420 ESR Steel

420 ESR (ESR = Electro Slag-Refined or Remelted), a corrosion-resistant cold work steel, belonging to the plastic mold steels, with a high chromium content it has very good corrosion resistance (in its hardened condition) and good wear resistance. It can easily be machined and is, due to the purity of the ESR material highly polishable. With high compression strength and high wear resistance, the low-distortion through-hardener is suitable for injection molds of all types where good resistance to chemical aggressive molding compounds are required.

The re-melting process provides this steel with a very low inclusion content, which makes it possible to provide a mirror finish when used for instance for lens molds or photoetching.

Applications

Applications with corrosion or staining resistance, e.g. for molding of corrosive materials like PVC, acetates, and for molds subjected to humid working conditions.

Applications with wear resistance, e.g. for molding abrasive materials.

Applications with high surface finish, e.g. for the production of optical parts, such as lenses for cameras and sunglasses, and for medical containers.

Corrosion resistance

420 ESR is corrosion resistant in water, steam, mild organic acids, diluted solutions of nitrates, carbonates and other salts.

Heat treatment

Annealing

Heat the material thoroughly to 1630°F (890°C). Then furnace cool slowly to 1290°F (650°C) and then air cool to room temperature.

Stress relieving

After machining 420 ESR heat the part through to 1200°F (650°C) and hold for 2 hours. Cool down to 930°F (500°C) and then cool further in air.

Hardening

Preheat the part to 1110-1560°F (600-850°C).

To austenitize the material heat to 1850-1952°F (1010-1067°C).

Quenching media

• Fluidized bed or salt bath at 480-1020°F (250-550°C), then cool in air blast
• Vacuum with sufficient positive pressure
• Warm oil, approx. 176°F (80°C)

Cool quickly to obtain the best properties for the tool, but care should be taken that the rate of cooling is not as fast as to distort or crack the material. It is recommended when heat treating in a vacuum furnace to use a minimum of 4-5 bars of overpressure.

Then temper immediately when the parts reach the temperature of 120-160°F (50-70°C).

Tempering

Choose the tempering temperature that needs to be achieved, temper twice and cool between tempering to room temperature.

Do not let the tempering temperature drop below 480°F (250°C) and hold at the chosen temperature for a minimum of 2 hours.  The temperature of 480°F (250°F) is recommended to achieve the best blend of hardness, toughness as well as corrosion resistance.

For our tempering diagram, please click here

Dimensional changes

Depending on temperature, type of equipment and cooling media used during hardening and tempering, dimensional changes may vary.

Machinability

Welding

Welding should be avoided, if possible, due to the high risk of cracking.

Should welding be essential, heat material through to 392-482°F (200-250°C) and hold at that temperature to prevent cracking. After welding, temper hardened material at 50-70°F (10-20°C) below the original tempering temperature. For soft annealed material heat through to 1630°F (890°C) in a protected atmosphere. Then furnace cool at 40°F (20°C) per hour to 1560°F (850°C) and then at 20°F (10°C) per hour to 1290°F (700°C). From there it can be cooled further in air. 

Fillers with the same composition as the base metal should be used.

Photo-etching

Due to the ESR process, 420 ESR has a very low inclusion content and makes it therefore suitable for photo-etching.

Grinding and polishing

To grind this material, use only well honed, soft grinding wheels. Use medium speed and sufficient lubricant. It can be polished when soft annealed and even better when hardened. Polishing should be done in smaller steps and stopped immediately as soon as the last scratch has been removed.