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First Gen AHSS (Transformation-Induced Plasticity (TRIP) (Factors…
First Gen AHSS
Transformation-Induced Plasticity (TRIP)
Definition
Isothermal Transformation @ subcritical temp after intercritical temp
Strain-Induced Transformation
A => M
Enhance Plastic Deformation
Purpose
Combination of strength & ductilities
Better Ductilities @ High Strength Levels
Factors
Alloying
Temp
Isothermal Time
Microstructure (Everything)
B & RA & F & M & High C
Transform to M as strain increases
Larger Smooth Etching Islands
Acicular Ferritic Structures
Lower Ms temp
Stabilise RA on cooling to rtp
Processing (IAIT)
Step 1: Intercritical Annealing
Step 2: Isothermal Transformation
Modification
Alloying
Si (CO)
Cementite Formation decreases
Stable Oxides form during hot rolling
Problems
Bad Surface Finish
Reduce coat ability during galvanizing
Al (FW)
Ferrite-Stabilising Tendency
Affects hot workability
Test Temp
Low
A transforms by stress-induced mechanisms
Little deferring of high strain necking
High
A too stable
A non-transformation
20-50 °C
Ductility Max
Properties
Initial High Work Hardening Rate
High n-value
Dual Phase (DP)
Definition
Cooling: Intercritical => RTP
F all round with M Islands
Process
Subcritical Temp
A => B
RTP
A => M
Properties (SSDD)
High Strength
M Formation
Strain Hardening
M Formation
High Dislocation Densities
Soft Ferrite
Excellent Ductility
Component
Retained A
Purpose
Combinations of strength and ductility
Results
Greater Strain Hardening Capacity than HSLA
Lower Yield Strength than HSLA
Applications
Automotive
Bumper
Door
Seat Components
Springback
Modes
Angular
Sidewall Curl
Twist
AHSS > HSLA
Martensite (M)
Strain-Induced
Properties (SDN)
Promotes Ductility
Increase Strain Hardening
Defers Necking Instability
Metastable Phase
BCT
BCC
Forms in Steel
Speed of Sound Growth
Rapid Diffusionless Transformation
Fine and Complex Crystallography
Strong
Relatively Brittle
Complex Phase (CP)