Breakout during continuous casting of high alloy steel 1

[WLR]

Recently we've experienced breakouts during continuous casting of a high alloy steelgrade. These breakouts occurred +/- 2 minutes after starting - the bloom lengths were nearly 2 meters. All the casting parameters were carefully checked and no deviations were found. Investigation of the blooms that broke revealed severe cracks on the head of the blocks at a distance of nearly 200mm from the head of the blocks. When casting is started, the moulds are packed with a certain amount of cooling scrap to chill the first steel that enters the mould in order to start the strand.

My theory at this stage is that we might be cooling the steel too severely at the start. Due to the chemistry of the steel (very high alloy content) it is extremely hardenable which thus leads to thermal cracking of the shell especially on the corners and ultimately results in breakouts.

The steel has high C (>0.8%), Mn%, Si%, Cr%, Ni%, moderate V% and according to a simplified model, is fully hardenable (completely martensite) up to a diameter of +/- 100mm round bar.

If anyone can share some info or have another theory on what might be possible causes, I’ll appreciate it.

Thanks
WLR

 

[TVP]

I think your theory about excessive cooling with such a high hardenability grade is a good one. Is this a grade that you have previously cast? Do you have a set practice for casting temperature, speed, mold powder, etc.? A recent thread here on Eng-Tips about "jerking" during continuous casting had some very good information that you may find useful. Use the following link for more information:

thread330-100104