Anti-Wear Improvement of Stamping Die Materials Through Duplex Chroming

1. Introduction

2. Sample Matrix

3. Test Method

4. Test Results

5. Failure Mechanisms

6. Summary

7. Conclusions

Chrome plating and nitriding have been used to improve the durability and wear resistance of stamping dies.

• Chrome plating….

− is a thin hard coating

− is good for low load wear resistance

− can lower the coefficient of friction

− is not good for high load wear resistance and subject to peeling, chipping,deformation and wear, spalling, etc.

• Nitriding….

− produces a hard iron-nitride layer for improved wear resistance.

− not as good as chrome plating for low load wear resistance

− Better than chrome plating for high load wear resistance where the thicker nitride layer can better absorb vertical and tangential (sliding) loads

Project Hypothesis:

Adding a nitride layer between the chrome plating and the substrate die material can improve sliding-impact wear performance by combining the lower friction of the chrome coating with improved load support of the nitride coating. The combination of chrome

plating over nitriding is called …

Duplex 

Test Set-up

• A = Duplex Chrome: Thick chrome layer over nitrided substrate with a white layer

• B = Duplex Chrome: Thin chrome layer over nitrided substrate without a white layer

• C = Thin chrome plate over a relatively soft substrate

• D = Thin chrome plate over hardened substrate

A = Duplex Chrome: Thick chrome layer over nitrided substrate with a white layer

• The failure modes of all chrome plated samples included fatigue cracking, chipping, peeling, material transfer.

• Most cracks started from the surface of the chrome coating and extended into the interface between coatings and steel substrates.

• Sample A (Duplex Chrome: Thick chrome layer over nitrided substrate with a white layer)

− Appeared to also have cracks initiating from the interface between the coating and substrate, which may be due to the brittle white nitride layer.

− The chrome coating was worn out and the steel substrate was largely exposed at the head and middle regions of wear track.

Sample B (Duplex Chrome: Thin chrome layer over nitrided substrate without a white layer)

− Performed the best

− Seemed to have only a chipping problem at the middle region of the coating’s wear track and the steel substrate was not exposed at any of the test cycles.

• Sample C (Thin chrome plate over a relatively soft substrate)

− Showed large cracks and the coating peeled everywhere. The chrome coating seemed to have a good adhesion to the substrate but the relatively soft substrate was deformed (sunk in).

− Long-term durability of this surface treatment appears problematic.

Sample D (Thin chrome plate over hardened substrate)

− Showed a large transfer of material at the middle and head regions of the wear track.

− The steel substrate was locally exposed where the coating was worn off mainly by chipping and peeling.

• Duplex chrome surface treatments without a nitriding white layer can

significantly increase the wear resistance and durability of stamping die steels

• The ranking of all the S0050A samples:

at 150 test cycles: B ≥ A > C > D

at 300 test cycles: B > D > C > A

at 500 test cycles: B > D > C > A

at 3000 test cycles: B > D > C > A

Conclusions

A = Duplex Chrome: Thick chrome layer over nitrided substrate with a white layer

B = Duplex Chrome: Thin chrome layer over nitrided substrate without a white layer

C = Thin chrome plate over a relatively soft substrate

D = Thin chrome plate over hardened substrate