EDRO #8^™ is a chromium-alloyed stainless tool steel with the following properties:

• Excellent corrosion resistance
• Superior polishability
• Good wear resistance
• Good machinability
• Stability in hardening

These properties combine to give a steel with outstanding production performance. The practical benefits of good corrosion resistance in a plastics mold can be summarized as follows:

• Lower mold maintenance costs
• The surface of cavity impressions retain their original finish over extended running periods
• Molds stored or operated in humid conditions require no special protection
• Lower production costs
• Since water cooling channels are unaffected by corrosion (unlike conventional mold steels), heat transfer characteristics, and therefore cooling efficiency, are constant throughout the mold life, ensuring consistent cycle times.

These benefits, coupled with the high wear resistance of EDRO #8™ offer the molder low-maintenance, long-life molds for the greatest overall molding economy.

EDRO #8™ is produced using the Electro-Slag-Refining (ESR) technique, resulting in an extremely fine and consistent micro-structure with superior cleanliness.

Physical data

Hardened and tempered to 50 HRC. Data at room and elevated temperatures.

Tensile strength at room temperature

The tensile strength values are to be considered as approximate only. All samples were taken from a bar (in the rolling direction) 25mm (1") diameter. Hardened in oil from 1025 ± 10°C (1880 ± 20°F) and tempered twice to the hardness indicated.

*Soaking time=time at hardening temperature after the tool is fully heated through.

Correct grinding technique will avoid grinding cracks and improve tool life. Tools that have been tempered at low temperatures are especially sensitive during grinding. Only properly dressed, soft, open-grained grinding wheels should be used. Restrict the peripheral speed and use plenty of coolant.

More detailed instructions can be obtained from the grinding wheel manufacturer.

EDRO #8™ has a very homogeneous structure with a very low non-metallic inclusion content making it suitable for photo-etching. The special photo-etching process that might be necessary because of EDRO #8™ has good corrosion resistance is familiar to all the leading photo-etching companies.

EDRO #8™ has very good polishability in the hardened and tempered condition. Example of a typical polishing procedure:

• Use a grinding wheel or stone with a grain size of 180-320 for initial grinding or stoning.
• Use abrasive paper or powder with a grain size of 400-800.
• Polish with a diamond paste of a grain size between 12.6 and 3 µm using a polishing tool of soft wood or fiber.
• When a very high surface finish is demanded, use diamond paste of 1 µm grain size with a fibre polishing pad.

While EDRO #8^™ is recommended for all types of molding tools, its special properties make it particularly suitable for molds with the following demands:

• Corrosion/staining resistance, i.e., for molding of corrosive materials, e.g. PVC, acetates, and for molds subjected to humid working/storage conditions.
• Wear resistance, i.e., for molding abrasive/filled materials, including injection-molded thermosetting grades. Also for molds with exceptionally long production runs, e.g. electrical/electronic parts; disposable cutlery and containers.
• High surface finish, i.e., for production of optical parts, such as camera and sunglass lenses, and for medical containers, e.g. syringes, analysis phials.

EDRO #8™ is resistant to corrosive attack by water, water vapor, weak organic acids, dilute solutions of nitrates, carbonates and other salts.

A tool made from EDRO #8™ will have good resistance to rusting and staining due to humid working and storage conditions and when molding corrosive plastics under normal production conditions.

EDRO #8™ shows the best corrosion resistance when tempered at about 250°C (480°F) and polished to a mirror finish.

Soft annealing

Protect the steel and heat through to 780°C (1440°F). Then cool in the furnace at 10°C (20°F) per hour to 650°C (1200°F), then freely in air.

Stress-relieving

After rough machining, the tool should be heated through to 650°C (1200°F), holding time 2 hours. Cool slowly to 500°C (930°F), then freely in air.

Hardening

Preheating temperature: 600-850°C (1110-1560°F).

Austenitizing temperature: 980-1050°C (1800-1920°F) but usually 1025°C (1880°F).

Protection against decarburization

Protect the tool against decarburization and oxidation during the hardening process.

Quenching media

• Oil
• Martempering bath at 200-550°C (390-1020°F), for 1-100 minutes, then cool in air.
• Air blast
• Circulating air or atmosphere

Temper the tool as soon as its temperature reaches 50-70°C (120-160°F).

Tempering

Choose the tempering temperature according to the hardness required by reference to the tempering graph. Temper twice with intermediate cooling to room temperature. Lowest tempering temperature 180°C (350°F). Holding time at temperature minimum 2 hours.

Dimensional changes

During hardening

Sample plate, 100 x 100 x 25mm, 4" x 4" x 1"

Welding of tool steel should generally be avoided, due to the risk of cracking. Where repair welding is necessary, it is essential to pre-heat the part prior to welding. Immediately after the welding operation:

• Stress-relieve material that has been welded in soft annealed state.
• Temper material twice that has been welded in the hardened and tempered condition.