Effect of morphology of martensite–austenite phase on fracture of weld heat affected zone in vanadium and niobium microalloyed steels

Abstract

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Tackling the toughness of steel pipes produced by high frequency induction welding and heat-treatment

“…7b) throughout the wall-thickness except within 1 mm to both the inner and outer surfaces. These strings of M-A islands are normally found along the prior austenite grain boundaries [20][21][22] which on the fusion surface do not have much mobility under impact from two abutting edges on both sides.…”

Structure–Property–Fracture Mechanism Correlation in Heat-Affected Zone of X100 Ferrite−Bainite Pipeline Steel

“…It is generally accepted that CGHAZ and ICCGHAZ are the most detrimental regions from the point of view of toughness and cleavage fracture may occur in the two regions during impact. [3,[5][6][7][8] Thus, there is a need to understand the correlation of structure-property-cleavage fracture mechanism in the HAZ, especially in CGHAZ and ICCGHAZ.…”

“…In regard to nucleation, at least three possible mechanisms have been suggested and include: (a) crack initiation at grain boundaries caused by pile-up of dislocations, [9,10] (b) cracking of inclusions, large second phase particle or martensiteÀaustenite (MÀA) constituent present within the grains or along the grain boundaries, [5][6][7]11] , and (c) decohesion of inclusions/MÀA from matrix. [6][7][8] Cleavage fracture occurs when (1) the maximum principal stress (r yy ) close to the crack tip exceeds fracture stress (r f ) over a characteristic distance, [12] or (2) the microcracks, nucleated ahead of the main crack tip because of high stress field, [13] interconnect with each other. [14] During propagation, there is competition between the microcracks formed at the crack front.…”

“…[14] Main crack is generally difficult to characterize using EBSD primarily because of poor indexing rate introduced by the high strain and large residual stress after the destructive Charpy v-notch impact test. However, secondary microcracks that are nucleated at the crack tip and are retarded or arrested by the high angle boundary (HAB), small grains (packets) or in some instances MÀA constituent [7] can provide information on crack nucleation and propagation process. Recently, a few studies on the characterization of brittle cracks using EBSD have been reported.…”

“…This kind of MÀA constituent can promote nucleation of brittle fracture either through cracking or debonding from the matrix. [5][6][7] B. Charpy Impact Toughness and Fracture Surface Characterization Charpy impact energy of X100 base plate, samples with notch I, II, and weld metal at À20°C is presented in Table III. The average Charpy impact energy of notch I was 183 J and is~3.6 times that of notch II (51 J).…”