Heat Treatment of SKD-11 Die Steel

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SKD11 is made of cold working die steel, high carbon and high chromium alloy tool steel and vacuum degassing refining steel. The steel is pure and has good hardenability with good hardenability and small quenching deformation. After spheroidizing annealing and softening treatment, the steel has good machinability, fine and uniform carbide particles, and does not need to worry about the special addition of molybdenum and vanadium strengthening elements for quenching cracking.

SKD11 is produced in Hitachi and Datong Steel Works. Hitachi’s SKD11 is named SLD (the latest improved version is called SLD-MAGIC), and Datong Steel Company’s product is named DC11. Both of them have factories in China. They are most famous in the industry and have the highest price. SKD11 is an air-cooled hardening cold working die steel widely used in the world. After smelting in electric furnace and electroslag resolving, it has high purity, better toughness, uniform structure, good high temperature strength, toughness and high temperature fatigue resistance, and can withstand temperature abrupt change.

Eutectic carbides with high hardness and wear resistance are uniform, tough and not easy to crack. Hardness after quenching is higher than 62HRC. The nitriding treatment time at 525 ~C is 20h/30h/60h, the depth of nitriding layer is 0.25mm/0.30mm/0.35mm, and the surface hardness of parts is 1250HV. The nitriding treatment time at 570 ~C is 2h, the depth of nitriding layer is 10~20um, and the surface hardness of parts is 950HV.

Corresponding brand
China GB Standard Brand Cr12Mo1V, Taiwan cNS Standard Brand SKD11, Germany DlN Standard Material Number 1.26o1, Germany DIN Standard Brand x165CrM0v12, Japan Jis Standard Brand sKD11, Korea Ks Standard Brand sTD11, Italy UN1 Standard Brand x165CrM0W12KU, Sweden Standard Brand 2310, Spain UNE Standard Brand X160CrM0V12, USA AISi/sAE Standard Brand D2, Russia Standard brand x12M.

Characteristic
1. Good high temperature strength and toughness, good wear resistance and easy cutting;
2. SKD11 is a kind of cold die steel with good strength, toughness and heat-resistance balance. In recent years, with the development of isotropic products, it has been developing towards high toughness. It can make the die life longer, performance more stable, easy to process and heat treatment deformation smaller.

SKD-11 Product Characteristics

(1) Vacuum degassing refining has been carried out, so the internal quality is extremely clean.
(2) Good machinability.
(3) Good hardenability, air cooling can harden, without fear of quenching.
(4) The heat treatment deformation is very small, the quenching deviation is very small, and it is most suitable for the die with precision requirements.
(5) The wear resistance is excellent, and it is most suitable for the punching die of stainless steel or high hard material.
(6) Good toughness.

Cryogenic treatment
In order to obtain the highest hardness and dimensional stability, the die is cooled immediately after quenching from – 70 degrees Celsius to – 80 degrees Celsius, maintained for 3 – 4 hours, and then tempered. The hardness of the tool or die after cryogenic treatment is 1 – 3 HRC higher than that of conventional heat treatment. For parts with complex shape and large size change, cryogenic treatment is dangerous to crack.

Nitriding treatment
After nitriding, a layer of hardened structure with high hardness and corrosion resistance is formed on the surface of the die or workpiece.
Nitriding at 525 Temperature
The surface hardness of the workpiece is about 1250HV. The effect of nitriding time on the nitriding layer is shown in the table below. Nitriding time (hour) 2030 60 Nitriding layer depth mm 0.250.300.35
Soft Nitriding Treatment at 570 Temperature
The surface hardness of the workpiece is about 950HV. The depth of hardening layer can reach 10-20um after 2 hours of soft nitriding treatment. Grinding of die blanks or working in low temperature tempering state can easily lead to grinding cracking. In order to prevent cracks from occurring, small grinding feed should be used for multiple grinding, and good water cooling conditions should be added at the same time.
When WEDM is used to process dies with complex shapes or large sizes, cracking usually occurs when WEDM is used in the final line.
In order to prevent cracking, gas quenching and high temperature tempering are recommended to reduce heat treatment stress or to pre-process the mould embryo cavity.

Heat Treatment of SKD-11
Quenching: Preheat 700-750 C, then heat to 1000-1050 C and cool in static air. If the thickness of steel tool is more than 6 inches, it is better to heat to 980-1030 C and harden in oil.
Tempering: Heating to 150 – 200 C, staying at this temperature, then cooling in still air.
Hardness: HRC 61 or above.
Annealing: Heating to 800-850 C, staying at this temperature for 1-3 hours, let it gradually cool in the furnace.
Forging: 1050 – 950 C.
Specification for quenching and tempering
Quenching temperature 1010 C, air cooling, tempering temperature 200 C, hardness 58 ~ 60HRC.

SKD-11 uses
SKD11 is the most widely used die material for aluminium and zinc die casting. It contains tungsten high temperature resistant alloy steel. It is suitable for hot working, aluminium, magnesium, zinc, copper alloy die casting die, grooving knife, scissors and hot forging action, plastic mould, hot working reamer, rolling knife, general hot forging die, hot bolt die, hot-room tools, etc.

Usage method
Use under the condition of “quenching + tempering”
“Quenching + cold treatment + tempering” condition (suitable for high precision and dimensional stability requirements)
“Quenching + tempering + nitriding” condition (suitable for high surface hardness requirements)
The sawing speed should not be too fast when cutting material. The sawing efficiency should be kept in the range of 9cm2/min to 20cm2/min when the sawing speed is 25m/min.

Typical Application of SKD-11
Used for making plastic moulds, scissors, circular saws, metal stamping moulds, forming rolls
Making cold or hot work dressing die, drum edge, filament pattern, wire die, transformer core punching die, cutting steel skin rolling knife, steel tube forming drum, special forming drum, nail punching die, etc.
High-efficiency blanking die, blanking die and impression die for thin steel plate with thickness less than 6 mm
Various scissors, inlaid parts, thread rubbing dies.
Cold upsetting die, deep drawing forming die and cold extrusion die.
Thermosetting resin moulds, general plastic moulds.