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GB/T 8731-2008 PDF English

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GB/T 8731-2008: Free-cutting structural steel
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GB/T 8731: Evolution and historical versions

Standard IDContents [version]USDSTEP2[PDF] deliveryName of Chinese StandardStatus
GB/T 8731-2008English85 Add to Cart 0-9 seconds. Auto-delivery Free-cutting structural steel Valid
GB/T 8731-1988English285 Add to Cart 0-9 seconds. Auto-delivery Free-cutting steel--Technical requirements Obsolete

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GB/T 8731-2008: Free-cutting structural steel

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GB NATIONAL STANDARD OF THE PEOPLE’S REPUBLIC OF CHINA ICS 77.140.01 H 40 Replacing GB/T 8731-1988 Free-cutting Structural Steel Issued on. SEPTEMBER 11, 2008 Implemented on. MAY 01, 2009 Jointly issued by. General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ); Standardization Administration (SAC) of the People's Republic of China.

Table of Contents

Foreword... 3 Introduction... 5 1 Scope... 6 2 Normative References... 6 3 Terms and Definitions... 9 4 Classification... 9 5 Ordering Information... 10 6 Dimension, Shape, Weight and Tolerance... 10 7 Technical Requirements... 11 8 Test Methods... 15 9 Inspection Rules... 16 10 Packing, Marking and Quality Certificate... 17 Appendix A (Informative) Reference Values for Mechanical Properties of Bar Steels and Wire Rods Made from Free-cutting Structural Steel... 18 Appendix B (Informative) Comparison Table of Designations in this Standard with Foreign-countries’ Designations... 22

1 Scope

This standard specifies the scope, terms and definitions, ordering information, dimensions, shape, weight and tolerances, technical requirements, test methods, inspection rules, packing, marking and quality certificate of free-cutting structural steels. This standard is applicable to steels such as bar steels, wire rods, steel wires, steel plates, and steel strips that are used for mechanical machining. Their chemical compositions are also applicable to ingots, billets and their products.

2 Normative References

The following normative documents contain provisions which, through reference in this text, constitute provisions of this national standard. For dated references, subsequent amendments (excluding corrigendum) or revisions of these publications do not apply. However, the parties who have entered into an agreement according to this standard are encouraged to study whether the latest edition of the normative document is applicable. For undated references, the latest edition of the normative document referred to applies. GB/T 222 Permissible Tolerances for Chemical Composition of Steel Products GB/T 223.3 Methods for Chemical Analysis of Iron, Steel and Alloy - The Diantipyrylmethane Phosphomolybdate Gravimetric Method for the Determination of Phosphorus Content GB/T 223.11 Methods for Chemical Analysis of Iron, Steel and Alloy - The Ammonium Persulfate Oxidation Volumetric Method for the Determination of Chromium Content GB/T 223.12 Methods for Chemical Analysis of Iron, Steel and Alloy- The Sodium Carbonate Separation - Diphenyl Carbazide Photometric Method for the Determination of Chromium Content GB/T 223.19 Methods for Chemical Analysis of Iron, Steel and Alloy. The Neocuproine-chloroform Extraction Photometric Method for the Determination of Copper Content

3 Terms and Definitions

The following terms and definitions are applicable to this standard. 3.1 Free-cutting structural steel The structural steel that has favorable machining performance because of adding higher content of sulfur, lead, calcium and other free-cutting elements.

4 Classification

Steels shall be classified into the following two classes according to the different application and processing methods. The application and processing method for steel bars shall be noted in the contract; and the unnoted one shall be supplied as steels for machining.

5 Ordering Information

The contract for ordering goods according to this standard shall cover the following relevant contents.

6 Dimension, Shape, Weight and Tolerance

6.1 Dimension, shape, weight and tolerance of steels 6.1.1 The dimensions, shape, weight and tolerances for hot-rolled steel bars, hot-rolled hexagon bars and octagonal steels shall meet the requirements of GB/T 702. 6.1.2 The dimensions, shape, weight and tolerances for forged steel bars shall meet the requirements of GB/T 908. 6.1.3 The dimensions, shape, weight and tolerances for hot-rolled wire rods shall meet the requirements of GB/T 14981. 6.2 The deformation length at both ends of all shorn hot-rolled bar steels shall not be greater than 20mm. It shall be noted in the contract if the purchaser requires to clear burrs at both ends of bar steels. 6.3 The end of the cold drawn bar steels shall not be cut into a bent shape. The cut-end may have shear deformations when steels are shearing with the shears. And the maximum dimension of the end shall not be larger than the nominal dimension plus the tolerance value, after deformation.

7 Technical Requirements

7.1 Designation and chemical composition 7.1.1 The designations and chemical compositions (heat analysis) of steels such as sulfur free-cutting steels, lead free-cutting steels, tin free-cutting steels and calcium free-cutting steels shall be in accordance with those specified in Table 1, Table 2, 7.1.2 As required by the purchaser, other elements that are able to improve the cutting performance of steels may be properly added based on the agreement of both the supplier and the purchaser. 7.1.3 For the chemical composition tolerances of finished products of steels, the free-cutting elements such as sulfur and tin shall be in accordance with those specified in Table 5; other elements shall meet the requirements of GB/T 222. 7.2 Smelting process Unless the user has specific requirements, the smelting process shall be specified by the supplier. 7.3 Delivery condition Steels shall be delivered in conditions such as hot-rolled, hot forging or cold-rolled, cold drawn, and bright conditions; the delivery condition shall be indicated in the contract. They may also be delivered in other conditions as required by the purchaser. 7.4 Mechanical property 7.4.1 The Brinell hardness of the free-cutting bar steels and wire rods delivered in hot-rolled condition shall be in accordance with those specified in Table 6. 7.4.2 The mechanical property of bar steels and wire rods in conditions of hot-rolled, hardening and tempering, cold drawn and cold-drawn high tempering may refer to Appendix A based on the agreement of both the supplier and the purchaser. 7.7 Decarburized layer As required by the purchaser, the total decarburized layer depth on one side may be inspected, for steels with nominal carbon content larger than 0.30%; the acceptance criterion shall be negotiated by the supplier and the purchaser. 7.8 Nonmetallic inclusion As required by the purchaser, the nonmetallic inclusion of steels may be inspected; the grade of Class B, C and D inclusions shall all not be larger than Grade 3. 7.9 Surface quality 7.9.4 The surface quality of the bright steel shall meet the requirements of GB/T 3207. 7.9.5 The surface of steel plates and steel strips shall be free from cracks, bubbles, scars, folds, inclusions and embedded iron oxide scales. The steel plates shall be free from sub-layers.

8 Test Methods

8.1 The inspection items, sampling quantity, sampling positions and test methods of each batch of steels shall be in accordance with those specified in Table 9. 8.2 In the tensile test for bar steel, the scale distance of test sample L0=5d0 (d0 is the sample diameter). The sample diameter shall be in accordance with those specified in Table 10. 8.3 The scale distance of steel wire test samples shall be 100mm.

9 Inspection Rules

9.1 Inspection and acceptance The inspection and acceptance of steels shall be carried out by the quality supervision department of the supplier. 9.2 Batching rules The steels shall be inspected for acceptance in batches; each batch shall be composed of such steels of the same-designation, same-furnace number, same-thermal treatment heats (when steels are supplied in heat treatment condition), same-specification and same-delivery condition. 9.3 Sampling quantity The sampling quantity for steel inspection shall be in accordance with those specified in Table 9. 9.4 Re-inspection and judgement rules The re-inspection and judgement rules shall be carried out according to the relevant requirements of GB/T 17505 or the requirements of the agreement reached by supplier and the purchaser.

10 Packing, Marking and Quality Certificate

10.1 Packing, marking and quality certificate of bar steels and wire rods shall comply with those specified in GB/T 2101. 10.2 Packing, marking and quality certificate of steel wires shall comply with those specified in GB/T 2103. 10.3 Packing, marking and quality certificate of bright steel shall comply with those specified in GB/T 3207. 10.4 The steel plates and steel strips shall be in accordance with those specified in GB/T 247. ......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.


      

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