US 3792726 A
A metal surface strengthening method comprising attaching, with or without pressure, a preformed plate formed of a metal surface strengthening powder to a fundamental molten metal kept in a gas sprayed protective atmosphere in the mold.
Description (OCR text may contain errors)
waited States Patent [191 Sakai et a1.
[ Feb. 19, 1974 METHOD FOR STRENGHTNENING A METAL SURFACE  Inventors: Yoshifumi Sakai, Chiryu; Takeshi Sumi, Chita; Atsushi Wada, Tokai; Mitsuo Morishima, Tokai; Shigeto Kawakaki, Tokai; Takashi Kozawa, Nagoya, all of Japan  Assignee: Daido Deiko Kabushiki Kaisha,
' Aichi-ken, Japan  Filed: Dec. 22, 1971 21 App1. No.5 210,733
 Foreign Application Priority Data Dec. 29, 1970 Japan 45/121220  11.5}. C1 164/59, 164/98, 164/120  Int. Cl B22d 19/00, 322d 27/18  Field of Search. 164/59, 75, 120, 98, 100, 103,
 References Cited UNITED STATES PATENTS 2,161,597 6/1939 Swartz 164/75 X 2,034,550 3/1936 Adams 164/98 X FOREIGN PATENTS OR APPLICATIONS 431,372 1/1968 Japan 164/97 Primary ExaminerJ. Spencer Overholser Assistant Examiner-John E. Roethel 5 7 ABSTRACT A metal surface strengthening method comprising attaching, with or without pressure, a preformed plate formed of a metal surface strengthening powder to a fundamental molten metal kept in a gas sprayed protective atmosphere in the mold.
2 Claims, 7 Drawing Figures PATENTEB FEB l 9 I974 SHEET 1 [IF 2 FIG.4
sum 2 OF 2 VICKERS HARDNESS (HV) VALUES IN EACH LEVEL OF MICROSTRUCTURE FIG.7
METHOD F OR STRENGHTNENING A METAL SURFACE BACKGROUND OF THE INVENTION ing is under development (e.g., Japanese Pat. No. I
520,699). This method is concerned with an applied technique of squeeze casting, wherein the metal surface strengthening powder is directly scattered on wherein molten metal poured in the mold, and the pressure is subsequently applied thereto to form a strengthened metal layer. This method enables one to obtain the desired strengthened metal layer simultaneously with the completion of the product, and so is a method to be highly appreciated. At present, however, this method has drawbacks as mentioned below:
1. Since the molten metal surface in the mold is in an oxidized state at the time the powder is scattered thereon, the reaction between the powder and the molten metal becomes incomplete so that even if the pressure is sufficiently applied thereto, the resulting product often tends to tear off at the bonded portion.
2. Furthermore, as the powder, when scattered on the molten surface, is heated by the molten metal and is oxidized by oxygen in the air, it may lose its metal strengthening nature. For example, if the powder is of WC (tungsten carbide), W in the WC reacts with O so that the resulting layer is not sufficiently strengthened.
Because of these disadvantages, it has been difficult, as shown in FIGS. 1 and 2, to form products with smooth casting surfaces and uniform strengthened layers (A).
SUMMARY OF INVENTION This invention relates to a method for strengthening a metal surface comprising the steps of pouring a molten metal into a mold, placing or laying a preformed plate compacted from a mixture of one ormore of a powder of tungsten carbide, titanium carbide, tantalum carbide and ceramic and a powder of a binder on the surface of said molten metal, and applying pressure by means of a punch during the molten state or solidification course of said molten metal so that said plate is directly bonded to the surface of said metal whereby a strengthening layer is formed on the surface of said metal.
This invention aims at removing the defects mentioned hereinbefore, permitting strengthening of the metal surface by a relatively simple method, and further, permitting industrial mass production for the method.
BRIEF DESCRIPTION OF THE DRAWINGS metal layer strengthened in accordance with the con ventional powder scattering method;
FIG. 3 is a cross sectional view of one embodiment of this invention; and
FIGS. 4 7 are photomicrographs and a diagram of the embodiments effected in accordance with the present invention, wherein FIG. 4 is a photomicrograph (X of the casting surface of a strengthened layer; FIG. 5 is a photomicrograph (X k) of a. section of the thickness distribution of a strengthened layer; FIG. 6 is a photomicrograph (X 100) of the microstructure of the bonded part of a strengthened layer with a fundamental material; and FIG. 7 is a diagram of the distribution of hardness (Hv) of the strengthened layer shown in FIG. 6.
DESCRIPTION OF PREFERRED EMBODIMENTS The method of this invention will now be explained with reference to FIG. 3 of the accompanying drawings. I
The preformed plate is formed to one '5 mm thick piece from a mixture la of the powder comprising at least percent of one or more of tungsten carbide, titanium carbide, tantalum carbide, ceramics, etc., each having a good affinity with the molten metal, and approximately 10 percent of a binder such as a thermosetting resin, on an asbestine adiabatic sheet I 1b producting no slag when reacted with the molten metal.
A desired molten metal 3 is then poured into the mold 2 which is sprayed with a wash for accomplishing a releasing action at the inside wall of said mold, when the atmosphere in the mold 2 is kept non-oxidized protective to prevent the molten metal 3 from oxidizing. For this purpose, the nozzles 7 provided at the upper inside of the mold 2 are connected to the protective gas supplying pipe 6. The preformed plate 1 is then placed or laid on the surface of the molten metal 3, and after a lapse ofa proper time (e.g., about 10 sec.) a pressure punch 4 is lowered to apply thereto an amount of pressure (e.g., about 1 tonlcm about 30 sec.). Thereafter, the pressure is released and the product of a predetermined shape is taken out by means of a knockout pin 5.
FIG. 4 shows a casting surface of a strengthened surface formed according to the method of this invention and FIG. 5 illustrates a strengthened layer (B) formed by the method of this invention. It has been found that both of them have the merits as mentioned hereinafter in comparison with the conventional scattering method. As is clear from the comparison of FIG. 1 with FIG. 4, the casting surface is superior in the case of the present invention. For instance, the shortcomings such as blow holes, tearing off of the strengthened layer,
etc., that have often taken place with the prior method have been remarkably decreased. A comparison of the reference numeral A of FIG. 2 with the reference numeral B of FIG. 5 clearly shows that the strengthened layer with a uniform and desired thickness as shown in FIG. 5 can also be obtained by the method of the present invention.
Furthermore, in the product obtained by the method of this invention, the strengthened layer is so firmly bonded to the molten metal due to the application of pressure by means of the punch 4 that, when used for a punching die and the like requiring a substantial hardness and a toughness, such undesirable phenomena as half-wearing, lacking, and tearing-off in the case of the conventional die do not occur so that a remarkable effect results in that the life span of the product is prolonged.
FIG. 6 represents the microstructure (X 100) of the bonded part of the strengthened layer to the fundamental material obtained by the method of the present invention. This test material has been prepared by bonding to the molten metal of carbon steel a preformed plate formed of WC (tungsten carbide) powder, said test material having been subjected to an annealing process thereafter. From this figure, it can be seen that the attachment near the boundary portion (C) is perfect and no noxious defects such as an inclusion or gas effect are recognized.
FIG. 7 is a diagram showing the distribution of Vickers hardness (I-Iv) extending from the strengthened layer as shown in the photomic'rograph of FIG. 6 to the fundamental material. As is clear from the diagram, the strengthened layer (made from tungsten carbide) re- I mains sufficiently strengthened after it has been annealed.
As described above in detail, it has been shown that the method of the present invention is far superior to that of the conventional powder scattering method. For instance, in case a strengthened layer is to be attached to an uneven metal surface, it has been very difficult to attach it uniformly due to the fluidity of the molten metal. According to this invention, however, a pre formed plate formed to any desired shape from the powder for strengthening a metal surfaceis placed or laid on the molten metal in the mold or core mold so that products with evenly strengthened surfaces can be obtained.
According to the present invention, as described above, the metal surface strengthening can be carried out by the relatively simple method. Moreover, various composite materials in the fields of wearing, heat, and erosion resistance industries can be manufactured at remarkably low costs. Also, the object of using the preformed plate in this invention is that the operation can be carried out effectively and a smoothed casting surface and uniform thickness of strengthened layer can be obtained. Furthermore, in case the features of the molten metal and those of the powder for strenghening are quite different thereby making the attachment therebetween difficult, they can be attached by adding to the preformed plate one or more layers of materials required for their attachment.
What is claimed is:
1. A method for strengthening a metal surface comprising the steps of pouring a molten metal into a mold, placing a preformed plate compacted from a mixture of one or more of a powder of tungsten carbide, titanium carbide, tantalum carbide and ceramics and a powder of a binder on the surface of said molten metal, and applying pressure by means of a punch during the molten state of said molten metal so that said plate is directly bonded to the surface of said metal whereby a strengthened layer is formed on the surface of said metal.
2. The method of claim 1 wherein the pressure is applied during the solidification of said molten metal.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,792,726 Dated February 19, 197
Inventor) Yoshifumi Sakai, Takeshi Sumi, et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
On the first page, column 1, line 8, the Assignee's name should read --Daido Seikoinstead of "Daido Deiko" Signed and sealed this 13th day of August 197 (SEAL) Attest:
MCCOY M. GIBSON, JR. C. MARSHALL DANN I =Attesting Officer Commissioner of Patents ORM po'mso USCOMM-DC wan-ps9 U. 5. GOVERNMENT PRINTlNG OFFICE t '9', U3 33,