Steel P1-HOB (Cold hobbed)
Supply condition
AISI/SAE P1 · UNS T51601
Expect this work-hardened state (190 HB, 10% elongation) after cold-pressing the cavity; follow with recrystallization annealing or feed the part directly into carburizing.
Values for the HOB condition
Other P1 tempers and conditions
P1 is listed in 6 conditions; see the grade overview at P1.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNDefault Annealed | Order this ≤130 HB soft state for cold hobbing cavities or for rough and finish machining, then carburize and quench; at 240 MPa yield it is not a service condition. | 240 | 380 | 35 | 120 HB | — |
Normalized | Normalize at 900–925 °C with air cooling after forging or heavy deformation to remove coarse, uneven structure before carburizing; treat it as a preparation step only. | 280 | 420 | 32 | 135 HB | 11 % IACS |
Carburized, quenched & tempered 230–260 °C | Pick the 230–260 °C temper (case 55–58 HRC) for cavities with sharp corners or impact loading, trading a little hardness for higher case toughness and lower residual stress. | 430 | 620 | 20 | 56 HRC | 10 % IACS |
Carburized, quenched & tempered 150–200 °C | Choose carburizing plus a 150–200 °C temper (case 58–62 HRC) as the usual final production state, pairing a wear-resistant case with a tough core for medium-volume cavities. | 460 | 650 | 18 | 60 HRC | — |
Carburized & quenched | Carburize at 900–925 °C and oil quench after cavity machining for a 0.5–1.5 mm case at 60–64 HRC; low-temperature tempering must follow immediately to avoid cracking. | 500 | 700 | 15 | 62 HRC | 9 % IACS |
HOBThis page Cold hobbed | Expect this work-hardened state (190 HB, 10% elongation) after cold-pressing the cavity; follow with recrystallization annealing or feed the part directly into carburizing. | 520 | 620 | 10 | 190 HB | 11 % IACS |
What is P1-HOB?
P1-HOB is P1 supplied in the HOB condition — expect this work-hardened state (190 HB, 10% elongation) after cold-pressing the cavity; follow with recrystallization annealing or feed the part directly into carburizing. P1-HOB has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 620 MPa (89.9 ksi) — stronger than 67% of steel grades. Elongation at break is 10% and the elastic modulus is 205 GPa (29.7 Msi). P1-HOB has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). ANN is the default condition FabDigit quotes; HOB is available on request or by drawing note.
Advantages
- High electrical conductivity — 11 % IACS, better than 98% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- Conducts heat well — 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades
- Readily welded — 80/100, better than 79% of steel grades
Limitations
- Limited ductility — 10%, worse than 91% of steel grades
- Limited service temperature — 300°C (572 °F), worse than 78% of steel grades
P1-HOB properties
Typical room-temperature values for P1-HOB; 22 are specific to this condition. Other listed values are P1 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
P1-HOB has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
P1-HOB has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 620 MPa (89.9 ksi) — stronger than 67% of steel grades. Elongation at break is 10% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
P1-HOB is rated for continuous service to 300°C (572 °F). It conducts heat at 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
P1-HOB conducts electricity at 11 % IACS, better than 98% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of P1-HOB takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability8
P1-HOB's machinability is good (55/100, better than 62% of steel grades); weldability very good (80/100); formability fair (40/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with P1-HOB
Is P1 easy to machine?
In the annealed condition the steel is very soft and prone to built-up edge, so use sharp tools with large positive rake, high surface speed and plenty of coolant. Once carburized and quenched, the part can only be ground or EDM'd.
Can P1 be welded?
Carbon content is very low, so weldability is good; repair with low-hydrogen electrodes or TIG. On carburized areas, grind away the case layer before welding and re-carburize the part afterwards.
Can P1 be formed, bent or molded?
Cold hobbing is the core process for this grade: the soft cavity blank is pressed to shape by a hardened master hob in one or several strokes, with recrystallization annealing between passes.
What surface finishes work on P1?
After carburizing and quenching, finish grind and polish the cavity. Hard chrome or electroless nickel is common for rust protection and release; nitriding can be used to strengthen surfaces that were not carburized.
P1 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 P1: 0.10 % max | ≤ 0.1 | 0.08 |
| Mn | 0.1 – 0.4 | 0.25 |
| Si | 0.1 – 0.4 | 0.2 |
| Pimpurity limit | ≤ 0.03 | — |
| Simpurity limit | ≤ 0.03 | — |
| Febalance; no intentional Cr/Ni/Mo additions — hardness comes from carburizing | balance | — |
P1-HOB — frequently asked
What is P1-HOB used for?
P1-HOB is typically used for plastic injection mould cavities, die-casting inserts, cold-hobbed cavity blocks, carburized mould inserts and wear faces, compression and transfer moulding dies and rubber and shoe-sole moulds. In short: hobbable mould steel; case-hardening P-series grade; softest mould steel supplied.
What is the yield strength of P1-HOB?
P1-HOB has a typical yield strength of 520 MPa (75.4 ksi) and a tensile strength of 620 MPa (89.9 ksi) — stronger than 67% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is P1-HOB easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). In the annealed condition the steel is very soft and prone to built-up edge, so use sharp tools with large positive rake, high surface speed and plenty of coolant. Once carburized and quenched, the part can only be ground or EDM'd.
Can P1-HOB be welded?
Yes — weldability is rated very good (80/100). Carbon content is very low, so weldability is good; repair with low-hydrogen electrodes or TIG. On carburized areas, grind away the case layer before welding and re-carburize the part afterwards.
What surface finishes work on P1-HOB?
After carburizing and quenching, finish grind and polish the cavity. Hard chrome or electroless nickel is common for rust protection and release; nitriding can be used to strengthen surfaces that were not carburized.
Can P1-HOB be formed, bent or molded?
Cold hobbing is the core process for this grade: the soft cavity blank is pressed to shape by a hardened master hob in one or several strokes, with recrystallization annealing between passes.
What is the maximum service temperature of P1-HOB?
P1-HOB is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between P1-ANN and P1-HOB?
ANN is the default condition — order this ≤130 HB soft state for cold hobbing cavities or for rough and finish machining, then carburize and quench; at 240 MPa yield it is not a service condition. HOB: expect this work-hardened state (190 HB, 10% elongation) after cold-pressing the cavity; follow with recrystallization annealing or feed the part directly into carburizing. Yield strength is 240 MPa in ANN versus 520 MPa in HOB.
Sources
- ASTM A681 — Standard Specification for Tool Steels Alloy — ASTM International (2022)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (Mold Steels) — ASM International (1990)
- Tool Steels, 5th ed. (Roberts, Krauss, Kennedy) — ASM International (1998)
- ASM Handbook Vol.4 — Heat Treating (Carburizing) — ASM International (1991)
- UNS T51601 alloy designation record — SAE/ASTM Unified Numbering System (2020)
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.