Bainitic steel for moulds

Abstract

1—“BAINITIC STEEL FOR MOULDS”, with a composition of alloy elements that consist, in mass percentage, of Carbon between 0.05 and 1.0; Manganese between 0.5 and 3.0; Phosphorous, Boron, Titanium and Vanadium given by the ratio NU=[Ti+P+10B+(V−0.10)], being the values of NU between 0.02 and 0.30, with titanium always above 0.005, boron always below 0.010 and Vanadium may be partially or totally replaced with Niobium, in the proportion of two parts in mass of niobium for one part of Vanadium; Nickel, Molybdenum and Chromium given by the ratio G=[0.13Ni+0.60Mo+0.26Cr], with values of G above 0.10 and below 1.0; Sulphur up to 0.10; Silicon between 0.05 and 3.0; Nitrogen below 0.10; Calcium with contents up to 0.02; Aluminum below 0.5, Cobalt lower than 2.0, the remaining being substantially Iron and impurities that cannot be avoided in the elaboration process; for its production the final hardness may be obtained by calm air cooling, directly after hot conformation or by previous heating in furnace, even in blocks with section up to 1000 mm; the values of hardness, in Vickers scale, are defined by the equation: HV=(450±140) % C+(210±45), for values between 280 and 450 HV (30 to 45 HRC); for applications of high toughness, the steel of present invention may also be produced with quick cooling, from temperatures above 900° C., in water or oil mediums.

1 . Bainitic steel for moulds comprising a chemical composition of elements including, in mass percentage, Carbon between 0.05 and 1.0; Silicon up to 1.0, Manganese between 0.5 and 5.0; Phosphorous, Boron, Titanium and Vanadium given by the ratio NU=[Ti+P+10B+(V−0.10)], being the values of NU between 0.02 and 0.30, with titanium always above 0.005, boron always below 0.010 and Vanadium may be partially or totally replaced with Niobium, in the proportion of two parts in mass of niobium for one part of Vanadium; Nickel, Molybdenum and Chromium given by ratio G=[0.13Ni+0.60Mo+0.26Cr], with values of G above 0.10 and below 1.0; Sulphur up to 0.20; Silicon between 0.05 and 3.0; Nitrogen below 0.10; Calcium with contents up to 0.010; Aluminum below 0.5, Cobalt lower than 2.0, the remaining being substantially Iron and impurities that cannot be avoided in the elaboration process. 
     
     
         2 . Bainitic steel for moulds, according to  claim 1 , comprising a chemical composition of elements including, in mass percentage, Carbon between 0.10 and 0.6; Silicon up to 1.0, Manganese between 0.8 and 3.0; Phosphorous, Boron, Titanium and Vanadium given by the ratio NU=[Ti+P+10B+(V−0.10)], being the values of NU between 0.08 and 0.30, with titanium always above 0.005, boron always below 0.010, titanium between 0.005 and 0.10, and Vanadium may be partially or totally replaced with Niobium, in the proportion of two parts in mass of niobium for one part of Vanadium; Nickel, Molybdenum and Chromium given by ratio G=[0.13Ni+0.60Mo+0.26Cr], with values of G above 0.20 and below 0.50; besides this ratio, Chromium contents must be between 0.1 and 1.5, and Nickel contents above 0.3; Sulphur up to 0.05; Silicon between 0.05 and 3.0; Nitrogen below 0.05; Calcium contents up to 0.005; Aluminum below 0.1, Cobalt lower than 1.0, the remaining being substantially Iron and impurities that cannot be avoided in the elaboration process; the material may be produced in blocks of up to 850 mm of thickness, being obtained the hardness between 250 and 450 HV through air cooling from a temperature above 700° C., and the value of this hardness is given by the equation HV=(450±140) % C+(210±45). 
     
     
         3 . Bainitic steel for moulds, according to  claim 1 , comprising a chemical composition of elements including, in mass percentage, Carbon between 0.10 and 0.6; Silicon between 0.05 and 0.6; Manganese between 1.3 and 3.0; Phosphorous, Boron, Titanium and Vanadium given by the ratio NU=[Ti+P+10B+(V−0.10)], being the values of NU between 0.10 and 0.20, with titanium always above 0.010, boron always below 0.0050, and Vanadium may be partially or totally replaced with Niobium, in the proportion of two parts in mass of niobium for one part of Vanadium; Nickel, Molybdenum and Chromium given by ratio G=[0.13Ni+0.60Mo+0.26Cr], with values of G above 0.25 and below 0.40; besides this ratio, Chromium contents must be between 0.1 and 1.0, and Nickel contents between 0.2 and 1.0; Sulphur between 0.001 and 0.010; Silicon between 0.20 and 1.5; Nitrogen between 0.0040 and 0.0150; Calcium with contents between 0.0005 and 0.0030; Aluminum below 0.05, Cobalt lower than 1.0, the remaining being substantially Iron and impurities that cannot be avoided in the elaboration process; the material may be produced in blocks of up to 850 mm of thickness, being obtained the hardness between 280 and 450 HV through air cooling, directly after hot conformation, with the value of this hardness given by the equation HV=(450±140) % C+(210±45). 
     
     
         4 . Bainitic steel for moulds, according to  claim 1 , comprising a chemical composition of elements including, in mass percentage, Carbon between 0.18 and 0.52, Chromium between 0.30 and 0.60. Molybdenum between 0.10 and 0.50, Nickel between 0.30 and 0.50, Vanadium between 0.04 and 0.10; Boron between 0.0010 and 0.0030; Sulphur between 0.0010 and 0.0100; Calcium between 0.005 and 0.030; Nitrogen between 0.0030 and 0.0100; where final use hardness is obtained directly after forging or lamination, with relatively high gauges, thicknesses between 100 and 1000 mm, without the need to use oil or water hardening processes; thermal treatment must be calm air cooling with forced convection, being the Vickers hardness value determined by alloy carbon contents, according to following ratio: HV=(450±140) % C+(210±45), for hardness values between 280 and 420 HV, equivalent to 29 and 42 HRC. 
     
     
         5 . Bainitic steel for moulds, according to  claim 1 , comprising a G ratio lower than 0.10, for applications in gauges lower than 400 mm of thickness, being G calculated by following ratio: G=[0.13Ni+0.60Mo+0.26Cr], where symbols represent contents in mass percentage of relevant elements. 
     
     
         6 . Bainitic Steel for Moulds Comprising, according to  claim 1 , comprising manganese contents, partially or totally replaced with Nickel or Copper, in equal quantities, in mass percentage. 
     
     
         7 . Bainitic steel for moulds, according to  claim 1 , comprising, in mass percentage, the elements Niobium, Zirconium or Tantalum replacing, partially or totally the elements Titanium or Vanadium, in a relation of 2 parts of Niobium corresponding to 1 part of Vanadium or Titanium, and 1 part of Tantalum or Zirconium corresponding to 2 parts of Vanadium or Titanium. 
     
     
         8 . Bainitic steel for moulds, according to  claim 1 , comprising, in mass percentage, Boron between 0.0015 and 0.0030; Silicon between 0.40 and 1.2. 
     
     
         9 . Bainitic steel for moulds, according to  claim 1 , comprising, in mass percentage, Sulphur between 0.002 and 0.090 and Calcium between 0.0005 and 0.0030. 
     
     
         10 . Bainitic steel for moulds, according to  claim 1 , wherein a final hardness obtained by air cooling, directly after hot conformation or through previous heating in furnace, being the final hardness obtained (in the Vickers scale) given by the equation: HV=(450±70) % C+(210±22), or even an equation equivalent via a hardness conversion by the measures of other scales. 
     
     
         11 . Bainitic steel for moulds, according to  claim 1 , comprising, in parts per million in mass, sulphur between 0.002 and 0.30, and calcium between 0.0005 and 0.010, and by having in its microstructure a volumetric fraction of carbonitrides lower than 0.25%, applied to situations where high machining capacity is needed. 
     
     
         12 . Bainitic steel for moulds, according to  claim 1 , comprising an increase in toughness via quick cooling, after hot conformation or heating at temperatures above 900° C. 
     
     
         13 . Bainitic steel for moulds, according to  claim 1 , comprising an increase in toughness via quick cooling, after hot conformation or heating at temperatures above 900° C., being this cooling process given by following thermal treatment: air cooling up to the temperature of 700° C., then going to a water tank for 30 minutes (maintaining the temperature of water below 80° C.), followed by air cooling up to the ambient air temperature; in case of parts susceptible to cracks, the time of water cooling may be replaced with 60 minutes in oil cooling, maintaining constant all other conditions of thermal treatment.