Thick Steel Microstructure for Hydrogen-Induced Cracking Resistance
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Solution Overview
Problem
Existing steel materials for pressure vessels, particularly those with thicknesses of 100 to 300 mm and tensile strengths of 500 MPa, lack sufficient hydrogen-induced cracking resistance, especially when exposed to hydrogen sulfide environments.
Innovation Solution
A steel material composition with specific weight percentages of elements such as carbon, silicon, manganese, aluminum, phosphorus, sulfur, niobium, vanadium, molybdenum, copper, nickel, titanium, chromium, and calcium, combined with a manufacturing process involving multiple heating and rolling stages to achieve a ferrite structure with 70% area ratio and a retained pearlite structure, resulting in a maximum pore size of 1 μm or less and enhanced hydrogen-induced cracking resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional steel material technologies are applied to thick steel sheets (100 to 300 mm) with tensile strength of 500 MPa, then structural stability is improved, but hydrogen-induced cracking resistance is insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.10-0.25%, Si: 0.05-0.50%, Mn: 1.0-2.0%, Al: 0.005-0.1%, P: ≤0.010%, S: ≤0.0015%, Nb: 0.001-0.03%, V: 0.001-0.03%, Mo: 0.01-0.15%, Cu: 0.01-0.50%, Ni: 0.05-0.50%) and processing parameters (heating temperatures, rolling reduction rates, cooling rates) to achieve both structural stability and hydrogen-induced cracking resistance in thick steel sheets
Solution Approach 2:
The patent creates a composite microstructure consisting of ferrite matrix with dispersed pearlite colonies and fine precipitates of NbC, VC, and Mo2C. This composite structure at the microlevel provides both the structural stability needed for thick sections and the hydrogen-induced cracking resistance required for reliability
2Stability of the object's composition
If carbon equivalent is reduced to secure structural stability, then welding zone stability is improved, but hydrogen-induced cracking resistance becomes stricter to achieve
Solution Approach 1:
The patent maintains low carbon equivalent (Ceq ≤ 0.35%) for welding zone stability while achieving hydrogen-induced cracking resistance through optimized alloy composition parameters, particularly the balanced addition of microalloying elements (Nb, V, Mo) and control of impurity elements (P, S)
Solution Approach 2:
The patent uses microalloying elements (Nb, V, Mo) that form fine precipitates copying the strengthening effect of higher carbon content without increasing carbon equivalent, thereby maintaining both welding stability and cracking resistance
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 steel material achieves excellent hydrogen-induced cracking resistance, low-temperature toughness, and meets the requirements for pressure vessels with a hydrogen-induced cracking length ratio of 5% or less and Charpy impact absorption energy of 250 J or more at -46°C.
Implementation Method 1
Hydrogen atoms, generated by the corrosion of the steel material, permeate and diffuse into the steel material to be present in an atomic state in the steel material
Implementation Method 2
The steel material has a ferrite structure of 70 area % and a retained pearlite structure as a microstructure
Data Source
AI summary
A steel material showing excellent hydrogen-induced cracking resistance according to an aspect of the present invention comprises, in weight %, 0.10-0.25% of C, 0.05-0.50% of Si, 1.0-2.0% of Mn, 0.005-0.1% of Al, 0.010% or less of P, 0.0015% or less of S, 0.001-0.03% of Nb, 0.001-0.03% of V, 0.01-0.15% of Mo, 0.01-0.50% of Cu, 0.05-0.50% of Ni, and the remainder being Fe and unavoidable impurities, and has a thickness of 100-300 mm. The maximum size of pores formed inside can be 1 μm or less.