ISO Material Group "P" is part of the ISO classification system for cutting tool materials, specifically referring to steel and steel alloys.
This article aims to offer a simple guide to the characteristics that affect machinability and are used to help select appropriate cutting tools and speeds for different materials.
This breakdown explains the 5 main categories of Steel
P1 – Low-Carbon, Non-Alloy Steels
- AKA: Free Cutting Steel, Structural Steel, Mild Steel, Carbon Steel
- Hardness: Generally <200HB
- Description: Includes low-carbon, unalloyed steels with carbon content typically less than 0.25%.
- Properties: These steels are generally softer, more ductile, and have lower tensile strength, making them easier to machine.
- Applications: Common in structural applications and general engineering components where high strength isn’t the primary concern.
- SubGroups (Europa ref Group 11)
- VDI 3323 1 Non-alloyed steel About 0.15% C, Annealed ≤125 HB
- VDI 3323 2 Non-alloyed steel About 0.45% C, Annealed ≤13 HRc ≤190 HB
- Examples of P1 Steel include: S275; AISI 1010 (SAE 1010); A36 Steel; EN3B
P2 – Medium-Carbon, Non-Alloy Steels
- AKA: Mid Carbon Steel. Mechanical Steel
- Hardness: Generally <250HB
- Description: Medium-carbon steels with around 0.25% to 0.55% carbon content, unalloyed.
- Properties: These steels offer moderate hardness and strength, balancing machinability and mechanical properties.
- Applications: Used in parts requiring higher strength than low-carbon steel, such as shafts, axles, and gear
- SubGroups (Europa ref Group 12)
- VDI 3323 3 Non-alloyed steel About 0.45% C, Annealed ≤25 HRc ≤250 HB
- VDI 3323 4 Non-alloyed steel About 0.75% C, Annealed ≤28 HRc ≤270 HB"
- Examples of P2 Steel include: AISI/SAE 1040 and 1045; EN8; C40 and C45
P3 – High-Carbon, Non-Alloy Steels
- AKA: High Carbon Steel; Spring Steel
- Hardness: Generally < 300HB
- Description: High-carbon steels with more than 0.55% carbon content, unalloyed.
- Properties: Higher carbon content gives them more hardness and wear resistance but reduces machinability due to increased brittleness.
- Applications: Suitable for tools, springs, and high-stress applications where wear resistance is critical.
- Subgroups: (Europa Group 13)
- VDI 3323 5 Non-alloyed steel About 0.75% C, Quenched & Tempered ≤32 HRc ≤300 HB"
- Examples of P3 Steel Include: AISI 1095 and 1055, C60, C65
P4 – Low-Alloy Steels
- AKA: High Strength Steel; Chromium and Molybdenum Steels
- Hardness: Generaly <350HB
- Description: Steels with added alloying elements (such as chromium, nickel, and molybdenum) in low concentrations to improve properties.
- Properties: Better hardness, strength, and toughness compared to non-alloy steels, often heat-treated to enhance these properties further.
- Applications: Widely used in automotive, aerospace, and machinery parts where high strength and toughness are essential
- Subgroups (Europa Code 14)
- VDI 3323 6 Low-alloyed steel Annealed ≤10 HRc ≤180 HB
- VDI 3323 7 Low-alloyed steel Quenched & Tempered ≤29 HRc ≤275 HB
- VDI 3323 8 Low-alloyed steel Quenched & Tempered ≤32 HRc ≤300 HB
- VDI 3323 9 Low-alloyed steel Quenched & Tempered ≤38 HRc ≤350 HB"
- Examples of P4 Steels include AISI 4130; 4140; EN24
P5 – High-Alloy Steels
- Hardness: Generally <325 HB
- AKA: Tool Steel;
- Description: Steels with a high concentration of alloying elements, generally more than 5%, including materials like stainless steels and tool steels.
- Properties: High-alloy steels have enhanced properties such as increased hardness, toughness, corrosion resistance (especially in stainless steels), and wear resistance. These steels often require specific machining parameters and tools due to their toughness and strength.
- Applications: Commonly used in demanding environments, including aerospace components, medical devices, cutting tools, dies, and molds, as well as in applications requiring corrosion resistance
- Subgroups (Europa Code 15
- VDI 3323 10 High-alloyed steel, Tool steel Annealed ≤15 HRc ≤200 HB
- VDI 3323 11 High-alloyed steel, Tool steel Quenched & Tempered ≤35 HRc ≤325 HB"
- Examples of P5 Steels include AISI 52100, AISI D2, 304, 316