Cracking and Failure Characteristics of Flame Cut Thick Steel Plates

Abstract

The manufacturing of thick wear-resistant steel plates commonly leads to a layered structure and non-uniform properties in the thickness direction which makes the processing and utilization of the plates problematic. The processing steps of thick plates include flame cutting, which generates a heat-affected zone and high residual stresses into the cut edge. In the worst case, the cutting causes cracking. However, the residual stress level alone is not high enough to break a wear-resistant steel plate that behaves normally. Therefore, high-tensile stress also requires a microstructurally weak factor for crack initiation. For this reason, the main objective of this study is to reveal the main microstructural reasons behind the cracking of plates in flame cutting. To achieve this, plate samples containing cracks are mechanically tested and analyzed by electron microscopy. The results show that cracks are commonly formed horizontally into the tempered region of the heat-affected zone. Cracks initiate in the segregations, which typically have a higher amount of impurity and alloying elements. Increased impurity and alloying content in the segregations decreases the cohesion of the prior austenite grain boundaries. These weakened grain boundaries combined with high-residual tensile stress generate the cracks in the flame-cutting process.

Influence of the Thermal Cutting Process on Cracking of Pearlitic Steels

“…Heating to high temperature in the cutting process causes the near‑surface zone to become hardened during the rapid cooling of the material. Compressive stresses occur in the hardened zone due to the phase transitions ( Figure 6 a) [ 19 , 26 , 27 , 28 , 29 ]. Based on the conducted research, it is possible to present the mechanism of steel cracking in the thermal cutting process.…”

“… ( a ) Distributions of circumferential residual stresses in induction hardened 41Cr4 specimen to a depth of 2.3 mm (1) based on [ 26 ] and in cutting edge of 40 mm wear‑resistant steel plate ( 2 ) based on [ 19 ]; ( b ) scheme of crack development under the thermally cutting surface. …”

“…These structural changes can influence the corrosive properties of the steels. Microcracks, similar to quenching cracks, also occur in HAZ, which can become corrosion centers and stress concentration notches [ 19 ]. Due to the presence of HAZ and geometric deviations on the edges of the cut, it is often recommended to finish them mechanically by cutting or grinding.…”

Revealing the Enhancement Mechanism of Laser Cutting on the Strength–Ductility Combination in Low Carbon Steel

“…Specifically, the microstructure near the laser cutting surface is totally different from the base metal (BM) and it can be divided into laser remelted layer (LRL) and HAZ. Based on the relatively narrow phase transformation region with a width of ~0.9 mm in Figure 3a, it may be easily deduced that the depth of the HAZ under the process of laser cutting is narrower than that of the other thermal cutting methods, such as flame cutting, plasma arc cutting, and so on [20,21]. This may be ascribed to the high energy density of the laser beam and high cutting speed of the laser cutting, leading to less heat input [13].…”

Prevention of Thermal Crack in Steel Slab Using Neural Networks Model to Predict Impact Absorption Energy

“…[5][6][7][8][9] Thermal cracks and fractures of slabs occur frequently after casting of high-carbon steel and high-alloyed steel. [10,11] Especially, fractures can initiate at inclusions that have low ductility and different elasticity from the bulk steel. [12] External stress is concentrated around these inclusions, so they result in thermal cracks.…”