Q345 steel plate classification and welding characteristics
Q345 is a steel material. It is low alloy steel (C<0.2%) and is widely used in buildings, bridges, vehicles, ships, pressure vessels, etc. Q represents the yield strength of this material, and the following 345 refers to the yield value of this material, which is around 345 MPa. And as the thickness of the material increases, its yield value decreases.
Chinese name Q345 steel and foreign name Q345 type is a kind of steel material used in buildings. The yield value of bridges, vehicles and ships is 345
Q345 has good comprehensive mechanical properties and acceptable low temperature performance. It has good plasticity and weldability and is used as medium and low pressure vessels, oil tanks, vehicles, cranes, mining machinery, power stations, bridges and other structures that bear dynamic loads, mechanical parts, building structures, and general metal structural parts. It is used in hot-rolled or normalized conditions. , can be used in various structures in cold areas below -40℃.
Level classification
Q345 can be divided into Q345A, Q345B, Q345C, Q345D and Q345E according to the grade. What they represent is mainly that the temperature of the impact is different.
Q345A level, no impact;
Q345B level, 20 degree normal temperature impact;
Q345C level, 0 degree impact;
Q345D level is -20 degree impact;
Q345E level is -40 degree impact.
At different impact temperatures, the impact values are also different.
Welding characteristics of Q345 steel:
3.1 Calculation of carbon equivalent (Ceq)
Ceq=C+Mn/6+Ni/15+Cu/15 +Cr/5+Mo/5+V/5
Calculate Ceq=0.49%, which is greater than 0.45%. It can be seen that the welding performance of Q345 steel is not very good, and strict process measures need to be formulated during welding.
Problems that are likely to occur when Q345 steel is welded
1 The hardening tendency of the heat-affected zone
During the cooling process of Q345 steel during welding, the heat-affected zone is prone to hardening The quenched structure - martensite is formed, which increases the hardness of the near-seam area and decreases the plasticity. The result is post-weld cracking.
2 Cold crack sensitivity
The welding cracks of Q345 steel are mainly cold cracks.