Process of using a chromium steel as raw material for corrosion-resistant spring elements

Abstract

A ferritic chromium steel comprising, by weight-%, 0.03 to 0.1% of carbon, 0.2 to 0.9% of silicon, 0.3 to 1% of manganese, 13 to 20% of chromium, up to 0.5% of nickel, 0.1 to 1.5% of molybdenum, 0.1 to 0.5% of copper, 0.03 to 0.05% of nitrogen, less than 10 ppm of boron, up to 0.01% of titanium, 0.01 to 0.10% of niobium, 0.02 to 0.25% of vanadium and up to 0.002% of aluminum, remainder iron, is distinguished by a high corrosion resistance and is suitable as a material for cold-formed spring elements with improved spring properties and a high dimensional accuracy, in particular for leaf springs, spring rails for windscreen wipers and reed lamellae for textile machines, oil stripper rings for internal combustion engines and sealing lamellae for hydraulic installations.

1 . A process of using a ferritic chromium steel for fabricating an object and imparting spring properties to the object, said process comprising the steps of: 
 cold-working a ferritic chromium steel of a composition comprising, by weight-%, 0.03 to 0.1% of carbon, 0.2 to 0.9% of silicon, 0.3 to 1% of manganese, 13 to 20% of chromium, less than 0.5% of nickel, 0.1 to 1.5% of molybdenum, 0.1 to 0.5% of copper, 0.03 to 0.05% of nitrogen, less than 10 ppm of boron, less than 0.01% of titanium, 0.01 to 0.10% of niobium, 0.02 to 0.25% of vanadium, less than 0.002% of aluminum, remainder iron, to a degree of deformation of up to 65%;    solution-annealing the steel;    quenching the steel; and    stamping or cutting the steel to produce a dimensionally stable, low-distortion object.    
     
     
         2 . The process of  claim 1 , wherein the steel contains less than 10 ppm of boron.  
     
     
         3 . The process of  claim 1 , wherein the carbon and nitrogen contents satisfy the condition  
         (% C)/(% N)=0.8 to 2.0.  
     
     
         4 . The process of  claim 1 , wherein the niobium, vanadium and titanium contents satisfy the condition  
         [(% Nb)+(% V)]/10(% Ti)=5 to 17.  
     
     
         5 . The process of  claim 1 , wherein the steel is metastable when solution-annealed, and further comprising the steps of cold-working the object and tempering the object at low temperatures.  
     
     
         6 . The process of  claim 1 , wherein the object is a member selected from the group consisting of leaf spring, spring rail for windscreen wipers, piston ring for internal combustion engines, sealing lamellae for hydraulic installations, reed lamellae, and object which comes into contact with human skin.  
     
     
         7 . The process of  claim 1 , wherein the step of solution annealing is executed at a temperature of 1000° C. to 1200° C.  
     
     
         8 . The process of  claim 1 , further comprising the step of cold-working the annealed steel with a degree of deformation of up to 40% following the quenching step.  
     
     
         9 . The process of  claim 8 , wherein the annealed steel is cold-worked to a degree of deformation of up to 30%.  
     
     
         10 . The process of  claim 1 , further comprising the step of age-hardening the cold-worked object at a temperature from 100° C. to 400° C.  
     
     
         11 . The process of  claim 1 , further comprising the step of age-hardening the cold-worked object at a temperature of 300° C. for 10 to 15 min.  
     
     
         12 . The process of  claim 1 , further comprising the step of cold-working the object with a degree of deformation of up to 12% to provide a mean grain size of less than 15 μm.  
     
     
         13 . The process of  claim 1 , further comprising the step of final annealing the object under stress.  
     
     
         14 . The process of  claim 13 , further comprising the step of subjecting the object to a tensile stress from 20 to 100 N/m m 2 .  
     
     
         15 . The process of  claim 1 , wherein the steel contains less than 0.002% of aluminum.  
     
     
         16 . The process of  claim 1 , wherein the steel has a grain size of less than 20 μm.  
     
     
         17 . The process of  claim 1 , wherein the steel has a composition, by weight-%, of 0.03 to 0.08% of carbon, 0.2 to 0.9% of silicon, 0.4 to 0.8% of manganese, 15 to 18% of chromium, less than 0.2% of nickel, in each case 0.1 to 0.5% of molybdenum and copper, 0.03 to 0.05% of nitrogen, less than 8 ppm of boron, less than 0.005% of titanium, 0.01 to 0.05% of niobium and 0.05 to 0.20% of vanadium, remainder iron.