Spot-Welded Joint Structure for High-Hardness Steel Strength
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing spot-welded joints using high-strength steel members with a Vickers hardness of 530 HV or higher suffer from low tensile shear strength (TSS) due to embrittlement caused by high carbon content.
Innovation Solution
A spot-welded joint design that includes a high-strength steel sheet portion with a Vickers hardness of 530 HV or higher, a nugget that joins the steel portions, and a corona bond formed without a coating layer, with an oxygen concentration of 15.0 mass % or lower in the corona bond.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the oxygen concentration in the corona bond is reduced to prevent embrittlement, then the tensile shear strength is improved, but the manufacturing complexity increases due to the need for precise oxygen concentration control
Solution Approach 1:
The invention performs preliminary action by specifying the oxygen concentration requirement (15.0 mass % or lower) in the corona bond region before the spot welding process. This allows manufacturers to control oxygen concentration during steel sheet production or surface treatment, rather than attempting to control it during the welding process itself, thereby reducing manufacturing complexity.
2Strength
If a coating layer is removed from the corona bond region to achieve low oxygen concentration, then the tensile shear strength is improved, but the ease of manufacture decreases due to additional surface treatment steps
Solution Approach 1:
The invention applies local quality by requiring no coating layer specifically in the corona bond region, while allowing coating layers on other parts of the steel sheets. This localized approach minimizes the impact on manufacturing by only affecting a small specific area rather than requiring complete removal of coating from entire surfaces.
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
The proposed solution significantly improves the tensile shear strength (TSS) of the spot-welded joint while maintaining the high hardness of the steel members, effectively addressing the embrittlement issue.
Implementation Method 1
a nugget that joins the high-strength steel sheet portion and another steel sheet portion
Implementation Method 2
a corona bond which is formed in a ring shape around the nugget in a plan view in a direction perpendicular to a surface of the high-strength steel sheet portion and which solid-phase-joins the high-strength steel sheet portion and the other steel sheet portion
Data Source
AI summary
A spot-welded joint according to an aspect of the present invention includes: a plurality of steel sheet portions including a high-strength steel sheet portion having a Vickers hardness of 530 HV or higher; a nugget joining the high-strength steel sheet portion and another steel sheet portion of the plurality of steel sheet portions; and a corona bond which is formed in a ring shape around the nugget in a plan view in a direction perpendicular to a surface of the high-strength steel sheet portion and at which solid-phase joining is performed between the high-strength steel sheet portion and the other steel sheet portion. A coating layer is not present in a region where the corona bond is present, and an oxygen concentration of the corona bond at a position 50 μm apart outward from an outer circumference of the nugget in the plan view is 15.0 mass % or lower.