Nitriding Technical Data
Materials and the method of enhancing component life through heat treatment should be considered at the design stage. All too frequently we have to refuse requests to nitride unsuitable materials where no thought has been given to the possible distortion resulting from an alternative surface hardening process. Other, superficially cost-effective methods of enhancing surface hardness (or case hardness), involve much higher temperatures than nitriding. Also, the distortion-inducing thermal shock caused by rapid cooling is often overlooked. The cost of remedial work following an inappropriate method of surface hardening can, in many cases, render the “cheap” solution uncompetitive.
Very basically, the process
works by the load components absorbing some of the nitrogen present in the
furnace atmosphere (at the process operating temperature).
Virtually all steels nitride
to some extent but to provide a useful increase in surface hardness certain
amounts and
types of alloying elements need to be present, generally Chromium, Molybdenum
and in some cases Aluminium, Vanadium and Tungsten.
Surface hardness achieved is due to this alloy content/combination and is not greatly adjustable because of the narrow process temperature band. Case depth can be varied by extending or reducing cycle time. Longwear offers cycle times from 12 to 90 hours duration on a regular, scheduled basis. The case properties achievable with commonly nitrided materials can be seen in the chart below:
|
CYCLE TIME |
MATERIAL |
|||||
| BS
970: |
BS970 817M40 (EN24) |
BS
970: 722 M24 (EN40B) |
BS
970: 905 M39 (EN41) |
Tool
Steel P20 |
Tool
Steel H13 (5% Chrome) |
|
| 12 |
.006/.010" (.15/.25mm) |
.006"/.008"
(0.15/0.2mm) |
.005/.006"
(.125/.15mm) |
.006/.008" (.15/.2mm) |
.008"
(0.2mm) |
c.004"
(c.0.1mm) |
| 24 |
.010/.014"
(.25/.35mm) |
.010/.014"
(.25/.35mm) |
.008/.010"
(.2/.25mm) |
.010/.012"
(.25/.3mm) |
.012"
(0.3mm) |
c.0.006"
(c.0.15mm) |
| 45 |
.018/.024"
(.45/.6mm) |
.018/.024"
(.45/.6mm) |
.012/.014"
(.3/.35mm) |
.016/.018"
(.4/.45mm) |
.016"
(0.4mm) |
c.0.010"
(c.0.25mm) |
| 70 |
.024/.028"
(.6/.7mm) |
.024/.028"
(.6/.7mm) |
.014/.016"
(.35/.4mm) |
.020/.022"
(.5/.55mm) |
.02"
(0.5mm) |
c.012"
(c.0.3mm) |
| 90 |
.028/.036"
(.7/.9mm) |
.028/.036"
(.7/.9mm) |
.016/.020"
(.4/.5mm) |
.022/.026"
(.55/.65mm) |
.024"
(0.6mm) |
c.016"
(c.0.4mm) |
| VICKERS Surface Hardness ROCKWELL "C" |
550 - 650 52 - 58 |
510 - 550 50 - 52 |
750 - 950 62 - 68 |
950 - 1150 68 - 71 |
650 - 700 58 - 60 |
1000 - 1250 69 - 72 |
12 hour cycles -
24 hour cycles -
45 hour cycles -
90 hour cycles -
5 loads per week (including 1 over weekends)
4 loads per week (including 1 over weekends)
2 loads per week:
- on every Friday - ready Monday
- on every Tuesday - ready Friday
At least 1 load per week:
- on Thursday - ready Tuesday
We can (and frequently do) provide additional cycles to order.
Many other steels can
be nitride hardened, for example:
D2, P20, D3, L6 and A2 tool steels, also alloy steels such as BS970: 817M40
(EN24)
For advice please contact
us. We offer a full range of furnace cycle times on a regular, scheduled basis.
