Proceedings of the International Conference on the Technology of Plasticity 2017

(1)

ScienceDirect

Available online at www.sciencedirect.com

Procedia Engineering 207 (2017) 1850–1855

Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity.

10.1016/j.proeng.2017.10.950

Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity.

1877-7058 Available online at www.sciencedirect.com

ScienceDirect

www.elsevier.com/locate/procedia

Peer-review under responsibility of

the scientific committee of the International Conference on the Technology of Plasticity

.

International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017, Cambridge, United Kingdom

Influence of burnishing condition on static recrystallization of an iron sheet

Motoki Terano

^a

, Fan Zhang

^b

, Masahiko Yoshino

^b

*

aOkayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama-shi, Okayama, 700-0005, Japan

bTokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8550, Japan

Abstract

This paper intends to study an effect of burnishing and annealing on static recrystallization. The result is expected to be used for a new technology to control only material surface microstructure in a steel plate. In this process, the stored strain energy by burnishing and the thermal energy by annealing lead to static recrystallization and grain growth in a material, which improve the microstructure of the material. In this paper, roller burnishing is employed to introduce the shear strain into the surface of the pure iron sheet. And effects of burnishing and annealing on static recrystallization in the finished surface layer are investigated utilizing Electron Back Scattering Diffraction (EBSD) analysis technique. The generation of shear deformation was confirmed by Kernel Average Misorientation (KAM) values at the surface layer. By conducting a series of the annealing and EBSD analyses, the static recrystallization process is observed. Since enough strain energy is accumulated by the burnishing in a specimen with large shear deformation zone, the static recrystallization occurs on the burnished surface preferentially after the annealing.

the scientific committee of the International Conference on the Technology of Plasticity

.

Keywords:Burnishing; Static recrystallization, pure iron

1. Introduction

In recent years, the widening imbalance between rising resource demand and falling supply has drawn the attention of many researchers. To save energy and resource saving purposes, comprehensive study works on thermo-

* Corresponding author. Tel.: +86-256-9829; fax: +86-256-9829.

E-mail address:[email protected]

Available online at www.sciencedirect.com

ScienceDirect

the scientific committee of the International Conference on the Technology of Plasticity

^.

International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017, Cambridge, United Kingdom

Influence of burnishing condition on static recrystallization of an iron sheet

Motoki Terano

^a

, Fan Zhang

^b

, Masahiko Yoshino

^b

*

Abstract

the scientific committee of the International Conference on the Technology of Plasticity

.

1. Introduction

2 Motoki Terano/ Procedia Engineering 00 (2017) 000–000

mechanical control processing have been carried out to improve physical properties of metallic materials without adding rare elements [1]-[3]. The feature of the material made by rolling and heat treatment method is of uniform characteristics [4]. However, it is more efficient if suitable characteristics can be generated at required position [5].

In this paper, a new technology to control only material surface microstructure is studied. Effects of the burnishing and the annealing on the static recrystallization in the finished surface layer are investigated utilizing Electron Back Scattering Diffraction (EBSD) analysis technique. The roller burnishing, which improve the surface quality [6], is employed to introduce the shear strain into the surface of the specimens. And by conducting a series of the annealing and the EBSD analyses, the static recrystallization process is observed.

2. Experimental methods 2.1. Burnishing tool

In this study, a roller burnishing is employed to introduce shear strain into the surface of the specimens. Then the specimens are sent to annealing so that recrystallizations are induced in the burnished surface. Figure 1 shows structure of a burnishing tool used for the experiment. There are three rollers at the bottom of the burnishing tool.

Diameter of the rollers is 3 mm, and length of the rollers is 5 mm. The coned disk springs are set into burnishing tool.

The burnishing load is determined by compression distance of the springs of the tool.

Table 1. Burnishing conditions.

(a) Schematic illustration (b) Picture Fig. 1. Burnishing tool.

Fig. 2. Example of burnishing and EBSD analysis position. Fig. 3. Annealing conditions.

2.2. Experimental conditions

A pure iron sheet is used as the specimen. It is annealed at 700ºC for 1 hour for normalization, in which residual strain is removed, prior to the burnishing experiment. Table 1 shows the experimental conditions. A CNC milling

Burnishing load

Rotation direction Roller 20mm

10mm

Machining device Universal CNC Milling Machine (MAKINO AE74)

Rotation Speed 15rpm

Lubricant Superoll-oil

(SUGINO MACHINE LIMITED)

Spring Coned disk springs

Burnishing load (Pushing stroke)

2.4kN (2mm) 3.8kN (3mm) 6.8kN (4mm) The number of rotations

(Processing Time)

15turns (20s) 30turns (40s) 60turns (80s) Cross-section

10 mm Rotation direction

WEDM

IPF Map of EBSD result

Burnished surface

0.5min(0.5min)

Temp. /ºC

600

R.T.

EBSD analysis Time

1min (2min) 1min (3min) 2min (5min) 2min (7min) 3min (10min)

Increment (Total) 60min (70min)

0.5min (1min)

Burnishing

(2)

Motoki Terano et al. / Procedia Engineering 207 (2017) 1850–1855 1851

ScienceDirect

the scientific committee of the International Conference on the Technology of Plasticity

.

International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017, Cambridge, United Kingdom

Influence of burnishing condition on static recrystallization of an iron sheet

Motoki Terano

^a

, Fan Zhang

^b

, Masahiko Yoshino

^b

*

Abstract

the scientific committee of the International Conference on the Technology of Plasticity

.

1. Introduction

ScienceDirect

the scientific committee of the International Conference on the Technology of Plasticity

^.

International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017, Cambridge, United Kingdom

Influence of burnishing condition on static recrystallization of an iron sheet

Motoki Terano

^a

, Fan Zhang

^b

, Masahiko Yoshino

^b

*

Abstract

the scientific committee of the International Conference on the Technology of Plasticity

.

1. Introduction

mechanical control processing have been carried out to improve physical properties of metallic materials without adding rare elements [1]-[3]. The feature of the material made by rolling and heat treatment method is of uniform characteristics [4]. However, it is more efficient if suitable characteristics can be generated at required position [5].

In this paper, a new technology to control only material surface microstructure is studied. Effects of the burnishing and the annealing on the static recrystallization in the finished surface layer are investigated utilizing Electron Back Scattering Diffraction (EBSD) analysis technique. The roller burnishing, which improve the surface quality [6], is employed to introduce the shear strain into the surface of the specimens. And by conducting a series of the annealing and the EBSD analyses, the static recrystallization process is observed.

2. Experimental methods 2.1. Burnishing tool

In this study, a roller burnishing is employed to introduce shear strain into the surface of the specimens. Then the specimens are sent to annealing so that recrystallizations are induced in the burnished surface. Figure 1 shows structure of a burnishing tool used for the experiment. There are three rollers at the bottom of the burnishing tool.

Diameter of the rollers is 3 mm, and length of the rollers is 5 mm. The coned disk springs are set into burnishing tool.

The burnishing load is determined by compression distance of the springs of the tool.

Table 1. Burnishing conditions.

(a) Schematic illustration (b) Picture Fig. 1. Burnishing tool.

Fig. 2. Example of burnishing and EBSD analysis position. Fig. 3. Annealing conditions.

2.2. Experimental conditions

A pure iron sheet is used as the specimen. It is annealed at 700ºC for 1 hour for normalization, in which residual strain is removed, prior to the burnishing experiment. Table 1 shows the experimental conditions. A CNC milling

Burnishing load

Rotation direction Roller 20mm

10mm

Machining device Universal CNC Milling Machine (MAKINO AE74)

Rotation Speed 15rpm

Lubricant Superoll-oil

(SUGINO MACHINE LIMITED)

Spring Coned disk springs

Burnishing load (Pushing stroke)

2.4kN (2mm) 3.8kN (3mm) 6.8kN (4mm) The number of rotations

(Processing Time)

15turns (20s) 30turns (40s) 60turns (80s) Cross-section

10 mm Rotation direction

WEDM

IPF Map of EBSD result

Burnished surface

0.5min(0.5min)

Temp. /ºC

600

R.T.

EBSD analysis Time

1min (2min) 1min (3min) 2min (5min) 2min (7min) 3min (10min)

Increment (Total) 60min (70min)

0.5min (1min)

Burnishing

(3)

1852 Motoki Terano/ Procedia Engineering 00 (2017) 000–000Motoki Terano et al. / Procedia Engineering 207 (2017) 1850–1855 3 machine is used for the burnishing. The Rotation speed is set to 15rpm. The lubricant is “Superoll-oil” which is often used for burnishing. Nine kinds of the experiments are conducted under different burnishing loads and rotation numbers.

Figure 2 shows an example of the burnishing surface and the EBSD analysis position. In order to observe the cross-section of the burnished specimen, each specimen is cut into strips parallel to the burnishing direction by using the wire electrical discharge machine. These strips are embedded in the acrylic resin. Then they are polished and analyzed with EBSD. Then the specimens are taken out from the acrylic resin, and they are annealed at 600ºC in argon atmosphere. After that, the specimens are analyzed by EBSD again. In this way, the annealing and the EBSD analysis are repeated as the schedule shown by Figure 3.

3. Correction method for EBSD analysis results

In this study, the EBSD analysis is repeated for the observation of the static recrystallization and the grain growth after annealing. However, the EBSD data contain error of the crystal orientation due to slight misalignment of the specimen after re-mounting. Figure 4(a) shows the specimen holder. Figure 4(b) and (c) compare Inverse Pole Figure (IPF) maps of before and after re-mounting of a specimen on the specimen holder. Here, the average crystal orientation is used as the reference orientation because the crystal orientation at a particular position is possibly affected by some defects on the surface of the observing cross section. Figure 4(b) and (c) apparently show difference of the colors of the crystal orientation due to alignment error of specimen. Thus, a correction method is developed to rectify the orientation error caused by misalignment of the specimen. In this method, the crystal orientation of all grains of the secondary IPF map is compensated so that its reference crystal orientation corresponds with that of the first IPF map.

(a) Specimen holder (b) IPF map of before re-mounting (c) IPF map of after re-mounting Fig. 4. Influence of Misalignment of specimen mounting on EBSD analysis results.

OIM Analysis (Version: 7.0.1 x64, TSL solutions co. ltd.) calculates the crystallographic texture data, such as the grain orientation, from the EBSD data on each crystal grain, and expresses them by three Euler angles. In the texture analysis, the Euler angles provide a mathematical depiction of the orientation of individual crystallites within a polycrystalline material. In this OIM analysis software, Bunge's description of Euler angles (i.e. ZXZ convention) is used to depict the grain orientation. However, this software also provides a function of XYZ convention to rotate the EBSD result.

Figure 5 shows the relationship between two rotation conventions, and they are expressed by the following equations,

𝑤𝑤1= 𝑹𝑹1𝑤𝑤� (1)

𝑤𝑤2= 𝑹𝑹2𝑤𝑤� (2)

So, following equations are obtained.

𝑤𝑤� = 𝑹𝑹2−1𝑤𝑤2 (3)

𝑤𝑤1= 𝑹𝑹1𝑹𝑹2−1𝑤𝑤2 (4)

(4)

Here 𝑹𝑹 is defined by𝑹𝑹=𝑹𝑹₁𝑹𝑹₂⁻¹, and we have 𝑤𝑤₁=𝑹𝑹𝑤𝑤₂. Then using the inverse XYZ convention, 𝑹𝑹 is transferred to the angles (ψ θ ϕ) as shown in Figure 6. These angles are input to the OIM Analysis system as the rotation command for correction of grain orientations.

Figure 7 shows the correction results. Compared with “Image 1” and “Corrected image 2”, the error of all crystal orientation is less than 1°.

Fig. 5. Relationship between two rotation conventions. Fig. 6. Flow chart of correction method.

Fig. 7. Before and after correction of rotated specimens.

4. Results and discussions

Figure 8 shows Kernel Average Misorientation (KAM) map of a cross section of a specimen burnished under conditions of 3.8 kN and 15 turns. Here, the step size of EBSD analysis is 2 µm. The KAM values are corresponded to the dislocation density [7], [8]. The upper surface is the burnished surface and the burnishing direction is from left to right. The generation of the shear deformation can be confirmed by the KAM values at the surface layer. The shear deformation zone is defined as the depth from the burnished surface to the border where the color begins to change. The depths of the shear deformation zone in all burnished conditions are summarized in Figure 9. The depth of the shear deformation zone increases with the number of rotation and the burnishing load.

By conducting a series of the annealing and the EBSD analyses, the static recrystallization process is observed.

Figure 10 shows the IPF maps and the KAM maps of the specimen burnished under the conditions of 2.4 kN and 15 turns. The annealing time is 0, 1, 5 and 70 minutes after burnishing and the annealing temperature is 600ºC. Before the annealing, the KAM value at the burnished surface is very large. This is attributed to the shear deformation introduced to the burnished surface. The static recrystallization occurs only in the shear deformation zone near the burnished surface when the annealing time was 1 minute. The static recrystallized grains have grown with increase

001

111 101

𝑹𝑹=𝑹𝑹₁𝑹𝑹₂⁻¹ Correction angle (𝜓𝜓 𝜃𝜃 𝜙𝜙)

Error of crystal orientations less than 1°

Image 2 after correction

𝑹𝑹₁

𝑹𝑹₂

Image 1

Image 2

(5)

1854 Motoki Terano/ Procedia Engineering 00 (2017) 000–000Motoki Terano et al. / Procedia Engineering 207 (2017) 1850–1855 5 of the annealing time. The KAM value is reduced in the recrystallized grains. Since the first annealing at 700ºC for 1 hour prior to the burnishing to remove residual strain is conducted, the second annealing at 600ºC would not have affect the base microstructure, i.e. only the region which was deformed is affected due to the stored energy of deformation. Therefore the imported shear strain energy works as the driving force of the static recrystallization and the grain growth.

Fig. 8. Example of KAM map (3.8 kN, 15 turns). Fig. 9. Relationship between shear deformation zone and burnished conditions.

Fig. 10. IPF map and KAM map before/after annealing (2.4 kN, 15 turns).

The recrystallized area in each specimen is calculated from the recrystallized grains determined in the KAM map as shown in Figure 10. Figure 11 shows variation of the total recrystallized area against the annealing time. It is found that the total recrystallized area increased quickly in the first 10 minutes, but became almost stable after 10 minutes. In addition, the total recrystallization area increased with the increase of the burnishing load and the number of rotation when the annealing time was less than 10 minutes. As a result, the recrystallized area, i.e. the thickness of recrystallized region, can be controlled by adjusting the burnishing load.

Figure 12 shows the relationship between the number of the recrystallized grain and the annealing time. When the burnishing load is small, i.e. 2.4 kN, the number of recrystallized grain increases with the annealing time.

However, when the burnishing load is large, i.e. 6.8 kN, the number of the recrystallized grain decreases with the annealing time. As a result, the average grain size can be controlled by adjusting the burnishing load and the number of burnishing time.

It is apparent from these results that the recrystallized area and feature of the recrystallized grains depend on the burnishing conditions and the annealing conditions. In summary by the burnishing work, the number of generation of recrystallized grain was increased and the recrystallized grain size was decreased when the burnishing work was

Shear Deformation Burnished Zone

surface

Burnished direction

100μm 0° 5°

Annealing time

001 111 101

0 min 1 min 5 min 70 min

mapIPF

(001)

0° 5°

KAM map

500μm

Recrystallized part 0

50 100 150 200 250 300

0 10 20 30 40 50 60 70

Depth of Shear deformation zone /μm

The number of rotation /turn 6.8 kN

2.4 kN 3.8 kN

large. They indicate possibility of the partial control of the microstructure by utilizing the burnishing technique. As the future works, we would like to analyze by the following method. Influence of burnishing conditions and heat treatment conditions on nucleation rate and grain growth kinetics will be quantitatively evaluated from the experimental data. In addition, effects of the stored energy and plastic strain in the burnished layer, which will be calculated by the plasticity theory, on the nucleation and grain growth process will be evaluated. Based on these analyses, a microstructure prediction system for the burnishing process can be developed. It is expected that this microstructure prediction system will enable us microstructure control by burnishing.

Fig. 11. Recrystallization area. Fig. 12. Number of recrystallization grain.

5. Conclusions

Shear strain was imported into the material surface layer by the burnishing process and the static recrystallization process was investigated by the repeated annealing and the EBSD analysis. The method to compensate the grain orientations of all observation results of the same specimen by EBSD was developed. The depth of the recrystallization zone was calculated and the relation between the recrystallization rate, burnishing load and the number of rotations was discussed. Since enough strain energy was accumulated by the burnishing in a specimen with large shear deformation zone, the static recrystallization occurred on the burnished surface preferentially after the annealing. This is because the stored energy from deformation arising from the burnishing process is the driving force for the static recrystallization. It was shown that the partial control of the microstructure on a material surface is possible by the combination of the burnishing and the annealing.

Acknowledgements

This work was supported by JSPS KAKENHI (Grant Number 15K17947), Grant-in-Aid for Young Scientists (B).

References

[1] Dorothe´e D., Stefan Z., Ludger L., Dierk R., Overview of Microstructure and Microtexture Development in Grain-oriented Silicon Steel, Journal of Magnetism and Magnetic Materials, 304(2006), 183–186.

[2] Akinobu S., Hamidreza J., Nobuhiro T., Microstructure and Crystallographic Features of Martensite Transformed from Ultrafine-Grained Austenite in Fe–24Ni–0.3C Alloy, Materials Transactions, 53(2006), 81-86.

[3] Yasuyuki H., Takeshi O., Takeshi I., Onset of Secondary Recrystallization in High Purity 3.3%Si Steel, ISIJ International, 54 (2014), 2385- 2393.

[4] Kubota, T., Evolution of Electrical Steel Sheet, Journal of the Magnetics Society of Japan, 27(2003), 787-792.

[5] Yuji H., Motoki T., Masahiko Y., Influence of repeated shear strain on recrystallization of iron sheet, Procedia Engineering, 81(2014), 1324- 1329.

[6] Klicke F., Liermann J., Roller Burnishing of Hard Turned Surfaces, Int. J. Mach. Tools Manufact. 38(1998), 419-423.

[7] Masayuki K., Assessment of Local Deformation Using EBSD: Quantification of Local Damage at Grain Boundaries, Materials characterization, 66(2012), 56-67.

[8] Jiang J., Britton T.B., Wilkinson A.J., Evolution of Dislocation Density Distributions in Copper During Tensile Deformation, Acta Materialia, 61(2013), 7227–7239.

Total recrystallized area /mm2

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

0 20 40 60 80

Annealing time /min

2.4 kN 3.8 kN 6.8 kN 15 turns

30 turns 60 turns

0 20 40 60 80 100 120 140

0.1 1 10 100

Number recrystallized grain

Annealing time /min

2.4 kN 3.8 kN 6.8 kN 15 turns

30 turns 60 turns

(6)

of the annealing time. The KAM value is reduced in the recrystallized grains. Since the first annealing at 700ºC for 1 hour prior to the burnishing to remove residual strain is conducted, the second annealing at 600ºC would not have affect the base microstructure, i.e. only the region which was deformed is affected due to the stored energy of deformation. Therefore the imported shear strain energy works as the driving force of the static recrystallization and the grain growth.

Fig. 8. Example of KAM map (3.8 kN, 15 turns). Fig. 9. Relationship between shear deformation zone and burnished conditions.

Fig. 10. IPF map and KAM map before/after annealing (2.4 kN, 15 turns).

The recrystallized area in each specimen is calculated from the recrystallized grains determined in the KAM map as shown in Figure 10. Figure 11 shows variation of the total recrystallized area against the annealing time. It is found that the total recrystallized area increased quickly in the first 10 minutes, but became almost stable after 10 minutes. In addition, the total recrystallization area increased with the increase of the burnishing load and the number of rotation when the annealing time was less than 10 minutes. As a result, the recrystallized area, i.e. the thickness of recrystallized region, can be controlled by adjusting the burnishing load.

Figure 12 shows the relationship between the number of the recrystallized grain and the annealing time. When the burnishing load is small, i.e. 2.4 kN, the number of recrystallized grain increases with the annealing time.

However, when the burnishing load is large, i.e. 6.8 kN, the number of the recrystallized grain decreases with the annealing time. As a result, the average grain size can be controlled by adjusting the burnishing load and the number of burnishing time.

It is apparent from these results that the recrystallized area and feature of the recrystallized grains depend on the burnishing conditions and the annealing conditions. In summary by the burnishing work, the number of generation of recrystallized grain was increased and the recrystallized grain size was decreased when the burnishing work was

Shear Deformation Burnished Zone

surface

Burnished direction

100μm 0° 5°

Annealing time

001 111

101