Ultra High Tensile Strength Fasteners
During the last 5 years a new generation of fasteners have entered the market in Europe; Ultra High Tensile Strength Fasteners (ultimate tensile strength exceeding 1300MPa). The driving force behind the development is engine down-sizing and the fact that current grade 12.9 is not strong enough and most often not considered safe enough to use, due to risk of hydrogen induced breakage.
Ultra high tensile strength fasteners however, are not unique nor new in any way. Literature, lists several material options for fasteners which by far can exceed 1300MPa. The main difference of those known technologies and our new generation of fasteners is that the new development is cost efficient and designed to stay in line with current generations of fasteners for features like microstructure, ultimate tensile strength and yield point. Plus the fact that the material is designed to resist hydrogen induced damage.
The steel applied is similar to the alloy steels specified in ISO898-1 but with one important difference: carbide formers (carbide formers are elements which reacts strong with carbon and forms alloy carbides) are added to the steel. Carbide formers make it possible to regulate and minimize the grain structure of the austenite and to create a dispersion of fine carbides inside the martensite. This new steel will achieve strength and toughness via the same mechanisms as the traditional high strength grades as it also consists of quenched and tempered martensite. However, In addition to the features of normal steel, the fine austenite structure will add extra strength and toughness, and the fine alloy carbides will add extra strength and resistance to hydrogen embrittlement.
- Fasteners for high load applications (> 1300 MPa)
- Ultra high strength material without hydrogen embrittlement
- Down sizing of constructions
- Reduction of weight
- Supporting emission reduction programmes
- Mechanical properties in line with ISO898-1