White Layer in Nitriding

Well as far as I know which is limited in respect to Forging but forging die's need to be constantly checked for dimensional changes and resurfaced once out of parameter and this is standard practice to ensure a constant dimensionally stable part. As to what can be done to ensure longer life, well make two dies and run one until necessary to resurface then swop them around, that would be my solution. Hope this helped

This knowledge is mid- seventies, Oil field tube upsetting dies. We used H-13 tool steel with a heat treat of 38-42 Rockwell C, we then deep nitrided, (.015-.025 inches deep) the punches and die inserts for extending wear. But, we also used water soluable oil coolant to maintain the dies at no more than 120-150 Degrees F. at the surface. We were getting 8,000 hits with the punches and upwards of 15,000 hits on the die inserts. I theorized that the tooling if allowed to exceed 900 degrees (during the forging contact 'hit' then the base metal (H13- at 38-42 Rockwell C ) will begin the anneal and soften, then the nitride 'skin' will crack and the surfaces begin to degrade.

The difficulty was determining when the core temperature of the tool began to reach these higher temperatures. Our cycles were one hit each 10 to 15 seconds, with coolant flow as soon as the forged part left the die area.

Contact me if you have questions. Regards Peter