Steel HPM38-ANN (Annealed)
Heat-treated state · default condition
also S136
Standard mill delivery condition — rough and finish machine the cavity, then harden and temper.
Values for the ANN condition
Other HPM38 tempers and conditions
HPM38 is listed in 7 conditions; see the grade overview at HPM38.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNDefaultThis page Annealed | Standard mill delivery condition — rough and finish machine the cavity, then harden and temper. | 520 | 760 | 18 | 18 HRC | — |
Pre-hardened 30–34 HRC | Pick when the mould must go into service straight from the machine tool with no distortion risk from hardening. | 860 | 1,030 | 13 | 32 HRC | — |
Hardened & tempered 48–50 HRC | Compromise condition — good toughness with adequate wear resistance for medium-run cavities. | 1,400 | 1,650 | 6 | 49 HRC | — |
ESR remelted quality | Specify when the cavity needs A1 mirror finish or uniform chemical texturing — cleanest inclusion rating, supplied annealed or hardened. | 1,450 | 1,750 | 9 | 51 HRC | 3.1 % IACS |
Hardened + gas/plasma nitrided surface | Use on slides, ejector holes and abrasive-resin cores; raises surface hardness to ~1000 HV but reduces corrosion resistance and prevents further polishing to mirror. | 1,450 | 1,750 | 7 | 51 HRC | 3.1 % IACS |
Hardened & tempered 50–52 HRC | The usual working hardness for optical and high-gloss cavities — best balance of polish, wear and corrosion resistance. | 1,520 | 1,780 | 5 | 51 HRC | — |
Hardened & tempered 52–54 HRC | Choose for glass-filled or highly abrasive resins where wear beats toughness; accept lower impact strength. | 1,620 | 1,900 | 3 | 53 HRC | — |
What is HPM38-ANN?
HPM38-ANN is HPM38 heat treated to ANN — standard mill delivery condition — rough and finish machine the cavity, then harden and temper. HPM38-ANN has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 760 MPa (110 ksi) — stronger than 67% of steel grades. Elongation at break is 18% and the elastic modulus is 205 GPa (29.7 Msi). HPM38-ANN 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).
Advantages
- Polishes to a fine finish — 85/100, better than 99% of steel grades
- Good corrosion resistance — 48/100, better than 98% of steel grades
Limitations
- Poor heat conductor — 20 W/m·K (11.6 BTU/hr·ft·°F), worse than 96% of steel grades
- High embodied carbon — 3.6 kg CO₂/kg, worse than 94% of steel grades
- Low electrical conductivity — 2.9 % IACS, worse than 93% of steel grades
- Difficult to weld — 25/100, worse than 77% of steel grades
HPM38-ANN properties
Typical room-temperature values for HPM38-ANN; 12 are specific to this condition. Other listed values are HPM38 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
HPM38-ANN 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).
Mechanical16
HPM38-ANN has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 760 MPa (110 ksi) — stronger than 67% of steel grades. Elongation at break is 18% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
HPM38-ANN is rated for continuous service to 400°C (752 °F). It conducts heat at 20 W/m·K (11.6 BTU/hr·ft·°F), worse than 96% of steel grades. Thermal expansion is 10.8 µm/m·K (6 µin/in·°F).
Electrical3
HPM38-ANN conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is fair (48/100), better than 98% of steel grades.
Sustainability4
Producing a kilogram of HPM38-ANN takes about 52 MJ of energy and emits 3.6 kg of CO₂ — more than 94% of steel grades. Typical recycled content is 40%.
Manufacturability7
HPM38-ANN's machinability is fair (45/100, worse than 65% of steel grades); weldability poor (25/100); formability poor (25/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with HPM38-ANN
Is HPM38 easy to machine?
Machine in the annealed or 30–34 HRC state with sharp coated carbide, positive rake and rigid setups; the low-sulphur stainless work-hardens and smears, so keep feed constant and avoid dwell — above 48 HRC switch to CBN/ceramic or EDM.
Can HPM38 be welded?
Repair-weld only with matching 13Cr filler, 200–300 °C preheat maintained through welding, slow cooling and a post-weld temper 20–30 °C below the original tempering temperature.
Can HPM38 be formed, bent or molded?
Not a cold-forming grade; harden from 1020–1050 °C with vacuum/nitrogen quench (protect from decarburisation), double temper at 200–250 °C, and stress-relieve at 550–600 °C after heavy roughing to control distortion.
What surface finishes work on HPM38?
Excellent diamond mirror polishing to Ra < 0.01 µm and uniform photochemical texturing in the hardened state; can be plasma nitrided or PVD (CrN/TiAlN) coated below the tempering temperature, and needs no chrome plating for corrosion protection.
HPM38 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 |
|---|---|---|
| C | 0.35 – 0.42 | 0.38 |
| Si | 0.6 – 1 | 0.85 |
| Mn | 0.3 – 0.6 | 0.45 |
| Crgives the stainless/corrosion behaviour | 13 – 14.5 | 13.6 |
| Mo | 0.2 – 0.4 | 0.3 |
| Vgrain refinement / wear carbides | 0.2 – 0.4 | 0.3 |
| P | ≤ 0.03 | — |
| Skept very low for mirror polishability | ≤ 0.01 | — |
| Fe | balance | — |
HPM38-ANN — frequently asked
What is HPM38-ANN used for?
HPM38-ANN is typically used for optical lens molds, medical device molds and corrosion-prone molds. In short: stainless mirror-polish mold steel; best for corrosive resins; pre-hardened, machine-ready blocks.
What is the yield strength of HPM38-ANN?
HPM38-ANN has a typical yield strength of 520 MPa (75.4 ksi) and a tensile strength of 760 MPa (110 ksi) — stronger than 67% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is HPM38-ANN easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 65% of steel grades). Machine in the annealed or 30–34 HRC state with sharp coated carbide, positive rake and rigid setups; the low-sulphur stainless work-hardens and smears, so keep feed constant and avoid dwell — above 48 HRC switch to CBN/ceramic or EDM.
Can HPM38-ANN be welded?
Not readily — weldability is rated poor (25/100). Repair-weld only with matching 13Cr filler, 200–300 °C preheat maintained through welding, slow cooling and a post-weld temper 20–30 °C below the original tempering temperature.
What surface finishes work on HPM38-ANN?
Excellent diamond mirror polishing to Ra < 0.01 µm and uniform photochemical texturing in the hardened state; can be plasma nitrided or PVD (CrN/TiAlN) coated below the tempering temperature, and needs no chrome plating for corrosion protection.
Can HPM38-ANN be formed, bent or molded?
Not a cold-forming grade; harden from 1020–1050 °C with vacuum/nitrogen quench (protect from decarburisation), double temper at 200–250 °C, and stress-relieve at 550–600 °C after heavy roughing to control distortion.
What is the maximum service temperature of HPM38-ANN?
HPM38-ANN 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 HPM38-ANN and HPM38 QT52-54?
ANN is the default condition — standard mill delivery condition — rough and finish machine the cavity, then harden and temper. QT52-54: choose for glass-filled or highly abrasive resins where wear beats toughness; accept lower impact strength. Yield strength is 520 MPa in ANN versus 1,620 MPa in QT52-54.
Sources
- HPM38 Plastic Mould Steel data sheet — Hitachi Metals / Proterial (2020)
- Stavax ESR (AISI 420 modified) data sheet — Uddeholm/voestalpine (2022)
- ASSAB S136 / S136H mould steel data sheet — ASSAB (2021)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- GB/T 1220 / JIS G4303 martensitic stainless bar (4Cr13 / SUS420J2 base) — SAC / JISC (2007)
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.