GB/T 3098.1-2000 Mechanical properties of fasteners Bolts, screws and studs
Some standard content:
National Standard of the People's Republic of China
Mechanical properties of fasteners
Bolts, screws and studs
GB/T3098.1—2000
Approved and issued by: State Administration of Quality and Technical Supervision Issue date: September 26, 2000
Implementation date: February 1, 2001
147- 1
This standard is equivalent to the international standard IS0)898:1:1999 "Mechanical properties of fasteners made of carbon steel and alloy steel - Part 1: Bolts, screws and studs"
(The general title of GB/T3098 is "Mechanical properties of fasteners", including the following parts:
—G13/T3098.1-2000 Mechanical properties of fasteners Bolts, screws and studs
-GB/T 3098.2--2000
Mechanical properties of fasteners
Female coarse thread
GB/T 3098.3-2000
Set screws
Mechanical properties of fasteners
—~GB/T 3098.4-2000
Mechanical properties of fasteners
Fine thread
-GH/T 3098.5—2000
Tapping screws
-GB/T 3098.6-2000
Stainless steel bolts, screws and studs
-G3/T 3098.7--2000
Extrusion screws
GB/T 3098.8—1992
Heat-treatment threaded connection pairs
-GB/T 3098.9--1993
Rectangular steel hexagonal lock nuts
—GB/T 3098.10-1993
Mechanical properties of fasteners
Mechanical properties of fasteners
Mechanical properties of fasteners
Mechanical properties of fasteners
Mechanical properties of fasteners
Mechanical properties of fasteners
Bolts, screws, studs and nuts made of non-ferrous metals-GB/T 3098.11--1995
Self-drilling and self-tapping screws
-GB/T 3098.12—1996
Conical proof load test for nuts
-GB/T 3098.13—1996
Mechanical properties of fasteners
Mechanical properties of fasteners
Torque test and breaking torque of bolts and screws Nominal diameter 1~
-GB/T 3098.14--2000
Nut hole expansion test
-GB/T 3098.1S--2000
Stainless steel nuts
-GB/T 3098. 16--2000
Stainless steel set screws
GB/T 3098.17-2000
Mechanical properties of fasteners
Mechanical properties of fasteners
Mechanical properties of fasteners
Mechanical properties of fasteners
Preload test for checking hydrogen embrittlement Parallel bearing surface method ISO 898-1 does not specify the mounting position of the screwed-in body end for the physical tensile test and proof load test of the studs, which is stipulated in this standard (Articles 8.2 and 8.5).
ISO 898-1 does not specify the test mold for square neck and head with bolts. This standard specifies it (Figure 4). ISO) 898-1 does not specify the stud mark for left-hand thread, this standard specifies it (Article 9.4)
This standard is a revision of GB/T3098.1-1982, and the main modifications are as follows:
a) It only specifies the mechanical properties tested under the condition of ambient temperature of 10~35℃. The mechanical and physical properties of fasteners may be different at higher or lower temperatures (Chapter 1);
b) It is clearly stated that fasteners whose head shear area is smaller than the stress cross-sectional area of the thread due to the geometric dimensions of the head may not meet the requirements of tension and torque, such as countersunk heads, semi-countersunk heads and cylindrical heads (Chapter 1); c) It is clarified that this standard does not specify shear stress resistance and fatigue resistance (Chapter 1);
d) Add the provisions for the content of sintered (B) and specify the minimum content of manganese for low carbon boron alloy steel [Notes 1 and 4 in Table 2]; e) Specify the content of alloying elements for alloy steels used in grades 10.9 and 12.9 [Note 7 in Table 2)];) It is specified that the surface of grade 12.9 is not allowed to have a white phosphorus accumulation layer [Table 2 g) The chemical composition and tempering temperature given for grade 12.9 alloy steel are still under investigation [Table 2, Note 9]; h) Performance indicators such as "breaking torque", "shrinkage rate" and "surface defects" are added, and some hardness indicators are adjusted (5.35.5, 5.10, 5.12, 5.18 in Table 3);
i) The acceptance test is adjusted to: "○" is applicable to "thread diameter d≤3mm or length l<2.5d\; "" is applicable to "thread diameter d>3mm and length l≥2.5d" (Table 4); j) The "For fasteners with thread diameter d>4mm and length ≥3d, the minimum hardness test can also be used instead of the tensile test" is cancelled. ; Adjusted the specification range for head strength test, Table 5 footnotes 7), 9);
k) It is stipulated that "re-tempering test" is not mandatory and is only applicable to arbitration tests in case of disputes [Table 5 footnote 10)]; 1) When the tensile test and proof load test are carried out on the bolts, screws and studs, the length of the thread that bears the tensile load and is not screwed is changed to: - times the thread diameter (1d) (8.2); m) It is stipulated that "hardness and theoretical tensile strength may not have a direct conversion relationship"; "wedge load test is not applicable to countersunk screws"; (8.4 and 8.6);
n) It is clearly stipulated that "slotted and cross-slot screws do not use markings" (Chapter 9);
0) Regulation If the distributor uses his own identification mark on the fastener, it should be regarded as the manufacturer's identification mark (Article 9.1); p) For small bolts, screws or products with limited head shape, it is stipulated that the "clock face method" symbol can be used to mark the performance level) (Table 15) q) For all performance levels of d ≥ 5mm, hexagonal head and hexagonal flower head bolts and screws (including flange products), marking is mandatory (Article 9.3.1);
r) It is stipulated that studs should be marked on the unthreaded shank (Article 9.3.4, Figure 10);
s) It is stipulated that the manufacturer's trademark or identification mark and performance level are mandatory on all packages of all specifications (Article 9.6); t) Text instructions for guiding use are added in Appendix ^. This standard replaces GB/T3098 from the date of implementation.1-1982.
Appendix A of this standard is a reminder appendix.
This standard is proposed by the State Machinery Industry Bureau
This standard is under the jurisdiction of the National Technical Committee for Standardization of Fasteners. This standard is under the responsibility of the Mechanical Science Research Institute, and Xi'an Standard Parts General Factory, Shanghai High Strength Bolt Factory, Shanghai Fastener and Welding Material Technology Research Institute, Beijing Standard Parts Industry Group Corporation, Wuhan Automobile Standard Parts Research Institute, Shanghai Jinma High Strength Fastener Co., Ltd. and Shenzhen Aviation Standard Parts Co., Ltd. participated in the drafting.
This standard is interpreted by the Secretariat of the National Technical Committee for Standardization of Fasteners.
ISO Foreword
ISC) (International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies) of various countries. The formulation of international standards is usually carried out through ISO technical committees. Each member body may also participate in the committee if it is interested in the project carried out by a technical committee. International organizations related to IS() may also participate in this work. ISO has close ties with the International Electrotechnical Commission (IE) in the field of electrical standardization. The draft international standard adopted by the technical committee is circulated to all member bodies for voting. The official publication of the international standard requires at least 75% of the member bodies to vote in favor.
International Standard ISO898-1 was prepared by ISO/TC 2 Technical Committee SC1 Mechanical Properties of Fasteners Subcommittee. The third edition has deleted and supplemented the second edition (1S0898-1: 1988) and is a technical revision.
IS()898 is generally called "Mechanical properties of carbon steel and alloy steel fasteners" and includes the following parts:
-Part 1: Bolts, screws and studs
Part 2: Coarse pitch threads of nuts with specified proof load values - Part 5: Set screws and similar threaded fasteners not subject to tensile stress
-Part 6: Fine pitch threads of nuts with specified proof load values - Part 7: Torque test and minimum torque for bolts and screws
Nominal diameter 1 to 10 mm
Appendix A of this standard is a prompt appendix. 14 7 3
1 Scope
This standard specifies the mechanical properties of bolts, screws and studs made of carbon steel or alloy steel when tested at an ambient temperature of 10 to 35°C.
Products judged to comply with this standard under this ambient temperature condition may have different mechanical and physical properties at higher or lower temperatures. Appendix A (informative appendix) provides examples of service points (α.) or specified non-proportional elongation stresses (α0.2) under high temperature conditions. At ambient temperatures below this, product properties, especially impact toughness, may change and users should pay attention to this. Some fasteners, such as countersunk heads, semi-countersunk heads and cylindrical heads (Chapter 6), may not meet the requirements of this standard for tension or torque due to their head geometry resulting in a head shear area smaller than the thread stress cross-sectional area.
This standard applies to bolts, screws and studs: coarse thread M1.6~M39; fine thread M8×1~M39×3; ordinary thread in accordance with GB/T 192; diameter and pitch combination in accordance with GB/T193; basic dimensions in accordance with GB/T196; tolerances and fits in accordance with GB/T 197; made of carbon steel or alloy steel.
This standard does not apply to set screws and similar threaded fasteners that are not subject to tension.
This standard does not specify the following performance requirements:
Weldability;
Corrosion resistance (GB/T 3098.6);
Performance requirements for working temperatures above +300℃ (250℃ for grade 10.9) or below -50℃;
Shear stress resistance;
Fatigue resistance.
Note: For specifications greater than the limit specified in this standard, such as d>39mm, the marking system of this standard can be used as long as all requirements of the performance level are met.
2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T 192—1981
Ordinary thread
Basic tooth profile
GB/T 193--1981
(diameter 1~600mm)
Ordinary thread diameter and pitch series
GB/T 196--1981
Basic size (diameter 1
Ordinary thread
--600mm)
GB/T 197—1981
Ordinary thread tolerance and fit (diameter 1~355mm)
GB/T 228--1987
6892:1984)
14—7— 4
Metal tensile test method (neqISO)
GB/T229--1994Metal Charpy notched impact test method (eqv ISO 148: 1983 and ISO 83: 1976)GB/T 230--1991
Metal Rockwell hardness test method
Metal Brinell hardness test method
GB/T 231-1984
GB/T 3098 .2--2000
Mechanical properties of fastenersNuts
Coarse thread (idtISO898-2:1992)GB/T3098.3--2000Mechanical properties of fastenersNail (idt ISO898-5:1998)
GB/T 3098.6--2000
Mechanical properties of fasteners
Bolts, screws and studs (idtISO3506-1:1997)
Stainless steel
GB/T 3098.13—1996 Mechanical properties of fasteners Bolts
And screws Torque test and breaking torque
(idt ISO 898-7:1992)
Nominal diameter 1 to 10 mm
Metal Vickers hardness test
GB/T 4340,1—1999
Part: Test methods (eqvISO6507-1:1997)GB/T 5277—1985
(eqv ISO 273:1979)
GB/T 5779.1—2000
Complex hardware
Through holes for bolts and screws
Surface defects of fasteners
Bolts,
Screws and studs
General requirements (idt ISO6157-1:1988) GB/T5779.32000Surface defects of fasteners Bolts
Special requirements (idt ISO6157-3:1988) Screws and studs
Marking system
The marking system for the performance grades of bolts, screws and studs is shown in Table 1. The abscissa represents the nominal tensile strength value αb (in N/mm2), while the ordinate represents the minimum elongation after fracture 35 (in %). The marking code of the performance grade consists of two parts of numbers: the first part of the number represents 1/100 of the nominal tensile strength (Table 3 and 5.1); the second part of the number represents 10 times the ratio of the nominal yield point (α) or the nominal specified non-proportional elongation stress (αp0.2) to the nominal tensile strength (α). The product of these two parts of the number is 1/10 of the nominal yield point. The minimum yield point (αmin) or the minimum specified non-proportional elongation stress (a0.2 mia) and the minimum tensile strength (obmin) is equal to or greater than its nominal value (Table 3).
4 Materials
Metric 2 specifies the steel types and tempering temperatures of various performance grades of bolts, screws and studs.
The chemical composition of the material shall comply with the provisions of the relevant material standards. Mechanical or physical properties
When tested at ambient temperature according to the methods specified in Chapter 8, bolts, screws and studs shall comply with the mechanical or physical properties specified in Table 3.
Test items for mechanical and physical properties
Use the methods specified in Chapter 8 to conduct mechanical and physical property tests on bolts, screws and studs according to the A or B items specified in Tables 4 and 5. Regardless of which type of test is selected, all requirements specified in Table 3 shall be met.
Class B items should be used as much as possible, but must be used for products with tensile load less than 500kN.
Nominal tensile strength Q
Minimum elongation after fracture accounts for
Relationship between service point and tensile strength
Part II digital code
Nominal yield point (α,)2
Nominal tensile strength (%) × 100%
Nominal specified non-proportional elongation stress (a.2)2) × 100%
Nominal tensile strength (o)
or products that are not applicable to Class A items. Class A items are applicable to bolts, screws and studs whose cross-sectional area of the non-threaded part of the machined specimens and the screw is smaller than the stress cross-sectional area of the thread.
Marking system for coordinate representation
400500
600700800
Note: Although this table gives high-level performance levels, it does not mean that these levels are applicable to all products. Applicable performance levels should be in accordance with the provisions of the product standards. For non-standard fasteners, refer to similar standard fasteners as much as possible. 1) Only applicable to d≤16mm.
2) Nominal values are as specified in Table 3.
14 7 5
Property level
10.95).6）
12.96).8),9)
Material and heat treatment
Low carbon alloy steel (such as boron, manganese or chromium), quenched and tempered or medium carbon steel, quenched and tempered
Low carbon alloy steel (such as boron, manganese or chromium), quenched and tempered or medium carbon steel, quenched and tempered
Low carbon alloy Steel (such as sintered, manganese or chromium), quenched and tempered medium carbon steel, quenched and tempered or low and medium carbon alloy steel (such as sintered, manganese or chromium), quenched and tempered or alloy steel quenched and tempered7)
Alloy steel, quenched and tempered7)
Chemical composition, %
0:154)
1) Boron content can reach 0.005%, and its non-effective boron can be controlled by adding titanium and (or) aluminum. 0.05
0.040.0350.035
2) These performance grades allow the use of free-cutting steel, the maximum content of which is sulfur, phosphorus and lead: sulfur 0.34%; phosphorus 0.11%; lead 0.35%. 3) To ensure good hardenability, fasteners with a thread diameter exceeding 20mm must use steel specified for grade 10.9. Tempering temperature
4) The minimum manganese content of low carbon boron alloy steel with a carbon content of less than 0.25% (barrel analysis) is: 8.8: 0.6%; 9.8, 10.9 and 10.9: 0.7%, 5) This product should add a horizontal line mark under the performance grade code (Chapter 9). 10.9 grade should meet all the properties specified in Table 3 for 10.9 grade, and the lower tempering temperature will cause different degrees of stress weakening under the condition of increasing temperature (Appendix A). 6) The material used for this performance grade should have good permeability to ensure that the core of the threaded section of the fastener obtains about 90% martensite structure after braiding and before tempering.
7) The alloy steel should contain at least one of the following elements, and its minimum content is: chromium 0.30%; nickel 0.30%; molybdenum 0.20%; vanadium 0.10%. 8) Considering the tensile stress, the surface of grade 12.9 is not allowed to have a white phosphorus accumulation layer that can be measured by metallography. 9) The chemical composition and tempering temperature are still under investigation. 14-7-6
Mechanical properties and physical properties
Nominal tensile strength b nominal, N/mm2
Minimum tensile strength,
Vickers hardness HV
F≥98N
Brinell hardness HB
F=30D2
Rockwell hardness HR
Surface hardness HV0.3
"Service point, N/mm2
Specified non-proportional elongation stress
a.2, N/mm2
Guaranteed stress
Mechanical and physical properties of bolts, screws and studs
Sp/o, or Sp/op0.2
Sp, N/mm2
Failure torque MB, N·m
Elongation after fracture, %
Reduction of area, %
Wedge load 5)
Impact absorption work Aku,
Head strength Hardness
Minimum height E of undecarburized layer of thread
Maximum depth G of fully decarburized layer, mm
Hardness after tempering
Surface defects
120130
114124
2096）
310280
d≤163|d>163)
According to GB/T3098.13||tt ||Testing of bolts and screws (excluding studs) shall comply with the requirements of Table 6 or Table 8.25
No fracture
The difference in the average hardness before and after tempering shall not exceed 20HVAccording to GB/T5779.1 or GB/T5779.31) When the load exceeds the guaranteed load due to over-tightening, the risk of nut disengagement increases for 8.8 grade bolts with thread diameter d≤16mm. It is recommended to refer to GB/T3098.2.
2) Only applicable to thread diameter d≤16mm
3) 12mm for bolts for steel structures.
4) The minimum tensile strength applies to products with nominal length I≥2.5d; the minimum hardness applies to products with length I<2.5d and other products that cannot be subjected to tensile tests (such as the influence of head structure).
5) When wedge load tests are carried out on bolts, screws and studs, the sb min calculation. 6) The maximum hardness tested at the end of bolts, screws and studs is: 250HV, 238HB or 99.5HRB. 7) The surface hardness should not be higher than the core hardness by 30 Vickers hardness values. The surface hardness of 10.9 grade should not be greater than 390HV0.3. 8) When the yield point a, cannot be determined, it is allowed to measure the specified non-proportional elongation stress p0.2 instead. The α value of 4.8, 5.8 and 6.8 grades is only for calculation, not test value.
9) The yield ratio and the specified non-proportional elongation stress 0.2 marked by the property grade are applicable to machined test pieces. Due to the influence of the test piece processing method and size, these values are different from the values measured on the actual bolts and screws. 14-7-7
Acceptance test
1) See Table 5.
Test item\index
Thread diameter d3mm
or length 12.5
2) Also includes bolts and screws with special head shape or shank structure that is weaker than the thread section strength. Qiu 5
Type A and Type B test items for acceptance
(This procedure applies to mechanical properties but not chemical properties) Type A test item
Performance level
Test method
Bulk small tensile strength ob min
Minimum hardness 2)
Maximum hardness
Maximum surface hardness
Minimum service point mi
Service strength α0.2
Guaranteed stress Sp
Fracturing torque Mn
Minimum elongation after fracture 24)
Minimum section reduction min
Wedge load)
Minimum impact absorption Aku
Head firmness"
Maximum decarburized layer
Hardness after re-tempering||tt ||Surface defects
Tensile test 1)
Hardness test 3)
Tensile test
Tensile test
Tensile test
Tensile test
Impact test 7》
Decarburization test
8.10|Retempering test 14),
8.11Surface defect test
3.6, 4.68.8, 9.8
Thread diameter ±>3mm
and length 12.5d
B:Type of test items
Performance level
Test method
Tensile test
Hardness test3)
Proof load test
Torque test5)
「Wedge load test\)
8.8Head solidity test
Decarburization test
8.10Retempering test10)
8.11Surface defect test
3.6、4.68.8、9.8
4.8、5.6
5.8、6.8
1) If the wedge load test is carried out, the tensile test is not necessary. 2) The minimum hardness is only applicable to the nominal length I<2.5d and the tensile test or torque test cannot be carried out The product to be tested (such as the shadow of the head structure). 3) Vickers, Brinell or Grignard hardness can be used for testing. In case of dispute, the Vickers hardness test shall be used as the basis for acceptance. 4) It is only applicable to bolts, screws and studs with a length of l ≥ 6d. 5) It is only applicable to bolts and screws that cannot be subjected to tension test. 6) Bolts and screws with special head types whose head structure is weaker than the strength of the thread section shall not be subjected to wedge load test. 7) According to user requirements, it is only applicable to bolts, screws and studs with a thread diameter of d16mm. 8) It is only applicable to grade 5.6.
9) The instrument is applicable to bolts and screws with a thread diameter of d<10mm and a length that is too short to allow wedge load test. 10) It is not necessary to conduct, and is only applicable to arbitration tests in case of disputes. 14—7- 8
Minimum tensile load and guaranteed load
The minimum tensile load and guaranteed load shall be as specified in Tables 6 to 9. 6
Thread specification
Stress of thread
Cross-sectional area
100000
116000
152000
185000
229000
270000
322000
1) A. See 8.2 for calculation.
121000
141000
184000
224000
278000
327000
390000
Minimum tensile load
Coarse thread
Property level
(A.Xahmin), N
Minimum tensile load
118300||t t||103000
127000
148000
193000
236000
292000
343000||tt ||410000
122000
152000
176000
115000
127000
158000||tt| |184000
239000
230000
280000
347000
408000
488000
292000
361000
425000
508000
2) For bolts used in steel structures, use 70000N, 95500N and 130000N respectively. Wrap 7
Thread specification
Thread stress
Cross-sectional area
A!'mm?
Guaranteed shear load
147000
182000
212000
674002)
920002
1250003)
159000
203000
252000
293000
275000
337000
416000
490000
586000|| tt||Coarse thread
381000
466000
576000
678000
810000
Guaranteed load (A .×S,), N
104000
141000
120000
163000
200000
255000| |tt||315000
367000
477000
583000
722000
850000
102 0000
103000
140000
192000
234000
299000
370000||tt ||431000
560000
684000
847000
997000
1200000
14—7— 9
Thread specification
Stress of thread
Cross-sectional area
Alimm?
101000
125000
147000
176000
1）A, for calculation, see 8.2.
103000
126000
156000
184000
220000
109000
142000
174000
1215000
253000
Guaranteed load
(.4.× $.).
108000
115000
134000
128000
157000
174000
213000
194000
264000
303000
273000
310000
133000
155000
202000
247000
305000||tt| |359000
489002
667003)
910002)
115000
147000
182000
212000
275000
337000
416000
490000
429000586000
371000
2) For bolts used in steel structures, use 50700N, 68800N and 94500N respectively. Table 8
Thread specifications
M10×1.25
M12×1.25
M24×2
M27×2
M30×2
M33×2
M36×3
M39×3
Thread stress
Cross-sectional area
A2)mm2
One pitch.
2)A. See 8 for calculation.2 items.
14-7—10
110000
127000
164000
205000
251000
285000||t t||340000
109000
133000
154000
198000
248000
304000
3 46000
412000
Minimum tensile load 1
114000
140000
161000
208000
261000||tt| |320000
363000
433000
Fine thread
Minimum tensile load
(A,×abmm).
108000| |tt||136000
166000
192000
248000
310000
380000
432000||tt| |515000
112000
141000
173000
200000
258000
323000
396 000
450000
536000
100000
130000
163000
200000
230000| |tt||298000
373000
457000
519000
618000
100000
134000
179000
226000
276000
319000
412000
515000
632000
7180 00
855000
748010
102000130000
159000
203000
252000
29 3004)
381000
466000
576000
678000
810000
112000
15000 0
130000
174000
225000
283000
346000
399000
516000||tt ||646000
791000
900000
112000
152000
186000
238000
29 4000
342000
445000
544000
673000
792000
947000
112400
107500
152000
204000
264000
332000
406000
469000||tt ||605000
758000
928000
1055000
1070000
1260000
Thread specification
M8 × 1
M10×1.25
(M(2×1.25]
M12 ×1.5
M20 × 1.5
M24×2||tt| |M27×2
M30×2
M36×3
M39×3
Stress of thread
Cross-sectional area
Pitch.
2) For the calculation of A, see Section 8.2.
Test method
112000
137000
156000
185000
Tensile test of machined specimens
112000| |tt||140000
171000
195000
232000
Guaranteed load
103000
119000
154000|| tt||192000||t t||236000
268000
319000
Fine thread
Proof load (A.×S),
108000
139000
174000
213000
242000
288000
Carry out tensile test on the machined specimens according to Figure 1 and GB/T228 to check the following properties:| |tt||a) tensile strength b;
b) yield point α. Or specify non-proportional elongation stress α0.2; c) Elongation after fracture as:
Lo= Lo × 100%
d) Section shrinkage rate mountain:
So= S : × 100%
If the elongation after fracture cannot be determined due to the short length of the bolt, the section reduction should be measured according to Lo≥3d. For bolts, screws and For studs, when machining the test piece, the reduction in the shank diameter should not exceed 25% of the original diameter of the test piece (about 44% of the cross-sectional area). For products of grades 4.8, 5.8 and 6.8 (cold forming) , a physical tensile test should be carried out (Clause 8.2).
Physical tensile testing of bolts, screws and studs 14900
103000
126000
146000
188000
236000||tt| |289000
329000
391000
120000
146000
16900 0
218000
273000
No. 59900
130000
163000
200000
230000
298000
373000
457000
335000
519000
381000!
453000
618000
109000
104000
139000
179000bzxz.net
226000
276000|| tt||3 19000
412000
515000
632000
121000
162000
210000
264000
323000| | tt||372000
481000
602000
738000
839000
718000
855000
Figure 1 Tensile test Machining test piece
999000
u-nominal thread diameter; do-test piece diameter (tn<thread minor diameter); b-thread length (6≥d); Lo-5do or (5.65VSo) , the initial measurement length is used to determine the elongation after fracture; Li ≥ 3d is used to determine the section shrinkage; L. The length of a straight line part (L.tuo): L,=Total length of the test piece (L.+2r+6); S--cross-sectional area before tensile test; r-fillet radius (r≥4mm); α≥0
The actual bolts, screws and studs shall be subjected to tensile tests similar to those of machined test pieces (8.1) to determine their tensile strength. The tensile strength b shall be calculated according to the stress cross-sectional area A of the thread, A. is:
147-11
-basic size of the thread pitch diameter, mm;
where d,
basic size of the thread minor diameter (d) minus 1/6 of the original triangle height (H) of the thread, that is: H
-original triangle height of the thread (H=0.866025P), H-
p-pitch, mm;
pi, yuan=1.1416.
The loads for the tensile test of bolts, screws and studs are given in Tables 6 to 9.
When testing bolts, screws and studs, the length of the thread that is subjected to the tensile load and is not screwed in should be greater than or equal to one thread diameter (1d); the end of the stud that is screwed into the body should be tightened in a special fixture. When the test tensile force reaches the tensile load specified in Table 6 or Table 8, it shall not break; when the load is greater than this value, until it breaks, the breakage should occur in the rod or the unscrewed thread length, and should not occur at the intersection of the head and the rod.
To prevent the specimen from being subjected to lateral loads, the chuck of the testing machine should be able to automatically center. During the test, the moving speed of the chuck should not exceed 25mm/min.
8.3 Torque test
For torque test, see GB/T3098.13.
This test is applicable to bolts and screws with a nominal thread diameter of 3mm≤d≤10mm and whose length is too short to be subjected to a tensile test.
8.4 Hardness test
Routine inspection is carried out after the plating or other coating of the test piece is removed and after appropriate treatment. The hardness of bolts, screws and studs shall be measured at the head, end or shank.
For all performance levels, if the high hardness is exceeded, the test shall be carried out again at a section of 1/2 radius at a thread diameter from the end, and the hardness value shall not exceed the highest hardness. In case of any dispute during acceptance, the Vickers hardness shall be used as the arbitration test.
The surface hardness shall be measured at the end or on the hexagonal plane. In order to ensure the accuracy of the measurement and maintain the original properties of the material surface, the tested part shall be ground or polished. The surface hardness shall be measured by the HV0,3 Vickers hardness test as the arbitration test.
The surface hardness value of HVO.3 shall be compared with the core hardness value of the same test piece to determine its actual control value. The surface hardness is allowed to be higher than the core hardness, and the maximum difference is 30 Vickers hardness values; otherwise, it indicates carburization.
To determine the carburization of the surface of bolts, screws or studs, the difference between the core hardness and the surface hardness of 8.8~12.9 should be used as the basis. There may be no direct conversion relationship between hardness and theoretical tensile strength. In addition to considering the theoretical maximum tensile strength, other factors (such as brittle fracture) should be considered in determining the maximum hardness value. Note: It should be distinguished whether the increase in hardness is caused by carbon or by heat treatment or surface cold work hardening.
14—7—12
Vickers hardness test
Vickers hardness test shall be in accordance with GB/T4340.1. 8.4.2 Brinell hardness test
Brinell hardness test shall be in accordance with GB/T231.
8.4.3 Rockwell hardness test
Rockwell hardness test is in accordance with GB/T230.
Proof load test of bolts, screws and studs 8.5
Proof load test consists of two main procedures: a) applying a specified proof load (Figure 2): b) measuring the permanent elongation caused by the proof load. Shear load
Figure 2 Proof load test on fasteners The probe and the center hole at the end of the fastener should be in "ball-cone" contact. 1) d, in accordance with GB/T 5277 for medium assembly series. According to the proof load given in Table 7 or Table 9, apply axial load to the specimen on the tensile testing machine and maintain it for 15s. The length of the thread that is loaded and not screwed should be one thread diameter (1d). For full-threaded specimens, the length of the thread that is loaded and not screwed should be close to the actual one thread diameter (1d). When testing studs, the end screwed into the machine body (or either end of a stud of equal length) shall be tightened in a special fixture.
To measure the permanent elongation, each end of the specimen shall be suitably machined, see Figure 2. Before and after the proof load is applied, the specimen shall be mounted in a bench-type measuring device with a spherical probe. Gloves or pliers shall be used to minimize measurement errors.
To comply with the proof load test requirements, the length of the bolt, screw or stud after the load is applied shall be the same as before the load, with an error of ±12.5μm as the allowable measurement error.
To avoid lateral loads on the specimen, the chuck of the testing machine shall be able to center automatically. During the test, the chuck movement speed shall not exceed 3mm/min. Due to certain uncertainties, such as straightness and thread neutrality (increasing measurement errors), the first application of the proof load may cause a significant elongation of the fastener. In this case, a second proof load test may be carried out with a load 3% higher than the specified value. If the length after application of this load is the same as before loading (within ±12.5μm), it should be considered to meet the requirements.5
The proof load test consists of two main procedures: a) applying a specified proof load (Figure 2): b) measuring the permanent elongation caused by the proof load. Shear Load
Figure 2 Proof Load Test on Physical Fasteners The probe should be in "ball-cone" contact with the center hole at the end of the fastener. 1) d, as specified in GB/T 5277 for medium assembly series. Apply an axial load to the specimen on a tensile testing machine according to the proof load given in Table 7 or Table 9 and maintain it for 15 seconds. The length of the thread that is loaded and not screwed should be one thread diameter (1d). For fully threaded specimens, the length of the thread that is loaded and not screwed should be close to one actual thread diameter (1d). When testing studs, the end that is screwed into the machine body (or either end of a stud of equal length) should be tightened in a special fixture.
To measure the permanent elongation, each end of the specimen should be appropriately processed, see Figure 2. Before and after the proof load is applied, the specimen shall be mounted on a bench-type measuring device with a spherical probe. Gloves or pliers shall be used to minimize measurement errors.
To comply with the proof load test requirements, the length of the bolt, screw or stud after the load is applied shall be the same as before the loading, with an error of ±12.5μm as the allowable measurement error.
To avoid lateral loads on the specimen, the chuck of the testing machine shall be able to center automatically. During the test, the chuck movement speed shall not exceed 3mm/min. Due to certain uncertainties such as straightness and thread neutrality (increasing measurement errors), the first application of the proof load may cause a significant elongation of the fastener. In this case, a second proof load test may be carried out with a load 3% higher than the specified value. If the length after this load is the same as before the loading (with an error of ±12.5μm), it shall be considered to have met the requirements.5
The proof load test consists of two main procedures: a) applying a specified proof load (Figure 2): b) measuring the permanent elongation caused by the proof load. Shear Load
Figure 2 Proof Load Test on Physical Fasteners The probe should be in "ball-cone" contact with the center hole at the end of the fastener. 1) d, as specified in GB/T 5277 for medium assembly series. Apply an axial load to the specimen on a tensile testing machine according to the proof load given in Table 7 or Table 9 and maintain it for 15 seconds. The length of the thread that is loaded and not screwed should be one thread diameter (1d). For fully threaded specimens, the length of the thread that is loaded and not screwed should be close to one actual thread diameter (1d). When testing studs, the end that is screwed into the machine body (or either end of a stud of equal length) should be tightened in a special fixture.
To measure the permanent elongation, each end of the specimen should be appropriately processed, see Figure 2. Before and after the proof load is applied, the specimen shall be mounted on a bench-type measuring device with a spherical probe. Gloves or pliers shall be used to minimize measurement errors.
To comply with the proof load test requirements, the length of the bolt, screw or stud after the load is applied shall be the same as before the loading, with an error of ±12.5μm as the allowable measurement error.
To avoid lateral loads on the specimen, the chuck of the testing machine shall be able to center automatically. During the test, the chuck movement speed shall not exceed 3mm/min. Due to certain uncertainties such as straightness and thread neutrality (increasing measurement errors), the first application of the proof load may cause a significant elongation of the fastener. In this case, a second proof load test may be carried out with a load 3% higher than the specified value. If the length after this load is the same as before the loading (with an error of ±12.5μm), it shall be considered to have met the requirements.
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.