Steel H12-NIT
Finish state
AISI/SAE H12 · UNS T20812 · GB 4Cr5MoWVSi
NIT = hardened, tempered + gas/plasma nitrided case
Surface treatment for extrusion dies and die-casting inserts to resist soldering and abrasion; keep the case thin to avoid heat-check initiation.
Values for the NIT condition
Other H12 tempers and conditions
H12 is listed in 7 conditions; see the grade overview at H12.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ESR (electroslag remelted) premium quality, annealed | Specify for large die blocks and polished cavities needing low inclusion content, tighter isotropy and better transverse toughness. | 495 | 750 | 26 | 205 HB | 3.3 % IACS |
ANNDefault Annealed | Standard mill supply condition for bar and plate; machine the die cavity here, then harden and temper. | 500 | 760 | 24 | 210 HB | — |
Hot rolled | Low-cost oversize stock for roughing; must be annealed or hardened before use — hardness and structure are non-uniform. | 800 | 1,000 | 12 | 32 HRC | 28 W/m·K |
Hardened & tempered to 44–46 HRC | Choose for large forging dies and extrusion tooling where thermal-fatigue cracking, not wear, governs life. | 1,250 | 1,450 | 11 | 45 HRC | 27 W/m·K |
NITThis page Hardened, tempered + gas/plasma nitrided case | Surface treatment for extrusion dies and die-casting inserts to resist soldering and abrasion; keep the case thin to avoid heat-check initiation. | 1,300 | 1,560 | 9 | 48 HRC | 3.2 % IACS |
Hardened & tempered to 47–49 HRC | Balanced hardness/toughness setting used for most hot-forging, die-casting and extrusion tooling. | 1,400 | 1,600 | 9 | 48 HRC | 27 W/m·K |
Hardened & tempered to 51–54 HRC | Use for punches, dummy blocks and mandrels where abrasion at temperature dominates and shock loads are low. | 1,600 | 1,850 | 6 | 53 HRC | — |
What is H12-NIT?
H12-NIT is H12 supplied in the NIT condition — surface treatment for extrusion dies and die-casting inserts to resist soldering and abrasion; keep the case thin to avoid heat-check initiation. H12-NIT has a yield strength of 1,300 MPa (189 ksi) and a tensile strength of 1,560 MPa (226 ksi) — stronger than 95% of steel grades. Elongation at break is 9% and the elastic modulus is 210 GPa (30.5 Msi). H12-NIT has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,425°C (2,597 °F). ANN is the default condition FabDigit quotes; NIT is available on request or by drawing note.
Advantages
- High strength — 1,300 MPa (189 ksi), better than 95% of steel grades
- Good corrosion resistance — 30/100, better than 95% of steel grades
- High service temperature — 540°C (1,004 °F), better than 93% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Difficult to machine — 3/100, worse than 100% of steel grades
- Limited formability — 2/100, worse than 100% of steel grades
- Difficult to weld — 8/100, worse than 99% of steel grades
- Limited ductility — 9%, worse than 93% of steel grades
- Low electrical conductivity — 3.2 % IACS, worse than 87% of steel grades
H12-NIT properties
Typical room-temperature values for H12-NIT; 21 are specific to this condition. Other listed values are H12 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
H12-NIT has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical15
H12-NIT has a yield strength of 1,300 MPa (189 ksi) and a tensile strength of 1,560 MPa (226 ksi) — stronger than 95% of steel grades. Elongation at break is 9% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
H12-NIT is rated for continuous service to 540°C (1,004 °F). It conducts heat at 28 W/m·K (16.2 BTU/hr·ft·°F), worse than 85% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
H12-NIT conducts electricity at 3.2 % IACS, worse than 87% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (30/100), better than 95% of steel grades.
Sustainability4
Producing a kilogram of H12-NIT takes about 33 MJ of energy and emits 2.5 kg of CO₂ — more than 76% of steel grades. Typical recycled content is 40%.
Manufacturability8
H12-NIT's machinability is not recommended (3/100, worse than 100% of steel grades); weldability not recommended (8/100); formability not recommended (2/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with H12-NIT
Is H12 easy to machine?
Machine fully in the annealed condition (≈60 % of 1212) with rigid setups and coated carbide; above ~45 HRC use hard-milling or EDM plus stress relief.
Can H12 be welded?
Weldable for die repair only: preheat/interpass 350–400 °C, matching 5 % Cr filler, slow cool and immediately re-temper 15–20 °C below the last tempering temperature.
Can H12 be formed, bent or molded?
Hot work at 1050–1120 °C with slow cooling to 850 °C and immediate annealing at 845–900 °C; cold forming is not practical.
What surface finishes work on H12?
Takes a good mirror polish (best in ESR quality); protect with nitriding, PVD (CrN/AlTiN), phosphating or oil — do not anodize, and avoid decarburized skin before polishing.
H12 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CASTM A681 / GB/T 1299 4Cr5MoWVSi | 0.3 – 0.4 | 0.35 |
| Si | 0.8 – 1.2 | 1 |
| Mn | 0.2 – 0.5 | 0.35 |
| Cr | 4.75 – 5.5 | 5.1 |
| Mo | 1.25 – 1.75 | 1.5 |
| Wdistinguishes H12 from H13 | 1 – 1.7 | 1.4 |
| V | 0.2 – 0.5 | 0.4 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
H12-NIT — frequently asked
What is H12-NIT used for?
H12-NIT is typically used for extrusion dies, die-casting dies, hot forging dies and mandrels. In short: tungsten-bearing 5 % Cr grade; good hot hardness; reduced heat-check resistance.
What is the yield strength of H12-NIT?
H12-NIT has a typical yield strength of 1,300 MPa (189 ksi) and a tensile strength of 1,560 MPa (226 ksi) — stronger than 95% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is H12-NIT easy to machine?
Not especially — machinability is rated not recommended (3/100, worse than 100% of steel grades). Machine fully in the annealed condition (≈60 % of 1212) with rigid setups and coated carbide; above ~45 HRC use hard-milling or EDM plus stress relief.
Can H12-NIT be welded?
Not readily — weldability is rated not recommended (8/100). Weldable for die repair only: preheat/interpass 350–400 °C, matching 5 % Cr filler, slow cool and immediately re-temper 15–20 °C below the last tempering temperature.
What surface finishes work on H12-NIT?
Takes a good mirror polish (best in ESR quality); protect with nitriding, PVD (CrN/AlTiN), phosphating or oil — do not anodize, and avoid decarburized skin before polishing.
Can H12-NIT be formed, bent or molded?
Hot work at 1050–1120 °C with slow cooling to 850 °C and immediate annealing at 845–900 °C; cold forming is not practical.
What is the maximum service temperature of H12-NIT?
H12-NIT is rated for continuous use to about 540°C (1,004 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between H12-ANN and H12-QT52?
ANN is the default condition — standard mill supply condition for bar and plate; machine the die cavity here, then harden and temper. QT52: use for punches, dummy blocks and mandrels where abrasion at temperature dominates and shock loads are low. Yield strength is 500 MPa in ANN versus 1,600 MPa in QT52.
Sources
- ASTM A681 Standard Specification for Tool Steels Alloy — ASTM International (2022)
- GB/T 1299 (4Cr5MoWVSi) — SAC (2014)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels, and High-Performance Alloys (Tool Steels) — ASM International (1990)
- Tool Steels, 5th ed. — ASM International (1998)
- Hot-work tool steel datasheets (5 % Cr class, W-alloyed) — Böhler / voestalpine (2022)
- (H12/4Cr5MoWVSi ) (2025)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.