Title of Invention

AN IMPROVED PROTECTIVE COATING COMPOSITION FOR HOT DIP GALVANIZATION OF STEEL

Abstract The invention relates to an improved protective coating composition for hot dip galvanization of steel, the composition comprising zinc and strontium wherein the strontium is present in at least 0.01 to 0.1% by weight of the composition. The invention also relates to steel coated with the composition.
Full Text FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
An improved protective coating composition for hot dip galvanization of steel
APPLICANTS
Name : Indian Institute of Technology, Bombay
Nationality : an autonomous research and educational
institution established in India by a special Act of the Parliament of the Republic of India under the Institutes of Technology Act 1961 Address : Powai, Mumbai 400076, Maharashtra, India
INVENTORS
Names : Vngaranahalli Srinivasan Raja and Vagge Tukaram
Shashikant
Nationality : both Indian Nationals
Address : both of Indian Institute of Technology, Bombay,
Department of Metallurgical Engineering and Materials Science, Powai, Mumbai 400076, Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

Field of Invention
The invention relates to an improved protective coating composition for hot dip galvanization of steel and to steel coated by the composition.
Background
Hot dip galvanization is a widely used method for protecting steel from corrosion. In the hot dip galvanization method, the steel to be coated is dipped in a molten metal bath of zinc or of an alloy of zinc containing alloying elements such as Al, Mg, Ni Co and Mg. Hot dipping can also be followed by heat treatment (annealing) resulting in a Zn-Fe (galvanneal) coating over the steel. The zinc/zinc-based alloy coatings act as sacrificial anode thereby protecting the underlying steel from corrosion.
WO/1990/002043 discloses a method for producing a protective galvanneal coating comprising Zn-Fe alloy by hot dipping followed by heat treatment of the coating under controlled conditions. This coating could undergo powdering and flaking during forming operation. US 5049453 disclose a method for preparing an alloy coating comprising Zn, Fe and Al having anti-powdering and anti-flaking properties. The coatings disclosed in this patent are, however, prone to delamination on deformation of steel thereby exposing the steel to environment leading to corrosion.
There is a need for a composition for hot dip galvanization that provide protective coatings with enhanced adhesion strength, resistance to powdering, delamination resistance and corrosion resistance.


Detailed Description
Accordingly, the invention provides an improved protective coating composition comprising strontium for hot dip galvanization of steel.
In one embodiment, the invention provides an improved protective coating composition for hot dip galvanization of steel, the composition comprising zinc and strontium wherein the strontium is present in at least 0.01 to 0.1 % by weight of the composition.
In another embodiment, the invention provides an improved protective coating composition for hot dip galvanisation of steel, the composition comprising zinc and strontium along with other alloying elements wherein the strontium is present in at least 0.01 to 0.1 % by weight of the composition, the alloying elements being selected from aluminium, magnesium, lead and Si
In a further embodiment, the invention provides steel coated with a composition comprising zinc and strontium wherein the strontium is present in at least 0.01 to 0.1 % by weight of the composition.
The coating compositions of the invention are characterized by the presence of strontium. On hot dip galvanization of steel with the compositions of the invention, steel coated with a protective coating comprising at least 0.01 to 0.1% percentage by weight of strontium is obtained. The chemical composition of the


various coating compositions used for hot dip galvanization of steel are displayed in Table-1.
Table 1 Chemical composition (in percentages by weight) of the compositions used for hot dip galvanization

Coating composition Weight percentage of various elements in the different coating compositions
Al (xi) Mg (x2) Pb(x3) Si(X4) Sr (xs) Zn
Zn 0.13 0.004 0.03 0.02 — 100-SxiT
Zn-0.01%Sr 0.13 0.004 — 0.02 0.01
Zn-0.02 %Sr 0.14 0.004 — 0.02 0.02
Zn-0.05% Sr 0.14 0.004 — 0.02 0.05
Zn-0.1%Sr 0.15 0.004 — 0.02 0.1
Commercial hot dip galvanization (HDG) composition 0.12 0.003 0.10 0.03
SXI is the sum of percentages of the various elements, other than zinc, in a
composition
The hot dip galvanization was carried out by dipping the steel to be coated in a molten metal bath comprising zinc and strontium metal to form a protective coating on steel. The adhesion strength of coatings using each of the compositions


were measured by using portable pull off adhesion tester as per ASTM D 4541 and ASM C 633 standards. The degrees of delamination of the various coatings were calculated by determining the polarization resistance of the coatings using electrochemical corrosion techniques.
The adhesion strength of various galvanized coatings, whose compositions are listed in Table-1, obtained over steel is displayed in figure-1 of the accompanying drawings. It is clear from figure-1 that adhesion strength of the galvanized coatings using coating compositions comprising strontium is higher (by around 33%) than that using strontium free Zn compositions or using commercial HDG composition. The degree of delamination in response to effective strain (deformation) of the coatings using the various compositions is displayed in figure-2 of the accompanying drawings. The degree of delamination exhibited by the coatings using compositions comprising strontium is considerably lower (by around 75%) than the strontium free Zn compositions as well as the commercial hot dip galvanization (HDG) compositions. The polarization resistance (Rp) of each of the compositions listed in table-1 is displayed in Figure-3 of the accompanying drawings. The coatings using compositions containing strontium recorded higher (by around four times) values of Rp on exposure to salt spray as compared to strontium free Zn composition as well as to commercial HDG composition. Polarisation resistance is a measure of resistance of the coating to corrosion. Therefore the coatings using compositions comprising strontium have


relatively higher corrosion resistance as compared to the coatings using strontium free zinc composition as well as to those using commercial HDG composition.
The coatings using strontium containing compositions of the invention exhibit overall improvement in adhesion strength, delamination resistance as well as corrosion resistance as compared to the coatings using strontium free Zn composition or using the commercial HDG composition. The coatings using the compositions of the invention exhibit an improvement in adhesion strength by around 33%, in delamination resistance by around 75% and in corrosion resistance by around 4 times. The improved properties of the coatings ensure superior protection of steel. Due to the improved properties, the coatings using the compositions of the invention are more durable and resistant to environmental and mechanical stress. The protective coating compositions of the invention are, therefore, suitable for coating steel materials that require enhanced and prolonged protection.


We Claim
1. An improved protective coating composition for hot dip galvanization of steel, the composition comprising zinc and strontium wherein the strontium is present in at least 0.01 to 0.1 % by weight of the composition.
2. The composition as claimed in claim 1 additionally comprising alloying elements selected from aluminium, magnesium, lead and silicon.
3. A Steel coated with the composition as claimed in claim 1 or 2.




ABSTRACT
The invention relates to an improved protective coating composition for hot dip galvanization of steel, the composition comprising zinc and strontium wherein the strontium is present in at least 0.01 to 0.1 % by weight of the composition. The invention also relates to steel coated with the composition

Documents:

247-mum-2008-abstract.doc

247-mum-2008-abstract.pdf

247-MUM-2008-CLAIMS(AMENDED)-(15-10-2012).pdf

247-MUM-2008-CLAIMS(MARKED COPY)-(15-10-2012).pdf

247-mum-2008-claims.doc

247-mum-2008-claims.pdf

247-MUM-2008-CORRESPONDENCE(1-9-2009).pdf

247-MUM-2008-CORRESPONDENCE(13-9-2011).pdf

247-MUM-2008-CORRESPONDENCE(15-3-2013).pdf

247-mum-2008-correspondence(25-3-2008).pdf

247-MUM-2008-CORRESPONDENCE(5-11-2009).pdf

247-mum-2008-correspondence-received.pdf

247-mum-2008-description (complete).pdf

247-mum-2008-drawings.pdf

247-MUM-2008-FORM 1(13-9-2011).pdf

247-mum-2008-form 1(25-3-2008).pdf

247-mum-2008-form 13(13-9-2011).pdf

247-mum-2008-form 18(26-3-2008).pdf

247-mum-2008-form 2(title page)-(5-2-2008).pdf

247-mum-2008-form 26(25-3-2008).pdf

247-mum-2008-form 8(26-3-2008).pdf

247-mum-2008-form-1.pdf

247-mum-2008-form-2.doc

247-mum-2008-form-2.pdf

247-mum-2008-form-3.pdf

247-MUM-2008-REPLY TO EXAMINATION REPORT(15-10-2012).pdf


Patent Number 256103
Indian Patent Application Number 247/MUM/2008
PG Journal Number 18/2013
Publication Date 03-May-2013
Grant Date 02-May-2013
Date of Filing 05-Feb-2008
Name of Patentee INDIAN INSTITUTE OF TECHNOLOGY BOMBAY
Applicant Address POWAI, MUMBAI
Inventors:
# Inventor's Name Inventor's Address
1 VANGARANAHALLI SRINIVASAN RAJA INDIAN INSTITUTE OF TECHNOLOGY BOMBAY, DEPARTMENT OF METALLURGICAL ENGINEERING & MATERIALS SCIENCE, POWAI, MUMBAI 400076.
2 VAGGE TUKARAM SHASHIKANT INDIAN INSTITUTE OF TECHNOLOGY BOMBAY, DEPARTMENT OF METALLURGICAL ENGINEERING & MATERIALS SCIENCE, POWAI, MUMBAI 400076.
PCT International Classification Number B05D3/10; B05D7/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA