1. Q: What are the material properties of 8115 steel pipe?
A: 8115 is a medium-carbon chromium-molybdenum alloy structural steel (corresponding to AISI 8115), with a carbon content of 0.13%-0.18%, a chromium content of 0.70%-0.90%, and a molybdenum content of 0.15%-0.25%. Its core properties are:
Highly balanced strength and toughness: Quenching and tempering can achieve an excellent combination of strength and toughness;
Good hardenability: Suitable for uniform hardening of medium-section parts;
Optimized weldability: Low carbon content reduces cold cracking tendency, but preheating (150-200°C) is still required;
Fatigue resistance: Fatigue life is 2-3 times longer than that of ordinary carbon steel.
2. Q: What are the typical mechanical properties of 8115 steel pipe?
A: Typical properties in the quenched and tempered (quenched + tempered) state are:
Tensile strength: 850-1000 MPa
Yield strength: 700-850 MPa
Elongation: ≥14% (gauge length 50 mm)
Impact energy (room temperature): ≥40 J
Hardness range: HRC 25-32 (adjusted by tempering temperature).
3. Q: What are the key points in the heat treatment process for 8115?
A: Key process controls include:
Quenching: Oil quenching at 880-910°C to ensure complete austenitization;
Tempering: 550-650°C (low-temperature tempering increases strength, high-temperature tempering enhances toughness);
Post-weld treatment: Stress relief annealing at 600-650°C x 1 hour/25 mm is mandatory;
Defects to avoid: Slow cooling in the 350-550°C range is strictly prohibited to prevent temper brittleness.
4. Q: What are the advantages of 8115 compared to 4130 steel? A: Differentiated advantages of 8115:
Low-carbon design (0.13%-0.18% vs. 4130's 0.28%-0.33%): Improved weldability and cold formability;
Cost-effectiveness: Lower molybdenum content, suitable for mass production;
Fatigue performance: The synergistic effect of chromium and molybdenum improves life under alternating loads.
Limitations: High-temperature strength slightly lower than 4130 (caution is advised when using above 400°C).
5. Q: What are the main applications of 8115 steel pipe?
A: Typical applications include:
Automotive: High-performance drive shafts and steering knuckles;
Engineering machinery: Hydraulic cylinders and excavator connecting rods;
Energy equipment: Shale gas wellhead valve bodies;
Military components: Light armored vehicle suspension components.
