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Kaynak kabiliyeti ve bilgisayar yardımı ile karbon eşdeğeri hesapları

Weldability and computerizing of carbon equivalents

  1. Tez No: 21984
  2. Yazar: ALİ ZİYA
  3. Danışmanlar: PROF. DR. SELAHADDİN ANIK
  4. Tez Türü: Yüksek Lisans
  5. Konular: Makine Mühendisliği, Mechanical Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1992
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 65

Özet

ÖZET Bu çalışmada, özellikle mikro alaşımlı ve ince taneli çeliklerdeki karbon eşdeğerlerini hesaplayan bir bilgisayar programı yapılmıştır. Çalışmada, yöntem olarak kullanıcıdan esas metalin kimyasal bileşimini, kaynak ısı girdilerini, kaynak yöntemi ile dikiş türü ve ağız şeklini veri olarak isteyen ve bu verilere göre karbon eşdeğerlerini, ITAB'daki maksimum sertlik değerleri ile ön tavlama sıcaklıklarının hesaplanmasını sağlayan program hazırlanarak kullanıcıyla bilgisayar arasında iletişim sağlanmaya çalışılmıştır. Bilgisayar destekli çalışmaların, her konuda olduğu gibi bu konuda da geliştirilmesiyle, bu alanda çalışan mühendis ve uygulamacılara daha fazla seçeneği değerlendirme ve en tutarlı çözüme çok daha kısa sürede ulaşabilme şansı verecektir.

Özet (Çeviri)

SUMifiKY. HEHABILTÜY AND CCMEUIERIZING OF CARBON EQUTVAI^KS The most effective element in steel is carbon. There are no difficulties in welding of non-alloyed steels including carbon up to 0.20 %. Increasing the carbon content the weldability becomes worse. Depending on the cooling conditions during welding the hardness in the HAZ increases while the carbon content rises, and especially during the rapid cooling rates the cracking risk occurs. In welding of structural steels, the most important factor effecting the result of welding is the composition of base metal. Because phosphore, sulphure and nitrogen have negative effects on the weldability, it is desired not to be these elements in the composition of steel as much as possible. The manganese content in the non-alloyed structural steels changes according to the carbon content. In generally, the more the carbon content increases, the more the manganese content decreases. Because these two elements increase the hardness tendency of steel, while increasing their contents, occuring the risk of hardening and under-bead cracks increases. In the HSLA steels the other alloying elements than carbon and manganese also have some effects on the occuring of the hardening and under-bead cracks risk. The adding these elements to carbon content in the composition with a special rate is interpr i tended as a carbon- like effect. In this study, different CE formulation, which are proposed by different researchers, have been regulated as a computer program. The program has a structure formed with the calculation of CE with the inputs of chemical composition of base metal, welding parameters, welding method, the type of seam, the edge shape and the preheating temperatures with the maximum hardness value in HAZ.Fifty years ago, with a major war in progress, welding of high strength steels was hampered by a type of cracking whose cause- hydrogen-was not then known. Two researchers in the research laboratories of the Iiandon, Midland and Scottish Railway Company in Derby wrote a classical paper on the selection and welding of low alloy structural steels in which the concept of a carbon equivalent appreared for the first time. Although hardenability did not appear in the metallurgical textbooks of the time, John Dearden and Hugh O'Neill's carbon equivalent formula for assessing hardenability during welding has survived its first half century and been accepted into national and international standards the world over. Since Dearden and O'Neil proposed a carbon equivalent to predict steel strength and HAZ hardness, many carbon equivalents have been proposed to assess HAZ hardenability and HAZ hydrogen cracking susceptibility of steels, although most of them are based more or less on the carbon equivalent of Dearden and O'Neil. Recently, many findings have been made on effect of impurities and unspecified elements on HAZ hardenability. This effect, therefore, has to be taken into account in carbon equivalent for HAZ hardenability HAZ hardness limitation has been increasingly stipulated in the welding procedure specifications for the construction of offshore structures, pressure vessels and pipelines. Some structures are subjected to post-weld heat treatment (IWHT). After FWHT, a certain type of steel exhibits an unexpected increase in hardness. Offshore structures and pipelines consist of tubular or pipe members with longitudinal seam welds. As the seam welds are circumferential ly welded mostly in low heat input, a concern about weld metal HAZ hardness arises. Welding engineers have thus desired a unified formula to predict not only as-welded HAZ hardness but also post-EWHT HAZ hardness and weld metal HAZ hardness, with consideration of effects of inclusions and micro-alloying elements. Ihe effect of increasing carbon and alloy content of weld metal is in general, to increase strength and hardness. Carbon in particular has a strong effect on these properties. However, for the best combination of fracture toughness and cracking resistance, it is desirable to keep the carbon content within the range 0.05-0.12 %. VIA carbon equivalent was needed so that the chemical compositions of different steels could be described and understood world wide. A number of CE formula were considered and the following : Mn Cr + Ma + V Ni+Cu CEIIW = C + + + (3) 6 5 15 was selected for studying a range of C-Mn. steels having CE values between 0.40 and 0.60 (or 0.55), some of which also contained the elements Si, Nb, V and Al ; it was recognized that a different formula might be needed for low alloy steels. The hardened microstructure of a weld HAZ is susceptible to hydrogen induced cracking. The HAZ hardness is regarded as a rough index describing the susceptibility to hydrogen cracking. The maximum HAZ hardness is determined by the chemical composition of a steel and the post-weld cooling rate. The maximum HAZ hardness also depends on the welding cooling time between 800°C and 500°C, T(s). The T is preferably taken as a parameter for the phase transformation behavior in steel welding. In 1968 a cracking pramater was proposed by Yahinori Ito and Kiyoshi Bessyo : Pern = C + (4) 600 60 This formula is valid for t = 19-50 mm. plate thickness and H = 1.0-5.0 cm /100 gr. (Hydrogen in deposited metal). Elements of the steel should be between following restrictions : C = 0.07 - 0.22 % Mi - 0.40 - 1.40 % Si - 0.00 - 0.50 % Ni = 0.00 - 1.20 % Mo = 0.00 - 0.70 % V = 0.00 - 0.12 % B = 0.00 - 0.005 % VIIIWhen the carbon content is less than % 0.18, Pern gives a better conclusion than CE, but when the carbon content exceeds 0.18 %, CE is better. A good correlation holds between Pan and CE (3) for structural steels ; 2C + CE (3) Pan = + 0.005 (5) In the first section of the thesis, the meaning of carbon equivalent and its development are briefly explained. Ihe second section is about weldability and the factors which effect weldability. With the' third section, some carbon equivalent formulas, HAZ maximum hardness formulas and some preheating temperature formulas are given. Then cooling time formulas proposed some researchers and some mathematical functions about welding heat are located. In the last section the computer program is explained. Using and working of the program is as follows : 1- Input chemical composition of the steel : (as percent) At the screen Carbon (C %), Manganase Qfa. %), Silicon (Si %), Posphor (P %), Sülphüre (S %), Copper (Cu %), Chrcmiom (Cr %), Nickel (Ni %), Jfolybdenium (Ifo %), Vanadium (V %), Cobalt (Co %), Niobiam (Nb %), Titanium (Ti %), Zirkonium (Zr %), Boron (B %), Nitrogen (N %) are asked and input them to program. 2- Input welding heat parameters as arc voltage (volt), current intensity (Ampere), welding speed (cm/min), sheet thickness (cm) preheat temperature (deg C). 3- Input the type of Welding method for the relative heat effect ( y') by choosing from the following welding methods.“Shilded metal arc welding”“Arc welding with rut ile electrode”“Arc welding with basic electrode”“Gas metal arc welding Active gas-”“Gas metal arc welding- Inert gas-”“Gas tungsten arc welding”IX4- Input the welding method and the edge preparation for calculation of the effects on the cooling rate :“Filler welding”“Square-edge butt welding”“Single-V butt welding - Root run -”“Double-V butt welding - Root run -”“Single or double-V butt welding-filling run-”“Single or double butt welding - final run-”“Single or Double T-butt welding ”Single or Double T-butt welding - filling run-“ ”Corner butt welding" 5- Calculation of the Carbon equivalent formulas. 6- Calculation of the HAZ hardness depend on carbon equivalent formulas. 7- Calculation of the preheat temperatures depend on carbon equivalent formulas. 8- Output of chemical composition of steel 9- Output of heat inputs 10- Output of being two or three axial ly heat transfer 11- Output of carbon equivalents 12- Output of maximum hardnes of HAZ 13- Output of preheat temperatures In modern industries, it is obvious that the application of the solutions as the most suitable ones to the engineering problems in a short way is only possible by evalvating many different choises. In other words, the increase in the using of computers for engineering applications is important from the point of rapidly evalvating of a number of choises and giving the application chances. This computer program provides to be done a series of procedure to an engineer at a short time which can be done in a long period at normal conditions. This result is especially important for time-consuming procedures which are done in a definite way. Besides, it is clear that the application of computer technology to compute the Carbon Equivalents and related values in welding engineering will provide a lot of advantages such as time-saving and avoiding from computing defects.

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