Iron-based alloy composition, parts produced from this composition and production method

Abstract

An iron-based alloy composition includes 0.28-0.34% C, max 0.25% Si, max 0.8% Mn, 0.85-0.95% Cr, 1.10-1.50% Ni, 0.41-0.50% Mo, 0.001-0.007% B, 0.002-0.03% Nb, and balanced amount of Fe and inevitable impurities. Moreover, parts with a hardness of at least 480 HB, a tensile strength of at least 1700 MPa, a total elongation of at least 7% and an impact strength of at least 16 J are obtained by the iron-based alloy composition and a production method of the parts.

What is claimed is: 
     
         1 . An iron-based alloy composition developed for producing a hot formed armor steel, comprising 0.28-0.34% carbon, max 0.25% silicon, max 0.8% manganese, 0.85-0.95% chromium, 1.10-1.50% nickel, 0.41-0.50% molybdenum, 0.001-0.007% boron, 0.002-0.03% niobium by weight and a balanced amount of iron and inevitable impurities. 
     
     
         2 . The iron-based alloy composition according to  claim 1 , comprising one or more elements selected from the group containing trace amounts of phosphorus, sulfur, copper, aluminum, tungsten, cobalt, titanium, oxygen, hydrogen, and nitrogen. 
     
     
         3 . A hot formed armor steel, comprising 0.28-0.34% carbon, max 0.25% silicon, max 0.8% manganese, 0.85-0.95% chromium, 1.10-1.50% nickel, 0.41-0.50% molybdenum, 0.001-0.007% boron, 0.002-0.03% niobium by weight and a balanced amount of iron and inevitable impurities in a composition of the hot formed steel. 
     
     
         4 . The hot formed armor steel according to  claim 3 , comprising one or more elements selected from the group containing trace amounts of phosphorus, sulfur, copper, aluminum, tungsten, cobalt, titanium, oxygen, hydrogen, and nitrogen. 
     
     
         5 . The hot formed armor steel according to  claim 3 , wherein the hot formed armor steel has a hardness of at least 480 HB, a tensile strength of at least 1700 MPa, a total elongation of at least 7%, and/or an impact strength of at least 16 J. 
     
     
         6 . The hot formed armor steel according to  claim 3 , comprising at least 90% martensite in a microstructure of the hot formed armor steel. 
     
     
         7 . A hot formed armor steel production method, comprising the following steps:
 i. an ingot or slab casting of an alloy comprising 0.28-0.34% carbon, max 0.25% silicon, max 0.8% manganese, 0.85-0.95% chromium, 1.10-1.50% nickel, 0.41-0.50% molybdenum, 0.001-0.007% boron, 0.002-0.03% niobium by weight, and balanced amounts of iron and inevitable impurities to obtain an ingot or a slab,   ii. hot rolling the slab or the ingot into a plate,   iii. plate cooling and cutting,   iv. applying a primary heat treatment to cut the plate,   v. forming the plate by pressing in a cooled tool,   vi. applying a secondary heat treatment to formed steel parts.   
     
     
         8 . The hot formed armor steel production method according to  claim 7 , comprising one or more elements selected from the group containing trace amounts of phosphorus, sulfur, copper, aluminum, tungsten, cobalt, titanium, oxygen, hydrogen, and nitrogen in the step i. 
     
     
         9 . The hot formed armor steel production method according to  claim 7 , comprising heating the slab or the ingot to above 1050° C. for at least 4 hours. 
     
     
         10 . The hot formed armor steel production method according to  claim 7 , comprising cooling the plate down to 2° C./s or slower, a microstructure of ferrite+perlite, bainite, or a mixture of phases and obtaining a plate with a hardness scale below 300 HB, a heating process of the plate above 300° C. and transforming a microstructure of the plate into a tempered martensite, provided that the heating process is performed faster without cooling in the step iii. 
     
     
         11 . The hot formed armor steel production method according to  claim 7 , wherein the primary heat treatment for cutting the plate is performed by heating the plate to a temperature below 1000° C. and above AC3 for at least 10 minutes in the step iv. 
     
     
         12 . The hot formed armor steel production method according to  claim 7 , comprising forming the plate by cooling the plate to a temperature of 300° C. or less at a rate of over 4° C./s in the step v. 
     
     
         13 . The hot formed armor steel production method according to  claim 7 , comprising tempering of the formed steel parts in the step vi by applying the secondary heat treatment at a temperature of 250° C. or less, and obtaining at least 90% martensitic microstructure. 
     
     
         14 . The hot formed armor steel production method according to  claim 7 , comprising tempering of the formed steel parts at a temperature between 140° C.-200° C. by applying the secondary heat treatment for 2-8 hours and obtaining at least 90% martensitic microstructure in the step vi. 
     
     
         15 . The hot formed armor steel production method according to  claim 7 , wherein three-dimensional steel parts obtained after the step vi has a hardness of at least 480 HB, a tensile strength of at least 1700 MPa, a total elongation of at least 7%, and/or an impact strength of at least 16 J. 
     
     
         16 . The hot formed armor steel production method according to  claim 7 , comprising cleaning surfaces of the formed steel parts before or after the step vi.