Effect of boron segregation at grain boundaries on heat-affected zone cracking in wrought INCONEL 718

Abstract

Susceptibility to heat-affected zone (HAZ) cracking during electron-beam welding was studied in two INCONEL 718-based alloys doped with different levels of boron. By lowering the carbon, sulfur, and phosphorous concentrations to be "as low as possible," the occurrence of HAZ cracking was related directly to the level of segregation of boron at grain boundaries, which occurred by nonequilibrium segregation during a preweld heat treatment. The study has demonstrated a direct correlation between the amount of boron segregated at grain boundaries and their susceptibility to HAZ cracking, in terms of the total crack length and number of cracks observed in the HAZ. The analysis of results suggests that both the melting and resolidification temperatures of the boron-segregated grain boundaries can be about 100 ЊC to 200 ЊC lower than those of the grain boundaries that were susceptible to constitutional liquation of Nb carbides on them, making boron more deleterious in causing HAZ cracking.

Elemental segregation during resistance spot welding of boron containing advanced high strength steels

“…Table 5 Weld nugget diameters and tensile peel strengths of resistance spot welds at I(max). (See Table 2 The embrittlement of welds resulting from the segregation of phosphorous to grain boundaries is reported to be reduced due to the addition of boron [13,15]. EPMA analysis indicated that with an addition of 27 ppm of boron, the phosphorous segregation at the grain boundaries in the fusion zone of Steel-CPB was reduced considerably.…”

“…The formation of complex phosphides affects the amount of substitutional elements in solid solution in the matrix and thereby the hardenability of the steels [9][10][11]. The addition of boron to phosphorous containing steels is known to improve grain boundary cohesion by reducing phosphorous segregation, thereby reducing embrittlement [12,13]. Boron also improves the hardenability of steels, mainly by retarding the nucleation of polygonal ferrite at austenite grain boundaries [14][15][16].…”

Weldability of Directionally Solidified TMS-75 and TMD-103 Superalloys

“…SIMS analysis has shown in both cast and wrought IN718 that segregation of B to grain boundaries plays a dominant role in cracking of the alloy [8][9][10][11]. In the present case two of the alloy contained B levels of 0.005 wt.…”

“…However, Huang et al also working on cast alloy IN718, showed via a careful series of heat treatments combined with B segregation analysis by secondary ion mass spectroscopy (SIMS) that B was responsible for HAZ micro-fissuring in the alloy [7,8]. Similar work by Chen et al [9] and Guo et al [10] on wrought IN718 also showed that B was again the main culprit in HAZ micro-fissuring.…”

On the Mechanism of Serrated Grain Boundary Formation in Ni-based Superalloys with Low γ' Volume Fraction

“…It is believed that the melting point depressing element boron could be primarily involved in liquation since its segregation at GBs significantly lowers the melting point of the boundaries [16,17]. As shown in Figure 4, it is evident that the serrated GBs exhibit a lower concentration of boron than the unserrated GBs: the serrated sample contains 41.6% GBs resistant to boron enrichment as compared to 14.6% in the unserrated sample if GBs are classified as resistant to boron enrichment if intensity is lower than 10 3 counts per second in the Nano-SIMS boron images.…”