ISO 3506-7 Specification

Mechanical properties of corrosion-resistant stainless-steel fasteners

Scope

ISO 3506-7 specifies the mechanical and physical properties of flat washers made of corrosion-resistant austenitic, ferritic and duplex stainless steels, designed to be used in bolted joints in combination with bolts, screws, studs and nuts with a specified grades and property classes in accordance with ISO 3506-1 and ISO 3506-2.
These types of washers are also be used with other stainless steel fasteners such as screws forming their own mating thread (see e.g. ISO 3506-4).
ISO 3506-6 provides general rules and additional technical information on suitable stainless steels and their properties (detailed properties of stainless steel grades, corrosion behavior with regards to pitting, crevice and intergranular corrosion, magnetic properties, etc.)
WARNING — washers conforming to the requirements of ISO 3506-7 document are tested at the ambient temperature range of 10 °C to 35 °C and are used in applications ranging from -20 °C to +150 °C; however these washers are also used outside ISO 3506-7 range down to -196 °C and up to +300 °C for specific applications. It is possible that they do not retain the specified mechanical and physical properties at lower and/or elevated temperatures. Therefore, it is the responsibility of the user to determine the appropriate choices based on the service environment conditions of the assembly.
ISO 3506-7 document applies to the following flat non-captive and captive washers with thickness from 0,2 mm to 6 mm

• plain washers (with or without knurls, ribs or chamfers);
• square washers,
• square hole washers,
• shaped plates.

This document does not specify requirements for functional properties such as weldability.

Washer thickness limits in relation to stainless steel grades and property classes

Property classes	Maximum thickness for tnom (mm)
	Austenitic					Ferritic	Duplex
	A2	A3	A4	A5	A8	F1	D2	D4	D6	D8
100HV	6	6	6	6	a	6	a
200HV	4	4	4	4	6	b	6	6	6	6
300HV	3	3	3	3	c	b	c
a This grade does not allow to get property class 100HV because the hardness resulting from work hardening is above 200 HV. b This grade does not allow to get property classes 200HV and 300HV because the hardness is lower than 200 HV. c Critical availability of flat raw material in relation to property class: thickness availability shall be checked between the purchaser and the manufacturer before ordering

ISO 3506-7 Chemical Composition

Chemical Composition For Stainless Steel Grade

Stainless steel grade		Chemical composition a (cast analysis, %) b										Other elements and notes
		C	Si	Mn	P	S	Cr	Mo	Ni	Cu	N
Auste- nitic	A2	0,10	1,00	2,00	0,050	0,030	15,0 to 20,0	— c	8,0 to 19,0	4,0	—	d, e
	A3	0,08	1,00	2,00	0,045	0,030	17,0 to 19,0	— c	9,0 to 12,0	1,00	—	5C ≤ Ti ≤ 0,80 and/ or 10C ≤ Nb ≤ 1,00
	A4	0,08	1,00	2,00	0,045	0,030	16,0 to 18,5	2,00 to 3,00	10,0 to 15,0	4,0	—	e, f
	A5	0,08	1,00	2,00	0,045	0,030	16,0 to 18,5	2,00 to 3,00	10,5 to 14,0	1,00	—	5C ≤ Ti ≤ 0,80 and/ or 10C ≤ Nb ≤ 1,00 f
	A8	0,030	1,00	2,00	0,040	0,030	19,0 to 22,0	6,0 to 7,0	17,5 to 26,0	1,50	—	—
Ferritic	F1	0,08	1,00	1,00	0,040	0,030	15,0 to 18,0	— c	1,00	—	—	g
Duplex	D2	0,040	1,00	6,0	0,040	0,030	19,0 to 24,0	0,10 to 1,00	1,50 to 5,5	3,00	0,05 to 0,20	Cr+3,3Mo+16N ≤ 24,0 h
	D4	0,040	1,00	6,0	0,040	0,030	21,0 to 25,0	0,10 to 2,00	1,00 to 5,5	3,00	0,05 to 0,30	24,0 < Cr+3,3Mo+16N h
	D6	0,030	1,00	2,00	0,040	0,015	21,0 to 23,0	2,50 to 3,5	4,5 to 6,5	—	0,08 to 0,35	—
	D8	0,030	1,00	2,00	0,035	0,015	24,0 to 26,0	3,00 to 4,5	6,0 to 8,0	2,50	0,20 to 0,35	W ≤ 1,00

ISO 3506-7 Mechanical Properties

Combination of stainless steel flat washers property classes with bolts, screws, studs and nuts in relation to their mechanical properties

Threaded fasteners in accordance with ISO 3506-1 or ISO 3506-2		Mating property class for washers
Steel group	Property class of bolts, screws, studs, regular and high nuts	100HV	200HV	300HV
Austenitic	50	RC	a	a
	70	b	RC	a
	80	c	RC	a
	100	c	b	RC
Ferritic	45	RC	a	a
	60	RC	a	a
Duplex	70	b	RC	a
	80	c	RC	a
	100	c	b	RC

Mechanical and physical properties for stainless steel flat washers

Property class		100HV	200HV	300HV
Vickers hardness, HV	min.	100	200	300
	max.	200 a	300	370

Property class marking for stainless steel washers

Property class	100HV	200HV	300HV
Marking symbol	100	200	300

Clock Face Marking system for stainless steel washers

Property class	100HV	200HV	300HV
Marking symbol	Dash at 6 o'clock position	Dash at 8 o'clock position	Dash at 10 o'clock position

ISO 3506-7 Bolting Surface Treatment Specifications

ISO 3506-7 Bolting Components Marking

Product Shall be Marked with our manufacturing trade mark "TorqBolt" or "TB" along with the designated Grade.
Grade and manufacturer’s identification symbols shall be applied to one end of studs and to the heads of bolts and screws of all sizes. (If the available area is inadequate, the grade symbol may be marked on one end and the manufacturer’s identification symbol marked on the other end.) For bolts and screws smaller than 1⁄4 in. [6 mm] in diameter and studs smaller than 3⁄8 in. [10 mm] in diameter and for 1⁄4 in. [6 mm] in diameter studs requiring more than a total of three symbols, the marking shall be a matter of agreement between the purchaser and the manufacturer.