A Three-Stage Mechanistic Model for Solidification Cracking During Welding of Steel

Abstract

A three-stage mechanistic model for solidification cracking during TIG welding of steel is proposed from in situ synchrotron X-ray imaging of solidification cracking and subsequent analysis of fracture surfaces. Stage 1-Nucleation of inter-granular hot cracks: cracks nucleate inter-granularly in sub-surface where maximum volumetric strain is localized and volume fraction of liquid is less than 0.1; the crack nuclei occur at solute-enriched liquid pockets which remain trapped in increasingly impermeable semi-solid skeleton. Stage 2-Coalescence of cracks via inter-granular fracture: as the applied strain increases, cracks coalesce through inter-granular fracture; the coalescence path is preferential to the direction of the heat source and propagates through the grain boundaries to solidifying dendrites. Stage 3-Propagation through inter-dendritic hot tearing: inter-dendritic hot tearing occurs along the boundaries between solidifying columnar dendrites with higher liquid fraction. It is recommended that future solidification cracking criterion shall be based on the application of multiphase mechanics and fracture mechanics to the failure of semi-solid materials.

In Situ and Ex Situ Characterization of the Microstructure Formation in Ni-Cr-Si Alloys during Rapid Solidification—Toward Alloy Design for Laser Additive Manufacturing

“…The Ni-Cr-Si-based alloys studied in this work were selected with regard to potential use in commercial laser deposition processes, thus the following criteria need to be considered: The alloys need to possess a small solidification range to reduce the susceptibility to solidification cracking [ 25 , 26 ] The alloys need to solidify with a (near-)eutectic microstructure, preferably with a fine lamellar rather than large, blocky phases to enhance the mechanical properties A sufficiently high amount of Cr for improved corrosion resistance A sufficiently high amount of Si for the formation of hard and wear-resistant silicides …”

Getting the Strain Under Control: Trans-Varestraint Tests for Hot Cracking Susceptibility

“…In combination with the results of published research, [13][14][15]29,32,[38][39][40][41][42][43][44][45][46] the method presented could form the basis of standardized Trans-Varestraint tests. The results reported also identify a range of 'critical' depths where hot cracks initiate, which correlates with the dendrite growth orientation and maximum shear stress location.…”

“…[13] Furthermore, as the hot cracking phenomenon is more extensively researched, new models for crack generation and development are emerging. Recent developments that have been presented in 2017 and 2018 by Aucott et al include the three-stage mechanistic model for solidification cracking during welding of steel [14] and the initiation and growth kinetics of solidification cracks during welding. [15] Solidification in general is affected by the temperature gradients that are forming during the process and the direction of heat flow.…”

Mode I Stress Intensity Factor and T-Stress Solutions for Centre Cracked Orthotropic Plates

“…However, unlike isotropic materials where a crack grows perpendicularly to the direction of maximum tension [26], the direction of crack growth in orthotropic materials is governed by the material strength and the stress state [27,28]. Nevertheless, the SIF and the T-stresses as parameters independent of the crack growth direction and governing the crack stability, respectively, find practical significance in the fracture analysis of such materials [29].…”