GB/T 8749-1988 High-quality carbon structural steel hot-rolled strip

This standard applies to the manufacture of high-quality carbon structural steel hot-rolled narrow steel strips for cold-rolled steel strips. GB/T 8749-1988 High-quality carbon structural steel hot-rolled steel strips GB/T8749-1988 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Hot-rolled quality carbon structural steel strip
Hot-rolbed quality cerbon structural steel stripsThis standard applies to the manufacture of high-quality carbon structural steel strips and hot-rolled narrow steel strips for cold-rolled steel strips. 1 Classification and code
1.1 Classification by manufacturing accuracy
Ordinary precision steel strip
Thickness high precision steel strip
1.2 Classification by edge state
Trimmed steel strip
Untrimmed steel strip
2 Dimensions and appearance
2.1 Dimensions and allowable deviations of steel strips
+++++++++++++H
2.1.1 The thickness and width of steel strips shall comply with the requirements of Table 1. Table 1
Steel strip thickness
2.50,2.75, 3.00,
3.25,3.50,3.75,4.00.
1.25,4. 50,4.75.5.00
125，
170，
UDC 669. 14. 018
.29-418
GB 8749—88wwW.bzxz.Net
110,115，120.
180，
215,220,
150160,
200, 210,
According to the requirements of the buyer, the table can be provided after the cooperation of the supply and demand parties! 2 The allowable deviation of steel strip thickness shall comply with the provisions of Table 2. 2.1.2
Steel strip thickness
3.25~-3.75
4.00~5.00
2.1.3 Allowable deviation of steel strip width
The allowable deviation of the width of trimmed steel strip is ±1.00 mm, and the allowable deviation of the width of ordinary precision (P) steel strip without trimming shall comply with the provisions of Table 3. Approved by the Ministry of Metallurgical Industry of the People's Republic of China on February 15, 1988
240, 250
Relatively short (H)
1989 07-01 implementation
≥150
GE 874988
According to the requirements of the buyer, after the agreement between the supplier and the buyer, the strip with positive width deviation can be provided. The tolerance value shall comply with the provisions of Table 3. 2.1.4 The maximum difference between the thickness of the middle and the edge of the cross section of the steel strip (three-point difference) shall comply with the provisions of Table 4. Table 4
Steel strip width
Three-point difference·not intervened
2.1.5 The thickness of the steel strip along the rolling direction shall be uniform. The maximum difference (inter-strip difference) measured at any three points on the same straight line shall not exceed 0.25mm
2.2.1 The strip is delivered in coils. Each is composed of the same steel strip (separate or welded). The weld must be marked, and the inner diameter of the coil is not less than 30 cm. The coil weight is not less than 200 kg. If the coil weight is outside the above provisions, it shall be agreed upon by the supplier and the buyer according to the requirements of the buyer. 2.2.2 The steel strip can be delivered in straight strips or folded strips, and its length shall be agreed upon by the supplier and the buyer. 2.2.3 The tower shape of the steel strip coil shall not exceed 50 mm. 2.2.4 The sickle of the steel strip shall not exceed 4 mm per meter. 2.3 Marking example
The steel strip with ordinary precision, no edge cutting, thickness of 3 mm and width of 200 mm made of 20# steel heating rail is marked as: hot rolled steel strip 20-P-BQ-3X200-GB 8749--883 Technical requirements
3.1 The brand and chemical composition of the strip shall comply with the provisions of GB 699-88 Technical Conditions for High-quality Carbon Structural Steel. 3.2 According to the requirements of the buyer, after the agreement between the supplier and the buyer, the surface hardness test of the steel strip can be carried out, and the value is agreed by both parties. 3.3 The surface of the strip should be smooth and free of cracks, folds, tears and pressed iron oxide. The steel strip is allowed to have pits with a depth or height not greater than half of the thickness allowable deviation, bumps, scratches, pitting and red spots with a depth not greater than 0.8mm.
3.4 ​​Shaved strips shall not have looseness, shrinkage, bubbles, layered iron oxide, cracks and foreign inclusions caused by steel damage. 3.5 Edge state of steel strip
3. 5. 1 Except for burrs with a size not greater than 0.5 mm, there should be no other defects on the edge of the trimmed steel strip. 3.5.2 There shall be no cracks and burrs on both sides of the untrimmed steel strip: slight burrs are allowed, and their depth or height should not exceed half of the width allowable deviation.
3.6 Local defects of the steel strip are allowed to be removed. The depth of removal on the same surface should not exceed the negative deviation allowed by the thickness and width. The cleaning area should be flat.
3.7 According to the requirements of the buyer, the depth of the surface decarburization layer of the steel strip made of steel with steel grades above 85 (including 35) should be checked. The depth of the decarburization layer on one side (full decarburization layer and partial decarburization layer) should meet the following requirements. When the strip thickness is 3.00mm, the total decarburization layer depth is not more than 0.8mm. When the strip thickness is >3.00mm, the total decarburization layer depth is 2.5% of the actual thickness of the steel strip. 3.8 According to the agreement between the supply and demand parties, the ferrite grain size can be supplied with a certain grade of steel strip. GE874988
3.9 According to the requirements of the buyer, the strip with annealing state or other special performance requirements can be supplied after the agreement between the supply and demand parties. 4 Test method
4.1 The outer surface of the steel strip is inspected with the naked eye. 4.2 The dimensions of the steel strip shall be measured with measuring instruments or universal tools of corresponding accuracy. 4.2.1 The thickness of the uncut steel strip shall be measured at any point along the rolling direction at a distance of not less than 10mm from its edge and not less than 2m2 from the coil end; the thickness of the cut steel strip shall be measured at any point along the rolling direction at a distance of 5mm from its edge and not less than 400mm from the coil end. 4.2.2 The width of the steel strip shall be measured at a distance of not less than 2m2 from the coil end. 4.3 The method of checking the edge of the steel strip or the method of checking after the purchaser cuts it is used to check whether the steel strip has delamination. Ultrasonic or other non-destructive inspection methods are allowed to check the delamination of the steel strip. 4.4 The macrostructure of the steel strip shall be inspected on the steel bar of the produced steel strip according to the provisions of the macrostructure and defect acid etching test method of GB 226-77.
4.5 The hardness test of the steel strip shall be carried out in accordance with the provisions of GB 231-84 "Jinlian Brinell Hardness Test Method". 4.6 The decarburization depth of steel strip shall be in accordance with the provisions of GB 224-78 "Determination of Decarburization Depth of Steel". 4.7 The grain size of steel strip shall be in accordance with GB 6394-86 "Method for Determination of Average Grain Size of Metal". 4.8 When measuring the bend of steel strip, place the inspected part of the steel strip on the plane, use a one-meter ruler close to the concave edge of the steel strip, and measure the maximum distance between the steel strip and the ruler.
4.9 When the purchaser inspects the quality of each roll of steel strip, if the weight of the section that does not meet the surface requirements is found, and it does not exceed 3% of the weight of the roll, it is considered to meet the requirements of this standard.
5 Inspection Rules
5. 1 Steel strips shall be inspected in batches. Each batch consists of steel strips of the same steel grade, the same furnace number, the same specification and the same category. 5.2 The chemical composition of the steel strip shall be filled in the quality certificate according to the results of the smelting analysis. According to the requirements of the purchaser, the chemical composition of the finished steel strip can also be inspected.
5.3 From the steel strips with the same shape and size, two rolls of steel strips are selected from each batch for decarburization layer, hardness and grain size inspection. Two samples are selected for each item, which are respectively cut from the inner end of one steel strip roll and the outer end of another steel strip roll. 5.4 Sample cutting position
*5.4.1 The uncut steel strips shall be cut at a distance of not less than 10 mm from the edge and not less than 2 m from the roll end. 5.4.2 The cut steel strips shall be cut at a distance of not less than 5 mm from the edge and not less than 400 mm from the roll end. 5.5 Re-inspection regulations of steel strips
The re-inspection of steel strips shall be carried out in accordance with the general provisions of the acceptance, packaging, marking and quality certificate of steel plates and steel strips in GB217-88. 6 Packaging, marking and quality certificate
The packaging, marking and quality certificate of steel strips shall be in accordance with the provisions of GB 217-88. Additional Notes:
This standard was drafted by the Strip Steel Plant of Capital Steel Company. This standard shall be drafted by Li Xuequan.
This standard shall be marked with the level grade GB879-881
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