Research Article Properties and Tempering Stability of the FRW

Hindawi Publishing Corporation
Advances in Materials Science and Engineering
Article ID 819743
Research Article
Properties and Tempering Stability of the FRW Joints of
700 MPa Grade Fine-Grained Steel
Feng Tao, Sun Keqiang, and Sun Yongxing
College of Mechanical & Electronic Engineering, China University of Petroleum, Huangdao District, Qingdao 266580, China
Correspondence should be addressed to Feng Tao; ft [email protected]
Received 29 August 2014; Accepted 28 October 2014
Academic Editor: Liang-Wen Ji
Copyright © Feng Tao et al. This is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The friction welding (FRW) was used to weld 700 Mpa grade fine-grained steel and the changes on the microstructure state of joints
after low-temperature tempering treatment were analyzed. The testing result shows that it is better to adopt the high current to weld
to reduce the width of the heat-affected zone (HAZ) and maximum inhibition of the grain growth; the microstructure of welding
line and the HAZ is finer than the base metal, and the grain in the HAZ can be 9∼11 𝜇m in size; as the thermal stability of friction
welding joints of ultra-fine-grained (UFG) steel is poor, if it is necessary to release the residual stress of joints by tempering after
welding, the temperature should not exceed 300∘ C.
1. Introduction
Because of the excellent strength, toughness, and the good
prospect of the UFG steel, welding is an important means to
achieve its value. In countries’ UFG steel research projects,
welding has always been one of its main contents [1, 2].
In the welding process of UFG, since its microstructure is
extremely refined and the tendency of grain growth is large,
it makes the UFG steel sensitive to the welding thermal cycle
and more difficult to weld compared with traditional steel.
HAZ coarsened and HAZ softened, the local brittleness and
decline of global mechanical properties of joints that they
may cause are the main problems [3–6]. This paper adopts the
method of FRW in UFG welding, analyzing the changes on
the microstructure state and tempering stability of ultrafine
grain steel friction welding joint.
2. Materials and Methods
The material used in this experiment was produced by
microalloying and thermal mechanical control processing
(TMCP) and the samples are disc of 13 mm in diameter.
The microstructure of the workpiece was ferrite (F) and
pearlite (P) and its actual grain size can achieve 12 grades.
The average grain size of the base metal was about 5∼7 𝜇m.
The chemical constituents of the base metal were shown in
Table 1. The mechanical property parameters of the base
metal were shown in Table 2.
3. Results and Discussion
The welding parameters were strictly controlled in the experiments. The experimental parameters were friction pressure
40 Mpa, 60 Mpa, 80 Mpa; friction time 1 s, 3 s, 5 s; upset
pressure 80 Mpa, 100 Mpa, 120 Mpa; upset time 1 s, 2 s, 3 s.
The carbon equivalent of UFG is low; its welding HAZ
hardly has the tendency of hardening ability. In some working
conditions, that tempering is applied to release the residual
stress. The tempering stability of fine-grained steel friction
welding joint was studied. Maintaining the temperature for
1 h in 100∘ C, 300∘ C, and 500∘ C, respectively, and then air
cooling.
When the welding criterion is proper, the joint was
completely fin, the flanging was integrated, and its shape is
enclosing and sleek (seen in Figure 1). The microstructure of
the welding joint was shown in Figure 2. It can be seen that the
welding quality of the joint is good; defects such as cracks and
dispersed inclusion cannot be found. For the convenience
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Advances in Materials Science and Engineering
Table 1: Chemical constituents of the base metal.
Element C
Content 0.21
Mn
1.37
Ni
0.04
Si
0.13
P
0.015
S
0.005
V
0.03
Al
0.047
Table 2: Mechanical property parameters of the base metal.
Material
𝑅𝑚 /MPa Rel /MPa A/% Z/% Hardness/HV AKV /J
Actual
≥620
≥22 ≥52
Measurement 680
590
25 67.5
218
98
purpose, UFG steel friction welding joint is divided into four
zones: weld zone (WZ), heat-force-affected zone (HFZ), heataffected zone (HAZ), and base metal (BM). In the area close
to the fusion line, the denser the microstructure is, the more
fined the grain is.
In the HAZ, the grain deformation along the rolling
direction disappeared and it turns into the isometric grain,
but the lattice types were the same and it was still composed
of F and P. The grain size was larger than the base metal,
about 9∼10 𝜇m. The HAZ was not influenced by friction
torque, recovery, and recrystallization of the grain generate
with the increasing of deformation temperature. Due to the
fast thermal cycling speed, short residence time in high
temperature, and loaded by axial pressure, the growth of the
grain was inhibited. Dynamic recovery and recrystallization
of the HFZ metal generated with the friction torque, axial
pressure, and friction heat. This zone is mainly composed of
ferrite, pearlite, and little bainite. The grains in the WZ were
very fine and its microstructure could not be seen by optical
microscope. Only metal flow line which was consistent with
the workpiece radial could be seen in this area. This was
because of the flowing of the plastic metal outward circle
under the influence of upsetting.
Macroscopic metallographies of HAZ under different
tempering temperature were shown in Figure 3. The tempering stability of this zone was good. Although thermostability
of the UFG is poor, the microstructure in this zone during the
welding thermal cycle has undergone once normalizing and
it grows a little; the stability of microstructure and grain’s size
are proper.
HFZ microstructures of different tempering temperature
were shown in Figure 4. The microstructure tempering
stability of this zone was better when the temperature is at
the range of 100∼300∘ C; the microstructure and the grain’s
size do not change significantly. The grain begins to grow
when the tempering temperature reached 500∘ C. The original
microstructure is insulated into mesh. It indicates that the
microstructure in this zone is not stable and the tempering
stability is poor. Coarse carbide appeared in this zone.
HZ microstructures of different tempering temperature
were shown in Figure 5. The microstructure in this zone did
not change apparently when the tempering temperature is
lower than 300∘ C, and it also shows that the grain which
is under the tempering temperature of 300∘ C is a little
smaller compared to the welding state. When the tempering
temperature was risen to 500∘ C, the grain began to grow and
precipitate, and banded structure could be observed.
(a)
(b)
Figure 1: 700 MPa grade ultrafine grain steel friction welding joint.
500 𝜇m
Figure 2: Metallographic microstructure of friction welding joint.
4. Conclusion
(1) The friction weldability of UFG steels is good; it is
better to adopt the high current to weld to reduce the
width of the heat-affected zone (HAZ) and maximum
inhibition of the grain growth.
(2) UFG steel friction welding joint is composed of weld
zone (WZ), heat-force-affected zone (HFZ), heataffected zone (HAZ), and base metal (BM). The
microstructure of welding line and the HAZ is finer
than the base metal, and the grain in the HAZ
can be 9∼11 𝜇m in size; with the distance from the
fusion line increasing, the hardness from the center of
Advances in Materials Science and Engineering
3
50 𝜇m
50 𝜇m
∘
(a) Welding state
(b) 100 C
50 𝜇m
50 𝜇m
(c) 300∘ C
(d) 500∘ C
Figure 3: Microstructure of HAZ in different tempering temperature.
50 𝜇m
50 𝜇m
(b) 100∘ C
(a) Welding state
50 𝜇m
50 𝜇m
(c) 300∘ C
(d) 500∘ C
Figure 4: Microstructure of HFZ in different tempering temperature.
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Advances in Materials Science and Engineering
25 𝜇m
25 𝜇m
(b) 100∘ C tempering
(a) Welding state
25 𝜇m
25 𝜇m
(c) 300∘ C tempering
(d) 500∘ C tempering
Figure 5: Microstructure of WZ in different tempering temperature.
the weld to the base metal decreases roughly, but there
is a softened zone of 0.2 mm in width in the HAZ.
(3) As the thermal stability of friction welding joints
of ultra-fine-grained (UFG) steel is poor, if it is
necessary to release the residual stress of joints by
tempering after welding, the temperature should not
exceed 300∘ C.
Conflict of Interests
The authors declare that there is no conflict of interests
regarding the publication of this paper.
Acknowledgment
The authors would like to acknowledge the financial support
of Science and Technology Development Program of Shandong Province (2014GGX103013) which named The Study of
The Inner Wall of Large Diameter in Long Tube Nitrogen
Equipment and Process.
References
[1] Z. Wang, Y. Guan, P. Li et al., “The grain size and boundary
characteristics of ultra-low carbon bainitic steels,” Chinese
Journal of Stereology and Image Analysis, vol. 12, no. 2, pp. 84–87,
2007.
[2] Z. Yang, J. Zhang, N. Li, Z. Chu, W. Hui, and Y. Weng, “Fatigue
behavior of fine-grained high strength steel 42CrMoVNb,”
Jinshu Xuebao/Acta Metallurgica Sinica, vol. 40, no. 4, pp. 367–
372, 2004.
[3] B. Li, Y.-Z. Zhao, Y.-W. Shi, and Z.-L. Tian, “Microstructure and
fine structure in fusion zone of welded joint for high strength
fine grain steel,” Journal of Iron and Steel Research, vol. 15, no. 5,
pp. 35–39, 2003.
[4] Y. Fu, Z. Ma, D. Bin et al., “Microstructure and properties
of electro slag pressure welding joints of ultra-fine grained
reinforced bar with HRB400,” Welding Technology, vol. 38, no.
11, pp. 6–9, 2009.
[5] V. V. Satyanarayana, G. Madhusudhan Reddy, T. Mohandas,
and G. Venkata Rao, “Continuous drive friction welding studies
on AISI 430 ferritic stainless steel,” Science and Technology of
Welding and Joining, vol. 8, no. 3, pp. 184–194, 2003.
[6] X.-F. Mao, L. Fu, G.-F. Shang, R.-C. Zhao, and B. Shi, “Effect of
friction welding, heat treatment technology on the microstructure and property for drill rod S135,” Journal of Aeronautical
Materials, vol. 24, no. 1, pp. 57–62, 2004.
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