US2012174749A1PendingUtilityA1

Armour steel

38
Assignee: STUMPF WALDO EDMUNDPriority: Sep 25, 2007Filed: Sep 25, 2007Published: Jul 12, 2012
Est. expirySep 25, 2027(~1.2 yrs left)· nominal 20-yr term from priority
Inventors:Waldo Edmund StumpfMaweja Kasonde
C22C 38/44C21D 6/002C22C 38/48F41H 5/045C22C 38/42C22C 38/46C21D 9/42C21D 2211/008C22C 38/04C22C 38/50C22C 38/02
38
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Claims

Abstract

A low-carbon martensitic armour steel comprises at least Fe, C, Si and Ni and has a ratio of yield strength to ultimate tensile strength of less than 0.7. The steel includes retained austenite at a volume fraction of at least 1%. The low-carbon martensitic armour steel can be prepared by subjecting a steel which comprises at least Fe, C, Si and Ni and which has a martensite start temperature of less than 210° C. to an austenisation heat treatment step at a temperature of at least 800° C., quenching the steel, and subjecting the steel to a tempering step at a temperature of less than 300° C.

Claims

exact text as granted — not AI-modified
1 . A low-carbon martensitic armour steel comprising at least Fe, C, Si and Ni which has a ratio of yield strength to ultimate tensile strength of less than 0.7 and which includes retained austenite at a volume fraction of at least 1%. 
     
     
         2 . The armour steel as claimed in  claim 1 , which has a ratio of yield strength to ultimate tensile strength of less than or equal to 0.65. 
     
     
         3 . The armour steel as claimed in  claim 2 , which has a ratio of yield strength to ultimate tensile strength of less than or equal to 0.6. 
     
     
         4 . The armour steel as claimed in  claim 1 , which comprises 0.37-0.43 weight % C, 0.4-1.2 weight % Si, and 1.8-4.0 weight % Ni, with the balance being mostly Fe. 
     
     
         5 . The armour steel as claimed in  claim 1 , which comprises also Mn, Cr and Mo. 
     
     
         6 . The armour steel as claimed in  claim 5 , which comprises 0.5-2.0 weight % Mn, 0.8-1.5 weight % Cr, and 0.5-0.6 weight % Mo. 
     
     
         7 . The armour steel as claimed in  claim 1 , which has a martensite start temperature of less than 210° C. 
     
     
         8 . The armour steel as claimed in  claim 7 , which has a plate thickness of from 4.5 mm to 8 mm. 
     
     
         9 . The armour steel as claimed in  claim 8 , which has a plate thickness of from 4.5 mm to 6 mm. 
     
     
         10 . The armour steel as claimed in  claim 1 , which has a volume fraction of retained austenite of less than 7%. 
     
     
         11 . The armour steel as claimed in  claim 1 , which has a micro-structure in which the martensite is predominantly present as twinned plate martensite and not lath martensite. 
     
     
         12 . The armour steel as claimed in  claim 11 , in which the twinned plate martensite is combined with retained austenite in the same micro-structure. 
     
     
         13 . The armour steel as claimed in  claim 1 , in which any cementite is predominantly present as dispersed particles and not as coarse strings. 
     
     
         14 . The armour steel as claimed in  claim 1 , which is in the form of a plate with a thickness δmm, and which has a Ballistic Parameter BP of at least 0.01 where BP=volume fraction of retained austenite/exp(δ). 
     
     
         15 . A method of preparing a low-carbon martensitic armour steel, the method including
 subjecting a steel which comprises at least Fe, C, Si and Ni and which has a martensite start temperature of less than 210° C. to an austenisation heat treatment step at a temperature of at least 800° C.;   quenching the steel; and   subjecting the steel to a tempering step at a temperature of less than 300° C.   
     
     
         16 . The method as claimed in  claim 15 , in which the austenisation heat treatment step is at a temperature of between 870° C. and 950° C. 
     
     
         17 . The method as claimed in  claim 15 , in which the steel is subjected to the austenisation heat treatment step for a period of between 20 minutes and 60 minutes. 
     
     
         18 . The method as claimed in  claim 15 , in which the tempering step is at a temperature of between 150° C. and 250° C. 
     
     
         19 . The method as claimed in  claim 15 , in which the steel is subjected to the tempering step for a period of between 20 minutes and 60 minutes. 
     
     
         20 . The method as claimed in  claim 15 , in which the steel is in the form of a plate with a thickness of from 4.5 mm to 8 mm. 
     
     
         21 . The method as claimed in  claim 15 , in which the steel comprises 0.37-0.43 weight % C, 0.4-1.2 weight % Si, and 1.8-4.0 weight % Ni, the balance being mostly Fe. 
     
     
         22 . The method as claimed in  claim 15 , in which the steel comprises also Mn, Cr and Mo. 
     
     
         23 . The method as claimed in  claim 22 , in which the steel comprises 0.5-2.0 weight % Mn, 0.8-1.5 weight % Cr, and 0.5-0.6 weight % Mo. 
     
     
         24 . A low-carbon martensitic armour steel produced by the method as claimed in  claim 1 .

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