Welded Steel Blank Filler Composition for Strong Precoated Joints
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Solution Overview
Problem
Existing methods for producing welded steel blanks with precoated sheets fail to achieve satisfactory mechanical properties, particularly in the weld joint, due to the presence of aluminum in the precoating, leading to issues like incipient cracking, altered austenitization temperatures, and reduced quenchability, which result in weakened weld joints prone to failure.
Innovation Solution
A method involving the use of a filler wire with specific carbon content (0.01-0.45 wt.%) and controlled quenching and softening factors to form a weld joint with FTWJ-0.9FTBM ≥ 0 and CWJ ≤ 0.15 wt.%, ensuring a stable hardness and reduced hardness variation across the weld joint, while maintaining a high aluminum content for corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If precoated steel sheets with aluminum-based coating are welded without prior preparation, then corrosion resistance is maintained, but intermetallic compounds form in the weld joint causing incipient cracking and reduced mechanical strength
Solution Approach 1:
The precoating is removed in advance by shot blasting or brushing before welding to prevent the formation of harmful intermetallic compounds in the weld joint, while the underlying steel substrate remains intact for subsequent welding and hot press-forming operations
Solution Approach 2:
The aluminum-based precoating layer is selectively removed from the steel substrate surface through shot blasting or brushing, extracting the harmful aluminum that would otherwise dilute into the weld pool and form brittle intermetallic compounds
2Reliability
If aluminum content in the weld joint is increased to maintain corrosion resistance, then corrosion protection is improved, but austenitization temperature increases and complete austenitization cannot be achieved
Solution Approach 1:
The precoating is removed before welding to prevent aluminum from entering the weld joint, thereby maintaining the original austenitization temperature of the steel substrate and enabling complete austenitization during hot press-forming
Solution Approach 2:
The aluminum content in the weld joint is controlled by removing the precoating, which changes the chemical composition parameters of the weld metal and allows the austenitization temperature to remain within the optimal range for complete transformation
3Reliability
If aluminum content in the weld joint is increased, then corrosion resistance is maintained, but quenchability deteriorates and martensitic structure cannot be obtained after cooling
Solution Approach 1:
The precoating is removed before welding to prevent aluminum dilution in the weld joint, preserving the quenchability of the steel and enabling the formation of martensitic structure during rapid cooling after hot press-forming
Solution Approach 2:
The chemical composition of the weld joint is modified by eliminating aluminum from the precoating, which changes the critical cooling rate and enables martensitic transformation during the cooling phase of hot press-forming
4Strength
If precoating removal is performed by brushing or laser beam, then aluminum dilution is reduced, but production cost increases due to supplementary processing steps
Solution Approach 1:
Shot blasting uses abrasive particles that are consumed during the process to remove the precoating, providing a cost-effective and simple method compared to more sophisticated laser or mechanical brushing systems
Solution Approach 2:
Shot blasting replaces complex mechanical brushing systems or expensive laser equipment with a simpler pneumatic or water-based abrasive jet system, reducing equipment cost and operational complexity while achieving effective precoating removal
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 produces welded steel blanks with improved mechanical properties, reducing the risk of failure in the weld joint and Heat Affected Zone, even with high aluminum content, thereby ensuring robustness and cost-effectiveness in manufacturing.
Implementation Method 1
butt welding the precoated sheets using a filler wire so as to form a weld joint
Implementation Method 2
the precoating comprising an intermetallic alloy layer comprising at least iron and aluminum
Implementation Method 3
heating the welded steel blank so as to obtain a fully austenitic structure in the substrates of the precoated sheets
Implementation Method 4
heating the welded steel blank so as to obtain a fully austenitic structure
Implementation Method 5
cooling the steel part in the press tool
Implementation Method 6
obtain a welded, hot press-formed and cooled steel part
Data Source
AI summary
A method for producing a welded blank (1) includes providing two precoated sheets (2), butt welding the precoated sheets (2) using a filler wire. The precoating (5) entirely covers at least one face (4) of each sheet (2) at the time of butt welding. The filler wire (20) has a carbon content between 0.01 wt. % and 0.45 wt. %. The composition of the filler wire (20) and the proportion of filler wire (20) added to the weld pool is chosen such that the weld joint (22) has (a) a quenching factor FTWJ: FTWJ−0.9 FTBM≥0, where FTBM is a quenching factor of the least hardenable substrate (3), and FTWJ and FTBM are determined: FT=128+1553×C+55×Mn+267×Si+49×Ni+5×Cr−79×Al−2×Ni2−1532×C2−5×Mn2−127×Si2−40×C×Ni−4×Ni×Mn, and (b) a carbon content CWJ<0.15 wt. % or, if CWJ≥0.15 wt. %, a softening factor FAWJ such that FAWJ≥5000, where FA=10291+4384.1×Mo+3676.9Si−522.64×Al−2221.2×Cr−118.11×Ni−1565.1×C−246.67×Mn.