Claims:We Claim:
1) A cold rolled continuously annealed steel sheet with high tensile strength of 350 MPa or more comprising in terms of weight %:
Element, wt% Element, wt%
C: 0.0051-0.012 N: 0.004 or less
Mn: 0.20-0.40 Ti: 0.055-0.08
Si: = 0.03 P: 0.005-0.025

and balance being Fe and other unavoidable impurities and having [Ti]-0.012 >= 4[C]-0.52[Nb]+3.43[N] for said high strength interstitial free rephosphorised steel.

2) A cold rolled continuously annealed steel sheet as claimed in claim 1 wherein said [Ti]-0.012 >= 4[C]-0.52[Nb]+3.43[N] is maintained such that the mean value of X-ray random preferred ODF random intensity of (111)[1-10] and (111)[2-31], (111)[1-21] and (111)[1-23] is greater than 3.

3) A cold rolled steel sheet according to anyone of claims 1 or 2 , further comprising by mass % atleast one type of element selected from the group comprising of Zr, Mg, Cr, Mo, W, Hf, Co, Ni, Cu, Zn, Sc, Ca, Pb and Sn such that each element by content in the range of 0.002 to 0.03%.

4) A cold rolled steel sheet according to anyone of claims 1 to 3 , further comprising by weight % atleast one from Nb: 0.012 to 0.03 % and B: 0.0005% to 0.002%.
5) A cold rolled steel sheet according to anyone of claims 1 to 4 comprising of steel sheet having UTS =350 MPa, YS/UTS ratio from 0.4 to 0.6, mean planer anisotropy ratio (?) of 1.5 to 2, , and having no yield point elongation after accelerated aging for atleast 12 months.

6) A cold rolled steel sheet according to anyone of claims 1 to 5 comprising of steel sheet having a phosphate crystal size of 2 to 4 µm and phosphate coating weight of 1.5-2.5 g/m2 after zinc phosphate chemical conversion coating treatment on said steel sheet surface, Excellent formability and dent free surface.

7) A process for manufacture of cold rolled steel sheet as claimed in anyone of claims 1 to 6 comprising the steps of:

i) Involving selectively steel slab having composition in terms of weight %:
Element, wt% Element, wt%
C: 0.0051-0.012 N: 0.004 or less
Mn: 0.20-0.40 Ti: 0.055-0.08
Si: = 0.03 P: 0.005-0.025
and balance being Fe and other unavoidable impurities and having [Ti]-0.012 >= 4[C]-0.52[Nb]+3.43[N];
ii) reheating the slab having said composition to reheating temperature of 1160-1220 °C;
iii) roughing rolling said reheated slab in roughing mill with roughing mill delivery temperature of 1020 to 1060°C;
iv) subjecting said rough rolled steel to finish rolling after at temperature range of 880 to 930 °C;
v) coiling the finish rolled steel at with run out table cooling rate of 8 °C/sec to 12 °C/sec such as to preferably achieve coiling temperature range of 8800 to 9300C; and
Vi)cold rolling the said hot rolled steel sheet with cold reduction of 65 to 80%.

8) A process for manufacturing cold rolled steel sheet as claimed in claim 7, further comprising:
a) annealing at soaking section temperature range of 750°C to 800°C with residence time for 50 to 140 sec;
b) slow cooling the steel up to a temperature range of 660 to 720 °C after soaking;
c) rapid cooling the steel up to a temperature range of 420 to 500 °C with cooling rate of 10 to 30°C/sec;
d) overaging said steel at temperature range of 320 to 400 °C with residence time of 100 to 300 sec; and
e) subjecting the overaged steel to skin pass elongation of 0.3% to 1%.

9) A process for manufacturing cold rolled steel sheet as claimed in anyone of claims 7 or 8 , comprising subjecting the said steel sheet to:
a) batch annealing at core temperature range of 640 to 680°C and Edge Temperature ranges from 680 to 710 °C; Soaking time of 5 to 10 hrs;
b) furnace cooling rate ranges from 2 to 8 °C/hrs;
c) air cooling rate ranges from 30 to 50 °C/hrs;
d) water cooling rate ranges from 50-60 °C/hours;
e) subjecting to skin pass elongation of 0.3% to 1%.

Dated this the 29th day of October, 2018
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
IN/PA-199
, Description:FIELD OF THE INVENTION

Present invention relate to a method of manufacturing cold rolled annealed interstitial free steel sheet with tensile strength of 350 MPa or more comprising in terms of weight C: 0.0051-0.012%, Si: =0.03%, Mn :0.2-0.4%, P: 0.005-0.025%, N =0.004%, Nb: 0.012-0.03%, Ti: 0.055-0.08% and the balance being Fe and unavoidable impurities and selective processing thereof to get the mean value of X-ray random preferred ODF intensity such as random intensity of (111)[1-10] and (111)[2-31], (111)[1-21] and (111)[1-23] greater than 3 to avoid the precipitation of FeTiP type ternary phosphide.

BACK GROUND OF THE INVENTION
Automobile manufacturers are opting for manufacturing light and more fuel efficient vehicles to fulfill the norms of future legislation concerning emission and fuel consumption. This forces the development of materials having excellent drawability along with superior strength to fulfill the passenger safety norms.
A method for producing high strength Rephosphorised interstitial free steel with excellent surface quality and high yield ratio having yield strength of 220Mpa minimum is disclosed in patent EP0691415 A1. The said EP method comprises of manufacturing high strength cold rolled steel sheet with excellent formability. The European Patent method comprises of 0.0005 -0.01% of Carbon, not more than 0.8% silicon,0.5-3.0% of Manganese,0.01 to 0.2% of phosphorous, 0.005-0.1% of titanium and 0.003-0.1%of niobium,0.0001 to 0.002% of boron with cold rolling reduction of 60% or more continuously annealed at 700 to 900°C. The cold rolled steel sheet manufactured following this EP method has resulted in yield strength around 160 to 220Mpa with tensile strength above 350MPa and BH index more than 30 Mpa. However, the method of this EP patent involves a problem of poor formability because of segregation of FeTiP at Grain boundary (Ghost Band) and dent on surface because of broken chips of Mn-oxide which appears after forming of exposed panel component.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide cold rolled interstitial free steel sheet with tensile strength of 350 MPa or more and a process for its production through continuous annealing route.

A further object of the present invention is directed to provide said cols rolled and annealed high strength interstitial free rephosphorised steel having excellent formability and superior surface quality which are suitable for automotive skin panel applications.

A still further object of the present invention is directed to said cols rolled and annealed high strength interstitial free rephosphorised steel, aimed to solve the problem of poor formability because of segregation of FeTiP at Grain boundary (Ghost Band) and dent on surface because of broken chips of Mn-oxide which appears after forming of exposed panel component.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a cold rolled continuously annealed steel sheet with high tensile strength of 350 MPa or more comprising in terms of weight %:
Element, wt% Element, wt%
C: 0.0051-0.012 N: 0.004 or less
Mn: 0.20-0.40 Ti: 0.055-0.08
Si: = 0.03 P: 0.005-0.025
and balance being Fe and other unavoidable impurities and having [Ti]-0.012 >= 4[C]-0.52[Nb]+3.43[N] for said high strength interstitial free rephosphorised steel.

A further aspect of the present invention is directed to said cold rolled continuously annealed steel sheet wherein said [Ti]-0.012 >= 4[C]-0.52[Nb]+3.43[N] is maintained such that the mean value of X-ray random preferred ODF random intensity of (111)[1-10] and (111)[2-31], (111)[1-21] and (111)[1-23] is greater than 3.
A still further aspect of the present invention is directed to said cold rolled steel sheet further comprising by mass % atleast one type of element selected from the group comprising of Zr, Mg, Cr, Mo, W, Hf, Co, Ni, Cu, Zn, Sc, Ca, Pb and Sn such that each element by content in the range of 0.002 to 0.03%.
A still further aspect of the present invention is directed to said cold rolled steel sheet further comprising by weight % atleast one from Nb: 0.012 to 0.03 % and B: 0.0005% to 0.002%.

Another aspect of the present invention is directed to said cold rolled steel sheet comprising of steel sheet having UTS =350 MPa, YS/UTS ratio of 0.4 to 0.6, mean planer anisotropy ratio (?) of 1.5 to 2, , and having no yield point elongation after accelerated aging for atleast 12 months.

Yet another aspect of the present invention is directed to said cold rolled steel sheet comprising of steel sheet having a phosphate crystal size of 2 to 4 µm and phosphate coating weight of 1.5-2.5 g/m2 after zinc phosphate chemical conversion coating treatment on said steel sheet surface, Excellent formability and dent free surface.

A further aspect of the present invention is directed to a process for manufacture of cold rolled steel sheet comprising the steps of:
i) involving selectively steel slab having composition in terms of weight %:
Element, wt% Element, wt%
C: 0.0051-0.012 N: 0.004 or less
Mn: 0.20-0.40 Ti: 0.055-0.08
Si: = 0.03 P: 0.005-0.025
and balance being Fe and other unavoidable impurities and having [Ti]-0.012 >= 4[C]-0.52[Nb]+3.43[N];
ii) reheating the slab having said composition to reheating temperature of 1160-1220 °C;
iii) roughing rolling said reheated slab in roughing mill with roughing mill delivery temperature of 1020 to 1060°C;
iv) subjecting said rough rolled steel to finish rolling after at temperature range of 880 to 930 °C;
v) coiling the finish rolled steel at with run out table cooling rate of 8 to 12 °C/sec such as to preferably achieve coiling temperature range of 8800 to 9300C; and
Vi)cold rolling the said hot rolled steel sheet with cold reduction of 65 to 80%.

A still further aspect of the present invention is directed to said process for manufacturing cold rolled steel sheet further comprising:
a) annealing at soaking section temperature range of 750°C to 800°C with residence time for 50 to 140 sec;
b) slow cooling the steel up to a temperature range of 660 to 720 °C after soaking;
c) rapid cooling the steel up to a temperature range of 420 to 500 °C with cooling rate of 10 to 30°C/sec;
d) overaging said steel at temperature range of 320 to 400 °C with residence time of 100 to 300 sec; and
e) subjecting the overaged steel to skin pass elongation of 0.3% to 1%.

A still further aspect of the present invention is directed to said process for manufacturing cold rolled steel sheet comprising subjecting the said steel sheet to:
a) batch annealing at core temperature range of 640 to 680°C and Edge Temperature ranges from 680 to 710 °C; Soaking time of 5 to 10 hrs;
b) furnace cooling rate ranges from 2 to 8 °C/hrs;
c) air cooling rate ranges from 30 to 50 °C/hrs;
d) water cooling rate ranges from 50-60 °C/hours;
e) subjecting to skin pass elongation of 0.3% to 1%.

The above and other objects and advantages of the present invention are described hereunder in greater details with reference to following illustrative embodiment by way of exemplary trials.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING EXAMPLES

The present invention is directed to provide cold rolled interstitial free steel sheet with tensile strength of 350 MPa or more and a process for its production through continuous annealing route.
The present invention aims to solve the problem of the prior art and objective is to produce high strength interstitial free rephosphorised steel having excellent formability and superior surface quality which are suitable for automotive skin panel applications.

The present invention is to produce high strength with better formability, and superior surface quality. This can be obtained by producing steel slab containing a specific composition having P (wt%) less than 0.025 and Mn (wt%) less than 0.4% to produce cold rolled steel sheet, hot rolled and coiled at temperature above 600°C to precipitate TiC-TiN complex structure leaving less Ti and very less P to form ternary phosphide during batch or continuous annealing which provides good planar anisotropy for excellent formability during press forming and ensures free from scale marks because of less coiling temperature and very less Mn weight percentage.

The present invention aims to solve the problem of poor formability because of segregation of FeTiP at Grain boundary (Ghost Band) and dent on surface because of broken chips of Mn-oxide which appears after forming of exposed panel component.

Following abbreviations are used to describe the invention:
Abbreviations
SS – Soaking section in continuous annealing furnace
SCS – Slow cooling section in continuous annealing furnace
RCS- Rapid cooling section in continuous annealing furnace
OAS- Over aging section in continuous annealing furnace
YS – Yield strength in MPa
UTS- Ultimate tensile strength in MPa
BH – Bake hardening index in MPa
SPM %– Skin passes elongation in %
YPE- Yield Point Elongation %
El%-Total Elongation at 50mm gauge length sample
CCM%- Cold rolling reduction %
? - Mean planer anisotropy ratio

Manner of implementation of the invention in relation to a preferred embodiment:

With the endeavor of developing cold rolled Interstitial free high strength steel with atleast 350 MPa tensile strength level by continuous annealing route, effect of metallurgical factors affecting the mechanical properties and drawability are described in detail.

Cold rolled steel sheet described in scope of present invention consist in terms of weight C: 0.0051-0.012%, Si: =0.03%, Mn: 0.2-0.4%, P: 0.005-0.025%, N =0.004%, Nb: 0.012-0.03%, Ti: 0.06-0.08% and the balance being Fe and unavoidable impurities. Additionally, atleast one type of element selected from the group comprising Nb, Zr, Cr, Mg, Mo, W, Hf, Co, Ni, Cu, Zn, Ca, Pb and Sn such that each element by content in the range of 0.002 to 0.03 % in terms of weight %.
Carbon: Present as interstitial solute is a major element deteriorating the drawability as well as increasing the strength of steel. It is well known that lower the C wt%, softer will be the material and aging property & drawability will be better. Furthermore, reducing the C wt% reduces the amount of alloy addition (Nb, Ti) to fix the same ultimately reducing the production cost. Also, C in steel as an interstitial element prevents the formation of {111} texture, deteriorating the drawability. Hence the C wt% is restricted to 0.012 wt% or less.
Manganese: It is an effective solid solution strengthening element which facilitates achieving the desired level of Tensile strength of 350 MPa or more. Effect on Yield strength is not significant hence; Mn helps in achieving desired yield ratio of 0.6 or less. However, to achieve any noticeable strengthening effect the minimum level should be more than 0.2 wt%, and therefore its lower limit should preferably be atleast 0.2 wt%. Keeping the Mn wt% on higher side significantly hampers the drawing property (? value) and scalability of interstitial free high strength rephosphorized steel hence upper limit is restricted to 0.4 wt% for present steel.
Phosphorus: It is the most important strengthening element in present invention as the name itself implies as an Interstitial free high strength rephosphorized steel. P is as an element which improves the strength at low cost, and the amount of addition thereof varies depending on a target strength level. For the strength level of more than 350 MPa as described in scope of present invention the minimum amount of P should be more than 0.005 wt%. However, when added amount exceeds more than 0.025 wt% the yield strength level increases significantly. In addition, higher amount of P promotes formation of Ghost Band. So, maximum limit of P is kept 0.025 %.
Silicon: It is an element utilized for increasing the strength of steel. As the silicon content increases the ductility and r-value noticeably deteriorates. Since silicon deteriorates plating / phosphatability properties by forming SiO2 type of oxides (scale). It is advantageous to add as low an amount of silicon in the steel as is possible, the added amount of silicon is preferably 0.03 wt% or less.
Titanium: It is added to fix carbon, nitrogen and Sulphur to make steel interstitial free. Keeping Titanium level below 0.055 wt% will be insufficient to fix the carbon and nitrogen; but if it is more than 0.08 wt% it will lead to higher product cost as well as increased Yield Strength of product.
Nitrogen (0.004wt% or less): The upper limit for nitrogen is 0.004 wt%. It is advisable to keep it to minimum level. Higher nitrogen content requires higher Ti addition to fix extra nitrogen and increase the TiN precipitates which strengthens the material, but deteriorating the drawing property.
Niobium (0.012-0.03 wt %): Niobium has been added with intension to fix solute Carbon as NbC. Niobium is a strong carbide former as compared to titanium and leads to grain size refinement. It has been reported that the addition of higher P and Mn deteriorates the surface quality and make the steel unsuitable for exposed panel applications. The strength is increased by addition of Nb. To achieve the same, the Nb level is kept in the range of 0.012 -0.03 wt% in present steel product.
[Ti]% -0.012 >= 4[C]%-0.52[Nb]%+3.43[N]% wherein the value of X=[Ti]% - 4[C]%-0.52[Nb]%+3.43[N]% has a major impact on planner anisotropy ratio and phosphatibility. To achieve r-bar value >1.5 and desired UTS of = 350 MPa, the value of X must be greater than 0.12wt%. In spite of having tensile strength value more than 350 MPa, in present invention it is ensured that the value of X must be greater than 0.12 wt%. This has been achieved by keeping C =0.0051 wt%, Nb level = 0.012 wt% and Ti level = 0.055 wt%.
Present inventive steel further includes at least one element from Zr, Mg, Cr, Mo, W, Hf, Co, Ni, Cu, Zn, Sc, Ca, Pb and Sn in a range of 0.002-0.03 wt%. These elements are added as they form carbide and/or nitride and/or sulfide which support the aging resistance and low BH index. However, amount more than 0.03 wt% adds additional cost of production and also reduces the drawability.
Complete description of the process:
To achieve slab chemistry as described in scope of the invention, Heat (batch of steel) from basic oxygen furnace (BOF) is processed through RH degasser and subsequently cast through continuous casting process. Special measures have been taken to hot roll resulted slabs by keeping slab reheating temperature in the range of 1160°C to 1220°C intended to control roughing mill delivery temperature under 1060°C and finishing mill entry temperature under 1020°C to check surface defects like rolled in scale. During hot rolling finishing mill temperature range of 880°C to 930°C and run-out table cooling rate from finishing mill to coiler of more than 8 0C/sec was maintained to achieve coiling temperature range of 620 °C to 670 °C. Hot rolled coils were subsequently processed through pickling coupled with tandem cold rolling mill to remove the oxide surface present in the surface and to provide cold reduction of 65% or more.
Subsequent to pickling and cold rolling of the desired sheet thickness, cold rolled sheets are processed through continuous annealing line, where electrolytic cleaning removes rolling emulsions present on the surface. Cleaned surface passes through the preheating and heating section where the strip is heated at the rate of 1-10 0C/sec to soaking section temperature maintained at 750 °C - 800 °C.
Annealing time of 50-140 seconds gives desired results for present interstitial free 350MPa tensile strength grade. After soaking steel strip passes through slow cooling section at cooling rate of less than 3°C/sec. Slow cooling section temperature of 660 – 720 °C was maintained. Following slow cooling section annealed strip sheet been rapid cooled at 10 - 30 °C/sec to rapid cooling section temperature maintained in the range of 420-500 0C. After rapid cooling section annealed strip was over aged keeping the over aging section temperature of 320 - 400 °C for 100 to 300 seconds. Subsequent to over aging, steel strip is given a skin-pass elongation (temper rolling) in the range of 0.30 to 1% to avoid yield point elongation and to improve flatness of steel strip. In order to achieve the improved texture with mean value of X-ray random intensity of (111)[1-10] and (111)[2-31], (111)[1-21] and (111)[1-23] orientation component must be at least 3 in order to achieve planer anisotropy ratio of = 1.5 and yield ratio of =0.6. In addition, following relation must be fulfilled in favor of chemical composition and annealing;
[Ti]-0.012-4[C]+0.52[Nb]-3.43[N] = 0, where [M] represents wt% of the element.
Method of evaluating phosphatability: Phosphating process can be defined as the treatment of a metal surface so as to give a reasonably hard, electrically non-conducting surface coating of insoluble phosphate which is contiguous and highly adherent to the underlying metal and is considerably more absorptive than the metal which provides excellent corrosion resistance and paintability to steel surface. The coating is formed as a result of a topochemical reaction, which causes the surface of the base metal to integrate itself as a part of the corrosion-resistant film. To evaluate phosphatability firstly alkali degreasing was performed on steel sheet at 400 C for 120 sec using Fine Cleaner chemical manufactured by NIHON PARKERIZING India Pvt. Ltd. to the obtained cold rolled steel sheet without any oil/grease on surface. Degreasing was followed by water rinsing and then surface conditioning at room temperature for 30 seconds using PL-Z chemical manufactured by NIHON PARKERIZING India Pvt. Ltd. Phosphate treatment using PB-L chemical, manufactured by NIHON PARKERIZING India Pvt. was done at 40 0C for 120 seconds. Subsequently, the surface after phosphate treatment was observed under a Scanning electron microscope using Secondary Electron Image mode. Average grain size was measured assuming circular phosphate crystals. Crystal size <4 µm is considered as excellent for phosphatability. The phosphate coating weight was measured using the XRF method and steel sheet with average coating weight after zinc phosphate chemical conversion coating of 1.5-2.5 g/m2 is considered to have excellent phosphatability.

Method of evaluating accelerated aging resistance: Tensile test specimen as per JIS Z2241 No.5 with 50mm gauge length 25 mm width was prepared across the rolling direction of steel sheet. Prepared specimen was kept in an oil bath at 1000C for 3 and 6 hours respectively. Subsequently the specimen was tested in tensile test machine with strain rate of 0.008/sec. Specimen which showed YPE>0.15% after the test are be prone to accelerated aging and does not confirm to the scope of invention.
Complete description of Inventive steel and comparative steel grades are illustrated from Table I and V.
Table I- Elemental Compositions of the inventive steel sheets along with comparative example and their respective values of Eq1= [Ti] %-0.012-4[C%]+0.52[Nb%]-3.43[N%].
Table II- Hot rolling, cold rolling, Continuous and Batch annealing parameters and the value of inventive and comparative steel sheets.
Table III- Mechanical properties, phosphate crystal size and phosphate coating weight, Ghost Band and Dent after forming remarks of inventive and comparative steel sheets.
Table-IV –Mean value of X-ray random intensity ratio of group of (111)[1-10] orientation along with mean value of X-ray random intensity for (111)[2-31], (111)[1-21] and (111)[1-23] orientation component for inventive and comparative steel.

Table I:

* All compositional elements are in terms of weight %
* I - Present inventive example, C- Comparative Examples
** Underlined “outside the appropriate range”
However, Steel 2, 4, 6, 8 and 10 are marked as comparative examples as atleast one of their composition is outside the range of scope of the invention, also the value of Eq1 is outside the range of greater than 0.

Table II:

I - Present inventive example, C- Comparative Examples
* FT- hot finish rolling temperature , CT- Hot coiling temperature , SS- soaking section ,SCS- Slow cooling section , RCS- Rapid cooling section , OAS- Overaging section , SPM- Skin pass elongation
** Underline indicates “outside the appropriate range”
Note: steel 1A, 1B, 3, 5A, 5B, 7A and 9A are marked inventive examples as their hot and cold rolling parameters are well within the range of scope of the invention, excellent phosphatability and improved {111}<110> texture as listed in subsequent tables.
However, Steel 2, 4A, 4B, 6, 7B, 8, 9B and 10 are marked as comparative examples as atleast one of their composition is outside the range of scope of the invention as the value/Remarks of YS/UTS ratio, poor phosphatability, Ghost Band after Forming and Dent after Forming and low ratio of X-ray intensity for (111)[1-10] and (111)[2-31], (111)[1-21] and (111)[1-23] textures as listed in subsequent tables.

Table III
Steel No. YS, MPa UTS, MPa YS/UTS ? Total EL% Phosphate Crystal Size, µm Phosphate Coating weight , g/m2 Ghost Band After Forming Dent After Forming Remarks

1A 205 360 0.57 1.8 40 2.5 1.8 No No I
1B 195 370 0.53 1.9 43 3 2 No No I
2 220 350 0.63 2 44 6 4 Yes No C
3 205 360 0.57 1.75 39 2.8 1.9 No No I
4A 250 340 0.74 1.4 44 5 3.6 Yes Yes C
4B 260 345 0.75 1.45 45 4.5 3.8 Yes Yes C
5A 208 360 0.58 1.9 41 3 1.75 No No I
5B 210 370 0.57 1.85 42 3.2 1.6 No No I
6 240 345 0.70 2 46 4.8 1 Yes Yes C
7A 185 365 0.51 1.75 41 3 2 No No I
7B 260 345 0.75 1.9 44 3 2 No No C
8 240 340 0.71 2 42 5 4 Yes Yes C
9A 210 360 0.58 1.8 42 3 2 No No I
9B 250 360 0.69 1.6 38 3 2 No No C
10 220 350 0.63 1.7 40 2.5 2.5 Yes Yes C
I – inventive steel, Comp. C- Comparative steel
* Underlined indicate “outside the appropriate range”.
*** ? is mean planer anisotropy ratio. YS- Yield Strength, UTS- Tensile strength
* Steel sheets having YS/UTS ratio >0.6 does not conform to the scope of the present invention, also steels with phosphate crystal size after zinc phosphate chemical conversion coating >4µm and phosphate coating weight >3g/mm2 are suggests poor phosphatability and marked as comparative. * Steel 4, 8 and 10 having higher Mn and P wt%, appear ghost band and Dent after forming and also give poor phosphatibility.
TABLE IV:
Steel Number X ray random intensity for (111)[1-10] X ray random intensity for (111)[2-31], (111)[1-21] and (111)[1-23] Remarks
1A 4.6 3.4 I
1B 4.5 3.6 I
3 5 3.8 I
4A 2.5 1.5 C
4B 2.1 1.7 C

Note: Table IV listing a mean value of X-ray random intensity ratio of group of (111)[1-10] and (111)[2-31], (111)[1-21] and (111)[1-23] . Steel 1A, 1B and 3 having X–ray random intensity ratio of (111)[1-10] and (111)[2-31], (111)[1-21] and (111)[1-23] than 3 are mentioned as inventive example. Therefore 1A, 1B and 3 are complying with the r-bar value of = 1.5 and YS/UTS ratio of 0.6 or less .Whereas comparative steel 4A and 4B with X-ray intensity ratio of (111)[1-10] and (111)[2-31], (111)[1-21] and (111)[1-23] orientation component lower than 3 does not comply with ? (Drawability) requirement . Also inventive steel 1A, 1B and 3 complying with mean value of X ray random intensity of (111)[1-10] and (111)[2-31], (111)[1-21] and (111)[1-23] where steel 4A and 4B does not comply.