1. Process Selection and Parameter Optimization
Quenching and Tempering Treatment (Quenching + Tempering):
Quenching temperature is controlled at 920-950℃ (e.g., 45# steel), and the cooling rate of salt water quenching needs to be ≥200℃/s to ensure complete transformation of austenite into martensite.
Tempering temperature is 550-630℃, and the holding time is calculated at 1.5 minutes per millimeter of wall thickness, forming a uniform tempered sorbite structure, with impact energy at -20℃ ≥40J.
Normalizing Process: Heated to 850±10℃ and then air-cooled, achieving a grain size of ASTM 7-8, laying the organizational foundation for subsequent quenching.
2. Cooling Medium and Technological Innovation
Composite Quenching Liquid: Using a sodium chloride-nanosilicon carbide mixed quenching liquid (e.g., patent CN119979840A) to improve low-temperature impact resistance.
Controlled Cooling Technology: Graded cooling (fast cooling at 15-20℃/s to 600℃ followed by slow cooling) to avoid cracking caused by structural stress.
3. Microstructure Control
Grain Refinement: Through controlled rolling and controlled cooling (TMCP), the grain size reaches ASTM 8 or higher, increasing fatigue life by 75%.
Inclusion Management: Using magnesium-carbon refractory materials, the non-metallic inclusion level is controlled below 1.5.
4. Adaptation to Special Needs
Low-Temperature Environment: Adding nickel (Ni) or niobium (Nb) elements, with impact energy at -60℃ ≥60J (e.g., L245NS material).
Wear Resistance Requirements: Surface hardening (induction hardening) to achieve a hardness of HRC55-60, increasing fatigue strength by 2-3 times.
5. Balancing Quality and Cost
Stress Relief Annealing: After cold deformation, hold at 650±10℃ for 1.5-2 hours, with a residual stress elimination rate ≥85%. Energy-saving process: Normalizing instead of annealing reduces costs by 30% and results in superior overall performance.
