Manufacturing high-quality 1.2714 die steel (56NiCrMoV7) requires strict production process control and multi-link quality management. The following are its key manufacturing processes and technical points:

1. Raw Material Selection & Smelting

• Composition control
  Ensure compliance with DIN standards (typical composition: C 0.50-0.60%, Ni 1.50-2.00%, Cr 1.00-1.30%, Mo 0.50-0.70%, V 0.07-0.12%), and accurately control impurity elements (S, P ≤0.03%).
• Melting process
  Use electric arc furnace (EAF) primary refining + secondary refining (LF furnace, VD/VOD vacuum degassing) to reduce the content of gas (O, H, N) and inclusions and improve the purity of molten steel.
• Casting method
  Use mold casting or continuous casting process, and control the cooling rate to avoid segregation. Large ingots need high-temperature diffusion annealing (1100-1200℃ insulation) to eliminate composition inhomogeneity.

2. Forging & Rolling

• Forging temperature
  Heat to 1150-1200℃, final forging temperature ≥850℃, avoid cracks caused by low temperature forging.
• Deformation control
  Multi-directional forging (upsetting + drawing) refines the grains to ensure isotropy of forgings, forging ratio ≥3:1.
• Homogenization treatment
  Immediately after forging, isothermal annealing (650-700℃ slow cooling) is performed to eliminate internal stress and homogenize the structure.

3. Heat Treatment Process

(1) Preliminary heat treatment

• Annealing
  Heat to 780-800℃, keep warm and then slowly cool to below 500℃, hardness ≤250 HB, easy for subsequent machining.
• Spheroidizing annealing (optional)
  For high carbon steel parts, uniform spherical carbides are obtained by cyclic heating (750℃↔680℃).

(2) Final heat treatment

• Quenching
  Preheat to 500-600℃, then heat to 830-860℃ for austenitization, keep warm for a certain time according to thickness (1.5-2 minutes/mm), oil cooling or high pressure gas quenching (avoid water cooling cracking).
• Tempering
  Select the tempering temperature according to the target hardness:
  – 48-52 HRC: temper at 450-500℃ (twice, 2 hours each time).
  – High toughness requirement: temper at 550-600℃ (hardness drops to 42-46 HRC).
  Slow cooling (furnace cooling) is required to prevent temper brittleness.

4. Finishing & Surface Treatment

• Machining
  Rough machining before quenching (leave 0.2-0.5mm), fine grinding/EDM after quenching and tempering.
• Stress relief annealing
  Tempering at low temperature (200-300℃) after finishing to eliminate residual stress.
• Surface strengthening
  – Nitriding treatment: 500℃ gas nitriding, surface hardness ≥1000 HV, improve wear resistance.
  – PVD coating (such as TiAlN): suitable for high-wear molds to extend life.

5. Quality Control & Testing

• Composition analysis
  Spectrometer detects the content of elements such as C, Ni, Cr, Mo, etc.
• Non-destructive testing
  – Ultrasonic flaw detection (UT): detect internal cracks and inclusions.
  – Magnetic particle testing (MT): check surface defects.
• Performance testing
  – Hardness: HRC, HV gradient detection.
  – Impact toughness: Charpy V-notch specimen (room temperature ≥40 J).
  – Metallographic structure: check carbide distribution and grain size (target 10-12 level).

6. Key Process Control Points

•  Purity control: reduce oxide inclusions through vacuum degassing.
• Forging uniformity: avoid banded structure and ensure isotropy.
•  Heat treatment accuracy: temperature control accuracy ±5℃, prevent decarburization (use protective atmosphere furnace).
•  Avoid tempering brittleness: rapid cooling (oil cooling) after tempering should be cautious, furnace cooling is preferred.

Common Problems & Solutions For 1.2714 Steel

• Risk of cracks: fully preheat before quenching to avoid cross-section mutation design.
• Insufficient hardness: check whether the austenitizing temperature is too low or the holding time is insufficient.
• Poor wear resistance: optimize the nitriding process or add surface coating.

Summary

The core of high-quality 1.2714 steel manufacturing lies in:

• Accurate composition + purity
• Uniform forging structure
• Optimized heat treatment process (quenching + tempering curve)
• Strict defect detection

Through the above process, it can be ensured that the 1.2714 steel has high strength, high toughness and thermal fatigue resistance to meet the requirements of harsh industrial working conditions.