1.About the account　　

       Q345 steel is a kind of material. It is a low alloy steel（c<0.2%)，Comprehensive performance is good, good low temperature performance, ling stamping performance, welding performance and cutting performance is good.Widely used in Bridges, vehicles, ships, buildings, pressure vessels, etc. Q represents this kind of material yield, behind the 345, is refers to the material yield value, at around 345. And with the increase of the thickness of the material and reduce the yield value. Analogous to the naming of q235 method.

　　Q345a, q345b, q345c q345d, q345e. And this is the distinction between grade, represents the main impact of temperature is different! Q345a, don't do impact; Grade q345b, impact is 20 degrees at room temperature; Grade q345c, impact is 0 degrees; Q345d grade, is 20 degrees - impact; Q345e level, it is - hit 40 degrees. In the impact of different temperature, impact value is also different.
 
        In the sheet, is a low alloy series. In low alloy material, this material is the most common. Q345 past as a way of saying: 16 mn.

2.Execution standard

        External standards for q345: gb709, internal standards: gb/t1591-94, due to the implementation of standards, this kind of steel plate to allow delivery minus tolerance.

3.The difference between the q235 and q345

　　Different: q235 yield strength of the lower limit of 235 mpa, yield strength of q345 lower limit is 345 mpa (q) for the meaning of Chinese characters "bow" of the word, the back of the lower limit value represents the yield strength)
 
        The two different alloy content: for ordinary carbon steel q235, q345 low alloy steel. (with the old standard 1591-1591 grades 12 MNV 16 mnre, 18, 16 mn nb, 14 MNNB)

    Performance and application

　　Strength requirement of q235, metal structure, the core of carburized or cyanide parts, tie rod, connecting rod, hook, coupler, bolt and nut, sleeve, shaft and welding parts.
 
        Q345 - good comprehensive mechanical properties, low temperature performance may also, plasticity and good weldability, used in low pressure vessel, oil tank, vehicles, cranes, mining machinery, power stations, Bridges under moving load of the structure, mechanical parts, building structure, general metal parts, hot rolled or normalizing state, can be used in various structure below 40 ℃ cold areas. 

　  Such as structural strength is controlled, can consider is stiffness control with q345, such as structure, can consider to use q235 q345 price a little expensive, but because of its high strength, material can be saved. Specific selection can from the above several comprehensive comparison.