Spring Wire, Tension Clamp Formed Therefrom and Method for Manufacturing Such a Spring Wire

Abstract

A spring wire which can be cold formed well at diameters of at least 9 mm, but has improved mechanical properties. The spring wire is manufactured from a steel including, in % by weight, C: 0.35-0.42%, Si: 1.5-1.8%, Mn: 0.5-0.8%, Cr: 0.05-0.25%, Nb: 0.020-0.10%, V: 0.020-0.10%, N: 0.0040-0.0120%, Al: ≤0.03% and as the remainder iron and unavoidable impurities, wherein the total content of impurities is limited to at most 0.2% and the impurities include up to 0.025% P and up to 0.025% S. The spring wire is in particular suitable for the manufacture of a tension clamp with optimized usage properties. Also, a method which enables the practice-oriented production of the spring wire.

1 . A spring wire manufactured from a steel comprising, in % by weight:
 C: 0.35-0.42%,   Si: 1.5-1.8%,   Mn: 0.5-0.8%,   Cr: 0.05-0.25%,   Nb: 0.020-0.10%,   V: 0.020-0.10%,   N: 0.0040-0.0120%,   Al: ≤0.03%,   and a remainder of iron and unavoidable impurities, wherein a total content of impurities is limited to at most 0.2% and the impurities include up to 0.025% P and 0.025% S.   
     
     
         2 . The spring wire according to  claim 1 , wherein the C content is at most 0.40% by weight. 
     
     
         3 . The spring wire according to  claim 1 , wherein the Cr content is at least 0.1% by weight. 
     
     
         4 . The spring wire according to  claim 2 , wherein the Cr content is at least 0.18% by weight. 
     
     
         5 . The spring wire according to  claim 1 , wherein the Mn content is at least  0 . 6  % by weight. 
     
     
         6 . The spring wire according to  claim 5 , wherein the Mn content is at least 0.7% by weight. 
     
     
         7 . The spring wire according to  claim 1 , wherein the Nb content is at least 0.030% by weight. 
     
     
         8 . The spring wire according to  claim 1 , wherein the Nb content is at most 0.070% by weight. 
     
     
         9 . The spring wire according to  claim 1 , wherein the V content is at most 0.060% by weight. 
     
     
         10 . The spring wire according to  claim 1 , wherein the N content is at least  0 . 0060 % by weight. 
     
     
         11 . The spring wire according to  claim 1 , wherein the spring wire has a reduction of area at fracture Z of at least 55% determined in a tensile test according to DIN EN ISO 6892-1. 
     
     
         12 . The spring wire according to  claim 1 , wherein a granularity of a microstructure of the spring wire determined according to ASTM E112 is at least ASTM 10. 
     
     
         13 . A tension clamp for holding down a rail for rail vehicles in a rail fastening point manufactured from a spring wire provided according to  claim 1 . 
     
     
         14 . A method for manufacturing a spring wire according to  claim 11 , comprising the following work steps:
 a) melting a steel comprising (in % by weight), C: 0.35-0.42%, Si: 1.5-1.8%, Mn: 0.50-0.80%, Cr: 0.05-0.25%, Nb: 0.020-0.10%, V: 0.020-0.10%, N: 0.0040-0.0120%, Al: ≤0.03% and a remainder of iron and unavoidable impurities, wherein a total content of impurities is limited to at most 0.2% and the impurities include up to 0.025% P and up to 0.025% S;   b) casting the steel into a primary product;   c) hot rolling the primary product into a hot-rolled spring wire with an end diameter of 9-15 mm, wherein the hot rolling is carried out in at least two partial steps, wherein the spring wire is finished hot-rolled thermomechanically in the last partial step of the hot rolling at a temperature which is below the recrystallisation stop temperature of the steel of the spring wire and above the Ar3 temperature of the steel of the spring wire;   d) cooling the thermomechanically finished hot-rolled spring wire at a cooling rate of 1-5° C./s to a winding temperature of 550-65° C.;   e) placing or winding the spring wire cooled to the winding temperature into a coil; and   f) cooling the spring wire in the coil to room temperature.   
     
     
         15 . The method according to  claim 14 , wherein the partial steps of the hot rolling (work step c)) are completed in a continuous process.