1. February 4, 2008

2. Primary Steel Production

3. Steel Finishing Production

4. Steel Finishing Production

5. Typical Steel Production Facility
Figure 1.3 Layout of finishing facilities at Granite City Steel Division (Fornadley)

6. General Types of Steels
Table 1.4 Classification of Steels on the Basis of Microstructure and Metallurgical Properties
TYPE
DESCRIPTION
END USES
Very low-carbon (pure iron)
Steels with very low contents of carbon and other elements (carbon content 0.02% max.)
For application where alloying elements must be kept to a minimum
Interstitial-free (IF steels)
Steels with 0.008% C max. and 0.006% N max.
Used in very difficult deep drawing and combined drawing/stretching operations
Low-carbon
CQ, DQ and DQSK hot and cold-rolled sheet and tin-mill products Carbon usually less than 0.10% and manganese 0.2 to 0.5%
General applications of low-carbon steel including coated sheets and tinplate
Enamelling steels
A special class of low-carbon steels
Used for enamelled products
Electrical steels
Silicon steels and specially processed low-carbon steels
For transformer cores and motor laminations
Carbon steels
Steels with carbon content 0.10 to 0.80%
Structural applications, plate, ERW pipes and linepipe
Nitrogenized steels
Hot-rolled steels strengthened by nitrogen as a solid solutions strengthener
For high-strength structural applications
High-strength, low-alloy (HSLA) steels
Low-carbon steels microalloyed with such elements as niobium, vanadium and titanium
For applications where high strength and formability are required
Dual and multiphase steels
Low-carbon, hot- or cold-rolled steels with ferrite matrix containing dispersed martensite and/or bainite
For applications where a more uniform distribution of strain is required during the forming of complex, high-strength parts, such as automobile bumpers and wheels

7. Sequence of Operations
Table 1.5 Sequence of Processing Operations for Carbon Steels
OPERATION
PURPOSE
Continuous casting or slabbing
To produce slabs suitable for rolling on hot-strip mill
Reheating
To raise temperature of slabs for entry into roughing stands and develop an austenitic structure
Hot rolling
To produce coils of desired width, thickness, and microstructure
Temper rolling
To flatten and provide a small clongation to the hot-rolled strip
Picking or descaling
To remove oxides from the surface of the hot-rolled strip
Cold rolling
To reduce thickness of the strip
Cleaning
To remove residual rolling lubricant and other contaminants from the strip surfaces
Annealing
To restore the formability of the work-hardened strip
To suppress the yield point extension of the steel, to provide the desired surface texture and to flatten. In some cases, to provide a small reduction to facilitate subsequent annealing
Secondary cold reduction
To reduce thickness and partially work-harden strip used for tinplate production
Coating operations (tinning, galvanizing, etc)
To apply desire metallic coating to the sheet or strip

8. Strain Ageing
Figure 2.2. Effects of strain aging on the stress-strain curve of a low-carbon steel

9. Example of gridded and formed stamping
Forming Deformation
Example of gridded and formed stamping
The circle grid allows visualization of the amount and direction of the principal strains as they change from point to point on the stamping.
This gridded bumper jack hook has become a universal symbol for circle grid analysis or CGA.
Note the one highly strained circle on the edge of jack hook bend. The strain level drops to one-half in the adjacent circles and to zero at a distance of three circles.
The original study was conducted with 0.1 inch diameter circle grid pattern.

10. Breakdown of a complex stamping
Forming Modes
Breakdown of a complex stamping
The average sheet metal stamping requires a number of different forming modes to convert the flat sheet into a usable shape.
The names of the forming modes shown are international technical terms which may not agree with local press shop "jargon".
Identification of the specific forming mode is required to understand the respective forming mode before corrective action can be planned.

11. Hot Rolling Mill
Fig. 16 – General layout of a large capacity hot strip mill (Sollac Fos sur Mer)

12. Grain Size During Hot Rolling
Figure 2.11 Change in grain size during roughing for plain carbon and microalloyed steels

13. Recrystallization
Fig. 9 Strain hardening followed by static recrystallization
Fig. 10 The kinetics of static recrystallization

14. Controlled Rolling
Figure 1. Schematic illustration of the three stages of rolling process and change in microstructure in each stage; after [2]

15. Effect of Processing on Grain Size
Figure 2.19 Effects of finishing and coiling temperatures on the grain size of hot-rolled, aluminum-killed steel sheet
Ac3 = 910 – 25Mn – 11Cr – 20Cu + 60Si + 700P – 25Al - Fn

16. Runout Table Cooling
Figure 2.20 Schematic cooling paths for a fixed difference between finishing and coiling temperatures on a hot-strip mill runout table.

17. Transformation during Cooling
Figure 2.21 Cooling cycle of hot-rolled strip superposed on TTT-diagram of a low-carbon rimmed steel (0.06%C-0.43%Mn).
Figure 2.22 Schematic diagram of transformation behviour of low-carbon steel

18. Effect of Processing Temperature on Properties
Figure 2.27 Iso-strength contours for an 0.016C-0.62Mn steel hot-rolled to 0 thick bands

19. Final Properties of ULC Steels
Table 2.3 Composition and Properties of a Hot-Rolled 0.003C-0.17Mn Steel
Chemical Composition by Sheet Check Analysis, wt% C Mn P S Si Al N B
<0.005*
0.17
0.015
0.004
0.014
0.025
0.0010
0.0018
* Ladle analysis was 0.003C
Tensile Properties and Grain Sizes of Hot-Rolled Sheet
Coil
LD.
Average
Finish
Temp.,°F
Coiling
0.2% Offset
Yield Strength,*
ksi
Tensile
Strength,*
Elongation in
2 Inches* % n
Value*
Ferrite Grain
Size, **
ASTM No. A
1650
1365 H M T
31.3
28.7
30.2
42.5
40.5
41.1 50 54 51
0.20
0.22
0.21
6.5
6.3 B
1665
1275
30.0
27.6
28.8
41.8
40.3
41.2
6.0
5.7
6.2 C
1685
1145
29.5
40.4
40.8 52
6.9
6.4
7.0 D
1680
1075
29.2
28.2
28.4
41.5
40.9 53
6.7
6.6
6.1
* Average of three values determined at quarter, center and three-quarter width locations.
** Determined at the midthickness of the sample taken from the quarter width location.

20. Final Properties of ULC Steels
Table 2.4 Interstitial-Free Steels - Ranges of Chemical Compositions of Sheets from Trial IF Steel Heats, Weight Percent
STEEL C Mn P S Si Ti Cb N
Al T
Min
0.006
0.18
0.002
0.007
0.02
0.17
<0.005
0.005
0.077
Max
0.008
0.20
0.003
0.03
0.083
Ranges of Tensile Properties and Grain Sizes of Hot-Rolled Sheets of the Above Heats of IF Steel
Average Coiling Temp., °F
Yield Strength, ksi
Tensile Strength, ksi
Elong. in 2 Inches, %
n Value
1290
Min
32.7
48.4
41.0
0.183
Max
36.1
50.7
45.0
0.208

21. Range of Properties for Carbon Steels
Figure 2.31 Lower and upper bounds of tensile strength for carbon steels

22. Range of Properties for Carbon Steels
Figure 2.32 Estimated tensile strengths of C-0.8Mn steels coiled at various temperatures

23. HSLA Steels
Table 2.9 General Effects of Cb, V, and Ti in 40 to 60 ksi Minimum Yield Hot-Rolled Sheet Steels
Micro-Alloying element
Steelmaking
Stab Heating
Hot Rolling
Grain
Refinement
Overall
Strengthening Nb V Ti
Can be added to semikilled or fully killed steels
Can only be added to aluminum-killed steels.
Combines with nitrogen, and sulfur before carbon.
Careful control of slab heating is required to dissolve Nb (C, N) in austenite.
Dissolution of VC and in austenite is relatively easy. If AL is present, may need full AIN dissolution.
TiN essentially insoluble; TiC is readily soluble.
Finishing-mill loads increase substantially with increasing Nb content
Finishing-mill loads not substantially increased with V or V-N additions.
Ti increases all loads in a manner similar to Nb.
Strongly refines grain size through austenite grain flattening during finishing and through hardenability during transformation.
Moderate to strong grain refinement produced.
Strong grain refiner similar to Nb.
Maximum strengthening effect is about 7.5 ksi per 1.01% Nb (grain refinement plus precipitation strengthening)
Similar strengthening to Nb but requires 3.3 times as much V as Nb for equal effects.
Very high precipitation strengthening can be obtained (about 2.5 ksi per 0.01% Ti up to 0.25 Ti).

24. HSLA Alloying
Figure 2.34 Relative effects of niobium and vanadium on the yield strength of 0.08C-0.50Mn steels

25. Cold Working
Figure 2.35 Increase of tensile strength of plain carbon steel with increasing amounts of cold working

26. Cold Working
Figure 2.36 Effect of cold working on the ductility of plain carbon steel

27. Figure 23.13 Schematic stress-strain diagram
Strain Hardening
Figure Schematic stress-strain diagram

28. Annealing Low-C Steels
Grade
Temp.(oC)
Batch annealing of coils
Continuous annealing
Aluminum-killed extra mild steel with nitrogen in solution
Slow heating cycle
= 30 ± 10 h
Annealing temp. 710°C
AIN precipitation
Recrystallization
Grain growth
Texture reinforcement
Solutioning and partial spheroidizing of Fe3C
Renitriding in the case of annealing in HNX*(N tied up by excess Al)
Start of secondary coarsening
Coalescence of cementite
Renitriding
Loss of toughness
(coarse grains)
25 ± 5 h
Formation of Fe3C nuclei
Complete precipitation of dissolved carbon
Rapid heating cycle
= 90 ± 30 s
30 to 60 s hold
Annealing temp. 850°C
Start of primary recrystallization
Start of AIN precipitation
Grain growth impeded
End of Primary recrystallization
End of AIN precipitation, grain growth impeded
Very slow grain growth
Start of spheroidizing of cementite
10 ± 5 mn
Partial precipitation of dissolved carbon
Residual C 4 to 15 ppm depending on the overaging cycle
*HNX: mixture of nitrogen and 5% hydrogen

29. Annealing Low-C Steels
Batch annealing and cooling of coils
Continuous annealing and cooling
Final properties
Grain size 7.9 ASTM
YS: MPa
UTS: MPa
EI.: 40-44% r:
Grain size ASTM
YS: MPa
UTS: MPa
EI.: 31-38% r:

30. Fig. 1.1 Section across the strip width
Strip Dimension
Fig. 1.1 Section across the strip width
1.2 Key Thickness of Strip Profile
Generally, the strip profile can be described as a set of thickness measured at predetermined intervals across the strip width. Although this approach gives the most precise description of each individual profile, it may not be as effective in the evaluation or comparison of various strip profile. It was found that this evaluation or comparison of strip profiles can be satisfactorily accomplished with the use of the following key thickness[1] as shown in Fig. 1.1 and 1.2.
Center gauge (hc) - Center gauge is the workpiece thickness measured at the centerline dividing the workpiece width into two equal halves. The center gauge is one of the principal parameters characterizing the geometry of flat rolled products.
Edge drop thickness (hJ) - Edge drop thickness is usually measured at the distance J ranging from 50 to 75mm (2 to 3 in.) from the strip edge. At this distance, the strip thickness starts to rapidly decrease toward the edge which is the phenomenon known as edge drop.
Feather thickness (hl) - Feather thickness defines the strip thickness at the distance I ranging from 9.5 to 25mm (0.375 to 1.0 in.) from the strip edge. The portion of the strip profile that begins from this distance and extends toward the strip edge is known as the feather zone. In the feather zone, the rate of the decrease in thickness is usually much greater than in the edge drop zone.
Edge thickness (he) - Edge thickness is measured at the distance e ranging from 2 to 3mm (0.08 to 0.12 in.) from the strip edge.
Since the strip profile is not exactly symmetrical, the key strip profile thickness are measured from both operator and drive sides of the strip. The arithmetic average of these measurements is also commonly used as defined and illustrated in Table 1.1.

31. Fig. 1.2 Main parameters of strip profile. Adapted from Ginzburg [2]
Strip Crown
1.3 Types of Profile Crowns
The following two types of crowns can be identified in the workpiece profile (Table 1.2):
a) Center crown.
b) Side crown.
Center crown - Center crown is usually defined as the difference between the center gauge and the arithmetic average of either the feather thickness or edge drop thickness. The former is designated as an overall center crown and the latter as a partial center crown [2]. Thus the overall center crown is equal to the following:
chl = hc – hl (1-1)
where
hc = center gauge
hl = arithmetic average feather thickness.
Fig. 1.2 Main parameters of strip profile. Adapted from Ginzburg [2]

32. Figure 1.19 Relationship between various flatness parameters
Strip Flatness
Figure 1.19 Relationship between various flatness parameters

33. Measures of Flatness 1.18 Formulas for Strip Flatness
The five principal parameters that are commonly used for the quantitative evaluation of strip flatness [3] are as follows (See Table 1.5):
a) I-unit (I).
b) Height (H).
c) Percent (%) steepness (S).
d) Percent (%) elongation (e).
e) Percent (%) flatness(f).