Fracture Split Connecting Rod Rolled Material
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Solution Overview
Problem
Conventional connecting rods face challenges in achieving high fatigue strength, proof stress, and machinability, with existing materials like DIN C70S6 material being unsuitable for fracture splitting due to deformation and precision assembly issues during the fracture splitting process.
Innovation Solution
A rolled material with specific chemical composition and microstructural characteristics, including controlled carbon, sulfur, and sulfide inclusion morphology, is developed to enhance fracture splitting characteristics, machinability, and strength, allowing for precise splitting into semicircles for crankshaft assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If DIN C70S6 material is used for fracture splitting, then the material is suitable for the fracture splitting process, but it cannot meet the high level of fatigue strength and proof stress demanded and has unsatisfactory machinability
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.25-0.60%, Si: 1.00-2.50%, Mn: 1.50-3.50%, S: 0.05-0.20%, P: 0.010-0.100%, Cr: 0.10-2.00%, Mo: 0.10-0.60%, B: 0.0005-0.0100%) and microstructural parameters (ferrite area ratio: 5-30%, pearlite area ratio: 70-95%, sulfide inclusion aspect ratio: ≤10.0) to achieve both high strength and good machinability. This systematic parameter optimization resolves the contradiction between strength requirements and manufacturing ease.
Solution Approach 2:
The patent creates a composite microstructure consisting of ferrite and pearlite phases with controlled proportions, along with controlled sulfide inclusions (MnS, CaS, etc.). This composite material structure combines the softness and ductility of ferrite with the strength of pearlite, while the controlled sulfide inclusions improve machinability, thereby achieving both high strength and good manufacturability.
2Productivity
If conventional hot forging and cut-machining methods are used, then connecting rod main body and cap can be manufactured, but material yield is lowered and cost is inflated due to large number of steps
Solution Approach 1:
The patent merges multiple manufacturing operations into a single hot forging process. The integrated forging simultaneously forms the connecting rod main body, cap, and through-hole in one operation, eliminating the need for separate cutting and machining steps. This consolidation increases material yield by reducing scrap from multiple operations and simplifies the manufacturing process.
Solution Approach 2:
The patent performs preliminary action by pre-forming the through-hole and fracture split lines during the hot forging process itself, before final cooling and fracture splitting. The through-hole is created as an integral part of the forging process, and the fracture split lines are pre-positioned, which simplifies subsequent processing and reduces the number of manufacturing steps.
3Manufacturing precision
If high ferrite area ratio is used (≥60% as in patent document 1), then random unevenness on fracture faces is produced, but ferrite being soft phase causes deformation during fracture splitting process
Solution Approach 1:
The patent optimizes the ferrite area ratio parameter to a specific range (5-30%) rather than using high ferrite content (≥60%). This parameter change balances the competing requirements: sufficient ferrite to provide ductility and absorb energy during fracture, but limited enough to prevent excessive deformation. The controlled ferrite content alongside high pearlite content (70-95%) achieves both fracture face uniformity and shape stability.
4Ease of manufacture
If low ferrite area ratio is used (≤10% as in patent document 2), then machinability is improved, but increased load during fracture splitting leads to increased deformation
Solution Approach 1:
The patent adjusts the ferrite area ratio parameter to an optimal range (5-30%), which is higher than the ≤10% in patent document 2. This parameter optimization ensures sufficient ductility and energy absorption capacity during fracture splitting, preventing excessive deformation while maintaining good machinability through controlled pearlite content (70-95%) and sulfide inclusion morphology.
Data Source
Figure 1~2
Figure 3~4
Figure 5(a)~5(b)
AI summary
The present invention provides a rolled material having excellent fracture splitting characteristics and suitable for the manufacture of a connecting rod in which a through-hole section for assembly in a crankshaft is fracture split in substantially semicircles. Prescribed components are contained, an average aspect ratio of a sulfide-based inclusion as observed in a D/4 portion (D is the diameter of the rolled material) in a cross-section parallel to a longitudinal direction of the rod-shaped rolled material is not more than 10.0, a Pc indicated in Equation (1) below is between 0.41 and 0.75, and a Veq indicated in Equation (2) below is not less than 0.18 mass% Pc=C1-α/100 {In Equation (1), C represents the carbon content in steel (mass%) and α represents the ferrite fraction (area ratio%)} Veq=V+Ti/2+Si/20 {In Equation (2), V, Ti and Si represent the content of each element in steel (mass %)}.