Effect of the microstructure on the crack initiation during thermal cycling of Nb–Ti-bearing continuous casting slabs

Abstract

To discussed the influence of reheating and cooling on the crack initiation mechanism under the hot cycle mode of a continuous casting slab, during thermal cycling and analysed the relationship between the lower grain size and the crack initiation toughness under different temperature fluctuations. A thermal expansion tester and a Gleeble-3500 thermodynamical simulator were used to perform thermal processing experiments on the samples, where in the temperature fluctuations during solidification were 25 K, 50 K, and 75 K. Scanning electron microscopy (SEM), optical microscopy (OM) and other characterization methods were used to analyse the morphology, microstructure, thermoplasticity and residual stress of the cracked tensile test samples, which were taken from the Nb-Ti-bearing slabs. The result shows that with the intensification of the temperature-returning process, the grain size at the fracture and the size of the slab fracture toughness are increases, which leading to a decrease in crack initiation toughness.

Effect of Carbides on Thermos-Plastic and Crack Initiation and Expansion of High-Carbon Chromium-Bearing Steel Castings

“…The reduction in area (R.A.) was usually defined as the standard for the high-temperature thermoplastic range [31], and the lower the reduction in area was, the worse the thermoplastic. R.A. value of 60% was used as the standard for judging the brittle range [32], and the calculation of the reduction in area is shown in Equation ( 9):…”

“…When the continuous casting temperature was less than 800 • C, phase transformation and solidification structure transformation were the reasons for the rapid increase in the ultimate tensile strength. Usually, an increase in the ultimate tensile strength of a casting is caused by the refinement of the solidification structure [32].…”

“…When the continuous casting temperature was less than 800 °C, phase transformation and solidification structure transformation were the reasons for the rapid increase in the ultimate tensile strength. Usually, an increase in the ultimate tensile strength of a casting is caused by the refinement of the solidification structure [32]. The calculation results of the true fracture strength and true fracture ductility of the sample at the continuous casting temperature are shown in Figure 2b.…”