High strength electrical steel sheet and method of production of same

Abstract

The present invention has as its object the production of high strength electrical steel sheet, having a high strength of a tensile strength TS of for example 500 MPa or more, having wear resistance, and having superior magnetic properties of magnetic flux density and iron loss, that is, provides a method of production of high strength electrical steel sheet containing, by mass %, C: 0.060% or less, Si: 0.2 to 6.5%, Mn: 0.05 to 3.0%, P: 0.30% or less, S or Se: 0.040% or less, Al: 2.50% or less, N: 0.020% or less, and further one or more of Cu: 0.001 to 30.0% and Nb: 0.03 to 8.0% and having worked structures remaining inside the steel sheet, said method of production of high strength electrical steel sheet coarsening an average crystal grain size D (μm) of a sheet right before a step of forming the worked structures to finally remain inside the steel sheet to D≧20 μm, imparting strain in the final working step as a preferred process, then not performing any heat treatment causing the worked structures to disappear and high strength electrical steel sheet obtained by that method.

1 . A method of production of high strength electrical steel sheet containing, by mass %, C: 0.060% or less, Si: 0.2 to 6.5%, Mn: 0.05 to 3.0%, P: 0.30% or less, S or Se: 0.040% or less, Al: 2.50% or less, and N: 0.040% or less, having a balance of Fe and unavoidable impurities, and having worked structures remaining inside the steel sheet, said method of production of high strength electrical steel sheet characterized by making an average crystal grain size d of the steel sheet right before the step of forming the worked structures to finally remain inside the steel sheet 20 μm or more. 
   
   
       2 . A method of production of high strength electrical steel sheet containing, by mass %, C: 0.060% or less, Si: 0.2 to 6.5%, Mn: 0.05 to 3.0%, P: 0.30% or less, S or Se: 0.040% or less, Al: 2.50% or less, and N: 0.040% or less, having a balance of Fe and unavoidable impurities, and having worked structures remaining inside the steel sheet, said method of production of high strength electrical steel sheet characterized by making an average crystal grain size d (μm) of the steel sheet right before the step of forming the worked structures to finally remain inside the steel sheet d≧(220−50×Si %−50×Al %). 
   
   
       3 . A method of production of high strength electrical steel sheet as set forth in  claim 1  characterized by making an average crystal grain size d (μm) of the steel sheet right before the step of forming the worked structures to finally remain inside the steel sheet
     d ≦(400−50×Si %) and       d ≦(820−200×Si %)   
   
   
       4 . A method of production of high strength electrical steel sheet as set forth in  claim 1  characterized by making a recrystallization rate of the steel sheet right before the step of forming the worked structures to finally remain inside the steel sheet 50% or more. 
   
   
       5 . A method of production of high strength electrical steel sheet as set forth in  claim 1  characterized in that the steel ingredients further contain, by mass %, one or both of Cu: 0.001 to 30.0% and Nb: 0.03 to 8.0%. 
   
   
       6 . A method of production of high strength electrical steel sheet as set forth in  claim 1  characterized in that the steel ingredients further contain, by mass %, one or more types of Ti: 1.0% or less, V: 1.0% or less, Zr: 1.0% or less, B: 0.010% or less, Ni: 15.0% or less, and Cr: 15.0% or less. 
   
   
       7 . A method of production of high strength electrical steel sheet as set forth in  claim 1  characterized in that the steel ingredients further contain, by mass %, one or more types of Bi, Mo, W, Sn, Sb, Mg, Ca, Ce, La, and Co in a total of 0.5% or less. 
   
   
       8 . A method of production of high strength electrical steel sheet as set forth in  claim 1  characterized in that the worked structures present inside the steel sheet are 1% or more by area rate in observation of the cross-section. 
   
   
       9 . A method of production of high strength electrical steel sheet as set forth in  claim 1 , characterized in that an average dislocation density in the worked structures inside the steel sheet is 1×10 13 /m 2  or more. 
   
   
       10 . A method of production of high strength electrical steel sheet as set forth in  claim 1 , characterized by being a single ferrite phase in a temperature region from room temperature to 1150° C. and satisfying, by mass %,
   980−400×C+50×Si−30×Mn+400×P+100×Al−20×Cu−15×Ni−10×Cr>900   
   
   
       11 . A method of production of high strength electrical steel sheet as set forth in  claim 1 , characterized in that heat treatment at 450° C. for 30 minutes is used to make a tensile strength 100 MPa or more. 
   
   
       12 . A method of production of high strength electrical steel sheet characterized by producing steel sheet as set forth in  claim 10  during the process of which making a final heat treatment after cold rolling a heat treatment holding the sheet in a temperature region of 800° C. or more for 5 sec or more and not allowing formation of an austenite phase in the steel material even at a peak temperature in this heat treatment. 
   
   
       13 . A method of production of high strength electrical steel sheet characterized by producing steel sheet as set forth in  claim 10  during the process of which making a cooling step after holding the sheet in a temperature region of 800° C. or more for 5 sec or more cooling by a cooling rate of 40° C./sec or more to 300° C. or less. 
   
   
       14 . A method of production of high strength electrical steel sheet as set forth in  claim 10 , characterized by making a residence time in 700 to 400° C. in said cooling step 5 sec or less.