Steel for X70-grade tube bundle outer bearing tube and production method thereof

The steel comprises the following chemical components in percentage by weight: 0.1 percent to 0.20 percent of C, 0.20 percent to 0.35 percent of Si, 1.75 percent to 1.85 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.003 percent of S, 0.040 percent to 0.060 percent of V, 0.035 percent to 0.055 percent of Nb, 0.10 percent to 0.15 percent of Sb, 0.04 percent to 0.06 percent of RE, 0.045 percent to 0.06 percent of Als, less than or equal to 0.003 percent of N, 0.004 percent to 0.009 percent of Ca, more than or equal to 0.5 percent of RE/V, more than or equal to 1.8 percent of Ca/S and the balance of Fe and inevitable impurities. According to the invention, the yield strength is 485-540 MPa, the tensile strength is 570-620 MPa, and the ductility is 24-28%; the impact absorbing energy at the temperature of 20 DEG C below zero is 180-280 J; and at the high temperature of 650 DEG C, the yield strength is 485-550 MPa, the tensile strength is 570-625 MPa, and the ductility is 25%-29%.