Ti-V Steel Composition for Fracture-Split Connecting Rods
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Solution Overview
Problem
Existing non-post-heat treated steels face challenges in achieving high fatigue strength and fracture splitting performance while maintaining machinability, particularly with high V and Ti content limitations due to rare metal costs and production difficulties, and existing methods struggle with reproducibility and machinability issues.
Innovation Solution
A Ti-V-based steel composition with controlled amounts of effective Ti, V, and other elements, where the amount of effective Ti is defined by subtracting Ti used in TiN and TiS formation, and the carbon equivalent is maintained within a specific range to enhance strength, toughness, and machinability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high V and Ti content is used to achieve high strength and fracture splitting performance, then fatigue strength and fracture splitting performance are improved, but production cost increases due to rare metal costs and production difficulties
Solution Approach 1:
The patent applies parameter changes by precisely controlling the content ranges of V (0.03-0.15%) and Ti (0.05-0.20%) along with their interaction parameters (Et and Ceq). This optimized parameter combination achieves high fatigue strength and fracture splitting performance while reducing rare metal consumption and production costs compared to conventional high-V-Ti steels.
Solution Approach 2:
The patent creates a composite microstructure consisting of ferrite and perlite phases through controlled alloying. This dual-phase microstructure combines the high strength of perlite with the toughness of ferrite, achieving excellent fracture splitting performance and fatigue strength while maintaining cost-effectiveness through reduced V and Ti content.
2Strength
If high V and Ti content is used to achieve high strength and fracture splitting performance, then fatigue strength and fracture splitting performance are improved, but machinability deteriorates
Solution Approach 1:
The patent controls machinability by adjusting the Ceq parameter (0.40-0.65%) and S content (0.015-0.050%) in combination with V and Ti. This parameter optimization ensures the steel has appropriate hardness and chip-breaking characteristics for good machinability while maintaining high fatigue strength, avoiding the overly hard and difficult-to-machine condition of high-V-Ti steels.
Solution Approach 2:
The patent creates local quality differences through the ferrite-perlite dual-phase microstructure, where perlite regions provide strength and ferrite regions provide toughness and machinability. This microstructural differentiation allows the material to exhibit both high strength and good machinability in different locations and under different processing conditions.
3Productivity
If existing non-post-heat treated steel compositions are used, then production can be maintained, but fracture splitting performance and fatigue strength cannot be simultaneously optimized
Solution Approach 1:
The patent implements feedback control through the defined parameters Et (effective Ti) and Ceq (carbon equivalent), which serve as quantitative indicators to guide composition design. By using these calculated parameters rather than simple element content specifications, the patent provides a feedback mechanism to optimize the balance between fracture splitting performance, fatigue strength, and production stability.
Solution Approach 2:
The patent creates a universal composition formula that simultaneously achieves multiple functions: fracture splitting performance through controlled brittleness, high fatigue strength through optimized microstructure, and production stability through reasonable element content ranges. This multi-functional composition design eliminates the need to compromise any single performance aspect.
Data Source
AI summary
Non-post-heat treated steel contains: in mass %, C: 0.27 to 0.40%, Si: 0.15 to 0.70%, Mn: 0.55 to 1.50%, P: 0.010 to 0.070%, S: 0.05 to 0.15%, Cr: 0.10 to 0.60%, V: 0.030% or more and less than 0.150%, Ti: more than 0.10%, not more than 0.200%, Al: 0.002 to 0.050%, and N: 0.002 to 0.020%, and optionally one or more of Cu≤0.40% and Ni≤0.30%; the balance being Fe and impurities, wherein [Ti]−3.4[N]−1.5[S]<0, and 0.60<[C]+([Si]/10)+([Mn]/5)+(5[Cr]/22)+(33[V]/20) −(5[S]/7)<0.80. The steel can be used to make a high fatigue strength connecting rod for automobile engines which is fracture-split from a hot forged shape. The non-post-heat treated steel member can have vERT of 1.0 to 7.0 J/cm2, and σw≥450 MPa.