104613345-Effect-of-post-–-quenching-heat-treatments-on-Tensile-properties-of-alloy-steel

7/29/2019 104613345-Effect-of-post-–-quenching-heat-treatments-on-Tensile-properties-of-alloy-steel

http://slidepdf.com/reader/full/104613345-effect-of-post-quenching-heat-treatments-on-tensile-properties-of-alloy-steel 1/8

Effect of post – quenching heat treatments on

Tensile properties of alloy steel

Yuanyuan You ID: 0700061Lecturer: Professor S Hampshire

Results:Table 1: Data collected from the lab and part of calculation.

Sample Diameter

(mm)

Gauge

length(mm)

Peak load(N)

extension(mm)

C.S.A

(mm2)

0.2%Extension

A(700 )℃ 3.66 17.71 7817.333 5.495 10.52 0.03542

B(650 )℃ 3.48 18.16 8846.667 4.421 9.51 0.03632

C(550 )℃ 3.65 18.12 12078.67 3.471 10.46 0.03624

D(450 )℃ 3.63 18.37 13882 3.228 10.35 0.03674

E(250 )℃ 3.69 17.61 18316.67 3.547 10.69 0.03522F(900 )℃ 3.71 17.98 8811.999 4.62 10.81 0.03596

N.B. 0.2% proof stress was calculated for Yield strength.

Table 2: The mechanical properties calculated from table 1.

Sample Yield strength(MPa) UTS (MPa) Strain to failure

A (700 )℃ 560.79 743.03 0.31028

B (650 )℃ 809.55 930.10 0.24345

C (550 )℃ 1003.49 1154.36 0.19156

D (450 )℃ 1159.52 1341.37 0.17572

E (250 )℃ 1346.54 1712.79 0.20142F (900 )℃ 536.53 815.15 0.25695

Fig 1: Yield strength Vs Tempering temperature

Fig 2: UTS Vs Tempering temperature

700

650

550

450

250

0

200

400

600

800

1000

1200

1400

1600

200 300 400 500 600 700 800

Temperature ( )℃

YS (MPa)

Yield strength Vs Tempering temperature



Fig 1, 2, 3 are based on the table 2 (sample A-E), as a trend, tensile properties

decreases, with the heat treatment temperature increases.

Hardness test carried out by Vickers microhardness machine.

Table 3: Data of steel hardness VHN (HV20).

Sample VHN (HV20)

1 2 3 4 5 Mean Standard deviation

A(700 )℃ 253.6 256.1 247.1 256.1 267.1 256 7.2146

B(650 )℃ 305.8 321.2 316.7 320 298.1 312.36 10.0216

C(550 )℃ 382.7 373.5 382.7 380.9 380.5 380.06 3.8037

D(450 )℃ 403.9 401.5 418.7 411.2 419 410.86 8.1224

E(250 )℃ 522.9 526.5 539.4 543.6 514.4 529.36 12.0135

F(900 )℃ 285.8 274.9 273.7 276.4 258.6 273.88 9.7850

Fig 4: Steel hardness Vs Tempering temperature.

UTS Vs Tempering temperature

700

650

550

450

250

0

200

400

600

800

1000

1200

1400

1600

1800

200 300 400 500 600 700 800

Temperature ( )℃

)℃

UTS

(MPa)

700

650

250

450

550

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

200 300 400 500 600 700 800

Temperature (℃)

Strainto

failure

Strain to failure Vs Tempering temperature



Fig 4 is based on the table 3 (sample A-E), Fig 4 shows that the hardness decreases

with the increasing of heat treatment temperature.

Microstructures:

Sample A:

Sample B:

As shown in the Microstructure above, Sample A and Sample B, the pearlite lath

spacing decreases and the pearlite grain in Sample B are finer Sample C:

Hardness Vs Tempering temperature

700650

250

450

550

0

100

200

300

400

500

600

200 300 400 500 600 700 800

Heat treatment Temperature (℃)

Hardness

VHN



Sample D:

Microstructure of Sample C and Sample D give the presence of Bainite + pearlite

In Sample C the Bainite present is upper Bainite

In Sample D the Bainite present is lower Bainite

The difference between them cannot be observed from these photos

Sample E:



In sample E martensite cannot be observed

Sample F:

Microstructure of Sample F gives pearlite + Martensite.

Discussion:Fig 4: Phase diagram of alloy steel.



The phase diagram above is not complete diagram, it is only plotted for

concentrations (in weight percent) less than 6.67 percent carbon, this because of the

reason that steel that has higher than 6.67 percent has little commercial significance

and is usually ignored. As shown above the microstructures obtained when a steel is

slowly cooled from the austenitic (FCC) region depend on the original carbonconcentration of the steel, if carbon concentration is less than 0.77 percent, the

microstructure will contain two primary constituents: pearlite (BCC) and ferrite, if the

carbon concentration is higher than 0.77 percent it will contain cementite and pearlite,

for our case, when the carbon concentration is 0.77, austenite will transforms to

pearlite only.

By studying the transformation from austenite to pearlite,

a Time-Temperature-Transformation curve can be obtained, as shown below:

Fig 5: Time-temperature-transformation curve of the alloy steel.

For this experiment, as shown in the TTT curves, 6 hour is more than enough for the

transformation, so for Sample A – E all transformations are completed.

The influence of ferrite grain size (D) on the steel Properties:

According to the Hall – Petch equation:

σy = σi + k y/d1/2

,Where σy = yield stress, i = friction stress opposing dislocation motion, k = constant.



transformation as the specimen approaches room temperature.

Conclusion:

Undergoes heat treatment at different temperatures, the austenite transformation will

give different structures, which will result in different mechanical properties.

Steel can be strengthened by some methods:

Grain refinement/pearlite lath spacing

Solid solution

Carbide strengthening

Bainite formation

Martensite formation

References:

William D. Callister, Jr. (2007) MATERIALS SCIENCE AND ENGINEERING: AN

INTRODUCTION 7 thed . United States of America: John Wiley & Sons, Inc.

Reed-Hill, Robert Ellis. (1992) Physical metallurgy principles 3rd ed. Boston: PWS-

KENT Publishing Co.

104613345-Effect-of-post-–-quenching-heat-treatments-on-Tensile-properties-of-alloy-steel

Documents

Transcript of 104613345-Effect-of-post-–-quenching-heat-treatments-on-Tensile-properties-of-alloy-steel