Flexible Steel Ring Nitriding Process for CVT Drive Belt
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Solution Overview
Problem
The existing dualling process for flexible steel rings in drive belts is sensitive to process settings and alloying composition variations, leading to inconsistent material properties and brittleness, especially for maraging steel compositions that age slowly, making it challenging to achieve the required core hardness and nitrided surface layer thickness within a narrow window.
Innovation Solution
The dualling process is optimized by introducing nitrogen during the aging process at a temperature range of 515 to 525°C, with a chromium-enhanced maraging steel composition, which forms chromium nitrides and allows molybdenum to form inter-metallic Ni3Mo precipitates, while controlling the ammonia content to suppress the formation of detrimental compound layers, thereby stabilizing the hardness and fatigue strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the dualling process is applied to achieve both aging and nitriding in a single step, then processing time and handling effort are reduced, but the process becomes highly sensitive to settings and alloying composition variations, leading to inconsistent material properties
Solution Approach 1:
The patent applies parameter changes by optimizing the dualling process temperature to a specific range (515-525°C) and controlling the ammonia content (1-5 vol.%) to achieve consistent material properties. This resolves the sensitivity issue by establishing precise parameter windows that ensure reproducible results despite process integration.
Solution Approach 2:
The patent utilizes composite material principles by enhancing the maraging steel composition with chromium (0.5-2.5 mass-%) which forms chromium nitrides during nitriding. This compositional modification stabilizes the dualling process and improves consistency of the resulting material properties.
2Strength
If maraging steel compositions that age slowly are used, then the required core hardness is difficult to achieve within the narrow process window, but using faster-aging compositions may result in excessive nitrided surface layer thickness and brittleness
Solution Approach 1:
The patent resolves this contradiction by changing the temperature parameter to an optimized range (515-525°C) that accelerates aging while controlling nitride formation. This temperature window enables slow-aging steel compositions to achieve required core hardness without excessive surface layer thickness or brittleness.
Solution Approach 2:
The patent applies local quality by creating different material properties at different locations: the core achieves required hardness through controlled precipitate formation, while the surface develops an optimized nitrided layer with appropriate thickness and composition, preventing brittleness.
3Reliability
If the nitrided surface layer thickness is increased to improve wear resistance and fatigue strength, then the rings become too brittle, but reducing the thickness compromises wear resistance
Solution Approach 1:
The patent changes the process temperature parameter (515-525°C) and ammonia content (1-5 vol.%) to control the nitrided surface layer formation rate and depth. This produces an optimized layer thickness that provides wear resistance while maintaining adequate toughness and preventing brittleness.
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
This approach broadens the tolerances for alloying compositions, enhances the consistency of material properties, and improves the control over the dualling process, resulting in more robust and fatigue-resistant flexible steel rings with improved hardness and wear resistance.
Implementation Method 1
ammonia gas is dissociated into hydrogen gas and nitrogen atoms that are absorbed from a process gas into the metal lattice through the outer surface of rings
Implementation Method 2
the heat treatment of nitriding, in which process ammonia gas is dissociated into hydrogen gas and nitrogen atoms that are absorbed from a process gas into the metal lattice
Implementation Method 3
at which temperature these latter elements form and grow into precipitates, such as Ni 3 Mo. Such inter-metallic precipitates significantly increase the hardness and toughness of the maraging steel
Implementation Method 4
During the so-called aging heat treatment of such maraging steel at a temperature exceeding 400 degrees Celsius (deg.C.), typically of around 480 deg.C.
Implementation Method 5
ammonia gas is dissociated into hydrogen gas and nitrogen atoms
Implementation Method 6
ammonia gas is dissociated into hydrogen gas and nitrogen atoms that are absorbed from a process gas
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a method for the simultaneous precipitation hardening and (gas soft) nitriding of an endless flexible ring (32) made from maraging steel to be used as or in a drive belt (3) for a continuously variable transmission. The ring (32) comprises between 0.5 and 2.5 mass-% chromium and the simultaneous precipitation hardening and nitriding is carried out at a temperature of 500 degrees centigrade or more. After simultaneous precipitation hardening and nitriding, the ring (32) is provided with a nitrided surface layer of the ring (32) comprising chromium nitride precipitates.