#135 MODIFIED
| Typical Chemistry | |
| Carbon | 0.40% |
| Manganese | 0.60% |
| Silicon | 0.30% |
| Chromium | 1.60% |
| Molybdenum | 0.35% |
| Aluminum | 1.15% |
| Typical Applications | ||
| Bushings | Pump Parts | |
| Gears | Valve Sleeves | |
| Pinions | Injection Screws | |
- Hardening
Note: Nitriding #135 is usually supplied in the prehardened condition, about 26/30 HRC, ready for nitriding. Further heat treatment is generally not required.
Preheat: 1300/1400F, equalize.
High Heat: 1700/1750, hold 20/45 minutes at temperature.
Quench: Oil quench to 150F. Sections over 2" thick may require water quenching.
Temper: 1100/1200F, hold two hours at temperature, air cool.
Surface Treatments
Nitriding #135 is designed for maximum response to nitriding. Typical case depths and hardnesses are shown below. Consult nitrider for specific nitriding practice used and expected results.
The nitriding treatment is undertaken after all grinding and polishing has been completed. Nitriding is usually done between 950 and 1000F (510 and 540C).
In the design of parts to be nitrided, every effort should be made to eliminate sharp protruding corners and points, since the nitrided case will have a tendency to spall at these locations.
Parts increase slightly in size on nitriding. Experience has shown that the growth is approximately .001 to .002" (.025 to .051mm). This growth is variable and is mainly dependent upon the time and temperatures of nitriding; however, the amount of growth is constant under the same conditions of nitriding. Allowances are sometimes made for the growth in the final grinding or machining operation. Where feasible, however, it is better practice to remove the growth by careful grinding or lapping. This will also have the effect of removing the outer surface of the case with a resulting increase in hardness.
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Case Properties
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| Nitriding Time 950/1000F (hours) |
Approx Case Depth (inches) |
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| 10 | .007 | ||
| 20 | .012 | ||
| 30 | 015 | ||
| 40 | .019 | ||
| 60 | .025 | ||
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| Depth Below Surface* | Hardness | ||
| Inch | mm | HR30N | Vickers |
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| Surface | 86 | 1110 | |
| .003 | .076 | 87 | 1140 |
| .005 | .127 | 86 | 1120 |
| .008 | .203 | 84 | 1040 |
| .010 | .254 | 82 | 950 |
| .015 | .381 | 70 | 600 |
| .020 | .508 | 62 | 420 |
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* Nitrided at 975F (525C) for 48 hrs.
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At times, distortion may take place in the nitriding treatment. This is usually due to design and may occur even after proper stress relieving. In this case, straightening should be done while the parts are still warm or after reheating to temperatures up to 1200F (650C).
Annealing
Heat to 1450F, hold 2 hours, cool slowly (50F/hr maximum) to 1200F, air cool.
Typical annealed hardness: 187/229 BHN.
Stress Relieving
Annealed Material: Heat 1200/1250F, hold 2 hours, cool in still air.
Hardened Material: Heat to 50F below tempering temperature, (1000/1100F if tempering temperature not known). Hold 2 hours. Cool in still air.
Welding
Nitriding #135 is a modification of 4140, and similar filler material and welding practices are satisfactory. Nitriding #135 contains about 1% aluminum, which may cause excess slag or oxide formation during welding.
Annealed Material: Preheat to 500/600F. Maintain above 500F during welding. Reanneal or temper 1300, 2 hours.
Hardened Material: Preheat to 50F below tempering temperature (400F minimum). Maintain above 400F during welding. Cool to 150F. Temper 50F below original tempering temperature.
Physical Properties
Modulus of Elasticity ...................................................................30 psi x 106
Density ..............................................................................................0.28 lb/in3
Thermal Conductivity .............200F.......................................24 BTU/hr/ft/°F
Thermal Expansion
RT - 250F .......................................................................7.0 X 10-6 in./in./°F
RT - 400F ......................................................................7.1 X 10-6 in./in./°F
RT - 800F .....................................................................7.25X 10-6 in./in./°F