MFT8 material is a fine-grained non-quenched and tempered steel wire rod used for manufacturing fasteners. It does not require quenching and tempering processes, which helps avoid overall bending deformation and offers significant energy-saving and consumption-reducing benefits. MFT8 steel wire rod is produced through thermo-mechanical rolling with controlled temperature and cooling. Its resulting microstructure consists of ferrite and pearlite, with an average grain size of grade 12 and a grain dimension of about 5 μm. In addition to high strength and high plasticity, MFT8 steel wire rod also exhibits excellent impact toughness and resistance to low-temperature fatigue, making it particularly suitable for manufacturing 8.8-grade high-strength bolts.When manufacturing fasteners using MFT8 steel wire rod, the total drawing compression ratio is controlled between 22% and 35%, with the optimal total compression ratio being around 30%. This allows the omission of pre-treatment annealing and the quenching and tempering processes, while adding a stabilization and aging treatment process combined with surface treatment. The aging treatment is conducted at temperatures ranging from 200 to 400 °C for 0.5 to 2 hours.The raw MFT8 steel material is a hot-rolled wire rod with a diameter of φ9 mm. Its chemical composition includes: carbon (C) 0.21%, silicon (Si) 0.13%, manganese (Mn) 1.37%, aluminum (Al) 0.047%, niobium (Nb) 0.04%.The ferrite phase in MFT8 non-quenched and tempered steel contains noticeable submicron-scale precipitated particles. These submicron precipitates enhance the strength level of cold-drawn MFT8 non-quenched and tempered steel after aging through second-phase strengthening effects.
SKD-11 is a grade of Japanese tool steel, produced by both Hitachi and Daido Steel mills. The Hitachi-produced SKD-11 is commercially known as SLD (with the latest improved version called SLD-MAGIC), while Daido’s version is called DC11. It is an air-hardening cold work die steel that offers high purity, good high-temperature strength, toughness, and resistance to high-temperature fatigue, and can withstand sudden temperature changes.SKD-11 is a high-wear-resistance, high-toughness general-purpose cold work die steel. It is a high-carbon, high-chromium alloy tool steel and a vacuum degassed refined steel. It features excellent hardenability and minimal quenching deformation. The steel, after undergoing spheroidizing annealing for softening, offers good machinability. Its carbide particles are fine and uniformly distributed, eliminating concerns about quench cracking. The special addition of strengthening elements such as molybdenum and vanadium results in highly wear-resistant, uniformly distributed eutectic carbides. It offers good toughness and is not prone to cracking. After quenching, its hardness exceeds 62 HRC.Under nitriding treatment at 525 °C for durations of 20 h / 30 h / 60 h, the nitrided layer depth reaches 0.25 mm / 0.30 mm / 0.35 mm, and the surface hardness of the parts is 1250 HV. Under soft nitriding treatment at 570 °C for 2 hours, the nitrided layer depth is 10–20 μm, and the surface hardness of the parts is 950 HV.
Carbon (C): 1.40–1.60%, Silicon (Si): ≤0.40%, Manganese (Mn): ≤0.60%, Phosphorus (P): ≤0.030%, Sulfur (S): ≤0.030%, Chromium (Cr): 11.0–13.0%, Molybdenum (Mo): 0.80–1.20%, Nickel (Ni): ≤0.50%, Vanadium (V): 0.20–0.50%, Copper (Cu): ≤0.25%.
SKD-11 is known by different names under various standards. For example:
China GB Standard: Cr12Mo1V
Taiwan CNS Standard: SKD11
Germany DIN Standard Material No.: 1.2601
Germany DIN Standard Grade: X165CrMoV12
Japan JIS Standard: SKD11
Italy UNI Standard: X165CrMoW12KU
Spain UNE Standard: X160CrMoV12
USA AISI/SAE Standard: D3
Russia GOST Standard: X12M
(1) Due to vacuum degassing refining, its internal quality is extremely clean.(2) It has good machinability.(3) It offers excellent hardenability and can be air-hardened without concerns about quench cracking.(4) It has very small heat treatment deformation and minimal quenching deviation, making it ideal for molds with precision requirements.(5) It provides outstanding wear resistance, making it especially suitable for blanking dies for stainless steel or high-hardness materials.(6) It has good toughness.
To achieve maximum hardness and dimensional stability, molds should be immediately subjected to deep cryogenic treatment at -70 °C to -80 °C for 3–4 hours after quenching, followed by tempering. Tools or molds treated with deep cryogenics exhibit a hardness that is 1–3 HRC higher than those treated with conventional heat treatment. However, there is a risk of cracking for parts with complex shapes or large dimensional variations.
After nitriding, a hardened surface layer with high hardness and certain corrosion resistance forms on the mold or workpiece. In the case of nitriding at 525 °C, the surface hardness of the workpiece is approximately 1250 HV, while at 570 °C for soft nitriding, the surface hardness is about 950 HV. Typically, a soft nitriding process lasting 2 hours achieves a hardened layer depth of 10–20 μm.
Quenching:First preheat to 700–750 °C, then heat to 1000–1050 °C and cool in still air. For steel parts thicker than 6 inches, heating to 980–1030 °C and oil quenching is better.Tempering:Heat to 150–200 °C, hold at this temperature, then cool in still air.Hardness:HRC 61 or higher.
Annealing:Heat to 800–850 °C, hold for 1–3 hours, then allow it to cool gradually in the furnace.Quenching and Tempering Specifications:
Quenching Temperature: 1010 °C, air-cooled.
Tempering Temperature: 200 °C, hardness 58–60 HRC.
Tempering:Heat to 150–200 °C, hold at this temperature, then cool in still air.Hardness:HRC 61 or higher.Annealing:Heat to 800–850 °C, hold for 1–3 hours, then allow it to cool gradually in the furnace.Quenching and Tempering Specifications:
Quenching Temperature: 1010 °C, air-cooled.
Tempering Temperature: 200 °C, hardness 58–60 HRC.
