Claims:WE CLAIM:

1. A formable and localized corrosion-resistant Ferritic stainless steel comprising:
a ferritic stainless steel base material comprising Fe and Cr;

wherein the ferritic stainless steel base material comprises about Ferritic stainless steel composition of C (0.01 to 0.1 wt %), Mn (0.1 to 1 wt %), S (up to 0.03 wt %), P (up to 0.03 wt %), Si (0.10 to 0.5 wt%), Cr (16 to 20 wt %) and balance being Fe;

2. The formable and localized corrosion-resistant Ferritic stainless steel as claimed in claim 1, wherein the said steel compositions has a yield strength in the range of 300 Mpa to 400 Mpa, ultimate tensile strength in the range of 500 Mpa to 600 Mpa and elongation is in the range of 20 to 30%.

3. The formable and localized corrosion-resistant Ferritic stainless steel as claimed in claim 1, wherein the said stainless steel composition has corrosion rate in the range of 0.05 to 0.2 mpy, Pitting resistance with pitting potential in the range of 250 to 350 mpy and corrosion current density ranging from 0.1 to 1 µA cm-2 in 3.5% NaCl solution.

4. The formable and localized corrosion-resistant Ferritic stainless steel as claimed in claim 1, wherein the said stainless steel composition has formability with Plastic Strain Ratio (rm) ranging from 1.0 to 1.5 and lower ‘Earing’ tendency (?r) (0 to 0.1).

5. The formable and localized corrosion-resistant Ferritic stainless steel as claimed in claim 1, wherein the said stainless steel composition has partial recrystallization of ferritic grains with formable texture component ‘? fiber’ of about 20 to 30%.

6. A process for the formable and localized corrosion-resistant Ferritic stainless steel comprising the steps of:
reheating steels base material ingots/slabs and soaking in a reheating furnace to 1150 to 1250o C for 3 hours;
hot-rolling of 16 mm plate with finish rolling temperatures of 900 to 800o C, wherein the hot rolling reduction is about 80-90% at the rate of 6mm strip;
performing annealing in a solution at 1050 to 1150o C for 2 hours and subsequently water quenching is carried out;
performing final cold rolling reduction to the range about 60-90%;
performing annealing of the said cold rolled strips in the range of 800 to 900o C for 2 to 10 min and subsequent water quenching is done wherein the ferritic stainless steel base material comprises about Ferritic stainless steel composition of C (0.01 to 0.1 wt %), Mn (0.1 to 1 wt %), S (up to 0.03 wt %), P (up to 0.03 wt %), Si (0.10 to 0.5 wt %), Cr (16 to 20 wt %) and balance being Fe.

7. The process for the formable and localized corrosion-resistant Ferritic stainless steel as claimed in claim 6, wherein the said steel compositions has a yield strength in the range of 300 Mpa to 400 Mpa, ultimate tensile strength in the range of 500 Mpa to 600 Mpa and elongation is in the range of 20 to 30%.

8. The process for the formable and localized corrosion-resistant Ferritic stainless steel as claimed in claim 6, the said stainless steel composition has corrosion rate in the range of 0.05 to 0.2 mpy, Pitting resistance with pitting potential in the range of 250 to 350 mpy and corrosion current density ranging from 0.1 to 1 µA cm-2 in 3.5% NaCl solution.

9. process for the formable and localized corrosion-resistant Ferritic stainless steel as claimed in claim 6, the said stainless steel composition has formability with Plastic Strain Ratio (rm) ranging from 1.0 to 1.5 and lower ‘Earing’ tendency (?r) (0 to 0.1).

10. process for the formable and localized corrosion-resistant Ferritic stainless steel as claimed in claim 6, wherein the said stainless steel composition has partial recrystallization of ferritic grains with formable texture component ‘? fiber’ of about 20 to 30%.
, Description:FERRITIC STAINLESS STEEL WITH SUPERIOR MECHANICAL PROPERTY AND LOCALIZED CORROSION RESISTANCE FOR ELEVATOR APPLICATION AND PROCESS FOR ITS PRODUCTION.

FIELD OF INVENTION

The present invention relates to an formable and localized corrosion-resistant, ferritic stainless steel, a process of manufacturing the steel, and more particularly, to an formable and localized corrosion -resistant ferritic stainless steel having a Cr in the base material, a process of manufacturing the steel with, high formability with plastic strain ratio in the range of 1 to 1.5.

BACKGROUND ART

Ferritic stainless steels, which generally contain 11% by weight or more of Cr, are cheaper than austenitic stainless steels and stress corrosion cracking due to chlorides does not occur in ferritic stainless steels. Due to these characteristics, demands for ferritic stainless steels have been gradually increased.

In a conventional art, formability of ferritic stainless steels has been improved by lowering interstitial elements such as C and N, and adding other alloy elements such as Ni, Mo, Cu, Zr, and rare earth metals.

AISI 304 stainless steel is traditionally the material of choice for fabrication of elevator doors & frames, because of its excellent formability and corrosion properties. Due to high cost and non-availability of Ni, most of the elevator manufacturers have started using AISI 441, a Ti-stabilised grade of ferritic stainless steel. AISI 441 stainless steel has marginally higher proof strength than standard austenitic stainless steel grade AISI 304 with lower work hardening rate. Owing to titanium stabilization, its r-value is higher compared to non-stabilized ferritic stainless steel leading to excellent deep-drawing capability. Titanium and niobium alloying in this steel also reduces sensitivity to intergranular corrosion. Relatively high chromium content also improves the resistance of this steel to crevice corrosion and oxidation resistance up to 950°C, which are better compared to other ferritic stainless steels.

Outokumpu and AK Steel are the world leaders in producing AISI 441 grade stainless steel. Indian elevator manufacturers are importing AISI 441 stainless steel from Outokumpu or AK Steel, as none of the Indian stainless steel manufacturers produce this grade regularly. Because of import, the elevator manufacturers face problems in terms of increase in production cost and time delay in getting the material. Recently, Indian elevator manufacturers have been approaching Salem Steel Plant (SSP) for a ferritic grade with mechanical properties & corrosion resistance equivalent to AISI 441 grade for elevator application. SSP regularly produces AISI 430 grade ferritic stainless steel, with mechanical property more or fewer equivalents to AISI 441 grade, but with inferior corrosion resistance compared to AISI 441 stainless steel. It is therefore planned to develop a ferritic stainless steel with suitable alloy chemistry having mechanical properties and corrosion resistance equivalent to AISI 441 stainless steel, for elevator application.

Most of the prior art on the subject are related to the novelty in:

(a) Processing of steel through costlier route AOD (Argon-Oxygen-Decarburization) VOD (Vacuum-Oxygen-Decarburization) producing technology.
(b) Properties were achieved with Lean austenitic stainless steel
(c) Properties were achieved with dual phase stainless steel containing austenite and ferrite
(d) Properties were achieved with ultra-low-carbon less than 0, 01 % carbon,
(e) Properties were achieved with titanium or niobium
(f) Properties were achieved with dual titanium and niobium stabilized ferritic stainless steel
(g) Properties were achieved with dual titanium and vanadium stabilized ferritic stainless steel
(h) Properties were achieved with dual Mo, Ni and N combination stabilized ferritic stainless steel
(i) Properties were achieved with combination of Mo, Cu and N combination stabilized ferritic stainless steel
(j) Properties were achieved with Cr >20 %
(k) Lowering C and Cr and increasing Si and Mn to higher end in AISI 430SS
(l) Properties were achieved with Zr or Sn

SUMMARY OF INVENTION

The novelty of present invention lies in formulation of a comprehensive methodology for manufacturing low cost ferritic stainless steel with Alloy composition as:
Ferritic stainless steel composition of C (0.01 to 0.1%), Mn (0.1 to 1%), S (up to 0.03%), P (up to 0.03%), Si (0.10 to 0.5%), Cr (16 to 20%) and balance being Fe.

The Manufacturing process of claimed high corrosion resistant and high formable steel, comprising following steps:
• The steels ingots/slabs are reheated and soaked in a reheating furnace to 1150 to 1250o C for 3 hours.
• Hot-rolled to 16 mm plate with finish rolling temperatures of 900 to 800o C.
• Hot rolling reduction is about 80-90% (~6mm strip).
• Solution annealing at 1050 to 1150o C for 2 hours and subsequent water quenching is done
• The final cold rolling reduction is about 60-90%.
• Annealing the cold strips after cold rolling was carried out in the range of 800 to 900o C. for 2 to 10 min and subsequent water quenching is done

Mechanical properties:
The disclosed steel compositions have a yield strength in the range of 300 MPa to 400 MPa, ultimate tensile strength in the range of 500 MPa to 600 MPa and elongation in the range of 20 to 30%.

Corrosion resistance:
• The claimed stainless steel composition has corrosion rate in the range of 0.05 to 0.2 mpy in 3.5% NaCl solution.
• The claimed steel composition has better Pitting resistance with pitting potential in the range of 250 to 350 mpy in 3.5% NaCl solution.
• The claimed has better corrosion resistance corrosion current density ranging from 0.1 to 1 µA cm-2 in 3.5% NaCl solution.

Intergranular corrosion resistance:
• The claimed steel compositions were virtually immune to intergranular corrosion (IGC), and this was discerned from the quantification of degree of sensitization (DoS) through double loop electrochemical potentiokinetic reactivation (DL-EPR) testing in 0.5 M H2SO4 + 0.01 M KSCN as per ASTM G 108. The DoS values of ? 0.05 for the claimed steels

Formability:
• The claimed steel compositions found to have superior formability with Plastic Strain Ratio (rm) ranging from 1.0 to 1.5 and lower ‘Earing’ tendency (Dr) (0 to 0.1)
• The claimed steel composition found to have partial recrystallization of ferritic grains with formable texture component ‘? fiber’ of about 20 to 30%.

The above-described methodology for manufacturing low cost ferritic stainless steels with superior mechanical and corrosion properties than that of AISI 441 stainless steel is very different from the existing prior art, as discussed above.

The innovation presents viable prospect of being utilized/ commercialized manufacturing the low cost ferritic stainless steel with superior mechanical and corrosion resistance than that of AISI 441 stainless steel for elevator application in India and abroad.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure1 illustrates Phase diagram constructed using Thermo-Calc software for AISI 430 SS showing narrow range for hot rolling and formation of many intermetallics compounds below 8000 C in accordance with the present invention;

Figure 2 illustrates Phase diagram constructed using Thermo-Calc software for AISI 441 SS showing narrow range for hot rolling and formation of many intermetallics compounds below 7200 C in accordance with the present invention;

Figure 3 illustrates Phase diagram constructed using Thermo-Calc software for Cr-added AISI 430 SS showing narrow range for hot rolling and formation of many intermetallics compounds below 9000 C in accordance with the present invention;

Figure 4 illustrates Phase diagram constructed using Thermo-Calc software for Cr—Mo added AISI 430 SS showing narrow range for hot rolling and formation of many intermetallics compounds below 9000 C in accordance with the present invention;

Figure 5 illustrates Phase diagram constructed using Thermo-Calc software for Cr-Ni added AISI 430 SS showing narrow range for hot rolling and formation of many intermetallics compounds below 8000 C in accordance with the present invention;

Figure 6 illustrates Optical microstructure of 65% cold rolled annealed modified ferritic stainless steels and commercially produced AISI 430 and AISI 441 ferritic stainless steels (etchant: 60% HNO3) in accordance with the present invention;

Figure 7 illustrates Optical microstructure for 65% Cold rolled annealed modified ferritic stainless steels (a) Cr added, (b) Cr-Mo added (c) Cr-Ni added and commercially produced (d) AISI 430 and (e) AISI 441 ferritic stainless steels in 10 % oxalic acid test as per ASTM A262 A in accordance with the present invention;

Figure 8 illustrates Typical double-loop electrochemical potentiokinetic reactivation (DL-EPR) plots of 65% Cold rolled annealed modified ferritic stainless steels and commercially produced AISI 430 and AISI 441 ferritic stainless steels showing their relative insusceptibility to intergranular corrosion (Test solution: 0.5 M H2SO4 + 0.01 M KSCN; Test temperature: 30±1o c; ASTM G 108) in accordance with the present invention;

Figure 9 illustrates Polarization plots of 65% Cold rolled annealed modified ferritic stainless steels and commercially produced AISI 430 and AISI 441 ferritic stainless steels in 3.5% NaCl in accordance with the present invention;

Figure 10 illustrates Polarization plots of 80% Cold rolled annealed modified ferritic stainless steels and commercially produced AISI 430 and AISI 441 ferritic stainless steels in 3.5% NaCl in accordance with the present invention;
Figure 11 illustrates Pitting potentials and corrosion rates of 65% Cold rolled annealed modified ferritic stainless steels and commercially produced AISI 430 and AISI 441 ferritic stainless steels in 3.5% NaCl in accordance with the present invention;

Figure 12 illustrates Pitting potentials and corrosion rates of 80% Cold rolled annealed modified ferritic stainless steels and commercially produced AISI 430 and AISI 441 ferritic stainless steels in 3.5% NaCl in accordance with the present invention;

Figure 13 illustrates Average Plastic Strain Ratio (rm) of Cold rolled annealed modified ferritic stainless steels and commercially produced AISI 430 and AISI 441 ferritic stainless showing improvement in formability Cr added ferritic stainless steels in accordance with the present invention;

Figure 14 illustrates Planar Anisotropy (?r) measurements for of Cold rolled annealed modified ferritic stainless steels and commercially produced AISI 430 and AISI 441 ferritic stainless steels showing lower earing tendency for Cr added ferritic stainless steel in accordance with the present invention;

Figure 15 illustrates Microtectural analysis of commercial available AISI 441 ferritic stainless steels showing formation of ? fiber (35%) confirming partial recrystallization in accordance with the present invention;

Figure 16 illustrates Microtectural analysis of 65% Cold rolled annealed Cr added modified ferritic stainless steels showing weak formation of ? fiber (26%) confirming partial recrystallization in accordance with the present invention.

DETAILED DESCRIPTION

Accordingly laboratory heats were undertaken at RDCIS with controlled additions of Cr, Ni and Mo. Three heats were made with Cr (~ 19 wt. %), Mo (0.9 wt. %) and Ni (0.75 wt. %) in 100-kg air induction furnace. Heats of designed FSS compositions were melted in an Inductotherm-USA make 100 kg air induction furnace in separate campaigns using 430SS slab pieces and precisely weighed alloy additions of espect Mn, espect FeCr, low carbon FeCr & FeMo lumps, Mn metal chips, shredded copper scrap, and nickel briquettes. In all, three laboratory heats were made and target chemistries were effectively achieved in three heats i.e. with higher Cr (~19%), with Cr-Ni and Cr-Mo stainless steel heats. The molten steel from each heat was cast into 100 mm square cross-sectioned 25 kg ingots. Two ingots were obtained for each heat. The top and bottom end of the ingots were cropped to exclude the pipe and other solidification defects. The ingots were subsequently reheated and soaked in a furnace at 1250o C for 3 hours for thermal/ compositional homogenization and then hot-rolled in Hillé-UK make experimental rolling mill in 2 rolling campaigns to 5-6 strips with finish rolling temperatures of 850oC to avoid edge cracking. The 100 mm square cross-sectioned ingots were initially hot-rolled to 50 mm plates using 4-pass draft schedule, 100?95?78?65?50 mm and then further down to 5-6 mm strips using a 3-pass draft schedule, 50?37?25?17?9?6 mm, after reheating the plates at 1250o C for 1 hr. After each rolling campaign, the plates were allowed to air cool. The hot rolled strips were subsequently conferred a solution annealing treatment by soaking them at 1150o C for 2 hours followed by rapid quenching in water for dissolution of deleterious intermetallic compounds and secondary phases and to prevent their re-precipitation in the steels.

Stainless strips solution-annealed at 850o C were further subjected to scale removal and cold rolled in laboratory rolling mill with overall cold reductions to the tune of 65-90% through multipass cold rolling to final thickness of 1.08 to 0.3 mm. Finish thickness as low as 0.30-0.34 mm could be achieved in these stainless materials, which demonstrated their excellent cold reducibility. Cold rolled strips were eventually annealed at 850o C to evolve favourable espectively tion texture for achieving superior tensile and formability properties.

Table 1 shows the designed chemistry for ferritic stainless steel and the chemical composition of the steels, produced in laboratory. Three heats were made with Cr (~ 19 wt. %), Mo (0.9 wt. %) and Ni (0.75 wt. %.) Also interstitials elements such as C and N) are kept very low for improving formability and intergranular corrosion (IGC) resistance

Table 1: Chemical compositions of the alloys (in wt. %)

Figure 1-5 shows the phase diagrams constructed for designed composition of modified AISI 430 SS and also commercially produced AISI 441 and AISI 430 SS using Thermo-Calc software. The phase diagram indicates thermodynamic stability of secondary phases (or, precipitates) such as carbides, nitrides, intermetallic compounds (IMCs, Sigma, Laves) between 750-300oC. It is understood that these precipitates could potentially affect the dynamic softening process and recrystallisation kinetics during hot deformation and annealing treatments as well as have marked influence on resultant mechanical and corrosion properties. In modified AISI 430 stainless steels the formation of these intermetallic compounds and secondary phases occurs even at higher temperatures (900o C). In general it is safe to operate (hot rolling) above 900o C for all chosen composition, i.e., final finishing rolling temperature should be kept above 900o C.

The phase diagram clearly shows the stability of ferrite phase with no major transformation over a wide temperature range. This implies that grain refinement would pose a challenge in the steel and may only be achieved through recrystallization annealing after sufficient cold deformation. It also means high temperature exposures, such as during hot rolling, would lead to irrevocable coarsening of the ferrite in steel leading to considerable diminution in mechanical properties.

Metallographic specimens were sectioned in longitudinal transverse direction from annealed stainless steel strips and prepared using conventional grinding-polishing procedures and electrolytically etched in 10% oxalic acid solution at 6 V dc for 90 s for microscopic observation of modified 430 stainless steels The newly developed modified 430 stainless steels (Table -1) compositions were met as per the designed chemistry. Microstructural analysis was carried out for all the steels at 65% cold rolled solution annealed condition and the microstructure are given in Figure 6. Modified 430 SS and commercially produced AISI 430 SS found to exhibit rather coarse, elongated but recovered ferrite grains replete with copiously dispersed precipitates. In contrast, AISI 441SS steel revealed more equiaxed ferrite grain structure with multimodal grain size distribution.

The mechanical properties of the developed modified AISI 430 SS were given in the Table 2 and 3. For comparison the mechanical properties of commercial available AISI 430 and AISI 441 SS are also given in the table. The developed modified AISI 430 SS steels for both 65 and 80% cold rolled annealed (CRA) conditions revealed a reasonable combination of properties: yield strength, tensile strength and elongation compared to that of commercial available AISI 441 SS, but exceptional compared to AISI 430 SS.

Table 2: Room temperature tensile properties of steel 65% cold rolled annealed modified 430 SS vis-à-vis 430 and 441 ferritic stainless steels

Table 3: Room temperature tensile properties of steel 85% cold rolled annealed modified 430 SS vis-à-vis 430 and 441 ferritic stainless steels

The steels have been observed to be virtually immune to intergranular corrosion (IGC), and this was discerned from the quantification of degree of sensitization through ASTM A 262 10% oxalic acid test (no ditch structure) (Figure 7)

Table 4: Intergranular corrosion (IGC) susceptibility of the stainless steels determined using double-loop electrochemical potentiokinetic reactivation (DL-EPR) technique (Test solution: 0.5 M H2SO4 + 0.01 M KSCN, Test temperature: 30±1oC, ASTM G 108)

Table 4 shows the intergranular corrosion (IGC) susceptibility of modified AISI 430 stainless steel (for both 65% and 80% cold rolled annealed steel (CRA) steel) including AISI 441, AISI 430 stainless steels evaluated using double-loop electrochemical potentiokinetic reactivation (DL-EPR) procedure in 0.5 M H2SO4 + 0.01 M KSCN test solution. Figure 8 depicts the superimposed DL-EPR plots for investigated stainless steels. The plots exhibit marked differences between the peak current densities of the anodic (forward) and reactivation (reverse) polarization scans. Also, the peak anodic current density (Ia) of the forward potential scan is greater than the peak reactivation current density (Ir) corresponding to the reverse potential sweep. The ratio of peak reactivation current density (Ir) and the peak anodic current density (Ia) is taken as a measure of degree of sensitization (DoS) and is termed the “current amplitude ratio (Ir/Ia)”. The lower the ratio or lesser the magnitude of peak reactivation current (Ir) with respect to the peak anodic current (Ia) or, in other words, the greater the area under the curve for the DL-EPR plot, the lower is the apparent susceptibility of the stainless steel to IGC. In the present case, the current amplitude ratios for modified AISI 430 stainless steels were evaluated to be in the range of 0.025–0.03 for 65% CRA steel and 0.005 to 0.03 for 80% CRA steel. Since the AISI 441 ferritic stainless steel have been stabilized against these stainless steels were found to exhibit extremely low current amplitude ratio of 0.01, revealing their insusceptibility to intergranular corrosion. It has been shown previously that a sensitized stainless steel showing ditched structure (one or more grains completely surrounded by ditches) in an oxalic acid etch test (as per ASTM A 262 Practice A) is characterized by current amplitude ratio, Ir/Ia > 0.05. The results thus show that the modified AISI 430 ferritic stainless steels are not vulnerable to intergranular corrosion (IGC). The DL-EPR plots presented in Figure 8 are essentially cyclic polarization plots and can therefore be used to evaluate the pitting tendencies of investigated stainless steels in the test medium. The modified AISI 430 ferritic stainless steel were found to exhibit “negative” electrochemical hysteresis loops during the reverse scan, indicating their invulnerability to pitting up to the threshold potential of 700 mV.

Figures 9 and 10 show the typical potentiodynamic polarization plots for chosen modified AISI 430 ferritic stainless steels in 3.5% NaCl solution. Tables 5 and 6 give the electrochemical corrosion properties deduced from these potentiodynamic polarization scans, respectively. The figures and tables also depict and present correspondingly the electrochemical corrosion especti and properties of austenitic stainless steel AISI 441 SS and AISI 430 SS for comparison and reveal the corrosion, passivation and pitting characteristics of the investigated steels in the corrosive aqueous media.

The 65 and 80% CRA modified AISI 430 stainless steels were found to exhibit spontaneous and stable passivities in the aggressive test environment of 3.5% NaCl solution. It can be discerned from Tables 5 and 6 that the 65 and 80% CRA modified AISI 430 stainless steels show relatively nobler electrochemical corrosion potentials, improved passivities, and lower corrosion currents compared to austenitic stainless steel commercially produced AISI 441 and AISI 430 SS. The experimental stainless steels revealed the tendency for formation of more protective, tenacious passive films in the chloride environment than AISI 441 and AISI 430 SS. This observation was concluded from the lower passive current density values of 0.4-0.7 µA/cm2 for 65% and 0.5-0.8 µA/cm2 for 80% CRA modified AISI 430 stainless steels exhibited at 70 mV as compared to the corresponding value of 1.5 µA/cm2 measured for AISI 441 SS and 3.6 µA/cm2 for AISI 430 SS. CRA modified AISI 430 stainless steels were also found to exhibit high pitting potentials of 260-380 mV and very low corrosion rates of 0.08-0.25 mpy, underlining their superior localized as well as general corrosion resistance in the chloride environment. The general corrosion performance of CRA modified AISI 430 stainless steels was apparently superior to commercially produced AISI 441 and 430 stainless steels which were found to exhibit corrosion rate of 0.25 mpy and 0.4 mpy respectively. The pitting potentials and the corrosion rates of CRA modified AISI 430 stainless steels steels in 3.5% NaCl vis-à-vis commercially produced AISI 441 and 430 stainless steels have been graphically depicted in Figures 11 and 12 for comparative evaluation.

Table 5: Electrochemical corrosion parameters of 65% cold rolled annealed modified 430 SS in aqueous chloride medium vis-à-vis 430 and 441 ferritic stainless steels

Table 6: Electrochemical corrosion parameters of 80% cold rolled annealed modified 430 SS in aqueous chloride medium vis-à-vis 430 and 441 ferritic stainless steels

Figures 13 and 14 graphically depicts the formability properties for cold rolled and annealed modified 430 ferritic stainless steels, commercially produced AISI 430 and AISI 441 stainless steel in terms of average Plastic Strain Ratio (rm) and Planar Anisotropy (?r) values. It is clear that superior Plastic Strain Ratio (rm ~1.0) and lower ‘Earing’ tendency (Dr) can be achieved in modified 430 ferritic stainless steels with 65% cold reduction followed by annealing at 850oC.

Figures 15 and 16 show the result of EBSD analysis including textural aspects for commercially produced AISI 441 ferritic stainless steel and Cr added 430 ferritic stainless steels after ~65% cold reduction followed by annealing at 850oC. The EBSD images clearly delineate the high angle grain boundaries (HAGBs) and low angle grain boundaries (LAGBs) and the associated grain boundary misorientation distribution clearly confirm the sub-grain formation indicative of a dynamic recovery process. From EBSD images (Figure 15) of AISI 441 SS it is clear that the steel has recrystallized
grains with (?) fibre texture plane (111) around 35% suitable for formable bcc material. In Cr added AISI 430 ferritic stainless steel the EBSD image (Figure 16) reveal partial recrystallization of grains with formation of weak gamma (?) fibre texture plane (111) around 26% suitable for formable bcc material.

From the above results, it can be concluded that Cr added modified 430 stainless steel with improved corrosion and formability property comparable to AISI 441 can replace existing AISI 441 ferritic stainless steel in elevator panels application where not much welding in required.

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration by way of examples and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.