Steel HPM38
also S136
HPM38 is a martensitic stainless plastic mold steel of the 13% Cr S136 type, stocked annealed, pre-hardened to 30–34 HRC, quenched and tempered to 48–50, 50–52 or 52–54 HRC, as ESR quality or nitrided.
Reference datasheet — HPM38 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
HPM38 tempers and conditions
HPM38 is supplied in 7 conditions, soft to hard. ANN is the default FabDigit quotes; the values on this page are for it.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNDefault 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?
HPM38 is a martensitic stainless plastic mold steel of the 13% Cr S136 type, stocked annealed, pre-hardened to 30–34 HRC, quenched and tempered to 48–50, 50–52 or 52–54 HRC, as ESR quality or nitrided. It is chosen for cavity blocks, cores and inserts that must hold a mirror polish while resisting corrosive resins and cooling-line rust; annealed stock gives 520 MPa yield, 760 MPa tensile, 18% elongation and 215 HB (18 HRC). Service temperature is capped near 400 °C, machinability is modest (score 45) and cost sits above P20-type 3Cr2Mo, which stays the cheaper choice for non-corrosive resins. HPM38 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). HPM38 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).
What is HPM38 used for?
- Optical lens molds
- Medical device molds
- Corrosion-prone molds
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 properties
Typical room-temperature values for HPM38-ANN; bars are the position among steel grades.
Physical3
HPM38 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 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 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 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 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'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. 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. HPM38 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with HPM38
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.
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 |
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.
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 HPM38 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Trade names
- S136
How much does HPM38 cost?
HPM38 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.
HPM38 — frequently asked
What is HPM38 used for?
HPM38 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?
HPM38 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 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 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?
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 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?
HPM38 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.
How much does HPM38 cost?
HPM38 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
- 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; 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.