Steel 420 Mod Mold · heat-treated state
Steel 420 Mod Mold Prehard
Properties of the Prehard condition, compared with the other 420 Mod Mold tempers.
Pick for cavity/core blocks machined to final shape with no further heat treatment and no distortion risk.
What is 420 Mod Mold Prehard?
420 Mod Mold Prehard is 420 Mod Mold heat treated to Prehard — pick for cavity/core blocks machined to final shape with no further heat treatment and no distortion risk. 420 Mod Mold Prehard has a yield strength of 860 MPa (125 ksi) and a tensile strength of 1,030 MPa (149 ksi) — stronger than 89% of steel grades. Elongation at break is 13% and the elastic modulus is 200 GPa (29 Msi). 420 Mod Mold Prehard has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 93% of steel grades. It melts at 1,425°C (2,597 °F). Annealed is the default condition FabDigit quotes; Prehard is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 85/100, better than 99% of steel grades
- Good corrosion resistance — 50/100, better than 98% of steel grades
- High strength — 860 MPa (125 ksi), better than 89% of steel grades
- High service temperature — 450°C (842 °F), better than 86% of steel grades
Limitations
- High embodied carbon — 3.6 kg CO₂/kg, worse than 93% of steel grades
- Poor heat conductor — 24 W/m·K (13.9 BTU/hr·ft·°F), worse than 90% of steel grades
- Low electrical conductivity — 3.1 % IACS, worse than 89% of steel grades
- Difficult to machine — 35/100, worse than 83% of steel grades
- Limited ductility — 13%, worse than 78% of steel grades
420 Mod Mold Prehard properties
Typical room-temperature values for 420 Mod Mold Prehard — 15 properties are specific to this condition; the rest are grade-level values shared by every 420 Mod Mold temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
420 Mod Mold Prehard has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 93% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical15
420 Mod Mold Prehard has a yield strength of 860 MPa (125 ksi) and a tensile strength of 1,030 MPa (149 ksi) — stronger than 89% of steel grades. Elongation at break is 13% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
420 Mod Mold Prehard is rated for continuous service to 450°C (842 °F). It conducts heat at 24 W/m·K (13.9 BTU/hr·ft·°F), worse than 90% of steel grades. Thermal expansion is 10.5 µm/m·K (5.83 µin/in·°F).
Electrical3
420 Mod Mold Prehard conducts electricity at 3.1 % IACS, worse than 89% of steel grades.
Chemical & Environmental3
Corrosion resistance is fair (50/100), better than 98% of steel grades.
Sustainability4
Producing a kilogram of 420 Mod Mold Prehard takes about 52 MJ of energy and emits 3.6 kg of CO₂ — more than 93% of steel grades. Typical recycled content is 60%.
Manufacturability7
420 Mod Mold Prehard's machinability is fair (35/100, worse than 83% of steel grades); weldability poor (25/100); formability fair (35/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 420 Mod Mold tempers and conditions
420 Mod Mold is also supplied in 3 other conditions. The full side-by-side table is on the 420 Mod Mold overview.
- AnnealedDefaultStandard stock condition for shops that will rough-machine and then harden the cavity themselves.470 MPa yield · 220 HB
- Q&T 52-54Top-hardness option for small inserts, gate areas and wear-critical details where toughness is secondary.1,600 MPa yield · 53 HRC
- Q&TUse for high-wear, high-gloss cavities and inserts running abrasive or glass-filled resins.1,450 MPa yield · 50 HRC
- PrehardPick for cavity/core blocks machined to final shape with no further heat treatment and no distortion risk.860 MPa yield · 31 HRC
Working with 420 Mod Mold Prehard
Is 420 Mod Mold easy to machine?
Machine in the annealed or prehard state with rigid setups, sharp coated carbide and generous coolant — the alloy work-hardens and gums at low speeds; hardened 50 HRC parts need CBN/hard-milling or EDM.
Can 420 Mod Mold be welded?
TIG repair only with matching 420-type or 410NiMo filler, preheat 250–325 °C, weld hot and temper immediately below the last tempering temperature to avoid cracking.
Can 420 Mod Mold be formed, bent or molded?
Not a cold-forming grade; hot work 1100→850 °C with slow cooling, then soft anneal at ~850 °C furnace-cooled before machining.
What surface finishes work on 420 Mod Mold?
Excellent mirror (A1) polishability in the hardened ESR condition; stress-relieve before finish machining and consider nitriding, PVD CrN/TiN or hard chrome for extra wear resistance — no anodizing on steel.
420 Mod Mold 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 |
|---|---|---|
| Craised vs standard 420 for full hardening | 0.33 – 0.45 | 0.38 |
| Si | 0.2 – 1 | 0.4 |
| Mn | 0.3 – 1 | 0.5 |
| Cr | 12.5 – 14.5 | 13.5 |
| Momodification for hardenability/temper resistance | 0 – 0.6 | 0.3 |
| Vgrain refinement, wear resistance | 0 – 0.4 | 0.25 |
| Nioptional, toughness in heavy sections | 0 – 0.6 | 0.25 |
| P | ≤ 0.03 | — |
| Skept very low (ESR) for polishability | ≤ 0.01 | 0 |
| Fe | balance | — |
420 Mod Mold Prehard — frequently asked
What is 420 Mod Mold Prehard used for?
420 Mod Mold Prehard is typically used for plastic injection-mold cavities and cores, optical-part molds, mold inserts for PVC and other corrosive polymers, blow-mold cavities, extrusion dies for plastics and medical and packaging mold tooling. In short: modified mold-cavity plate.
What is the yield strength of 420 Mod Mold Prehard?
420 Mod Mold Prehard has a typical yield strength of 860 MPa (125 ksi) and a tensile strength of 1,030 MPa (149 ksi) — stronger than 89% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is 420 Mod Mold Prehard easy to machine?
Not especially — machinability is rated fair (35/100, worse than 83% of steel grades). Machine in the annealed or prehard state with rigid setups, sharp coated carbide and generous coolant — the alloy work-hardens and gums at low speeds; hardened 50 HRC parts need CBN/hard-milling or EDM.
Can 420 Mod Mold Prehard be welded?
Not readily — weldability is rated poor (25/100). TIG repair only with matching 420-type or 410NiMo filler, preheat 250–325 °C, weld hot and temper immediately below the last tempering temperature to avoid cracking.
What surface finishes work on 420 Mod Mold Prehard?
Excellent mirror (A1) polishability in the hardened ESR condition; stress-relieve before finish machining and consider nitriding, PVD CrN/TiN or hard chrome for extra wear resistance — no anodizing on steel.
Can 420 Mod Mold Prehard be formed, bent or molded?
Not a cold-forming grade; hot work 1100→850 °C with slow cooling, then soft anneal at ~850 °C furnace-cooled before machining.
What is the maximum service temperature of 420 Mod Mold Prehard?
420 Mod Mold Prehard is rated for continuous use to about 450°C (842 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 420 Mod Mold Annealed and 420 Mod Mold Prehard?
Annealed is the default condition — standard stock condition for shops that will rough-machine and then harden the cavity themselves. Prehard: pick for cavity/core blocks machined to final shape with no further heat treatment and no distortion risk. Yield strength is 470 MPa in Annealed versus 860 MPa in Prehard.
Can FabDigit make parts in 420 Mod Mold Prehard?
Yes — 420 Mod Mold Prehard is available for CNC machining with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A681 — Alloy Tool Steels — ASTM International (2015)
- GB/T 1299 / GB/T 1220 (4Cr13, 4Cr13 ) — SAC (2014)
- ASM Specialty Handbook: Stainless Steels — ASM International (1994)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- Stainless plastic mould steel datasheets (13% Cr ESR mould grades) — Tool steel producers (2023)
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.