Free-Cutting Steel Bars and Sub-Surface Defects

Milo,

The guy who posted is a metallurgical engineer with 30 years experience (at least that's what he states)! Everybody's angry that the metalworking industry is moving to China and India. Really!! Who's going to do it here? Some metallurgist guy who's looking for answers to his job description on a blog?

Oh. Well maybe his background was in flat roll or aluminum. or strictly melt shop. But process focus will make the data speak. You look pretty cozy in that chair. milo

Well, thank you. I feel cozy. My fur is getting a bit frizzy though. It needs a trim. titi

Thanks for your valuable guidance.

Steel is cast with shrouded Ladle to tundish and to mold through submerged entry nozzle.

Addition of lead is done through Lead shots in Laddle Furnace refining stage .
Checked Billet surface condition also and some surface cleaning done by grinding.This gave better results.

Depth of defects observed varied from 0.020 -0.040" and grinding of such defects more than 0.040" is not accepted in bars diameter 1.25' to 2.0"

I wish to know the experience in production of free cutting steel through continuous casting route and bar mill rolling with special reference to sub-surface defects.

Problem with adding lead in ladle furnace will be segregation. Presuming argon stirring in ladle furnace, (YOU HAVE NOT SHARED ANY DETAILS OF YOUR PROCESS!) When ladle is taken to caster, there will be no stirring, and the density difference of lead to steel will cause lead to move to bottom of ladle. Who picked the ladle furnace for location of addition? on the basis of what? Why? When you say lead shot, How is the addition made? How do you assure that it is getting through the slag? details of process and process control method. Or are your guys just throwing a few 25# bags in? I don't have data, but I conjecture that your first third of ladle cast will be double to lead out of the ladle compared to last third. Now, did you water model the tundish? Once the lead gets into the tundish, It will behave differently than the steel, and there will be eddies and collection areas, again due to density primarily but also do to different viscosity. What is inside of tundish Geometry?How many strands are you feeding? (WITH NO DETAILS ABOUT YOUR PROCESS< IT IS DIFFICULT TO VISUALIZE YOUR PROCESS) are nozzles to molds all at exactly the same level? EXACTLY? IF tundish is cocked by say 1/4-1/2" end to end and one nozzle is 1/4-1/2" lower than others then that 1/2-1" of differential could get draw off much higher lead than other strands. Have you collected any data about lead yield loss? Like how much is left in the bottom of the ladle? how much is left in the tundish? Or are your guys collecting it and taking it out in their lunchboxes to sell for scrap? What about lead content consistency- strand to strand? Beginning of cast to end of cast? Within billet? Within section? I understand that grinding off bad surface improves yield loss on rolling. But what are the causes of the surface imperfections that are being removed? is it aspiration of slag? exogenous materials? Inclusion related due to sulfur? Mold related? DO you run oscillator at different frequency for these grades? should you? What good is telling us the depth of defects of 0.020-0.040" if we don't know if you are talking about on the billets o on the bars, and we don't know your billet size? As I posted earlier AISi stock removal is 0.0015" per sixteenth of diameter per side, So a 0ne inch bar is 16 sixteenths. 0.0015* 16= 024 per side, or 0.048 off the diameter. SO while you say more than 0.040" is not accepted in bars diameter 1.25" to 2.0" the fact is these resulfurized grades are prone to greater surface imperfections because of the Sulfur. You still have not shared with us what the results of your investigation into these subsurface defects has provided. What is your plan for assuring no gross lead segregation in your product? What is your company's Product liability coverage when, say, your leaded product is machined into brake hose fittings for say, chrysler, and they need to recall cars or tucks across the country because of gross lead segregation and crimp cracking. Or fluid power fittings for sky lifts or cranes or man lifts and a part blows out and someone gets hurt? milo milo

the procees is 65 ton oxygen furnace with ladle furnace with bottom argon stirring and lead addition through lead cored wire and lead shots.tundish capacity is 18 tons section cast 160mm square, strand distance 1800 mm. casting is completely closed(submerged), with mould ems. and air mist spray cooling. this problem comes in non leaded free cutting steel also(C - .05, Si - .05, Mn - 1.05, P - .04, S - .25, Pb - .25) kindly help we tried degassing partially with better results but not able to completely eliminate the problem.

Good morning Mageswar.

You gave the analysis for a leaded steel in your post calling it nonleaded steel (.25 Pb) Presuming you didn't mean that.

Appears that your carbon and phos are really on the low side, IMHO. (from an end users standpoint.)

Are you serious about that 0.05 Silicon analysis?

We have given more information about understanding the problem than we have recieved describing the true nature of the problem.

No information at all has been provided characterising the defects_ what metallographic work has been done? Is there inclusion material associated with these 'defects' (your word, not mine)? What is its analysis? is it metallic, non metallic, exogenous? Oxide? Sulfide?

Before one starts prescribing "fixes" it is important to have a clear understanding of what the actual problem to be treated is.

Is there only one failure mode? how do you know? show us the data so we can help.

More description please of process of lead addition- Why both wire and 'shots'? what is quantity of both added (how do you measure) and what is recovered in your refractory after the cast ? How do you know? How much is walking out the door in mason's lunchboxes? Can I see a print of your Tundish.

Milo

milo,

lead is added in wire form 13mm steel cored wire, approx 250+/-10 kg for a ladle of 65 tons. recovery will be on the order of 70-80%. we check for the sample report if suppose recovery is less we may use lead shots or wire for futher trimming. we have seen the lead getting deposited in the slider plates and mechanism.

the problem of "seams" in rolled product is in both leaded and non leaded free cutting steel, not much in lower dimension sections ie below 15 mm but gets aggravated with increase in section(both bars and coils). i will try to get u photos of the tundish/ladle slide gates and if possible the defect in the rolled product at the earliest.

in the meantime give me any suggestion that can be tried on the process for improving.

i thank you for your immediate and prompt response. iam workingin the same plant as Mr. hegde in the procees division.