Ferrous Materials and Non-Ferrous Metals and Alloys 1 introduction

(3) Nitriding:

 This process of surface hardening is used to obtain hard surface of steel

components only. The technique is normally employed for those steels which are alloyed

with aluminium, chromium, molybdenum and manganese, etc. The nitriding operation

---

Ferrous Materials and Non-Ferrous Metals and Alloys

29

is the last operation being performed after performing operations such as oil hardening

at 840°C to 900°C, tempering, rough machining, stabilizing (for removing internal stresses)

final machining of the components. The machined and finished steel components are

placed in an airtight container of nickel chromium steel provided with inlet and outlet

tubes through with NH

3

 is circulated. The process is carried out at 450°C to 540°C. The

NH

3

 in the furnace gets dissociated to liberate nascent nitrogen which reacts with the

surface of components and form nitrides which are very hard.

The nitriding process is used in the production of machine components which require

high wear resistance at elevated temperatures such as pump shafts, gauges, drawing

dies, gears, mandrels, automobile and aeroplane valves, crankshafts and cylinder lines.

It also finds applications in the production of ball and roller bearing parts.

Advantages

(1) Very high surface hardness with good wear resistance.

(2) Due to elimination of quenching, the distorsion and cracks are minimum.

(3) Economical for base production and machining and finishing is completed for

applying this method.

(4) Nitrided components retain hardness upto 510°C.

Limitations

(1) The operation time is long for small depth of case hardened component and may

lead to oxidation.

(2) Applicable for limited steels only as discussed above which can form good nitrides.