343 | 44-46 HRC | Extra toughness and conductivity spread the strain |
Cores, slides and thin walls running hot | 1.2367 | 46-50 HRC | Holds hardness near 600 °C where 1.2344 draws back |
Zinc die casting | 1.2344 or 1.2343 | 44-46 HRC | Lower melt temperature, wear is the limit |
Brass and other high temperature work | 1.2367 | 47-50 HRC | 1.2344 softens too quickly at these temperatures |
The costliest error in grade selection is specifying a large structural insert in 1.2344 hardened to 50 HRC simply for higher hardness. This mold will crack at sharp corners after only a few thousand shots, rendering the entire insert scrap.
Choosing between 1.2344, 1.2343, and 1.2367 starts with identifying the main operating challenge.
If your production involves conventional aluminum die casting and requires a well-established hot work tool steel, 1.2344 is often a sensible first option.
It offers a balance of hot strength, toughness, wear resistance, and thermal fatigue performance. It is widely used in industrial tooling, and its established processing practices can make it easier to specify and source.
Consider 1.2344 when:
The mold operates under typical industrial die casting conditions.
A balance of service life and material cost is important.
Standard hot work tool steel processing routes are preferred.
The application does not require a specialized high-molybdenum grade.
If the mold component is vulnerable to cracking under impact or mechanical loading, 1.2343 deserves consideration.
Its suitability depends on the balance between toughness, hardness, thermal fatigue resistance, and wear requirements. For some applications, a high-quality remelted 1.2343 may be more appropriate than a standard-grade alternative.
Consider 1.2343 when:
Toughness is a major design requirement.
The tooling experiences substantial mechanical stress.
The application benefits from carefully controlled steel cleanliness and microstructure.
The mold designer has identified cracking as a key failure mode.
For molds exposed to severe thermal loading, elevated operating temperatures, or rapid tempering-related deterioration, 1.2367 may provide an advantage.
Its higher molybdenum content supports high-temperature strength and resistance to softening. Nevertheless, its benefits should be assessed against the specific failure mechanism, the additional material cost, and the heat treatment route.
Consider 1.2367 when:
Conventional hot work steel experiences premature softening.
High-temperature strength is a critical requirement.
Heat checking or hot wear remains a problem despite appropriate process controls.
A material upgrade can be justified by expected improvements in mold life and maintenance costs.
A 500 kg die block is a large piece of steel, and the segregation from the ingot is still in it. The centre of a conventional block carries more carbon, chromium and molybdenum than the surface, arranged in bands. Machine a polished cavity across those bands and they open as pinholes. Under thermal cycling they also give cracks an easy path along the banding.
Two measures reduce this. The first is forging ratio. An ingot reduced 5:1 has more of its cast dendritic structure broken down and more of its centre porosity closed than one reduced 3:1, and for a cavity that will be polished to SPI A1 or A2 the difference shows up directly.
The second is remelting. Electroslag remelted stock usually comes in under 0.005 percent sulfur and with oxygen in the low tens of ppm, against 0.010-0.020 percent sulfur for conventional air melted heats of the same grade. Smaller and fewer inclusions mean fewer polishing defects and fewer initiation sites on the cavity surface. Inclusion ratings to ASTM E45 or ISO 4967 and a grain size number to ASTM E112 are worth writing into the order when the cavity will be polished.
In our experience with large aluminium inserts, ESR forged stock runs 30 to 50 percent more shots before the first heat check network needs rework than conventional quality cut from the same design. The spread depends on cooling layout, spray practice and the hardness the die is run at, so test one insert before converting the whole set.
A1: The two describe the same steel family, and SKD61 and 4Cr5MoSiV1 sit in it as well. The ranges are not identical. ASTM A681 and EN ISO 4957 set slightly different carbon and vanadium windows, so a certificate written to one standard does not automatically satisfy a drawing that calls the other. Compare the actual figures before accepting a substitution.
A2: For most aluminium dies, 44-48 HRC covers the work, with cores and slides toward the top of that band and large blocks toward the bottom. A very hard insert resists wear and gate wash and cracks earlier. Ask what the die is expected to do before picking a number.
A3: Yes, if the shop has vacuum or a controlled atmosphere and can run two tempers. The failures we see come from a single temper, from loading a cold furnace straight to austenitizing temperature without a staged preheat, and from hardening an insert that was machined with no allowance for distortion.
A4: It depends on the cavity. A small insert in a well-cooled die does not usually justify it. A large block or a cavity that will be polished to a mirror finish does, because that is where banding and inclusions turn into visible defects and early cracks.
A5: Three causes cover most cases. Hardness above 48-49 HRC in a section with a sharp corner is a specification problem. A single temper that left retained austenite to transform in service is a heat treatment problem. A die run with a heavy spray while cold is a process problem on the machine.
At Qilu Steel, buyers can discuss their requirements for hot work tool steel, including 1.2344, 1.2343, and 1.2367, with reference to the required dimensions, supply condition, quality level, and intended application. Confirm the exact grade and inspection requirements before placing an order.
Contact Qilu Steel to discuss your die casting mold steel requirements and request a quotation.
