" The Hot Ductility of Steels and its Relationship to the Problem of Transverse Cracking During Continuous Casting "

Abstract

The . present programme concentrated on tensile samples which were generally cast in situ and cooled to test temperatures in the range 1150 to 700°C, this covering the temperature range of the straightening operation. The influence of cooling rate has been examined on a number of steels and in all instances increasing the cooling rate causes worse ductility.

This conclusion is likely to be particularly important for thin slab casting in that the faster cooling rates will encourage the problem of transverse cracking.

The seven steels examined in the thesis were typical commercial grades of continuously cast steels, these being:-

1. C-Mn steel (VC4013), air cast.

2. C-Mn-AI-Nb steel (VS1270B), vacuum cast.

3. C-Mn-AI steel (4P57H), air cast.

4. C-Mn-AI-Ti steel (4P58H), air cast.

5. C-Mn-AI-Ti-Nb steel (4P59H) with lowS level, air cast.

6. C-Mn-AI-Nb steel (4P60H), air cast.

7. C-Mn-AI-Ti-Nb steel (4P61H), with highS level, air cast.

Additional information on the effects of AI, Nb, Ti, and S on the hot ductility behaviour of steels was thus obtained. For all the steels tested, the following conclusions can be drawn:-

1. For the low Mn highS steel (VC4013), tested after the solution treating at 1330°C, it was established that the intergranular failure in the region of low ductility was mainly due to the thin film of deformation induced ferrite at the austenite grain boundaries. The trough occurs because ferrite is the softer, of the two phases and strain concentration takes place in this film causing voiding around the MnS inclusions situated at the boundaries. The ductility of the trough was very narrow at 850 °C.