（可以含翻译，但非必要）
Electromagnetic pure iron hot rolled thick plate (GB / T6984-1986)
Electromagnetic pure iron hot rolled thick plate is a hot-rolled strip steel product with special material,shape and surface finishing requirements. GB/T6984-1986 (hereinafter referred to as “the standard”) specifies the order chemical composition and mechanical properties, stepwise precision and size, flattening test, dimensional tolerance, surface quality and test items for production, as well as the requirements for inspection and trademark of the products.
The chemical composition and mechanical properties of the steel based on GB/T6984-1986 are as follows:
Chemical composition (mass fraction %):
C: 0.04 ~ 0.05;
Si: 0.08 ~ 0.13;
Mn: 0.36 ~ 0.50;
Cr: 0.10 ~ 0.20
S:≤ 0.02
P:≤ 0.008
Mechanical properties:
Yield strength: ≧215MPa (N/mm2);
Tensile strength: ≧330MPa (N/mm2).
The stepwise precision of the product: When the thickness of the plate is less than 4mm, the deviation of the thickness should be no more than 0.2mm, and the deviation of the width should be no more than ±2mm. When the thickness of the plate is more than 4 mm, the thickness should be no more than 0.3mm, and the width should be no more than ±3mm.
Flattening test: For plates with thickness of 5mm and above, it is necessary to carry out flattening test on the standard flat surface. In general, the welding or bonding width should not be less than 25mm, and the deviation at any point of the edge should not exceed 2% of the thickness of the plate.
Dimensional tolerance: Thickness tolerance: for plates with thickness of 4mm and below, the allowable deviation of thickness shall be no more than +20%, -10% of the nominal thickness; for plates with thickness of more than 4mm, the allowable deviation of thickness shall be no more than +10%, -7.5% of the nominal thickness. Width tolerance: the allowable deviation of width shall be no more than -2.5mm and +2.7mm of the nominal width. The deviation of length should not exceed -3.0mm (including -3.0mm) and +3.0mm of the nominal length.
Surface quality: The surface quality should be flat and smooth, and the surface defects such as local indentation, burr and crack should be eliminated. The surface should be free of peeling and rolling and other injuries, and the surface shall be free of oil, scale and rust spots and other dirty materials.
Test items: Complete product analysis: 100% analysis for C, Si and Mn; spot sample analysis for S and P. Mechanical performance test: tensile strength test and yield strength test should be conducted according to GB/T228. Metallographic Quality Test: According to GB/T4340.7, test the plate by using SEM and observe the metallographic structure, ferrite grains and distribution of inclusion.
The inspection and verification requirements of the product according to GB/T6984-1986 are as follows:
Manufacturing supervision: The manufacturer shall appoint a scientific and technological personnel or a professional and technical personnel to participate in the production process and take the responsibility of product inspection.
Inspection and verification: Chemical composition test, mechanical performance test, flattening test and surface quality test should be carried out in all batches of products in accordance with the requirements of GB/T 2154 and GB/T228.
In order to ensure product quality, it is also necessary to carry out nondestructive testing (penetrant testing or eddy current test). The inspection results show that the qualified product should be shown in the quality certificate of the product, indicating it in the products trademark accordingly.
In summary, GB/T6984-1986 stipulates the order, chemical composition and mechanical properties, stepwise precision and size, flattening test, dimensional tolerance, surface quality and test items for the production of electromagnetic pure iron hot rolled thick plate, as well as the requirements for inspection and trademark of the products. Among them, the quality inspection of the product mainly includes chemical composition test, mechanical performance test, flattening test, surface quality test and nondestructive testing. All of these requirements provide necessary conditions for electromagnetic pure iron hot rolled thick plate to have qualified mechanical properties, surface protection and long service life.
