Effectiveness of hot tensile test in simulating straightening in continuous casting

Abstract

The extent to which the hot tensile test can be used to assess the relationship of steel composition to the incidence of transverse cracking in continuous casting has been examined. The influence ofS, Ca, Ti, and Nb on the hot ductility ofC-Mn-Al steels was investigatedfor the temperature range 700-1100°C and the results were compared with available commercial data on the effect of these elements on transverse cracking. Three different heat treatments that were carried out before straining have been examined: (i) reheating hot rolled plate to 1330°C; (ti) in situ casting of tensile samples; an.d (iii) asfor (ii) followed by reheating to 1330°C. After these treatments, the samples were cooled directly to test temperature at a cooling rate of 100 K min-l and strained to failure at a strain rate of 2 x 10-3 S-l.All heat treatments showed that Nb gave"the worst ductility in accordance with its known propensity to favour transverse cracking. Reheating hot rolled plate was found to be the simplest and most successful method for examining the influence of the microalloying additions Al and Nb (and probably V) on ductility in relation to the transverse cracking problem. Although in situ casting is a difficult technique and tends to suppress the relative changes in ductility with composition, it is the only method that can be used to assess the influence of elements such as Ti and S which do not return or dissolve fully into solution on reheating. The hot ductility curves are discussed in relation to the precipitation and grain sizes generated by the various treatments.MSTj 1480

The Influence of Composition on the Hot Ductility of Steels and to the Problem of Transverse Cracking.

“…2(b). 5) Generally, for the micro-alloying additions Nb and V and A1,5) The effect of sulpher content on the hot ductility of reheated CMn-Nb-AI steels, Ref, lO),…”

Evaluation of the Hot Ductility of a C–Mn Steel Produced from Scrap Recycling

“…Moreover, the effect of S on hot ductility can only be detected by means of in-situ solidification, since only these experimental conditions dissolve the MnS. 2,22) After the homogenization treatment, samples were cooled down at a rate of 10°C/s to the testing temperature, ranging from 650 to 1 100°C. The strain rate used for the tensile tests was 5 · 10 Ϫ3 s Ϫ1 .…”

Effect of High Temperature Deformation on the Hot Ductility of Nb Microalloyed Steel

“…The strain rate is chosen to be the same as that used during the straightening operation, 10-3 to 10-4 the effect of S can not be studied by this simple method and it would lead to the false conclusion that the level of S has no effect on the hot ductility, Figure 2 Test temperature, oC heating the steel to ~ 1350°C), prior to the tensile test, has been found adequate to assess likelihood of a steel to exhibit a transverse cracking problem. [80) On the contrary, for Ti and S, the tensile specimens must be tested directly after in situ melting and solidification to ensure dissolution of the TiN particles and MnS inclusions. [49, [80][81][82] Provided these precautions are taken, precipitate sÏze and distribution in the tensile specimens foliows closely that found near the surface of the continuously cast slabs.…”

“…[80) On the contrary, for Ti and S, the tensile specimens must be tested directly after in situ melting and solidification to ensure dissolution of the TiN particles and MnS inclusions. [49, [80][81][82] Provided these precautions are taken, precipitate sÏze and distribution in the tensile specimens foliows closely that found near the surface of the continuously cast slabs. [9,78] However, even in situ casting of the tensile specimens is not ideal, as smali castings in general produce neither the exact segregation patterns experienced near the surface of conventionaliy cast strand nor the columnar grain structure that is often present and which may be directly responsible for the ease of crack propagation during straightening.…”