Process Principles of

High Pressure Gas Quenching

In ModulTherm® and DualTherm®

Reduction of hardening distortion and/or variation of distortion

Quenching intensity adjustable by of gas pressure and gas velocity

Process flexibility

Clean, non-toxic working conditions

Integration into manufacturing lines

Reproducible quenching results

Clean and dry parts, no washing

Simple process control

High Pressure Gas Quenching (HPGQ) Advantages

Bubble Boiling

Film Boiling

Convection

t = 10 s

750°C

700°C

700°C 600°C

500°C 400°C 300°C

200°C

Temperature distribution

t = 10 s

Heat transfer coefficient

5000 10000 15000 20000

Öl oil Wasser

water

[W/m K] 2

ref.: Stick, Tensi, HTM 50, 1995

Heat Transfer & Temperature Distribution

Immersion Quenching

Heat transfer coefficient

1000 2000 3000 4000 [W/m K] 2

Temperature distribution

750°C

650°C

550°C

450°C

350°C

250°C

Gas direction

Only convection

Heat Transfer & Temperature Distribution

High Pressure Gas Quenching (HPGQ)

Heat Transfer Coeffizient (W / m2 K)

0 500 1000 1500 2000 2500 3000 3500 4000

Water (15-25 °C)

Agitated oil (70-180 °F)

Air 1 bar

He 20 bar (hot chamber)

He 20 bar (cold Chamber)

Saltbath quench (1020 °F)

N2 6-10 bar (hot chamber)

Still oil (70-180 °F)

Fluidised bed

N2 / He 1 - (10) / 20 bar

Heat Transfer Coefficient different quenching media

Chemical symbol

Density at 15 oC and 1 bar

Density relative to air

Molar mass (kg / kmol)

Specific heat capacity Cp (kJ / kg K)

Dynamic viscosity (N s / m 2)

Thermal conductivity (W / m K)

Argon Nitrogen Helium Hydrogen

Ar

1,6687

1,3797

39,948

0,5024

177x10- 4

22,6x10- 6

N 2

1,170

0,967

28,0

1,041

259x10- 4

17,74x10- 6

He

0,167

0,138

4,0026

5,1931

1500x10- 4

19,68x10- 6

H 2

0,0841

0,0695

2,0158

14,3

1869x10- 4

8,92x10- 6

(at 25 oC und 1 bar)

Gas Properties

High Pressure Gas Quench

0

2

4

6

8

10

12

14

16

0 2 4 6 8 10 12 14 16 18 20

0

2

4

6

8

10

12

14

16

0 2 4 6 8 10 12 14 16 18 20

Relative Motorpower for

cooling gas fans

Relative

Heat Transfer Coefficient

Gas pressure (bar) Gas pressure (bar)

HPGQ Influencing Parameters

Multi Chamber Vacuum Furnace

(Cold Chamber)

Backfill time to

final pressure >> 10 sec

Backfill time to

final pressure << 10 sec

Gas flows

through the

charge and inpart

around the charge

Hot wall

and hot

graphite elements

Gas must

flow through

the charge

Cold Wall

Single Chamber Vacuum Furnace

(Hot Chamber)

HPGQ Quenching Chamber Influences

Reversing Gas Flow Increased Quenching Uniformity

Modular Design Flexible and Expandable

Compact Chamber Design Short Gas Recycling Cycles

High Pressure Gas Quenching (HPGQ) Quenching Chamber

Cooling curves in the tooth root of Truck- Gear Wheels (GW)

0

100

200

300

400

500

600

700

800

900

-50 0 50 100 150 200 250

Time /sec.

Te

mp

. /°

C

GW bottom, no rev.

GW, top, no rev.

gas-temp. bottom, no rev.

GW bottom, with rev.

GW, top, with rev.

gas-temp. bottom, with rev.

Quench behavior in the tooth root of heavy truck gears

HPGQ Quench Chamber

Reverse Gas Flow Quenching

300

320

340

360

380

400

420

440

460

No reversing With reversing

Co

re h

ard

ne

ss

at

Mid

-to

oth

/ H

V3

0

Bottom min

Bottom average

Bottom max

Top min

Top average

Top max

Gas flow Gas flow

300

310

320

330

340

350

360

370

380

390

400

No reversing With reversing

Co

re h

ard

ne

ss

at

To

oth

ro

ot

/ H

V3

0

Bottom min

Bottom average

Bottom max

Top min

Top average

Top max

Gas flow Gas flow

Tooth

root

Mid-

tooth

Core hardness influence in the tooth root of heavy truck gears

HPGQ Quench Chamber

Reverse Gas Flow Quenching

High Pressure Gas Quench Chamber Cold Chamber, 20 Bar with Reverse Gas Flow Quenching

20

25

30

35

40

45

50

0 5 10 15 20 25 30 35 40 45

Jominy Distance (mm)

Hard

ness (

HR

C)

20NiCrMo2 (SAE 8620)

20MoCr4 (SAE 4118)

16MnCr5 (SAE 5115)

20MnCr5 (SAE 5120)

20NiCrMoS6-4

18CrNiMo7-6

20

bar

He

20

bar

N2

Jominy Curves of steel grades with

high hardenability acc. to EN 10084

Core Hardness Influences

Case Hardened Steel

D Ovality of Outer Diameter (mm)

Oil A : Houghton Quench A Oil B : Bellini FN 10 bar He 20 bar He

Cold Chamber

0

0,01

0,02

0,03

0,04

0,05

0,06

10 bar He

20 bar He

Oil A Oil B

Average and Standard Deviation

n=12

7

12

6

Material: SAE 52100, (D=70 mm, H=15 mm, S=5 mm)

Dimensional Changes

Bearing Rings

Process Comparison Drive Shafts

Shaft Length up to 750 mm (29.5 inches)

Material 17CrNiMo6 (similar SAE 9310)

Past H. T. Process

Gas Carburizing

Quench in Salt Bath

Distortion over Length of Shaft

Average 3 mm (0.12 inches)

Straightening Scrap 20 %

New H. T. Process

Vacuum Carburizing with

High Pressure Gas Quench with 8 bar

Helium

No Washing – Clean and Dry Parts

Distortion over Length of Shaft Average

1.0 mm (0.039 inches)

Less Straightening Work

No Scrap

Significant Characteristics

Product Quality

High Pressure Gas Quenching

500 kg gross Load of Pinions, 20 bar Helium, SAE 8620

0

2

4

6

8

10

12

14

16

18

20

1 2 3 4 5 6

Runout (1/1000 in)

Gas carburizing & Oil quench

Vacuum Carburizing & High Pressure Gas quench

HPGQ versus Oil Quench Distortion Analysis

Frec

Summary

• High pressure Gas quenching can significantly reduce distortion

and/or variation of distortion

• Microstructure, Hardness and Distortion are strongly influenced by:

- Part

- Quenching Parameters

- Cold Chamber Design

• 20 bar Helium Quenching Technology is capable of successfully

hardening low alloyed case hardening steels if material

hardenability can be controlled

• Alloy modification offers the chance to reduce gas

pressure/velocity thereby reducing distortion and/or investment

costs

For more information contact us at:

ALD Vacuum Systems, Inc.

50477 Pontiac Trail

Wixom MI 48393

(248) 956-7610

www.ALDVac.com