CA1253039A - Process for chemical and thermal treatment of steel workpiece - Google Patents
Process for chemical and thermal treatment of steel workpieceInfo
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- CA1253039A CA1253039A CA000453849A CA453849A CA1253039A CA 1253039 A CA1253039 A CA 1253039A CA 000453849 A CA000453849 A CA 000453849A CA 453849 A CA453849 A CA 453849A CA 1253039 A CA1253039 A CA 1253039A
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Abstract
PROCESS FOR CHEMICAL AND THERMAL TREATMENT OF STEEL
WORKPIECES
Abstract A process for chemical and thermal treatment of steel workpieces accompanied by the formation thereon of a coat-ing includes diffusive precipitation onto the base metal of the workpiece of an intermetallic compound from a melt of a low-melting-point metal, such as sodium or lithium, at a temperature of from 720 to 820°C for a duration of time necessary for obtaining a coating layer of required thickness.
WORKPIECES
Abstract A process for chemical and thermal treatment of steel workpieces accompanied by the formation thereon of a coat-ing includes diffusive precipitation onto the base metal of the workpiece of an intermetallic compound from a melt of a low-melting-point metal, such as sodium or lithium, at a temperature of from 720 to 820°C for a duration of time necessary for obtaining a coating layer of required thickness.
Description
~3Q3~
Field_of the Invention This invention relates ~enerall~ to the metal science and therm~l treatment of metals and alloys. More specifi-cally, the invention relates to processes for chemical and thermal treatment of steel ~workpieces to obtain coatings by diffusive precipitation.
The proce~ according to the inventiorl can find appli-cation for obtaining coatin~s capable of imitating, in terms of their physical and chemical properties,~uch pre-cious metals a9 gold and platinum with the aim of rsducing consumption of these metals or using ~uch coatings as al-ternative materials for parts and components in instrument making (precision friction pairs, electrical contacts, ter-minals, variable resistor wires), in medicine (for making dentures and surgical toDls), in electrical engineering (electrical contacts), in horology (fabricating watcb ca-9ing9, bracelets and watch Parts), in jewelr~ practice (fDr making decorations and di~hware), and in the chemical industry (for protecting parts ~rom corrosion or making them more resistant to heat).
The process according to the invention can also be used duri~g fabrication of reflector screens of various designation9 and for application Df coatings to protect parts from ~ea-watcr corrosion.
Backgrou~d of the Tnvention Widely used nowdays are various techniques for obtailing, normall~ galvanically, precious metal coatings (gold-plating ~ ~3039 and palladizi~g). However, galvanizi~g most o~ten ~ails to ensure reliable coatings on parts of shaped con~igura-tion. Thus, coatings obtained by the known methods are in-herentl~ disadvantaæeous because of low bonding with the base metal, non-uniform thickness especially at the corners o~ workpieces, low hardness, and susceptibili-ty to wear.
Also, application o~ thase known processes necessitates workpiece sur~ace pretreatment, such as mechanical cleani~g and pickling.
To improve the physical and chemical properties of coatinæs, new shop processes have made way to industrial use lately, one such process involving chemical a~d thermal treatment o~ metal parts by di~usive precipitation.
~ usion coatings are sur~ace layers characterized by low porosity and high bondi~g with the b~se matal. Di~u-sion coatine processes can provide surface layers o~
various chemical compositions to guarante~ such advantageou~
properties as high resistance to wear, su~ficient hardness, tolerance to corrosive atmosphere, and high mechanical strenæth.
There is known a process for chemical ~nd thermal treatment o~ steel workpieces accompanied by the formation of a coating thereon obtained by di~u~ive precipitation or deposition onto the ba~e metal o~ a substance from a melt of a low-melting-point metal (cf. USSR Inventor's Certificate ~o. 582,329; IPC C 23 C 9/10).
Sodium is used a~ the lo~-melting-point metal o~ the ~ ~3~3~
melt, whereas platinum is employed a~ the substancs which forms a coating in the course of diffusive precipitation.
Preferred conditions of the diffusive precipitation temperature - 630 to 6700C; duration - 5 to 6 hr~.
Therefore, -the aforedescribed process resides in the use of a fu~ible or low-melting-point metal in nhich there are introduced other metal elements to precipitate onto the base metal and thus L orm a diffusion coating. An i90-thermal proce~s of mas~ transfer takes place in ~hich the gub9tance i9 dissolved in the form of metal elements in the melt of fusible metal to be transferred and adsorbed on the surface of the workpiece being coated to bond there-with, and the element(s) are interacted with the metal of the workpiece through diffusion. As a result, a coating i9 formed on the base metal composed of the elements taking part in the diffusive precipitation.
However, this process fails to provide coatings of predetermined stoichiometric composition with substantially uniform coating layer thickness.
In addition, the use of the known processe~ of chemical and thermal treatment by diffusive precipitation with preci-ous metals snd alternative imitation metals is disadvantage-ous due to high losses of such metals during the processes.
Summary of the Invention It is therefore an ob~ect of the present invention to provide a process for chemical and thermal treatment of steel workpieces to obtain on the base metal thereof a coating of a predetermined 9toichiometric composition.
3~3 9 Another o~ject i5 provide a process for chemical and thermal treatment of steel workpieces to obtain on the base metal thereof a coating of predetermined thickness su~ficient for meetin~ the demands of designated service conditions.
O~e more object is to provide a process for chemical and thermal treatment of steel workpieces to obtain on the base metal thereof a coating which ~ould imitate in physical and chemical propertie 5 precious metals, that is a coating possesing high resistance to corrosion a~d having luster and coloration imitating gold or platinum.
~ hese and other attending objects and advantages are attained by that in a proces~ ~or chemical and thermal trsat-ment o~ steel workpieces to form a coating thereon by di~usi-ve precipitation on the base metal o~ the steel workpiece o~ a substance ~rom a low-melting-point metal melt according to the invention, the diffusive precipitation process i9 carried out at a temperature of between 720 and 820C ~or a duration su~ficient to obtain a coati~g layer o~ required thickness, t~e melt pre~erably containing sodium or lithium as the low-melti~g-point metal, the substance beiDg precipi-tated having the form o~ an intermetallic compound.
The use o~ molten sodium or lithium make 9 it possible to obviate the need for the workpiece sur~ace pretreatment b~ pickling, since melts of the above metals act to remove sur~ace oxides and enable to clean ~Norkpieces and parts of complex configuration, as well as i~terior cavities 53e:~39 and grooved portions thereof due to the fact that such melts have high wetting power and ~luidity. Also, the use of baths o~ such molten metals makes a subsequent mecha-nical cleanin~ of the workpiece sur~ace super~luous, as the remainder o~ the melt penetrated into slits and cle~ts of tAe workpiece can be evacuated by washing the workpiece in water. In addition, the loss o~ the substance used for precipitating a coati~g by di~fusion is negligeable, because such a substance dissolves in sodium or lithium melts is small quantities, whereas the chemical and thermal treatment process follows a pattern whereby the amount of the substance dissolYed in the melt i9 substantially equal to the amount thereof diposited on the workpiece surface being coated.
Introduced to the melt as a substance being precipitated is an intermetallic compound o~ stoichiometric composition having predetermined physical and chemical properties, such as compounds capable of imitating precious metals, to enable to obtain coatings composed o~ the compound introduced into the melt, that is coatings of predetermined composition, since dissolution in the melt, transfer and precipitation o~ the compound elements takes place according to the stoichiometric proportion corresponding to the composition of the compound introduced, whereby the composition o~ the coating layer obtained tends to be uniform throughout the thickness thereof.
The process is conducted at a temperature within a range o~ between 720 and 820C. Such temperature conditions 53 ~3 9 provide ~or all the basic physical and chemical processes necessary for ensuring chemical and thermal treatment to take place, particularly, sufficiently vigorous dissolution of various intermetallic compounds in the melt, diffusive transfer of the elements being precipitated from the melt toward the base metal of the workpiece, and formation of coatings having a thickness suf~icient to meet the demands imposed by intended service conditions of the workpiece. The thickness of the coating depends on the duration of diffusive precipitation in turn determined by the physical and chemical parameters of the process.
For effecting the process the amount of the intermetallic compound to be introduced into the melt is preferably determined by:
G1 ~ 0.03 G2 ~ S ~- ~ , where G1 = weight of the intermetallic compound, in g;
G2 = weight o~ the low-melting-point metall, in g;
S = surface area of the workpiece being coated, in cm2;
= required thickness of the coatinæ layer, in cm; and = density of the intermetallic compound, in g/cm3.
In order to obtain coatings imitating in color platinu~
and having su~f~cient resistance to corrosion, tolerance to oxidation at high temperatures, and high mechanical characteristics (hardness and wear resistance), it is advisable for the di~fusive precipitation to be conducted at a temperature of from 72~ to 78~C for a duration bet-ween 6 and 8 hrs in a molten bath containing lithium and ;3039 an intermetallic compound of nickel and aluminum.
For obtaining coating~ imitating gold the diffusiveprecipitation is preferably carried out at a temperature between 780 and 820C for 6 to 8 hrs in a melt containing ~odium and an intermetallic compound of palladium and indium.
~ olten sodium likewise provides necessary conditions for obtaining a coating of required properties (sufficient solubility of the compound, deposition of the compound elements on the base metal of the steel workpiece, no vi~ible steel dissolution at a phase combination: intermetal-lic compound of palladium and indium -- sodium -- steel).
Preferred proce3s parameters of 730 to 820C and the precipitation time of 6 to 8 hrs ensure the deposition of a coating having a thickness practicable for a wide range of applications.
Detailed Description of the Invention ~ he invention ~ill now be described in greater detail with reference to various preferred modes of carrying it out.
A wor~piece to be coated is placed into a reaction ves-sel such as an ampoule fabricated from an inert material (one that fails to dissolve in the molten metal used for pre-c~pitating the coating). rhereafter, in a neutral gaseous atmosphere, ~uch a3 argon, the ampoule is filled with a melt of a lo~-melting-point alkali me-tal, such as sodium or lithium, and a substance to be precipitated onto the base metal in the form of an intermetallic compound.
303~
The ampoule is then sealed in the argon atmosphere by welding or ~oint stopp~ and placed in a furnace, such as a muffle electric furnace, for the process of diffusive precipitation to be carried out therein at a temperature of from 72~ to 820C for a duration o~ time necessary to obtain a la~er of coating of required thickness.
The proporti on o~ the intermetallic compourLd to be present in the melt is determined by:
G1 = 3 G2 + S~ , where G1 = wei~ht of the lntermetallic compound, in g;
G2 ~ weight of the low-melting-point metal, in g;
S = surface area of the workpiece, in cm2;
= required thickness of the coating layer, in cm; and = density of the intermetallic compound, in g/cm2.
~ he first term of the above equation takes account of the amount o~ compound necessary for saturation oY the molten sodium or lithium, and for a wide range of compounds it corresponds to 0.03~ G2, that is saturation concentration is ensured by a value of close to 3 mass per cent.
~ he second term of the equation takes account oY the amount of compound necessary for dipositing a required thickness of -the coating layer, and is determined by the size of the ~orkpiece to be coated, the thickness of the coating layer and the density o~ the compound, that is this term establishes a general connection between the geometrical dimensions and the mass o~ substance through its densit~.
_9_ ~ 3 9 A~ter holding the ampoule at a temperature providi~g ~or diffusive precipitation, and subsequent to cooling, it is opened for the workpiece having a coating deposited thereon to bs extracted -therefrom and washed in the running water.
In order to obtain a coating which would imitate platinum in terms of color and physical-chemical properties, the workpiece is subjected -to diffusive precipitation at a temperature between 720 and 780C ~or 6 to 8 hrs in a molten metal composition comprising lithium a~d an i~ter-metallic compound of nickel and aluminum, the amount of the compound being determined accordiDg to the aforecited equa-tion.
~ or obtaining a coatiDg which would imitate gold in terms of color and physical-chemical properties, the di~fu-sive precipitation is carried out at a temperature between 780 and 820C within 6 to 8 hrs in a melt composed of molten sodium and an intermetallic compound of palladium and indium.
Described hereinbelow are ~arious specific examples of the best mode ~or carrying out the process according to the in~ention.
Example 1 Placed in an ampoule is 8 tea-spoonfulL of steel o~
the following compositio~ (in mass per cent): C ~ 0.08;
~n = 1 - 2; Cr = 17 - 19; ~i = 9 - 11; ~i = 0.7; ~e = the balance, and a sample of intermet~llic compound comprising -1()-53~39 a mixture of palladium and indium in the ratio of 56 to 44 mass per cent, respecti~ely, for the ampoule to be filled with molten sodium.
~ he amount G1 = 5.17 g of the intermetallic compound is determined by the above equation, where G2 = 150 g;
S = 37 cm2;
= 0.0018 cm; a~d ~ = 10 g/cm3.
Subsequent to seali~g in argon a-tmosphere, the ampoule is placed into a muf~le electric furnace where it is held ~or 6 hrs at a temperature of 780C. Thereafter, the ampoule is ope~ed for the workpiece to be retrieved therefrom and washed in the runnin~ water.
As a result of the chemical and thermal treatment, a coating i~ ~ormed o~ the workpiece which is similar in corrosion resista~t properties and luster to gold, this coating layer having a thickness of 18 mkm, a mîcrohardness o~ between 2,100 and 2,400 MPa, and a gold-pink coloration.
100 hrs o~ testing in acidic and alkaline media evide~-ced no coating surface corrosion.
E~ample 2 As distinct from Example 1, an ampoule ~ith a workpiece in the ~orm of a steel ri~g of the following composition (in mass per cent): C = 0.24 - 0.32; Fe = the balance, was subjected to thermal treatment at a temperature of 800C
for 7 hrs.
The initial data for determining the value o~ G1 ~ 1.16 g of the întermetallic compound (palladium and indium) is found from the above equation, where G2 = 3 ~i S = 9.4 cm2;
= 0.0025 cm; and = 10 g/cm3.
As a result of the chemical and therrr~al treatment, a coating layer is formed on the steel ring in corrosion resistance and luster imitating gold and having a thickness of 25 mkm, microhardness of between 1~850 and 29025 ~Pa, and gold-pink in color. Corrosion resistance property is sub-stantially the same as described with reference to the coa-ting obtained according to Example 1 Example 3 Placed into an ampoule is a watch case of a steel of the following composi-tion (in mass per cent): C = 0.07 -- 0.13; Fe = the balance, and a sample of an intermetallic compound of palladium and indium proportioned 56 to 44 mass per cent, respectively, the ampoule beinæ then ~illed with molten sodium.
The amount of the intermetallic compound is determined according to the above equation, where G2 - 70 æ;
S = 28 cm2;
= 0.0035 cm; and = 10 ~/cm3.
~ 3~3 9 As a result, G1 = 3.08 g.
~ he ampoule with the 3~0redescribed content i9 held in a muffle electric furnace for ~ hrs at a temperature of 820C.
~ he resultant chemical reaction and heat treatment produce a coatin~ layer o~ 35 mkm in thickness and having a microhardness of between 1t800 and 2,1~0 ~Pa, The color o~ the coating thu~ obtained and corrosion resistance the-reo~ are similar to those indicated with reference to Example 1.
Example 4 A tea-spoonfull of steel is placed into an ampoule, the steel having the followinæ composition (in mass per cent):
C = 0.24 - 0.32; Fe = the balance, and a sample of an intermetallic compound o~ nickel and aluminum (G1 = 3-35 g)1 the ampoule being then ~illed with molten lithium. The amount of G1 of the intermetallic compound is determined accordin~ to the equation mentioned before, where G2 = 82 g, S = 37 cm ;
= 0.004 cm; and = 6 g/cm .
Subsequent to sealing of the ampoule in an atmosphere o~ argon, it is held in a furnace for 6 hrs at a temperature o~ 720C. Therea~ter, the ampoule is opened and the ste~l is removed there~rom to be ~ashed in the running water.
~he chemical and thermal treatment provides for the ;3039 formation of a coating layer in corrosion resistance propert~ and luster similar to platinum, a thickness of 40 mkm, and microhardness of between 4,10~ and 4,200 MPa.
The color of the thus obtained coating is light-grey, while resistance to corrosive acidic a~d alkaline media i9 comparable to a chrome-nickel steel.
Example 5 Placed into an ampoule is a watch case of a steel having the following composition (in mass per cent):
C = 0.07 - 0.13; Fe _ the balance, and a sample of an inter-metallic compound of nickel and aluminum (G1 = 2~9 g), the ampoule being then filled with molten lithium. The amount of G1 is determined from the equation applicable to the previous examples, where G2 ~ 40 g, S = 28 cm ;
= 0.010 cm; a~d = ~ g/cm~
~ he ampoule is held for 7 hrs at a temperature of 750C.
As a result of chemical and thermal treatment, a coa-ting layer is formed approximating in corrosion resistant properties and luster to platinum and having a thickness of 130 mkm, and microhardness of between 4,500 and 4,800 MPa.
The corrosive resistance and color of the thus obtained coating are similar to those produced by the process descri-bed in Example 4.
~\
~ ~303 9 Example 6 The process is conducted substantially as described in Example 5, the difference being in that an intermetallic compound of nickel and aluminum in the amount of G1 = 3.~8 g is used determined from the same equation, where G2 = 4~ g~
S = 28 cm ;
= 0.013 cm; and d = 6 g/cm3.
The ampoule is heat~treat~d for 8 hrs at a temperature o~ 780C.
A coating is formed on the base metal of the workpiece in corrosion resistance and luster similar to platinum ~ d having a thickness of 130 mkm and microhardness of be~ween 4,500 and 4,800 MPa, the color and resistance to corrosion being substantially similar to the coating described with reference to Example 4.
Field_of the Invention This invention relates ~enerall~ to the metal science and therm~l treatment of metals and alloys. More specifi-cally, the invention relates to processes for chemical and thermal treatment of steel ~workpieces to obtain coatings by diffusive precipitation.
The proce~ according to the inventiorl can find appli-cation for obtaining coatin~s capable of imitating, in terms of their physical and chemical properties,~uch pre-cious metals a9 gold and platinum with the aim of rsducing consumption of these metals or using ~uch coatings as al-ternative materials for parts and components in instrument making (precision friction pairs, electrical contacts, ter-minals, variable resistor wires), in medicine (for making dentures and surgical toDls), in electrical engineering (electrical contacts), in horology (fabricating watcb ca-9ing9, bracelets and watch Parts), in jewelr~ practice (fDr making decorations and di~hware), and in the chemical industry (for protecting parts ~rom corrosion or making them more resistant to heat).
The process according to the invention can also be used duri~g fabrication of reflector screens of various designation9 and for application Df coatings to protect parts from ~ea-watcr corrosion.
Backgrou~d of the Tnvention Widely used nowdays are various techniques for obtailing, normall~ galvanically, precious metal coatings (gold-plating ~ ~3039 and palladizi~g). However, galvanizi~g most o~ten ~ails to ensure reliable coatings on parts of shaped con~igura-tion. Thus, coatings obtained by the known methods are in-herentl~ disadvantaæeous because of low bonding with the base metal, non-uniform thickness especially at the corners o~ workpieces, low hardness, and susceptibili-ty to wear.
Also, application o~ thase known processes necessitates workpiece sur~ace pretreatment, such as mechanical cleani~g and pickling.
To improve the physical and chemical properties of coatinæs, new shop processes have made way to industrial use lately, one such process involving chemical a~d thermal treatment o~ metal parts by di~usive precipitation.
~ usion coatings are sur~ace layers characterized by low porosity and high bondi~g with the b~se matal. Di~u-sion coatine processes can provide surface layers o~
various chemical compositions to guarante~ such advantageou~
properties as high resistance to wear, su~ficient hardness, tolerance to corrosive atmosphere, and high mechanical strenæth.
There is known a process for chemical ~nd thermal treatment o~ steel workpieces accompanied by the formation of a coating thereon obtained by di~u~ive precipitation or deposition onto the ba~e metal o~ a substance from a melt of a low-melting-point metal (cf. USSR Inventor's Certificate ~o. 582,329; IPC C 23 C 9/10).
Sodium is used a~ the lo~-melting-point metal o~ the ~ ~3~3~
melt, whereas platinum is employed a~ the substancs which forms a coating in the course of diffusive precipitation.
Preferred conditions of the diffusive precipitation temperature - 630 to 6700C; duration - 5 to 6 hr~.
Therefore, -the aforedescribed process resides in the use of a fu~ible or low-melting-point metal in nhich there are introduced other metal elements to precipitate onto the base metal and thus L orm a diffusion coating. An i90-thermal proce~s of mas~ transfer takes place in ~hich the gub9tance i9 dissolved in the form of metal elements in the melt of fusible metal to be transferred and adsorbed on the surface of the workpiece being coated to bond there-with, and the element(s) are interacted with the metal of the workpiece through diffusion. As a result, a coating i9 formed on the base metal composed of the elements taking part in the diffusive precipitation.
However, this process fails to provide coatings of predetermined stoichiometric composition with substantially uniform coating layer thickness.
In addition, the use of the known processe~ of chemical and thermal treatment by diffusive precipitation with preci-ous metals snd alternative imitation metals is disadvantage-ous due to high losses of such metals during the processes.
Summary of the Invention It is therefore an ob~ect of the present invention to provide a process for chemical and thermal treatment of steel workpieces to obtain on the base metal thereof a coating of a predetermined 9toichiometric composition.
3~3 9 Another o~ject i5 provide a process for chemical and thermal treatment of steel workpieces to obtain on the base metal thereof a coating of predetermined thickness su~ficient for meetin~ the demands of designated service conditions.
O~e more object is to provide a process for chemical and thermal treatment of steel workpieces to obtain on the base metal thereof a coating which ~ould imitate in physical and chemical propertie 5 precious metals, that is a coating possesing high resistance to corrosion a~d having luster and coloration imitating gold or platinum.
~ hese and other attending objects and advantages are attained by that in a proces~ ~or chemical and thermal trsat-ment o~ steel workpieces to form a coating thereon by di~usi-ve precipitation on the base metal o~ the steel workpiece o~ a substance ~rom a low-melting-point metal melt according to the invention, the diffusive precipitation process i9 carried out at a temperature of between 720 and 820C ~or a duration su~ficient to obtain a coati~g layer o~ required thickness, t~e melt pre~erably containing sodium or lithium as the low-melti~g-point metal, the substance beiDg precipi-tated having the form o~ an intermetallic compound.
The use o~ molten sodium or lithium make 9 it possible to obviate the need for the workpiece sur~ace pretreatment b~ pickling, since melts of the above metals act to remove sur~ace oxides and enable to clean ~Norkpieces and parts of complex configuration, as well as i~terior cavities 53e:~39 and grooved portions thereof due to the fact that such melts have high wetting power and ~luidity. Also, the use of baths o~ such molten metals makes a subsequent mecha-nical cleanin~ of the workpiece sur~ace super~luous, as the remainder o~ the melt penetrated into slits and cle~ts of tAe workpiece can be evacuated by washing the workpiece in water. In addition, the loss o~ the substance used for precipitating a coati~g by di~fusion is negligeable, because such a substance dissolves in sodium or lithium melts is small quantities, whereas the chemical and thermal treatment process follows a pattern whereby the amount of the substance dissolYed in the melt i9 substantially equal to the amount thereof diposited on the workpiece surface being coated.
Introduced to the melt as a substance being precipitated is an intermetallic compound o~ stoichiometric composition having predetermined physical and chemical properties, such as compounds capable of imitating precious metals, to enable to obtain coatings composed o~ the compound introduced into the melt, that is coatings of predetermined composition, since dissolution in the melt, transfer and precipitation o~ the compound elements takes place according to the stoichiometric proportion corresponding to the composition of the compound introduced, whereby the composition o~ the coating layer obtained tends to be uniform throughout the thickness thereof.
The process is conducted at a temperature within a range o~ between 720 and 820C. Such temperature conditions 53 ~3 9 provide ~or all the basic physical and chemical processes necessary for ensuring chemical and thermal treatment to take place, particularly, sufficiently vigorous dissolution of various intermetallic compounds in the melt, diffusive transfer of the elements being precipitated from the melt toward the base metal of the workpiece, and formation of coatings having a thickness suf~icient to meet the demands imposed by intended service conditions of the workpiece. The thickness of the coating depends on the duration of diffusive precipitation in turn determined by the physical and chemical parameters of the process.
For effecting the process the amount of the intermetallic compound to be introduced into the melt is preferably determined by:
G1 ~ 0.03 G2 ~ S ~- ~ , where G1 = weight of the intermetallic compound, in g;
G2 = weight o~ the low-melting-point metall, in g;
S = surface area of the workpiece being coated, in cm2;
= required thickness of the coatinæ layer, in cm; and = density of the intermetallic compound, in g/cm3.
In order to obtain coatings imitating in color platinu~
and having su~f~cient resistance to corrosion, tolerance to oxidation at high temperatures, and high mechanical characteristics (hardness and wear resistance), it is advisable for the di~fusive precipitation to be conducted at a temperature of from 72~ to 78~C for a duration bet-ween 6 and 8 hrs in a molten bath containing lithium and ;3039 an intermetallic compound of nickel and aluminum.
For obtaining coating~ imitating gold the diffusiveprecipitation is preferably carried out at a temperature between 780 and 820C for 6 to 8 hrs in a melt containing ~odium and an intermetallic compound of palladium and indium.
~ olten sodium likewise provides necessary conditions for obtaining a coating of required properties (sufficient solubility of the compound, deposition of the compound elements on the base metal of the steel workpiece, no vi~ible steel dissolution at a phase combination: intermetal-lic compound of palladium and indium -- sodium -- steel).
Preferred proce3s parameters of 730 to 820C and the precipitation time of 6 to 8 hrs ensure the deposition of a coating having a thickness practicable for a wide range of applications.
Detailed Description of the Invention ~ he invention ~ill now be described in greater detail with reference to various preferred modes of carrying it out.
A wor~piece to be coated is placed into a reaction ves-sel such as an ampoule fabricated from an inert material (one that fails to dissolve in the molten metal used for pre-c~pitating the coating). rhereafter, in a neutral gaseous atmosphere, ~uch a3 argon, the ampoule is filled with a melt of a lo~-melting-point alkali me-tal, such as sodium or lithium, and a substance to be precipitated onto the base metal in the form of an intermetallic compound.
303~
The ampoule is then sealed in the argon atmosphere by welding or ~oint stopp~ and placed in a furnace, such as a muffle electric furnace, for the process of diffusive precipitation to be carried out therein at a temperature of from 72~ to 820C for a duration o~ time necessary to obtain a la~er of coating of required thickness.
The proporti on o~ the intermetallic compourLd to be present in the melt is determined by:
G1 = 3 G2 + S~ , where G1 = wei~ht of the lntermetallic compound, in g;
G2 ~ weight of the low-melting-point metal, in g;
S = surface area of the workpiece, in cm2;
= required thickness of the coating layer, in cm; and = density of the intermetallic compound, in g/cm2.
~ he first term of the above equation takes account of the amount o~ compound necessary for saturation oY the molten sodium or lithium, and for a wide range of compounds it corresponds to 0.03~ G2, that is saturation concentration is ensured by a value of close to 3 mass per cent.
~ he second term of the equation takes account oY the amount of compound necessary for dipositing a required thickness of -the coating layer, and is determined by the size of the ~orkpiece to be coated, the thickness of the coating layer and the density o~ the compound, that is this term establishes a general connection between the geometrical dimensions and the mass o~ substance through its densit~.
_9_ ~ 3 9 A~ter holding the ampoule at a temperature providi~g ~or diffusive precipitation, and subsequent to cooling, it is opened for the workpiece having a coating deposited thereon to bs extracted -therefrom and washed in the running water.
In order to obtain a coating which would imitate platinum in terms of color and physical-chemical properties, the workpiece is subjected -to diffusive precipitation at a temperature between 720 and 780C ~or 6 to 8 hrs in a molten metal composition comprising lithium a~d an i~ter-metallic compound of nickel and aluminum, the amount of the compound being determined accordiDg to the aforecited equa-tion.
~ or obtaining a coatiDg which would imitate gold in terms of color and physical-chemical properties, the di~fu-sive precipitation is carried out at a temperature between 780 and 820C within 6 to 8 hrs in a melt composed of molten sodium and an intermetallic compound of palladium and indium.
Described hereinbelow are ~arious specific examples of the best mode ~or carrying out the process according to the in~ention.
Example 1 Placed in an ampoule is 8 tea-spoonfulL of steel o~
the following compositio~ (in mass per cent): C ~ 0.08;
~n = 1 - 2; Cr = 17 - 19; ~i = 9 - 11; ~i = 0.7; ~e = the balance, and a sample of intermet~llic compound comprising -1()-53~39 a mixture of palladium and indium in the ratio of 56 to 44 mass per cent, respecti~ely, for the ampoule to be filled with molten sodium.
~ he amount G1 = 5.17 g of the intermetallic compound is determined by the above equation, where G2 = 150 g;
S = 37 cm2;
= 0.0018 cm; a~d ~ = 10 g/cm3.
Subsequent to seali~g in argon a-tmosphere, the ampoule is placed into a muf~le electric furnace where it is held ~or 6 hrs at a temperature of 780C. Thereafter, the ampoule is ope~ed for the workpiece to be retrieved therefrom and washed in the runnin~ water.
As a result of the chemical and thermal treatment, a coating i~ ~ormed o~ the workpiece which is similar in corrosion resista~t properties and luster to gold, this coating layer having a thickness of 18 mkm, a mîcrohardness o~ between 2,100 and 2,400 MPa, and a gold-pink coloration.
100 hrs o~ testing in acidic and alkaline media evide~-ced no coating surface corrosion.
E~ample 2 As distinct from Example 1, an ampoule ~ith a workpiece in the ~orm of a steel ri~g of the following composition (in mass per cent): C = 0.24 - 0.32; Fe = the balance, was subjected to thermal treatment at a temperature of 800C
for 7 hrs.
The initial data for determining the value o~ G1 ~ 1.16 g of the întermetallic compound (palladium and indium) is found from the above equation, where G2 = 3 ~i S = 9.4 cm2;
= 0.0025 cm; and = 10 g/cm3.
As a result of the chemical and therrr~al treatment, a coating layer is formed on the steel ring in corrosion resistance and luster imitating gold and having a thickness of 25 mkm, microhardness of between 1~850 and 29025 ~Pa, and gold-pink in color. Corrosion resistance property is sub-stantially the same as described with reference to the coa-ting obtained according to Example 1 Example 3 Placed into an ampoule is a watch case of a steel of the following composi-tion (in mass per cent): C = 0.07 -- 0.13; Fe = the balance, and a sample of an intermetallic compound of palladium and indium proportioned 56 to 44 mass per cent, respectively, the ampoule beinæ then ~illed with molten sodium.
The amount of the intermetallic compound is determined according to the above equation, where G2 - 70 æ;
S = 28 cm2;
= 0.0035 cm; and = 10 ~/cm3.
~ 3~3 9 As a result, G1 = 3.08 g.
~ he ampoule with the 3~0redescribed content i9 held in a muffle electric furnace for ~ hrs at a temperature of 820C.
~ he resultant chemical reaction and heat treatment produce a coatin~ layer o~ 35 mkm in thickness and having a microhardness of between 1t800 and 2,1~0 ~Pa, The color o~ the coating thu~ obtained and corrosion resistance the-reo~ are similar to those indicated with reference to Example 1.
Example 4 A tea-spoonfull of steel is placed into an ampoule, the steel having the followinæ composition (in mass per cent):
C = 0.24 - 0.32; Fe = the balance, and a sample of an intermetallic compound o~ nickel and aluminum (G1 = 3-35 g)1 the ampoule being then ~illed with molten lithium. The amount of G1 of the intermetallic compound is determined accordin~ to the equation mentioned before, where G2 = 82 g, S = 37 cm ;
= 0.004 cm; and = 6 g/cm .
Subsequent to sealing of the ampoule in an atmosphere o~ argon, it is held in a furnace for 6 hrs at a temperature o~ 720C. Therea~ter, the ampoule is opened and the ste~l is removed there~rom to be ~ashed in the running water.
~he chemical and thermal treatment provides for the ;3039 formation of a coating layer in corrosion resistance propert~ and luster similar to platinum, a thickness of 40 mkm, and microhardness of between 4,10~ and 4,200 MPa.
The color of the thus obtained coating is light-grey, while resistance to corrosive acidic a~d alkaline media i9 comparable to a chrome-nickel steel.
Example 5 Placed into an ampoule is a watch case of a steel having the following composition (in mass per cent):
C = 0.07 - 0.13; Fe _ the balance, and a sample of an inter-metallic compound of nickel and aluminum (G1 = 2~9 g), the ampoule being then filled with molten lithium. The amount of G1 is determined from the equation applicable to the previous examples, where G2 ~ 40 g, S = 28 cm ;
= 0.010 cm; a~d = ~ g/cm~
~ he ampoule is held for 7 hrs at a temperature of 750C.
As a result of chemical and thermal treatment, a coa-ting layer is formed approximating in corrosion resistant properties and luster to platinum and having a thickness of 130 mkm, and microhardness of between 4,500 and 4,800 MPa.
The corrosive resistance and color of the thus obtained coating are similar to those produced by the process descri-bed in Example 4.
~\
~ ~303 9 Example 6 The process is conducted substantially as described in Example 5, the difference being in that an intermetallic compound of nickel and aluminum in the amount of G1 = 3.~8 g is used determined from the same equation, where G2 = 4~ g~
S = 28 cm ;
= 0.013 cm; and d = 6 g/cm3.
The ampoule is heat~treat~d for 8 hrs at a temperature o~ 780C.
A coating is formed on the base metal of the workpiece in corrosion resistance and luster similar to platinum ~ d having a thickness of 130 mkm and microhardness of be~ween 4,500 and 4,800 MPa, the color and resistance to corrosion being substantially similar to the coating described with reference to Example 4.
Claims (7)
1. A process for chemical and thermal treatment of steel workpieces accompanied by the formation of a coating thereon which includes diffusive precipitation onto the base metal of the workpiece of a substance in the form of an intermetallic compound from a melt of a low-melting-point metal, at a tempera-ture of from 720 to 820°C for a duration of time necessary for obtaining a coating layer of required thickness.
2. A process as defined in claim 1, in which said low-melting-point metal is selected from the group consisting of sodium and lithium.
3. A process as defined in claim 1, in which the amount of intermetallic compound in said melt is determined from:
G1 = 0.03 G2 + S ? .delta. ? .gamma. , where G1 = weight of the intermetallic compound, in g;
G2 = weight of the low-melting-point metal, in g;
S = surface area of the workpiece, in cm2;
.delta. = required thickness of the coating layer, in cm, and .gamma. = density of the intermetallic compound, in g/cm3.
G1 = 0.03 G2 + S ? .delta. ? .gamma. , where G1 = weight of the intermetallic compound, in g;
G2 = weight of the low-melting-point metal, in g;
S = surface area of the workpiece, in cm2;
.delta. = required thickness of the coating layer, in cm, and .gamma. = density of the intermetallic compound, in g/cm3.
4. A process as defined in claim 1, in which said diffusive precipitation is carried out at a temperature of from 720 to 780°C for a duration of time of between 6 and 8 hrs in said melt containing lithium and an intermetallic compound of nickel and aluminum.
5. A process as defined in claim 1, in which said diffusive precipitation is carried out at a temperature of from 780 to 820°C for a duration of time between 6 and 8 hrs in said melt containing sodium and an intermetallic compound of palladium and indium.
6. A process as defined in claim 3, in which said diffusive precipitation is carried out at a temperature of from 720 and 780°C for a duration of time between 6 and 8 hrs in said melt containing lithium and an intermetallic compound of nickel and aluminum.
7. A process as defined in claim 3, in which said diffusive precipitation is carried out at a temperature of from 780 and 820°C for a duration of time between 6 and 8 hrs in said melt containing sodium and an intermetallic compound of palladium and indium.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000453849A CA1253039A (en) | 1984-05-08 | 1984-05-08 | Process for chemical and thermal treatment of steel workpiece |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000453849A CA1253039A (en) | 1984-05-08 | 1984-05-08 | Process for chemical and thermal treatment of steel workpiece |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1253039A true CA1253039A (en) | 1989-04-25 |
Family
ID=4127824
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000453849A Expired CA1253039A (en) | 1984-05-08 | 1984-05-08 | Process for chemical and thermal treatment of steel workpiece |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1253039A (en) |
-
1984
- 1984-05-08 CA CA000453849A patent/CA1253039A/en not_active Expired
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