Problems in Continuous Casting of Resulfurized Free-Cutting Steels

1) Why are you adding aluminum and titanium to a nonkilled grade? At 1.30% Mn, what are you trying to do with these?

2) How uniform is manganese analysis at beginning and end of cast heat of ingots?

3) Tell me about the magnetic stirring at the caster, submerged nozzles. What is radius of caster and metallurgical distance?

What is your melt process? Is there ladle met after inital melt? Stirring? Or just turn down into ladle transport to caster? How good is your control of turndown temperature? How good is your control of superheat?CpK please, not adjectives.

Milo

Answer to the questions of milo:

1)process is made of arc furnace+ ladle furnace, in the arc furnace we use from 80% DRI + 20% scrap, but at the time of tapping we use from Al for killing.

you know that this grade is not non-killed and is semi-killed, but if we use just from manganese then the activity of oxygen will be so much and pinhole and blowhole will be next problem. and also there is a restriction for the usage of this grade from standard and customer that Al must not be higher than 0.005(because of change in the morphology of MnS from monotectic(spherical) to eutectic and reduction in machining). then for inhibiting the problem of pinhole and blowhole and also having a good machinable grade we use from titanum in two aspect:

a; inhibiting from reoxdation of steel at the time of casting(at the same time without any danger for the changing of the morphology of MnS)

b; nucleation sites for (Mn,Fe)S inclusions and reduction of problmes of splitting in rolling

2)if we use from Al and Ti then the yield of lowcarbon ferro manganese willl be more than of 95%.

3)until now we use from ingot casting for this grade but continuous caster just use from one stirrer at the mold, and also we use from ladle shroud and SEN ( but not special for this grade because we didn't produce this until now), and also the metallurgical length for most of the grades is approximately 16-18 meter.

but we think that we must use from more water in footroll part and less in mobile and fixed sector for inhibiting of breakout, i'll say u later about radius of mold.

and also after arc furnace there is LF with argon stirrer (magnetic stirrer is not in use in one of two ladlefurnaces but we can use from that in one of them), but always there are some problems in temperature control.

there is not any same answers between the temperatures of ladlefurnace and caster and then i can not control superheat temperature. and also there is something wierd for me that maybe you can help me, here there is a rule for CCM between temperature of casting and speed of that:

eg: the liquidus of this grade is 1510, they will add 15 to liqudus for lowcarbon grades and will made this rule:

1510+15=1525

1526-1532 at 1 m/ min

1533-1539 at 0.9m/min

1540-1546 at 0.8m/min

1547-1553 at 0.7m/min

the maximum speed of casting for this two bloom caster(230*250mm) is 1 and minimum is 0.7. and on the basis of this table they say that the temperature of coming melt from ladle furnace must be liqudus +(100-110 c) i.e.1610-1620 and on the basis of the temperature of tundish they will decide for the speed of casting and on the basis of speed software will decide the flow of water which i think we must increase flow of water in footrolls.

did u see anything looklike this table before?

answer to the questions of milo:

radius of mold (inner radius=6mm and outer radius=25mm)

and also results of simulations for just low carbon grades(not low carbon and resulfurized) show that metallurgical distance is about 15 m.

we don't have a simulator here for simulating of this conditions but i think that problem of internal cracking of this grade is not related to liquid phase under compression and tension of rolls of straithening, but it must be more related to the brittlenes of presence of FeS phase and then we must reduce the power of secondary cooling( but because of danger of breakout we need to the severe water in foot roll and for prediction of severe reheating of bloom the intensity of cooling of the other zones must increase also)

I am NOT AT all comfortable with the deliberate addition of aluminum and Titanium, even at the 0.005 level you mentioned. You are correct that Manganese sulfide shape follows oxygen level.

Not sure why you think you need nucleation sites for MnS 's either...

my aims were 0.002 MAx wt% Al, though we published 0.005 wt %. Never deliberately added aluminum or titanium to resulfurized material. I think inland did some trials back in early 1980's- Scrapped as seamy and poor tool life.

What is the sulfur level in the furnace? are you just trimming in the Ladle furnace, using the carryover sulfur from scrap charge ?

Or are you melting clean and low sulfur, then resulfurizing in ladle furnace? BIG DIFFERENCE.

Frankly, I would be looking at macroetch of as cast blooms.

The link below gives a model that Tata published that will allow you to confirm the temperatures that you were puzzled about.

Superheat and temperature aims:

http://www.docstoc.com/docs/51129133/casting-super-heat Its worth the $5.00 to download.

If you are above 1.00% Manganese, why do you think you will have FeS?

Who has done lab report on cracked blooms?

Milo

to milo:

if you don't agree with addition of Al or Ti, what will you do with problem of poor surface quality(pinhole and blowhole)?

and also the aim of creating nucleation sites for (Mn,Fe)S inclusions is reduction of problem of splitting in heavy mill unit.

it's right that we have more than 1 percent Mn but severe segregation of sulphur in ingot casting (specially in top and hot top part) will cause lack of enough Mn for absorbing sulphur in front of 98 percent iron.

process of melt preparation:

at the first step in arc furnace we use from 80 percent DRI and just 20 percent Scrap then our melt is free from sulphur, but at the time of tapping we use from pyrite for increasing sulphur and then in final step in ladle furnace we use from sulphur wire.

thankyou for this adress but i don't have any internet credit in our country, if you can give me one easy access case.

What country are we talking about and what is the interent credit?

to milo:

1- you know that there is a lower limit for oxygen total in high sulfur(0.4) free cutting steels( e.g. 200 ppm), with this condition is there any control on the formation of oxide inclusions and how?

In other words can we control the size and distribution of globular complex oxides?

2- what is exactly the way of preventing blowholes formation in this non-killed grades? I mean that when there is a limit on nitrogen content(70-120 ppm) and on oxygen soluble(at least 30 ppm for formation of globular sulphides) what must do?

is there any relation in quantity of sulfur and prevention of blow holes?

are there related to the time of sulfur addition, i mean that sooner sulfur addition helps to more surface tension of melt and less gas pick up?