CHROMIZING COATING PDF

Chromizing is a thermo-chemical process consisting of saturating, by way of diffusion, of ferrous alloys, predominantly of steel, with chromium. Diffusion chromizing is classified, according to its application, into two types: anti-corrosion and surface hardening. Anti-corrosion chromizing is applicable to alloys containing carbon in amounts of less than 0. Their thickness is usually 0. Chromizing for surface hardening is applicable to steels containing more than 0. Skip to main content Skip to table of contents.

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May 27, G. Samuel, White Plains, N. The purpose of the invention is to simplify the chromizing of ferrous metal articles by avoiding the necessity of packing a chromizing compound in a box around the articles. A further purpose is to permit chromizing ferrous metal articles in existing furnaces or in modified furnaces having atmosphere control.

A further purpose is to accelerate the chromizing of ferrous metal articles by obtaining intimate adherence between a coating of chromizing compound and the surface to be chromized, while at the same time permitting ready'removal of the residue which is rendered friable after chromizing. A further purpose is to employ a stagnant or substantially quiescent relatively light protecting gas which will exert a minimum of washing action which might dissipate heavier chromizing gas.

A further purpose is to place the work in a container or containers open at the top which will trap chromizing gas and prevent its dissipation in the effluent protecting gas. In thedrawings I have chosen toillustrate a few only' of the numerous embodiments in which my invention may appear, ,selecting the formsshown fromthe standpoints of convenience in illustration, satisfactory operation and clear demonstration of the principles involved.

Figure l is a diagrammatic central vertical section of one form of furnace useful in the invention. Chromizing as usually carried out at the present time involves packing of a powdery chromizing composition around ferrous metal articles placed in a chromizing box. Chron'iizing by this technique 'is tedious and' expensive because of the labor involved in packing, and. It is particularly difficult to chromize sheet and strip by packing ,becauseY of the labor involved in spreading the powder in a position to adjoin the side of the sheet.

I have discovered that a relatively simple procedure can be 4used to obtain uniform, inexpensive chromizing of many :ferrous metal articles including sheet, plate and strip. The invention does not require box techniques as at present practiced and lends itself toapplication in atmosphere heating furnaces, car-bottom furnaces, bell furnaces, muflie furnaces and the like, and on chain and roller hearth furnaces having atmosphere control.

Thus the cost of additional equipment can be reduced to a minimum, while the results obtained are comparable to the best pack methods. The invention is also applicable to sheet, strip, plate, fabricated forms, Wire, rod, bar and tubing, as well as a wide variety of other forms of steel. In accordance with the invention, an adhering chromizing coating is applied which.

It will be evident, of course, that the coating can be applied by any suitable technique such as roller coating, doctoring, spraying, dipping, brushing, or the like. Where desired, the coating can be applied selectively and if other surfaces are not brought in contact with coating they will not be chromized. For example, one side only of a sheet can be coated and in making a stack the two coated sides of adjoining sheets will be placed together, placing two noncoated sides of adjoining sheets together.

The sheets will be chromized then only on one side. Considering rst the form of Figure 1, I make up an adhesive coating or slurry of chromizing compound which has the inherent property of becoming friable by the end of the chromizing operation.

The slurry is non-carbonaceous, and therefore has the advantage that it does not carburize the work. Since the coating is applied directly to the surface of the work, the chromizing gas, which will include lluorine, does not have a tendency to travel great distances in high concentrations, where pickling and etching eects might be obtained, and undergoes a minimum of reactions, but performs very effective transfer of chromium to the work, thus giving better penetration in a given time.

The catalyst used is a compound of chromium and flourine. While any one of the uorides of chromium may be employed, it is decdedlypreferable for several reasons to use a complex chromium ammonium fluoride. Onea'dvantage is that this compound breaks down, liberating hydrogen and nitrogen and tending to sweep out air which might otherwise be entrapped adjacent the work. Another advantage is that when the compound breaks down, chromium or chromium and halide is available in nascent form.

While chromium jiuoride or a complex ammonium chromium liuoride can be used from any suitable source of such materials, it is preferable to produce the catalyst by a reaction in making the compound. The slurry or dispersion has some remarkably advantageous properties. When coated by brushing, spraying, dipping or otherwise on the ferrous metal article and allowed to dry, the adhesion is so firm that the work can Any other inert bodying powder may be Yto its. Make up a mixture of 80 percent by weight of Aferro chromium powder and 20 Vpercent by weight of alumina.

Allow they resulting slurry to. VIt is then readyV for use. There is of course a great excess ofV chromium in the above mixture and the quantityof ammonium biuorideis notl critical. The inert protecting gas should preferably be a gas whose density is relatively light comparedto that of iluorine. The inert protecting gas is'preferably introduced atfthe bottom by pipe 24 and taken out the top by'pipe 25;.

This protects against removal of uon'ne or chromium fluoride vapor by washing or sweeping action which would seriously interfere with the chromizing;. This further reduces the possibility of dissipatingthe chromizing gas by washing or sweeping action since the relatively heavychromizing gas tendsV to till the lower container portion 26,.

In Figure 1, the Work is shown as a stack of Ysheets while as in Figure 2 I illustrate the work consisting of a roll of strip held by a band It will be evident thatV the lstrip has beensuitably coated with chromizing com'- poundwhile unwound and then after drying has been wound Vup in roll form. The chromizing temperature may be between and degrees Fahrenheit, preferably between and ldegrees Fahrenheit, and most desirably about degrees Fahrenheit.

The high temperatures are usually to be avoided because of grain growth. The Time of chromizing is suitably in excess of 3 hours, and usually in excess of 5 Vhours, in many cases being as long as about 18 hours.

The final chromizing coating is bright andrmly adherent, while the powder deposit on the. The improvement in penetration according tothe pres-- ent invention' is of the orderl of 50 to 75 percent over the pack method as normally applied.

The deposit will commonly be of the order of 0. The particles used in making up the slurry should preferably be throughV mesh per linear inch. In operation, it will be evident that it is merely neces-A sary to coat the work with the chromizing compound,Y allow thecompound to dry, then insert the work in the furnace, heat the work up to chromizingV temperature, cool the work down' to.

The method of chromizingferrous metal articles, which comprises coating therarticles with a watery dis- I claim as persion of chromium, the complex fluoride of ammonium Y and'chro'mium and an inert bodying agent, to for-m an Y adhesive bonded chromizing layer on the ferrous metal articles, and heating the ferrousmetal articles to a temperature of tofd'egrees F.

Further purposes appear in the specication and in the claim. VV In thedrawings I have chosen toillustrate a few only' of the numerous embodiments in which my invention may appear, ,selecting the formsshown fromthe standpoints of convenience in illustration, satisfactory operation and clear demonstration of the principles involved. VFigure 2 is a similar view showing a modification. Describing in illustrationrbut not in limitation and referring to the drawings: Chromizing as usually carried out at the present time involves packing of a powdery chromizing composition around ferrous metal articles placed in a chromizing box.

Chron'iizing by this technique 'is tedious and' expensive because of the labor involved in packing, and because of the danger that in certain types of Work a high rejection rate may result through inability to obtain uniform and pore free chromizing; I It is particularly difficult to chromize sheet and strip by packing ,becauseY of the labor involved in spreading the powder in a position to adjoin the side of the sheet.

The result is that a minimum of undesired ferrous halide is produced. Y Y The improvement in penetration according tothe pres-- ent invention' is of the orderl of 50 to 75 percent over the pack method as normally applied. Y ' The deposit obtained can be of any desired thickness inthe range from" 0. Athe ferro chromium powder Vand the alumina in'dispersion v i when coating thework. USA en.

A method for increasing the corrosion resistance of the switching magnet of silicon-iron for electromagnetic switching devices. Process for preparing chromized ferrous metal sheet material and the resultant articles. A method and apparatus for forming oberflaechendiffusionslegierungen, and treated with these workpieces.

Methods of forming a protective diffusion layer on nickel, cobalt and iron base alloys. JPA en. DEC1 en. Magnesium workpiece and method for forming a corrosion-protective top layer of a magnesium workpiece. CAA en. Cheng et al. Observation of high-temperature phase transformation in the Si-modified aluminide coating on mild steel using EBSD. Tsipas et al. Degradation behaviour of boronized carbon and high alloy steels in molten aluminium and zinc. EPB1 en. DED1 en. Method of improving the ductility of the coating of an aluminum-zinc alloy coated ferrous product.

USB2 en. Method for depositing a variable thickness aluminide coating on aircraft turbine blades. NLA en. Process for the deposition of refractory metal and metalloid carbides on a base material. EST3 en.

Flexible coated abrasive product having a binder including a binder of maleimide.

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US2885301A - Chromizing coating - Google Patents

We are global specialists in the application of protective coatings against metal degradation. Chromising is a surface treatment carried out at elevated temperatures in which an alloy is formed by the inward diffusion of chromium into the base metal. Diffusion Alloys was the first company world-wide to launch in the s chromising as a commercial industrial diffusion coating process. Chromising, or chromising, can protect components from corrosion, wear, abrasion and oxidation. Chromide diffusion coatings were originally developed by Diffusion Alloys for hot section industrial gas turbine blades and vanes to protect them against high temperature oxidation and hot corrosion. Steels with carbon content greater than 0.

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Chromizing

Samuel, White Plains, N. Application August 2, Serial No. A further purpose is toprovide a glass forming chromizing skin for coating which is rendered friable and disintegrates on cooling. A'further purpose is to prevent escape of the chromizing catalyst during chromizing. A further purpose is to permit chromizing powdered iron compactswithout atmospheric control. This constitutes a serious limitation, as it necessitates use of very expensive equipment, and also in many ,cases re- 2 percent, and which are to be chromized or chromized and sintered.

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US2836513A - Chromizing, adhering coating - Google Patents

May 27, G. Samuel, White Plains, N. The purpose of the invention is to simplify the chromizing of ferrous metal articles by avoiding the necessity of packing a chromizing compound in a box around the articles. A further purpose is to permit chromizing ferrous metal articles in existing furnaces or in modified furnaces having atmosphere control. A further purpose is to accelerate the chromizing of ferrous metal articles by obtaining intimate adherence between a coating of chromizing compound and the surface to be chromized, while at the same time permitting ready'removal of the residue which is rendered friable after chromizing. A further purpose is to employ a stagnant or substantially quiescent relatively light protecting gas which will exert a minimum of washing action which might dissipate heavier chromizing gas. A further purpose is to place the work in a container or containers open at the top which will trap chromizing gas and prevent its dissipation in the effluent protecting gas.

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