GB/T 8731-1988 Technical requirements for free-cutting structural steel
Some standard content:
National Standard of the People's Republic of China
Technical conditions for free-cutting structural steel
Free-cutting steel Technical requirementsUDC: 699. 14. 018
GB8731-88
This standard applies to hot-rolled, cold-drawn steel and steel wire for cutting processing in ordinary machine tools and automatic machine tools. Its chemical composition is also suitable for chains, steel bars and their products.
Dimensions and Shape
1.1 The dimensions, shape and permissible deviations of hot-rolled, cold-drawn steel bars, steel wires and bright steels shall conform to the requirements of Table 1.1
Angle steel
Bright steel
Relevant standards
GB 702—B6
GB 705—B3
GB 702—86
Dimension accuracy and shape level
According to the requirements of the purchaser, the product can also be delivered with a higher level of accuracy than that in Table 1. Relevant standards
GB 905—82
GB 906—B2
.GB 342—82
GB 3207— 82
Dimensional accuracy and appearance level
Level 9, 10
The deformation length of both ends of hot-rolled bars cut by shears shall not exceed 20mm. According to the requirements of the purchaser, the burrs at both ends of the bars shall be removed.
1.3 The ends of cold-drawn bars shall not be bent. When shearing steel with shears, the cut end is allowed to be sheared and deformed. After deformation, the maximum size of the end shall not be greater than the nominal size such as tolerance. When packaging, the deformed end should be placed in the direction of the cut. 2 Technical requirements
2.1 Grade and chemical composition
2.1.1 The chemical composition (melting analysis) of steel shall comply with the provisions of Table 2. 2.1.2 The allowable deviation of the chemical composition of finished steel products, of which the allowable deviation of calcium is ±8.8. The allowable deviation of other elements shall comply with the provisions of Table 2 in "C222-84" for chemical analysis of steel samples and allowable deviation of chemical composition of finished products. Approved by the Ministry of Metallurgical Industry of the People's Republic of China on February 2, 1988 and implemented on March 1, 1989
￥40Mn
Y 0. 16 ~-0. 351
0.70~1.00
0.16 ~-0. 35
0. 70--1. 10
0.80~1.20
0. 80~1. 20
0. 70~-1. 00
0.70~~1. 00 | | tt | 70~1. 00
0. 15~-0. 35
1.20~~1. 55
0. 20~0. 40 0. 60~0. 90
0. 10~- 0. 20
0.15~0.25
0. 23~~0. 33
0. 23~~0. 33
D. 08 ~~ 0. 15
0. 08 ~~ 0. 15
0.08~~0.15
0. 20 ~~0. 30
0. 04~0. 08 | | tt | ~~0. 35
0.002~0.006
2.1. 3Y15Ca The residual elements Ni, Cr and Cu in steel shall not exceed 0.25% respectively; when used for hot pressure processing, the copper content shall not exceed 0.20%. If the supplier can guarantee that this value is not exceeded, no analysis is required. 2.2 Delivery status
Y40Mn is delivered in the state of high temperature tempering after hot rolling or cold drawing, and other steel grades are delivered in the state of hot rolling or cold drawing. The delivery status should be indicated in the contract. It can also be delivered in other states according to the requirements of the purchaser, and its mechanical properties are negotiated by the supply and demand parties. 2.3 Mechanical properties
2.3.1 The longitudinal mechanical properties and Brinell hardness of bars and wire rods delivered in the hot rolled state shall comply with the provisions of Table 3. Table 3
Mechanical properties
Tensile strength α
390~540
390--540
390--540
450~600
510~655
510~655
590735
600~745
Elongation,
not less than
Shrinkage
not less than
Brinell hardness HB
not more than
For steel with a diameter of more than 16mm, the mechanical properties of the steel measured by the test specimen made of heat-treated rough pieces shall comply with the provisions of Table 4.
Service point.
GB873188
Mechanical properties
Tensile strength
Elongation 6:
not less than
Impact As
Summarize: Tensile specimen rough (a25) normalizing treatment, heating temperature is 830~850C, holding time is not less than 30min, impact specimen rough (g15) quenching and tempering, rate quenching temperature is 840±20℃ (Ji water), tempering degree is recommended to be 600. 2. 3. 3
For bars delivered in cold drawn state, its longitudinal properties and Brinell hardness shall comply with the requirements of Table 5. Table 5
Mechanical properties
Tensile strength oN/mm
8～20
530--755
530-755
530-~755
530-~755
570785||tt ||600825
625~815
695920
Steel size, mm
>20~30
510~735
510~735
510~735
510~7 35
530-746
560--765
590-~785
655--855
490~685
490-~685
490-685
490~685
510~705
640--736
570~765
635--835
The mechanical properties and Brinell hardness of steel wire with a diameter less than 8mm shall be negotiated by both the supply and demand parties. The mechanical properties and Brinell hardness of Y40Mn cold-drawn steel in high temperature tempering state shall comply with the provisions of Table 6: 2. 3. 5
Mechanical properties
Tensile strength
590-785
Macrostructure
Elongation ratio:
Not less than
Brinell hardness HB
152~217
152~217
152~217
152~217
167--217
174--223
176~229bZxz.net
196255
Brinell hardness IB
179~229
GB8731-88
2.4.1. The cross-section acid-etched macrostructure test piece of steel shall not have visible pores, bubbles, inclusions, cracks, delamination, peeling and spots. When evaluating the macrostructure level, general looseness, central looseness and segregation shall not exceed level 3. 2.4.2 According to the requirements of the buyer, the steel can be tested for tower shape, and the grid mark shall be negotiated by the supply and demand parties. 2.5 Decarburization layer
According to the strip force requirements, steel with a carbon content greater than 0.30% can be tested for a total decarburization layer depth (ferrite + transition layer), and the qualified standard shall be negotiated by the supply and demand parties
2.6 Non-metallic inclusions
According to the requirements of the buyer, steel can be tested for brittle inclusions, and its level shall not exceed 3. 2.7 Surface quality
2.7.1 The surface of hot-rolled bars and wire rods shall not have cracks, folds, tears and scars. The above defects must be removed, and the cleaning depth shall not exceed half of the tolerance. The surface of hot-rolled bars and wire rods shall not have scratches, black spots and pits exceeding half the tolerance, and the depth of hairline shall not exceed one-quarter of the tolerance.
2.7.2 The surface of cold-drawn bars and wires must be clean, smooth and bright, and shall not have cracks, scars, roughness, hairline, folds, pores and oxide scale. The surface of bars supplied in the heat-treated state is allowed to have oxidation color, and the surface of 11-level precision bars and wires is allowed to have individual small scratches, concave surfaces, pores, black spots and a small number of pits, the depth of which shall not exceed half of the tolerance calculated from the actual size. According to the requirements of the purchaser, the depth may not exceed one-quarter of the tolerance. The surface of 11-level precision bars and wires for cold machining (turning, grinding) is allowed to have scratches, pits, four pits and cleaning marks not exceeding half of the tolerance calculated from the actual size, and individual small hairlines not greater than half of the tolerance are allowed, but the bars shall not be smaller than the minimum size.
2.7.3 The surface of silver-finished steel is not allowed to have any defects. 3 Test methods
3.1 The size of steel is measured by using a sample plate and a measuring tool. 3.2 The surface quality of steel is checked by naked eyes one by one. If necessary, it can be checked after grinding with a chain knife or silicon wheel, or after pickling. 3.3 The inspection items, sampling requirements and test methods for each batch of steel are in accordance with the provisions of Table 7. No.
Test Item
Chemical Composition
Macrostructure
Brine Thickness
La Shenwu Test
Shenjigong
Demagnetization Layer
Non-metallic Inclusions
GB 873188
Test Method
GB 223. 1~ 223. 5— 81
B 223. 29— 84
GB 226— 77
GB 1979:80
GI 231— 84
GB228—87
GB22984
GD 224— 87
YB 25—77
Lianxiang requires
GB 222— 84
equivalent to the head of the rim ingot or
steel end
rod means three steel ends
GB 2975—82
any one steel end
any two coils
GB 2975- 82
any two steel ends
uninterrupted steel
different steel
jiang, () calcium content is analyzed by atomic absorption spectrometry, and the specific provisions are temporarily based on the enterprise standard sampling quantity agreed upon by the supply and demand parties. When the tensile test is carried out on each
) steel bar, the specimen gauge length L=5d, where t& is the specimen diameter, and the specimen diameter is specified in Table 8. The wire specimen gauge length is 100mml.
Steel size
Test sample straightening
Inspection rules
4.1 Inspection and acceptance
No addition!
The inspection and acceptance of steel shall be carried out by the supplier's technical supervision department. 4.2 Batch rules
220～30
4.2.1 Steel wires shall be inspected in batches, and each batch shall consist of steel wires with the same steel grade, the same furnace number, the same heat treatment furnace (when supplied in the heat treatment state), the same size, and the same supply state. 4.2.2 The batch rules of steel wires shall comply with the relevant provisions of GB2103-88 "General Provisions for Acceptance, Packaging, Marking and Quality Certificate of Steel Wire".
4.3 Maximum number of samples
The number of samples to be taken for steel inspection shall be as specified in Table 7. 4.4 Re-inspection and determination rules
4.4.1 The re-inspection and determination rules for steel bars shall comply with the relevant provisions of GB 2101-80 General provisions for acceptance, packaging, marking and quality certificates of steel.
4.4.2 The re-inspection and determination of steel wires shall comply with the relevant provisions of GB2.103-88. 5 Packaging, marking and quality certificates
The packaging, marking and quality certificates of steel bars and steel wires shall comply with the provisions of GD 2101-80 and GB 2103-88 respectively. The packaging, marking and quality certificates of bright steel shall comply with the provisions of YB 247-64. Additional remarks:
GB 873-88
This standard was proposed by the Information and Standards Research Institute of the Ministry of Metallurgical Industry. This standard was drafted by Capital Iron and Steel Corporation. The main drafter of this standard is Liu Lekai. From the date of implementation of this standard, the former Ministry of Metallurgical Industry Standard YB3191-75 ≤ Free Cutting Structural Steel Technical Conditions" will be invalid. This standard water half grade mark
GB 8731-88 180
GI 231— 84
GB228—87
GB22984
GD 224— 87
YB 25—77
Union requirements
GB 222— 84
Equivalent to the head of the rim ingot or
The end of the steel
The end of the rod or the end of the three steel bars
GB 2975—82
Any one end of the steel
Any two discs
GB 2975- 82
The ends of any two steel bars
Uninterrupted steel bars
Different steel bars
River, () The calcium content is analyzed by atomic absorption spectrometry. The specific provisions are temporarily based on the enterprise standard sampling quantity agreed upon by the supply and demand parties. When the tensile test is conducted on each
) steel bar, the specimen gauge length L=5d, where t& is the specimen diameter, and the specimen diameter is as specified in Table 8. The wire specimen gauge length is 100mml.
Steel size
Specimen straightening
Inspection rules
4.1 Inspection and acceptance
Not subjected to!
The inspection and acceptance of steel shall be conducted by the technical supervision department of the supplier. 4.2 Batch rules
220～30
4.2.1 Steel wires shall be inspected in batches, and each batch shall consist of steels with the same steel grade, furnace number, heat treatment furnace (when supplied in heat treatment state), size and supply state. 4.2.2 The batch rules of steel wires shall comply with the relevant provisions of GB2103-88 "General Provisions for Acceptance, Packaging, Marking and Quality Certificate of Steel Wire".
4.3 Maximum number of samples
The number of samples to be taken for steel inspection shall be as specified in Table 7. 4.4 Re-inspection and determination rules
4. 4.1 The re-inspection and determination rules of steel wires shall comply with the relevant provisions of GB 2101-80 "General Provisions for Acceptance, Packaging, Marking and Quality Certificate of Type Steel".
4. 4.2 The re-inspection and determination of steel wires shall comply with the relevant provisions of GB2103-88. 5 Packaging, marking and quality certificate
The packaging, marking and quality certificate of steel bars and steel wires shall comply with the provisions of GD 2101-80 and GB 2103-88 respectively. The packaging, marking and quality certificate of bright steel shall comply with the provisions of YB 247-64. Additional remarks:
GB 873-188
This standard was proposed by the Information and Standards Research Institute of the Ministry of Metallurgical Industry. This standard was drafted by the Capital Iron and Steel Company. The main drafter of this standard is Liu Lekai
From the date of implementation of this standard, the former Ministry of Metallurgical Industry standard YB3191-75≤Technical Conditions for Free Cutting Structural Steels" will be invalidated. This standard is marked with water and half grade
GB 8731-88 180
GI 231— 84
GB228—87
GB22984
GD 224— 87
YB 25—77
Union requirements
GB 222— 84
Equivalent to the head of the rim ingot or
The end of the steel
The end of the rod or the end of the three steel bars
GB 2975—82
Any one end of the steel
Any two discs
GB 2975- 82
The ends of any two steel bars
Uninterrupted steel bars
Different steel bars
River, () The calcium content is analyzed by atomic absorption spectrometry. The specific provisions are temporarily based on the enterprise standard sampling quantity agreed upon by the supply and demand parties. When the tensile test is conducted on each
) steel bar, the specimen gauge length L=5d, where t& is the specimen diameter, and the specimen diameter is as specified in Table 8. The wire specimen gauge length is 100mml.
Steel size
Specimen straightening
Inspection rules
4.1 Inspection and acceptance
Not subjected to!
The inspection and acceptance of steel shall be conducted by the technical supervision department of the supplier. 4.2 Batch rules
220～30
4.2.1 Steel wires shall be inspected in batches, and each batch shall consist of steels with the same steel grade, furnace number, heat treatment furnace (when supplied in heat treatment state), size and supply state. 4.2.2 The batch rules of steel wires shall comply with the relevant provisions of GB2103-88 "General Provisions for Acceptance, Packaging, Marking and Quality Certificate of Steel Wire".
4.3 Maximum number of samples
The number of samples to be taken for steel inspection shall be as specified in Table 7. 4.4 Re-inspection and determination rules
4. 4.1 The re-inspection and determination rules of steel wires shall comply with the relevant provisions of GB 2101-80 "General Provisions for Acceptance, Packaging, Marking and Quality Certificate of Type Steel".
4. 4.2 The re-inspection and determination of steel wires shall comply with the relevant provisions of GB2103-88. 5 Packaging, marking and quality certificate
The packaging, marking and quality certificate of steel bars and steel wires shall comply with the provisions of GD 2101-80 and GB 2103-88 respectively. The packaging, marking and quality certificate of bright steel shall comply with the provisions of YB 247-64. Additional remarks:
GB 873-188
This standard was proposed by the Information and Standards Research Institute of the Ministry of Metallurgical Industry. This standard was drafted by the Capital Iron and Steel Company. The main drafter of this standard is Liu Lekai
From the date of implementation of this standard, the former Ministry of Metallurgical Industry standard YB3191-75≤Technical Conditions for Free Cutting Structural Steels" will be invalidated. This standard is marked with water and half grade
GB 8731-88 1
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