Abstract: To study the effects of microstructure of heat affected zone (HAZ) after welding, cold crack sensitivity and microalloying element on the welding properties of the Nb-microalloyed steel plates used for the specified thick spokes of car wheels, of which both the rolling and cooling processes were controlled, the cold crack sensitivity and hardening trend of the steel were evaluated by theoretical calculation. The steel plate was welded by DC argon arc process and the welding parameters were simulated just like what role they play in actuality. The microstructure of welded joints of steel plate were investigated by optical microscopy and EMS, as well as the mechanical properties by testers. The results showed that in the spoke plate the heat-affected zone (HAZ) tends to be small cold cracking and the Nb addition improves greatly the properties of HAZ with no obvious change in properties found in other zones after welding. It can thus be concluded that the thick spoke steel we developed has high weldability.