Dear Sir,

I feel that temperature non uniformity in the radial direction ( more temp on the skin and less at the center), depth of decarb which will affect the flow properties,  the soaking time and roll surface roughness  will be some of  the control parameters for prevention of sliver defects. Also surface scale may be getting rolled into the subsequent rolling operations 

Dear Mr. Vadavkar,

Thank you very much for your reply which is very interesting. This can be one of the causes.

There is another factor which need little clarification. We observed that the defect is existing only in high carbon grade and more prominent in higher section. The above explanation what you mention (heating) is it equally applicable to all grades or specific to some only . 

There is another observation. We found sometime in intermediate rolling stands, if we do wood burning (by keeping a thin wood strip on the running stock) to get the actual shape of the stock, we found there are some steel chip attached to the wood piece . this occurrence is random. Is this phenomena common in long product rolling. Can it be a substantial cause for sliver defects. How the generation of this kind random chip be prevented ? Appreciate your feedback on this queries. 

Dear Sir,

Metallurgically  high carbon steels are prone to cracking / sliver defects.

I think that the rolling process is a complex one and will surely be having many more parameters responsible   for the sliver defects. It would be better if statistical methods are used to zoom down on the actual cause for defect occurrence Data like location of the defects , distance between the defects, size of the defects, material grade, stock size etc will help in locating the exact cause of the defect. This exercise  will  involve a great deal of work. I had done this assignment  when i worked in a seamless  pipe rolling plant. 

Dear Mr. Vadavkar,

                                     Thank you very much for your constructive inputs. You are very right to indicate the fact that statistical data analysis on various rolling parameters in relation to defects is required to narrowed down the root cause or probably to find out the root cause itself. 

This because of late addition of Aluminium due to late additiin alumina will not float because of viscous steel. Low tundish level opening also reason for sliver occutences. Mould level fluctuation also causes sliver.

If u have a data on type slivers defects faced please share a data i will clarify ur doubt. My mail Id [email protected]

Check the temperature at wood placing area itmay be due to temperature hunting.

Before that pl cast at constant speed of perticuler grade.

1.

Cause:

If from mill it will be on proper interval

Action:check all guides and pass condition and make healthy.

2.cause:Reheating furance

Action:check front and back flame should not contact direct to billet.

3.cause:Billet we got from caster

Action:however root cause is casting process of billet but by taking follwing process defect free rolling can continue,eventhough problm may occur at customer end.

Increase heating zone temp by 20degree,Roll billet at higher temp,decrease the mill speed by 10mps if you are rolling at higher speed beyond 80-85mps.Rolling Rejected coil instead of less coils is feasible.

I was Chief Technology Officer of Tata Steel till two years ago. Without a proper investigation of sliver defect through micro structural study, any conclusion drawn will not eliminate the problem. Slivers are caused by poor practices in steelmaking, casting, billet dressing, reheating and rolling. A thorough micro structural study along with inclusion analysis by EDS will provide information regarding the sources of the defect.