Treatment Process for Bars

Abstract

Treatment process for stainless steel bars, in particular a solution quenching, to be performed directly in-line downstream of the rolling mill which makes it possible to obtain a material devoid of intergranular corrosion and with microstructural characteristics suitable for subsequent uses. Advantageously, said process also makes it possible to improve the productivity of the entire rolling plant. The treatment is suitable to be performed on austenitic, ferritic, or austeno-ferritic stainless steel bars, Al—Cu alloy bars, Nickel alloy bars, and all other alloys requiring rapid cooling in order to prevent undesired phase precipitations. Prevention of intergranular corrosion obtained with the treatment process of the invention makes it possible to prevent problems, and relative costs, during surface treatment of the bars and those that could occur in final use.

1 - 14 . (canceled) 
   
   
       15 . In-line heat treatment of bars exiting a rolling mill wherein, immediately after at least one stage of rolling, there is provided a solution heat-treatment in a solution heat-treatment line ( 10 ,  10 ′,  10 ″), with an initial temperature of the bars comprised between 900 and 1200° C., characterised in that there is provided a quenching speed comprised between 10 and 150° C./sec, and in that the final temperature of the solution heat-treatment of the bars is between 350 and 650° C., such that a first curve ( 1 ), which represents the temperature pattern at the core of the treated bar over time, does not intersect and remains below a second curve ( 5 ) showing precipitation of carbides, specific to the material of the treated bar. 
   
   
       16 . Process according to  claim 15 , wherein said bars are of circular, square, hexagonal, rectangular section. 
   
   
       17 . Process according to  claim 16 , wherein said bars are in stainless steel. 
   
   
       18 . Process according to  claim 16 , wherein said bars are in nickel alloys. 
   
   
       19 . Process according to  claim 15 , wherein two stages of rolling take place before the solution heat-treatment in said first solution heat-treatment line ( 10 ), said stages including the passage of the bars to a roughing train ( 7 ) and an intermediate train ( 8 ) respectively. 
   
   
       20 . Process according to  claim 15 , wherein three stages of rolling take place before the solution heat-treatment in said first solution heat-treatment line ( 10 ), said stages including the passage of the bars to a roughing train ( 7 ), an intermediate train ( 8 ) and a finishing train ( 9 ) respectively. 
   
   
       21 . Process according to  claim 15 , wherein said at least one stage of rolling includes the passage of the bars into a roughing train ( 7 ) downstream of which the bars undergo said solution heat-treatment in a second line of solution heat-treatment ( 10 ′,  10 ″). 
   
   
       22 . Process according to  claim 19 , wherein said solution heat-treatment includes two stages, the first of which on said solution heat-treatment line ( 10 ) and the second of which in a quenching medium ( 12 ) that is integrated into a first bar discharge device ( 11 ). 
   
   
       23 . Process according to  claim 20 , wherein said solution heat-treatment includes two stages, the first of which on said solution heat-treatment line ( 10 ) and the second of which in a quenching medium ( 12 ) that is integrated into a first bar discharge device ( 11 ). 
   
   
       24 . Process according to  claim 19 , wherein after said solution heat-treatment the bars are discharged into a first discharge device ( 11 ), called first device ( 11 ) as it is situated immediately downstream of said first solution heat-treatment line ( 10 ). 
   
   
       25 . Process according to  claim 20 , wherein after said solution heat-treatment the bars are discharged into a first discharge device ( 11 ), called first device ( 11 ) as it is situated immediately downstream of said first solution heat-treatment line ( 10 ). 
   
   
       26 . Process according to  claims 15  or  21 , wherein after said first stage of rolling there is a stage in which the bars are transferred to a second solution heat-treatment line ( 10 ″). 
   
   
       27 . Plant for rolling and in-line heat treatment of bars including
 means for heating ( 6 ) a semi-finished product,   means for rolling said semi-finished product, including a roughing train ( 7 ), an intermediate train ( 8 ) and a finishing train ( 9 ),   a first solution heat-treatment line ( 10 ) including a series of quenching tanks with water or other quenching fluids,   a first bar discharge device ( 11 ) equipped with a quenching tank ( 12 ).   
   
   
       28 . Plant according to  claim 27 , wherein between said roughing train ( 7 ) and said intermediate train ( 8 ) there is a second line of solution heat-treatment ( 10 ′). 
   
   
       29 . Plant according to  claim 28 , wherein immediately downstream of said second solution heat-treatment line ( 10 ′) there is a second bar discharge device ( 11 ′). 
   
   
       30 . Plant according to  claim 27 , wherein downstream of the roughing train ( 7 ) there is a device ( 13 ) to transfer the bars to a second solution heat-treatment line ( 10 ″) followed by a second discharge device ( 11 ″).