Delamination Fracture Related to Tempering in a High-Strength Low-Alloy Steel

Abstract

The delamination or splitting of mechanical test specimens of rolled steel plate is a phenomenon that has been studied for many years. In the present study, splitting during fracture of tensile and Charpy V-notch (CVN) test specimens is examined in a high-strength low-alloy plate steel. It is shown that delamination did not occur in test specimens from plate in the as-rolled condition, but was severe in material tempered in the temperature range 500°C to 650°C. Minor splitting was seen after heating to 200°C, 400°C, and 700°C. Samples that had been triple quenched and tempered to produce a fine equiaxed grain size also did not exhibit splitting. Microstructural and preferred orientation studies are presented and are discussed as they relate to the splitting phenomenon. It is concluded that the elongated as-rolled grains and grain boundary embrittlement resulting from precipitates (carbides and nitrides) formed during reheating were responsible for the delamination.

Short review: Potential impact of delamination cracks on fracture toughness of structural materials

“…The authors observed that on all studied HSLA steels, the fracture surface displayed longitudinal delamination cracks in both directions. Similarly, Yan et al [6] investigated the influence of tempering temperature on a HSLA steel. The 200°C, 400°C and 700°C tempered specimens exhibited a typical cup-and-cone tensile fracture (cf.…”

“…In this study, it was shown that delamination cracks may have positive effect on the impact toughness properties if their number is relatively low. Fracture surface of specimens from plate of HSLA steels which underwent a tempering step [6] and were tested at room temperature did not display any delamination cracks, unlike those tested at -30°C (cf. It was observed that at higher tempering temperatures delamination cracks increase both in number and in length, then decrease both in number and in length when the tempering temperature reaches 700°C.…”

“…secondary cracks parallel to the rolling plane, have been observed on high strength steels [1][2][3][4][5][6][7][8][9][10], aluminum-lithium alloys [11][12][13][14][15], Ti-stabilized stainless steels [16,17] and ultrafine-grained steels [18]. Different types of delamination cracks in combination with different orientations of the specimen direction had been identified [13,19].…”

Microstructure and microtexture assessment of delamination phenomena in charpy impact tested specimens

“…Furthermore, crystallographic plane materials, with (100) orientation aligned in the rolling direction, show a strong tendency to occur cleavage fracture during impact test 3,4,[6][7][8][9]14 . To identify whether the separation of the (100) planes occurred in this case, the microtexture on the edge of the parallel section's (Figure 3b)) fractured surface was measured, where the delamination was generated.…”

“…In addition, this allows a better understanding of the mechanisms responsible for the nucleation and propagation of delamination cracks, which are a major problem in HSLA steels 4,5 . Furthermore many works have investigated the influence of the delamination phenomena on impact toughness of microalloyed HSLA steels [5][6][7][8][9] . Some of these works reported that the presence of delamination can decrease the uppershelf higher energy in an impact test.…”