Induction Hardened Hollow Driving Shaft Steel Composition
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Solution Overview
Problem
Existing hollow driving shafts face challenges in simultaneously achieving cold workability, hardenability, toughness, and torsional fatigue strength, particularly due to issues with crack formation during manufacturing and inadequate deformation energy absorption under torsional torque, which affects their stability and longevity.
Innovation Solution
A chemical composition for the steel pipe is specified, including 0.30 to 0.47% C, 0.5% or less Si, 0.3 to 2.0% Mn, 0.018% or less P, 0.015% or less S, 0.15 to 1.0% Cr, 0.001 to 0.05% Al, 0.005 to 0.05% Ti, 0.004% or less Ca, 0.01% or less N, 0.0005 to 0.005% B, and the balance Fe and impurities, with a prior austenite grain size of 9 or more, to enhance cold workability, hardenability, and torsional fatigue strength through induction hardening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the hardened layer is made excessively deep to improve fatigue strength, then the fatigue strength of the driving shaft is improved, but there is a risk of quench crack
Solution Approach 1:
The patent applies induction hardening with controlled parameters to achieve a hardened layer depth of 0.8-1.5mm, which is optimized to improve fatigue strength while avoiding quench cracks. The specific hardening parameters (temperature, time, cooling rate) are carefully controlled to prevent excessive hardening depth that would cause cracking.
2Strength
If higher C and lower Cr are aimed in composition design to secure hardness of the hardened layer, then the hardness is improved, but the cold workability deteriorates
Solution Approach 1:
The patent specifies an optimized chemical composition range: C: 0.25-0.45% and Cr: 1.00-2.00%, which balances hardness achievement with cold workability. This composition allows the steel to be cold-formed into hollow shafts with complex shapes while still achieving sufficient hardness after induction hardening.
Solution Approach 2:
The patent creates a composite microstructure consisting of a hardened outer layer (martensite) and a ductile core (ferrite-pearlite), achieving both surface hardness and overall toughness. The controlled composition enables this dual-phase structure that combines the benefits of different microstructural components.
3Strength
If MnS is granulated and made finer to inhibit crack occurrence and propagation, then the torsional fatigue strength is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent controls the size and distribution of MnS inclusions through composition control (Mn: 1.00-2.00%, S: 0.010-0.050%) and processing parameters, achieving fine granulated MnS that inhibits crack propagation without requiring complex additional manufacturing steps. The inclusion morphology is controlled through standard steelmaking practices.
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 enables the production of hollow driving shafts with improved cold workability, hardenability, toughness, and torsional fatigue strength, preventing crack formation during processing and ensuring stable fatigue lifetime by securing the strength of the prior austenite grain boundary.
Implementation Method 1
an induction hardened hollow driving shaft
Implementation Method 2
prior austenite grain size number indicates a transformation from austenite to other phases during hardening
Data Source
AI summary
The present invention provides an induction-hardened hollow driving shaft that comprises, as a raw material, a steel pipe that contains, by mass %, 0.30 to 0.47% C, 0.5% or less Si, 0.3 to 2.0% Mn, 0.018% or less P, 0.015% or less S, 0.15 to 1.0% Cr, 0.001 to 0.05% Al, 0.005 to 0.05% Ti, 0.004% or less Ca, 0.01% or less N, 0.0005 to 0.005% B and 0.0050% or less O (oxygen) and the balance Fe and impurities and of which Beff defined by an equation (a) or (b) below is 0.0001 or more, wherein a prior austenite grain size number (JIS G0551) after the hardening is 9 or more. Here, in the case of Neff=N−14×Ti/47.9≧0, Beff=B−10.8×(N−14×Ti/47.9)/14 . . . (a), and, in other cases, Beff=B . . . (b). According to the present invention, a hollow driving shaft that is simultaneously provided with excellent cold workability, hardenability, toughness and torsional fatigue strength and can exert stable fatigue lifetime can be obtained and can be widely utilized.