Comparison of Differences From Upgrading Q345B to Q355B

    Steel, as the foundation of modern construction and machinery manufacturing industries, has a direct impact on the quality and safety of engineering projects. With the advancement of science and technology and changes in industrial needs, steel standards are constantly being updated.

    The introduction of the GB/T 1591-2018 standard, especially the upgrade of Q345B steel to Q355B, also marks the alignment of China steel standards with international standards.

Q355B: A Product of International Integration

    The upgrade of Q345B steel is an important part of the GB/T 1591-2018 standard update. The introduction of the new grade Q355B implies its similarity to S355JR of the European standard EN 10025.

Optimization of Chemical Components

    It is not only reflected in the grade, but also in the chemical components and mechanical properties. For example, the upper limit of some carbon content has been raised from ≤0.20 to 0.24, which is the same as the JR grade of the European standard, and harmful elements such as Cu are also kept consistent with the European standard as much as possible.

Minor Adjustment on Mechanical Properties

    In terms of mechanical properties, the yield strength of Q355B steel has been raised from ≥345 MPa of Q345B to ≥355 MPa, but the original lower yield ReL judgment has been changed to the upper yield ReH judgment consistent with the European standard. This change has a relatively small impact on production and use, and can even be regarded as not a big change in the selection of load design materials.

    In fact, the main purpose of the change in yield value is to keep consistent with European standards, increase the circulation of materials, and reduce the cost of design conversion.

Conclusion:

    The upgrade of Q345B to Q355B is an important step for China's steel standards to be in line with international standards. This change is not only reflected in the optimization of chemical components and mechanical properties, but also in the correspondence between grades and international standards.

The Benefits:

    1. In recent years, China and Europe have increasingly cooperated in many fields, and many engineering projects have chosen to purchase steel in China. However, due to different standard systems, this often leads to some problems. 

    For example, when purchasing S355JR steel, it is usually necessary to re-order with the steel mill. However, with the implementation of the new national standard, S355JR can be directly replaced with Q355B in terms of performance, and the docking of the two can achieve almost zero difference. This means that as long as the design party slightly modifies the drawing markings, it can be docked smoothly.

    2. Although the demand for European standard products has increased year by year, due to the differences in standard systems and component performance, production organization has become very inconvenient, resulting in rising production costs.

    However, the implementation of the new national standard makes S355JR and Q355B almost interchangeable. For steel mills, this is basically just a matter of modifying the MTC.