Steel P4 CARB-HT
Heat-treated state
AISI/SAE P4 · UNS T51604
CARB-HT = carburized, hardened & tempered
Working condition for finished cavities: carburize 900–930 °C, air/oil quench, temper 150–200 °C for a hard wear-resistant skin with a tough core.
Values for the CARB-HT condition
Other P4 tempers and conditions
P4 is listed in 4 conditions; see the grade overview at P4.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNDefault Annealed | Standard as-supplied bar/block condition: soft enough for cold hobbing and rough machining of the cavity before carburizing. | 300 | 500 | 25 | 122 HB | — |
Normalized | Grain-refining pre-treatment used between forging and annealing; not a delivery condition for finished molds. | 480 | 750 | 18 | 21 HRC | 2.8 % IACS |
Hardened & tempered | Use when a tough, dimensionally stable air-hardened body is needed without a wear case (bolsters, inserts with plated surfaces). | 1,050 | 1,300 | 12 | 41 HRC | — |
CARB-HTThis page Carburized, hardened & tempered | Working condition for finished cavities: carburize 900–930 °C, air/oil quench, temper 150–200 °C for a hard wear-resistant skin with a tough core. | 1,150 | 1,400 | 8 | 61 HRC | — |
What is P4 CARB-HT?
P4 CARB-HT is P4 heat treated to CARB-HT — working condition for finished cavities: carburize 900–930 °C, air/oil quench, temper 150–200 °C for a hard wear-resistant skin with a tough core. P4 CARB-HT has a yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,400 MPa (203 ksi) — stronger than 94% of steel grades. Elongation at break is 8% and the elastic modulus is 203 GPa (29.4 Msi). P4 CARB-HT has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,420°C (2,588 °F). ANN is the default condition FabDigit quotes; CARB-HT is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 92/100, better than 100% of steel grades
- High strength — 1,150 MPa (167 ksi), better than 94% of steel grades
- Good corrosion resistance — 22/100, better than 90% of steel grades
Limitations
- Difficult to machine — 12/100, worse than 99% of steel grades
- Limited formability — 3/100, worse than 99% of steel grades
- Limited ductility — 8%, worse than 95% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Low electrical conductivity — 2.9 % IACS, worse than 93% of steel grades
P4 CARB-HT properties
Typical room-temperature values for P4 CARB-HT; 20 are specific to this condition. Other listed values are P4 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
P4 CARB-HT has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical15
P4 CARB-HT has a yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,400 MPa (203 ksi) — stronger than 94% of steel grades. Elongation at break is 8% and the elastic modulus is 203 GPa (29.4 Msi).
Thermal6
P4 CARB-HT is rated for continuous service to 200°C (392 °F). It conducts heat at 26 W/m·K (15 BTU/hr·ft·°F), worse than 87% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
P4 CARB-HT conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (22/100), better than 90% of steel grades.
Sustainability4
Producing a kilogram of P4 CARB-HT takes about 32 MJ of energy and emits 2.4 kg of CO₂ — more than 70% of steel grades. Typical recycled content is 30%.
Manufacturability7
P4 CARB-HT's machinability is not recommended (12/100, worse than 99% of steel grades); weldability poor (15/100); formability not recommended (3/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with P4 CARB-HT
Is P4 easy to machine?
Machine and EDM in the annealed state (soft, slightly gummy — use sharp positive-rake carbide, moderate speeds); after carburizing/hardening only grinding, EDM or CBN finishing is practical, and leave grind stock for the ~0.5–1.5 mm case.
Can P4 be welded?
Weld only in the annealed or pre-hardened state with matching low-alloy/Cr-Mo filler, preheat 300–400 °C, and re-anneal or re-temper immediately; welding through a carburized case will cause cracking and soft spots.
Can P4 be formed, bent or molded?
Annealed P4 is soft enough for cold hobbing of cavities (its classic advantage); stress-relieve after hobbing or heavy machining at ~650 °C before carburizing to limit heat-treat distortion.
What surface finishes work on P4?
Takes a very high mirror polish and photo-etched textures after hardening; not stainless, so protect with rust preventive, or hard chrome / electroless-nickel plate cavities running PVC or moisture-rich resins.
P4 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 |
|---|---|---|
| Clow carbon for hobbability and carburizing response | ≤ 0.12 | 0.07 |
| Mn | 0.2 – 0.6 | 0.4 |
| Si | 0.1 – 0.4 | 0.25 |
| Crgives air-hardening and case hardness | 4 – 5.25 | 4.75 |
| Mo | 0.4 – 1 | 0.75 |
| Niresidual; some producer grades add Ni for core toughness | ≤ 0.5 | — |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
P4 CARB-HT — frequently asked
What is P4 CARB-HT used for?
P4 CARB-HT is typically used for carburized mold cavities, wear-resistant mold surfaces and die-casting tooling components. In short: cr-Al carburizing grade; very hard shallow case; classic cold-hobbing steel.
What is the yield strength of P4 CARB-HT?
P4 CARB-HT has a typical yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,400 MPa (203 ksi) — stronger than 94% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is P4 CARB-HT easy to machine?
Not especially — machinability is rated not recommended (12/100, worse than 99% of steel grades). Machine and EDM in the annealed state (soft, slightly gummy — use sharp positive-rake carbide, moderate speeds); after carburizing/hardening only grinding, EDM or CBN finishing is practical, and leave grind stock for the ~0.5–1.5 mm case.
Can P4 CARB-HT be welded?
Not readily — weldability is rated poor (15/100). Weld only in the annealed or pre-hardened state with matching low-alloy/Cr-Mo filler, preheat 300–400 °C, and re-anneal or re-temper immediately; welding through a carburized case will cause cracking and soft spots.
What surface finishes work on P4 CARB-HT?
Takes a very high mirror polish and photo-etched textures after hardening; not stainless, so protect with rust preventive, or hard chrome / electroless-nickel plate cavities running PVC or moisture-rich resins.
Can P4 CARB-HT be formed, bent or molded?
Annealed P4 is soft enough for cold hobbing of cavities (its classic advantage); stress-relieve after hobbing or heavy machining at ~650 °C before carburizing to limit heat-treat distortion.
What is the maximum service temperature of P4 CARB-HT?
P4 CARB-HT is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between P4-ANN and P4 CARB-HT?
ANN is the default condition — standard as-supplied bar/block condition: soft enough for cold hobbing and rough machining of the cavity before carburizing. CARB-HT: working condition for finished cavities: carburize 900–930 °C, air/oil quench, temper 150–200 °C for a hard wear-resistant skin with a tough core. Yield strength is 300 MPa in ANN versus 1,150 MPa in CARB-HT.
Sources
- ASTM A681 — Standard Specification for Tool Steels, Alloy (P-type mold steels) — ASTM International (2015)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (Mold Steels) — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating (Carburizing and Heat Treating of Mold Steels) — ASM International (1991)
- ASM Handbook Vol.16 — Machining (machinability ratings of tool steels) — ASM International (1989)
- UNS T51604 / AISI P4 alloy record — SAE/ASTM Unified Numbering System (2017)
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.