GOST R ISO 3506-2-2009 Mechanical Properties of Corrosion-Resistant Stainless Steel Fasteners. Part 2. Nuts

GOST R ISO 3506-2-2009 establishes the mechanical properties of nuts made of austenitic, martensitic and ferritic grades of corrosion-resistant stainless steels, when tested at an ambient temperature of 15°C to 25°C. Mechanical properties change as the temperature increases or decreases.

The standard applies to nuts:

• with a nominal thread diameter up to and including 39 mm;
• with triangular metric thread, with diameter and pitch to ISO 68-1, ISO 261 and ISO 262;
• of any design;
• with width across flats per ISO 272;
• with a nominal height of not less than 0.5.

This standard does not apply to nuts with special properties (locking capability, weldability) and does not establish requirements for corrosion resistance or oxidation resistance under special environmental conditions.

The standard classifies corrosion-resistant stainless steel fasteners by property class. Certain steels may be used at low temperatures down to minus 200°C, others — at high ambient temperatures up to 800°C. The effect of temperature on mechanical properties is given in Annex D.

Corrosion resistance, oxidation resistance and mechanical properties at elevated and reduced temperatures are agreed between the manufacturer and the purchaser in each specific case. The change in the risk of intergranular corrosion with increasing temperature, depending on carbon content, is shown in Annex E.

Fasteners made of austenitic stainless steels are non-magnetic under normal conditions; magnetic properties may appear after cold forming (Annex F).

Normative references

The standard references ISO 68-1, ISO 261, ISO 262, ISO 272:1982, ISO 898-2:1992, ISO 898-6:1994, ISO 3651-1, ISO 3651-2, ISO 6506:1981, ISO 6507-1:1997, ISO 6508:1986.

Designations, marking and treatment

The material designation consists of two parts separated by a hyphen: the steel grade and the property class.

The steel grade designation is the letter A (austenitic steel), C (martensitic steel) or F (ferritic steel) followed by a digit indicating the range of limit values of the chemical composition class. Stainless steels with a carbon content of not more than 0.03% are additionally marked with the letter L.

The property class designation is two digits for Type 1 nuts (0.1 of the proof stress) or three digits for low nuts, where the first digit indicates the reduced load capacity and the next two digits indicate 0.1 of the proof stress.

Designation examples:

1. Austenitic stainless steel, cold-formed, proof stress (type 1) not less than 700 N/mm² (700 MPa) — A2-70.
2. Martensitic steel, quenched and tempered, proof stress (type 1) not less than 700 N/mm² (700 MPa) — C4-70.
3. Austenitic steel, cold-formed, proof stress (low nuts) not less than 350 N/mm² (350 MPa) — A2-035.

Marking is mandatory on nuts with a nominal thread diameter of 5 mm or more and includes the steel grade and property class, as well as the manufacturer’s trademark where technically feasible. The marking is applied to only one side of the nut, either as an indentation on the bearing surface or on the side face.

Type 1 nuts	Low nuts

If the marking is made in the form of grooves and the property class is not indicated, property class 50 or 025 is implied.

All packaging must be marked with the product designation and the manufacturer’s trademark.

Unless otherwise specified, fasteners are supplied without additional treatment. Passivation is recommended to achieve maximum corrosion resistance.

Chemical composition

The chemical composition of stainless steels for fasteners is given in Table 1.

Steel class	Grade	Chemical composition, %									Footnote
		C	Si	Mn	P	S	Cr	Mo	Ni	Cu
Austenitic	A1	0.12	1	6.5	0.2	0.15-0.35	16-19	0.7	5-10	1.75-2.25
	A2	0.1	1	2	0.05	0.03	15-20	-	8-19	4
	A3	0.08	1	2	0.045	0.03	17-19	-	9-12	1
	A4	0.08	1	2	0.045	0.03	16-18.5	2-3	10-15	1
	A5	0.08	1	2	0.045	0.03	16-18.5	2-3	10.5-14	1
Martensitic	C1	0.09-0.15	1	1	0.05	0.03	11.5-14	-	1	-
	C3	0.17-0.25	1	1	0.04	0.03	16-18	-	1.5-2.5	-
	C4	0.08-0.15	1	1.5	0.06	0.15-0.35	12-14	0.6	1	-
Ferritic	F1	0.12	1	1	0.04	0.03	15-18	-	1	-
Maximum values are given unless otherwise specified. Sulphur may be replaced by selenium. If the nickel content is less than 8%, the manganese content shall be not less than 5%. If the nickel content exceeds 8%, the lower limit for copper content does not apply. Molybdenum may be present at the steel manufacturer’s discretion. If the molybdenum content affects the conditions of use of the steel, its content shall be agreed between the steel manufacturer and the purchaser. Molybdenum may be present at the steel manufacturer’s discretion. If the chromium content is less than 17%, the nickel content shall be not less than 12%. For austenitic steels with a minimum carbon content of 0.03%, the nitrogen content shall not exceed 0.22%. For stabilization, the titanium content shall be not less than 5 × %C, but not more than 0.8%, or the niobium and/or tantalum content shall be not less than 10 × %C, but not more than 1.0%. At the steel manufacturer’s discretion, the carbon content may be higher to achieve special mechanical properties, but shall not exceed 0.12%. A titanium content of not less than 5 × %C, but not more than 0.8%, is permitted. A niobium and/or tantalum content of not less than 10 × %C, but not more than 1.0%, is permitted.
Notes 1 A description of the listed stainless steel grades, including their properties and application areas, is given in Annex A. 2 Examples of stainless steels per ISO 683-13 and ISO 4954 are given in Annexes B and C respectively.

The choice of chemical composition within the specified limits is at the manufacturer’s discretion, unless the composition is agreed between the manufacturer and the purchaser.

Where there is a risk of intergranular corrosion, testing per ISO 3651-1 or ISO 3651-2 is recommended. In such cases, it is recommended to use stabilized stainless steels A3 and A5, or steels A2 and A4 with a carbon content of not more than 0.03%.

Mechanical properties

The mechanical properties of nuts shall comply with Table 2 or 3. The following are used to determine them: a hardness test (only for grades C1, C3 and C4, quenched and tempered) and a proof load test.

Table 2 — Mechanical properties of nuts made of austenitic steels

Steel class	Grade	Property class		Thread diameter range , mm	Proof stress , N/mm, not less than
		Type 1 nuts ()	Low nuts ()		Type 1 nuts ()	Low nuts ()
Austenitic	A1	50	025	39	500	250
	A2, A3	70	035	24	700	350
	A4, A5	80	040	24	800	400
For fasteners with a nominal thread diameter greater than 24 mm, mechanical properties are agreed between the purchaser and the manufacturer, while the grade and property class designations are as given in this table.

Table 3 — Mechanical properties of nuts made of martensitic and ferritic steels

Steel class	Grade	Property class		Proof stress , N/mm, not less than		Hardness
		Type 1 nuts ()	Low nuts ()	Type 1 nuts ()	Low nuts ()	HB	HRC	HV
Martensitic	C1	50	025	500	250	147-209	-	155-220
		70	-	700	-	209-314	20-34	220-330
		110	055	1100	550	-	36-45	350-440
	C3	80	040	800	400	228-323	21-35	240-340
	C4	50	-	500	-	147-209	-	155-220
		70	035	700	350	209-314	20-34	220-330
Ferritic	F1	45	020	450	200	128-209	-	135-220
		60	030	600	300	171-271	-	180-285
Quenching and tempering with a minimum tempering temperature of 275°C. Nominal thread diameter of not more than 24 mm.

Test methods

The hardness test is carried out per ISO 6506 (HB), ISO 6508 (HRC) or ISO 6507-1 (HV). In disputed cases, the Vickers hardness test (HV) is decisive for acceptance. Test methods are per ISO 898-2 and ISO 898-6. Hardness values shall be within the limits specified in Table 3.

The method for proof load testing of nuts and the evaluation criteria are per ISO 898-2 and ISO 898-6.

Annex A. Description of classes and grades of stainless steels

ISO 3506-1, ISO 3506-2 and ISO 3506-3 describe steel grades from A1 to A5, from C1 to C4, and F1.

austenitic steel	A1 to A5;
martensitic steel	C1 to C4;
ferritic steel	F1.

Information is also given on the non-standardized FA class of steels with a ferritic-austenitic structure.

Class A steels (austenitic structure). Five main grades — from A1 to A5. They are not hardenable and are generally non-magnetic. Copper may be added to the steel to improve wear resistance (Table 1).

For unstabilized steels A2 and A4, low carbon content is important: due to the affinity between chromium and carbon, chromium carbide forms instead of chromium oxide, especially at elevated temperatures (Annex E). For stabilized steels A3 and A5, the elements Ti, Nb or Ta bind the carbon, allowing the chromium oxide to fully exhibit its properties. For open-sea applications, steels with approximately 20% chromium and nickel and 4.5% to 6.5% molybdenum are required. Where the probability of corrosion is high, consultation with experts is necessary.

• A1 — for mechanical engineering; due to their high sulfur content, less corrosion-resistant than other grades in the group.
• A2 — the most commonly used; kitchen equipment, chemical industry apparatus; not suitable for non-oxidizing acids and chlorine-containing compounds (seawater, swimming pools).
• A3 — stabilized, with the properties of A2.
• A4 — acid-resistant, alloyed with molybdenum, more corrosion-resistant; in demand in the paper industry (work with sulfuric acid), partially suitable for chlorine-containing environments; also used in the food and shipbuilding industries.
• A5 — stabilized, acid-resistant, with the properties of A4.

Class F steels (ferritic structure). Grade F1 is described in ISO 3506-1/2/3. Generally not hardenable; magnetic. Used for simple equipment, with the exception of superferritic steels with a very low carbon and nitrogen content — such steels can replace A2 and A3 and be used in environments with a high chlorine content.

Class C steels (martensitic structure). Grades C1, C3, C4; can be hardened to very high strength; magnetic.

• C1 — limited corrosion resistance; turbines, pumps, knives.
• C3 — limited corrosion resistance, better than C1; pumps and valves.
• C4 — limited corrosion resistance; mechanical engineering, similar to C1.

Class FA steels (ferritic-austenitic structure). Not described in ISO 3506 or in this standard, but likely to be described in the future. Known as duplex steels. The first steels of this class had shortcomings that have been eliminated in more recent developments. Better than A4 and A5, especially in terms of strength properties; increased resistance to pitting and crevice corrosion.

Table A.1 — Chemical composition of ferritic-austenitic steels

Steel class	Chemical composition, %
	C, max	Si	Mn	Cr	Ni	Mo	N
Ferritic-austenitic	0.03	1.7	1.5	18.5	5	2.7	0.07
	0.03	1	2	22	5.5	3	0.14

Annex B. Chemical composition of stainless steels

(extracts from ISO 683-13:1986)

Steel type	Chemical composition, %														Fastener grade designation
	C	Si	Mn	P	S	N	Al	Cr	Mo	Nb	Ni	Se, min	Ti	Cu
		max
Ferritic steels
8	0.08	1.0	1.0	0.040	0.030	-	-	16.0-18.0	-	-	1.0	-	-	-	F1
8b	0.07	1.0	1.0	0.040	0.030	-	-	16.0-18.0	-	-	1.0	-	7 x % C1.10	-	F1
9c	0.08	1.0	1.0	0.040	0.030	-	-	16.0-18.0	0.90-1.30	-	1.0	-	-	-	F1
F1	0.025	1.0	1.0	0.040	0.030	0.025	-	17.0-19.0	1.75-2.50	-	0.60	-	-	-	F1
Martensitic steels
3	0.09-0.15	1.0	1.0	0.040	0.030	-	-	11.5-13.5	-	-	1.0	-	-	-	C1
7	0.08-0.15	1.0	1.5	0.060	0.15-0.35	-	-	12.0-14.0	0.60	-	1.0	-	-	-	C4
4	0.16-0.25	1.0	1.0	0.040	0.030	-	-	12.0-14.0	-	-	1.0	-	-	-	C1
9a	0.10-0.17	1.0	1.5	0.060	0.15-0.34	-	-	16.5-17.5	0.60	-	1.0	-	-	-	C3
9b	0.14-0.23	1.0	1.0	0.040	0.030	-	-	15.0-17.5	-	-	1.5-2.5	-	-	-	C3
5	0.26-0.35	1.0	1.0	0.040	0.030	-	-	12.0-14.0	-	-	1.0	-	-	-	C1
Austenitic steels
10	0.03	1.0	2.0	0.045	0.030	-	-	17.0-19.0	-	-	9.0-12.0	-	-	-	A2
11	0.07	1.0	2.0	0.045	0.030	-	-	17.0-19.0	-	-	8.0-11.0	-	-	-	A2
15	0.08	1.0	2.0	0.045	0.030	-	-	17.0-19.0	-	-	9.0-12.0	-	5 x % C0.80	-	A3
16	0.08	1.0	2.0	0.045	0.030	-	-	17.0-19.0	-	10 x % C1.0	9.0-12.0	-	-	-	A3
17	0.12	1.0	2.0	0.060	0.15-0.35	-	-	17.0-19.0	-	-	8.0-10.0	-	-	-	A1
13	0.10	1.0	2.0	0.045	0.030	-	-	17.0-19.0	-	-	11.0-13.0	-	-	-	A2
19	0.03	1.0	2.0	0.045	0.030	-	-	16.5-18.5	2.0-2.5	-	11.0-14.0	-	-	-	A4
20	0.07	1.0	2.0	0.045	0.030	-	-	16.5-18.5	2.0-2.5	-	10.5-13.5	-	-	-	A4
21	0.08	1.0	2.0	0.045	0.030	-	-	16.5-18.5	2.0-2.5	-	11.0-14.0	-	5 x % C0.80	-	A5
23	0.08	1.0	2.0	0.045	0.030	-	-	16.5-18.5	2.0-2.5	10 x % C1.0	11.0-14.0	-	-	-	A5
19a	0.030	1.0	2.0	0.045	0.030	-	-	16.5-18.5	2.5-3.0	-	11.5-14.5	-	-	-	A4
20a	0.07	1.0	2.0	0.045	0.030		-	16.5-18.5	2.5-3.0	-	11.0-14.0	-	-	-	A4
10N	0.030	1.0	2.0	0.045	0.030	0.12-0.22	-	17.0-19.0	-	-	8.5-11.5	-	-	-	A2
19N	0.030	1.0	2.0	0.045	0.030	0.12-0.22	-	16.5-18.5	2.0-2.5	-	10.5-13.5	-	-	-	A4
19aN	0.030	1.0	2.0	0.045	0.030	0.12-0.22	-	16.5-18.5	2.5-3.0	-	11.5-14.5	-	-	-	A4
1) Elements not specified in this table shall not be added to the steel without agreement between the steel manufacturer and the purchaser, except for elements intended to complete the melting process. All necessary precautions shall be taken to prevent elements that could affect the strength, mechanical properties, and workability of the steel from entering it through scrap and materials used in production. 2) Type numbers are provisional and will be revised upon publication of the corresponding standard. 3) Tantalum is designated as niobium. 4) Not per ISO 683-13. 5) (C+N) not more than 0.040%. 6) 8×(C+N)(Nb+Ti)0.80%. 7) By agreement at the time of order placement, steel may be supplied with a Mo content of 0.20%-0.60%. 8) High resistance to intergranular corrosion. 9) Stabilized steels. 10) The manufacturer may add molybdenum up to 0.70%. 11) The maximum nickel content in semi-finished products for the manufacture of seamless tubes may be increased by 0.5%.

Appendix C. Stainless steels for cold heading and stamping

(extracts from ISO 4954:1993)

Steel type (designation)			Chemical composition, %									Fastener grade desig- nation
Number	Designation	Per ISO 4954:1979	C	Si	Mn	P	S	Cr	Mo	Ni	Other
				max
	Ferritic steels
71	X 3 Cr 17 E	-	0.04	1.00	1.00	0.040	0.030	16.0-18.0		1.0		F1
72	X 6 Cr 17 E	D1	0.08	1.00	1.00	0.040	0.030	16.0-18.0		1.0		F1
73	X 6 CrMo 17 1 E	D2	0.08	1.00	1.00	0.040	0.030	16.0-18.0	0.90-1.30	1.0		F1
74	X 6 CrTi 12 E	-	0.08	1.00	1.00	0.040	0.030	10.5-12.5		0.50	Ti: 6 x % C1.0	F1
75	X 6 CrNb 12 E	-	0.08	1.00	1.00	0.040	0.030	10.5-12.5		0.50	Nb: 6 x % C1.0	F1
	Martensitic steels
76	X 12 Cr 13 E	D 10	0.90-0.15	1.00	1.00	0.040	0.030	11.5-13.5		1.0		C1
77	X 19 CrNi 16 2 E	D 12	0.14-0.23	1.00	1.00	0.040	0.030	15.0-17.5		1.5-2.5		C3
	Austenitic steels
78	X 2 CrNi 18 10 E	D 20	0.03	1.00	2.00	0.045	0.030	17.0-19.0		9.0-12.0		A2
79	X 5 CrNi 18 9 E	D 21	0.07	1.00	2.00	0.045	0.030	17.0-19.0		8.0-11.0		A2
80	X 10 CrNi 18 9 E	D 22	0.12	1.00	2.00	0.045	0.030	17.0-19.0		8.0-10.0		A2
81	X 5 CrNi 18 12 E	D 23	0.07	1.00	2.00	0.045	0.030	17.0-19.0		11.0-13.0		A2
82	X 6 CrNi 18 16 E	D 25	0.08	1.00	2.00	0.045	0.030	15.0-17.0		17.0-19.0		A2
83	X 6 CrNiTi 18 10 E	D 26	0.08	1.00	2.00	0.045	0.030	17.0-19.0		9.0-12.0	Ti: 5 x % C0.80	A3
84	X 5 CrNiMo 17 12 2 E	D 29	0.07	1.00	2.00	0.045	0.030	16.5-18.5	2.0-2.5	10.5-13.5		A4
85	X 6 CrNiMoTi 17 12 2 E	D 30	0.08	1.00	2.00	0.045	0.030	16.5-18.5	2.0-2.5	11.0-14.0	Ti: 5 x % C0.80	A5
86	X 2 CrNiMo 17 13 3 E	-	0.03	1.00	2.00	0.045	0.030	16.5-18.5	2.5-3.0	11.5-14.5		A4
87	X 2 CrNiMoN 17 13 3 E	-	0.03	1.00	2.00	0.045	0.030	16.5-18.5	2.5-3.0	11.5-14.5	N: 0.12-0.22	A4
88	X 3 CrNiCu 18 9 3 E	D 32	0.04	1.00	2.00	0.045	0.030	17.0-19.0		8.5-10.5	Cu: 3.00-4.00	A2
1) The first column gives sequential numbers. The second column gives designations in accordance with the system proposed by International Technical Committee ISO/TC 17/SC 2. The third column gives obsolete numbers per ISO 4954:1979 (revised 1993). 2) Elements not specified in this table shall not be added to the steel without agreement between the steel manufacturer and the purchaser, except for elements intended to complete the melting process. All necessary precautions shall be taken to prevent elements that could affect the strength, mechanical properties, and workability of the steel from entering it through scrap and materials used in production. 3) Not per ISO 4954. 4) Very high resistance to intergranular corrosion.

Appendix D. Mechanical properties at elevated temperatures, use at low temperatures

If bolts, screws and studs are correctly designed, the mating nuts will automatically correspond to them. Therefore, when used at elevated or low temperatures, it is sufficient to take into account the mechanical properties of the bolts, screws and studs.

The values given in the appendix are for reference only. The actual chemical environment, loading and environmental conditions may differ significantly from the reference values. For variable loads, extended periods of exposure to elevated temperatures, or a high likelihood of stress corrosion, consultation with the manufacturer is required.

Table D.1 — Effect of temperature on yield strength

Steel grade	and , %, at temperature
	100 °C	200 °C	300 °C	400 °C
A2A4	85	80	75	70
C1	95	90	80	65
C3	90	85	80	60
Note — The values apply only to property classes 70 and 80.

Table D.2 — Use of stainless steel bolts, screws and studs at low temperatures (austenitic steels only)

Steel grade	Lower limit of operating temperature for sustained exposure
A2	-200 °C
A4	bolts and screws	-60 °C
	studs	-200 °C
Due to the presence of the alloying element Mo, the stability of austenite decreases and the transition temperature shifts to higher values if the fasteners were subjected to a high degree of deformation during manufacturing.

Appendix E. Temperature-time diagram of intergranular corrosion in austenitic stainless steel grade A2

Approximate time of onset of risk of intergranular corrosion for grade A2 (18/8) steel with varying carbon content at temperatures from 550 °C to 925 °C.

Appendix F. Magnetic properties of austenitic stainless steels

Fasteners made of austenitic stainless steels are non-magnetic under normal conditions, but may exhibit magnetic properties after cold deformation.

The magnetic permeability of a material is denoted by a coefficient showing the ratio of the material’s magnetic permeability to the magnetic permeability of a vacuum. A material has low magnetic permeability if the coefficient is close to 1.

A2:	1.8;
A4:	1.015;
A4L:	1.005;
F1:	5.

Appendix DA. Information on the conformity of referenced international standards to the national standards of the Russian Federation

Designation of the referenced international standard	Degree of con- formity	Designation and title of the corresponding national standard
ISO 68-1	MOD	GOST 9150-2002 (ISO 68-1:1998) “Basic norms of interchangeability. Metric thread. Profile”
ISO 261	MOD	GOST 8724-2002 (ISO 261:1998) “Basic norms of interchangeability. Metric thread. Diameters and pitches”
ISO 262**	-	*
____________ ** Access to international and foreign documents referenced in the text, here and elsewhere, can be obtained by following the link. - Note of the database compiler.
ISO 272:1982	NEQ	GOST 24671-84 “Hexagon head bolts, screws, wood screws, and hexagon nuts. Width across flats”
ISO 898-2:1992	MOD	GOST R 52628-2006 (ISO 898-2:1992, ISO 898-6:1994) “Nuts. Mechanical properties and test methods”
ISO 898-6:1994	MOD	GOST R 52628-2006 (ISO 898-2:1992, ISO 898-6:1994) “Nuts. Mechanical properties and test methods”
ISO 3651-1**	-	*
ISO 3651-2**	-	*
ISO 6506:1981	NEQ	GOST 9012-59 “Metals. Method of Brinell hardness measurement”
ISO 6507-1:1997	IDT	GOST R ISO 6507-1-2007 “Metals and alloys. Vickers hardness test. Part 1. Test method”
ISO 6508:1986	NEQ	GOST 9013-59 “Metals. Method of Rockwell hardness measurement”
* No corresponding national standard exists. Until it is adopted, it is recommended to use the Russian translation of this international standard. The translation of this international standard is held in the Federal Information Fund of Technical Regulations and Standards. Note - This table uses the following designations for the degree of conformity of standards: - IDT - identical standards; - MOD - modified standards; - NEQ - non-equivalent standards.

Bibliography

[1] ISO 683-13:1986, Heat-treated steels, alloy steels and free cutting steels — Part 13: Wrought stainless steels.

[2] ISO 4954:1993, Steels for cold heading and cold extruding.