The main difference between 1.q235 and Q345 is that the intensity is different: the lower limit of yield strength of Q235 is 235mpa,gb150, and Q235-b is 0~350℃. The lower limit of yield strength of Q345 is 345mpa,gb150, the q345-b temperature is -20~425℃ (the meaning of Q is "Qu" of Chinese character, the following value represents the lower yield strength), and the yield value decreases with the increase of material thickness.
Yield strength: When the material stress exceeds the elastic limit, the deformation increases faster, at this time, in addition to producing elastic deformation, but also produce partial plastic deformation. When the stress reaches a value, the plastic strain increases sharply and the curve appears a small platform of fluctuation, which is called yielding. The maximum and minimum stress at this stage is called the upper yielding point and the lower yielding point respectively. Because the value of the lower yielding point is more stable, it is called the yield point or yield strength as the index of the material resistance.
2.q235a,q235b,q235c,q235d,q235e. This is the level of distinction represented by the impact of the main temperature is different. A,b,c,d,e, different, refers to their performance in the impact temperature difference. Respectively: q235a level, is not to do impact; Q235B grade, is 20 degrees room temperature impact; Q235C grade, is 0 degree impact; Q235D grade, is-20 degree impact; Q235E grade, is-40 degree impact. At different impact temperatures, the impact value is also different. In the plate, is the most common material, the General Board series. A term used in the past is: A3.
3.q345a,q345b,q345c,q345d,q345e. This is the level of distinction represented by the impact of the main temperature is different. Q345A level, is not to do shock; Q345B grade, is 20 degrees room temperature impact; Q345C grade, is 0 degree impact; Q345D grade, is-20 degree impact; Q345E grade, is-40 degree impact. At different impact temperatures, the impact value is also different. In the plate, is a low alloy series. In the low alloy material, this kind of material is the most common. Q345 used to call it: 16Mn.
4.Q235 is a yield point not less than 235 newtons per square millimeter, tensile strength is not less than 370N per square millimeter, it is low carbon steel light round steel bar, strength grade is Ⅰ class, weldability is good, elongation rate is big; Q345 steel refers to the yield point, the tensile strength is not less than each square millimeter 510N, it is the lower alloy steel deformed steel bar, The strength grade is Ⅱ grade, the weldability is slightly poor, the elongation is slightly small. Q345 not in the old standard, suspected to be a clerical error. They can not be replaced by each other, must be replaced by the design unit recognition. The essential difference is that the steel composition is different, the yield point is different, the strength is different.
5. The alloy content is different: Q235 is ordinary carbon steel, Q345 is low alloy
q235--Metal structural parts, carburizing or cyanide parts not requiring high strength of heart, lever, connecting rod, hook, coupler, bolt nut, sleeve, shaft and welding parts.
q345--has good comprehensive mechanical properties, low temperature performance, good plasticity and weldability, and is used as medium and low pressure vessel, oil tank, vehicle, crane, mining machinery, power station, bridge and other structure, mechanical parts, building structure, general metal structural parts, hot-rolled or normalizing state, Can be used for 40 ℃ of the following cold areas of various structures.
According to the design of the structure of the specific circumstances. If the structure is strength control, can consider the use of Q345 such as structure is stiffness control, can consider the use of Q235 price Q345 slightly more expensive, but because of its high strength, can save material. Q235\q345 is based on the yield strength of steel is divided into 235MPa and 345mpa,q345 slightly more expensive, but the price difference is not very big.