Integrated high throughput cold spray coating manufacturing system
In some embodiments, a coating applied to steel reinforcement bar (e.g., steel rebar) that could considerably extend the lifetime of concrete structures by reducing steel rebar corrosion is disclosed. The coating includes a thin, passivating steel (e.g., stainless steel) layer that is applied to the outside of conventional steel rebar. The coating can be applied in-line through metal cold spray manufacturing, which is a high throughput coating technique that can be integrated into existing steel manufacturing plants. Furthermore, a novel, high performance ferritic steel with tailored resistance to corrosion from chlorides is described. The new ferritic steel is distinct from other commercial and experimental steels, and is better suited for coating low-cost steel structures like rebar. Multiple alloying elements including Cr, Al, and Si will each form protective oxides independently, increasing the total amount of protection and extending it over much wider ranges of pH and electrical potential.
1. A method of applying a stainless steel coating to a steel component, comprising:
providing a carrier gas at a high pressure in a first gas flow path to a gas heater to heat the carrier gas to a high temperature along the first gas flow path;
providing the carrier gas at the high pressure in a second gas flow path to a particle feeder of stainless steel particles that are carried by the carrier gas along the second gas flow path;
mixing the heated carrier gas in the first flow path with the carried stainless steel particles in second flow path at an array of spray nozzles in fluidic communication with the first and second flow paths;
ejecting a plume of gas and stainless steel particles from the array of spray nozzles to coat an outer surface of the steel component with a coating of stainless steel as it is transported through the plume, the stainless steel coating being ferritic;
heat treating the stainless steel coating on the steel component, the heat treating comprises:
heating the stainless steel coating on the steel component to 1100° C. for 1 hour;
quenching the stainless steel coating on the steel component to room temperature; and
tempering the stainless steel coating on the steel component at 600° C. for 1 hour, wherein:
the ejected stainless steel particles impact the surface of the steel component at a high velocity and form a metallurgical bond to the surface of the steel component to form an outer coating comprising stainless steel;
the high temperature of the carrier gas is between 900° C. and 1100° C.;
the high pressure of the carrier gas is between 700 psi and 800 psi; and
the high velocity of the ejected stainless steel particles is supersonic velocity.
2. The method of claim 1 , wherein each of the nozzles in the array of spray nozzles:
compresses the mixed heated carrier gas and particles through a converging section of each nozzle
expands the mixed heated carrier gas and particles through a diverging section of each nozzle; and
accelerates the mixed heated carrier gas and particles to supersonic velocities.
3. The method of claim 1 , wherein:
the steel component is a steel billet;
the steel billet has a rectilinear cross section;
the array of spray nozzles circumscribe the steel billet in a rectilinear configuration to ensure there is an unobstructed line of sight between each region of the surface of the billet and at least one of nozzles in the array of spray nozzles;
the stainless steel coating covers the entire external surface of the steel billet; and
the thickness of the stainless steel coating is between 150 microns and 2000 microns.
4. The method of claim 3 , wherein the method further comprises:
heating the stainless steel coating on the steel billet and the steel billet at 1200° C. for a duration between 3 hours and 9 hours; and
hot rolling the stainless steel coating on the steel billet and the steel billet to form a rebar component having the stainless steel coating.
5. The method of claim 1 , wherein the stainless steel particles comprise at least one of:
spherical particles fabricated through gas atomization;
near-spherical particles fabricated through water atomization; or
irregular shaped particles fabricated through mechanical crushing.
6. The method of claim 1 , wherein the stainless steel particles have a ceramic material alloyed with the stainless steel particles to improve the bonding of the stainless steel coating to the steel component.
7. The method of claim 6 , wherein the ceramic material comprises at least one of a metal carbide or a metal oxide.
8. The method of claim 1 , wherein the heat treating the stainless steel coating on the steel component comprises a laser heat treatment.
9. The method of claim 1 , wherein:
the stainless steel particles comprise: 16-20 weight percent chromium (Cr); 3-6 weight percent molybdenum (Mo); and at least one or more of: 0-4 weight percent aluminum (Al); 0-2 weight percent silicon (Si); 0-0.1 weight percent nickel (Ni); 0.1-0.5 weight percent manganese (Mn); 0.0-0.1 weight percent carbon (C); 0.0-0.1 weight percent nitrogen (N): or 0.0-0.05 weight percent sulfur(S); and the balance of iron (Fe).
10. The method of claim 1 , wherein the stainless steel particles have a mean particle size of between 5 microns and 45 microns.
11. The method of claim 1 , wherein the stainless steel particles have a mean particle size of between 5 microns and 20 microns.
12. The method of claim 1 , wherein the outer coating has a mean grain size of between 500 nanometers and 10 microns.
13. The method of claim 1 , wherein the outer coating has a mean thickness of between 10 microns and 100 microns.
14. The method of claim 1 , wherein the steel component is a rebar.