Processing of W-Cr-V-Mo tool steel swarf by the powder metallurgy technique

Conclusions

• 1. In an investigation of the sintering process of compacts from powders obtained by grinding W-Cr-V-Mo high-speed steel (R18) swarf, the effect of the following factors promoting intense densification was determined and elucidated:

• a) use of powder, containing 0.3–0.4% oxygen, which is not subjected to reduction after grinding;

• b) addition of carbon black to the powder in an amount equivalent to its oxygen content;

• c) thorough drying of hydrogen;

• d) high compaction pressure (up to 7–10 tons/cm²);

• e) rapid temperature rise to 1250‡C and holding for 1–2 h.

Combining all these measures made it possible to attain relative densities of 95–96% for compacts weighing 4–5 kg and 97–98% for small compacts.

• 2. The phenomenon was discovered of formation of a ledeburitic eutectic in the course of sintering at 1200–1250‡C, which is attributed to the possible generation, at the beginning of sintering, of a liquid phase (subsequently disappearing) with the participation of oxide impurities.

• 3. Zero porosity is attained by subjecting sintered blanks to hot forging.

• 4. The structure of sintered blanks resembles that of blanks from cast R18 steel, but has finer and more uniformly distributed carbides, which impart higher hardness, red hardness, and thermal conductivity to the sintered material.

• 5. The physicomechanical and cutting properties of forged tips from the sintered steel are comparable to, or even slightly superior to, those of cast and forged R18 steel.

• 6. Tentative calculations have shown that the cost of sintered steel from machining waste is some 50% less than the cost of standard cast steel.