Application of Intensive Quenching Processes for Carburized Parts

Michael A. Aronov, Nikolia I. Kobasko, Joseph A. Powell IQ Technologies Inc Akron, Ohio, USA

Pratap Ghorpade, D. Gopal Hightemp Furnaces Limited

Bangalore, India

Abstract

The paper describes results of extensive experimental study of

intensive water quenching techniques for carburized steel

parts. Experiments were performed for a variety of steel

products including automotive parts, railroad parts, etc. Paper

presents detailed metallurgical analysis data obtained for the

intensively quenched parts, particularly for universal joint

crosses. The following parameters have been evaluated for

both intensively quenched and oil quenched parts: surface and

core hardness, micro hardness distribution, microstructure, etc.

The results of these experiments clearly demonstrated that the

duration of the carburization cycle could be reduced by 40-

50% when using intensive water quenching techniques.

Introduction Since 1997, IQ Technologies Inc (IQT) of Akron, Ohio, has

conducted over one hundred “intensive quenching” (IQ)

demonstration studies for a variety of steel products (see, for

example, References 1 and 2). Our working definition of “IQ

process” is the following two elements: (1) Parts are through

heated and then quenched in highly agitated water to form a

uniform hardened shell on the part surface, while eliminating

film boiling and distortion. (2) Once the surface is under

optimal compressive stress (as determined by the IQT

computer models), the “intensive” quench is “interrupted” by

removing the part from the IQ tank and the cooling of the part

is finished in still air.

The results of the IQ demonstrations have proved that, in

many cases, the carburization cycle can be significantly

shortened or even fully eliminated when applying the IQ

process. This is because of the following reasons:

IQ process provides higher hardness and deeper

hardness depth into the part compared to conventional

quenching.

Steel may have lower carbon content or a lower alloy

content yet IQ can still provide the required hardness. For

example, 12.7 mm bar made of 1060 steel and quenched

in oil has the same as-quenched hardness (59 HRC) as the

same bar made of 1040 steel and intensively quenched.

When intensively quenching carburized parts to specified

case depth, the carbon content in the part case can be less

compared to that needed to achieve the same hardness in

the same part quenched in oil.

This paper presents the results of one of the IQT studies

conducted in cooperation with Hightemp Furnaces Ltd of

Bangalore, India. In this study, we evaluated the application

of the IQ processes to the universal joint crosses made of 8620

steel (Figure 1).

Figure 1 8620 Universal Joint Cross

Currently, Hightemp Furnaces Ltd processes the universal

joint crosses in integral, oil quench furnaces of their own

design. A typical effective furnace size is 1230x660x650 mm.

The furnace is atmosphere tight, allowing precise control of

the furnace atmosphere. A typical universal joint cross load is

presented in Figure 2. As seen, the parts are placed in a

special fixture.

Figure 2 Typical Universal Joint Cross Load

1. IQ Process Evaluation

Hightemp Furnaces carburized four sets of crosses. Two sets

were carburized and quenched in oil using a “standard”

thermal cycle (Figure 3). An additional two sets were

carburized only, using a reduced-time carburization cycle: one

set of parts was carburized for 60% of the standard

carburization time (“60% carburized”), and the second set of

parts was carburized for only 50% of the standard

carburization cycle (“50% carburized”).

Figure 3 Applied Carburization Cycles

The two sets of parts from the reduced carburization cycles as

well as the parts from one set that was fully carburized to the

“standard” cycle were reheated in a neutral salt bath furnace

and intensively quenched individually in IQT’s experimental

500-gallon IQ system (Reference 3).

The IQ system uses highly agitated water with a low

concentration of sodium nitrite (primarily as a rust inhibitor)

as the quenchant in this system. Once the part surface has

reached the temperature of the bath and has the optimal

compressive surface stresses (as determined by the IQT

computer models), it is removed from the “intensive” quench

and permitted to cool in air. The core cools by uniform

conduction through the cold, intensively quenched shell. The

entire intensive quench process takes less than a minute on the

subject parts. (The quenchant flow velocity in the 500-gallon

system is the same as in our 6,000-gallon and 11,000-gallon

production batch-type IQ systems. The production systems

use the same water quenchant as well.) To evaluate the effect

of the IQ process, we measured the following parameters and

compared them to the “standard” carburization, oil quenched

parts:

Surface hardness

Core hardness

Case depth

Microstructure

Inter granular oxidation

Products of non-martensitic transformation

Part distortion

Figure 4 shows the location on each of the crosses where we

took these measurements.

Figure 4 Schematic of Points of Measurements

2. Metallurgical Analysis Results

The results of the metallurgical analysis are the following:

No unacceptable distortion or cracks were observed

The case depth was uniform throughout the

intensively quenched surface of the cross

The specified mean case depth of 1.5 mm was

achieved with 60% of the “standard” process time

and intensive water quenching

The core hardness was greater than the required

minimum

No inter granular oxidation was observed in the

intensively quenched crosses

Let’s consider the above results in more detail.

2.1 Hardness Profile And Case Depth. Figure 5 presents the

hardness distribution in the universal joint crosses for different

carburization cycle times. The hardened depth is defined as a

depth of the part surface layer with a minimum hardness of 50

HRC (513 HV1). Figure 6 presents the relationship of the part

case depth from the carburization time for both the oil

quenched parts and intensively water quenched parts. As seen

from Figures 5 and 6, the case depth is 1.5 mm for standard oil

quenched crosses. Fully carburized crosses that were

intensively quenched have a case depth of 1.7 mm or 13%

greater than the standard case depth. The crosses that were

partially carburized for 60% of the standard carburization time

(for 5 hours 10 minutes instead of 8 hours 30 minutes) have

the same case depth as the standard cycle carburized and oil

Figure 5 Hardness Distribution for Different

Carburization Times

Figure 6 Case Depth vs. Carburization Time

quenched parts. Note also that the intensively water quenched

crosses have a greater core hardness compared to the standard

parts by 50-115 HV1 units.

Figures 7 and 8 present the hardness profiles in the crosses

that were carburized for 50% and 60% of the standard

carburization cycle time. As seen from the figures, the 50%

carburized and 60% carburized, intensively quenched crosses

have a deeper case depth at 50 HRC compared to standard

carburized and oil quenched crosses, by 10% and 32%,

respectively.

Figure 7 Hardness Profile in 50% Carburized Cross

Figure 8 Hardness Profile in 60% Carburized Cross

Figure 9 presents the uniformity of hardness distribution in the

60% carburized cross. As seen from the figure, the IQ process

provides very uniform hardness distribution throughout the

part surface. Samples 1, 2 and 3 were taken from different

surface areas (see Figure 5 above). The uniformity of

hardness throughout the part surface from intensive water

quenching is mainly due to the absence of the sporadic film

boiling on the part surface in the “intensively agitated”

quench; no film boiling, equals no soft spots.

400

450

500

550

600

650

700

750

800

850

0.00 0.50 1.00 1.50 2.00

Depth From Surface, mm

Ha

rdn

es

s, H

V1

100% Carburized Oil

100% Carburized IQ

60% Carburized IQ

50% Carburized IQ

Minimum case hardness

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

250 300 350 400 450 500 550

Carburization Time, minutes

Cas

e D

epth

, m

m

Oil quenched

IQ

400

450

500

550

600

650

700

750

800

850

0.00 0.50 1.00 1.50 2.00

Depth From Surface, mm

Hard

ness,

HV

1

50% Carburized Oil

50% Carburized IQ

Minimum case hardness

300

350

400

450

500

550

600

650

700

750

800

0.00 0.50 1.00 1.50 2.00

Depth From Surface, mm

Hard

ness,

HV

1

60% Carburized Oil

60% Carburized IQ

Minimum case hardness

Figure 9 Uniformity of Hardness Distribution in 60%

Carburized and Intensively Quenched Cross

2.2 Part Microstructure. Figures 10–13 present the

photographs of the part microstructure in the case and in the

core for the standard cycle carburized, quenched in oil cross,

and for the 60% carburized intensively quenched cross.

Figure 10 Case Structure of 60% Carburized IQ Cross

Figure 11 Case Structure of 100% Carburized Oil Quenched

Cross

Figure 12 Core Structure of 60% Carburized IQ Cross

Figure 13 Core Structure of 100% Carburized Oil Quenched

Cross

For both parts, the case microstructure consists of fine

tempered martensite with approximately 5% of retained

austenite with no products of non-martensitic transformation

and no carbide network. However, as seen from Figures 10

and 11, the martensitic structure was finer in the intensively

quenched part compared to the standard oil quenched part.

The intensively quenched cross core consists of low carbon

martensite, while the core of the standard cross consists of low

carbon martensite and bainite.

3. Carburization Cycle Shortening for Different

Parts

Table 1 summarizes the results of previous IQ Technology

demonstration studies performed for different steel parts. As

the data in the table shows, the carburization cycle can be

reduced significantly using the IQ process; approximately

40%-50% less furnace carburization time from the standard

carburization cycle using conventional oil quenching.

450

500

550

600

650

700

750

800

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00

Depth From Surface, mm

Ha

rdn

es

s, H

V1

Sample 1

Sample 2

Sample 3

Table 1 Carburization Cycle Reduction for Different Parts

Part Steel Case Depth,

mm

Cycle Time

Reduction

Universal joint

cross

8620 1.5 40%

Bearing cage 8617 1.8 50%

Crankshaft

8620 1.5 40%

Railroad part 4130 2.0 50%

Railroad part 4138 2.0 Full

elimination

4. Summary

Numerous intensive quenching studies conducted by IQ

Technologies Inc for carburize grades of material have

demonstrated significant benefits to part properties and

processing efficiencies. Environmentally friendly, intensive

water quench processes provide the following benefits for

carburized steel parts:

Increased case depth for a given carburization cycle

Improved core hardness

Acceptable distortion and no part cracking

Reduced carburization cycle for the same case depth

or full elimination of the carburization process

Possible use of lower alloy or smaller, lighter steel

parts with the same performance as oil quenched

parts

No use of hazardous quench oil or expensive

polymers.

For more information on the intensive quenching methods, see

the IQ Technology Inc web site www.IntensiveQuench.com.

Acknowledgements

The authors wish to acknowledge the Edison Material

Technology Center (EMTEC) of Ohio, USA for its support in

the commercialization of the intensive quenching methods, as

well as the personnel of the Hightemp Furnaces Ltd,

Bangalore, India for conducting the metallurgical analysis.

References

1. M. A. Aronov, N. I. Kobasko, J. A. Powell, “Application

of Intensive Quenching Process for Steel Parts”,

Proceeding of The 22nd

ASM Heat Treating Conference,

Indianapolis, Indiana, (2001).

2. M. A. Aronov, N. I. Kobasko, J. A. Powell, “Review of

Practical Application of Intensive Quenching Process for

Steel Parts”, Proceeding of The 13th

International

Federation for Heat Treatment and Surface Engineering

Congress, Columbus, Ohio, (2002).

3. M. A. Aronov, N. I. Kobasko, J. A. Powell, D.V.

Lipnicki, “Peculiarity of Intensive Quenching

Equipment”, Proceeding of The 13th International

Federation for Heat Treatment and Surface Engineering

Congress, Columbus, Ohio, (2002).