Hypoid Gear Steel Composition for Low-Distortion Carburizing
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Solution Overview
Problem
Differential hypoid gears in automobiles face challenges in achieving high strength while minimizing distortion and noise vibration (NV) due to carburization, especially in large sizes, where the addition of boron enhances grain boundary strength but increases deformation, and without boron, sufficient strength is not attained.
Innovation Solution
A differential hypoid gear with a specific chemical composition and metallographic structure, including tempered martensite, optimized to control distortion by approximating the Ms point of the carburized layer to that of the non-carburized layer, and using pinion gears with matching properties to form paired hypoid gears, which satisfy specific formulas to enhance strength and reduce distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If B (boron) is added to strengthen grain boundaries, then strength is improved, but distortion by carburization increases
Solution Approach 1:
The patent optimizes the boron content parameter within a specific range (0.0005-0.0050 mass%) and combines it with controlled amounts of other alloying elements (C, Si, Mn, Cr, Ti, Mo, Nb, Al) to achieve the desired balance between strength and distortion control. By precisely controlling chemical composition parameters, the patent resolves the contradiction between gaining strength from boron addition while minimizing carburization distortion.
2Productivity
If quenching by high-density energy heating is used, then manufacturing efficiency is improved, but internal hardness is insufficient
Solution Approach 1:
The patent specifies particular chemical composition parameters (C: 0.15-0.30 mass%, Si: 0.55-1.00 mass%, Mn: 0.50-1.20 mass%, Cr: 0.50-1.50 mass%, etc.) that enable the steel to achieve sufficient internal hardness through conventional quenching processes. The optimized composition allows for complete quenching of large-sized differential hypoid gears while maintaining manufacturing efficiency, resolving the contradiction between productivity and hardness achievement.
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 effectively achieves higher strength and reduced distortion in differential hypoid gears, improving their durability and noise vibration performance, even in large sizes, by optimizing the chemical composition and metallographic structure to manage the transformation points and martensite ratios.
Implementation Method 1
addition of B causes an increase in deformation by carburization
Implementation Method 2
quenching in whole is performed after carburizing treatment to fully increase an internal hardness
Implementation Method 3
strengthening of grain boundaries by addition of B
Implementation Method 4
chemical component composition comprising C, Si, Mn, Cr, Al, B, Ti, N, Mo, and Nb
Data Source
AI summary
A differential hypoid gear, a pinion gear, and paired hypoid gears formed by a combination thereof are provided. The differential hypoid gear includes a ring-shaped main body and a tooth-forming surface, and has a chemical component composition including C: 0.15-0.30 mass %, Si: 0.55-1.00 mass %, Mn: 0.50-1.20 mass %, Cr: 0.50-1.50 mass %, Al: 0.020-0.080 mass %, B: 0.0005-0.0050 mass %, Ti: 0.01-0.08 mass %, N: 0.0020-0.0100 mass %, Mo: 0.25 mass % or less, and Nb: less than 0.10 mass %, the remainder being Fe and unavoidable impurities. The chemical component composition satisfies Formulae 1 and 2. The differential hypoid gear has a metallographic structure including mainly tempered martensite. A martensite ratio at an inside of a dedendum differs between an end portion of a tooth and a central portion of the tooth within a range of 15% or less. A core hardness of the dedendum at the central portion falls within 350-500 HV.