US2553865A

US2553865A - Case hardening composition

Info

Publication number: US2553865A
Application number: US149203A
Authority: US
Inventors: Newell Isaac Laird
Original assignee: Individual
Current assignee: Individual
Priority date: 1950-03-11
Filing date: 1950-03-11
Publication date: 1951-05-22
Anticipated expiration: 1968-05-22

Description

chlorides and carbonates.

Patented May 22, 1951 2,553,855 CASE HARDENING 66 IsaacLaird-Newll, Wethersfield, Conn.

N0 Drawing. Application March 11, 1950, Serial No. 149,203

" 11 Claims.

This invention relates to a fusible salt bath for the treatment of iron or steel or ferrous alloys by a process generally known as carbur-izing. cementation or case hardening. More particularly the invention relates to a novel composition and method for a case hardening treatment.

Case hardening baths have long been known and used to give a surface hardness to iron and steel parts by the introduction of carbon and nitrogen into the surface of the metal. Such baths are usually composed of a cyanogen compound with or without an activating material to accelerate or control the rate of case hardening. There is also generally present such diluents as Cementation with carbon and nitrogen will occur slowly when mixtures of sodium and potassium canides are used. By the addition of such activators as the alkaline earth metals especially calcium and barium in the form of chlorides and carbonates the rate of cementation is markedly increased and a higher proportion of carbon is introduced into the metal. There are objectionable features to each of case hardening compound consists essentially of the sodium salts of cyanide, cyanate, chloride and carbonate the bath is unstable and requires frequent and large additions of cyanides. This bath is unreliable and does not give uniform depths of case.

Calcium compounds such as calcium oxide and calcium chloride are frequently used as energizers or activators for cyanide baths, and while controlled cementation is accomplished, the bath is hygroscopic and corrosive to the work and furnace parts. The work is often coated with lime salts and acid treatment is required to clean the work.

Barium compounds are also successfully used to regulate the carburizing action of salt baths but are characterized by the great diificulty encountered in cleaning the work after cement-ation. As with the calcium salts, the compounds of barium are difiicultly soluble in water, and alkali cleaners and acid treatment is frequently necessary to clean the metal parts.

Other energizers such as fluorides are also used, but their effect is slight and results are often erratic.

I have found that a cyanide containing salt bath composition can be activated or energized by the addition of an alkali metal fluosilicat'e also known as silico fluoride. The resulting bath is not open to the objections cited, and in addition has the following advantages: it is completely water soluble, and treated parts when quenched in water have a clean bright finish. The carburizing action is rapid and case depths are obtained which are equivalent to those found when using barium and strontium activated L-bath's.

The baths containing fluosilicates are very stable and little or no fuming or foaming is noted at operating temperatures. An added advantage is the low cost of the accelerator especially when compared to strontium and barium compounds.

The amount of fiuosilicate salt necessary to produce effective activation of a carburizing bath is low, and as small an amount as 2% is sufficient in some cases. Satisfactory energizing is also obtained when as much as 20% is used, but the bath becomes somewhat viscous and tends to sludge when as much as this is used. The preferred compositions contain from 4 to 12% of the fluosilicate salt.

The following examples will serve to further illustrate the invention:

Example 1 Iron wire having a diameter of 0.125 inch and a carbon content 0.10 percent was treated at 1600 F. in a fused salt bath of the following composition;

Parts by weight Sodium cyanide 20 Sodium chloride 44 Sodium carbonate 34 Sodium fluosilicate 2 After an immersion time of one hour the depth of case was .012 inch and the surface was bright and file hard. The salt bath gave no evidence of sludge formation and fuming was slight.

Example 2 A steel rod having a carbon content of 0.012

percent was immersed in a fused salt bath of the following composition:

Parts by weight Sodium cyanide 20 Sodium chloride 43 Sodium carbonate 30.99 Potassium fiuosilicate 6 Carbon .01

After an immersion time of one hour during which period the temperature :of the bath was maintained at 1650 F., the depth of case was found to be 0.014 inch. The surface was bright and clean and file hard. No sludging, frothing or foaming was noted.

Example 3 A case hardening bath was prepared by blending together the following materials in powder form.

Parts by Weight Sodium cyanide 20 Sodium chloride 3'9 Sodium carbonate 32 Sodium fiuosilicate 8 Carbon 1 The mixture was fused and maintained at a temperature of 1600 F. In order to maintain the bath level from loss due to dragout on the work and maintain activity which might have been lessened due to surface decomposition, a replenisher was added regularly at the rate of 10 percent by weight of the bath per 8 hour day, the replenisher having the following proportions:

Parts by weight Sodium cyanide 40 Sodium chloride 39 Sodium carbonate 12 Sodium fluosilicate 8 Carbon l 1 Steel rods, carbon 0.20%, manganese 0.40%, phosphorus 0.04%, sulfur 0.04%, were treated in this bath and cyanide and case depths determina tions made.

Cyanide Concentration in Bath (Percent Sodium Cyanide) Days in Operation Microscopic examinations for case depths showed the following average figures:

Depth of case Inches hr .010 1 hr .015 2 hrs .022

3 hrs .027 4 hrs .030

Example 4 A steel bolt having a carbon content of 015 percent was treated in a fused salt bath of the following composition:

Parts by weight Sodium cyanide 40 Sodium cyanate 2 Sodium chloride 30 Sodium carbonate 9 Potassium chloride Lithium fiuosilicate; 12

Carbon 2 The temperature was maintained at 1700 F. and after hr. immersion the case depth was found to be 0.011 inch.

Example 5 A salt bath of the following composition was fused and maintained at a temperature of 1550 F.:

Parts by weight Sodium cyanide Sodium cyanate 5 Sodium carbonate 25 Sodium chloride 34.5 Sodium fluosilicate 20 Carbon 0.5

The level of the bath in the pot was maintained by the regular addition of the following mixture,

making the addition at the rate of percent per hour.

Parts by weight Sodium cyanide '75 Sodium cyanate 4 Sodium carbonate .5 Sodium fiuosilicate 15 Carbon 0.5

Steel rods having a carbon content of 0.15 percent were immersed in this bath for 2 hours. A

- depth of case of 0.020 inch was produced.

Starting Replen- Salt isher Parts by Paris by weight weight Sodium Cyanide l. 70-40 4075 Sodium Oyanate l 0-5 0-5 Sodium Chloride" 5-45 5-40 Sod um Carbonate. 5-35 5-20 Potassium Chloride.. 0-30 0-30 Alkali Metal Fluosilicate. 2-20 220 Carbon 0-2 0-2 The higher the operating temperature, the faster the rate of cementation. Temperatures as high as 1900 F. have been used without excessive frothing or foaming of the bath. And ternperatures as low as 1400 F. have been employed with effective carburizingl What is claimed is:

l. A composition of matter for a case hardenin bath for iron, steel, and ferrous alloys consisting of a mixture of the following ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Alkali metal fiuosilicate 2 to 20 2. A composition of matter for a case hardening bath for iron, steel, and ferrous alloys consisting of a mixture of the following ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate less than 5 Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Alkali metal fluosilicate 2 to 20 3. A composition of matter for a case hardening bath for iron, steel, and ferrous alloys consisting of a mixture of the following ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate less than 5 Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Potassium chloride less than 30 Alkali metal fluosilicate 2 to 20 4. A composition of matter for a case hardening bath for iron, steel, and ferrous alloys consisting of a mixture of the following ingredients:

Parts by weight Sodium cyanide to 40 Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Potassium chloride less than 30 Alkali metal fluosilicate 2 to 5. A composition of matter for a case hardening bath for iron, steel, and ferrous alloys consisting of a mixture of the followin ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Potassium chloride less than Carbon less than 2 Alkali metal fiuosilicate 2 to 20 6. A composition of matter for a case hardening bath for iron, steel, and ferrous alloys consisting of a mixture of the following ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate less than 5 Sodium chloride 5 to 45 Sodium carbonate 5 to Carbon less than 2 Alkali metal fiuosilicate 2 to 20 '7. A composition of matter for a case hardening bath for iron, steel, and ferrous alloys consisting of a mixture of the following ingredients:

Parts by Weight Sodium cyanide 10 to 40 Sodium chloride 5 to Sodium carbonate 5 to 35 Carbon less than 2 Alkali metal fiuosilicate 2 to 20 8. A composition of matter for a case hardening bath for iron, steel, and ferrous alloys consisting of a mixture of the followin ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate less than 5 Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Carbon less than 2 Sodium fiuosilicate 2 to 20 9. A composition of matter for a case hardening bath for iron, steel, and ferrous alloys consisting of a mixture of the following ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate less than 5 Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Carbon less than 2 Potassium fiuosilicate 2 to 20 10. A composition of matter for a case hardening bath for iron, steel, and ferrous alloys consisting of a mixture of the following ingredients;

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate less than 5 Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Carbon less than 2 Lithium fiuosilicate 2 to 20 11. A composition of matter for a case hardening bath for iron, steel, and ferrous alloys consisting of a mixture of the following ingredients:

Parts by weight Sodium cyanide 10 to 40 Sodium cyanate Less than 5 Sodium chloride 5 to 45 Sodium carbonate 5 to 35 Potassium chloride Less than 30 Carbon Less than 2 Alkali metal fluosilicate 2 to 20 ISAAC LAIRD NEWELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,804,454 Beck May 12, 1931 OTHER REFERENCES Molten Salt Baths, page '7, published by Du Pont de Nemours & Co. Inc., 1946.

Claims

1. A COMPOSITION OF MATTER FOR A CASE HARDENING BATH FOR IRON, STEEL, AND FERROUS ALLOYS CONSISTING OF A MIXTURE OF THE FOLLOWING INGREDIENTS: