1. Q: For applications requiring high surface hardness but a tough core, which grade is preferable?
A: Both are excellent for case hardening (like carburizing), but 20Cr is the prime choice. Its low-carbon core remains very tough and ductile after the surface is hardened, making it ideal for gears and shafts that withstand impact.
2. Q: Which grade can be effectively heat-treated to a higher bulk strength (quenching and tempering)?
A: 40Cr responds much better to through-hardening (quenching and tempering) because its higher carbon content allows it to achieve a higher and more uniform hardness and strength throughout the cross-section.
3. Q: Which steel has better impact toughness?
A: 20Cr generally has better inherent impact toughness due to its lower carbon content and higher ductility.
4. Q: What is the most common heat treatment for 40Cr pipes/cylinders to achieve a good balance of strength and toughness?
A: Quenching and Tempering (also known as quenching and drawing). This process results in a tempered martensite structure with high strength and good toughness.
5. Q: What is the typical quenching medium for 40Cr?
A: 40Cr has good hardenability and can often be quenched in oil, which results in less distortion and lower quenching stresses compared to water quenching.
