The Application of Hot Stamped Boron

Steel 15B22 on the Automotive Parts

Cheng-Kai ChiuHuang

Co-authors: S.W. Wang, P.K. Lee, T.R. Chen

Product Application Research Section

Iron & Steel Research & Development Department

China Steel Corporation

2016/11/15

1

Outline

• Background

• Hot Stamping Manufacturing Process

• Characteristics of CSC Boron Steel 15B22

• Examples of Hot Stamping Die Tryout

• Conclusions

2

3

Background• Body Structure lightweight and safety are the main driving forces for the

development of hot stamping process.

• The strength of the parts made by hot stamping is higher than the

traditional forming technology.

The Application and Global Market for Hot Stamping Parts

Ref: www.schuler.com

• Due to the CO2 emission regulation and vehicle safety issue, the application

of hot stamping parts on the body structure shows a fast growth.

• Schuler forecasts that the hot stamping market will reach 5.7 billion Pcs by

2018.

4

Ref: www.Gestamp.com

Ref: www.stampingjournal.com December 2006

Direct Process

Hot Stamping Manufacturing Process

• The blank is heated to 910 degree Celsius in the furnace.

• Then the blank is transferred to the die within 6 secs.

• Die closing for 15-20 secs to quench the blank.

• The part is trimmed by laser cutting.

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Mechanical Properties of Boron Steel 15B22

Ref: Garcia Aranda et al., 2002

• The blank is heated to austenite state followed by fast die quenching.

• The critical cooling rate to obtain the martensite microstructure is 27 K/sec.

15B22

Annealed

15B22

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Pros and Cons of Hot Stamping Process

Pros

• High Strength (TS > 1500 MPa)

• Good Formability (Forming at high Temperature)

• Lower Press Capacity Required (<1000 Ton)

• Good Part Dimension Control (No Springback)

Cons

• Higher Energy Consumption (Furnace for blank heating)

• Higher Die manufacturing cost (Cooling ducts required)

• Higher Investment for the Production line

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Example: U-Hat Hot Stamping Die

U-Hat Hot Stamping DieCSC 200 Ton Hydraulic Press

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CAE Model: Forming and Drawing

9

Blank

Holder

Temperature Distribution and Phase Fraction

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Top

Top

Flange

Flange

Quench 2 Sec

Side wall

Side wall

Quench 2 Sec

Quench 10 Sec

Quench 10 Sec

CSC Hot Stamping R&D Capability

Die Design

Computer Simulation (Forming)

Inlet

Outlet

Cooling ducts design

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Computer

Computer Simulation (Water Flow)

Springback Comparions for Different Materials

Al 5182

270 Mild Steel

15B22

(No Springback)

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• Hot stamping parts have good size stability (No Springback).

Strength and Hardness Verification

Location

Str

ength

(M

Pa)

Location

Har

dnes

s (H

RC

)

• The strength meet the requirement of GM and Volkswagen standard.

GMW14400: TS 1000～1700MPa、YS 950～1250MPa、EL 5% min

TL4225: TS 1300～1650MPa、YS 1000～1250MPa、EL 5% min

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Mechanical Properties Before and After Hot StampingMechanical Properties Before and After Hot Stamping

0

200

400

600

800

1000

1200

1400

1600

0 5 10 15 20 25

Strain (%)

Ste

rss

(MP

a)

Before H.T.

After H.T.

CSC HC 15B22

Blank Status

Yielding

Strength(MPa)

Tensile

Strength (MPa)

Elongation(%)GL=50mm

Hardness(HRC)

Before H.S. 280 450 20 -

After H.S. 950 ~ 1250 1300 ~ 1650 6 40~49

Flat Area

Drawing

15B22

t=1.4 mm

Microstructure after Die Quenching

Forming

15B22

t=1.4 mm

• With appropriate die design, a uniform high-strength

martensite structure can be obtained after die quenching.

Corner Side Wall

Flat Area Corner Side Wall

Flat areaSide wall

Corner

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Before Hot Stamping

Ferrite + Pearlite

Hardness 80 ~ 90HRB

After Hot Stamping (Die quenching)

Martensite

Hardnbess 43 ~ 47HRC

(Heating to 930℃，Transfer to the die in 5 secs

followed by 15 secs die quenching)

CSC HC 15B22 Microstructure (Before and After Die

Quenching)

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Double-layeredFurnace

800 Ton Press

Blank TransferAutomatic blanking

Bumper(15B22)

A pillar(15B22)

Hot Stamping R&D Capacity-Cooperate with Local Research Institute

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Patchwork B-pillar

Patchwork B Pillar30% Lightweight compared to the cold-stamping design A-pillar and Door Beam

Automotive Parts Developed by Hot Stamping CSC 15B22

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Conclusions

• The demand for the hot stamping parts from the automotive industry

shows a strong growth. The annual demand is predicted to reach 5.7

billion pcs by 2018.

• China Steel Corporation has successfully developed non-coated and

coated high temperature oxidation resistant 15B22 boron steel for the

hot stamping process.

• After hot stamping (die quenching), the YS, TS and Elongation of

CSC 15B22 can reach 1090 MPa, 1510 MPa and 6.75% respectively.

• Through the test, it is sure that the developed 15B22 steel can meet

the requirement of GM standard (GM 14400) and VW standard

(TL4225) for hot stamping.

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