Editorial Technical Reference

Die-casting mould cavity insert in hot-work tool steel

Die-casting die inserts · hot-work steel and hardness by insert size, heat checking, nitriding without a white layer, EDM finish and cooling

A die-casting mould cavity insert is the block of hardened hot-work tool steel set into the die holder that carries the cavity shape of the casting, with cooling channels behind its surface; it is replaced when heat checking, soldering or wear end its life while the holder stays in service. Ask three things first: which hot-work steel and hardness suit the insert size and the alloy cast, how its surface will be finished and nitrided, and how its cooling channels are laid out.

Cavity inserts, cores and core pins of hot-work tool steel, or additively made maraging steel, for high-pressure and other permanent-mould die-casting dies for aluminium, magnesium and zinc. The die-casting machines themselves are covered on the High-pressure die casting machine page. Plastic injection mould inserts, sand cores, ejector pins sold alone, press-brake die inserts and complete dies are outside this page.

CNFX editorial research · Sources checked October 12, 2026 · 3 sources

Choose steel and hardness Finish and nitride the surface

Polished steel mould cavity insert with a contoured cavity on a granite inspection table beside a height gauge, square and micrometer, with two mould halves and a CNC machining centre behind — Machined cavity insert on an inspection table

Start with your task

Choose steel and hardnessBy insert size. Finish and nitride the surfaceHeat checking.

Choose the hot-work steel and hardness for the insert size

Uddeholm's Dievar datasheet names heat checking as a failure mechanism in die casting and states that higher hardness improves heat-checking resistance, so hardness can be raised by up to 2 HRC where gross cracking is not a factor. It lists dies for aluminium and magnesium die casting at 44–50 HRC, and reports its properties after hardening at 1025 °C, oil quenching and tempering twice at 615 °C for a working hardness of 44–46 HRC, with toughness of at least 25 J to the NADCA standard. [1]

Small inserts are run harder. Böhler states that its W360 ISOBLOC electroslag-remelted steel is adapted for tool hardnesses of 51–57 HRC and suited to smaller die-casting components such as mould inserts, cores, core pins and ejector pins. [2] Uddeholm notes that changes in the automotive industry have pushed demand for larger and more complex die inserts, which is where toughness matters. [1]

Editorial note: give the supplier the insert size, wall thickness to the cooling channels and the alloy cast, and ask for the steel grade, heat-treatment route, measured hardness and impact toughness on the insert you receive.

Give the insert maker the casting model and alloy, insert envelope and parting line, required steel grade or equivalent, hardness, cooling-channel layout, surface finish and texture, nitriding or coating, tolerances, expected shot count, and the die holder or machine it fits.

Finish and nitride the cavity surface without a brittle layer

Uddeholm states that nitriding and nitrocarburizing can improve resistance to wear, soldering and premature heat checking, but warns that the brittle white compound layer they can form may crack or spall under heavy mechanical or thermal loads. Gas nitriding at 510 °C or plasma nitriding at 480 °C gives about 1,100 HV0.2 at the surface, with case depths of 0.16 mm after 10 h and 0.22 mm after 30 h of gas nitriding, 0.15 mm after 10 h of plasma nitriding, and 0.13 mm or 0.08 mm after nitrocarburizing at 580 °C in gas (2 h) or salt (1 h). The process temperature should stay 25–50 °C below the highest previous tempering temperature. [1]

Electrical-discharge machining leaves a resolidified white layer and an untempered rehardened layer, both brittle; Uddeholm says the white layer must be removed completely by grinding or stoning and the insert tempered again at about 25 °C below the highest previous tempering temperature. [1]

A 2025 study in Materials compared H13 inserts with 300-grade maraging steel inserts made by laser powder bed fusion with conformal cooling channels, plasma nitrided at 450 °C and coated with 6–12 µm CrAlN, in a two-cavity die on a 560 kN machine cooled with water at 65 °C and 6 bar. It reports surface hardness of 1,100 HV0.05 nitrided and 2,780 HV0.05 after PVD for H13, against 1,230 and 2,850 HV0.05 for the maraging inserts, and service lives of 30,000 and 80,000 cycles. [3] Editorial calculation: 80,000 ÷ 30,000 ≈ 2.7, which the authors round to about 2.6× in their summary. [3]

Compare insert materials by published data

Material	Published hardness	Stated use or result
Uddeholm Dievar (hot-work steel)	44–50 HRC for Al/Mg die-casting dies; 44–46 HRC test condition [1]	Heat-checking resistance; larger die inserts [1]
Böhler W360 ISOBLOC	51–57 HRC [2]	Small inserts, cores, core pins [2]
H13 insert, nitrided + CrAlN	1,100 HV0.05 nitrided; 2,780 after PVD [3]	30,000 cycles in the study [3]
LPBF maraging 300, nitrided + CrAlN	545 HV0.05 core; 1,230 nitrided; 2,850 after PVD [3]	80,000 cycles with conformal cooling [3]

Insert body, cavity surface, nitrided case, cooling channels and seating faces

Element	Role	Fix in the order
Insert body	Carries the cavity; hot-work steel at set hardness. [1]	Grade, hardness, toughness.
Cavity surface	Forms the casting; EDM layer removed. [1]	Finish and inspection.
Nitrided case or coating	Resists wear, soldering, heat checking. [1] [3]	Process, case depth, no white layer.
Cooling channels	Control die temperature; conformal channels possible by LPBF. [3]	Layout, size, distance to surface.
Seating faces and fixing	Locate the insert in the holder.	Tolerances to the holder.

Steel grade, working hardness, machining stock and finish for a die-casting cavity insert

Envelope dimensions, draft and tolerance grade come from your casting drawing and die holder; the published values here cover steel grade, hardness and surface treatment.

Field	What it means and published values	Ask the supplier for
Insert Length (mm)	Insert envelope.	Drawing dimension.
Insert Width (mm)	Insert envelope.	Drawing dimension.
Insert Height (mm)	Insert envelope; Uddeholm recommends at least 0.3% machining stock on a stress-relieved Dievar tool for heat-treatment distortion. [1]	Stock and finish dimensions.
Draft Angle (degrees)	Set by the casting design.	Draft on each cavity face.
Hardness (HRC)	44–50 (Dievar, Al/Mg dies); 51–57 (W360, small inserts). [1] [2]	Measured hardness on the insert.
Operating Temperature (°C)	Coolant at 65 °C in the cited trial. [3]	Die temperature range in service.
Surface Roughness (μm Ra)	Set by casting finish; EDM layer to be removed. [1]	Ra and finishing method.
Tolerance Grade	Set by the die holder fit.	Tolerances and inspection report.
Material Grade	Dievar, W360, H13 or LPBF maraging 300 in the sources. [1] [2] [3]	Grade and certificate.
Weight (kg)	Depends on insert size.	Weight for handling.

Send the casting, insert and treatment data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Casting: [model; alloy; shot count expected]
Insert: [envelope; parting line; fit in holder]
Steel: [grade; hardness; toughness test]
Surface: [finish; EDM layer removal; nitriding or coating]
Cooling: [channel layout; coolant; conformal option]
Inspection: [dimensions; hardness; reports]

See manufacturer records Send an enquiry through CNFX

Buyer questions

What hardness should a die-casting insert have?

Uddeholm lists 44–50 HRC for aluminium and magnesium die-casting dies in Dievar; Böhler offers W360 at 51–57 HRC for smaller inserts, cores and core pins. [1] [2]

Why are die-casting inserts nitrided?

Uddeholm states nitriding can improve resistance to wear, soldering and premature heat checking, while the brittle white layer should be avoided. [1]

Do conformal cooling channels extend insert life?

In a 2025 study, LPBF maraging inserts with conformal cooling and duplex treatment reached 80,000 cycles against 30,000 for H13 inserts. [3]

Sources and what still needs a direct check

Sources checked 2026-10-12. Uddeholm and Böhler (both voestalpine High Performance Metals) publish datasheets for their own steels; the insert life comparison is a peer-reviewed open-access study in Materials (MDPI).

Uddeholm — Uddeholm Dievar technical datasheet (EN, PDF) ↗ Maker datasheet Return to text ↑
BÖHLER — W360 ISOBLOC datasheet (EN, PDF) ↗ Maker datasheet Return to text ↑
de Lima M.J. et al. — Aluminium Injection Mould Behaviour Using Additive Manufacturing and Surface Engineering, Materials 18(17):4216, 2025 (PMC12430277) ↗ Peer-reviewed paper Return to text ↑

Still to check yourself

Fix steel grade and hardness by insert size.
Remove the EDM white layer and re-temper.
Specify nitriding without a white layer.
Review the cooling-channel layout.
Verify the legal supplier and factory.