Grain Stabilized 16-20 MnCr5 for Inner Races & Tripods

OverviewNithin SHARMA | 10/03/2015

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Content

Introduction

Process flow for Inner Races (IR) & Tripods

Industrial Experience

Potential Improvements

Draft Plan for Master Thesis

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INTRODUCTION

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Continuous Velocity Joints (CVJ) [Fixed Joints]

Fixed Ball AC Joint

Fixed Ball Joint UF

Fixed Joint countertrack

Inner Races

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Continuous Velocity Joints (CVJ) [Plunging Joints]Tripod GI

Tripod AARiTrunion

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Why Nb Steels?

Nb has threefold influence on Mechanical properties of Steel:• Grain size refinement during Thermo Mechanical Treatment hot forming• Lowers the, Austenite Ferrite transition temperature• Precipitation hardening

Problems with Nb steels:• Clealiness

These effects are used in low, medium and high carbon engineering steels for different automotive applications

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Problem Statement

Grain Size Scale ASTM

Coarse Fine

Coarse grain formation in the Heat Treated Cold & Warm forged, Case Carburized components (IR & Tripods )

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Inner Race

Location Grain Size

Sphere Core ASTM 3 - 4

Location Grain Size

Track Vertex Case ASTM 7 - 8

Coarse Grains

Inner Race

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Tripod

Coarse Grains

ASTM 3-4

Trunion

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PROCESS FLOW

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State of the Art in GKN Driveline (Forming Process)

Inner Races

LEG(Spain)

TRI(Germany)

OLE(France)

PRESTA(Lichtenstein)

AC Warm Cold

UF Cold

DO

Tripods LEG TRI OLE PRESTA

AAR WarmGIiGI3

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State of the Art in GKN Driveline (Process Flow IR & Tripods)

Material

Cropping

Annealing

Shotblasting

Inner Races Tripods

• The steel bar is pushed through the driver until the length stop. The mobile blade is moved cropping the steel bar into billets

• Shear deformations are introduced during cropping.• Annealing Temperatures : ? (unknown)

• Ensures removal of scale, after forging and HT related to forged parts

16 MnCr5/ 20 MnCr5 16 MnCr5 (AAR) / 20 MnCr5 (GI)

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State of the Art in GKN Driveline (Process Flow IR & Tripods)

Coating

Preforming

Stress Relief • Process time and temperature is dependent on material specification.?

(Unknown)

Coating

• The preforms are loaded into a drum. The drum is submerged into a series of baths in order to clean the pieces and coat them with phosphate and soap

• Pickling, Rinse, Phosphate, Rinse in neutraliser, Soap

Inner Races Tripods

Forming at room temperature

Warm forming at temperature 925º C

NA X NA

Shotblasting

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State of the Art in GKN Driveline (Process Flow IR & Tripods)

Weight grading

Final forming

Case carburising

Inner Races Tripods

Forged at room temperature

NA

X NA

Shotblsting

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State of the Art in GKN Driveline (Process Flow IR)

Material

SB;CO

SB;CO;WG

Annealing

Preforming

Stress Relief

CP

Final forming

Case carburising

CP: CroppingSB: ShotblastingCO: CoatingWG: Weight grading

Temp Involved Strain Involved

Tem

pera

ture

Time

Temper 165 -190ºC, 1-2 hrs

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State of the Art in GKN Driveline (Process Flow Tripods)

Material

SB

SB;CO

Material

Annealing

Preforming

Stress Relief

Case carburising

CP

CP: CroppingSB: ShotblastingCO: Coating

Temp Involved Temp + Strain

Involved

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INDUSTRIAL EXPERIENCE

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Industrial Experience: MS43 (16MnCr5) steel with Nb

Increase in Nb results in decrease of C = High volume fraction of Nb[C,N]

Tem

pera

ture

Time

1 hour, 900 - 920º C

Heat Up

Air Cool

Final forming

Case carburising

Normalizing

0.05% Nb addition to 0.14% C, prevents coarse grain formation, for joints treated with inter stage annealing or normalizing treatments

Addition of Al formed coarse AlN precipitates, therefore a controlled TMT in hot rolling can ensure that Al addition to be utilized to form maximum volume fraction of AlN in fine form in the as rolled bar

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Industrial Experience:16MnCr5 steel with Nb in Auburn Hills= 16MnCr5

Al/N2 ratio of 2:1 is preferred

Nb[C,N] present in the solution is more effective than AlN (since the later forming coarse precipitates)

Ressistance of coarse grain formation ~ Vf of Nb [C,N]

Proposed to increase times in carburising furnace temperature

For maximum volume of [C,N] modifications on Temperatures of Roll Mill & Slab soaking can be done

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Industrial Experience:16MnCr5 steel with Nb in Auburn Hills

Location Grain Size

Sphere Core ASTM 3 - 4

Location Grain Size

Track Vertex Case ASTM 7 - 8

Inner Race

Coarse Grains

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POTENTIAL IMPROVEMENTS

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Potential Improvements

Grain size is influenced by processing conditions

Important to understand the process chain from end to end

Need quantitative data for process steps like :

* Temperature & time;

* Microstructure study; TEM observations

* Degree of deformation and strain induced during forging;

* Microstructure study (Grain Size); TEM observations (Precipitates Size)

When informed with all process parameters, simulate the kinetics of AlN/ Nb(C,N) precipitates using MATCALC, THERMOCALC software and try to validate

- reduces time and cost

- greater flexibility

Annealing

Preforming

Stress Relief

Final forming

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PLAN FOR MASTER THESIS

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Which Process Flow?

* Tripods warm forged

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Which Simulation Software?

MATCALC

Precipitation kinetics can be studied with this software

Optimal processing parameters may be defined, leading to optimal particle pinning and thus inhitbited grain coarsening

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Probable procedure followedSimulation of the precipitate evolution as function of chemical composition and thermo-mechanical processing in terms of mean radius volume fraction by MATCALC

Comparison of experimentally investigated precipitation sizes and validation of simulation parameters

Evaluation of the Zener force according to precipitate size and volume

Optimization of the processing parameters in order to achieve maximum Zener forces

Note: The above following approach was followed by Patrick Fayek, Thomas Petermann and Dr Prahl at IEHK, Aachen on the project titled „ Simulation of Precipitate and Grain-Size Evolution in Case Carburizing Steels“.

Chemical Composition TMT Processing

MATCALC

Precipitate size distribution Precipitate volume fraction

Zener Force

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THANK YOU!