Vacuum carburizing provides advantages over traditional gas carburizing methods, including faster carbon transfer without surface oxidation, improved case depth uniformity, and integration into manufacturing processes with little consumption of carburizing gas and no need for furnace atmospheres. Vacuum carburizing allows for higher carburizing temperatures and shorter treatment times compared to gas carburizing. Parts treated with vacuum carburizing have cleaner surfaces without intergranular oxidation, more consistent case depths and carbon profiles, less distortion and variation, and potential operational cost advantages.

1. Vacuum Carburizing
Low Pressure Carburizing or LPC

2.  Fast Carbon Transfer
 No Surface Oxidation
 Good Case Depth Uniformity
 Integration into Manufacturing
 Little Consumption of Carburizing Gas
 No Formation of Furnace Atmosphere
 High Carburizing Temperatures possible
Advantages of Vacuum Carburizing

3. Material Temperature ECD Treatment Treatment
(0.35 % C) time* time*
vacuum gas
carburize carburize
16 MnCr 5 930°C 0.6 mm 2.00 hours 2.75 hours
~ SAE 5115 (1700°F)
17 CrNiMo 6 960°C 1.6 mm 7.50 hours 9.50 hours
~ SAE 9310 (1760°F)
* treatment time = carburizing + diffusion + lowering to quenching temperature
Cycle Time Comparison
LPC vs. Batch Atmosphere

4. Time
Convective
Heating
Carburizing Diffusioning
Quenching
1
10-1
10-3
10-5
20
940
850
20
Pressure (bar)
Temperature (°C)
Time
LPC Cycle

5. Process - LPC Exhaust Contents
100%
5 %
90 %*) Approx. 5% other
Hydrocarbons
part of it
< 0.03 Vol.-% Benzene
10 %
45 %
40%
10 %*)
End of
pause
Average over
boost cycle
End of
boost cycle
N2
N2
HC
H2
No thermal off gas
incinerator necessary
5 %
N2
C2Hx
*) depends on Gas ballast flow rate
H2

6. 24/7, 50 weeks per year, 6 hour cycles, 2250 net pounds per load, 3050 gross pounds per load, 4,100,625 pounds per year.
Electrically heated atmosphere furnace process gas figures:
2,810,813 ft3 of CH4 = 2,810,813 ft3 of CO2 x 0.117 lbs per ft3 = 328,865 lbs CO2 or
149.5 Metric tons of CO2 per year per furnace
Vacuum Carburizing (ModulTherm LPC):
95,886 ft3 C2H2 x .05 C2H2 up the stack <5% C2H2 in Exhaust 4794.3 ft3 C2H2 will oxidize to 9,588.6 ft3 CO2 = 1121.9 lbs CO2 or
0.51 metric tons CO2 per year
Naturally, all of these calculations are theoretical and assume properly adjusted systems. The LPC system assumes C2H2 disassociation
>95%. >75% C absorbed by the steel. A known stack discharge of 0-5% C2H2 during boost. The majority of carbon not absorbed by the
load is recovered as particulates in the pump oil filtering system.
Process – Greenhouse Gas Exhaust Volume
LPC vs. Batch Atmosphere
A very
“green”
process

7. Bright and shiny parts after heat treatment
due to
 Clean, vacuum process with inert gases.
Highest repeatability / reproducibility
due to
 precision of the process.
(ECD uniformity of +/- 0.05 mm or 0.002”
@ CD 0.5 – 0.9 mm or 0.02 – 0.035”)
Significant Characteristics
Product Quality

8. Clean Parts
Significant Characteristics
Product Quality

9. Higher fatigue strength and wear resistance
due to
 NO intergranular oxidation at the surface,
 higher consistency of case depth between tooth root
and tooth flank,
ECD @ tooth root/tooth flank*
VC + Gas Quench: 80 – 90 %
VC + Oil Quench: 70 – 75 %
Gas Carb. + Oil Quench: < 70 %
*depending on the part size.
 greater depth of hardness > 58 HRC in tooth root and
tooth flank (SAE 8620).
Significant Characteristics
Product Quality

10. • No surface or subsurface (intergranular) oxidation (No IGO)
– Atmosphere carburizing typically produces both surface oxidation (dealloying)
and an intergranular oxidation (IGO) layer of 7.5 – 12.5 micron.
Gas-Carburized Vacuum-Carburized
Significant Characteristics
Product Quality

11. Significant Characteristics
Product Quality
• Case Depth Consistency
• Carbon Profile Uniformity

12. Atmosphere Carburize (Oil Quench):
Pitch Line & Root Comparison
180
220
240
260
280
.010
300
200
.020 .030 .040 .050 .060 .070 .080.000
58 HRC
AC @ pitch line
AC @ root
50 HRC
50 HRC
58 HRC
Depth (inches)
Hardness(microns)
 Root case depth is
significantly lower than
Pitch-line case depth
Significant Characteristics
Product Quality

13. Vacuum Carburize (HPGQ):
Pitch Line & Root Comparison
180
220
240
260
280
.010
300
200
.020 .030 .040 .050 .060 .070 .080.000
58 HRC
VC @ pitch line
VC @ root
50 HRC
50 HRC
58 HRC
Depth (inches)
Hardness(microns)
 Root case depth is in
the same level as Pitch-
line case depth
Significant Characteristics
Product Quality

14. Less distortion and Less variation
due to
 Optimal controllability of the quenching process by
• Single-phase “uniform” heat transfer during quenching
• Controllable quenching intensity:
- Free choice of gas pressure (from 1 to 20 bar).
- Free choice of gas speed (2 speeds of the quenching fan).
- Using different gases (Helium, Nitrogen).
(Optimized quenching achieves desirable hardness & minimal distortion)
Significant Characteristics
Product Quality

15. Operational cost advantages:
 Environmentally and workplace friendly.
 Flexible in operation
 Potential to eliminate post HT press quenching or straightening
Significant Characteristics
Operation

16. For more information contact us at:
ALD Vacuum Systems, Inc.
50477 Pontiac Trail
Wixom MI 48393
(248) 956-7610
www.ALDVac.com