Safety Armor for Protection Against Gunfire and Process for Producing it

Abstract

A safety armor for protection against gunfire, comprising a shield composed of an alloy steel which has a base carbon content of less than 0.3% by mass of carbon and has been enriched in strength-increasing elements including at least one of carbon and nitrogen by means of a thermochemical treatment in a surface zone extending from at least one outer surface of the shield, with the steel of the surface zone having an increased surface hardness as a result of a thermal treatment including at least one of hardening and tempering carried out after the thermochemical treatment, the steel is enriched to at least 0.5% by mass of carbon in the surface zone and has a minimum hardness of 55 HRC on the outer surface with the presence of carbides in the surface zone, with the shield having a silicon content of not more than 0.4% by mass both in the surface zone and in a lower hardness region adjoining the surface zone which has a carbon content and hardness less than the surface zone.

1 . A safety armor for protection against gunfire, comprising a shield a composed of an alloy steel which has a base carbon content of less than 0.3% by mass of carbon and has been enriched in strength-increasing elements including at least one of carbon and nitrogen by means of a thermochemical treatment in a surface zone extending from at least one outer surface of the shield, with the steel of the surface zone having an increased surface hardness as a result of a thermal treatment including at least one of hardening and tempering carried out after the thermochemical treatment, the steel following the thermochemical and thermal treatment is enriched to at least 0.5% by mass of carbon in the surface zone and has a minimum hardness of 55 HRC on the outer surface with the presence of carbides in the surface zone, with the shield having a silicon content of not more than 0.4% by mass both in the surface zone and in a lower hardness region adjoining the surface zone which has a carbon content and hardness less than the surface zone. 
   
   
       2 . The safety armor as claimed in  claim 1 , characterized in that the shield has two surface zones which extend from a first and a second of the outer surfaces and have a comparatively high hardness and have identical or different carbon contents and identical or different hardnesses and which, as the carbon content decreases, blend into the lower hardness region between the surface zones. 
   
   
       3 . The safety armor as claimed in  claim 1  wherein the chemical treatment of the shield is a carburization, in particular, in the surface zone(s) to enrich the surface zone in carbon. 
   
   
       4 . The safety armor as claimed in  claim 1  wherein the thermochemical treatment of shield is is carbonitrization in the surface zone to enrich the surface zone in carbon. 
   
   
       5 . The safety armor as claimed in  claim 1  wherein the alloy steel is a low- or high-alloy steel containing chromium, together with at least one of manganese and molybdenum. 
   
   
       6 . The safety armor as claimed in  claim 1  wherein the alloy steel is a low-alloy, predominantly manganese-containing steel. 
   
   
       7 . The safety armor as claimed in  claim 1  wherein the manganese content of the alloy steel is greater than about 0.8% by mass, but less than about 2.5% by mass. 
   
   
       8 . The safety armor as claimed in any of  claim 1  wherein the chromium content of the alloy steel is not greater than about 1.6% by mass. 
   
   
       9 . The safety armor as claimed in  claim 1  wherein the alloy steel has the following values of the chemical melt analysis: C—0.17 to 0.20% by mass, Si—0.20 to 0.30% by mass, Mn—1.15 to 1.30% by mass, P— not more than 0.030% by mass, S— not more than 0.030% by mass, Al—0.020 to 0.050% by mass, Cu— not more than 0.25% by mass, Ni— not more than 0.25% by mass, Cr—1.15 to 1.30% by mass, Ti—0.02 to 0.05% by mass; B—0.0015 to 0.004% by mass. 
   
   
       10 . The safety armor as claimed in  claim 1  wherein the alloy steel is a high-alloy, in particular nickel-containing steel X 19 NiCrMo 4. 
   
   
       11 . The safety armor as claimed in  claim 1  wherein the alloy steel is enriched with carbon to at least 0.8% by mass, in the surface zone. 
   
   
       12 . The safety armor as claimed in  claim 1  wherein the alloy steel has a hardness of more than 60 HRC in the surface zones. 
   
   
       13 . The safety armor as claimed in  claim 1  wherein after the thermal treatment and thermochemical treatment, the surface zone is at least about 50% of the thickness of the shield. 
   
   
       14 . The safety armor as claimed in  claim 1  wherein after the thermal treatment and thermochemical treatment, the surface zone is at least about ⅔ of the thickness of the shield. 
   
   
       15 . The safety armor as claimed in  claim 1  wherein the surface zone following the thermochemical and thermal treatment comprises a matrix with a microstructure which contains martensite and at least one of a small proportion of residual austenite and intermediate microstructures including bainite. 
   
   
       16 . The safety armor as claimed in  claim 1  wherein the surface zone following the thermal and thermochemical treatments comprise(s) carbides, including one or more of secondary iron carbides and mixed carbides of chromium and mixed carbides of molybdenum, and nitrides. 
   
   
       17 . The safety armor as claimed in  claim 1  wherein the shield is configured in the form of a plate having at least two, of the outer surfaces which are generally parallel which have larger dimensions than edge faces formed by the plate. 
   
   
       18 . The safety armor as claimed in  claim 1  wherein the shield has a minimum thickness of about 3.0 mm. 
   
   
       19 . The safety armor as claimed in  claim 1  wherein the shield has a maximum thickness in the range from about 10.0 mm to 25.0 mm. 
   
   
       20 . The safety armor as claimed in  claim 1  wherein the shield has been only partly thermochemically treated in the region of one or more of the surface zones. 
   
   
       21 . The safety armor as claimed in  claim 1  wherein the shield is joined to a substrate which has one or more characteristics including high strength, impact toughness, tear resistance, chemical resistance, flame resistance and self-extinguishing. 
   
   
       22 . A process for producing safety armor for protection against gunfire, in which a shield composed of an alloy steel which has a base carbon content of less than 0.3% by mass of carbon comprising the steps of enriching the shield in strength-increasing elements including one or more of carbon and nitrogen by means of a thermochemical treatment in a surface zone extending from at least one outer surface of the shield and a subsequent thermal treatment including one or more of hardening and tempering, the alloy steel having a silicon content of not more than 0.4% by mass is enriched to at least 0.5% by mass of carbon in the surface zone by means of the thermochemical treatment and in that a minimum hardness of 55 HRC is set on the outer surface by means of the thermal treatment. 
   
   
       23 . The process as claimed in  claim 22  wherein the thermochemical treatment is carried out as a carburization at a temperature in the range from 900° C. to 1040° C. for a treatment time in the range from 30 to 720 minutes, a gaseous medium. 
   
   
       24 . The process as claimed in  claim 22  wherein the thermochemical treatment is carried out as a carbonitridation. 
   
   
       25 . The process as claimed in  claim 22  wherein the shield is enriched with carbon in a pair of the surface zones extending from two of the outer surfaces of the shield with the surface zones having a relatively high hardness being configured with identical or different carbon contents and identical or different hardnesses and blending, as the carbon content decreases, into a lower hardness region, between the surface zones, of comparatively low hardness which is enriched at most only slightly with carbon. 
   
   
       26 . The process as claimed in  claim 22  wherein the alloy steel is enriched with carbon to at least 0.8% by mass by the thermochemical treatment in the surface zones. 
   
   
       27 . The process as claimed in  claim 22  wherein following thermal treatment the surface zone comprises austenite formation, and is carried out a temperature in the range from 800° C. to 880° C., with subsequent quenching. 
   
   
       28 . The process as claimed in  claim 27  wherein the quenching is carried out in a chill roll unit with forcing of the shape of the shield by applying pressure. 
   
   
       29 . The process as claimed in  claim 27  wherein austenite formation and subsequent quenching is carried out as double hardening, with the austenite formation temperature being matched to the lower hardness region of the steel in a first hardening step and the austenite formation temperature is matched to the surface zone of the steel in a second hardening step. 
   
   
       30 . The process as claimed in  claim 27  wherein a hardness of from about 60 to 67 HRC is set on the one or more outer surface(s) of the shield by means of the austenite formation and the subsequent quenching. 
   
   
       31 . The process as claimed in  claim 22  wherein the subsequent thermal treatment comprises tempering, in particular for a tempering time in the range up to 3 hours at a temperature in the range up to 300° C. 
   
   
       32 . The process as claimed in  claim 22  wherein a hardness of from about 35 to 47 HRC is set in the lower hardness region of the shield. 
   
   
       33 . A process for protecting against gunfire comprising the steps of providing an alloy steel which has a base carbon content of less than 0.3% by mass of carbon enriching the steel in strength-increasing elements of one or more of carbon and nitrogen by means of a thermochemical treatment in a surface zone, the steel having a lower hardness zone blending into the surface zone. 
   
   
       34 . The process as claimed in  claim 33  wherein the carbon content set in the surface zone is at least 0.5% by mass of carbon following the enriching stem. 
   
   
       35 . The process as claimed in  claim 33  wherein the carbon content set in the surface zone has a hypereutectoidic concentration, in particular a concentration of from 1.1% by mass to 3.5% by mass following the enrichment step. 
   
   
       36 . The process as claimed in  claim 33  wherein the alloy steel provided is a low or high-alloy steel containing chromium, together with one or more of manganese and molybdenum. 
   
   
       37 . The process as claimed in any  claim 33  wherein the steel is a low-alloy, predominantly manganese-containing steel such as 16 MnCr 5, 16 MnCr 5 BP, 16 MnCrS 5, 20 MnCr 5, 21 MnCr 5 or 20 MnCrS 5. 
   
   
       38 . The process as claimed in  claim 33  wherein the manganese content of the steel provided is greater than about 0.8% by mass but less than about 2.5% by mass. 
   
   
       39 . The process as claimed in  claim 33  wherein the chromium content of the steel provided is not greater than about 1.6% by mass. 
   
   
       40 . The process as claimed in  claim 33  wherein the steel has the following values of the chemical melt analysis: C—0.17 to 0.20% by mass, Si—0.20 to 0.30% by mass, Mn—1.15 to 1.30% by mass, P— not more than 0.030% by mass, S— not more than 0.030% by mass, Al—0.020 to 0.050% by mass, Cu— not more than 0.25% by mass, Ni— not more than 0.25% by mass, Cr—1.15 to 1.30% by mass, Ti—0.02 to 0.05% by mass, B—0.0015 to 0.004% by mass. 
   
   
       41 . The process as claimed in  claim 33  wherein the steel provided is a high-alloy, nickel-containing steel.