Tool Steels - Water-Hardening Tool Steels

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Water-hardening tool steels, also known as group W steels, comprise the W1, W2, and W3 types. Carbon is the main alloying element found in group W steels. Water-hardening steels are produced with different nominal carbon contents ranging from 0.60 to 1.40%. About 1.00% C is present in the popular grades of tool steels.


Wear resistance and hardenability of water-hardening tool steels are increased by the addition of a small quantity of chromium. Grain size is maintained by the addition of vanadium, thus enhancing the toughness of water-hardening tool steels. A fully hardened thin zone is developed by the group W steels due to their shallow hardening nature and this hardening takes place even when the group W steels are drastically quenched. At high temperatures, the group W steels have low resistance to softening. Sections of the water-hardening tool steels having thickness above 13mm develop a resilent core and a tough case, when quenched.


The following table highlights the composition of water-hardening tool steels along with their AISI and UNS designations.

Designation Compositiona, %
AISI UNS C Mn Si Cr Ni Mo W V Co
W1 T72301 0.70-1.50 0.10-0.40 0.10-0.40 0.15 max 0.20 max 0.10 max 0.15 max 0.10 max -
W2 T72302 0.85-1.50 0.10-0.40 0.10-0.40 0.15 max 0.20 max 0.10 max 0.15 max 0.15-0.35 -
W3 T72305 1.05-1.15 0.10-0.40 0.10-0.40 0.40-0.60 0.20 max 0.10 max 0.15 max 0.10 max -

aAll the steels (except group W) contain 0.25 max Cu, 0.03 max P, and 0.03 max S; Group W contains 0.20 max Cu, 0.025 max P, and 0.025 max S. Where mentioned, sulfur can be increased from 0.06 to 0.15% to enhance machinability of group A, D, H, M, and T steels.


Water-hardening tool steels find applications in the following tools and dies:

  • Drills, reamers, taps, blanking dies, cold-striking, countersinks and jewelry dies
  • Woodworking tools, striking, cold heading, embossing and coining tools and hard metal-cutting tools like reamers and taps
  • Cutlery and wear-resistant machine tool components.

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