Influence of Isothermal Treatment on MnS and Hot Ductility in Low Carbon, Low Mn Steels

Abstract

Hot ductility tests were used to determine the hot-cracking susceptibility of two low-carbon, low Mn/S ratio steels and compared with a higher-carbon plain C-Mn steel and a low C, high Mn/S ratio steel. Specimens were solution treated at 1623 K (1350 °C) or in situ melted before cooling at 100 K/min to various testing temperatures and strained at 7.5 x 10-4 s -1, using a Gleeble 3500 Thermomechanical Simulator. The low C, low Mn/S steels showed embrittlement from 1073 K to 1323 K (800 °C to 1050 °C) because of precipitation of MnS at the austenite grain boundaries combined with large grain size. Isothermal holding for 10 minutes at 1273 K (1000 °C) coarsened the MnS leading to significant improvement in hot ductility. The highercarbon plain C-Mn steel only displayed a narrow trough less than the Ae3 temperature because of intergranular failure occurring along thin films of ferrite at prior austenite boundaries. The low C, high Mn/S steel had improved ductility for solution treatment conditions over that of in situ melt conditions because of the grain-refining influence of Ti. The higher Mn/S ratio steel yielded significantly better ductility than the low Mn/S ratio steels. The low hot ductility of the two low Mn/S grades was in disagreement with commercial findings where no cracking susceptibility has been reported. This discrepancy was due to the oversimplification of the thermal history of the hot ductility testing in comparison with commercial production leading to a marked difference in precipitation behavior, whereas laboratory conditions promoted fine sulfide precipitation along the austenite grain boundaries and hence, low ductility.

Hot Ductility Behavior of a Peritectic Steel during Continuous Casting

“…Percent reduction of area (RA %) is a good measure of cracking tendency [3,22]. Gleeble 3500 simulator can control thermal and mechanical cycles simultaneously by a computer and perform hot tensile tests at strain rates between 10 −5 s −1 and 10 2 s −1 .…”

Effect of Interdendritic Impurity Segregation on Hot Ductility Behavior of Low‐Carbon Steels

“…Especially, the increase in segregation and precipitate-forming element degrades the surface quality of continuously cast steel. [1][2][3][4][5][6][7][8][9][10] Therefore, the content of these elements must be controlled effectively.…”

“…RHT also changes the original grain size and precipitation behavior, and these changes may also affect the steel's hot ductility behavior. [7,8,14,15] Therefore, a re-melting tensile test (RMT) should be used to quantify the hot ductility of continuously cast steels.…”

Influence of Thermal History on the Hot Ductility of a Continuously Cast Low Alloyed Cr-Mo Steel

“…To evaluate the hot ductility of steels, hot tensile testing of samples using similar thermomechanical conditions and measuring the percentage reduction in area after fracture (RA) has proved to be an effective method ( Ref 8,9). This RA value should exceed the limit of 40% to avoid transverse cracks (Ref 10).…”