Steel is one of the most widely used engineering materials for CNC machining, sheet metal fabrication, injection molds, die casting dies, tooling, shafts, gears, and high-strength mechanical components.

Different steel grades provide different combinations of strength, hardness, toughness, wear resistance, corrosion resistance, machinability, heat resistance, and dimensional stability. Material selection should consider the application, operating environment, required service life, heat treatment, machining process, and surface treatment.

Material note: Mechanical properties depend strongly on grade, product form, thickness, heat-treatment condition, and applicable standard. Actual values should be verified against the material supplier’s TDS or relevant ASTM/EN specification.

Common Steel Grades

GradeSteel TypeKey PropertiesTypical Applications
AISI 1018Low Carbon SteelGood machinability, weldability and ductilityCNC parts, shafts, pins, brackets
AISI 1045Medium Carbon SteelGood strength, hardness and wear resistanceShafts, gears, pins, bolts
AISI 4130Alloy SteelHigh strength, toughness and weldabilityAerospace, automotive, shafts
AISI 4140Alloy SteelHigh strength, toughness and fatigue resistanceGears, shafts, axles, machine parts
AISI 4340Alloy SteelVery high strength, toughness and hardenabilityAerospace, gears, shafts, heavy-duty parts
AISI 8620Carburizing Alloy SteelExcellent case-hardening and wear resistanceGears, pinions, shafts, bushings
AISI A2Cold Work Tool SteelHigh wear resistance and dimensional stabilityDies, punches, forming tools
AISI D2Cold Work Tool SteelExcellent wear resistance and high hardnessStamping dies, cutting tools, punches
AISI S7Shock-Resistant Tool SteelExcellent impact toughnessPunches, dies, shear tools
AISI H13Hot Work Tool SteelExcellent thermal fatigue, toughness and heat resistanceInjection molds, die casting dies, extrusion dies
AISI H11Hot Work Tool SteelHigh toughness and thermal fatigue resistanceDie casting and hot-forming dies
AISI P20Pre-Hardened Mold SteelGood machinability, polishability and toughnessPlastic injection molds, mold bases
P20+NiPre-Hardened Mold SteelGood toughness, polishability and dimensional stabilityLarge plastic injection molds
AISI 420Martensitic Stainless SteelHigh hardness, wear resistance and corrosion resistancePlastic molds, medical tools, blades
AISI 440CMartensitic Stainless SteelVery high hardness and wear resistanceBearings, precision tools, blades
AISI 303Austenitic Stainless SteelExcellent machinabilityCNC turned parts, fittings, fasteners
AISI 304Austenitic Stainless SteelExcellent corrosion resistance and formabilitySheet metal, enclosures, food and medical equipment
AISI 316 / 316LAustenitic Stainless SteelExcellent corrosion and chemical resistanceMarine, chemical and medical equipment
17-4 PH / UNS S17400PH Stainless SteelHigh strength, hardness and corrosion resistanceAerospace, valves, shafts, mechanical parts
15-5 PH / UNS S15500PH Stainless SteelHigh strength, toughness and corrosion resistanceAerospace, marine and precision components

Plastic Injection Mold Steels

For injection molding, steel selection depends on mold life, resin abrasiveness, corrosion, surface finish, polishing requirements, and production volume.

European GradeCommon US / International EquivalentKey PropertiesTypical Applications
1.2311AISI P20Good machinability, toughness and polishabilityGeneral injection molds
1.2312AISI P20 ModifiedImproved machinability, pre-hardenedMold bases, general tooling
1.2738P20 + NiBetter toughness and dimensional uniformityLarge injection molds
1.2083AISI 420 ModifiedCorrosion resistance, polishabilityOptical and medical molds
1.2085Corrosion-Resistant Mold SteelCorrosion resistance, pre-hardenedMold components and bases
1.2316AISI 420-typeExcellent corrosion resistance and polishabilityMedical, optical and PVC molds
1.2343AISI H11High toughness and thermal fatigue resistanceHigh-temperature tooling
1.2344AISI H13Excellent hot strength, toughness and thermal fatigue resistanceInjection molds, die casting dies
1.2344 ESRH13 ESRImproved cleanliness and polishabilityHigh-quality molds and tooling
1.2767AISI 6F7-typeHigh toughness and polishabilityLarge molds, compression tooling

S136 Mold Steel

S136 is a commonly used mold steel designation in Asian mold manufacturing, but it is not an original AISI designation. For a Western-facing website, it is better to identify it by its European equivalent:

S136 ≈ EN/DIN 1.2083 / AISI 420-type stainless mold steel

It is widely used for high-polish, corrosion-resistant injection molds, especially for medical, optical, transparent and PVC applications.

Die Casting Tool Steels

Die casting dies require steels with excellent hot strength, thermal fatigue resistance, toughness, temper resistance, and resistance to heat checking.

GradeCommon StandardKey PropertiesTypical Applications
AISI H13 / 1.2344ASTM / EN / DINExcellent hot strength, toughness and thermal fatigue resistanceAluminum die casting dies
AISI H11 / 1.2343ASTM / EN / DINHigher toughness and thermal fatigue resistanceDie casting dies, hot tooling
AISI H10 / 1.2365EN / DINHigh hot strength and temper resistanceHot forming and die casting
AISI H19 / 1.2714EN / DINHigh toughness and thermal strengthHeavy-duty hot tooling
AISI H13 ESRESR Tool SteelHigh cleanliness, toughness and thermal fatigue resistanceHigh-performance die casting dies

AISI H13 / EN 1.2344 is one of the most widely used choices for aluminum die casting dies because it provides a good balance of hot hardness, toughness, thermal fatigue resistance and machinability.

Material Selection Guide

RequirementRecommended Steel
General CNC machiningAISI 1018, 1045
High-strength CNC partsAISI 4140, 4340
Carburized gearsAISI 8620
General plastic injection molds1.2311 / P20
Large injection molds1.2738 / P20+Ni
High-polish molds1.2083 / 420-type
Corrosion-resistant molds1.2083, 1.2316
High-wear toolingAISI D2
High-impact toolingAISI S7
Hot injection moldingAISI H13 / 1.2344
Aluminum die castingAISI H13 / 1.2344
High thermal fatigue resistanceH13 / 1.2344, H11 / 1.2343
High-strength stainless parts17-4 PH
Corrosion-resistant CNC parts304, 316L
High-hardness stainless parts420, 440C

Common Steel Failure Factors

  • Excessive mechanical loading
  • Fatigue and cyclic stress
  • Wear and abrasion
  • Corrosion and oxidation
  • Thermal fatigue and heat checking
  • Improper heat treatment
  • Insufficient hardness
  • Excessive residual stress
  • Welding-induced cracking or distortion
  • Stress concentration
  • Poor cooling or thermal management in molds and dies

Steel Design Considerations

When designing steel components or tooling, consider:

  • Material grade and heat-treatment condition
  • Required hardness and toughness
  • Operating temperature
  • Wear and corrosion environment
  • Machinability and cutting conditions
  • Heat-treatment distortion
  • Wall thickness and structural rigidity
  • Fillets and stress concentration
  • Cooling-channel layout for molds and dies
  • Surface finish and polishing requirements
  • Dimensional tolerances and mold shrinkage
  • Surface treatment such as nitriding, carburizing, plating or coating

Common Steel Surface Treatments

Common treatments include quenching and tempering, carburizing, nitriding, black oxide, zinc plating, electroless nickel plating, PVD coating, passivation, polishing, and shot/bead blasting.

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