Overall, P355NH exhibits strong mechanical properties suitable for pressure vessel applications, making it a popular choice in industries such as petrochemical, oil and gas, and power generation.

The mechanical properties of P355NH and P355GH are as follows:

1. Tensile Strength: The minimum tensile strength of P355NH is 490-630 MPa, while for P355GH, it is 510-650 MPa. Tensile strength refers to the maximum stress that a material can withstand before breaking or fracturing.

2. Yield Strength: The minimum yield strength of P355NH is 355 MPa, while for P355GH, it is 355-510 MPa. Yield strength refers to the stress required to cause a specific amount of permanent deformation in a material.

3. Elongation: The minimum elongation at break for P355NH is 22%, while for P355GH, it is 22-27%. Elongation refers to the ability of a material to stretch or deform before breaking.

4. Impact Strength: The impact strength of P355NH at a temperature of -20°C is 27 J, while for P355GH, it is 20°C. Impact strength refers to the ability of a material to absorb energy under impact loading.

5. Hardness: The hardness value for P355NH is typically 180 HB, while for P355GH, it is 160-210 HB. Hardness refers to the resistance of a material to surface indentation or penetration.

These properties indicate the strength, ductility, toughness, and resistance to deformation of P355NH and P355GH, which are both low alloy steel grades commonly used in pressure vessel and boiler applications.