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How to Choose the Right Material for Q235R and Q345R


 Difference Between Q345R and Q245R Steel Plate

Q235R and Q345R are 2 common steel materials for pressure vessel equipments, for a long time many pressure vessel manufacturers have some misunderstandings on how to choose between these 2 steel materials. For example: Obviously Q345R has the advantage on pressure vessel yield strength; while Q245R shows advantage on Calculation of container stiffness, and for Q245R is carbon steel, it has price advantage compared to low alloy steel-Q345R. In fact, it is not true.

 Chemical Composition Comparison of Q235R and Q345R

Steel GradeQ245R and Q345R Chemical Composition %

The table above shows that except for Element Si and Mn content are different, other elements’ limitation of Q245R and Q345R are the same. As boiler steel weld performance is influenced by its chemical element content, especially for Carbon content. As carbon content in the steel increases, steel plasticity decreases, steel hardening tendency tends to increase, and crack would be easy to produce. Generally steel plate contains many alloy elements, together they have comprehensive influence on steel mechanical property. So Carbon Equivalent is key figure for calculating steel weld performance. Usually steel plate with Ceq<0.45% has good weld performance.

For Q345R has higher Mn content, its CeQ is 0.1% higher than Q245R. Q345R notch sensitivity is larger than Q245R, low fatigue strength made it easier to produce cracks when welding. So in some application environments, it shall be considered on the medium that can influence these 2 steel types. For example: in wet H2S stress corrosion environment, for low carbon steel q235r and Carbon Manganese steel q345r, Ceq<0.40%. As Q245R has lower Ceq, it has better H2S Stress Corrosion Resistance performance.

Q345R Boiler Steel Plate

 Mechanical Property Comparison of Q245R and Q345R

Under the condition of same designed temperature, tensile strength of Q345R is always (80-100) higher than Q245R. This is caused by alloy element Mn, Manganese can be dissolved in ferrite steel structure, the use of manganese solid solution strengthening makes its strength significantly increased. So if the pressure vessel container thickness is decided by steel strength, stiffness advantage of Q245R shall not be maximized.

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