US20070169856A1

US20070169856A1 - Method for making a hybrid casting and forging stainless steel product

Info

Publication number: US20070169856A1
Application number: US11/339,757
Authority: US
Inventors: Chia-Kan Chien
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-01-25
Filing date: 2006-01-25
Publication date: 2007-07-26

Abstract

A method for making a hybrid casting and forging stainless steel product includes a) casting a stainless steel to form a cast billet, b) heat forging the cast billet to eliminate micro-shrinkage pores and gas holes produced in the cast billet during the casting process so as to form a forged element having a compact structure, and c) performing a solution treatment on the forged element to form a hybrid casting and forging stainless steel product. Thus, the hybrid casting and forging stainless steel product has mechanic specifications similar to that of the forged element by the forging process and the solution treatment, so that the stainless steel product has greater mechanic features and lower price, thereby enhancing the quality of the stainless steel product, and thereby decreasing costs of fabrication.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a method for making a stainless steel product and, more particularly, to a method for making a hybrid casting and forging stainless steel product.
2. Description of the Related Art
A metallic working process is used to work a metallic material, such as the stainless steel or the like, to form a worked metallic product. The conventional metallic working process comprises a casting process and a forging process.
The casting process forms the worked metallic product at the liquid state so that the cast metallic product is formed easily. Thus, the casting process can be used to make a metallic product having a complicated shape. In addition, the cast metallic product approaches the final shape and size to save the material and to reduce the working cost. In addition, the casting process can use waste melting to reduce the cost of material. In addition, the noil produced by the casting process can be recycled to reduce the cost of material. In addition, the die of the casting process has a cheaper price to reduce the cost of fabrication. However, the metallic product worked by the casting process has greater crystal grain sizes, so that the cast metallic product has worse mechanic features. In addition, the cast metallic product easily produces gas holes and micro-shrinkage pores to reduce the relative density of the cast metallic product, so that the cast metallic product has worse mechanic features and leakproof effects. In addition, the casting process consumes the energy greatly.
The forging process forms the worked metallic product at the solid state. Thus, the metallic product worked by the forging process has smaller crystal grain sizes, so that the forged metallic product has better mechanic features. In addition, the forged metallic product does not produce gas holes and micro-shrinkage pores to increase the relative density of the forged metallic product, so that the forged metallic product has better mechanic features and leakproof effects. However, the forging process forms the worked metallic product at the solid state so that the forged metallic product is not formed easily. Thus, the forging process cannot be used to make a metallic product having a complicated shape. In addition, the forging process needs multiple working steps and dies, thereby increasing the cost of fabrication. In addition, the die of the forging process has a more expensive price to increase the cost of fabrication. In addition, the forging process uses rolled forging material having greater price, thereby increasing the cost of material.
In conclusion, the metallic product worked by the casting process has a lower price. However, the metallic product worked by the casting process has a worse quality. On the other hand, the metallic product worked by the forging process has a better quality. However, the metallic product worked by the forging process has a greater price.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a method for making a hybrid casting and forging stainless steel product comprises a) casting a stainless steel by a casting process to form a cast billet, b) heat forging the cast billet by a forging process to eliminate micro-shrinkage pores and gas holes produced in the cast billet during the casting process so as to form a forged element having a compact structure, and c) performing a solution treatment on the forged element to form a hybrid casting and forging stainless steel product having mechanic specifications similar to that of the forged element.
The primary objective of the present invention is to provide a method for making a hybrid casting and forging stainless steel product, wherein the method combines the advantages of the casting and forging working processes to produce a hybrid casting and forging stainless steel product having a lower price and a better quality.
Another objective of the present invention is to provide a method for making a stainless steel product, wherein the stainless steel is worked by a casting process to form a cast billet to reduce the cost of fabrication, the cast billet is then worked by a forging process to increase the strength of the cast billet to form a forged element, and the forged element is finally performed by a necessary heat treatment to form a hybrid casting and forging stainless steel product that combines the advantages of the casting and forging working effects so as to reduce the price and increase the quality.
A further objective of the present invention is to provide a method for making a stainless steel product, wherein the hybrid casting and forging stainless steel product has mechanic specifications (such as the mechanic strength) similar to that of the forged element by the forging process and the solution treatment, so that the stainless steel product has greater mechanic features and lower price, thereby enhancing the quality of the stainless steel product, and thereby decreasing costs of fabrication.
A further objective of the present invention is to provide a method for making a stainless steel product, wherein the hybrid casting and forging stainless steel product saves the material consumption and the working steps and reduces the energy loss.
Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a comparison graph of a load curve of a method for making a hybrid casting and forging stainless steel product in accordance with the preferred embodiment of the present invention.
FIG. 2 is a comparison graph of an elongation of the method for making a hybrid casting and forging stainless steel product in accordance with the preferred embodiment of the present invention.
FIG. 3 is a comparison graph of a yield stress of the method for making a hybrid casting and forging stainless steel product in accordance with the preferred embodiment of the present invention.
FIG. 4 is a comparison graph of a tensile stress of the method for making a hybrid casting and forging stainless steel product in accordance with the preferred embodiment of the present invention.
FIG. 5 is a comparison graph of a hardness of the method for making a hybrid casting and forging stainless steel product in accordance with the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, a method for making a hybrid casting and forging stainless steel product in accordance with the preferred embodiment of the present invention comprises a) casting a stainless steel by a casting process to form a cast billet, b) heat forging the cast billet by a forging process to eliminate micro-shrinkage pores and gas holes produced in the cast billet during the casting process so as to form a forged element having a compact structure, and c) performing a solution treatment on the forged element to form a hybrid casting and forging stainless steel product having mechanic specifications similar to that of the forged element.
In the preferred embodiment of the present invention, the cast billet is treated by the forging process at a forging temperature of about 1000° C. to 1100° C. In addition, the upset ratio (h/h0) between the cast billet and the forged element is about 0.25 to 0.75 so that the cast billet has determined deformation and flow during the forging process. In addition, the forged element is treated by the solution treatment during two hours at a temperature of about 1100° C.
The features of the method of the present invention are described as follows.
First of all, the hybrid casting and forging technology includes forming a cast billet having a similar shape by a casting process, and then forging the cast billet to form a hybrid casting and forging product. In such a manner, the hybrid casting and forging technology uses a cast element formed by waste melting without having to use an expensive bar-shaped material. In addition, the cast billet has enhanced features after the cast billet is forged to satisfy the specifications required by the forged element. In addition, the product having a complicated shape can be cast previously to reduce the forging working steps. In practice, the hybrid casting and forging technology needs to build a database of the hybrid casting and forging procedure. The conventional forging technology uses rolled forging material which has a smaller crystal grain size and a greater relative density, and the conventional casting technology uses casting material which has a greater crystal grain size (with tree shaped crystalline) and a smaller relative density, and contains micro-shrinkage pores and gas holes, so that the forging features of the casting material are different from that of the rolled forging material. Thus, the hybrid casting and forging technology needs to establish the relationship between the upset ratio, the forging temperature, the solution treatment and the mechanic specifications under the casting state to determine the optimum casting and forging conditions so as to build a complete database of the hybrid casting and forging procedure. In such a manner, the casting and forging conditions are combined by the database of the hybrid casting and forging procedure. For example, the database of the hybrid casting and forging procedure is based on the popular SUS304 stainless steel to functions as the technology interface of the hybrid casting and forging technology.
Next, it is necessary to choose a casting and forging product having proper size and shape. Then, by the database of the hybrid casting and forging procedure, the upset ratio is determined according to the requirement of the forged product. Then, a proper cast billet is formed by a casting process. Then, the cast billet is forged according to proper conditions, such as the forging temperature, forging pressure or the like, to form a product billet. Then, the product billet samples are treated by tests of the mechanic specification and the metallographic organization and are compared with the data stored in the database of the hybrid casting and forging procedure. Finally, the product billet is performed by a mechanic working process to form a hybrid casting and forging product.
The procedures of the complete hybrid casting and forging stainless steel product are described as follows.
First of all, it is necessary to establish the parameter database of the hybrid casting and forging stainless steel product, wherein the upset ratio (h/h0) is about ¾, ⅔, ½, ⅓and ¼, the forging temperature of the stainless steel cast element is about 1000° C. and 1100° C., and the height of the cast billet is about 20 mm and 50 mm. In addition, after the testing sample is forged, the testing sample is performed by a solution treatment to judge the difference between the mechanic features of the testing sample before and after the solution treatment is performed. The temperature of the cast billet is increased at about 200° C. to 300° C. per hour during the heat forging process. The heat conductive coefficient of the stainless steel is smaller than that of the low carbon steel or the low alloy steel, so that the stainless steel has a longer heating period. In addition, the stainless steel cannot be kept too long under the forging temperature, so that the stainless steel is taken out immediately when the temperature of the stainless steel billet is uniform to be forged. In addition, the temperature of the die is kept at about 200° C. to 300° C. to decrease the temperature differential between the cast billet and the die so as to eliminate the experimental error. In addition, the forged element is cooled rapidly (the cooling speed is about 2° C./sec) after the heat forging process to prevent the feature of the forged element from being changed.
In fabrication, the cast billet is heated during 30 to 50 minutes according to the preset experimental parameters. Then, the cast billet is taken out rapidly and is placed onto the die to be forged. At this time, the cast billet cannot be placed onto the die too long to prevent the die from being annealed and softened and to enhance the lifetime of the die. In addition, the die is heated to the temperature of about 200° C. to 300° C. to prevent the bulk material from producing a chilling effect. Then, the forged element of taken out and is placed into the water to be cooled. The experiment uses two groups of testing samples, wherein the testing sample (the forged element) of the first group is not performed by any treatment after the cooling process, and the testing sample of the second group is treated by the solution treatment during two hours at a temperature of about 1100° C. Then, the mechanic features of the testing samples are tested as shown in FIGS. 1-5 to compare the difference between the mechanic features of the testing samples before and after the solution treatment is performed under the conditions of different upset ratios and forging temperatures so as to build a complete parameter database of the procedure of the complete hybrid casting and forging stainless steel product. Then, by the database, the corresponding parameters of the procedure are taken according to the required mechanic strength to facilitate forging the stainless steel product.
Thus, according to the experimental results, after the cast billet is forged and performed by the solution treatment, the hybrid casting and forging stainless steel product has mechanic specifications similar to that of the forged element. In the preferred embodiment of the present invention, the forging temperature is about 1000° C. to 1100°, the upset ratio (h/h0) is about 0.25 to 0.75, and the solution treatment temperature is about 1100° C.
Accordingly, the stainless steel is worked by a casting process to form a cast billet to reduce the cost of fabrication, the cast billet is then worked by a forging process to increase the strength of the cast billet to form a forged element, and the forged element is finally performed by a necessary heat treatment to form a hybrid casting and forging stainless steel product that combines the advantages of the casting and forging working effects so as to reduce the price and increase the quality. In addition, the hybrid casting and forging stainless steel product has mechanic specifications (such as the mechanic strength) similar to that of the forged element by the forging process and the solution treatment, so that the stainless steel product has greater mechanic features and lower price, thereby enhancing the quality of the stainless steel product, and thereby decreasing costs of fabrication. Further, the hybrid casting and forging stainless steel product saves the material consumption and the working steps and reduces the energy loss.
Although the invention has been explained in relation to its preferred embodiment(s) as mentioned above, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the present invention. It is, therefore, contemplated that the appended claim or claims will cover such modifications and variations that fall within the true scope of the invention.

Claims

1. A method for making a hybrid casting and forging stainless steel product, comprising:

a) casting a stainless steel by a casting process to form a cast billet;

b) heat forging the cast billet by a forging process to eliminate micro-shrinkage pores and gas holes produced in the cast billet during the casting process so as to form a forged element having a compact structure; and

c) performing a solution treatment on the forged element to form a hybrid casting and forging stainless steel product having mechanic specifications similar to that of the forged element.

2. The method in accordance with claim 1, wherein the cast billet is treated by the forging process at a forging temperature of about 1000° C. to 1110° C.

3. The method in accordance with claim 1, wherein the upset ratio (h/h0) between the cast billet and the forged element is about 0.25 to 0.75 so that the cast billet has determined deformation and flow during the forging process.

4. The method in accordance with claim 1, wherein the forged element is treated by the solution treatment during two hours at a temperature of about 1100° C.