O1 tool steel Vs D2: What are the difference?

O1 tool steel Vs D2: O1 tool steel and D2 tool steel are both widely used cold-work tool steels, but they possess distinct characteristics that make them suitable for different applications. A detailed comparison reveals their strengths and weaknesses.

O1 tool steel Vs D2: Chemical Composition

Element	O1 Tool Steel (%)	D2 steel composition (%)
Carbon (C)	0.85 – 1.00	1.40 – 1.60
Chromium (Cr)	0.40 – 0.60	11.00 – 13.00
Manganese (Mn)	1.00 – 1.40	0.10 – 0.60
Vanadium (V)	0.15 – 0.30	0.50 – 1.10
Molybdenum (Mo)	–	0.70 – 1.20
Tungsten (W)	0.40 – 0.60	–
Silicon (Si)	0.10 – 0.50	0.10 – 0.60
Phosphorus (P)	≤ 0.03	≤ 0.03
Sulfur (S)	≤ 0.03	≤ 0.03

O1 tool steel Vs D2: Mechanical Properties

1. Hardness. O1 steel and D2 steel have similar working hardness. The typical O1 steel hardness is 58–60 HRC. D2 steel hardness is 58–61 HRC and can reach 60–62 HRC through heat treatment, even up to 63-64 HRC when produced by Powder Metallurgy (P/M) processing. Generally, the O1 steel Rockwell hardness is slightly lower than that of D2.
2. Strength. O1 has a yield strength of 829 MPa (758 MPa UTS). Its compression yield strength was higher than D2 steel. The yield strength of D2 is 411 MPa (350 MPa UTS), and the tensile strength (UTS) is 758 MPa.
3. Toughness. Compared with O1, D2 has lower toughness. The large amount of carbides in D2 steel reduces its toughness.
4. Ductility/Plasticity. O1 steel has higher ductility than D2 steel. O1 exhibits significant necking before fracture, with a calculated area reduction of approximately 19.7%. D2 showed almost no necking before fracture, with an area reduction of 1.3%.
5. Wear Resistance/Abrasion Resistance. D2 has better wear resistance compared to O1. O1 steel has moderate wear resistance, while D2 steel has very high wear resistance. This is because the high carbon and chromium content in D2 steel produces a large amount of M7C3-type chromium-rich carbides.
6. Dimensional Stability/Distortion. Compared to other tool steels, D2 steel has the best dimensional stability during heat treatment, although O1 also exhibits minimal dimensional changes during oil quenching. D2 steel is primarily air-hardened, with expansion or contraction of approximately 0.0005 inches per inch.
7. Machinability/Grindability. O1 has excellent machinability, rated at 90 compared to 100 for 1% carbon steel. D2 is particularly poor in terms of machinability, with a rating of 45 compared to 100 for 1% carbon steel. Obviously, O1 steel has much better machinability.

Heat Treatment Comparison

Feature	O1 Steel heat treatment	Heat treat D2 Steel
Hardening/Austenitizing Temperature	802–816 °C (1475–1500 °F)	1010–1024 °C (1850–1875 °F)
Quenching Medium	Oil-hardening. Achieves full hardness when quenched in oil.	Primarily air-hardening. Oil quenching may be required for heavier sections.
Tempering	Typically tempered at 149–232 °C (300–450 °F).	Tempered at low temperatures, around 200 °C (392 °F), to achieve high hardness.
Decarburization and Cracking	Suffers from decarburization during heat treatment and is subject to cracking from thermal shock during oil quenching.	D2 has high resistance to cracking during metal formation and fabrication.

Applications

O1 is a versatile, general-purpose tool steel often chosen for small tools that require good machinability and balanced toughness and hardness. D2 tool steel application is preferred for long-run dies and demands maximum wear resistance and dimensional stability.