6CrW2Si Steel Technical Overview

6CrW2Si Steel Technical Overview: 6CrW2Si is a versatile alloy tool steel that is effective for both cold and hot work applications, especially where impact resistance and wear are critical factors. It’s recognized as an impact-resistant grade and is commonly used for cold heading dies. Compared to 4CrW2Si and 5CrW2Si grades, 6CrW2Si typically achieves higher hardness after quenching and offers better strength at elevated temperatures.

However, users should be aware of certain characteristics. In larger cross-sections, there’s a tendency for banded carbide segregation, which can decrease toughness. Additionally, this grade is sensitive to decarburization during heating, and controlling deformation during the quenching process requires careful attention.

1. 6CrW2Si Steel Chemical Composition(GB/T 1299-2000 / GB/T 1299-2014 (T40296))

• Carbon (C):55 – 0.65%
• Silicon (Si):50 – 0.80%
• Manganese (Mn):≤ 0.40%
• Chromium (Cr):10 – 1.30%
• Tungsten (W):20 – 2.70%
• Phosphorus (P):≤ 0.030%
• Sulfur (S):≤ 0.030%
• Nickel (Ni):≤ 0.30% (≤ 0.25% in 2014 standard)
• Copper (Cu):≤ 0.30% (≤ 0.25% in 2014 standard)

2. 6CrW2Si Steel Equivalent International Grades

• ISO: 60WCrV8
• EN: 60WCrV8
• DIN: 2550 (or 60WCrV7)
• ASTM: S1 (T41901)
• JIS: SKS4
• NF (France): 55WC20
• UNI (Italy): 55WCrV8
• SIS (Sweden): 2550

3. 6CrW2Si Steel Physical Properties

Key transformation temperatures for 6CrW2Si are approximately:

• Ac1: 775 °C
• Ac3: 810 °C
• Ms: 280 °C
• Ar1: 700 °C

4. 6CrW2Si Steel Heat Treatment

Proper heat treatment is crucial for achieving the desired properties in 6CrW2Si.

4.1 Forging

• Heating:Ingots: 1170-1200 °C; Billets: 1150-1170 °C.
• Initial Forging Temp:Ingots: 1150-1180 °C; Billets: 1100-1140 °C.
• Finish Forging Temp:Ingots: ≥ 850 °C; Billets: ≥ 800 °C.
• Cooling: Slow cooling after forging is essential.

4.2 Annealing

• General Annealing: Heat to 800-820 °C, hold for 3-5 hours, cool the furnace to below 550 °C, then air cool. Expected hardness: 229-285 HBW. Microstructure: Granular pearlite with minor carbides.
• Isothermal Annealing: Heat to 830-840°C (2-3h), furnace cool to 680-700°C, hold (3-4h), furnace cool to 500°C, then air cool. Hardness ≤ 289 HBW.
• High-Temperature Tempering (for Machinability): Heat to 700-730 °C, hold for 2-4 hours, and then furnace or air cool.

4.3 Quenching

• Temperature: 860 – 900 °C.
• Medium: Oil (at 20-40 °C).
• Expected Hardness: ≥ 57 HRC after cooling to oil temperature.

4.4 Tempering

The tempering temperature depends on the application requirements:

• Stress Relief/Stabilization: Temper at 200-250 °C (oil or molten alkali). Air cool. Hardness: 53-58 HRC.
• Reduced Hardness/Stress Relief: Temper at 430-470 °C (air furnace or molten alkali/nitrate). Air cool. Hardness: 45-50 HRC.
• Temper Brittleness: Be aware of slight temper brittleness occurring between 300-350 °C.
• Common Tempering Points: Tempering around 250 °C yields 54-56 HRC. Tempering near 450 °C results in 50-52 HRC with improved impact toughness.

4.5 Hardness vs. Tempering Temperature (after 880°C Oil Quench):

• Untempered: ~59 HRC
• 200 °C: ~56 HRC
• 400 °C: ~49 HRC
• 600 °C: ~35 HRC

5. Mechanical Properties

• Hardness: High quenched hardness (can reach 60-62 HRC).
• Toughness: Relatively high, though potentially reduced in larger sections due to carbide segregation.
• Strength: Good high-temperature strength and high-fatigue strength.
• Wear Resistance: Good wear resistance, slightly better than 5CrW2Si.
• Temper Resistance: Good resistance to softening during tempering.

6. Applications

6CrW2Si is a solid choice for manufacturing tools and dies subjected to impact loads and requiring high wear resistance. It is frequently used for:

• Heavy-duty punching and forming dies (where wear/collapse are failure modes).
• Pneumatic tool components.
• Impact dies.
• Cold shear blades.
• Blanking and trimming dies.
• Air hammer tools.
• Hot riveting punches.
• Piercing mandrels (for high-temp light alloy die-casting).
• Hot forging dies.
• Casting finishing tools.

It serves as a practical alternative when:

• Carbon tool steels lack sufficient load capacity.
• Oil-quenching standard grades don’t provide enough hardness.
• Cr12-type steels are prone to cracking.
• High-speed steel (HSS) is not economically justified for the required wear resistance.

Compared to W-type high-speed steels like SKH2, 6CrW2Si offers a substitute for various hot and cold work dies, punches, and cutting tools, though toughness may be lower in larger sizes.