W1 steel belongs to a famous class of water hardenable tool steel. There are total 7 grades for this category from W1 to W7. W1 is considered the most common one among all grades. This type of tool steel majorly contains high carbon responsible for all properties. To boost mechanical properties and to refine microstructure, alloying additions like Chromium is carried out.
Topic Covered in “Water hardenable tool steel guide” are; What is W1 steel, W1 steel composition, properties, heat treatment, and application. Along with these topics, mechanical processes feasible will also be discussed.
D2 Steel – High chromium – High Carbon Cold Worked steel
What is W1 steel?
W1 steel is high carbon steel with carbon ranging from 0.6% to 1.4%. With such high carbon, this steel usually has high tensile strength and hardness with low ductility and toughness. That’s why water hardenable tool steel is avoided in applications that require energy absorption or impact loading. Due to excellent machinability characteristics, this high carbon percentage is used extensively for tools used in diverse areas of life. Other designations are;
UNS Number –T72301
DNS Number – C100 W1
W1 steel Composition
Composition of water hardenable tool steel is shown below;
|C||0.95 - 1.14|
|Si||0.15 - 0.30|
|Mn||0.15 - 0.25|
Water hardened steel Physical Properties
|Melting Point||1430 C|
W1 steel Mechanical Properties
Follow Brinell Hardness test for insight into procedure of hardness testing and for reading hardness number and hardness scale.
|Yield Strength||1500 Mpa|
|Poisson ratio||0.27 - 0.3|
|Elastic Modulus||200 GPa|
|Impact Energy (Charpy test)||86 J|
|Hardness (Brinell)||498 HBN|
|Hardness (Vicker)||531 HV|
|Hardness (Rockwell)||50 - 51 HRC|
Firstly, Thermal conductivity graph with respect to temperature for work hardenable tool steel is mentioned;
|W1 steel||Thermal Conductivity (W/m. K)|
Thermal expansion in relation to temperature for work hardenable tool steel containing high carbon is shown below;
|W1 Steel||Thermal Expansion [µm/m.K from 20 C]|
W1 steel heat treatment
This high carbon % must be properly utilized. For this, proper heat treatment is necessary. The proper heat treatment in water hardenable tool steel produces a good combination of resistance to deformation, resistance to softening, wear resistance for tool steel applications.
Common defects that you may encounter during heat treatment can be found in the article, “Common defects in heat treatment of steel and their possible remedies“.
Due to high carbon, most of structure after hardening treatment will be converted to martensite. This martensitic formation depends alot on quenching treatment. To understand non-equilibrium or fast cooling importance, study TTT diagram in steel.
Here, first mentioned things are hardening and tempering cycle for W1 tool steel; Quenchant mentioned here are brine or water. You can study the quenchant role in martensitic transformation at, “Role of Quenching media in Martensitic Formation“.
|Rate of Heating||Slowly|
|Pre-heating (hardening)||560 - 650 C|
|Hardening Temperature||760 - 815 C|
|Holding temperature||10 - 30 min|
|Quenching Medium||Brine or Water|
|Tempering temperature||175 - 345 C|
Initially, Water hardenable tool steel is received in the annealed condition. In annealed condition hardness of steel is low. This enables the effective machining of products. To measure hardness, Vicker hardness is reliable or labortary scale. For industrial scale, rockwell C scale is used for hardness measurement of tool steels. After proper machining, the hardening process is carried out to achieve the necessary mechanical properties mentioned above. Below mentioned table enlist variation in hardening temperature in relation to carbon percentage;
|Composition||Hardnening Temperature (C)||Hardness (as-quenched)||Tempering||Hardness (after tempering)|
|0.7 - 0.8 %C||800 - 820||65 - 67||175 - 275||56|
|0.8 - 0.9 % C||790 - 810||65 - 67||175 - 275||56|
|0.9 - 1.05 % C||780 - 800||65 - 67||175 - 275||56|
|1.05 - 1.2 % C||760 -780||65 - 67||175 - 275||56|
|1.2 - 1.35 % C||760 - 780||65 - 67||175 - 275||56|
Normally, all steel parts are received in wrought form. They are annealed condition. Tool is machined before giving tool hardening treatment. Annealed condition is considered the softest state. Recommended annealing is spheroidized annealing for better machinability.
To Study Annealing processes, Follow Steel Annealing process
After machining, steel is given hardening treatment. Annealing and normalizing cycle commonly employed for this specific work hardenable tool steel is given below;
|Grade of Steel||W1 Steel|
|Normalizing||Possible (790 - 925)|
|Annealing Temperature||790 - 925|
|Annealing (Rate of Cooling)||22 C/ hr|
|Hardness after Annealing||156 - 201|
Normalizing treatment is carried out for W1 steel to breakup non-uniform structure, to refine grain size, and to relieve residual stresses. This type of treatment is delivered after forging and before full annealing steps. To avoid decarburization, the steel part can be packed in a furnace in a protective atmosphere. Normalizing cycle is given below along with annealing cycle.
Water-hardenable tool steels can be forged between 1038o C and 816o C. After forging, W1 tool steel is given normalizing and annealing treatment to refine the structure and relieve stresses.
All mechanical process and service conditions for Tools steel are given in table;
|Resistance to decarburization||Highest|
|Amount of Distortion||High|
|Resistance to cracking||Medium|
|Approximate Hardness(HRC)||50 - 64|
|Resistance to softening||Low|
|Resistance to wear||Low to Medium|
W1 steel Applications
- Heavy forging hammers
- Knife and Blades
- Lathe centers
- Milling cutter and boring tools
- Forging dies
- Bending Dies
- Large Blanking tools
- Drift punches