Cracking and segregation in high-alloy steel 0.4C1.5Mn2Cr0.35Mo1.5Ni produced by thick continuous casting

Abstract

Based on our innovative application of using thick continuous casting slab 0.4C1.5Mn2Cr0.35Mo1.5Ni (high alloy) for the production of high-quality mould steel, the present study investigated the high cracking susceptibility of high-alloy steel and segregation in continuous casting slab. The thermal expansion and the continuous cooling transformation (CCT) curve measurement, together with a high temperature in situ observation, confirmed the martensite phase transition happening at approximately 583 K that would result in an increase in the hardenability and cracking susceptibility. The cracking susceptibility zone was determined by high-temperature mechanical properties measurement. The high-alloy mould steel has no II brittle zone, and III brittle zone is 973–1148 K. As a conclusion, the straightening temperature should be above 1148 K to avoid the cracking during the continuous casting. Moreover, the elemental segregation of carbon, sulfur, chromium, and molybdenum along the cracking was examined by electron probe microanalysis (EPMA) quantitative analysis that might be another reason for the steel crack formation. It shows that Martensite phase transition happened at approximately 583 K that would result in an increase in the hardenability and cracking susceptibility.

Cracking and Failure Characteristics of Flame Cut Thick Steel Plates

“…For these reasons, the segregations effectively maintain their hardness (and brittleness) during tempering while the surrounding structure becomes softer and more ductile. Similar behavior has been reported earlier [28] where segregation transforms to hard phase which would not withstand further manufacturing conditions (for example forging). It was also noticed that crack location had higher concentrations of C, Cr, Mo, P, and S due to the segregation.…”

“…It was also noticed that crack location had higher concentrations of C, Cr, Mo, P, and S due to the segregation. [28] In the present study, segregations also contain inclusions, and titanium nitride precipitates which can create harmful discontinuities and stress concentrations to the steel structure.…”

“…Segregations are known to produce locally harder regions in the structure. [6,28] Segregations here consist of a fully martensitic structure and areas surrounding the segregations have a mostly bainitic structure. In addition, segregations may contain inclusions and precipitates.…”

Optimization of the Continuous Casting Process of Hypoeutectoid Steel Grades Using Multiple Linear Regression and Genetic Programming—An Industrial Study

“…Accordingly, orientation (relative to the principle direction of working), location (related to segregations originating from the solidification process) and preparation (cutting, machining and heat treatment) of these test pieces are essential. On the other hand, the basis for typical steel tensile strength prediction is its chemical composition [4][5][6][7], but contemporary models also involve solidification influences, including grain size and morphology [8][9][10], microstructure [8][9][10][11][12][13][14][15][16][17], macrostructure [8,10,12,15,18,19], chemical non-homogeneities segregations [6,7,[19][20][21][22][23] and casting defects [24,25]. The tensile strength researches are related mostly with individual steel grades, but also more general prediction models were developed [5,14,26].…”

“…Hardenability related to the cracking of high alloyed steel 0.4C1.5Mn2Cr0.35Mo1.5Ni steel was analyzed in paper [20]. The influence of segregations of carbon, sulfur, chromium and molybdenum were also studied, besides the time-temperature influence on martensite formation.…”