1. Q: What are the material properties of 6120 steel pipe? A: 6120 is a medium-carbon chromium-vanadium alloy structural steel (corresponding to AISI 6120), with a carbon content of 0.18%-0.23%, a chromium content of 0.70%-0.90%, and a minimum vanadium content of 0.15%. Its core characteristics are high strength, excellent fatigue resistance, and good hardenability. The addition of vanadium significantly refines the grain size, improving toughness and wear resistance. Compared to 6118 steel, 6120 has better impact resistance and high-temperature stability.
2. Q: What are the typical mechanical properties of 6120 steel pipe? A: After quenching and tempering (quenching + tempering), typical properties are: tensile strength 900-1100 MPa, yield strength 750-950 MPa, elongation ≥12%, and impact energy (room temperature) ≥45 J. By controlling the tempering temperature (typically 500-650°C), a balance between strength and toughness is achieved, typically achieving a hardness range of HRC 28-35. The precipitation of vanadium carbonitrides maintains stable high-temperature strength even at 400°C.
3. Q: What are the key heat treatment processes for 6120? A: Key processes include: oil quenching at 860-890°C (vanadium increases the austenitizing temperature); adjusting the tempering temperature based on performance requirements (hardness increases by approximately 2 HRC for every 50°C decrease); and pre-cold quenching of large-section parts to minimize distortion. Preheating to 250-300°C is required for welding, and stress relief annealing at 600-650°C is mandatory after welding. Tempering within 4 hours after quenching is particularly important to avoid the risk of hydrogen embrittlement.
4. Q: What are the advantages of 6120 compared to 4130 steel? A: 6120, due to its vanadium and higher chromium content, offers improved fatigue strength (approximately 20%-30% higher) and high-temperature oxidation resistance, while maintaining similar weldability. While 4130 is less expensive, 6120 offers a longer service life under alternating loads, making it particularly suitable for critical moving parts such as aircraft engine connecting rods.
5. Q: What are the main applications for 6120 steel pipe? A: Primarily used in high-end applications such as aircraft engine crankshafts, high-performance racing drive shafts, oil drilling tool joints, and suspension components for military armored vehicles. It excels in demanding operating conditions requiring high strength, fatigue resistance, and high-temperature resistance (≤450°C). Surface nitriding is recommended to further enhance wear resistance.
