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PT Krakatau Steel (Persero) Tbk
The Development of 490 MPa Class Hot Rolled Pickled Oiled Use Plain Carbon Steel for Automotive Pipe Application
Presented to SEAISI 2018 Conference
Jakarta, 27th June 2018
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Outline
• Introduction
• Product Requirement and Design
• Production Process
• Result and Discussion
• Summary
• Reference
Introduction
Steel is the material which is commonly used as raw material for several applications such as automotive, bridge structure, oil and gas, pipeline, etc.
Current trend of automotive steels demand are higher strength and thinner gage.
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Steel application
General Purpose
General & Welded
Structure
Pipe & Tube
Automotive Body & Parts
Oil & Gas Pipe
Home & Office
Appliance
Enamelwares
Introduction
No. Product Application Standard Specification
1. Hot Rolled Coil & Hot Rolled Pickled Oil*
Automotive Structure
JIS G 3113 SAPH 310, SAPH 370, SAPH 400, SAPH 440 and equivalent*
JIS G 3134 SPFH 540 and equivalent
2. Hot Rolled Coil & Hot Rolled Pickled Oil*
• Automotive Part • Automotive Pipe & Tube
JIS G 3131 SPHC, SPHD, and equivalent
JIS G 3132 SPHT 1, SPHT 2, SPHT 3, SPHT 4 & equivalent, KS 37, KS 39, KS 45
3 Cold Rolled Coil • Automotive part • Automotive Pipe & Tube
JIS G 3141 SPCC, SPCD, SPCE, SPCF JIS G 3141 SPCCT & equivalent, KS 34, KS 37, KS 39
PT KS Product Specification
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Questions
What
Why
Who Where When
How
Answer
490 MPa Class Tensile Strength Hot Rolled Pickled Oiled (HRPO) for automotive pipe and tube application, its specification called KS 49.
• PT Krakatau Steel (PT KS) product development activity is closely related with market situation
• Request product KS 49 from PT KS automotive pipe maker customer
PT Krakatau Steel Production facilities of PT KS 2017
• Use plain carbon steel slab • Optimizing rolling temperature
Product Requirement and Design
Product requirements of the developed steel are accordance in these following table. Steel raw material for automotive application should have excellent surface quality, it should be free from surface defect such as lamination, open scratch, and rolled in scale.
Element (%) Requirements Typical
C 0,30 max 0,16 – 0,18
Mn 0,30 – 1,00 0,8 – 1,0
Si 0,35 max. 0,03 max.
P 0,040 max. 0,025 max.
S 0,040 max. 0,02 max.
Chemical composition requirements and typical of product
Properties Requirements Typical
Tensile Strength 490 MPa min. 501 – 546
Elongation 18 % min.(*)
Note :(*) = for 1,60 ≤ T < 3,00
Mechanical properties requirements and typical of product
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Production Process Hot Rolling of The Developed Product
The plain carbon steel slab are reheated and soaked up to about 1200oC
First stage of reduction at roughing mill
Steel is rolled at a temperature between non-recrystallization and Ar3 transformation temperature in Finishing Mill to achieve the final thickness. Temperature after last stand rolling in finishing mill is called Finishing Temperature around 850oC
The steel strip pass through laminar cooling in order to get its exact mechanical properties.
Strip is then get its coil form in down coiler at about 560oC.
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Production Process Continuous Pickling Line
HRC as improved its flatness then processed in Continuous Pickling Line (CPL) to remove its scale.
Parameter of pickling process use as it is operation :
higher concentration of hydrochloric acid in the final tank.
Acid temperature around 80oC
CONTINUOUS PICKLING LINE CONTINUOUS TANDEM COLD MILL ELECTROLYTEC CLEANING LINE
BATCH ANEALING FURNACE
CONTINUOUS ANEALING LINE
COLD ROLLED COIL TEMPER MILL
SLITTING/RECOILING LINE
SHEARING LINE
COLD ROLLED COIL
SLITTED/RECOILED
SHEET
HOT ROLLED COIL
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HOT ROLLED PICKLED OILED
130
250
370
490
610
0 9 18 27 36 45
Te
nsil
e S
tre
ng
th (
MP
a)
Elongation (%)
Mechanical Properties of HRC KS 49
Result and Discussion Mechanical Properties Result
100% values of mechanical properties test result of the developed product are within specified values and meet the requirement.
Figure tensile test result of HRC KS 49
Thickness (mm) Properties Requirement Result
1,60 ≤ T < 3,00 Tensile Strength 490 MPa min. 500 – 580 MPa
Elongation 18 % min.(*) 28 – 40 %
Tensile test result of HRC KS 49
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Result and Discussion Hardness Value
Hardness value of the material in through thickness direction were also measured uniformity of about 144 – 180 HVN as can be seen in following figure.
Figure of Microhardness test result of HRC
0
50
100
150
200
Surface 1 Half thickness Quarter thickness 1 Quarter thickness 2 Surface 2
Mic
roh
ard
ne
ss (
HV
N)
Position
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Result and Discussion Metallography Observation
Microstructure of the hot rolled steel is shown in following figure.
(a) (b)
(c) (d)
Microstructure of the hot rolled steel plate in : (a) surface position, (b) half thickness, (c) and (d) quarter thickness
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Upper bainite were observed by means of optical microscope. It is well known that upper bainite consist of needles of ferrites separated by long cementite particles. Plates of bainite form without any diffusion, but shortly after transformation, the carbon partitions into the residual austenite and precipitates as cementite between the ferrite.
Summary
Summary
Product design by using plain carbon steel and optimizing finishing and coiling temperature has
improved mechanical properties and meet the requirement.
Pickling process after Hot Skin Pass Mill could achieve good surface quality of HRPO product.
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References
References
[1] Baskoro Agung, “The Development of 540 MPa Class High Strength Low Alloys Steel for Bridge
Structural Application”, 2012
[2] Shekhar Shashank, “Phases and Microstructure”, University of Tennessee Handour for MSE300.
[3] Bhadeshia, “Interpretation of the Microstructure of Steels’, University of Cambridge, 2005
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