Lab Material 3.docx

Table of Contents

No.

Contents

1.

Abstract

2.

Introduction

3.

List of Figures

4.

Theory

5.

Experimental Procedures

6.

Results

7.

Discussion

8.

Conclusion

9.

References

Abstract

This project investigated the effects of austenitizing temperatures and time on the hardness of a steel. The most common test for studying these effects is the Jominy End Quench test. In this test a sample of steel is heated into the austenite range for selected temperatures and times and water spray quenched at one end, producing a varying cooling rate across the sample. Currently the Jominy End Quench test focuses more on the hardenability of the steel. An improved model for correlating the Jominy End Quench curves and the resulting grain size curves proposed introduce a better defined heating and cooling cycle. The improved model obtained will optimistically result in less time spent in research and development. Through the process of preparing, etching, and observing the samples under an optical microscope, microstructural shape of the specimen are obtained. The experimental results show a difference between the prior austenitic grain size among the different heating times and temperatures used. The conclusion compares the effects of temperature and time in the grain growth of the prior austenitic grain size.

Introduction

The Jominy end quench test is used to measure the hardenability of a steel, which is a measure of the capacity of the steel to harden in depth under a given set of conditions. This considers the basic concepts of hardenability and the Jominy test. Knowledge about the hardenability of steels is necessary to be able to select the appropriate combination of alloy steel and heat treatment to manufacture components of different size to minimize thermal stresses and distortion. The Jominy end quench test is the standard method for measuring the hardenability of steels. This describes the ability of the steel to be hardened in depth by quenching. Hardenability depends on the chemical composition of the steel and also be can affected by prior processing conditions, such as the austenitizing temperature. It is not only necessary to understand the basic information provided from the Jominy test, but also to appreciate how the information obtained can be used to understand the effects of alloying in steels and the steel microstructure.

List of Figures

Figure 1.0 : Vicker Hardness Tester

Figure 2.0 : Jominy End-Quenches Furnace

Figure 3.0 : Optical Microscope

Theory The Jominy end quench test measures the hardenability of steel. This is the ability of the steel to partially or to completely transform from austenite to some fraction of martensite at a given depth below the surface, when cooled under a given condition from high temperature. The quench and temper heat treatment uses this phase transformation to harden steels. After tempering, the martensite microstructure gives the steel a good combination of strength and toughness. Without tempering, martensite is hard, but brittle. To select steels for a heat treated component, it is important to know their hardenability. The hardening of steels can be understood by considering that on cooling from high temperature, the austenite microstructure of the steel can transform to either martensite or a mixture of ferrite and pearlite (figure 1). The ferrite/pearlite reaction involves diffusion, which takes time. However, the martensite transformation does not involve diffusion and is essentially instantaneous. These two reactions are competitive, and martensite is obtained if the cooling rate is fast enough to avoid the slower formation of ferrite and pearlite. The hardenability describes the capacity of the steel to harden in depth under a givenset of conditions. For example, a steel of a high hardenability can transform to a highfraction of martensite to depths of several millimetres under relatively slow cooling, such as an oil quench, whereas a steel of low hardenability may only form a high fraction of martensite to a depth of less than a millimetre, even under quite rapid cooling such as a water quench. The steel sample is normalised (to eliminate differences in microstructure due to previous forging) and then austenitised . This is usually at a temperature of 800 to 925°C, and transforms the steel microstructure to austenite. The test sample is quickly transferred to the test fixture, which quenches the steel as its prays a controlled flow of water onto one end of the sample. The cooling rate varies along the length of the sample from very rapid at the quenched end where the water strikes the specimen, to slower rates that are equivalent to air cooling at the other end.

Iron-Carbon Cementite Phase Diagram

Partial Cu-Zn Phase Diagram

Age Hardening of Aluminum

Experimental Procedure 1) The specimen is heated in the Jominy End-Quench’s furnace until the temperature reaches 900°C. 2) The water flow is the adjusted until the height reaches approximately 65mm (2.5 inches) at Jominy End-Quench test bench. 3) The safety pin is pulled out from the furnace so that the specimens fall down to the quenching apparatus. 4) The water is applied within 5.5 seconds, care is taken so that the water strikes only the bottom of the specimen. 5) The specimen was left in the quenching unit for few minutes until it is cooled down. 6) The specimen was removed for hardness test and microstructure is evaluated using microscope. 7) The Vickers hardness(1kg) readings was taken at 1 mm intervals for the first 10 mm, 5 mm intervals for the next 40 mm and 10 mm intervals for the remaining 50 mm length of the specimen.

Results

Distance

0

1

2

3

4

5

6

7

8

9

10

D1, mm

58.5

73.8

73.1

70.6

82.8

89.5

84.6

79.5

86.9

97.2

89.6

D2, mm

59.6

77.7

73.1

75.2

91.4

87.1

88.2

82.7

88.3

99.0

92.1

(mm)

Hardness 531.8 323.1 346.7 249.1 244.6 237.9 248.5 282.0 241.9 192.9 224.5

Distance

15

20

25

30

35

40

45

50

D1, mm

91.2

99.5

D2, mm

91.9

100.7 103.0 101.9 110.3 109.9 110.9 112.5

(mm)

103.4 105.3 108.6 107.0 108.6 111.4

Hardness 221.3 185.0 174.1 172.7 154.8 157.6 154.0 147.9

Distance

60

70

80

90

100

(mm) D1, mm

107.0 105.1 105.1 114.7 118.1

D2, mm

105.1 105.1 105.1 114.7 118.1

Hardness 164.8 167.8 167.9 140.9 132.9

Table of Distance, Diameter 1 and 2 of specimen and Vicker Hardness readings

References 1. https://www.quora.com/What-characteristics-define-ferrous-metals 2. http://www.engineersedge.com/manufacturing_menu.shtml 3. https://smithy.com/machining-handbook/chapter-2/page/9 4. https://www.coursera.org/learn/material-science-engineering/lecture/7RSYM/2-29precipitation-hardening-in-al-cu-alloys