Quenched Tempered Spring Steel Carbide Control
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Solution Overview
Problem
Current methods for producing high-strength steel wires for springs face challenges in achieving both high strength and workability, as excessive alloy elements can form coarse undissolved carbides during cold coiling, leading to fractures and limitations in spring performance.
Innovation Solution
The development of quenched and tempered steel with specific chemical compositions, including controlled amounts of C, Si, Mn, V, and N, along with additional elements like Cr, Nb, Mo, and Ti, to suppress the formation of undissolved carbides and enhance precipitation of fine carbides, ensuring high strength and coilability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If large amounts of V, Nb, and other alloy elements are added to form fine carbides, then the strength and anti-setting property are improved, but coarse undissolved carbides form during cold coiling which become factors behind fracture
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.35-0.65%, Si: 0.50-2.50%, Mn: 0.50-2.00%, Cr: 0.50-2.00%, Mo: 0.10-0.65%, B: 0.0005-0.0050%) and heat treatment parameters (quenching temperature, tempering temperature, holding time) to optimize carbide dissolution and precipitation, resolving the contradiction between strength improvement and fracture resistance
Solution Approach 2:
The patent applies preliminary action by performing quenching and tempering heat treatment before cold coiling to pre-establish the microstructure and dissolve carbides in advance, preventing the formation of coarse undissolved carbides during subsequent cold coiling operations, thus ensuring both high strength and fracture resistance
2Strength
If the spring-use steel wire increases in strength, then the hardness is improved, but the wire breaks at the time of cold coiling and cannot be formed into a spring shape
Solution Approach 1:
The patent applies preliminary action by performing quenching and tempering heat treatment before cold coiling to pre-establish the microstructure and dissolve carbides in advance, preventing the formation of coarse undissolved carbides during subsequent cold coiling operations, thus ensuring both high strength and fracture resistance
3Ease of manufacture
If suppressing the carbides to achieve workability, then the coilability is improved, but the direct strengthening of spring performance is limited
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.35-0.65%, Si: 0.50-2.50%, Mn: 0.50-2.00%, Cr: 0.50-2.00%, Mo: 0.10-0.65%, B: 0.0005-0.0050%) and heat treatment parameters (quenching temperature, tempering temperature, holding time) to optimize carbide dissolution and precipitation, resolving the contradiction between strength improvement and fracture resistance
Solution Approach 2:
The patent applies preliminary action by performing quenching and tempering heat treatment before cold coiling to pre-establish the microstructure and dissolve carbides in advance, preventing the formation of coarse undissolved carbides during subsequent cold coiling operations, thus ensuring both high strength and fracture 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
This approach allows for the production of steel wires with tensile strengths over 2000 MPa, improved coilability, and enhanced spring performance by effectively managing carbide distribution and precipitation, thereby overcoming the limitations of previous technologies.
Implementation Method 1
quenched and tempered steel for use as spring steel
Implementation Method 2
adding V, Nb, Mo, or another element to form fine carbides dissolving by quenching and precipitating by tempering
Implementation Method 3
form fine carbides dissolving by quenching and precipitating by tempering and thereby limiting the movement of dislocations
Implementation Method 4
nitridation or shot peening, the surface hardness rises and the durability during spring fatigue is remarkably improved
Implementation Method 5
nitridation or shot peening, the surface hardness rises and the durability during spring fatigue is remarkably improved
Data Source
Figure 1
Figure 2(A)~2(B)
AI summary
The present invention provides spring-use heat treated steel which is cold coiled, can achieve both sufficient atmospheric strength and coiling workability, has a tensile strength of 2000 MPa or more, and can improve the performance as a spring by heat treatment after shaping the spring, that is, heat treated steel for high strength spring containing, by mass%, C: 0.45 to 0.9%, Si: 1.0 to 3.0%, Mn: 0.1 to 2.0%, V: over 0.1 to 1.0%, N: limited to 0.007% or less, and a balance of Fe and unavoidable impurities, and satisfying, in terms of the analyzed value of the extracted residue after heat treatment, [amount of V in filtrate filtered by 0.2 µm filter (mass%)]≥[amount of V in steel (mass%)]≥0.4.