International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
INTERNATIONAL JOURNAL OF MECHANICAL EN...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online),...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online),...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online),...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online),...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online),...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online),...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online),...
Upcoming SlideShare
Loading in …5
×

30120140502005 2

462 views

Published on

Published in: Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
462
On SlideShare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
Downloads
2
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

30120140502005 2

  1. 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 36-43, © IAEME AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 5, Issue 2, February (2014), pp. 36-43 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2014): 3.8231 (Calculated by GISI) www.jifactor.com IJMET ©IAEME METALLURGICAL BEHAVIOUR OF AISI 304 STEEL BUTT WELDS UNDER SEGREGATION Rati Saluja1, 1* K.M. Moeed2 Department of Mechanical Engineering, Goel Institute of Technology & Management, Lucknow, UP, India 2 Department of Mechanical Engineering, Integral University, Lucknow, UP, India ABSTRACT Correlation is to integrate depictions of fundamental microscopic phenomena of solidification, cooling, grain growth, segregation, metallurgical developments and its significance on mechanical properties for AISI 304 steel. When formulating the susceptibility of to cracking, segregation is not generally accountable, despite being a significant factor. Segregation is originated by incomplete mixing in the weld pool which promotes the dendrite envelope motion governed by the growth of dendrite tips. The growth model for dendrite tips can be obtained by solute transport near the tip progressed by tip stability. Due to high segregations of chromium and molybdenum, secondary ferrite is known to be susceptible to the formation of intermetallic phases such as sulfur or carbon. But segregation of nickel, chromium and molybdenum can be lowered with the use of nitrogen in the shielding gas. Competing factors add to the intricacy of the phenomenon, hence the main objective of this scanty literature is concerned with metallurgical behavior of this class of engineering materials under the influence of segregation. Keywords: Austenitic, Dendrites, Ferrite, Segregation, Supercooling 1. INTRODUCTION Selection of Type 304 steel as material of choice for a variety of engineering applications such as structural steel parts cannot be traced only to its good corrosion resistant and formability characteristics [1]. It is highly preferred due to its good welding characteristics, low cost, easy availability in the market places this class of materials at the forefront of metallurgical technology [2]. 36
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 36-43, © IAEME The AISI 304 steel has atleast of eight elements, and the use of binary and ternary phase systems to value higher order systems, which can lead to significant error, while predicting microstructures [3]. Furthermore, the σ phase usually precipitates in Grade 304 steels at 800℃ and that it has a strong effect on the properties of stainless steels [4]. σ phase has significant influence on material properties, it causes chromium impoverishment near the precipitates and reduces the corrosion resistance [5]. It has also been demonstrated that the σ phase does not affect the mechanical properties of stainless steels at 1000℃ because it dissolves in the matrix at this temperature [6]. Grade 304 steel series of austenitic stainless steels usually solidify during welding as a mixture of austenite and ferrite. The ferrite almost fully transforms to austenite on cooling, but there could be retention of a few percent of δ ferrite in the weld metal which leads to cracking processed by segregation [7]. This arises from larger solidification temperature range during primary austenitic solidification. The inhomogeneity is affected also by considerably slower diffusion of alloying elements in austenite than in ferrite [8]. Weld pool macro segregation occur by lack of weld pool mixing especially in welding of dissimilar metals, or some special types of rapidly solidified power metallurgy alloys. It also occurs during incomplete weld pool mixing in single pass welding (greater extent) and even in multipass welding [9]. When comparing the segregation behaviour for different solidification modes it has been demonstrated that microsegregation is stronger in welds having primary austenitic solidification [10]. To this end, the fundamental study of the microstructural development of Grade 304 steel presented here provides a baseline for comparison when the more complicated material behavior under segregation. The work presented in this paper represents the first step in understanding the complex solidification behavior of 304 steel, which are routinely used as parent metals for various fabrications in metallurgical, mechanical, chemical, automobile and nuclear industries process. The data gathered here will serve as the foundation for the continuing investigation of the intricate material behavior under rapid solidification conditions that can potentially be induced during various arc welding processes. 2. WELDING METALLURGY OF GRADE 304 STEEL WELDS 2.1 Solidification and cooling Under rapid solidification, a great number of welds having duplex microstructures are replaced by single phase austenitic or single phase ferritic microstructures in arc welding. According to Schaeffler diagram, in welds predicted to have less than 8% ferrite will transform to fully austenitic with cooling rates of as high as 200000 K/s [10]. At high ferrite content approximately more than 30% ferrite, arc welds predicted to have may become fully ferritic with these very high cooling rates. Massive transformation to austenite in these welds may, however, abruptly decrease the ferrite content [11,12]. The primary solidifying phase incorporates more solute than it does closer to equilibrium conditions promotes which further restrain the formation of second phase ferrite in AF-mode and second phase austenite in FA-mode [13]. Due to rapid solidification and retarded diffusion in FAwelds solid state transformation from ferrite to austenite is repressed [10, 14]. The difference between microstructure of fusion zone resulting from Type A, AF and F mode solidification can be easily distinguished as shown in figure 1 [15]. 37
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 36-43, © IAEME Fig. 1 Microstructure of fusion zone resulting from Type A, AF and F mode solidification [15] The growth of primary austenite dendrites or cells enhances as solidification rate and dendrite tip undercooling increases [16]. As an optical micrograph shows the change in dendrite morphology from cellular to dendritic as the growth velocity increases toward the center of spot weld towards top after the spot weld arc is extinguished. Fig. 2 Micrograph of dendrite morphology from cellular to dendritic [14] 2.2. Microstructure Development and its effects on mechanical properties The welding metal contains a skeletal and lathy ferrite type dendrite structure as shown in figure 3. It shows the morphology of the base material, which evidence the austenitic grain microstructure of an AISI 304 stainless steel [17]. The lathy ferrite microstructure can emerge due to greater ferrite contents and/or a characteristic cooling time after the welding procedure steel [18]. Fig. 3 Micrographs of the microstructures at the Fusion zone [19] In AISI 304 steel, the ferrite-promoting element segregation specially chromium promotes formation of ferrite stringers during solidification [19]. The final microstructure consists of γ 38
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 36-43, © IAEME dendrites with a Molybednum concentration gradient and interdendritic α phase [20]. The presence of Molybdenum rich liquid present near the termination of solidification wets the surface of the solidified dendritic structure promotes formation of cracking [21]. As austenite is more susceptible to this phenomenon than ferrite due to the lower solubility of tramp elements in austenite as in steel that form low melting point solids [22]. However, this is not an option, as a fully austenitic structure must be maintained to conserve the magnetic and corrosion resistance properties of Grade 304 steel. The change in scale morphology can be recognized to an edge effect phenomenon occurring during the cooling of the AISI 304 austenite stainless steel. Fig. 5 (a), (b) and (c) shows the stereo micrograph of WM, HAZ and FZ which could be discriminated easily. In welding zone, a small amount chromium carbide precipitation is formed. Whereas the microstructure analysis revealed that the ferrite to austenite formation contribute in increasing the weldment strength, whereby at weldment area ferrite form occurred due high temperature during welding. This makes the structure strength at weldment area weaker compare to HAZ and base metal [23]. Fig. 4 Micrographs of the Microstructures of PM, HAZ and Weldment [24]. 2.3. Segregation of Alloying Elements Solute undercooling predicts that solute is rejected from the solidifying metal into the liquid ahead of the solid liquid interface, resulting in a depression of the liquidus temperature of the liquid ahead of the interface due to solute buildup [25]. Due to continuous reduction in temperature till the termination of solidification, the dendrites that had initially formed continue to grow into the increasingly solute enriched liquid results a composition gradient within the dendritic substructure of the material, generally referred to as coring [12]. But Researchers suggests that segregation of nickel, chromium and molybdenum can be reduced with the use of nitrogen in the shielding gas. The segregation of nickel remains, reasonably weak [26].Development of dendrites in a nickel-based superalloy single-crystal weld has been demonstrated in figure 5. Fig. 5 Scanning-electron micrograph showing the development of dendrites in a nickel-based superalloy single-crystal weld [14] 39
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 36-43, © IAEME In the case of primary austenitic solidification and the segregation ratio above one indicates interdendritic segregation for all major alloying elements [27]. Correspondingly, the concentration of chromium and preferably molybdenum, at the dendrite cores decreases than in the bulk composition. This indicates that the segregation tendency of chromium and molybdenum reduces and that of nickel increases with respect to primary austenitic solidification [20]. In primary ferritic solidification the value of segregation ratio for all other elements except for nickel is lower than in primary austenitic mode [8]. At the end of solidification the last melt droplets can once again solidify as ferrite, known as secondary ferrite. Due to high segregations of chromium and molybdenum, secondary ferrite is known to be susceptible to the formation of intermetallic phases such as S or C [9]. Therefore, during cooling, the segregation profiles developed in austenitic solidification are not homogenised to the same extent as in ferritic solidification [28]. Fig. 6 Regions of fine scale dendritic, facetted and eutectic structure between primary dendrites [29] Macrosegregation arising from dendritic solidification is defined as compositional inhomogeneity on a scale larger than that of the dendrite arm spacings [29]. With a planar solidification front, this would, indeed, be a fair first-approximation, but less so with cellular growth and downright misleading with dendritic growth. The more removed is the topography of the solidification front from planar, the more the enriched liquid is held within that texture [30]. In so doing, it has also essentially removed the solute field ahead of the dendrite tips under the standard range of solidification conditions [31] and, hence, has removed the mechanism for 'normal' segregation. It is well known that the inhomogeneity of AISI 304 steel welds is greatly influenced by microsegregation as well as by the partitioning of alloying elements between ferrite and austenite during solid state transformation of delta ferrite to austenite. This has an effect on the final degree of inhomogeneity especially in primary ferritic solidification [22]. The enrichment of the interdendritic liquid in the mushy zone by especially silicon reduces liquid density for the majority of steels, which consequently reverses the predicted circulation currents. But steel compositions with addition of molybdenum and tungsten, may result in residual liquid of increasing density and the inverse channel geometry in channel segregation [32]. For example, comparison of core and interdendritic (ID) manganese contents is shown in table. 40
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 36-43, © IAEME TABLE 1 Comparison of core (D) and Interdendritic (ID) Manganese contents [33] Composition Average Cooling rate o C/s C Mn Liquid/ Solid Solid 0.21 1.60 0.25 0.28 0.40 0.40 1.58 1.58 0.30 4.15 0.31 4.45 Quench Temperature o C/s Spacing, µm EPMA- Mn Measurements Wt. % 2D, λ1 1D, λ1 ,Static 1D,λ2, Coarsening λ1 λ2 D ID D ID D ID D ID 1225 350 140 1.44 1.98 2.06 1.23 2.21 1.41 1.84 1.44 1.80 1200 1305 280 184 80 25 1.31 1.30 2.18 2.19 2.67 1.17 1.27 2.14 3.13 1.47 1.35 1.71 1.87 4. CONCLUSIONS AISI 304 steel transforms as alpha ferrite at the end of the solidification, which leads to segregation followed by cracking. Evidence is presented to suggest for a range 304 steel series, solidification, cooling rates, and secondary dendrite arm spacings under the influence of segregation reveal the following. 1. During the solidification both micro segregation and macro segregation occurs in AISI 304 steel weldments due to presence of low alloys. 2. Microsegregation appears to be associated with the cracking in fisheyes. A small gas pore, probably hydrogen, was found at the fraction initiation sites of each fish eye in the weld. 3. Macro segregation is found due to presence of manganese excessively in the composition which results due variations in welding parameters under rapid solidification. 4. The solidus temperature can be reduced significantly with independent increases in either the secondary dendrite arm spacing or cooling rate. 5. The solute-element concentration, especially phosphorus and sulfur, has a significant effect on the solidus temperature the LIT and ZDT, due to their enhanced segregation near the final stage of solidification. 6. Due to presence of Molybdenum rich liquid present near the termination of solidification in the final microstructure consists of γ dendrites with a Molybdenum concentration gradient and interdendritic α phase which results cracking. REFERENCES 2. 3. 4. 5. 6. R. J. Fowless and S.E. Blake, Influence of Heat Input on Austenitic Stainless Steel Weld properties, African fusion, Vol.1 (2), 2008, 17 24. J. P. Matthew, , A fundamental study of the microstructural development of superaustenitic stainless steel and Ni-base alloys in casting and conventional arc welds, thesis and dissertation Lehigh University,2003. V. Shankar et.al. , Solidification cracking in austenitic stainless steel welds, S¯ adhan¯ a, Vol. 28, Parts 3 & 4, India, , 2003, 359–382. M.E. Wilms, V. J. Gadgil, J. M. Krougman, F. P. Ijsseling, Corros. Sci. 36, 1994, 871-881. F.C. Hull, Welding J. 52, 104s-13s, 1973. S.N. Patankar, M.J. Tan, Mater. High Temp. 19, 2002, 41-44. ‐ 1. 41
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 36-43, © IAEME 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. C. Powell, A.M. Harte, R. Gaspar, An experimental investigation into the energy absorption and force/displacement characteristics of aluminum foam filled braided stainless steel tubes under quasi-static tensile loading conditions, International Journal of Crashworthiness, Vol. 10 No.1, 200521-31,. V. P. Kujanpaa, Effects of steel type and impurities in solidification cracking of austenenitic stainless steel welds, Met. Constr. 117: 985, 40R–46R N. Suutala, Effects of composition and solidification conditions on solidification in austenitic stainless steels, Lic. Tech. Thesis, Oulu University of Oulu, 1980. S. Katayama et al., Solidification crack susceptibility in weld metals of fully austenitic stainless steels (Report I) – Fundamental investigation on solidification behavior of fully austenitic and duplex microstructures and effect of ferrite on microsegregation, Transactions of JWRI, Vol. 5, No. 2, 1976, 35 - 51. J. W. Elmer, The influence of cooling rate on the microstructure of stainless steel alloys. Ph.D. Thesis, Massachusetts Institute of Technology, USA. 1988, 387 p. J. A. Brooks and A. W. Thompson, Microstructural development and solidification cracking susceptibility of austenitic stainless steel welds, Int. Mater. Rev. 36, 1991, 16-44. J. W. Elmer, S. M. Allen, and T. W. Eagar, The influence of cooling rate on the ferrite content of stainless steel alloys. In: Trends in Welding Research, Ohio: ASM International, USA, 1989, 123 - 134. S. A. David, and J. M Vitek, Analysis of weld metal solidification and microstructures. H. Cerjak, and K. E. Easterling, Mathematical Modelling of Weld Phenomena 1, The Institute of Materials. 1991, 42 - 59. John C. Lippold and Damian J. Kotecki, Welding Metallurgy and Weldability of Stainless Steels, John Wiley & Sons Inc, 2005. M. Bobadilla, J. Lacaze, and G. Lesoult, Effect of cooling rate on the solidification behaviour of austenitic stainless steels. Scandinavian Journal of Metallurgy, Vol. 25, 1996, 2 – 10. K.Rajasekhar, Microstructural evolution during solidification of austenitic stainless steel weld metals: a color metallographic and electron microprobe analysis study, Mater Charact, 38(2) ,1997, 53–65. S. F. Dirnfeld, M. Bamberger, Klodt, and B. Prinz, Liquid/Solid Equilibrium and Segregation Behaviour of Ni-Fe-Mo-Cr Alloys. Z. Metallkd. 84, 1993, 776-780. H. B. Cary, S. C. Hezler, Modern Welding Technology 6th Edition, Pearson Prentice HallTM, 2005 . M.1. Cieslak, T. 1. Headley, and A. D. Romig, Jr., The welding metallurgy of Hastelloy alloys C-4, C-22, and C-276. Metall. Trans. A 17A, 1986, 2035-2047. B. Weiss and R. Stickler, Metall. Mater. Trans. A 31A, 1972, 851. J. A. Brooks and A. W. Thompson, Microstructural development and solidification cracking susceptibility of austenitic stainless steel welds, Int. Mater. Rev. 36, 1991, 16-44. J. C. Lippold, W. F. Savage, 1979, Solidification of austenitic stainless steel weldments 1:a proposed mechanism, Welding Journal 58(12), 362-374. Mohd Shukor Salleh, Mohd Irman Ramli, Saifudin Hafiz Yahaya, On Mechanical Properties And Microstructure Analysis Of Aisi 304l Stainless Steel Weldments, Journal of mechanical engineering and technology, Vol. 3 No. 2, 2011. Brooks, J. A. & Thompson, A. W. 1991. Microstructural development and solidification cracking susceptibility of austenitic stainless steel welds. International Materials Reviews, Vol. 36, pp. 16 - 44. 42
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 36-43, © IAEME 27. R. B. Bhatt, H. S. Kamat, S. K. Ghosal, and P. K. De, Influence of nitrogen in the shielding gas on corrosion resistance of duplex stainless steel welds, J. Mater.Eng. Perform. 8, 1999, 591-597. 28. Kakani 2004, material science-book 29. P. L. Ferrandini, C. T. Rios, A. T. Dutra, M. A. Jaime, P. R. Mei, R. Caram, Solute segregation and microstructure of directionally solidified austenitic stainless steel, Materials Science and Engineering A, 435-436, 2006,139-144. 30. Y. H. Wang,Weld pool convection and its effect, Welding Journal, Vol. 65, 1986, 63 - 70. 31. W.A Tiller, JISI, 1959, 338. 32. R. D. Doherty and Melford, D.A., JISI, 1966, 1131. 33. A. Howe, Segregation and phase distribution during solidification of carbon, alloy and stainless steels, Published by the Commission of The European Communities, 1989, United Kingdom. 34. E. Gozlan, M. Bamberger, S. F. Dirnfeld, B. Prinz, and J. Klodt, Topologically Close-Packed Precipitations and Phase Diagrams of Ni-Mo-Cr and Ni-Mo-Fe and of Ni-Mo-Fe with Constant Additions of Chromium, Materials Science and Engineering A141, 1991, 85-95. 35. Ravi Butola, Shanti Lal Meena and Jitendra Kumar, “Effect of Welding Parameter on Micro Hardness of Synergic MIG Welding of 304l Austenitic Stainless Steel”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 3, 2013, pp. 337 - 343, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. 36. L.Suresh Kumar, Dr.S.M.Verma and Dr.V.V.Satyanarayana, “Impact of Voltage on Austentic Stainless Steel for the Process of TIG and MIG Welding”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 1, Issue 1, 2010, pp. 60 - 75, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. 37. Dr. Sami A. Ajeel, Basheer A. Abdul-Hussein and Yaqoob M. Baker, “Electrochemical Measurements of Anodizing Stainless Steel Type AISI 304”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 3, 2013, pp. 63 - 74, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. 43

×