Patent ID: 8202628

Claim:
A fusion-bonded product having a high-strength part, comprising: a first preform ( 2 a ) constituted by (a) integrally, frictionally pressure-welding a first low-carbon steel part (L 1 ) made of low-carbon steel containing less than 0.45% of C and a high-carbon steel part (H) made of high-carbon steel containing not less than 0.45% C, and (b) deforming the first preform by forging such that a border between the first low-carbon steel part (L 1 ) and the high-carbon steel part (H) comprises a V-shaped peak in cross section; and a second preform ( 2 b ) having a second low-carbon steel part (L 2 ) made of second low-carbon steel containing less than 0.45% of C; wherein the high-carbon steel part (H) of the first preform ( 2 a ) is provided with a high-strength part ( 9 ) that has been previously formed into a desired shape and quenched, the second low-carbon steel part (L 2 ) of the second preform ( 2 b ) has been previously formed into a predetermined shape, the first low-carbon steel part (L 1 ) of the first preform ( 2 a ) and the second low-carbon steel part (L 2 ) of the second preform ( 2 b ) are bonded to each other by fusion welding, and the high-carbon steel part (H) of the first preform is spaced from the second low-carbon steel part (L 2 ) of the second preform with the first low-carbon steel part (L 1 ) of the first preform disposed therebetween.