Steel P4
AISI/SAE P4 · UNS T51604
P4 (T51604) is a Cr-Al carburizing mold steel that develops a very hard, shallow case (about 0.5–1.5 mm) over a comparatively soft core, chosen where surface wear resistance governs.
Reference datasheet — P4 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the ANN condition
P4 tempers and conditions
P4 is supplied in 4 conditions, soft to hard. ANN is the default FabDigit quotes; the values on this page are for it.
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 | — |
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?
P4 (T51604) is a Cr-Al carburizing mold steel that develops a very hard, shallow case (about 0.5–1.5 mm) over a comparatively soft core, chosen where surface wear resistance governs. It is supplied annealed or normalized for cold hobbing and machining, with annealed values near 300 MPa yield, 500 MPa tensile, 25% elongation, 122 HB, 207 GPa modulus and service to 400 °C. Weldability is limited (score 45) and the steel is not stainless (corrosion score 20), so hardened cavities are ground or EDM'd and usually plated. P5 is the nearest carburizing alternative. P4 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). P4 has a yield strength of 300 MPa (43.5 ksi) and a tensile strength of 500 MPa (72.5 ksi) — weaker than 86% of steel grades. Elongation at break is 25% and the elastic modulus is 207 GPa (30 Msi).
What is P4 used for?
- carburized mold cavities
- wear-resistant mold surfaces
- die-casting tooling components
Advantages
- Polishes to a fine finish — 88/100, better than 100% of steel grades
- Ductile — tolerates forming and impact — 25%, better than 77% of steel grades
Limitations
- Low electrical conductivity — 2.9 % IACS, worse than 93% of steel grades
- Poor heat conductor — 26 W/m·K (15 BTU/hr·ft·°F), worse than 87% of steel grades
- Low strength — 300 MPa (43.5 ksi), worse than 86% of steel grades
P4 properties
Typical room-temperature values for P4-ANN; bars are the position among steel grades.
Physical3
P4 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 has a yield strength of 300 MPa (43.5 ksi) and a tensile strength of 500 MPa (72.5 ksi) — weaker than 86% of steel grades. Elongation at break is 25% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
P4 is rated for continuous service to 400°C (752 °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 conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (20/100), better than 87% of steel grades.
Sustainability4
Producing a kilogram of P4 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's machinability is good (60/100, better than 83% of steel grades); weldability fair (45/100); formability good (60/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. P4 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with P4
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.
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 |
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.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel P4 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- T51604
How much does P4 cost?
P4 is a premium-cost steel ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
P4 — frequently asked
What is P4 used for?
P4 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?
P4 has a typical yield strength of 300 MPa (43.5 ksi) and a tensile strength of 500 MPa (72.5 ksi) — weaker than 86% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is P4 easy to machine?
Reasonably — machinability is rated good (60/100, better than 83% 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 be welded?
With care — weldability is rated fair (45/100). 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?
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 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?
P4 is rated for continuous use to about 400°C (752 °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.
How much does P4 cost?
P4 is a premium-cost steel ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.