High-Hardness Steel Product and Method of Manufacturing the Same

Abstract

Described is a hot-rolled steel strip product including a composition consisting of, in terms of weight percentages, 0.14% to 0.35% C, 0% to 0.5% Si, 0.05% to 0.40% Mn, 0.1% or less Al, 0.1% to 0.4% Cu, 0.2% to 0.9% Ni, 0.2% to 0.9% Cr, 0.2% or less Mo, 0.005% or less Nb, 0.035% or less Ti, 0.05% or less V, 0.0005% to 0.0050% B, 0.025% or less P, 0.008% or less S, 0.01% or less N, 0.01% or less Ca, and the remainder being Fe and inevitable impurities, wherein the steel product has a Brinell hardness in the range of 420 to 580 HBW.

1 . A hot-rolled steel strip product comprising a composition consisting of, in terms of weight percentages (wt. %):
 C 0.14-0.35,   Si 0-0.5,   Mn 0.05-0.40,   Al 0-0.1,   Cu 0.1-0.4,   Ni 0.2-0.9,   Cr 0.2-0.9,   Mo 0-0.2,   Nb 0-0.005   Ti 0-0.035   V 0-0.05   B 0.0005-0.0050,   P 0-0.025,   S 0-0.008,   N 0-0.01,   Ca 0-0.01,   
       remainder Fe and inevitable impurities, wherein the steel product has a Brinell hardness in the range of 420-580 HBW. 
     
     
         2 . The steel product according to  claim 1 , wherein the steel product has a Brinell hardness in the range of 450-550 HBW. 
     
     
         3 . The steel product according to  claim 1 , wherein the steel product has a Charpy-V impact toughness of at least 50 J/cm 2  at a temperature of −40° C. 
     
     
         4 . The steel product according to  claim 1 , wherein the steel product has a minimum bending radius of 3.2 t or less in a measurement direction longitudinal to the rolling direction; a minimum bending radius of 2.5 t or less in a measurement direction transversal to the rolling direction; and wherein t is the thickness of the steel strip product. 
     
     
         5 . The steel product according to  claim 1 , wherein the steel product has a microstructure consisting of, in terms of volume percentages (vol. %), martensite in an amount of at least 90 vol. %; and remainder being retained austenite, bainite, ferrite, pearlite and/or cementite. 
     
     
         6 . The steel product according to  claim 1 , wherein the steel product has a prior austenite grain size of 50 μm or less. 
     
     
         7 . The steel product according to  claim 1 , wherein the steel product has a prior austenite grain structure with an aspect ratio in the range of 1.5-7. 
     
     
         8 . The steel product according to  claim 1 , wherein the steel strip product has a thickness of 10 mm or less. 
     
     
         9 . A method for manufacturing the steel comprising the following steps of
 providing a steel slab consisting of the chemical composition according to  claim 1 ;   heating the steel slab to the austenitizing temperature of 1150-1300° C.;   hot-rolling to the desired thickness at a temperature in the range of Ar 3  to 1250° C., wherein the finish rolling temperature is in the range of 800° C. to 960° C.;   direct quenching the hot-rolled steel strip product to a cooling end and coiling temperature of 450° C. or less; and   optionally, temper annealing at a temperature in the range of 150° C.-250° C.