Abrasion resistant steel plate which exhibits excellent weld toughness and excellent delayed fracture resistance

Abstract

Provided is an abrasion-resistant steel plate or sheet which exhibits excellent weld toughness and excellent delayed fracture resistance and is thus suitable for construction machines, industrial machines, and so on. Specifically provided is a steel plate or sheet which contains, in mass %, 0.20 to 0.30% of C, 0.05 to 1.0% of Si, 0.40 to 1.2% of Mn, 0.010% or less of P, 0.005% or less of S, 0.40 to 1.5% of Cr, 0.005 to 0.025% of Nb, 0.005 to 0.03% of Ti, 0.1% or less of Al, 0.01% or less of N, and, as necessary, one or more of Mo, W, B, Cu, Ni, V, REM, Ca and Mg, and has a DI* of 45 to 180 while satisfying the relationship: C+Mn/4−Cr/3+10P≦0.47, and which has a microstructure that comprises martensite as the matrix phase. DI*=33.85×(0.1×C) 0.5 ×(0.7×Si+1)×(3.33×Mn+1)×(0.35×Cu+1)×(0.36×Ni+1)×(2.16×Cr+1)×(3×Mo+1)×(1.75×V+1)×(1.5×W+1)

1 . An abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance, and having a composition containing by mass % 0.20 to 0.30% C, 0.05 to 1.0% Si, 0.40 to 1.2% Mn, 0.010% or less P, 0.005% or less S, 0.40 to 1.5% Cr, 0.005 to 0.025% Nb, 0.005 to 0.03% Ti, 0.1% or less Al, 0.01% or less N, and Fe and unavoidable impurities as a balance, wherein hardenability index DI* expressed by a formula (1) is 45 or more, and a base phase of the microstructure is formed of martensite.
   DI*=33.85×(0.1×C) 0.5 ×(0.7×Si+1)×(3.33×Mn+1)×(0.35×Cu+1)×(0.36×Ni+1)×(2.16×Cr+1)×(3×Mo+1)×(1.75×V+1)×(1.5×W+1)  (1),
   
       wherein the respective element symbols are contents (mass %) of the elements. 
     
     
         2 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 1 , wherein the steel composition further contains by mass % one, two or more kinds of components selected from a group consisting of 0.05 to 1.0% Mo, 0.05 to 1.0% W, and 0.0003% to 0.0030% B. 
     
     
         3 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 1 , wherein the steel composition further contains by mass % one or two or more kinds of components selected from a group consisting of 1.5% or less Cu, 2.0% or less Ni, and 0.1% or less V. 
     
     
         4 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 1 , wherein the steel composition further contains by mass % one, two or more kinds of components selected from a group consisting of 0.008% or less REM, 0.005% or less Ca, and 0.005% or less Mg. 
     
     
         5 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 1 , wherein surface hardness of the steel plate is 400 HBW10/3000 or more in Brinell hardness. 
     
     
         6 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 1 , wherein hardenability index DI* is 180 or less. 
     
     
         7 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 1 , wherein the steel plate satisfies a following formula (2).
   C+Mn/4−Cr/3+10P≦0.47  (2),
   
       wherein the respective element symbols are contents (mass %) of the elements. 
     
     
         8 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 2 , wherein the steel composition further contains by mass % one or two or more kinds of components selected from a group consisting of 1.5% or less Cu, 2.0% or less Ni, and 0.1% or less V. 
     
     
         9 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 2 , wherein the steel composition further contains by mass % one, two or more kinds of components selected from a group consisting of 0.008% or less REM, 0.005% or less Ca, and 0.005% or less Mg. 
     
     
         10 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 3 , wherein the steel composition further contains by mass % one, two or more kinds of components selected from a group consisting of 0.008% or less REM, 0.005% or less Ca, and 0.005% or less Mg. 
     
     
         11 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 2 , wherein surface hardness of the steel plate is 400 HBW10/3000 or more in Brinell hardness. 
     
     
         12 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 3 , wherein surface hardness of the steel plate is 400 HBW10/3000 or more in Brinell hardness. 
     
     
         13 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 4 , wherein surface hardness of the steel plate is 400 HBW10/3000 or more in Brinell hardness. 
     
     
         14 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 2 , wherein hardenability index DI* is 180 or less. 
     
     
         15 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 3 , wherein hardenability index DI* is 180 or less. 
     
     
         16 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 4 , wherein hardenability index DI* is 180 or less. 
     
     
         17 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 5 , wherein hardenability index DI* is 180 or less. 
     
     
         18 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 2 , wherein the steel plate satisfies a following formula (2).
   C+Mn/4−Cr/3+10P≦0.47  (2),
   
       wherein the respective element symbols are contents (mass %) of the elements. 
     
     
         19 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 3 , wherein the steel plate satisfies a following formula (2).
   C+Mn/4−Cr/3+10P≦0.47  (2),
   
       wherein the respective element symbols are contents (mass %) of the elements. 
     
     
         20 . The abrasion resistant steel plate having excellent weld toughness and excellent delayed fracture resistance according to  claim 4 , wherein the steel plate satisfies a following formula (2).
   C+Mn/4−Cr/3+10P≦0.47  (2),
   
       wherein the respective element symbols are contents (mass %) of the elements.