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Impact Toughness of 17MnSi Pipeline Steel without and after Modification by Ultrasonic Surface Impact Treatment
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 113 (2015) 525 – 529
International Conference on Oil and Gas Engineering, OGE-2015
Impact toughness of 17MnSi pipeline steel without and after modification by ultrasonic surface impact treatment Maruschak P.O.a, Panin S.V.a,c*, Vlasov I.V.b, Polivanaya U.V.a, Bishchak R.T.d a Ternopil Ivan Pul'uy National Technical University, 56, Ruska Str., Ternopil 46001, Ukraine Institute of Strength Physics and Materials Science SB RAS, 2/4 pr. Akademicheskii, Tomsk 634021, Russian Federation c Tomsk Polytechnic University, 30, pr. Lenina, Tomsk 634050, Russian Federation d Ivano-Frankivsk National Technical University of Oil and Gas, 15, Karpatska Str., Ivano-Frankivsk 76019, Ukraine
b
Abstract The basic regularities of the 17MnSi pipeline steel impact fracture without and after the ultrasonic impact surface treatment were identified. The diagrams of the material dynamic deformation which allowed determining quantitative characteristics of the crack initiation and crack propagation energy consumption in the Charpy specimens of the pipeline steel were analyzed. The crack was found out to correspond approximately to 25 % of the total energy consumption of the material fracture. The fractographic analysis of the specimen failure surfaces in the initial state and after the ultrasonic treatment was carried out. © 2015 2015The TheAuthors. Authors. Published Elsevier © Published by by Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the Omsk State Technical University. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Omsk State Technical University Keywords: impact toughness; fracture; crack initiation; fractography
1. Introduction The assurance of the safety and reliability of oil and gas transportation is one of the priority tasks for the experts in the field of fracture mechanics. The solution of this task will allow to mitigate the risks of the emergency failures of main oil and gas pipelines and to provide the most effective operation of these strategic objects [1]. The analysis of the gas pipelines service fracture accidents allows to state that their main reasons are the welding joints defects, construction and repair stress concentrators, improper welding conditions and also nonmetallic inclusions and structural damages formation in the heat-affected zone [1,2].
* Corresponding author. Tel.:+7-382-228-6904; fax: +7-382-249-2576. E-mail address: [email protected]
1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Omsk State Technical University
doi:10.1016/j.proeng.2015.07.346
526
P.O. Maruschak et al. / Procedia Engineering 113 (2015) 525 – 529
2. Study subject It is known that there is a number of methods of improving the materials resistance to the stress concentrators [3,4]. The modification of a thin surface layer can block certain fracture mechanisms and, thus improve the crack resistance of material. However, the surface strengthening methods scarcely ever give the positive effects that are caused by the peculiarities of the dislocation structure and microdefects concentration in the treatment area. The degradation processes in heat-affected zone of the welding joints are one of the negative effects manifestation [1,5]. Such effects also demand the research and development of the methods concerning their negative influence decrease. Consequently the considerable attention is paid to the research of the modified materials sensitivity to the impact loads. The objective of this study is 17MnSi pipeline steel impact toughness and also the high-energy effect influence in the form of the ultrasonic surface impact treatment on its fracture mechanisms. 3. Experimental The Charpy specimens of the K52 strength grade 17MnSi pipeline steel cut out of the pipe in the as supplied condition were investigated. The structure was analyzed with the use of the Axiovert 40 MAT metallographic microscope. The impact toughness was measured on Charpy specimens 8.0 u 7.5 u 55 mm sized. The radius of the Vshaped notch was equal to 0.25 r 0.025 mm. The various cutting directions specimens were used, Fig. 1. &
% $
Fig. 1. The scheme of Charpy specimens cutting from the pipe segment.
The specimens modification was carried out by means of equipment for the ultrasonic surface impact treatment including: the IL4 generator intended for current generation with a frequency of 25 kHz, power of 460 W and a working tool transforming the electric oscillations into the mechanical ones and performing the surface treatment with the help of high-strength pins. The ultrasonic vibrations excitation of the given frequency and amplitude is carried out by means of the electric generator. Under the impact of the deforming elements the machine part surface layer is deformed plastically that is followed by the defects density increasing. Simultaneously the smoothing of the surface irregularities occurs. The ultrasonic surface treatment (UST) by the oscillating tool is similar to the method of surface plastic straining by a sphere. The essential difference is that the detail surface pulsed deformation is conducted by the deforming element as a result of the ultrasonic vibrations of the given frequency and displacements amplitude. 3.1. 17MnSi steel microstructure The object under study is the low-alloyed hot-rolled 17MnSi steel (from the emergency reserve) having a hypopearlitic microstructure, Fig. 2a, b.
P.O. Maruschak et al. / Procedia Engineering 113 (2015) 525 – 529
a
527
b
Fig. 2. 17MnSi steel microstructure (u400)
3.2. The impact toughness of the 17MnSi steel The impact toughness of the 17MnSi steel of various cutting directions was determined on the INSTRON 450 automated impact tester. The results obtained after data processing with the help of the impact tester software allows to divide the specimen fracture energy into the components by means of the transformation of the "load-time" dependence (Р-t) into the "load-bending" one (Р - s). For this purpose for the known mass of the striker (loading device) m, initial impact velocity v0, taking into account the dependence Р(t), the striker displacement velocity change v(t) was determined by the double successive integration in the process of the specimens loading:
Q (t ) v0
t
1 P t dt m t³0
Then the dependence of the striker displacement value on the loading time is determined: t
s (t )
³ v t dt
t0
The energy consumption components for the specimens fracture in the separate stages were determined based on the area under the registered diagrams P(s). It should be noted that the total fracture energy of the specimens A was considered as the sum of the crack initiation energy Ai and the crack propagation one Ap [6]: A
Ai Аp
The material macroscale response to the impact loading is the specimen deformation diagram containing the summarized information concerning the variation of the energy and material deformation characteristics in the impact area. The fracture energy value of the specimens of all cutting groups is found out to fluctuate from 80.6 to 87.2 J. The graph has a nonsymmetrical domed shape typical for the ductile materials having the apparent areas of the crack initiation and rather stable areas of the crack propagation. All studied specimens had the similar form of the fracture diagram depicted in the following coordinates “P – Δl” and “E - t”, Fig. 3a,b. The ratio of the initiation energy to the total energy consumption of the specimens fracture also fluctuates in the narrow range from 23.4 to 25.6 %. This points to the fact that the general fracture pattern of the given specimens and about the lack of material macroscale properties anisotropy in the various directions of the pipe material.
528
P.O. Maruschak et al. / Procedia Engineering 113 (2015) 525 – 529
a 31
b 100
3PD[
E, J
3
60
40
20
80
0
0
1
2
3
4
5
ΔOPP
6
7
8
WPV
Fig. 3. The impact fracture diagrams of the 17MnSi steel in the initial state: a - "load - specimen bending" "P – Δl"; b - fracture energy consumption - time "Е-t"; 1,2,3 - is the number of the specimen shown in Table 1.
Under the impact loading the plastic deformation and fracture of the material are two successive stages of the single evolution process of the shear stability loss at various scales, Fig. 3. Moreover, the 0 - Pmax segment characterizes the crack initiation energy consumption, while the right branch of the diagram - the propagation one. The complete diagram characterizes the global shear stability loss at the macroscale level. The total energy consumption of the Charpy specimens impact fracture (A) data, as well as the crack initiation (Ai) and crack propagation (Ap) ones are presented in Table 1. Table 1. The results of experimental estimation of the fracture toughness. S.
The cutting
No
orientation
The treatment
Ai, (J)
Ap, (J)
A, (J)
KCV,
1
A
-
20.60
59.98
80.58
179
2
B
-
20.40
66.67
87.07
193
3
C
-
21.10
66.10
87.20
194
4
A
UST
3.1
68.64
71.74
145
5
C
UST
6.45
61.44
67.89
135
J/сm2
It should be noted that neither of the studied specimens was completely fractured. The specimens after the impact loading became the V-shaped ones with heavily deformed central area, Fig. 4. This points to the high ductility of the test material in every cutting direction. The photographs analysis of the tested specimens revealed that the fracture mechanism along the crack front varied from the absolutely ductile shear to the "shear+rotation" mechanism. The specimens after treatment have more brittle fracture mechanism that can be related to the increase in the properties gradient across the specimen cross-section (a high-strength surface having a ductile core). By means of the latter the deformation gradient occurs at the boundary between these layers under the impact. This gives rise to the less energy consuming crack initiation and accelerates the material fracture [4]. The particular importance of the strengthened surface is evident with the plastic flow development, that gave rise to the crack initiation energy reduction from 3.3 to 6.6 times in comparison with the material in the initial state.
529
P.O. Maruschak et al. / Procedia Engineering 113 (2015) 525 – 529
a
b
c
d
Fig. 4 The lateral face (a,c) and fracture surface (b,d) of the specimen in the initial state (a,b) and after the UST (c,d).
The obtained results can be interpreted from the viewpoint of the physical mesomechanics. The Charpy specimens fracture process is a hierarchically self-consistent plastic deformation which is carried out according to the “shear” scheme (crack initiation) and “shear+rotation” (crack propagation). Deformations by shear develop near the stress concentrators as the local deformation manifestations and occur as the relaxation process with the developed shear lips formation both in the treated and non-treated specimens [8], Fig. 4a,c. This results from the substantial amount of energy "supplied" into the material for the short time period. The deformation constraint of the treated material external layers initiates new stress concentrators that leads to the accelerated and less energyconsuming deformation and fracture, Fig. 4b,d. 4. Conclusion The basic regularities of the 17MnSi pipeline steel fracture in the non-treated and modified states were studied. The values of the crack initiation energy and crack propagation one was determined based on the recorded diagrams of the dynamic deformation. The crack initiation energy value takes approximately 25 % of the total energy consumption of the material fracture. The practical value of the study consists in the identification of the low 17MnSi steel sensitivity to the straining treatment (in this case to the UST), that can be used when planning the repair works of the main gas pipelines. References [1] G. Gabetta, H.M. Nykyforchyn, E. Lunarska, et al In-service degradation of gas trunk pipeline X52 steel // Materials Science 44 (2008) 104119. [2] Y. Liu, Y. Feng, Q. Ma, X. Song Dynamic fracture toughness of X70 pipeline steel and its relationship with arrest toughness and CVN // Materials and Design 23 (2002) 693-699. [3] G. Sun, R. Zhou, J. Lu, J. Mazumder Evaluation of defect density, microstructure, residual stress, elastic modulus, hardness and strength of laser-deposited AISI 4340 steel // Acta Materialia 84 (2015) 172-189. [4] P.O. Marushchak, R.T. Bishchak, T. Vuherer, V.B. Hlad’o Impact toughness of specimens cut out from the rollers of machines for continuous casting of blanks with fused layers // Materials Science 48 (2013) 704-714. [5] A.M. Guo, S.R. Li, J. Guo, P.H. Li, Q.F. Ding, Wu K.M., He X.L. Effect of zirconium addition on the impact toughness of the heat affected zone in a high strength low alloy pipeline steel // Materials Characterization 59 (2008) 134-139. [6] S.H. Hashemi Apportion of Charpy energy in API 5L grade X70 pipeline steel // International Journal of Pressure Vessels and Piping 85 (2008) 879–884. [7] M.A. Shtremel Informativeness of measurements of impact toughness // Metal Science and Heat Treatment 50 (2008) 544-557. [8] T. Kobayashi, I. Yamamoto, M. Niinomi Evaluation of dynamic fracture toughness parameters by instrumented Charpy impact test // Engineering Fracture Mechanics 24 (1986) 773-782.
ScienceDirect Procedia Engineering 113 (2015) 525 – 529
International Conference on Oil and Gas Engineering, OGE-2015
Impact toughness of 17MnSi pipeline steel without and after modification by ultrasonic surface impact treatment Maruschak P.O.a, Panin S.V.a,c*, Vlasov I.V.b, Polivanaya U.V.a, Bishchak R.T.d a Ternopil Ivan Pul'uy National Technical University, 56, Ruska Str., Ternopil 46001, Ukraine Institute of Strength Physics and Materials Science SB RAS, 2/4 pr. Akademicheskii, Tomsk 634021, Russian Federation c Tomsk Polytechnic University, 30, pr. Lenina, Tomsk 634050, Russian Federation d Ivano-Frankivsk National Technical University of Oil and Gas, 15, Karpatska Str., Ivano-Frankivsk 76019, Ukraine
b
Abstract The basic regularities of the 17MnSi pipeline steel impact fracture without and after the ultrasonic impact surface treatment were identified. The diagrams of the material dynamic deformation which allowed determining quantitative characteristics of the crack initiation and crack propagation energy consumption in the Charpy specimens of the pipeline steel were analyzed. The crack was found out to correspond approximately to 25 % of the total energy consumption of the material fracture. The fractographic analysis of the specimen failure surfaces in the initial state and after the ultrasonic treatment was carried out. © 2015 2015The TheAuthors. Authors. Published Elsevier © Published by by Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the Omsk State Technical University. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Omsk State Technical University Keywords: impact toughness; fracture; crack initiation; fractography
1. Introduction The assurance of the safety and reliability of oil and gas transportation is one of the priority tasks for the experts in the field of fracture mechanics. The solution of this task will allow to mitigate the risks of the emergency failures of main oil and gas pipelines and to provide the most effective operation of these strategic objects [1]. The analysis of the gas pipelines service fracture accidents allows to state that their main reasons are the welding joints defects, construction and repair stress concentrators, improper welding conditions and also nonmetallic inclusions and structural damages formation in the heat-affected zone [1,2].
* Corresponding author. Tel.:+7-382-228-6904; fax: +7-382-249-2576. E-mail address: [email protected]
1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Omsk State Technical University
doi:10.1016/j.proeng.2015.07.346
526
P.O. Maruschak et al. / Procedia Engineering 113 (2015) 525 – 529
2. Study subject It is known that there is a number of methods of improving the materials resistance to the stress concentrators [3,4]. The modification of a thin surface layer can block certain fracture mechanisms and, thus improve the crack resistance of material. However, the surface strengthening methods scarcely ever give the positive effects that are caused by the peculiarities of the dislocation structure and microdefects concentration in the treatment area. The degradation processes in heat-affected zone of the welding joints are one of the negative effects manifestation [1,5]. Such effects also demand the research and development of the methods concerning their negative influence decrease. Consequently the considerable attention is paid to the research of the modified materials sensitivity to the impact loads. The objective of this study is 17MnSi pipeline steel impact toughness and also the high-energy effect influence in the form of the ultrasonic surface impact treatment on its fracture mechanisms. 3. Experimental The Charpy specimens of the K52 strength grade 17MnSi pipeline steel cut out of the pipe in the as supplied condition were investigated. The structure was analyzed with the use of the Axiovert 40 MAT metallographic microscope. The impact toughness was measured on Charpy specimens 8.0 u 7.5 u 55 mm sized. The radius of the Vshaped notch was equal to 0.25 r 0.025 mm. The various cutting directions specimens were used, Fig. 1. &
% $
Fig. 1. The scheme of Charpy specimens cutting from the pipe segment.
The specimens modification was carried out by means of equipment for the ultrasonic surface impact treatment including: the IL4 generator intended for current generation with a frequency of 25 kHz, power of 460 W and a working tool transforming the electric oscillations into the mechanical ones and performing the surface treatment with the help of high-strength pins. The ultrasonic vibrations excitation of the given frequency and amplitude is carried out by means of the electric generator. Under the impact of the deforming elements the machine part surface layer is deformed plastically that is followed by the defects density increasing. Simultaneously the smoothing of the surface irregularities occurs. The ultrasonic surface treatment (UST) by the oscillating tool is similar to the method of surface plastic straining by a sphere. The essential difference is that the detail surface pulsed deformation is conducted by the deforming element as a result of the ultrasonic vibrations of the given frequency and displacements amplitude. 3.1. 17MnSi steel microstructure The object under study is the low-alloyed hot-rolled 17MnSi steel (from the emergency reserve) having a hypopearlitic microstructure, Fig. 2a, b.
P.O. Maruschak et al. / Procedia Engineering 113 (2015) 525 – 529
a
527
b
Fig. 2. 17MnSi steel microstructure (u400)
3.2. The impact toughness of the 17MnSi steel The impact toughness of the 17MnSi steel of various cutting directions was determined on the INSTRON 450 automated impact tester. The results obtained after data processing with the help of the impact tester software allows to divide the specimen fracture energy into the components by means of the transformation of the "load-time" dependence (Р-t) into the "load-bending" one (Р - s). For this purpose for the known mass of the striker (loading device) m, initial impact velocity v0, taking into account the dependence Р(t), the striker displacement velocity change v(t) was determined by the double successive integration in the process of the specimens loading:
Q (t ) v0
t
1 P t dt m t³0
Then the dependence of the striker displacement value on the loading time is determined: t
s (t )
³ v t dt
t0
The energy consumption components for the specimens fracture in the separate stages were determined based on the area under the registered diagrams P(s). It should be noted that the total fracture energy of the specimens A was considered as the sum of the crack initiation energy Ai and the crack propagation one Ap [6]: A
Ai Аp
The material macroscale response to the impact loading is the specimen deformation diagram containing the summarized information concerning the variation of the energy and material deformation characteristics in the impact area. The fracture energy value of the specimens of all cutting groups is found out to fluctuate from 80.6 to 87.2 J. The graph has a nonsymmetrical domed shape typical for the ductile materials having the apparent areas of the crack initiation and rather stable areas of the crack propagation. All studied specimens had the similar form of the fracture diagram depicted in the following coordinates “P – Δl” and “E - t”, Fig. 3a,b. The ratio of the initiation energy to the total energy consumption of the specimens fracture also fluctuates in the narrow range from 23.4 to 25.6 %. This points to the fact that the general fracture pattern of the given specimens and about the lack of material macroscale properties anisotropy in the various directions of the pipe material.
528
P.O. Maruschak et al. / Procedia Engineering 113 (2015) 525 – 529
a 31
b 100
3PD[
E, J
3
60
40
20
80
0
0
1
2
3
4
5
ΔOPP
6
7
8
WPV
Fig. 3. The impact fracture diagrams of the 17MnSi steel in the initial state: a - "load - specimen bending" "P – Δl"; b - fracture energy consumption - time "Е-t"; 1,2,3 - is the number of the specimen shown in Table 1.
Under the impact loading the plastic deformation and fracture of the material are two successive stages of the single evolution process of the shear stability loss at various scales, Fig. 3. Moreover, the 0 - Pmax segment characterizes the crack initiation energy consumption, while the right branch of the diagram - the propagation one. The complete diagram characterizes the global shear stability loss at the macroscale level. The total energy consumption of the Charpy specimens impact fracture (A) data, as well as the crack initiation (Ai) and crack propagation (Ap) ones are presented in Table 1. Table 1. The results of experimental estimation of the fracture toughness. S.
The cutting
No
orientation
The treatment
Ai, (J)
Ap, (J)
A, (J)
KCV,
1
A
-
20.60
59.98
80.58
179
2
B
-
20.40
66.67
87.07
193
3
C
-
21.10
66.10
87.20
194
4
A
UST
3.1
68.64
71.74
145
5
C
UST
6.45
61.44
67.89
135
J/сm2
It should be noted that neither of the studied specimens was completely fractured. The specimens after the impact loading became the V-shaped ones with heavily deformed central area, Fig. 4. This points to the high ductility of the test material in every cutting direction. The photographs analysis of the tested specimens revealed that the fracture mechanism along the crack front varied from the absolutely ductile shear to the "shear+rotation" mechanism. The specimens after treatment have more brittle fracture mechanism that can be related to the increase in the properties gradient across the specimen cross-section (a high-strength surface having a ductile core). By means of the latter the deformation gradient occurs at the boundary between these layers under the impact. This gives rise to the less energy consuming crack initiation and accelerates the material fracture [4]. The particular importance of the strengthened surface is evident with the plastic flow development, that gave rise to the crack initiation energy reduction from 3.3 to 6.6 times in comparison with the material in the initial state.
529
P.O. Maruschak et al. / Procedia Engineering 113 (2015) 525 – 529
a
b
c
d
Fig. 4 The lateral face (a,c) and fracture surface (b,d) of the specimen in the initial state (a,b) and after the UST (c,d).
The obtained results can be interpreted from the viewpoint of the physical mesomechanics. The Charpy specimens fracture process is a hierarchically self-consistent plastic deformation which is carried out according to the “shear” scheme (crack initiation) and “shear+rotation” (crack propagation). Deformations by shear develop near the stress concentrators as the local deformation manifestations and occur as the relaxation process with the developed shear lips formation both in the treated and non-treated specimens [8], Fig. 4a,c. This results from the substantial amount of energy "supplied" into the material for the short time period. The deformation constraint of the treated material external layers initiates new stress concentrators that leads to the accelerated and less energyconsuming deformation and fracture, Fig. 4b,d. 4. Conclusion The basic regularities of the 17MnSi pipeline steel fracture in the non-treated and modified states were studied. The values of the crack initiation energy and crack propagation one was determined based on the recorded diagrams of the dynamic deformation. The crack initiation energy value takes approximately 25 % of the total energy consumption of the material fracture. The practical value of the study consists in the identification of the low 17MnSi steel sensitivity to the straining treatment (in this case to the UST), that can be used when planning the repair works of the main gas pipelines. References [1] G. Gabetta, H.M. Nykyforchyn, E. Lunarska, et al In-service degradation of gas trunk pipeline X52 steel // Materials Science 44 (2008) 104119. [2] Y. Liu, Y. Feng, Q. Ma, X. Song Dynamic fracture toughness of X70 pipeline steel and its relationship with arrest toughness and CVN // Materials and Design 23 (2002) 693-699. [3] G. Sun, R. Zhou, J. Lu, J. Mazumder Evaluation of defect density, microstructure, residual stress, elastic modulus, hardness and strength of laser-deposited AISI 4340 steel // Acta Materialia 84 (2015) 172-189. [4] P.O. Marushchak, R.T. Bishchak, T. Vuherer, V.B. Hlad’o Impact toughness of specimens cut out from the rollers of machines for continuous casting of blanks with fused layers // Materials Science 48 (2013) 704-714. [5] A.M. Guo, S.R. Li, J. Guo, P.H. Li, Q.F. Ding, Wu K.M., He X.L. Effect of zirconium addition on the impact toughness of the heat affected zone in a high strength low alloy pipeline steel // Materials Characterization 59 (2008) 134-139. [6] S.H. Hashemi Apportion of Charpy energy in API 5L grade X70 pipeline steel // International Journal of Pressure Vessels and Piping 85 (2008) 879–884. [7] M.A. Shtremel Informativeness of measurements of impact toughness // Metal Science and Heat Treatment 50 (2008) 544-557. [8] T. Kobayashi, I. Yamamoto, M. Niinomi Evaluation of dynamic fracture toughness parameters by instrumented Charpy impact test // Engineering Fracture Mechanics 24 (1986) 773-782.