Effect of Microstructural Variation on Weld Metal Cold Cracking of HSLA-100 Steel

Abstract

KEY WORDS: hydrogen induced cold cracking (HICC); HSLA-100 steel; weld metal; susceptible microstructure; microhardness.is not relevant to that of single pass weld. Accordingly, the condition of three major factors, i.e. susceptible microstructure, diffusible hydrogen and residual stress, contributing to cold cracks in a multi-pass weldment is far different from those in single pass one. Several studies, mostly in Japan, have been performed on the risk of weld metal cracking in the multipass weld. [13][14][15] In Refs. (13) and (14), investigators have deposited weld beads into a highly restraint Vgroove joint with varying the weld metal strength, the hydrogen content and the height of weld metal. The preheat temperature necessary to prevent weld metal cracking was determined as a function of those variables and then proposed the following empirical equation, Eq. (1) (1) where Rm is the weld metal tensile strength, [H] is the weld metal diffusible hydrogen content, h w is the weld metal height, and A, B, C and D are constants. Unlike the various equations currently available for predicting the preheating temperature necessary to prevent HAZ cracking, 16,17) above equation does not contain a term like carbon equivalent but is showing a strong linear relationship with tensile strength of weld metal (Rm). If this is the case the multipass weld might have different resistance to HICC from location to location as it has a large variation in microhardness throughout the weldment, especially in high strength weld metals. Previously Moon et al. 18) measured the microhardness for multipass ultra-low carbon weld metal deposited in HSLA-100 steel and reported a variation of microhardness in the range between 260-320 Hv. The lowest hardness was recorded in the localized band that located in the outer portions of HAZ of weld bead. As this band was revealed in bright contrast in their optical micrographs they called it as 'white band'. The maximum hardness, on the other hand, was recorded in the midway between the fusion boundaries and white band and thus the distance between the maximum and minimum hardness was less than 1 mm. It means that the most susceptible microstructure is located just adjacent to the least susceptible one. Under such a situation, it would be very interesting to figure out the effect of local variation in microhardness on crack susceptibility and its propagation. This is the first purpose of this investigation.Traditionally, as described above, the microhardness has been regarded as a quantitative measure to evaluate the microstructural susceptibility to cold cracking not only in HAZ but also in the weld metal.11) In high strength steels, however, it has been well documented that hydrogen embrittlement is strongly affected by microstructure.19) For weld metal, it was also reported that higher hardness was not always corresponding to higher susceptibility and showed a combination of high strength and less susceptibility could be achieved through microstructural modification. 20,21) In other words, th...

Effect of microstructure and chemical composition on cold crack susceptibility of high-strength weld metal

“…9 and that, at least for 270 Hv5, the crack path was not preferentially located in grain boundary ferrite [21,22].…”

Effect of single pass welding heat input on microstructure and hardness of submerged arc welded high strength low carbon bainitic steel

“…1,2 However, when they are welded using an immature welding process, the welding cold crack and deterioration in toughness can occur easily in the welded joint. [2][3][4] Therefore, more attention should be given to the weldability of steels, especially for high strength steels. Meanwhile, the complexity of welding process to a large extent determines the uncertainty of final properties of the welded joint.…”

Local Control of Microstructure and Mechanical Properties Of High-Strength Steel in Electric Arc-Based Additive Manufacturing

“…17 that the ferrite grains have mostly an elongated morphology and cannot be linked entirely to the recrystallization phenomenon [25]. Previous research on white regions formed during multi-pass welding of HSLA-100 steels articulated the presence of tempered martensite in white regions leading to lower hardness [70]. The white regions can correspond to the softening associated with the inter-critically heat-affected zone (peak temperature is between Ac 1 and Ac 3 ) and the subcritical heat-affected zone (peak temperature Ac 1 ) [71,73].…”

“…The distance between the white region and the fusion line is fairly constant and is measured to be 539 mm ± 14 mm. Softened regions with lower hardness have already been reported for multi-pass welding of low-carbon steels and ultra-highstrength steels [70,71]. To comprehend the influence of the microstructure in the white band on hardness, hardness measurements were performed with a load of 0.2 kg across a white region (Fig.…”