| 摘要 |
Provided are an abrasion resistant steel plate or steel sheet having excellent low-temperature toughness and excellent cracking resistance in a portion which has been heated to a temperature range in which low-temperature temper embrittlement occurs and a method for manufacturing the steel plate. The steel plate has a chemical composition containing, by mass%, C: 0.100% or more and less than 0.175%, Si: 0.05% or more and 1.00% or less, Mn: 0.50% or more and 1.90% or less, P: less than 0.006%, S: 0.005% or less, Al: 0.005% or more and 0.100% or less, Cr: 0.10% or more and 1.00% or less, Nb: 0.005% or more and 0.024% or less, Ti: 0.005% or more and 0.050% or less, B: 0.0003% or more and 0.0030% or less, N: 0.0010% or more and 0.0080% or less, in which specific relational expressions 1 and 2 are satisfied, and, as needed, at least one of Mo, V, Cu, Ni, Ca, Mg, and REM, and a microstructure at positions located at 1/4 of the thickness and at 3/4 of the thickness including a martensite single phase microstructure having an average prior austenaite grain diameter of 20 µm or more and 60 µm or less or a mixed microstructure of martensite and bainite having a proportion of martensite-austenite constituent of less than 5% in terms of area ratio with respect to the whole microstructure. Steel having the chemical composition described above is subjected to direct-quenching following hot rolling. |
