Surface-Hardened Joining Element for High-Strength Steel Bolting
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Solution Overview
Problem
Existing joining elements fail to reliably connect components made of high-strength or ultra-high-strength steel with tensile strength above 800 MPa without slug separation or element failure during high-speed bolting.
Innovation Solution
A joining element with a hardened surface layer and a softer interior, produced through surface hardening techniques like nitriding, induction hardening, or applying a harder coating, allowing for successful connection of components with tensile strengths up to 2000 MPa without slug separation or deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the joining element is made of uniform hard material to resist high-strength steel components, then the hardness and strength increase, but the ductility and impact resistance decrease causing element failure
Solution Approach 1:
The joining element features a differentiated microstructure with a hard outer zone (500-650 HV) and a softer inner core (250-350 HV). This local quality variation allows the outer surface to resist wear and deformation against high-strength steel while the softer core maintains ductility and absorbs impact energy, preventing element failure during joining operations.
Solution Approach 2:
The joining element employs a composite microstructure consisting of different steel phases: a hard outer zone with martensitic or bainitic structure and an inner core with ferritic-pearlitic structure. This composite approach combines the advantages of both hard and soft materials, achieving high surface hardness for component engagement while maintaining core ductility for impact resistance.
2Strength
If the joining element material is hardened to connect high-strength steel components, then the connection strength increases, but the notched impact work decreases leading to element failure
Solution Approach 1:
The joining element features a differentiated microstructure with a hard outer zone (500-650 HV) and a softer inner core (250-350 HV). This local quality variation allows the outer surface to resist wear and deformation against high-strength steel while the softer core maintains ductility and absorbs impact energy, preventing element failure during joining operations.
Solution Approach 2:
The joining element employs a composite microstructure consisting of different steel phases: a hard outer zone with martensitic or bainitic structure and an inner core with ferritic-pearlitic structure. This composite approach combines the advantages of both hard and soft materials, achieving high surface hardness for component engagement while maintaining core ductility for impact resistance.
3Productivity
If high-speed bolting is used to join high-strength steel components, then the productivity increases, but the joining element fails or slugs separate due to excessive forces
Solution Approach 1:
The joining element features a differentiated microstructure with a hard outer zone (500-650 HV) and a softer inner core (250-350 HV). This local quality variation allows the outer surface to resist wear and deformation against high-strength steel while the softer core maintains ductility and absorbs impact energy, preventing element failure during joining operations.
Solution Approach 2:
The joining element is pre-manufactured with a differentiated microstructure through controlled rolling or forging processes before use. This preliminary creation of the hard-soft gradient structure ensures the element is optimally prepared to withstand the high-speed bolting process and the associated impact forces, preventing failure during operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables reliable one-stage joining of high-strength steel components with increased notched impact work and ductility, tolerating larger temperature differences and mechanical loads without adverse effects on the connection.
Implementation Method 1
at least the shaft and the end region of the joining element have a hardened surface layer
Implementation Method 2
surface hardening techniques like nitriding, induction hardening
Implementation Method 3
surface hardening techniques like nitriding, induction hardening
Implementation Method 4
with increased notched impact work and ductility, tolerating larger temperature differences and mechanical loads
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The present invention relates to an joining element (1) for creating a connection between at least two components, comprising: a head (10) at a first axial end, an end region (20) at a second axial end opposite the first axial end, and a shaft (30) arranged between the end region and the head, which defines a longitudinal axis of the joining element between the first and the second axial ends. According to the invention, at least the shaft and the end region of the joining element have a hardened surface layer, such that the material of the shaft and the end region has a lower hardness in the interior compared to an adjacent surface of the surface layer.