Cold forging steel having improved resistance to grain coarsening and delayed fracture and process for producing same
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United States of America Patent
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Jul 17, 2001
Grant Date -
N/A
app pub date -
May 18, 1999
filing date -
May 20, 1998
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Abstract
A cold forging steel excellent in grain coarsening prevention and delayed fracture resistance and method of producing the same are provided that enable omission of a step of annealing or spheroidization annealing before cold forging and improvement of delayed fracture resistance of a high-strength component used with a heat-treated surface. The cold forging steel is a steel of a specified composition having dispersed in the matrix thereof particles of not greater than 0.2 .mu.m diameter of one or more of TiC, Ti(CN), NbC, Nb(CN) and (Nb, Ti)(CN) in a total number of not less than 20/100 .mu.m.sup.2. The method of producing a cold forging steel includes the steps of heating this steel to not lower than 1050.degree. C., hot-rolling the steel into steel wire or steel bar, and slowly cooling the steel at a cooling rate of not greater than 2 C./s during cooling to a temperature not higher than 600.degree. C. to obtain a steel having dispersed in the matrix thereof particles of not greater than 0.2 .mu.m diameter of one or more of TiC, Ti(CN), NbC, Nb(CN) and (Nb, Ti)(CN) in a total number of not less than 20/100 .mu.m.sup.2.
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