Hot-Rolled Steel High Strength Weldability
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Solution Overview
Problem
Existing hot-rolled steel products with high yield strength lack adequate weldability and mechanical properties when welded, particularly in the heat-affected zone (HAZ), leading to potential fracture and reduced toughness.
Innovation Solution
A hot-rolled steel with a specific chemical composition, including carbon, manganese, molybdenum, vanadium, and nickel, combined with a manufacturing process involving austenitizing, hot-rolling, direct quenching, and temper annealing, to achieve high strength, toughness, and ductility, while preventing softened zones in welded seams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high carbon content steel is used to achieve high base material strength, then strength increases, but toughness decreases
Solution Approach 1:
The patent optimizes the carbon content parameter to a specific range (0.18-0.34%) rather than using high carbon content, and combines it with controlled amounts of alloying elements (Mn: 0.50-1.40%, Cr: 0.20-0.70%, Mo: 0.30-0.90%, Ni: 0.50-2.40%) to achieve the desired strength-toughness balance through parameter optimization
Solution Approach 2:
The patent creates a composite alloy system combining multiple elements (C, Si, Mn, Cr, Mo, Nb, Ni, V, Ti, Al, B) that work synergistically to achieve both high strength and toughness, rather than relying on carbon alone
2Strength
If high strength hot-rolled steel is used, then base material strength increases, but weldability deteriorates due to softened zones in welded seams
Solution Approach 1:
The patent specifies precise compositional parameters including C: 0.18-0.34%, Mn: 0.50-1.40%, Cr: 0.20-0.70%, Mo: 0.30-0.90%, and processing parameters (austenitizing temperature, quenching temperature, tempering temperature) to achieve high strength while maintaining weldability by preventing excessive softening in the heat affected zone
Solution Approach 2:
The patent uses controlled amounts of alloying elements that provide the necessary hardenability and strength, avoiding excessive alloying that would compromise weldability, achieving a balance where the steel can be welded without requiring extensive post-weld heat treatment
3Strength
If high strength steel is used, then base material strength increases, but fracture resistance in welded seams decreases
Solution Approach 1:
The patent optimizes the composition parameters (C: 0.18-0.34%, Mn: 0.50-1.40%, Cr: 0.20-0.70%, Mo: 0.30-0.90%, Ni: 0.50-2.40%) and heat treatment parameters to ensure that the heat affected zone maintains sufficient strength and toughness to prevent fracture, with the alloying elements promoting strength in the HAZ without creating brittle microstructures
Solution Approach 2:
The patent converts the potential harm of high strength steel creating soft zones in welded seams into a benefit by using specific alloying elements (Mn, Cr, Mo, Ni) that promote hardenability and strength in the heat affected zone, ensuring that the HAZ is not weaker than the base material and fracture occurs away from the fusion line
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 results in hot-rolled steel with a yield strength of at least 1100 MPa, impact toughness of 34 J/cm² or more, and ductility of 8% or higher, maintaining these properties in both the as-produced and welded states, with fracture occurring away from the fusion line, ensuring improved weldability and structural integrity.
Implementation Method 1
heating a steel slab to an austenitizing temperature
Implementation Method 2
quenching
Implementation Method 3
tempering
Data Source
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AI summary
Hot-rolled steel having a yield strength (Rp0.2) of at least 1100 MPa along and/or transverse to a rolling direction which has a chemical composition containing (in mass-%): C: 0.10 - 0.2, Si: 0 - 0.7, Mn: 1.1 - 2.2, Nb: 0 - 0.06, Ti: 0 - 0.15, V: more than 0.03 and ≤ 0.25, Al: 0.01 - 0.15, B: 0.0005 - 0.010, Cr: 0. 1 - 1.7, Mo: 0.15 - 0.8, Cu: 0 - 1.5, Ni: 0.3 - 2.5, P: 0 - 0.015, S: 0 - 0.008 Zr: 0 - 0.2, Ca: 0 - 0.004, preferably N 0-0.01, the balance Fe and unavoidable impurities, whereby a) when 0.1 < C < 0.11 then Mn ≥ 1.6 and V > 0.14 and Mo ≥ 0.5 (in mass-%), b) when 0.11 ≤ C < 0.125 then Mn ≥ 1.45 and V ≥ 0.13 and Mo ≥ 0.35 (in mass-%), c) when 0.125 ≤ C < 0.15, then Mn ≥ 1.35 and V ≥ 0.12 and Mo ≥ 0.20 (in mass-%), and d) when C ≥ 0.15 and V > 0.11, then Mn ≥ 1.3 and Mo ≥ 0.15 (in mass-%) or when C ≥ 0.15 and V 0.03 - 0.11, then Mn > 1.3 and Mo > 0.15 and Nb > 0.02 and Cr+Cu+Ni >1.4 (in mass-%).