4140 annealed in nitride process

[marmon]

What happens to 3/4" sq. stock 4140 when it is put through a liquid nitride process. Is the hardness dependant on time? or are results typical to the stock hardness?

 

[swall]

It depends. If the 4140 was quenched, then tempered at say, 800F, the 1000F nitriding temperature will drop the hardness. You would see the most hardness drop after one hour at 1000F. If you nitride as-rolled stock, nothing much will happen to the core hardness.