Journal of Materials Science and Engineering B 8 (3-4) (2018) 45-48 doi: 10.17265/2161-6221/2018.3-4.001

Effect of High Pressure Heat Treatment on

Microstructure and Compressive Properties of Low

Carbon Steel

Meng Deliang

College of Civil Engineering and Mechanics, Yanshan University, Qin Huang Dao 066004, China

Abstract: The effect of high pressure heat treatment on microstructure and compressive properties of low carbon steel were investigated by optical microscope, transmission electron microscope, hardness tester and compression test methods. The results show that martensite appears in low carbon steel at 1-5GPa GPa and 950 °C for 15 minutes treatment, high pressure heat treatment can improve the hardness and compressive properties of the steel, the yield strength of the steel increases with increasing pressure, and its compressive properties are better than that treated under normal pressure quenching. Key words: Low carbon steel, high pressure heat treatment, microstructure, compressive properties.

1. Introduction

Low carbon steel is a common steel for carbon

components, it has been widely used in various fields

of modern industry. However, the application of low

carbon steel is limited largely due to its lower strength

and compressive deformation resistance. Therefore,

researchers have paid much attention to the

performance potential of low carbon steel [1, 2]. It is

well known that high pressure heat treatment can

improve the microstructure and mechanical properties

of metal materials [3-5]. But there was still no clear

understanding of compressive properties of low

carbon steel after high pressure heat treatment. For

that reason, the microstructure and compressive

properties of low carbon steel before and after high

pressure heat treatment are observed and tested, and

the effect of high pressure heat treatment on

microstructure and compressive properties of the steel

were discussed. This will provide basis for giving full

play to the performance potential of low carbon steel.

2. Experiments

Corresponding author: Meng Deliang, senior engineer,

research field: metallic materials.

The experimental material is hot-rolled low carbon

steel, its chemical composition (mass fraction, %) is:

0.19C, 0.45Mn 0.29Si, 0.031P, 0.026S, and the

samples’ size is Ф6 mm × 10 mm. High heat treatment

was done on CS-IB type six-anvil high-pressure

equipment under high pressure which is 1 GPa, 3 GPa

and 5 GPa, after heating at 950 °C and lasting for 15

minutes, shutting off power and cooling to room

temperature on holding up pressure. Some low carbon

steel samples were also subjected to normal pressure

quenching in the KL-13D type resistance furnace, the

process is heated to 950 °C for 15 min, and then

cooling in 10% salt solution. The room temperature

compression test was carried out on the WDW3100

electronic universal testing machine, the compression

speed is 1 mm/min, the hardness of the samples before

and after treatment was tested by HR-150A hardness

tester. The microstructure of the samples was analyzed

by means of Axiovert200MAT optical microscope

and H-800 transmission electron microscope.

3. Results and Discussion

3.1 Microstructure

Fig. 1 shows the microstructure of low carbon steel

D DAVID PUBLISHING

Effect of High Pressure Heat Treatment on Microstructure and Compressive Properties of Low Carbon Steel

46

under different conditions. The microstructure of the

steel before high pressure heat treatment consisted of

ferrite and pearlite, after normal pressure quenching,

the microstructure of the steel is lath martensite,

martensite of the steel after high pressure heat

treatment is smaller than normal pressure quenching,

and refining with increasing pressure. After TEM

(transmission electron microscope) (Fig. 2)

observation, it was found that after high pressure heat

treatment, the orientation of martensite lath beam is

rather disorder, and the dislocation density is higher.

This may be the low carbon steel in the cooling

process, ultra high pressure can inhibit the diffusion of

carbon atoms [6], it causes low carbon steel to cool to

room temperature, carbon atoms are supersaturated

solid solution in the –Fe, thus, martensitic is formed.

This remains to be further explored.

3.2 Compressive Properties

It is known from the hardness result in Table 1 that

(a) hot rolling (b) normal pressure quenching

(c) 1 GPa treatment (d) 3 GPa treatment (e) 5 GPa treatment

Fig. 1 Microstructures of low carbon steel at different states.

(a) hot rolling (b) 3 GPa treatment

Fig. 2 TEM images of low carbon steel before and after cryogenic treatment.

(a)

0.5 μm

(b)

0.5 μm

40 μm

(c)

40 μm

(d)

40 μm

(e)

40 μm

(b)(a)

40 μm

Effect of High Pressure Heat Treatment on Microstructure and Compressive Properties of Low Carbon Steel

47

Table 1 The hardness of low carbon steel at different states.

Specimen Hot rolling Normal pressure quenching 1 GPa 3 GPa 5 GPa

Hardness (HRC) 12 35 45 46 47

Fig. 3 Stress-strain curves of low carbon steel at different states.

the hardness value of low carbon steel after 1~5 GPa

pressure treatment has little change, the hardness

value of the steel is HRC45~47, higher than normal

pressure quenched. When the pressure is 3 GPa, its

value is HRC36, and increased by 31.43% than that of

the steel at pressure quenching.

Fig. 3 shows stress-strain curve of low carbon steel

under different conditions. It can be seen that obvious

plastic deformation stage appeared in all specimens

under static compression. High pressure heat

treatment can improve the compression performance

of the steel, the compressive yield strength increases

with the increase of pressure. As you can see from Fig.

2 that the change of stress-strain curve trend of high

heat treatment and quenching treatment is similar

trend, however, the yield strength of the steel after

high pressure heat treatment is higher than that of

normal quenching. This indicates that the compressive

property of low carbon steel after high pressure heat

treatment is better than that of normal quenching. It is

known from the experimental results that the

compressive yield strength of the steel after 5 GPa

pressure heat treatment is 1,846.92 Mpa, and

increased by 665.21% and by 29.01% than that of the

steel at hot rolling and normal pressure quenching,

respectively.

Because of the existence of lath martensite in low

carbon steel after high pressure heat treatment, at the

same time, high pressure causes lattice distortion, it

causes the hardness and strength of the steel to

increase, and the compression ability of steel is

improved. Normally, the yield strength of metallic

materials increases with decreasing grain size [7], and

the martensite obtained by high pressure heat

treatment of low carbon steel is smaller than that of

normal pressure quenching, the martensitic lath

decreases with the increase of pressure. Therefore, the

yield strength of low carbon steel after high pressure

heat treatment is higher than that of normal quenching,

and the yield strength also increases with the increase

of pressure.

4. Conclusions

(1) Lath martensite is formed in low carbon steel

after high pressure heat treatment, its hardness and

compressive properties are improved, and the greater

the pressure, the smaller the martensite, the better the

compressive property.

(2) The compressive properties of low carbon steel

after 1~5 GPa pressure and at 950 °C for 15 minutes

treatment are better than that of normal quenching, the

compressive yield strength of the steel after 5 GPa

pressure heat treatment is 1,846.92 Mpa, and

increased by 665.21% and by 29.01% than that of the

steel at hot rolling and normal pressure quenching,

respectively.

References

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Strain%

Str

ess/

MP

a

5GPa

0 3 6 9 12 150

600

1200

1800

2400

3000

hot rolling

normal

1GPa

3GPa

Effect of High Pressure Heat Treatment on Microstructure and Compressive Properties of Low Carbon Steel

48

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