Weldable Steel Component Quenchability Weldability Balance
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Solution Overview
Problem
Structural steels face a trade-off between improved quenchability and weldability, as increasing quenching elements enhance quenchability but degrade weldability, and reducing quenching elements improves weldability but reduces quenchability, making it difficult to achieve both simultaneously.
Innovation Solution
A structural steel composition with specific weight percentages of elements like silicon, boron, and carbide-producing elements, along with controlled cooling and tempering processes, to enhance quenchability without compromising weldability, including a bainitic, martensitic, or martensitic-bainitic structure with 3-20% residual austenite, and a method involving austenitization, controlled cooling rates, and optional tempering to promote auto-tempering and retain austenite.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the content of quenching elements is increased to improve quenchability, then quenchability is improved, but weldability deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters by precisely controlling the content ranges of quenching elements (Mn: 1.50-3.00%, Ni: 2.00-5.00%, Cr: 1.00-4.00%, Mo: 0.10-1.00%, B: 0.0005-0.010%) and establishing specific relationships between elements (e.g., Mn+Ni/5+Cr/2+Mo≥2.0, Mn+Ni/5+Cr/2<3.5) to achieve optimal balance between quenchability and weldability
Solution Approach 2:
The patent creates a composite chemical composition system that combines multiple quenching elements (Mn, Ni, Cr, Mo, B) in specific proportions and relationships, where each element contributes to quenchability while the controlled combinations prevent excessive hardness in the HAZ, thereby resolving the contradiction between quenchability and weldability
2Ease of manufacture
If the content of quenching elements is reduced to improve weldability, then weldability is improved, but quenchability deteriorates
Solution Approach 1:
The patent establishes minimum content thresholds for quenching elements (Mn≥1.50%, Ni≥2.00%, Cr≥1.00%, Mo≥0.10%, B≥0.0005%) and specific relationship constraints (Mn+Ni/5+Cr/2+Mo≥2.0) to ensure sufficient quenchability while maintaining weldability, preventing the steel from becoming too soft during welding
3Reliability
If boron is added to improve quenchability, then quenchability is improved, but the HAZ becomes less quenching and weldability improves, limiting further improvement
Solution Approach 1:
The patent uses manganese as an intermediary element that works synergistically with boron. The controlled presence of Mn (1.50-3.00%) alongside B (0.0005-0.010%) creates a balanced quenching system where Mn provides base quenchability and B enhances it, while the combination prevents excessive HAZ hardness, resolving the saturation effect of boron alone
Solution Approach 2:
The patent creates a composite quenching system combining boron with multiple other quenching elements (Mn, Ni, Cr, Mo) in specific proportions. This composite approach distributes the quenching function across multiple elements, preventing any single element (including boron) from reaching saturation while maintaining overall quenchability and weldability balance
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 solution significantly improves quenchability without adversely affecting weldability, allowing for slower cooling and the precipitation of fine carbides, simplifying the manufacturing process while maintaining mechanical characteristics and reducing the risk of cracking during welding.
Implementation Method 1
the component is austenitized by heating at a temperature of from Ac3 to 1000° C., preferably from Ac3 to 950° C.
Implementation Method 2
it is then cooled to a temperature of less than or equal to 200° C. in such a manner that, at the core of the component, the cooling rate between 800° C. and 500° C. is greater than or equal to the critical bainitic velocity
Implementation Method 3
optionally, tempering is effected at a temperature of less than or equal to Ac1
Implementation Method 4
Between approximately 500° C. and ambient temperature and, in particular, between 500° C. and a temperature of less than or equal to 200° C., the cooling rate may optionally be slowed down, in particular in order to promote a phenomenon of auto-tempering and the retention of from 3% to 20% of residual austenite
Data Source
AI summary
The invention concerns weldable steel building components whereof the chemical composition comprises, by weight: 0.10%≦̸C≦̸0.22%, 0.50%≦̸Si≦̸1.50%, AI≦̸0.9%, 0%≦̸Mn≦̸3%, 0%≦̸Ni≦̸5%, 0%≦̸Cr≦̸4%, 0%≦̸Cu≦̸1%, 0%≦̸Mo+W/2≦̸1.5%, 0.0005%≦̸B<0.010%, N≦̸0.025%, optionally at least one element selected among V, Nb, Ta, S et Ca, in contents less than 0.3%, and/or among Ti and Zr in contents not more than 0.5%, the rest being iron and impurities resulting from preparation, the aluminium, boron, titanium and nitrogen contents, expressed in thousandths of %, of said composition further satisfying the following relationship: B≦̸⅓×K+0.5, (1) with K=Min (I*; J*), I*=Max (0; I) and J*=Max (0; J), I=Min (N; N−0.29(Ti−5)), J=Min {N; 0.5 (N 0.52 AI+√j(N 0.52 AI)2+283)}, the silicon and aluminium contents of the composition additionally verifying the following conditions: if C>0.145, then Si+AI<0.95 and whereof the structure is bainitic, martensitic or martensitic/bainitic and further comprises 3 to 20% of residual austenite.