How to choose the material of bolts production

The mechanical properties of bolts are affected by the raw materials and heat treatment. Generally, the raw materials have a greater impact on the properties of bolts because the properties of the raw materials determine the upper limit of heat treatment. For example, raw materials without Cr can never achieve the tensile strength of a 10.9 grade bolt.

Generally, when customers do not have specific requirements, we recommend determining the raw materials for bolt production based on the customer’s usage scenario. For example, in the construction industry, it is recommended to use bolts of grade 8.8 or higher for steel structures, and in the automotive industry, bolts of grade 10.9 or higher are recommended for connections.

When customers have specific requirements for the bolt grade, we typically choose bolts according to the ISO898 standard for metric bolts.

The following are the requirements for bolt raw materials in ISO898:

Property class	Material and heat treatment	Chemical composition limit					Tempering temperature
		(cast analysis, %)a
		C		P	S	B^b	°C
		min.	max.	max.	max.	max.	min.
4.6^{c d}	Carbon steel or carbon steel with additives		0,55	0,050	0,060	Not specified	—-
4.8^d		—
5.6^c		0,13	0,55	0,050	0,060
5.8^d		—	0,55	0,050	0,060
6.8^d		0,15	0,55	0,050	0,060
8.8^f	Carbon steel with additives (e.g. Boron or Mn or Cr) quenched and tempered	0,15e	0,40	0,025	0,025	0,003	425
	or
	Carbon steel quenched and tempered
	or	0,25	0,55	0,025	0,025
	Alloy steel quenched and tempered	0,20	0,55	0,025	0,025
9.8^f	Carbon steel with additives (e.g. Boron or Mn or Cr) quenched and tempered	0,15e	0,40	0,025	0,025	0,003	425
	or
	Carbon steel quenched and tempered
	or	0,25	0,55	0,025	0,025
	Alloy steel quenched and tempered	0,20	0,55	0,025	0,025
10.9^f	Carbon steel with additives (e.g. Boron or Mn or Cr) quenched and tempered	0,20e	0,55	0,025	0,025	0,003	425
	or
	Carbon steel quenched and tempered
	or	0,25	0,55	0,025	0,025
	Alloy steel quenched and tempered	0,20	0,55	0,025	0,025
12.9^{f h} ⁱ	Alloy steel quenched and tempered	0,30	0,50	0,025	0,025	0,003	425
12.9^{f h i}	Carbon steel with additives (e.g. Boron or Mn or Cr or Molybdenum) quenched and tempered	0,28	0,50	0,025	0,025	0,003	380
a In case of dispute, the product analysis applies.
b Boron content can reach 0,005 %, provided non-effective boron is controlled by the addition of titanium and/or aluminium.
c For cold forged fasteners of property classes 4.6 and 5.6, heat treatment of the wire used for cold forging or of the cold forged
fastener itself may be necessary to achieve required ductility.
d Free cutting steel is allowed for these property classes with the following maximum sulfur, phosphorus and lead contents:S: 0,34 %; P: 0,11 %; Pb: 0,35 %.
e In case of plain carbon boron steel with a carbon content below 0,25 % (cast analysis), the minimum manganese content shall be 0,6 % for property class 8.8 and 0,7 % for property classes 9.8 and 10.9.
f For the materials of these property classes, there shall be a sufficient harden ability to ensure a structure consisting of
approximately 90 % martensite in the core of the threaded sections for the fasteners in the “as-hardened” condition before tempering. g This alloy steel shall contain at least one of the following elements in the minimum quantity given: chromium 0,30 %, nickel 0,30 %, molybdenum 0,20 %, vanadium 0,10 %. Where elements are specified in combinations of two, three or four and have alloy contents less than those given above, the limit value to be applied for steel class determination is 70 % of the sum of the individual limit values specified above for the two, three or four elements concerned.
h Fasteners manufactured from phosphated raw material shall be dephosphated before heat treatment; the absence of white phosphorus enriched layer shall be detected by a suitable test method.
i Caution is advised when the use of property class 12.9/12.9 is considered. The capability of the fastener manufacturer, the service conditions and the wrenching methods should be considered. Environments can cause stress corrosion cracking of fasteners as processed as well as those coated.

If you have other question about the bolts production, pls feel to contact us.

Sherry Cen

JMET CORP., Jiangsu Sainty International Group

Address: Building D, 21, Software Avenue, Jiangsu, China

Tel. 0086-25-52876434

WhatsApp:+86 17768118580

E-mail [email protected]