Din931 Grade 8.8

Class 8.8 Bolts

Description

A hex bolt with metric thread pitch made from medium carbon steel and heat-treated. Grade-A bolts are the preferred style for most applications. Grade-B bolts have looser tolerances and can be manufactured in a cold or hot-forging process.

Applications/Advantages

Has greater tensile strength than Class 4.6, 4.8 and 5.8 bolts.

Material

Class 8.8 bolts can be made from a carbon steel with additives (such as Boron, Manganese or Chromium) which conforms to the

following chemical composition-- Carbon: 0.15-0.40%; Phosphorus: 0.035% maximum; Sulfur: 0.035% maximum. In case of plain carbon boron alloyed steel with a carbon content of less than 0.25% (ladle analysis), the minimum Manganese content shall be 0.6%

Class 8.8 bolts can be made from a carbon steel which conforms to the following chemical composition-- Carbon: 0.25-0.55%;

Phosphorus: 0.035% maximum; Sulfur: 0.035% maximum.

Heat Treatment

Class 8.8 bolts shall be heat treated by quenching in a liquid medium from above the transformation temperature and reheating to a tempering temperature of 425°C.

Core Hardness For dia less or equal to 16mm

Rockwell C22 - 32 (Vickers HV 250 - 320)

For diameters greater than 16mm

Rockwell C23 - 34 (Vickers HV 255 - 335)

Surface Hardness

Shall not be more than 30 Vickers points above the measured core hardness on the product

Proof Load For dia less or equal to 16mm

640 N/mm2 minimum

For diameters greater than 16mm

660 N/mm2 minimum

Tensile Strength For dia less or equal to 16mm

800 N/mm2 minimum

For diameters greater than 16mm

830 N/mm2 minimum

Elongation

12% minimum

Plating

Zinc,HDG,Plain,Dacrotized,Teflon,Colorful Dye