Electrolytic carburizing process using a carbonate electrolyte
United States Patent Hiyama Apr. 8, 1975 [54] ELECTROLYTIC CARBURIZING PROCESS 3.488.233 1/1970 Newell 148/155 3.635.768 1/1972 Mueller 148/155 I I I USING A CARBONATE ELECTROLYTE Inventor: Shinji Hiyama, Kamakura-shi,  
 Kanagawa, Japan Assignee: Nippon Furnace Koga Kaisha, Ltd.,  
 Minatoku, Tokyo, Japan Filed: Sept. 10, 1973 Appl. No.: 395,541  
 US. Cl 204/39; 204/140 Int. Cl C23b 11/00 Field of Search 204/39, 140; 148/155 References Cited UNITED STATES PATENTS 7/1967 Buitrus 204/39 FOREIGN PATENTS OR APPLICATIONS 155,812 7/1961 U.S.S.R 204/39 Primary Examiner-R. L. Andrews Attorney, Agent, or Firm.lohn W. Logan, Jr., Esq.  
 [57] ABSTRACT A carburizing process consisting of using the object to be carburized as a cathode and inserting the cathode into an electrolytic bath including a melted metallic salt in which the anode is graphite.  
 4 Claims, 2 Drawing Figures PATENTEUAPR ei&#39;zs 71.876512 CARBON POTENTIAL 0 A01 A/cm ELECTROLYTIC CARBURIZING PROCESS USING A CARBONATE ELECTROLYTE The present invention relates to a carburizing process by electrolysis.  
  In the conventional carburizing process. melted salt of cyanide is widely used because such process is comparatively simple. However. this conventional process has disadvantages that cyanide is poisonous. the control ofa bath is difficult and carburizing can not be prevented by electroplating steel with copper. The present invention eliminates the above disadvantages completely. above all it has a great advantage not to cause pollution.  
 IN THE ACCOMPANYING DRAWING FIG. 1 is a schematical illustration of electrolysis device used in the present invention: and  
  FIG. 2 shows the relation between current and carbon potential.  
  The process for carburizing according to the present invention will be explained with reference to the drawing. In the bath 4 of a furnace 1, an object article 2 to be carburized and a graphite electrode 3 are immersed. An electric power source 5 is connected between the object article and the graphite electrode through a variable resistor 6 and an ammeter 7. The reference numeral 8 designates a voltmeter and 9 indicates an electric heater. The principal component of the bath 4 is MCO (M is metal element), which metal element is melted by the electric heater. When principal component of the bath is Na. ,CO as an example of MCO and the positive and negative poles of the DC or pulsating current power source 5 are respectively connected to the object article 2 to be carburized as the cathode and to the graphite electrode 3 as the anode, the following reaction takes place.  
 Reaction on the cathode side:  
 Na Na (nascent state) Where, is Na electron, and CO is decomposed into CO or C0.  
 C0 4Na (nascent state) 2Na O C (nascent state. perform carburizing) C0 2Na (nascent state) Nil- O C (nascent state, perform carburizing) Reaction on the anode side:  
 CO CO3 (nascent state) CO C 2C0:  
  CO 2C 3C0 (Agitation occurs due to Peltier effect).  
  CO C 2C0 (Agitation occurs due to Peltier effect).  
 2C0 CO C (nascent state, perform carburizing) Reaction on the surface of the bath:  
 CO Na O Na CO 7 As mentioned above, melted salt whose principal component is MCO is ionized to produce M of nascent state on the cathode side (on the side of the object article). M of nascent state reacts with CO or CO generated by the decomposition of CO to produce C which performs carburizing. On the other hand. CO of nascent state produced on the anode side instantly produces CO: or CO by pure chemical reaction. The resulting CO reacts with C to form CO.  
  Voltage higher than the sum of the electrolytic potential of CO and overvoltage of the graphite electrode is applied to the anode. CO or CO thus produced diffuses toward the cathode rapidly by Peltier effect. Therefore. a complicated article such as a gear is uniformly carburized.  
  Further. in accordance with the present invention. decarburization can also be performed by controlling current. FIG. 2 shows the relationship between current and carbon potential at the cathode of an embodiment of the present invention. When the current is 0.0lA/cm or less. the carbon potential becomes negative. Thus. at this low current, carbon atoms are removed from the cathode resulting in decarburization of the cathode. so that carburizing can be adjusted easily by controlling the current. The above mentioned carburizing is a quite novel process. It is also possible to use a neutral salt by regulating current.  
  Another feature of the present invention is that sludge does not deposit on the bottom of the furnace unlike the conventional carburizing process. promising long life of the bath, since the reaction to produce MCO takes place on the surface of the bath.  
 EXAMPLE An automobile transmission gear was carburized by the above mentioned process according to the present invention. Object article to be carburized: Automobile transmission gears of 77mm and 42mm in diameter. made of SMCZl. Composition of the bath: 50 percent of Na CO percent of Nacl (Na CO alone will be effective, but Nacl was added to make carburing easier at lower temperatures.)  
 Voltage: 2\ Current: 0.3 A/cm Bath temperature: 927C Carburizing time: 60 minutes Quenching: Oil  
 What is claimed is:  
  l. Carburizing process characterized by connecting an object article to be carburized as cathode and graph ite as an anode in melted salt consisting of MCO and electrolyzing the melted salt.  
  2. A process in accordance with claim 1 in which the melted salt is Na. ,CO-  
  3. Carburizing process characterized by connecting an object article to be carburized as a cathode and graphite as an anode in melted salt consisting of MCO and NaCl. and electrolyzing the melted salt.  
  4. A process in accordance with claim 3 in which the melted salt consists of one part by weight of Na CO and three parts or less by weight of NaCl.  
  UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 318761512 a d April 1975 Inventor s Hiyama, Shinji It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:  
 Column 2, Line 16, after &#34;potential&#34; insert --at the cathode-.  
 In the Title Page, the following drawing should be shown in place of the figure illustrated.  
 Signed and Sealed this thirtieth Day Of September 1975 [SEAL] AIIGSI.  
 RUTH C MASON C. MARSHALL DANN Arresting Officer (ummim&#39;nnor of Pan-ms and Trademarks