Q345D steel is a commonly used low alloy steel plate.
The chemical composition of Q345D steel is as follows:
C≤0.18
Si ≤0.50
Mn≤1.70
P≤0.030
S≤0.025
Nb≤0.07
V≤0.15
Ti≤0.20
Cr≤0.30
Ni≤0.50
Cu≤0.30
N≤0.012
Mo≤0.10
Al≥0.015
Mechanical properties of Q345D steel
Yield strength ≥ 265
Tensile strength 450-600
Elongation after breaking ≥ 17
Impact work 27
Welding performance of Q345D steel
Q345D steel plate welding needs to be preheated first, because the carbon content is relatively high.
1. The purpose of preheating is to prevent cold cracks. Cold cracking is directly related to carbon equivalent. Therefore, it is necessary to distinguish the carbon equivalent of the material. The carbon equivalent of Q345 steel is less than 0.3%. Generally speaking, the sensitivity to cold cracks increases when the carbon equivalent is 0.4%. Q345A usually does not warm up. But when the plate is very thick, it still needs to be preheated due to the rapid cooling. If the plate thickness is above 70mm, the risk of not preheating is very high.
2. The difference between Q345D steel and Q345A steel is that the impurities S and P are less, and the impact performance at low temperature is better. From the welding point of view, when there are fewer impurity elements in the base metal, it is good for controlling welding hot cracks.
3. If the electrode manual says to preheat the base metal, preheat it. Because the welding material is not used according to the manufacturer's instructions, the performance of the weld will be greatly reduced.
