Steel plate and method of production of same

Abstract

A steel plate improved in formability and wear resistance, having a predetermined chemical composition, having a metal structure of the steel plate having a ratio of number of carbides at ferrite grain boundaries with respect to a number of carbides in ferrite grains of over 1 and having a ferrite grain size of 5 μm to 50 μm, and having a Vickers hardness of steel plate of 100 HV to 170 HV.

1 . A steel plate comprising, by mass %,
 C: 0.10 to 0.40%,   Si: 0.01 to 0.30%,   Mn: 1.00 to 2.00%,   P: 0.020% or less,   S: 0.010% or less,   Al: 0.001 to 0.10%,   N: 0.010% or less,   O: 0.020% or less,   Cr: 0.50% or less,   Mo: 0.10% or less,   Nb: 0.10% or less,   V: 0.10% or less,   Cu: 0.10% or less,   W: 0.10% or less,   Ta: 0.10% or less,   Ni: 0.10% or less,   Sn: 0.050% or less,   Sb: 0.050% or less,   As: 0.050% or less,   Mg: 0.050% or less,   Ca: 0.050% or less,   Y: 0.050% or less,   Zr: 0.050% or less,   La: 0.050% or less,   Ce: 0.050% or less and   a balance of Fe and unavoidable impurities,   herein a metal structure of the steel plate   has a ratio of a number of carbides at ferrite grain boundaries with respect to a number of carbides in ferrite grains of over 1,   has a ferrite grain size of 5μm to 50 μm, and   has an area ratio of pearlite of 6% or less; and   a Vickers hardness of the steel plate is 100 HV to 170 HV.   
     
     
         2 . The steel plate according to  claim 1  containing one or both of
 Ti: 0.10% or less and 
 B: 0.010% or less 
 instead of part of the Fe. 
 
     
     
         3 . A method of production of a steel plate, comprising
 hot rolling a steel slab of a chemical composition according to  claim 1  during which completing finish hot rolling at a 750° C. to 850° C. temperature region to obtain hot rolled steel plate,   coiling the hot rolled steel plate at 400° C. to 550° C.,   pickling the coiled up hot rolled steel plate,   holding the pickled hot rolled steel plate at a 650° C. to 720° C. temperature region for 3 hours to 60 hours as first stage annealing, then   holding the hot rolled steel plate at a 725° C. to 790° C. temperature region for 3 hours to 50 hours as second stage annealing, and   cooling the annealed hot rolled steel plate to 650° C. by a cooling rate of 1° C./hour to 30° C./hour.   
     
     
         4 . A method of production of a steel plate, comprising
 hot rolling a steel slab of a chemical composition according to  claim 2  during which completing finish hot rolling at a 750° C. to 850° C. temperature region to obtain hot rolled steel plate,   coiling the hot rolled steel plate at 400° C. to 550° C.,   pickling the coiled up hot rolled steel plate,   holding the pickled hot rolled steel plate at a 650° C. to 720° C. temperature region for 3 hours to 60 hours as first stage annealing, then   holding the hot rolled steel plate at a 725° C. to 790° C. temperature region for 3 hours to 50 hours as second stage annealing, and   cooling the annealed hot rolled steel plate to 650° C. by a cooling rate of 1° C./hour to 30° C./hour.