Low alloy steel and weld joint thereof excellent in corrosion resistance to hydrochloric acid and sulfuric acid

A low alloy steel excellent in hydrochloric acid corrosion resistance and sulfuric acid corrosion resistance, characterized in that:

• said steel contains, in mass,
• C:
• 0.001 to 0.2%,
• Si:
• 0.01 to 2.5%,
• Mn:
• 0.1 to 2%,
• Cu:
• 0.1 to 1%,
• Mo:
• 0.001 to 0.12%,
• Sb:
• 0.01 to 0.2%,
• Ni:
• 0.1 to 1%,
• P:
• 0.05% or less,
• S:
• more than 0.005% to less than 0.012%,
• N:
• 0.001 to 0.007%, and
• Cr:
• 0.1% or less,
• and further one or more of
• Nb:
• 0.005 to 0.1%,
• Ta:
• 0.005 to 0.1%,
• V:
• 0.005 to 0.1%,
• Ti:
• 0.005 to 0.1%, and
• W:
• 0.05 to 1%,
• with the balance being Fe and unavoidable impurities;
• and the acid corrosion resistance index EI, which is calculated from the following expression <2>, of said steel is zero to 75,
• EI/10,000=0.0005+0.045×Sb %−C %×Moeq <2>,
• where % means mass % and Moeq (mass %) is defined by the following expression,
• Moeq=Mo %+5.1×(Nb %+Ta %)+4.2×V %+9.3×Ti %+0.5×W %.