Carburising

Q: Why are we experiencing intermittent distortion on carburising some components manufactured from EN 36 (832M13) steel?
This 3% nickel–chrome–molybdenum steel is used when a core strength of 55 to 80 tons/sq.in is required along with a case hardness of around 60 Rockwell C.
Distortion can arise from:
• Heavy machining prior carburising
• Retained austenite on quenching
• Poor design
• Metallurgical anomalies in the steel.

Q: Why are we getting a non uniform surface hardness on carburising EN39 (835M15) grade steel?
This is most likely due to the presence of retained austenite on heat treatment. It is recommended that the steel is carburised and hardened in two separate cycles.

Q: We are looking for an alternative to EN34 (665M13) because of the nickel surcharge. What is available?
An alternative grade depends on the size of the component. However it is likely that a steel to AISI 8620 should form a cheaper alternative and yet produce the required properties. Similar carburising and heat treatment parameters are applicable to both steels.

Q: Can I carburise EN27 (830M31)?
This grade of steel can be successfully carburised. It is basically a 0.30%C version of carburising grade EN36 (832M13).
A greater carbon potential must be used in order to drive the carbon into the surface and a two stage treatment is recommended to overcome any potential problems with retained austenite.

Q: Can EN40B (722M24) be nitrided successfully?
Although EN 40B is often used in the un-nitrided condition for applications requiring high tensile strength at temperatures up to 600ºC, it is intended to be nitrided to improve wear and corrosion resistance.
Nitriding is usually carried out at temperatures around 500ºC and prior tempering should have been done at a higher temperature.

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