| 摘要 |
A method for manufacturing a hollow article having excellent durability is provided. In particular, an electric resistance welded steel pipe which is made from a steel sheet and in which the width of a low carbon layer is 2h (m) is subjected to a heat treatment that includes a quenching treatment in which the electric resistance welded steel pipe is heated to a heating temperature T (K) not lower than the Ac 3 transformation temperature at a heating rate V h (K/s), held for a soaking time k (s), immediately cooled to a quenching start temperature Tq (K) at a primary cooling rate V c (K/s), and then secondarily cooled (quenched). The heating rate V h , the maximum heating temperature T, and the primary cooling rate V c are adjusted so as to satisfy an inequality (herein C 0 (mass percent) is the C content (mass percent) of the steel sheet, t is the diffusion time (s), t = 50 / V h + 50 / V c + k, V h is the heating rate (K/s), V c is the primary cooling rate (K/s), k is the soaking time (s), D is the diffusion coefficient (m 2 /s), D (m 2 /s) = D 0 exp(-Q / RT), Do is 4.7 × 10 -5 (m 2 /s), Q = 155 (kJ/mol·K), R = 8.31 (J/mol·K), and T is the maximum heating temperature (K)) and the quenching start temperature Tq is higher than the Ar 3 transformation temperature. This prevents the hardness as quenching of the electric resistance welded portion from being reduced and significantly increases the durability of the heat-treated article. 0.83 ‰¤ 1 - 1 - 0.09 / C 0 ˆ« - h h exp - y 2 / 4 �¢ Dt / 4 �¢ ÀDt �¢ dy |
