Weld Seam Hardness in Tailored Blanks via Carbon Enrichment
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Solution Overview
Problem
In the production of tailored blanks for hot-formed components, the weld seam often experiences a loss of hardness due to incomplete austenite conversion and proeutectoid ferrite precipitation, leading to reduced strength compared to the base materials, especially under unfavorable cooling conditions or when the forming tool does not fit perfectly.
Innovation Solution
Applying a viscous liquid, such as mineral oil or a graphite dispersion, to the welding edges before welding, which increases the carbon content in the weld seam, allowing it to achieve a strength range of 1500 MPa to 2000 MPa after cooling and heat treatment, thereby matching or exceeding the hardness of the base materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If abrupt cooling is applied to harden the weld seam, then hardness is improved, but incomplete austenite conversion and proeutectoid ferrite precipitation occur leading to hardness loss
Solution Approach 1:
The patent applies a viscous liquid containing carbon (such as paste, oil, or graphite dispersion) to the welding edges before welding. This changes the chemical composition parameters of the weld seam by introducing additional carbon, which compensates for carbon loss during welding and provides sufficient carbon for complete austenite conversion during subsequent heat treatment, preventing proeutectoid ferrite precipitation and ensuring high hardness after cooling.
Solution Approach 2:
The carbon-containing viscous liquid is applied to the welding edges before the welding process begins. This preliminary action ensures that carbon is already present in the weld seam before welding occurs, so that during the subsequent heat treatment and cooling process, the austenite has sufficient carbon to fully convert to martensite, achieving the desired hardness without proeutectoid ferrite formation.
2Weight of moving object
If different sheet metal thicknesses and material qualities are welded together, then weight and manufacturing costs are reduced, but weld seam strength becomes inconsistent with base materials
Solution Approach 1:
The patent applies the carbon-containing viscous liquid specifically to the welding edges and joint areas, creating a localized carbon enrichment zone in the weld seam. This local quality change ensures that the weld seam achieves uniform high strength (1500-2000 MPa) that is consistent with or exceeds the strength of different base materials, even when welding together sheet metals of different thicknesses and material qualities.
3Strength
If carbon content in the weld seam is increased, then weld seam strength is improved, but excessive carbon may cause other material properties to deteriorate
Solution Approach 1:
The patent carefully controls the carbon content in the viscous liquid applied to the welding edges. The carbon content is optimized to achieve the desired weld seam strength (1500-2000 MPa) while maintaining compositional stability. The viscous liquid delivers a controlled amount of carbon that enriches the weld seam to the optimal level without causing excessive carbon accumulation that would lead to brittleness or other property deterioration.
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 method enhances the weld seam's strength and hardness, ensuring it remains at least identical to, and often surpasses, the strength of the connected steel blanks, even after hot forming, by introducing carbon into the molten weld pool and controlling its distribution for improved hardening.
Implementation Method 1
By introducing at least one component that increases the strength of the weld seam to be produced via at least one of the steel sheet edges defining the joint joint into the molten weld pool
Implementation Method 2
By specifically influencing the welding process, in particular by abrupt cooling of the weld seam with water after the joining process, the weld seam is hardened
Implementation Method 3
heating to a temperature above the austenitization temperature
Implementation Method 4
The sheet metal blanks are usually joined as a butt joint using laser welding
Data Source
Figure 1~2
AI summary
The invention relates to a method for producing sheet steel products, wherein steel blanks or steel strips (8, 9) of different thicknesses and/or material grades are welded to each other along a butt joint (7) formed by edges of the steel blanks or steel strips (8, 9). In order that the welding seam (10) of such a sheet steel product does not lose the hardened microstructure obtained by abrupt cooling during warm forming while heating to austenization temperature, according to the invention, a viscous fluid, in particular a paste, or a solid, powdered, or aerosol material is at least partially applied to at least one welding edge of the steel blanks or steel strips (8, 9) to be welded to each other before the welding process, said paste or material comprising at least one component increasing the strength of the welding seam (10) to be generated. The invention further relates to a correspondingly implemented sheet steel product.