1. The content is different:
The new standard has significant changes in content, including scope of application, grade, dimensional requirements, mechanical properties, surface quality, marking, detection and judgment methods, etc. There are different requirements in all aspects.
2. Different signs:
The sign is the mark engraved on the steel bar. The old standard HRB335 is represented by "2"; HRB400 is represented by "3"; HRB500 is represented by "4" . The logo of the new standard has been changed: HRB335 is represented by "3"; HRB400 is represented by "4"; HRB500 is represented by "5";
3. Different indicators:
New The tensile strength of threaded steel bars in the standard has been reduced. The old standard (HRB335, HRBF335) was 490Mpa, and the new standard was changed to ≥455Mpa; the old standard (HRB400, HRBF400) was 570Mpa, and the new standard dropped to ≥540Mpa.
As long as the threaded steel bars meet the standards stipulated by the country, they are called national standard threaded steel bars. How to distinguish national standard and non-standard steel bars? The simplest way is to read the warranty and label. National standard steel bars are printed with letters, while non-standard steel bars are not printed with letters. National standards have the GB symbol, while non-standard ones do not have this symbol.
Inspection of steel bars:
First of all, check the brand number and quality certificate of the steel bars; secondly, do an appearance inspection, take 5% of each batch of steel bars, and check that there are no traces on the surface. Cracks, wounds and laminations, the bumps on the surface of the steel bars shall not exceed the height of the transverse ribs, the depth and height of the defects shall not be greater than the allowable deviation of the location, and the curvature of the steel bars shall not be greater than four millimeters per meter; the next mechanical performance test , if each batch is less than 60 tons, take 2 pieces from it, cut off two sections from each piece, and conduct tensile and cold bending tests respectively.
When cutting out the test pieces, 100-500mm from both ends of the steel bars should be removed. When cutting out the test pieces over 60 tons, the corresponding steel bars should be removed. If a test result does not meet the requirements, double the number of samples from the same batch shall be taken for each test.
Baidu Encyclopedia-Steel Bar