7Cr7Mo2V2Si High-Strength and High-Toughness Cold-Work Die Steel

7Cr7Mo2V2Si (referred to as LD steel) is a high-carbon, high-alloy cold-work die steel independently developed in my country. Its chemical composition design centers on a high chromium content combined with the synergistic strengthening effects of molybdenum, vanadium, and silicon. The specific composition is as follows:
• Carbon (C): 0.65%–0.80%; forms carbides to enhance hardness and wear resistance;
• Chromium (Cr): 6.50%–7.50%; enhances hardenability, corrosion resistance, and wear resistance;
• Molybdenum (Mo): 1.80%–2.50%; refines grain size and improves high-temperature strength;
• Vanadium (V): 1.70%–2.20%; forms high-hardness vanadium carbides (VC, with a hardness of 2800 HV), significantly improving wear resistance;
• Silicon (Si): 0.70%–1.20%; suppresses high-temperature temper brittleness and enhances matrix stability;
• Impurity control: Phosphorus (P) ≤ 0.030%, Sulfur (S) ≤ 0.030%; reduces the tendency toward brittleness.
 
This composition system achieves a synergistic improvement in hardness, toughness, and wear resistance by utilizing high chromium content to form M₇C₃-type carbides, employing a molybdenum-vanadium combination to optimize carbide distribution, and using silicon to enhance tempering stability.
 
Key Performance Characteristics of 7Cr7Mo2V2Si:
1. High Hardness and Wear Resistance:
Achieves a hardness of 58–63 HRC after quenching and tempering; features uniformly distributed vanadium carbides (VC) and offers 30%–40% higher wear resistance than Cr12MoV. It is suitable for high-frequency blanking applications (e.g., blanking 0.5mm stainless steel sheet, with a service life exceeding 500,000 hits per sharpening).
2. Balanced Strength and Toughness:
Impact toughness reaches 25–35 J/cm² (superior to Cr12MoV) and flexural strength ranges from 3800 to 4200 MPa. It overcomes the traditional mold steel dilemma where "high hardness implies brittleness," capable of withstanding cold heading pressures of 3000–4000 MPa without brittle fracture.
3. Thermal Stability and Dimensional Accuracy:
• Short-term heat resistance up to 650°C, with high-temperature strength retention >70%;
• Retained austenite content <3% and low heat-treatment distortion (oil-quench deformation <0.05%), making it ideal for precision mold manufacturing.
4. Processing Adaptability:
Excellent cold and hot workability; compatible with wire-cut EDM and sinker EDM, with a lower risk of cracking compared to DC53 steel; annealed hardness ≤255 HB, facilitating ease of machining.