24 July 2021 High Speed Steel Bar
W18Cr4V High Speed Steel Bar
W18Cr4V belongs to the tungsten series high-speed steel, which has high hardness, red hardness and high temperature hardness. Its heat treatment range is wide, quenching is not easy to overheat, the heat treatment process is not easy to oxidize and decarburize, and the grinding performance is good. The steel maintains its hardness at HRC63-64 and HRC62-63 at 500°C and 600°C, respectively, and has good cutting performance for a large number of general processed materials.
W18Cr4V high-speed steel belongs to ledeburite steel, which is the longest used high-speed steel. Like other high-speed steels, it is often called "white steel", "front steel" or "wind steel" (quenched by air cooling). When the cutting temperature is 540 degrees, the hardness can be maintained at HRC66; when the cutting temperature is 600 degrees, the hardness can be maintained at HRC63.
The as-cast structure of W18Cr4V includes skeletal, ledeburite with carbide flakes and martensite or troostite arranged alternately, as well as black structure (δ segregation) and white structure (martensite and retained austenite) . The as-cast structure and chemical composition of high-speed steel are particularly uneven, and heat treatment cannot be changed. Therefore, pressure processing must be carried out to break the coarse eutectic carbides and distribute them evenly, and then use them to manufacture various cutting tools and Mould.
Chemical Composition:
| C(％) | Si(％) | Mn(％) | P(％) | S(％) | Cr(％) | V(％) | Mo(％) | W(％) |
|---|---|---|---|---|---|---|---|---|
| 0.70～0.80 | ≤0.40 | ≤0.40 | ≤0.030 | ≤0.030 | 3.80～4.40 | 1.00 ~ 1.40 | ≤0.30 | 17.50 ~ 19.00 |
Mechanical Propoerties:
| Yield Strength Rp0.2(MPa) | Tensile Strength Rm(MPa) | Elastic Modulus (N/mm) | Elongation A(%) | Coefficient of thermal expansion 1/℃ | Thermal conductivity W/m℃ | Hardness |
|---|---|---|---|---|---|---|
| ≥ 1880(110) | ≥ 1990(130) | 225000 | ≥ 9 | 12.1x10-6 | 24.0 | ≤63 HRC |
Heat treatment:
The pre-treatment of the heat treatment process is annealing, the temperature is 870~880 degrees, the holding time is 2~3 hours, then 800-840 degrees is preheated, and the graded quenching is from 1270 to 1280 degrees, and the grading temperature is 580-620, and then 560 degrees for three times. Fire, heat preservation for 1 hour during tempering.
W18Cr4V contains a large number of alloying elements: poor plasticity, poor thermal conductivity, thermal stress during rapid heating causes it to deform and crack, so it must be heated to a quenching temperature of 1270 to 1280 degrees and preheated at 800 to 840. For those with complex shapes, it should be preheated. Add a preheating at 500-650. V, W and other elements that mainly increase the red hardness must be dissolved at a very high temperature, but too high temperature will make the crystal grains coarser, and W and other alloying elements will shrink the A zone, which makes the eutectoid and eutectic temperature increase. So choose 1270 to 1280 degrees. Direct air cooling will precipitate secondary carbides, thereby reducing the red hardness of the steel.
The structure after quenching is M ten carbide ten residual A (up to 30%) tempering at 550 to 570 degrees, precipitation of WC, etc. cause secondary hardening, A decomposition, precipitation of C, reduce the content of alloying elements, make Ms rise, resulting in After the second quenching, the first tempering, there is 15% residual A, and the second tempering residual A is 3% to 5%.
Three times of tempering, only 1% to 2%, the final tempered tissue M ten carbide ten very small amount of residue.