The in-service behaviour of alloyed steel A-387 Gr. 11 Class 1, for pressure vessels, used for high temperature applications, depends on the properties of its welded joint, with parent metal (BM), heat-affected-zone (HAZ) and weld metal (WM), as constituents. Charpy testing of BM, WM and HAZ, together with, determination of the parameters of fatigue-crack growth and fatigue threshold ΔKth was used, in order to understand, how heterogeneity of structure and different mechanical properties of welded joint constituents affect on crack initiation and propagation

D. Kozak

M. Burzić

M. Manjgo

O. Popović

R. Prokić-Cvetković

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The effects of dynamic load on behaviour of welded joint A-387 Gr. 11 alloyed steel

The in-service behaviour of alloyed steel A-387 Gr. 11 Class 1, for pressure vessels, used for high temperature applications, depends on the properties of its welded joint, with parent metal (BM), heat-affected-zone (HAZ) and weld metal (WM), as constituents. Charpy testing of BM, WM and HAZ, together with, determination of the parameters of fatigue-crack growth and fatigue threshold Delta Kth was used, in order to understand, how heterogeneity of structure and different mechanical properties of welded joint constituents affect on crack initiation and propagation

Burzić, Meri

Manjgo, Mersida

Kozak, Dražan

Prokić-Cvetković, Radica

Popović, Olivera

Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade

27METALURGIJA 52 (2013) 1, 27-31M. BURZIĆ, M. MANJGO, D. KOZAK, R. PROKIĆ-CVETKOVIĆ, O. POPOVIĆTHE EFFECTS OF DYNAMIC LOAD ON BEHAVIOUR OF WELDED JOINT A-387 Gr. 11 ALLOYED STEELReceived – Prispjelo: 2012-03-21Accepted – Prihvaćeno: 2012-07-15Original Scientifi c Paper – Izvorni znanstveni radISSN 0543-5846METABK 52(1) 27-31 (2013)UDC – UDK 669.15:620.178.3=111M. Burzić, R. Prokić-Cvetković, O. Popović, University of Belgrade, Faculty of Mechanical Engineering, Belgrade, SerbiaM. Manjgo, Faculty of Mechanical Engineering, Mostar, Bosnia and Her-zegovinaD. Kozak, J. J. Strossmayer University of Osijek, Mechanical Engineer-ing Faculty in Slavonski Brod, CroatiaThe in-service behaviour of alloyed steel A-387 Gr. 11 Class 1, for pressure vessels, used for high temperature appli-cations, depends on the properties of its welded joint, with parent metal (BM), heat-aff ected-zone (HAZ) and weld metal (WM), as constituents. Charpy testing of BM, WM and HAZ, together with, determination of the parameters of fatigue-crack growth and fatigue threshold ΔKth was used, in order to understand, how heterogeneity of structure and diff erent mechanical properties of welded joint constituents aff ect on crack initiation and propagation.Key words: alloyed steel A-387 Gr. 11, fatigue, impact energy, Paris relationshipINTRODUCTIONExploitation properties of A-387 Gr. 11 Class 1 al-loyed steel, designed for manufacture of pressure ves-sels operating at elevated temperatures and pressures, largely depend on properties of the critical zones of a welded joint. Heat-affected zone (HAZ) and weld metal (WM) are latent locations of crack initiation, i.e. the lo-cations where local brittle zones to whom crack initia-tion is attributed could be formed [1].For better understanding of the causes and modes of crack initiation and crack growth in welded joints of steel designed for operation at elevated temperatures and under high pressure, it is necessary to establish how the heterogeneity of structure and mechanical proper-ties of a welded joint affects crack initiation and growth, and to quantify the parameters controlling local-strain behaviour and crack growth.The aim of this investigation is to assess the effects of heterogeneity of structure and mechanical properties of base metal and components of the welded joint of A-387 Gr.11 Class 1 steel on crack initiation and growth, as well as on the parameters of fatigue-crack growth (da/dN and ΔKth) at elevated temperature of 540 °C, based on the results obtained [1].MATERIALFor testing, the sample of a welded joint of A-387 Gr. 11 Class 1 steel, with weld metal in the middle (dou-ble U-shaped weld), was used, the dimensions of which were 350 x 500 x 96 mm. Chemical composition of A-387 Gr. 11 Class 11 is presented in Table 1 [2]. The procedure for testing at elevated temperature of 540 °C is defi ned by the standard EN 10002-5 [3]. The results of tensile test of mechanical properties of A-387 Gr. 11 Class 1 steel at operating tempera-ture are presented in Table 2 [2].Table 1 Chemical composition of tested material [2]Chemical composition / mas. %C Si Mn P S Cr Mo0,15 0,29 0,54 0,022 0,011 0,93 0,47Table 2 Results of tensile test [2]Rp0,2 / MPa Rm / MPa A / %220 280 36Welding of sheets new and exploited BM was con-ducted in two phases, as follows:–  root run – by manual arc procedure, using a plated electrode LINCOLN Sl 19G (AWS: E8018-B2), –  fi lling – by arc welding using powder protection, where the wire designated as LINCOLN LNS 150 and powder LINCOLN P230 were used as fi ller metals. Chemical composition of used electrode LINCOLN Sl 19G (FM A) and wire LINCOLN LNS 150 (FM B) according to attest documen-tation is presented in Table 3. Main mechanical properties according to attest docu-mentation are presented in Table 4.Table 3 Chemical composition of fi ller metal [4]Filler MetalChemical Composition / mass %C Si Mn P S Cr MoFM A 0,08 0,045 0,35 0,025 0,025 1,10 0,50FM B 0,11 0,18 0,37 0,020 0,020 1,04 0,4728  METALURGIJA 52 (2013) 1, 27-31M. BURZIĆ et al.: THE EFFECTS OF DYNAMIC LOAD ON BEHAVIOUR OF WELDED JOINT A-387 Gr. 11 ALLOYED STEELTable 4 Mechanical properties of fi ller metal [4]Filler Metal Rp0,2 / MPa Rm / MPa A / % KV / JFM A 505 640 23 > 95FM B 490 610 26 > 100RESULTS AND DISCUSSIONTesting by bending induced by impact effect of force on notched specimen can provide an explanation of ma-terial behaviour for disrupted strain. Determination of operation leading to fracture under established test con-ditions most frequently is used for current control of quality and homogeneity of the material, as well as of its treatment. This test procedure provides the possibil-ity to establish susceptibility to brittle fracture, i.e. sus-ceptibility to the increase of brittleness during exploita-tion (aging) [5].Impact testing of the notched specimens in base metal (BM), weld metal (WM) and heat-affected zone (HAZ) on the side of exploited BM in 540 °C, was conducted in order to dete-rmine total impact energy, as well as the components of the energy crack initiation and crack propagation. Test procedure and the shape and dimen-sions of the specimens, are defi ned by standard EN 10045-1 [6]. Position of the notch relative to the welded joint is defi ned by the standard EN 875 [7]. The testing itself was conducted on instrumented Charpy pendulum. The results of testing are presented in Table 5.Table 5  The values of impact energy for tested BM and welded jointSpec. Design.Tot. Impact Energy,Auk / JEnergy of Crack Initiat. AI / JEnergy of Crack propag. AP / JBM-1 119 51 68BM-2 109 49 60BM-3 115 50 65WM-1 141 62 78WM-2 132 59 73WM-3 137 60 77HAZ-1 96 44 52HAZ -2 79 39 40HAZ -3 85 42 43Typical diagrams force-time and energy–time ob-tained by testing of the specimens designated by BM-1, WM-1 and HAZ-1 at operating temperature are given in Figures 1 through 3. Structural life is expressed through crack driving time. To determine exploitation life means to predict crack driving time. Thus it has been concluded that sharp stress concentrators under conditions of variable loading after certain number of cycles result in crack initiation and its propagation if the fatigue threshold, ΔKth, is ex-ceeded. As the structure under certain loading conditions, as a rule, would not be jeopardized until the crack reaches critical dimensions, exploitation of a pre-cracked struc-ture can be allowed even during the period of crack growth, on condition that it had already been subjected to preliminary analysis. Knowledge on the crack -growth rate and its dependence on affecting loading is essential for the decision on further exploitation [8].Considering the fact that the stress fi eld at the crack tip is characterized by singularity, it would be best to express the effect of the stress-rate through the stress-intensity factor.; as this is the case of variable loading, varying from highest to lowest value it would be most appropriate to describe it by the range of the stress-in-tensity factors, ΔK.04080120160200   Energy / J0 1 2 3 4 5 6 7 8048121620Specimen BM - 1540 oCF o r c e /  kNT i m e /  ms04080120160200   Energy / J0 1 2 3 4 5 6 7 8048121620Specimen WM - 1t = 540 oCF o r c e /  kNT i m e /  ms04080120160200  Energy / J0 1 2 3 4 5 6 7 8048121620Specimen HAZ - 1t = 540 oCF o r c e /  kNT i m e /  msFigure 1  Diagrams obtained by impact testing of the specimen BM-1 [1]Figure 2  Diagrams obtained by impact testing of the specimen WM-1 [1]Figure 3  Diagrams obtained by impact testing of the specimen HAZ-1 [1]29METALURGIJA 52 (2013) 1, 27-31M. BURZIĆ et al.: THE EFFECTS OF DYNAMIC LOAD ON BEHAVIOUR OF WELDED JOINT A-387 Gr. 11 ALLOYED STEELThis is the basis of the Paris’ dependence, which is the foundation of the standard for determination of the parameters of fatigue-crack growth Standard ASTM E 647-00 [9] regulates the measurement of fatigue-crack growth rate, da/dN, propagating from a pre-crack, as well as calculation of the range of the stress-intensity factors, ΔK.Therefore, it is reasonable to compare the crack-growth rate, da/dN, with ΔK, in a form defi ned by Paris [10]: ( )mKCdNda∆⋅=For determination of the parameters of fatigue-crack growth and fatigue threshold ΔKth at operating tempera-ture of 540 °C, modifi ed CT-specimens were used. Dur-ing the testing, the specimens were in a high-tempera-ture chamber, placed on a high-frequency pulsator. The test itself was conducted in force control.In Table 6, the values obtained for the parameters of Paris’ equation, coeffi cient C and exponent m, as well as for fatigue threshold, ΔKth, for all tested specimens are presented. Table 6 Parameters of the Paris’ law Spec. Design. ∆Kth, / MPa m1/2 C mBM–1 5,7 3,11 ⋅ 10-13 4,08BM–2 5,9 2,79 ⋅ 10-13 4,13BM-3 5,9 2,97 ⋅ 10-13 4,07WM–1 6,3 3,27 ⋅ 10-13 4,14WM–2 6,2 3,41 ⋅ 10-13 4,06WM-3 6,3 3,36 ⋅ 10-13 4,03HAZ–1 6,1 3,38 ⋅ 10-12 3,17HAZ–2 6,0 3,31 ⋅ 10-12 3,28HAZ-3 6,0 3,55 ⋅ 10-12 3,35As one can see from the results presented, the loca-tion of the notch and crack initiation affect both the val-ues of fatigue threshold, ΔKth, and parameters of fatigue-crack growth [11].Typical diagrams fatigue-crack growth rate da/dN – variation of the range of the stress-intensity factor ΔK for the specimens with fatigue-crack tip in BM, WM and HAZ are shown in Figures 4 through 6.From the results obtained, one can see that the speci-mens with a crack in base metal have the lowest fatigue-crack growth rate, da/dN. For the same range of the stress-intensity factor, ∆K, fatigue-crack growth rate, da/dN, increases in the specimens with a crack in weld met-al, especially in the specimens with a crack in HAZ. Maximum growth rate of fatigue crack can be ex-pected at the level of the range of the stress-intensity factors approximating fracture toughness at plane strain, as brittle fracture is attained at that level [11].However, in spite of the differences, both the speci-mens with cracks in BM and the components of the welded joint of WM and HAZ had rather low growth rates of fatigue cracks in general, which favoured the assessment on good properties of this material and com-ponents of the welded joints in presence of the crack-type defects affected by variable loading [11].Successful application of A-387 steel and its maxi-mum creep resistance require guaranteed mechanical 100 101 10210-310-210-1100101102103104Specimen BM - 1t = 540 oCda/dN /  µm/ciklus∆K / MPa m1/2100 101 10210-310-210-1100101102103104Specimen WM - 1t = 540 oCda/dN /  µm/cycle∆K / MPa m1/2100 101 10210-310-210-1100101102103104Specimen HAZ - 1t = 540 oCda/dN /  µm/cycle∆K / MPa m1/2Figure 4  Diagram da/dN - ∆K for specimen BM [1]Figure 5  Diagram da/dN - ∆K for specimen WM [1]Figure 6  Diagram da/dN - ∆K for specimen HAZ [1]30  METALURGIJA 52 (2013) 1, 27-31M. BURZIĆ et al.: THE EFFECTS OF DYNAMIC LOAD ON BEHAVIOUR OF WELDED JOINT A-387 Gr. 11 ALLOYED STEELproperties at elevated temperatures (max. 550 °C) and creep resistance at operating temperature during the pe-riod of exploitation that can signifi cantly exceed 100 000 hours.Microstructure of basic metal is ferrite and perlite, Figure 7a. In heat-affected zone micro-structure are con-sists of ferrite, beinite and perlite, Figure 7b. In heat-af-fected zone, beinite forms because of higher cooling rate of a part of base metal that was heated to austenitisation temperature during welding. Beinite content decreases with increase of the distance from the joint line. The structure of weld metal where the coarse dendrites formed because of the water-bath size, due to the dimensions of the welded plates, is shown in Figure 7c [1].Technique of colour-metallography (by pre-cipita-tion of interferential fi lm) with BERAHA solution at larger magnifi cation (2000 x) has made it possible to detect structural modifi -cations. Namely, the period of exploitation exceeding 30 years at temperatures above 500 °C in presence of stresses strongly affected separa-tion of carbides at the boundaries and inside ferritic grain, Figure 8.CONCLUSIONBased on the tests conducted, one could conclude the following:Total impact energy obtained by testing of the speci-mens sampled from the zone of exploited welded joint and tested at operating temperature depends on the spot of notch engraving. The highest value of total impact energy is that of the specimens with a notch in WM, slightly lower is that of the specimens with a notch in BM, and the lowest value of total impact energy is that of the specimens with a notch in HAZ. The values of total impact energy, the components, energy of crack initiation and energy of crack propagation are primarily affected by heterogeneity of structure, and this effect is most prominent on the specimens with V-notch in the heat-affected zone (HAZ), as here the heterogeneity of structure is highest. The values obtained for fatigue threshold, ΔKth, and fatigue-crack growth rate, da/dN, are directly related to the location of fatigue-crack tip. The specimens with fatigue-crack tip in BM are most resistant to pre-crack growth. It is obvious that ferritic-perlitic structure pre-dominant in BM results in higher resistance to activa-tion of present crack, too, which refl ects in lower value of fatigue-crack growth rate, da/dN. (Exploitation conditions (operating tempera-ture) additionally decrease resistance of a crack to propaga-tion under variable loading, which can have decisive ef-fect on assessment of integrity and remaining life of the reactor itself. This increase of fatigue-crack growth rate, da/dN, is directly related to the structural modifi cations occurring in exploited material.Figure 7 Microstructure of  a) BM, b) HAZ and c) WM [1]Figure 8  Microstructure of exploited BM [1]31METALURGIJA 52 (2013) 1, 27-31M. BURZIĆ et al.: THE EFFECTS OF DYNAMIC LOAD ON BEHAVIOUR OF WELDED JOINT A-387 Gr. 11 ALLOYED STEELAcknowledgmentThis paper is part of the research included in the project TP 35024, TP 35002, supported by the Ministry of Science and Technological Development of the Re-public of Serbia.The authors would like to thank the Ministry for the fi nancing of this project.REFERENCE[1] M. Burzić, Uticaj eksploatacionih uslova na integritet i preostali vek posuda pod pritiskom, Doktorska disertacija, Univerzitet Novi Sad, (2008).[2] ASME Boiler and Pressure Vessel Code an International Code, MATERIALS Part-A Ferrous Material Specifi ca-tion, (2001). [3] EN 10002-5, Tensile testing of metallic materials. Method of test at elevated temperatures, (1992).[4] Lincoln Electric, Welding Handbook, (2006).[5] M. Burzić, Analysis of Crack Parameters of Welded Joint of Heat Resistant Steel, Structural Integrity and Life, 8(2008)1, 41-54.[6] EN 10045-1, Mechanical Testing of Metals; Charpy Pen-dulum Impact Test; Parts 1 and 2 Terms and Defi nitions, Test Method, (2004).[7] EN 875, Welded Joints in Metallic Materials - Specimen, Location and Notch Orientation for Impact Test, (1995).[8] M. Burzić, Z. Burzić, J. Kurai, Dž. Gačo, Fatigue beha-viour of alloyed steel for high temperature, First Serbian Congress on Theoretical and Applied Mechanics, Kopao-nik, Serbia, (2007), 1085-1090.[9] ASTM E647-00, Standard Test Method for Measurement of Fatigue Crack Growth Rates, Annual Book of ASTM Standards, 03.01(2000).[10] P. C. Paris, and F. Erdogan, A Critical analysis of crack propagation laws, Journal of Basic Engineering, 85(1963), 528-534.[11] M. Burzić, R. Prokić-Cvetković, B. Grujić, I. Atanasovska, Ž. Adamović, Safe Operation of Welded Structure with Cracks at Elevated Temperature, Strojniški vestnik - Journal of Mechanical Engineering 54(2008)11, 807-816Note:  The responsible translator for English language is Anđa Zorica, Belgrade, Serbia

English

The effects of dynamic load on behaviour of welded joint a-387 gr. 11 alloyed steel

machinery

Hrčak - Portal of scientific journals of Croatia

27METALURGIJA 52 (2013) 1, 27-31M. BURZIĆ, M. MANJGO, D. KOZAK, R. PROKIĆ-CVETKOVIĆ, O. POPOVIĆTHE EFFECTS OF DYNAMIC LOAD ON BEHAVIOUR OF WELDED JOINT A-387 Gr. 11 ALLOYED STEELReceived – Prispjelo: 2012-03-21Accepted – Prihvaćeno: 2012-07-15Original Scientifi c Paper – Izvorni znanstveni radISSN 0543-5846METABK 52(1) 27-31 (2013)UDC – UDK 669.15:620.178.3=111M. Burzić, R. Prokić-Cvetković, O. Popović, University of Belgrade, Faculty of Mechanical Engineering, Belgrade, SerbiaM. Manjgo, Faculty of Mechanical Engineering, Mostar, Bosnia and Her-zegovinaD. Kozak, J. J. Strossmayer University of Osijek, Mechanical Engineer-ing Faculty in Slavonski Brod, CroatiaThe in-service behaviour of alloyed steel A-387 Gr. 11 Class 1, for pressure vessels, used for high temperature appli-cations, depends on the properties of its welded joint, with parent metal (BM), heat-aff ected-zone (HAZ) and weld metal (WM), as constituents. Charpy testing of BM, WM and HAZ, together with, determination of the parameters of fatigue-crack growth and fatigue threshold ΔKth was used, in order to understand, how heterogeneity of structure and diff erent mechanical properties of welded joint constituents aff ect on crack initiation and propagation.Key words: alloyed steel A-387 Gr. 11, fatigue, impact energy, Paris relationshipINTRODUCTIONExploitation properties of A-387 Gr. 11 Class 1 al-loyed steel, designed for manufacture of pressure ves-sels operating at elevated temperatures and pressures, largely depend on properties of the critical zones of a welded joint. Heat-affected zone (HAZ) and weld metal (WM) are latent locations of crack initiation, i.e. the lo-cations where local brittle zones to whom crack initia-tion is attributed could be formed [1].For better understanding of the causes and modes of crack initiation and crack growth in welded joints of steel designed for operation at elevated temperatures and under high pressure, it is necessary to establish how the heterogeneity of structure and mechanical proper-ties of a welded joint affects crack initiation and growth, and to quantify the parameters controlling local-strain behaviour and crack growth.The aim of this investigation is to assess the effects of heterogeneity of structure and mechanical properties of base metal and components of the welded joint of A-387 Gr.11 Class 1 steel on crack initiation and growth, as well as on the parameters of fatigue-crack growth (da/dN and ΔKth) at elevated temperature of 540 °C, based on the results obtained [1].MATERIALFor testing, the sample of a welded joint of A-387 Gr. 11 Class 1 steel, with weld metal in the middle (dou-ble U-shaped weld), was used, the dimensions of which were 350 x 500 x 96 mm. Chemical composition of A-387 Gr. 11 Class 11 is presented in Table 1 [2]. The procedure for testing at elevated temperature of 540 °C is deﬁ ned by the standard EN 10002-5 [3]. The results of tensile test of mechanical properties of A-387 Gr. 11 Class 1 steel at operating tempera-ture are presented in Table 2 [2].Table 1 Chemical composition of tested material [2]Chemical composition / mas. %C Si Mn P S Cr Mo0,15 0,29 0,54 0,022 0,011 0,93 0,47Table 2 Results of tensile test [2]Rp0,2 / MPa Rm / MPa A / %220 280 36Welding of sheets new and exploited BM was con-ducted in two phases, as follows:–  root run – by manual arc procedure, using a plated electrode LINCOLN Sl 19G (AWS: E8018-B2), –  ﬁ lling – by arc welding using powder protection, where the wire designated as LINCOLN LNS 150 and powder LINCOLN P230 were used as ﬁ ller metals. Chemical composition of used electrode LINCOLN Sl 19G (FM A) and wire LINCOLN LNS 150 (FM B) according to attest documen-tation is presented in Table 3. Main mechanical properties according to attest docu-mentation are presented in Table 4.Table 3 Chemical composition of fi ller metal [4]Filler MetalChemical Composition / mass %C Si Mn P S Cr MoFM A 0,08 0,045 0,35 0,025 0,025 1,10 0,50FM B 0,11 0,18 0,37 0,020 0,020 1,04 0,4728  METALURGIJA 52 (2013) 1, 27-31M. BURZIĆ et al.: THE EFFECTS OF DYNAMIC LOAD ON BEHAVIOUR OF WELDED JOINT A-387 Gr. 11 ALLOYED STEELTable 4 Mechanical properties of fi ller metal [4]Filler Metal Rp0,2 / MPa Rm / MPa A / % KV / JFM A 505 640 23 > 95FM B 490 610 26 > 100RESULTS AND DISCUSSIONTesting by bending induced by impact effect of force on notched specimen can provide an explanation of ma-terial behaviour for disrupted strain. Determination of operation leading to fracture under established test con-ditions most frequently is used for current control of quality and homogeneity of the material, as well as of its treatment. This test procedure provides the possibil-ity to establish susceptibility to brittle fracture, i.e. sus-ceptibility to the increase of brittleness during exploita-tion (aging) [5].Impact testing of the notched specimens in base metal (BM), weld metal (WM) and heat-affected zone (HAZ) on the side of exploited BM in 540 °C, was conducted in order to dete-rmine total impact energy, as well as the components of the energy crack initiation and crack propagation. Test procedure and the shape and dimen-sions of the specimens, are deﬁ ned by standard EN 10045-1 [6]. Position of the notch relative to the welded joint is deﬁ ned by the standard EN 875 [7]. The testing itself was conducted on instrumented Charpy pendulum. The results of testing are presented in Table 5.Table 5  The values of impact energy for tested BM and welded jointSpec. Design.Tot. Impact Energy,Auk / JEnergy of Crack Initiat. AI / JEnergy of Crack propag. AP / JBM-1 119 51 68BM-2 109 49 60BM-3 115 50 65WM-1 141 62 78WM-2 132 59 73WM-3 137 60 77HAZ-1 96 44 52HAZ -2 79 39 40HAZ -3 85 42 43Typical diagrams force-time and energy–time ob-tained by testing of the specimens designated by BM-1, WM-1 and HAZ-1 at operating temperature are given in Figures 1 through 3. Structural life is expressed through crack driving time. To determine exploitation life means to predict crack driving time. Thus it has been concluded that sharp stress concentrators under conditions of variable loading after certain number of cycles result in crack initiation and its propagation if the fatigue threshold, ΔKth, is ex-ceeded. As the structure under certain loading conditions, as a rule, would not be jeopardized until the crack reaches critical dimensions, exploitation of a pre-cracked struc-ture can be allowed even during the period of crack growth, on condition that it had already been subjected to preliminary analysis. Knowledge on the crack -growth rate and its dependence on affecting loading is essential for the decision on further exploitation [8].Considering the fact that the stress ﬁ eld at the crack tip is characterized by singularity, it would be best to express the effect of the stress-rate through the stress-intensity factor.; as this is the case of variable loading, varying from highest to lowest value it would be most appropriate to describe it by the range of the stress-in-tensity factors, ΔK.04080120160200   Energy / J0 1 2 3 4 5 6 7 8048121620Specimen BM - 1540 oCF o r c e /  kNT i m e /  ms04080120160200   Energy / J0 1 2 3 4 5 6 7 8048121620Specimen WM - 1t = 540 oCF o r c e /  kNT i m e /  ms04080120160200  Energy / J0 1 2 3 4 5 6 7 8048121620Specimen HAZ - 1t = 540 oCF o r c e /  kNT i m e /  msFigure 1  Diagrams obtained by impact testing of the specimen BM-1 [1]Figure 2  Diagrams obtained by impact testing of the specimen WM-1 [1]Figure 3  Diagrams obtained by impact testing of the specimen HAZ-1 [1]29METALURGIJA 52 (2013) 1, 27-31M. BURZIĆ et al.: THE EFFECTS OF DYNAMIC LOAD ON BEHAVIOUR OF WELDED JOINT A-387 Gr. 11 ALLOYED STEELThis is the basis of the Paris’ dependence, which is the foundation of the standard for determination of the parameters of fatigue-crack growth Standard ASTM E 647-00 [9] regulates the measurement of fatigue-crack growth rate, da/dN, propagating from a pre-crack, as well as calculation of the range of the stress-intensity factors, ΔK.Therefore, it is reasonable to compare the crack-growth rate, da/dN, with ΔK, in a form deﬁ ned by Paris [10]: ( )mKCdNda∆⋅=For determination of the parameters of fatigue-crack growth and fatigue threshold ΔKth at operating tempera-ture of 540 °C, modiﬁ ed CT-specimens were used. Dur-ing the testing, the specimens were in a high-tempera-ture chamber, placed on a high-frequency pulsator. The test itself was conducted in force control.In Table 6, the values obtained for the parameters of Paris’ equation, coefﬁ cient C and exponent m, as well as for fatigue threshold, ΔKth, for all tested specimens are presented. Table 6 Parameters of the Paris’ law Spec. Design. ∆Kth, / MPa m1/2 C mBM–1 5,7 3,11 ⋅ 10-13 4,08BM–2 5,9 2,79 ⋅ 10-13 4,13BM-3 5,9 2,97 ⋅ 10-13 4,07WM–1 6,3 3,27 ⋅ 10-13 4,14WM–2 6,2 3,41 ⋅ 10-13 4,06WM-3 6,3 3,36 ⋅ 10-13 4,03HAZ–1 6,1 3,38 ⋅ 10-12 3,17HAZ–2 6,0 3,31 ⋅ 10-12 3,28HAZ-3 6,0 3,55 ⋅ 10-12 3,35As one can see from the results presented, the loca-tion of the notch and crack initiation affect both the val-ues of fatigue threshold, ΔKth, and parameters of fatigue-crack growth [11].Typical diagrams fatigue-crack growth rate da/dN – variation of the range of the stress-intensity factor ΔK for the specimens with fatigue-crack tip in BM, WM and HAZ are shown in Figures 4 through 6.From the results obtained, one can see that the speci-mens with a crack in base metal have the lowest fatigue-crack growth rate, da/dN. For the same range of the stress-intensity factor, ∆K, fatigue-crack growth rate, da/dN, increases in the specimens with a crack in weld met-al, especially in the specimens with a crack in HAZ. Maximum growth rate of fatigue crack can be ex-pected at the level of the range of the stress-intensity factors approximating fracture toughness at plane strain, as brittle fracture is attained at that level [11].However, in spite of the differences, both the speci-mens with cracks in BM and the components of the welded joint of WM and HAZ had rather low growth rates of fatigue cracks in general, which favoured the assessment on good properties of this material and com-ponents of the welded joints in presence of the crack-type defects affected by variable loading [11].Successful application of A-387 steel and its maxi-mum creep resistance require guaranteed mechanical 100 101 10210-310-210-1100101102103104Specimen BM - 1t = 540 oCda/dN /  µm/ciklus∆K / MPa m1/2100 101 10210-310-210-1100101102103104Specimen WM - 1t = 540 oCda/dN /  µm/cycle∆K / MPa m1/2100 101 10210-310-210-1100101102103104Specimen HAZ - 1t = 540 oCda/dN /  µm/cycle∆K / MPa m1/2Figure 4  Diagram da/dN - ∆K for specimen BM [1]Figure 5  Diagram da/dN - ∆K for specimen WM [1]Figure 6  Diagram da/dN - ∆K for specimen HAZ [1]30  METALURGIJA 52 (2013) 1, 27-31M. BURZIĆ et al.: THE EFFECTS OF DYNAMIC LOAD ON BEHAVIOUR OF WELDED JOINT A-387 Gr. 11 ALLOYED STEELproperties at elevated temperatures (max. 550 °C) and creep resistance at operating temperature during the pe-riod of exploitation that can signiﬁ cantly exceed 100 000 hours.Microstructure of basic metal is ferrite and perlite, Figure 7a. In heat-affected zone micro-structure are con-sists of ferrite, beinite and perlite, Figure 7b. In heat-af-fected zone, beinite forms because of higher cooling rate of a part of base metal that was heated to austenitisation temperature during welding. Beinite content decreases with increase of the distance from the joint line. The structure of weld metal where the coarse dendrites formed because of the water-bath size, due to the dimensions of the welded plates, is shown in Figure 7c [1].Technique of colour-metallography (by pre-cipita-tion of interferential ﬁ lm) with BERAHA solution at larger magniﬁ cation (2000 x) has made it possible to detect structural modiﬁ -cations. Namely, the period of exploitation exceeding 30 years at temperatures above 500 °C in presence of stresses strongly affected separa-tion of carbides at the boundaries and inside ferritic grain, Figure 8.CONCLUSIONBased on the tests conducted, one could conclude the following:Total impact energy obtained by testing of the speci-mens sampled from the zone of exploited welded joint and tested at operating temperature depends on the spot of notch engraving. The highest value of total impact energy is that of the specimens with a notch in WM, slightly lower is that of the specimens with a notch in BM, and the lowest value of total impact energy is that of the specimens with a notch in HAZ. The values of total impact energy, the components, energy of crack initiation and energy of crack propagation are primarily affected by heterogeneity of structure, and this effect is most prominent on the specimens with V-notch in the heat-affected zone (HAZ), as here the heterogeneity of structure is highest. The values obtained for fatigue threshold, ΔKth, and fatigue-crack growth rate, da/dN, are directly related to the location of fatigue-crack tip. The specimens with fatigue-crack tip in BM are most resistant to pre-crack growth. It is obvious that ferritic-perlitic structure pre-dominant in BM results in higher resistance to activa-tion of present crack, too, which reﬂ ects in lower value of fatigue-crack growth rate, da/dN. (Exploitation conditions (operating tempera-ture) additionally decrease resistance of a crack to propaga-tion under variable loading, which can have decisive ef-fect on assessment of integrity and remaining life of the reactor itself. This increase of fatigue-crack growth rate, da/dN, is directly related to the structural modiﬁ cations occurring in exploited material.Figure 7 Microstructure of  a) BM, b) HAZ and c) WM [1]Figure 8  Microstructure of exploited BM [1]31METALURGIJA 52 (2013) 1, 27-31M. BURZIĆ et al.: THE EFFECTS OF DYNAMIC LOAD ON BEHAVIOUR OF WELDED JOINT A-387 Gr. 11 ALLOYED STEELAcknowledgmentThis paper is part of the research included in the project TP 35024, TP 35002, supported by the Ministry of Science and Technological Development of the Re-public of Serbia.The authors would like to thank the Ministry for the ﬁ nancing of this project.REFERENCE[1] M. Burzić, Uticaj eksploatacionih uslova na integritet i preostali vek posuda pod pritiskom, Doktorska disertacija, Univerzitet Novi Sad, (2008).[2] ASME Boiler and Pressure Vessel Code an International Code, MATERIALS Part-A Ferrous Material Speciﬁ ca-tion, (2001). [3] EN 10002-5, Tensile testing of metallic materials. Method of test at elevated temperatures, (1992).[4] Lincoln Electric, Welding Handbook, (2006).[5] M. Burzić, Analysis of Crack Parameters of Welded Joint of Heat Resistant Steel, Structural Integrity and Life, 8(2008)1, 41-54.[6] EN 10045-1, Mechanical Testing of Metals; Charpy Pen-dulum Impact Test; Parts 1 and 2 Terms and Deﬁ nitions, Test Method, (2004).[7] EN 875, Welded Joints in Metallic Materials - Specimen, Location and Notch Orientation for Impact Test, (1995).[8] M. Burzić, Z. Burzić, J. Kurai, Dž. Gačo, Fatigue beha-viour of alloyed steel for high temperature, First Serbian Congress on Theoretical and Applied Mechanics, Kopao-nik, Serbia, (2007), 1085-1090.[9] ASTM E647-00, Standard Test Method for Measurement of Fatigue Crack Growth Rates, Annual Book of ASTM Standards, 03.01(2000).[10] P. C. Paris, and F. Erdogan, A Critical analysis of crack propagation laws, Journal of Basic Engineering, 85(1963), 528-534.[11] M. Burzić, R. Prokić-Cvetković, B. Grujić, I. Atanasovska, Ž. Adamović, Safe Operation of Welded Structure with Cracks at Elevated Temperature, Strojniški vestnik - Journal of Mechanical Engineering 54(2008)11, 807-816Note:  The responsible translator for English language is Anđa Zorica, Belgrade, Serbia

The effects of dynamic load on behaviour of welded joint A-387 Gr. 11 alloyed steel

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