Q345GJBZ25 steel plate is a high-strength low-alloy steel plate that complies with the standard GB/T19879-2015. It offers good mechanical properties and low-temperature resistance, making it widely used in engineering machinery manufacturing, building structures, shipbuilding, and other fields.

The differences in the Z-grade of Q345GJBZ25 steel plate are mainly reflected in the following aspects:

1. Resistance to lamellar tearing: The Z-grade determines the steel plate's resistance to lamellar tearing in the thickness direction. A higher Z-grade indicates better resistance to lamellar tearing. Q345GJBZ25 steel plate has a Z25 grade, meaning it exhibits good resistance to lamellar tearing in the thickness direction.

2. Chemical composition: Steel plates with different Z-grades have certain differences in chemical composition. The chemical composition of Q345GJBZ25 steel plate mainly includes elements such as C, Si, Mn, P, S, Nb, V, and Ti. Variations in the proportions of these elements affect the mechanical properties and resistance to lamellar tearing of the steel plate.

3. Mechanical properties: As the Z-grade increases, the mechanical properties of the steel plate vary. Q345GJBZ25 steel plate has specific requirements for mechanical performance indicators such as yield strength, tensile strength, and elongation. Steel plates with different Z-grades will differ in these performance indicators.

4. Application fields: The Z-grade of Q345GJBZ25 steel plate also influences its application areas. Generally, steel plates with higher Z-grades are suitable for applications requiring high resistance to lamellar tearing, such as bridges, pressure vessels, and ship structural components. In contrast, steel plates with lower Z-grades are suitable for applications with relatively lower requirements for resistance to lamellar tearing, such as building structures and general machinery manufacturing.

In summary, the Z-grade of Q345GJBZ25 steel plate is primarily reflected in its resistance to lamellar tearing, chemical composition, mechanical properties, and application fields. Steel plates with different Z-grades exhibit certain differences in these aspects. Therefore, when purchasing Q345GJBZ25 steel plate, it is necessary to select the appropriate Z-grade based on actual needs and application scenarios.