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Plasma Nitriding

 

The plasma nitriding (also known as ion nitriding, pulsed plasma nitriding) is a thermochemical heat treatment process used for increasing the reliability and wear resistance of mechanically stressed metal parts. It improves the fatigue strength and corrosion resistance of materials in a particularly gentle manner. Under the effect of heat a chemical conversion of the surface layer takes place by diffusion of nitrogen that forms nitrides together with the material. This leads to increased surface hardness and a considerably improved resistance to wear. The treatment of parts is carried out at significantly lower temperatures compared to conventional hardening processes. A comparison overview can be found here.

Since no time-consuming post-processing of hardened parts is required or it is reduced to a minimum, additional cost savings within the process chain can be achieved. The treated material can often be processed in the unhardened state to the final dimensions and finished without any post-processing or with just a little post-processing work. Furthermore, very low annealed, tempered steels can be treated without losing the core strength. Generally, various methods can be used for nitriding. Besides the plasma nitriding, such methods as bath nitriding or gas nitriding are also known.

 

Advantages of plasma nitriding and our plasma treatment systems:

  • Final cleaning of treated parts in the plasma
  • Depassivation of the surface and thus a good treatability of high-alloy steels
  • Low process temperatures
  • Low distortion
  • Layer structure can be adapted to the stress
  • Layers are less brittle and porous than with gas and bath nitriding
  • Shorter treatment times than with gas nitriding
  • Post-processing work is minimized
  • No post-cleaning required


A post-nitriding machining is often not required. The nitride layers essentially consist of the outer compound or white layer that may have a thickness of up to about 20 µm .
This layer consists of iron nitrides - the nitrogen-rich ε-nitride Fe2-3N and the iron rich γ`-nitride Fe4N.
The compound layer formed by plasma nitriding is more compact and less porous, thus offering better layer properties compared to gas nitriding. Beneath the compound layer the diffusion layer (DL) is located which consists of the base material with precipitated nitrides. The attainable hardness at the surface is the higher, the more nitride-forming elements are in the steel. This is the reason why non-alloyed steels attain a surface hardness of only 250 - 300 HV while low-alloy steels may have a hardness of 600 - 700 HV and nitrided and high-alloy steels even of 800 - 1,200 HV.

The characteristic value of nitriding hardness depth (NHD) is defined as the distance from the surface in which the hardness exceeds the hardness of the core by 50 HV (according to DIN50190 part 3). Typical NHD values of non-alloyed and low-alloy steels are up to 0.8 mm and may reach up to 0.15 mm in high-alloy steels.

The process of plasma nitriding is a vacuum-based principle. The parts to be treated (as charge) form the cathode and the furnace wall is the anode. After evacuation, an electric field is applied between the charge and the furnace wall. The treatment gas supplied is ionized in the electric field. The nitrogen ions are accelerated towards the cathode and hit the workpiece surfaces with high energy.

 

This leads to:

  • Fine cleaning of surfaces due to sputtering of impurities
  • Dissolution of passive layers (e.g. on stainless steels and titanium)
  • Heating up of parts
  • Diffusion of nitrogen into the workpieces at sufficient temperatures


Once the treatment temperature is reached, the holding time begins. Its duration depends on the type of material and desired nitriding hardness depth. Typical holding times are between 12 and 50 hours. Compared to the gas nitriding, approximately only half the holding time is required.
    
After the appropriate treatment time, a pressure equalization is carried out by flushing with a gas. Then the charge cools down in a controlled manner.

Selection of nitratable steels and treatment results



Material

Material no.

Hardness HV 1

NHD in mm

CL in µm

 

Nitrided steels

32 CrMoV 12 10

1.7765

750 - 1000

0,3 - 0,6

4 - 8

34 CrAl 6

1.8504

900 - 1200

0,3 - 0,5

6 - 10

34 CrAlMo 5

1.8507

900 - 1200

0,3 - 0,5

6 - 10

41 CrAlMo 7

1.8509

800 - 1000

0,3 - 0,5

6 - 10

31 CrMoV 9

1.8519

750 - 1000

0,3 - 0,5

4 - 8

34 CrAlNi 7

1.8550

900 - 1250

0,3 - 0,6

6 - 10

34 CrAl 6

1.8506

900 - 1200

0,3 - 0,6

6 - 10

31 CrAlV 9

1.8523

900 - 1200

0,3 - 0,6

6 - 10

31 CrMo 12

1.8515

800 - 1100

0,3 - 0,5

4 - 8

Case-hardened steels

Ck 15

1.1141

250 - 350

0,3 - 0,6

8 - 12

14 NiCr 15

1.5752

500 - 650

0,3 - 0,5

4 - 8

21 MnCr 5

1.2162

600 - 750

0,3 - 0,6

4 - 8

16 MnCr 5

1.7131

600 - 750

0,3 - 0,6

4 - 8

Quenched and tempered steels

Ck 45

1.1191

300 - 550

0,3 - 0,6

8 - 12

Ck 60

1.1221

300 - 550

0,3 - 0,6

8 - 12

40 CrMnMo 7

1.2311

700 - 850

0,3 - 0,6

6 - 8

40 CrMnMoS 8 6

1.2312

700 - 850

0,3 - 0,6

6 - 8

45 NiCr 6

1.2710

600 - 800

0,3 - 0,5

6 - 8

34 CrNiMo 6

1.6582

600 - 800

0,3 - 0,5

3 - 6

42 CrMo 4

1.7225

600 - 750

0,3 - 0,5

4 - 8

ETG® 100

 

400 - 650

0,3 - 0,5

4 - 8

39 CrMoV 13-9

1.8523

800 - 950

0,3 - 0,5

4 - 8

Structural steel

S 235

1.0038

200 - 350

 

4 - 8

S 355

1.0576

300 - 550

0,3 - 0,5

4 - 8

Hot work steels

X 38 CrMoV 5 1

1.2343

900 - 1250

0,2 - 0,4

4 - 6

X 40 CrMoV 5 1

1.2344

900 - 1250

0,2 - 0,4

4 - 6

X 32 CrMoV 3 3

1.2365

800 - 1000

0,2 - 0,4

4 - 6

X 3 NiCoMoTi 18-9-5

1.2709

800 - 1200

0,15 – 0,3

2 - 4

 






Material

Material no.

Hardness HV 1

NHD in mm

CL in µm

 

Cold work steels

X 210 Cr 12

1.2080

900 - 1200

0,1 - 0,15

2 - 4

X 100 CrMoV 5 1

1.2363

1000 - 1200

0,2 - 0,4

4 - 6

X 155 CrVMo 12 1

1.2379

900 - 1200

0,2 - 0,4

4 - 6

X 210 CrW 12

1.2436

700 - 900

0,15 - 0,3

2 - 4

X 165 CrMoV 12

1.2601

900 - 1200

0,15 - 0,2

2 - 4

X 45 NiCrMo 4

1.2767

700 - 900

0,15 - 0,3

2 - 4

90 MnCrV 8

1.2842

500 - 650

0,3 - 0,4

4 - 8

115 CrV 3

1.2210

350 - 500

0,3 - 0,4

4 - 6

62 SiMnCr 4

1.2101

500 - 600

0,3 - 0,6

4 - 8

High-speed steels

S 10-4-3-10

1.3207

1000 - 1400

0,05 - 0,25

= 2

S 6-5-2

1.3343

1000 - 1400

0,05 - 0,25

= 2

Maraging steels

X 2 NiCrMo 18 8 5

1.6359

1000 - 1200

0,15 - 0,3

1 - 2

Heat-resistant steels

X 15 CrNiSi 25 20

1.4841

800 - 1100

0,1

 

X 12 CrNi 25 21

1.4845

800 - 1100

0,1

Rust and acid resistant steels

X 40 Cr 14

1.2083

1000 - 1200

0,15

 

X 38 CrMo 16

1.2316

900 - 1200

0,15 - 0,3

 

X 20 Cr 13

1.4021

1000 - 1200

0,15

 

X 46 Cr 13

1.4034

1000 - 1200

0,15

 

X 90 CrMoV 18

1.4112

900 - 1100

0,15

 

X 35 CrMo 17

1.4122

1000 - 1400

0,15

 

X 12 CrNi 18 8

1.4300

800 - 1200

0,15

 

X 5 CrNi 18 10

1.4301

800 - 1200

0,15

 

X 10 CrNiS 18 9

1.4305

800 - 1000

0,15

 

X 5 CrNiMo 17 12 2

1.4401

800 - 1200

0,15

 

X 2 CrNiMo 18 14 3

1.4435

800 - 1200

0,15

 

X 5 CrNiMo 17 13

1.4449

800 - 1200

0,15

 

X 6 CrNiMoTi 17 12 2

1.4571

800 - 1200

0,15

 






Material

Material no.

Hardness HV 1

NHD in mm

CL in µm

 

Rolling bearing steels

100 MnCrW 4

1.2510

500 - 700

0,2 - 0,3

= 4

100 Cr 6

1.3505

350 - 600

0,2 - 0,3

= 4

Free-cutting steels

9 SMnPb 28

1.0718

200 - 350

 

4 - 8

44 SMn 28

1.0762

300 - 500

0,3 - 0,6

4 - 8

Spring steels

Ck 75

1.1248

350 - 550

0,3 - 0,6

4 - 8

60 SiMn 5

1.5142

400 - 600

0,3 - 0,6

4 - 8

67 SiCr 5

1.7103

500 - 650

0,3 - 0,6

4 - 8

50 CrV 4

1.8159

450 - 600

0,3 - 0,4

4 - 8

58 CrV 4

1.8161

450 - 600

0,3 - 0,4

4 - 8

Cast iron

GG 18

 

300 - 450

0,3 - 0,4

8 - 10

GG 25

 

350 - 500

0,3 - 0,5

8 - 10

GGG 42

 

400 - 600

0,3 - 0,5

8 - 10

GGG 60

 

500 - 700

0,3 - 0,6

8 - 10

GGG 70

 

500 - 700

0,3 - 0,6

8 - 10

 

The treatment results of nitriding refer to standard-time and long-time treatments. A higher or lower nitriding hardness depth (NHD) and compound layer (CL) thickness can be achieved by using special treatments. We would gladly inform you on the possibilities.

The treatment of parts is carried out at significantly lower temperatures compared to conventional hardening processes. A comparison overview can be found here.

 

 

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