The effect of micro Zr on structure and mechanical properties of welding coarse grain heat affected zone (CGHAZ)of ≤0.18C-1.2～1.6Mn HSLA steel has been studied by welding thermal simulation method. The test results showed that with 30~ 100 kJ/cm heat input welding thermal simulation

the strength

plasticity and impact toughness at -50 ℃ of CGHAZ of steel containing 0.01%～0.03% Zr were higher than that steel non-containing Zr

and microhardness HV10 value of Zr steels was 177~251.The Zr steels had excellent weldablity and at same heat input the grain in CGHAZ of non-containing steel was coarser than that of Zr steel and with heat input of 30 kJ/cm the bainite was dominant in structure of CGHAZ while with increasing the heat input the acicular ferrite and few pearlite occured in CGHAZ.