GOST 25556-82 Set Screws. Mechanical Properties and Test Methods

GOST 25556-82 applies to set screws and similar fasteners made of carbon or alloy steel with a nominal thread diameter from 1.0 to 39 mm, not subject to tensile loading.

The standard does not apply to set screws and similar fasteners with special requirements for weldability, corrosion resistance, operation at temperatures above plus 300°C (plus 250°C for free-cutting steel) and below minus 50°C.

SET SCREWS	GOST 25556-82
Mechanical properties and test methods
Set screws Mechanical properties and test methods

1. Mechanical properties

By mechanical properties, set screws are divided into property classes specified in Table 1.

Table 1

Screw property class	14H	22H	33H	45H
Vickers hardness, HV, min	140	220	330	450

The property class designation consists of the minimum Vickers hardness value divided by 10, and the letter H — the conventional symbol for hardness.

Set screws are made of carbon steel meeting the requirements of Table 2.

Table 2

Screw property class	Heat treatment of the screw	Content, %
		Carbon		Phosphorus, max	Sulfur, max
		max	min
14H	-	0.50	-	0.11	0.15
22H	Quenching and tempering	0.50	-	0.05	0.05
33H	Same	0.50	-	0.05	0.05
45H	-	0.50	0.19	0.05	0.05

For screws of property class 14H, free-cutting steel may be used with lead content not exceeding 0.35%, phosphorus not exceeding 0.11%, sulfur not exceeding 0.34%.

For square-head screws of property class 14H, carburizing is permitted.

For screws of property classes 22H, 33H and 45H, steel with a maximum lead content of 0.35% may be used.

For screws of property classes 22H, 33H, 45H, steel containing one or more alloying elements — chromium, nickel, molybdenum, vanadium or boron — may be used.

For screws of property class 45H, another material may be used provided the torsion test results per clause 2.3 are satisfactory.

At normal temperature, the mechanical properties of screws must conform to those specified in Table 3. For screws of property class 22H, exceeding the upper hardness limit by 10% is permitted.

Table 3

Parameter	Parameter value for screws of property class
	14H	22H	33H	45H
Hardness by:
Vickers HV	140 to 290	220 to 300	330 to 440	450 to 560
Brinell HB	133 to 276	209 to 285	314 to 418	-
Rockwell:
HRB	75 to 105	min 95	-	-
HRCe	-	max 30	33 to 44	45 to 53
Height of non-decarburized thread zone, mm, min	-
Depth of complete thread decarburization, mm, max	-	0.015	0.015	**

* h — screw thread profile height.

** For screws of property class 45H, complete decarburization is not permitted.

Steel grades used for manufacturing set screws are given in the appendix.

2. Test methods

The hardness of set screws is measured on the end face of the screw, as close to the center as possible. The hardness of screws with a drilled end is measured on the annular surface of the end face.

If the maximum hardness value is exceeded, a repeat measurement is taken on the cross-section of the screw at a distance of 0.5 mm from the end face. In disputed cases, the Vickers hardness measurement is decisive.

Instead of checking the hardness of property class 14H screws, it is permitted to check the hardness of the starting material.

The hardness of screws is measured:

• by Vickers — according to GOST 2999;
• by Brinell — according to GOST 9012;
• by Rockwell — according to GOST 9013 and GOST 8.064.

The depth of the decarburized layer is measured by microscopic examination according to GOST 1759.0, GOST 1759.1, GOST 1759.2, GOST 1759.4. The values of complete decarburization depth must conform to those specified in Table 3, and the values of the height of the non-decarburized thread zone — to Table 3 or 4.

Table 4, mm

Thread pitch	Thread profile height	Value of non-decarburized thread zone height, min, for screw property class
		22H	33H	45H
0.5	0.307	0.154	0.205	0.230
0.6	0.368	0.184	0.245	0.276
0.7	0.429	0.215	0.286	0.322
0.8	0.491	0.245	0.327	0.368
1	0.613	0.307	0.409	0.460
1.25	0.767	0.384	0.511	0.575
1.5	0.920	0.460	0.613	0.690
1.75	1.074	0.537	0.716	0.806
2	1.227	0.614	0.818	0.920
2.5	1.534	0.767	1.023	1.151
3	1.840	0.920	1.227	1.380
3.5	2.147	1.074	1.431	1.610
4	2.454	1.227	1.636	1.841

The torsion test for set screws with a hex socket of property class 45H is carried out according to the diagram shown.

Set screw 1 is screwed into the threaded hole (thread tolerance — 5H) of control plate 2 until it bears against screw 3, screwed in from the other side of the plate; the upper surface of the test screw must be recessed into the control plate.

The hardness of the control plate must be at least HRCe 50; the hardness of screw 3 must be HV 450…570.

A hex insert 4 is used to apply the torque, with a tolerance on the width across flats S of h9, a circumscribed circle diameter e ≥ 1.13 S min, and a hardness of HRCe 55…60. The insert must engage the hex socket of the test screw to its full depth.

Screws must withstand the torque specified in Table 5.

Table 5, mm

Nominal thread diameter	Length of test screw, min				Torque, Nm
	with flat end	with drilled end	with conical end	with cylindrical end
3	4	4	5	5	0.9
4	5	5	6	6	2.5
5	5	6	8	8	5
6	8	8	8	8	8.5
8	8	10	10	10	20
10	10	12	12	12	40
12	16	16	16	16	65
16	20	20	20	20	160
20	20	25	25	25	310
24	25	30	30	30	520

After testing, screws must show no cracks, chipping or other damage.

Appendix (recommended). Steel grades used for manufacturing set screws

Property class	Steel grade	Standard number
14H	10.20.30.35.45	GOST 1050 GOST 10702
22H	35, 45, 35Kh, 38KhA	GOST 1050 GOST 10702
33H	35, 45, 40KhN2MA	GOST 1050 GOST 10702
45H	45, 40Kh, 45Kh, 35Kh, 38KhA, 40KhN, 40KhN2MA	GOST 10702 GOST 4543

Informational data

1. Developed and submitted by the Ministry of Machine Tool and Tool Industry.
2. Approved and put into effect by Decree No. 5171 of the USSR State Committee for Standards dated 28.12.82.
3. The standard fully complies with ST SEV 3679-82.
4. The standard fully complies with international standard ISO 898-5-1980.
5. Introduced for the first time.
6. Referenced normative-technical documents:

Designation of the referenced regulatory document	Clause number, appendix
GOST 8.064-94	2.1
GOST 1050-88	Appendix
GOST 1759.0-87	2.2
GOST 1759.1-82	2.2
GOST 1759.2-82	2.2
GOST 1759.4-87	2.2
GOST 2999-75	2.1
GOST 4543-71	Appendix
GOST 9012-59	2.1
GOST 9013-59	2.1
GOST 10702-78	Appendix

7. Edition of 2006 with Amendment No. 1, approved in August 1987 (IUS 12-87).