Fuel Injection Steel Pipe Composition for High Burst Pressure
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Solution Overview
Problem
Current steel pipes for fuel injection in diesel engines face challenges in achieving high critical internal pressure without compromising fatigue life and increasing production costs, particularly due to the need for quenching and tempering processes that reduce workability and elevate costs.
Innovation Solution
A steel pipe with a tensile strength of 500 to 900 MPa and a yield ratio of 0.50 to 0.85, subjected to auto-frettage treatment at a pressure of 450 MPa or lower, with a chemical composition that includes specific elements like C, Si, Mn, Al, Ti, Nb, Cr, Mo, Cu, Ni, V, and controlled outer to inner diameter ratio, to achieve a critical internal pressure of 0.41×TS×α or higher.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If quenching and tempering processes are applied to increase tensile strength to 900 MPa or higher, then critical internal pressure increases, but production costs increase and workability decreases
Solution Approach 1:
The invention changes the material parameters by optimizing chemical composition (C: 0.15-0.30%, Si: 0.10-0.50%, Mn: 0.50-2.00%, Al: 0.01-0.06%, Ti: 0.01-0.04%, Nb: 0.02-0.05%, Cr: 0.05-1.00%, Mo: 0.05-1.00%, Cu: 0.05-0.50%, Ni: 0.05-0.50%, V: 0.02-0.15%, B: 0.0005-0.0050%) and microstructure parameters (prior-austenite grain diameter 5-15 μm, ferrite grain diameter 2-8 μm, bainite grain diameter 1-5 μm) to achieve high strength without quenching and tempering, thereby maintaining workability while achieving critical internal pressure of 255 MPa or higher
Solution Approach 2:
The invention creates a composite microstructure consisting of multiple phases (ferrite, bainite, and martensite) with specific grain size distributions. This multi-phase composite structure provides both high strength and good ductility, enabling the steel pipe to achieve high critical internal pressure without requiring expensive quenching and tempering processes
2Strength
If quenching and tempering processes are applied to increase tensile strength to 900 MPa or higher, then critical internal pressure increases, but production costs increase
Solution Approach 1:
The invention changes the material parameters by optimizing chemical composition (C: 0.15-0.30%, Si: 0.10-0.50%, Mn: 0.50-2.00%, Al: 0.01-0.06%, Ti: 0.01-0.04%, Nb: 0.02-0.05%, Cr: 0.05-1.00%, Mo: 0.05-1.00%, Cu: 0.05-0.50%, Ni: 0.05-0.50%, V: 0.02-0.15%, B: 0.0005-0.0050%) and microstructure parameters (prior-austenite grain diameter 5-15 μm, ferrite grain diameter 2-8 μm, bainite grain diameter 1-5 μm) to achieve high strength without quenching and tempering, thereby maintaining workability while achieving critical internal pressure of 255 MPa or higher
Solution Approach 2:
The invention replaces expensive heat treatment processes (quenching and tempering) with a more economical approach based on controlled chemical composition and microstructure development during normalizing treatment, thereby reducing production costs while achieving the required critical internal pressure of 255 MPa or higher
3Reliability
If auto-frettage treatment is applied to increase critical internal pressure, then fatigue life improves, but the steel pipe material requires high strength which reduces workability
Solution Approach 1:
The invention optimizes the yield ratio parameter to 0.50-0.85, which allows the steel pipe to undergo auto-frettage treatment effectively to generate beneficial compressive residual stresses on the inner surface, improving fatigue life while maintaining good workability for forming operations. The controlled chemical composition and microstructure enable this balance between strength and workability
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 solution enhances critical internal pressure while maintaining low auto-frettage treatment pressure, improving workability and fatigue resistance, and reducing production costs, making it suitable for automotive fuel injection pipes.
Implementation Method 1
subjected to auto-frettage treatment at an auto-frettage treatment internal pressure that is 450 MPa or lower
Implementation Method 2
a circumferential-direction residual stress on an inner surface of the steel pipe after the steel pipe is split in half in a pipe axis direction
Implementation Method 3
adjusting the diameter of the material steel pipe into an intended diameter by cold rolling, and thereafter performing quench and temper
Data Source
AI summary
A steel pipe for fuel injection pipe has a tensile strength of 500 to 900 MPa and a yield ratio of 0.50 to 0.85, and has a critical internal pressure (IP) satisfying [IP≥0.41×TS×α] (α=[(D/d)2−1]/[0.776×(D/d)2], where TS: tensile strength (MPa) of the steel pipe, D: steel pipe outer diameter (mm), and d: steel pipe inner diameter (mm)), wherein a circumferential-direction residual stress on an inner surface of the pipe is −20 MPa or lower after the steel pipe is split in half in a pipe axis direction.