A 4140 Alloy Steel Screw Can Be Nitrided Satisfactorily, However, A Nitriding Steel (such As Nitralloy 135M) Has Aluminum Added To Give A Better Response In Nitriding Hardness, Both As To Consistency And Depth. There Are Two Types Of Nitriding That Are Common To Screw Manufacture: Gas Nitriding And Ion Nitriding.Gas Nitriding Is Used To Create A Surface Hardness On The Screw. The Hard Layer Of Steel Will Vary In Depth From .007” To .015” Depending Upon The Length Of The Nitriding Cy... Read more