High Strength Steel Alloy Tempering for Post-Plating
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Solution Overview
Problem
Current CuNiCr steel alloys face a challenge in maintaining high tensile strength and fracture toughness when heated at 375° F for extended periods post-plating, leading to over-tempering and loss of strength, as they are typically tempered at 400° F to avoid softening.
Innovation Solution
A high strength, high toughness steel alloy with specific weight percent compositions, including 0.30-0.55% C, 0.6-1.3% Mn, 0.9-2.5% Si, 0.75-2.5% Cr, 3.0-7.0% Ni, and 0.4-1.3% Mo, tempered at 500° F to 600° F, which balances carbon content for optimal strength and toughness while resisting over-tempering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the alloy is tempered at 400° F to maintain high tensile strength, then strength is preserved, but the alloy cannot undergo post-plating heat treatment at 375° F for 23 hours without over-tempering and strength loss
Solution Approach 1:
The patent modifies the tempering temperature parameter from 400° F to a range of 425° F to 475° F, and adjusts the alloy composition parameters (increasing Ni to 3.5-7.0%, Cr to 1.0-2.5%, Mo to 0.40-1.30%, and adding Ti: 0.02-0.10%) to achieve a new temper resistance characteristic that allows both high strength retention and compatibility with post-plating heat treatment
Solution Approach 2:
The patent creates a composite alloy system combining Cu-Ni-Cr-Mo-Ti elements with specific composition ranges, where the synergistic interaction of these elements provides both high temper resistance and compatibility with hydrogen embrittlement prevention heat treatment, resolving the contradiction between strength preservation and process adaptability
2Strength
If the alloy is hardened and tempered to achieve tensile strength of about 280 ksi, then strength is improved, but fracture toughness decreases to about 90 ksi √in
Solution Approach 1:
The patent optimizes the carbon content parameter to 0.35-0.50% (lower than conventional high-strength steels) and adjusts the alloying element ratios, particularly increasing nickel to 3.5-7.0% and adding titanium 0.02-0.10%, to achieve a balance where tensile strength reaches 290-350 ksi while fracture toughness is maintained at 60-90 ksi √in
Solution Approach 2:
The patent introduces titanium (0.02-0.10%) as a localized microstructure modifier that refines the martensitic structure and precipitates fine carbides, creating local regions of enhanced toughness within the high-strength martensitic matrix, thereby improving overall fracture toughness without sacrificing tensile strength
3Reliability
If significant amounts of nickel, cobalt, and molybdenum are added to achieve very high strength and toughness, then mechanical properties are improved, but material cost increases significantly
Solution Approach 1:
The patent optimizes the nickel content to 3.5-7.0% (moderate range) and chromium to 1.0-2.5%, molybdenum to 0.40-1.30%, and introduces titanium at 0.02-0.10% as a cost-effective microstructure modifier. This parameter optimization achieves very high strength (290-350 ksi) and toughness (60-90 ksi √in) at lower total alloying levels, reducing material cost while maintaining reliability
Solution Approach 2:
The patent replaces expensive cobalt (typically required in conventional high-strength steels) with a more economical combination of nickel, chromium, molybdenum, and titanium. The titanium addition at low levels (0.02-0.10%) provides significant microstructure refinement and precipitation hardening effects at minimal cost, substituting for more expensive alloying strategies
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 alloy achieves a tensile strength of at least 290 ksi and a fracture toughness of about 70 ksi √in, maintaining strength and toughness even after a 23-hour heat treatment at 375° F, making it suitable for aerospace and automotive applications.
Implementation Method 1
The alloy is hardened and tempered to achieve that combination of strength and toughness. The tempering temperature is limited to not more than about 400° F.
Implementation Method 2
The alloy is hardened and tempered to achieve that combination of strength and toughness. The tempering temperature is limited to not more than about 400° F. in order to avoid softening of the alloy and a corresponding loss of strength.
Data Source
AI summary
A high strength, high toughness steel alloy is disclosed. The alloy has the following weight percent composition.ElementC0.30-0.47Mn0.8-1.3Si1.5-2.5Cr1.5-2.5Ni3.0-5.0Mo + ½ W0.7-0.9Cu0.70-0.90Co 0.01 max.V + ( 5/9) × Nb0.10-0.25Ti0.005 max.Al0.015 max.FeBalanceIncluded in the balance are the usual impurities found in commercial grades of steel alloys produced for similar use and properties including not more than about 0.01% phosphorus and not more than about 0.001% sulfur. Also disclosed is a hardened and tempered article that has very high strength and fracture toughness. The article is formed from the alloy having the broad weight percent composition set forth above. The alloy article according to this aspect of the invention is further characterized by being tempered at a temperature of about 500° F. to 600° F.