Method for producing helical springs or stabilizers

Abstract

The invention relates to a method for producing helical springs or stabilisers consisting of steel. According to said method, the parent material is heated to a temperature in excess of the re-crystallisation temperature, the structure is austenitised, held at an equalised temperature and then formed and subsequently quenched to form martensite and tempered. Round steel bars, whose re-crystallisation temperature is adjusted over the bar length in a compensation furnace, constitute the parent material. The round steel bars are subsequently re-modelled by cross-rolling, remaining substantially straight and after the critical deformation degree has been exceeded are subjected to dynamic re-crystallisation processes. The round steel bars are then subjected to a post-heating process above the Ac3 temperature, in order to undergo a complete static re-crystallisation, are wound to form a helical spring or bent to form a stabiliser and are finally quenched from the austenitic state to form martensite and tempered.

1 . Method for producing coil springs or stabilizers of steel, wherein the starting material is heated to a temperature; above the recrystallization temperature, austenitized, held for equalization of temperature, then deformed and finally quenched to martensite and tempered, characterized by starting out with round steel rods, the heating temperature of which is equalized over the rod length and which then are transformed by skew rolling, while remaining approximately straight, so that a predetermined twisting of the material in the marginal area and a desired transformation gradient is achieved over the cross section, and, after the (critical) degree of transformation is exceeded, dynamic recrystallization processes take place, whereupon the rods are reheated to a temperature above Ac3 , wound into a coil spring or bent into a stabilizer in order finally to be hardened and tempered.  
   
   
       2 . Method of  claim 1 , characterized in that the direction of the twisting of the structure in the marginal region of the round rod corresponds to the main direction of tension of the coil spring or the stabilizer stressed by torsion.  
   
   
       3 . Method of  claim 1 , characterized in that the direction of twist of the structure in the marginal region, with respect to the axis of the round rod, amounts to 35°-65°.  
   
   
       4 . Method of  1 , characterized in that the skew rolling is carried out in one step.  
   
   
       5 . Method of claims  1 , characterized in that the skew rolling of the rod is performed with an average degree of degree of stretching λ of at least 1.3.  
   
   
       6 . Method of claims  1 , characterized in that the maximum transformation in the marginal area amounts to between 0.65 and 1.0 times the diameter of the rod and is at least 0.3.  
   
   
       7 . Method of claims  1 , characterized in that the material is heated at a rate between 100°-400° K/s.  
   
   
       8 . Method of claims  1 , characterized in that the starting material is heated to a temperature between 700° and 1100° C.  
   
   
       9 . Method of claims  1 , characterized in that the heating is performed inductively.  
   
   
       10 . Method of claims  1 , characterized in that the equalization of the heating temperature of the rod takes place for at least 10 seconds.  
   
   
       11 . Method of claims  1 , characterized in that the temperature difference over the length of the rod does not exceed 5° K.  
   
   
       12 . Method of claims  1 , characterized in that the heating temperature of the rod is kept constant virtually up to its entry between the rolls.  
   
   
       13 . Method of claims  1 , characterized in that, during the skew rolling, a maximum local temperature increase of 50° K is not exceeded.  
   
   
       14 . Method of claims  1 , characterized in that the skew rolling is performed in a temperature range of 700°-1000° C.  
   
   
       15 . Method of claims  1 , characterized in that the rolls of the skew rolling stand are adjusted in the axial and/or radial direction during the transformation operation and the round rods are produced with a diameter, which varies over their length.  
   
   
       16 . Method of clams  1 , characterizd in that, during a reheating above Ac3 following the skew rolling, the temperature difference over the rod length is limited to a maximum of 5° K.  
   
   
       17 . Method of claims  1 , characterized in that it starts out from spring steel.  
   
   
       18 . Method of claims  1 , characterized in that it starts out from a silicon-chromium steel.  
   
   
       19 . Method of claims  1 , characterized in that it starts out from a microalloyed steel.  
   
   
       20 . Coil spring, produced by a method of claims  1 , characterized in that, under load, it has almost the same stress distribution over the cross-section.  
   
   
       21 . Stabilizer, produced by a method claims  1 , characterized in that, under load, the part, stressed in torsion, it has almost the same stress distribution over the cross-section.