1. Q: What are the material properties of 6118 steel pipe? A: 6118 is a medium-carbon chromium-molybdenum alloy structural steel (corresponding to AISI 6118), with a carbon content of 0.16%-0.21%, a chromium content of 0.70%-0.90%, and a molybdenum content of 0.15%-0.25%. It is characterized by high strength, good hardenability, and excellent fatigue properties, making it particularly suitable for components subject to alternating loads. Compared to ordinary carbon steel, 6118 offers superior high-temperature strength and corrosion resistance.
2. Q: What are the typical mechanical properties of 6118 steel pipe? A: After quenching and tempering (quenching + tempering), typical properties are: tensile strength 850-1000 MPa, yield strength 700-850 MPa, elongation ≥14%, and impact energy (room temperature) ≥40 J. A balance between strength and toughness can be achieved by controlling the tempering temperature (typically 550-650°C). The hardness range is generally HRC 25-32.
3. Q: What are the key points of the heat treatment process for 6118? A: Key processes include: oil quenching at 850-880°C to ensure complete austenitization; tempering temperature is selected based on performance requirements (low-temperature tempering increases strength, high-temperature tempering enhances toughness); and extended holding time is required for large-cross-section parts. Preheating to 200-300°C is required before welding, and stress relief annealing (600-650°C) is required after welding. Particular care should be taken to avoid slow cooling in the 350-550°C range to prevent temper brittleness.
4. Q: What are the advantages of 6118 compared to 4140 steel? A: 6118 has a lower carbon content (0.16%-0.21% vs. 0.38%-0.43%), resulting in better weldability and cold formability. It also maintains good high-temperature strength due to its molybdenum content. 4140 is more suitable for applications requiring high hardness, while 6118 is more suitable for components requiring a combination of mechanical properties and machinability.
5. Q: What are the main applications of 6118 steel pipe? A: Widely used in automotive drive shafts, hydraulic rods for construction machinery, oil drilling equipment components, and aerospace structural parts. It is particularly suitable for critical components subject to impact loads and fatigue stress, and maintains excellent performance even in high-temperature environments (≤400°C). Surface treatment (such as nitriding or galvanizing) is recommended to enhance corrosion resistance.
