METHOD OF MANUFACTURING A STAINLESS STEEL FASTENER

Abstract

A method of manufacturing a stainless steel fastener includes following operations. Firstly, a stainless steel blank is prepared and contains from 1 to 3.5 wt % molybdenum, from 10 to 16 wt % chromium, from 0.5 to 3.5 wt % nickel, from 0.05 to 0.3 wt % nitrogen, carbon which is not more than 0.2 wt %, iron, and other inevitable compositions. Initially, a steel crystalline structure of the blank is martensite whose hardness ranges from 230 to 350 HV. Then, the blank is annealed to transform a partial crystalline structure of the steel crystalline structure into ferrite. The annealed blank experiences a cutting operation, a head forming operation, and a thread forming operation sequentially. Thereafter, a heat treating operation is executed to transform the partial crystalline structure from ferrite into martensite to complete a stainless steel fastener whose hardness is increased and is at least 500 HV, which facilitates a direct drilling effect.

Claims

1. A method of manufacturing a stainless steel fastener, comprising: a preparing operation including preparing a stainless steel blank, said stainless steel blank having an overall composition containing a molybdenum content ranging from 1 wt % to 3.5 wt %, a chromium content ranging from 10 wt % to 16 wt %, a nickel content ranging from 0.5 wt % to 3.5 wt %, a nitrogen content ranging from 0.05 wt % to 0.3 wt %, and a carbon content which is not more than 0.2 wt %, and a remainder of said overall composition being iron and inevitable compositions inherent in said stainless steel blank, wherein said molybdenum content is at least 1 wt % and said nickel content is at least 0.5 wt %, whereby said molybdenum content is always larger than both of said nitrogen content and said carbon content, and a steel crystalline structure of said stainless steel blank being initially defined as martensite and having a hardness value ranging from 230 HV to 350 HV; an annealing operation including subjecting said stainless steel blank to an annealing treatment whereby a partial crystalline structure of said steel crystalline structure of said stainless steel blank is transformed from martensite into ferrite, and said hardness value of said stainless steel blank is reduced to a value which is not more than 200 HV; a cutting operation including cutting said stainless steel blank whose hardness is not more than 200 HV according to a length; a head forming operation including pressing one end of said stainless steel blank treated by said cutting operation to thereby form a head, a remainder of said stainless steel blank being defined as a shank connected to said head after said one end is pressed, with said shank having a distal end opposite to said head; a thread forming operation including shaping said distal end of said shank to form a drilling portion and also includes forming a threaded portion on said shank, with said threaded portion formed between said head and said drilling portion; and a heat treating operation including preparing a heat treatment device and subjecting said stainless steel blank treated by said thread forming operation to a heat treatment with said heat treatment device, wherein said partial crystalline structure of said stainless steel blank is transformed from ferrite into martensite during said heat treatment to thereby complete a stainless steel fastener, a hardness value of said stainless steel fastener being increased when a nitriding effect derived from said nitrogen content and said carbon content is caused during said heat treatment, with said hardness value of said stainless steel fastener being at least 500 HV, said molybdenum content, said chromium content, and said nickel content providing said stainless steel fastener with corrosion resistance properties.

2. The method according to claim 1, wherein said heat treatment device is a vacuum stove.

3. The method according to claim 1, further comprising a passivation operation, said passivation operation being executed after said heat treating operation and including immersing said stainless steel fastener in a passivation solution to thereby form a passivation film on a surface of said stainless steel fastener.

4. The method according to claim 2, further comprising a passivation operation, said passivation operation being executed after said heat treating operation and including immersing said stainless steel fastener in a passivation solution to thereby form a passivation film on a surface of said stainless steel fastener.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a block diagram showing the operations of a first preferred embodiment of this invention in sequential order; and

[0014] FIG. 2 is a block diagram showing the operations of a second preferred embodiment of this invention in sequential order.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Referring to FIG. 1, a method 3 of manufacturing a stainless steel fastener of a first preferred embodiment of this invention includes a preparing operation 31, an annealing operation 32, a cutting operation 33, ahead forming operation 34, a thread forming operation 35, and a heat treating operation 36. The preparing operation 31 prepares a stainless steel blank. The stainless steel blank has an overall composition. The overall composition contains a molybdenum content ranging from 1 wt % to 3.5 wt %, a chromium content ranging from 10 wt % to 16 wt %, a nickel content ranging from 0.5 wt % to 3.5 wt %, a nitrogen content ranging from 0.05 wt % to 0.3 wt %, and a carbon content which is not more than 0.2 wt %. The remainder of the overall composition of the stainless steel blank is iron and other inevitable or unavoidable compositions inherent in the manufacturing of the stainless steel blank. Besides, a steel crystalline structure of the stainless steel blank is initially defined as martensite, and particularly the structure of the stainless steel blank has a hardness value ranging from 230 HV to 350 HV. Regarding the iron, the iron content can be above 70 wt %, namely be equal to 70 wt % or more than 70 wt %. The inevitable compositions mean requisite constituents required in constituting the stainless steel blank when the blank is manufactured. It is possible that the inevitable compositions contain silicon, manganese, phosphorus, sulfur, and other impurities. Examples of a total content (100 wt %) of the overall composition are given as below.

TABLE-US-00001 Inevitable Molybdenum Chromium Nickel Nitrogen Carbon Iron compositions Example (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) 1 1 11 0.8 0.05 0.08 73 14.07 2 2 12.5 1 0.015 0.12 71 13.365 3 2.5 14 2.5 0.015 0.1 72 8.885 4 3.5 14 2.5 0.015 0.1 73 6.885 5 1.5 12 1.2 0.2 0.2 76 8.9

[0016] The annealing operation 32 subjects the stainless steel blank to an annealing treatment whereby a partial crystalline structure of the steel crystalline structure of the stainless steel blank is transformed into ferrite. The hardness value of the stainless steel blank is reduced to a value which is not more than 200 HV to thereby facilitate following operations.

[0017] The cutting operation 33 cuts the stainless steel blank according to a length. The head forming operation 34 presses one end of the stainless steel blank treated by the cutting operation 33 to thereby form a head. A remainder of the stainless steel blank is defined as a shank connected to the head after the one end is pressed. The shank has a distal end opposite to the head. The thread forming operation 35 shapes the distal end of the shank to form a drilling portion and also forms a threaded portion on the shank. The threaded portion is formed between the head and the drilling portion.

[0018] The heat treating operation 36 prepares a heat treatment device and subjects the stainless steel blank treated by the thread forming operation 35 to a heat treatment with the heat treatment device. The partial crystalline structure of the stainless steel blank is transformed from ferrite into martensite during the heat treatment to thereby complete a stainless steel fastener. A hardness value of the stainless steel fastener is increased when a nitriding effect derived from the nitrogen content and the carbon content is caused during the heat treatment. The hardness value of the stainless steel fastener is increased to be at least 500 HV, and that facilitates a direct drilling effect. Further, the molybdenum content, the chromium content, and the nickel content provide the stainless steel fastener with corrosion resistance properties. Hence, the stainless steel fastener can be adapted to drill into an object which is not provided with a pre-drilled hole directly. Because there is no need to pierce a hole on the object in advance, the drilling operation is simplified. Hence, the stainless steel fastener is provided with great hardness value, great strength, and corrosion resistance properties. The manufacturing costs and processing complexity are also reduced.

[0019] Referring to FIG. 2 shows a second preferred embodiment of the method 3 of this invention. The second preferred embodiment still includes the preparing operation 31, the annealing operation 32, the cutting operation 33, the head forming operation 34, the thread forming operation 35, and the heat treating operation 36 of the first preferred embodiment. This embodiment is characterized in that a passivation operation 37 is executed after the heat treating operation 36. The passivation operation 37 includes immersing the stainless steel fastener in a passivation solution to thereby form a passivation film on a surface of the stainless steel fastener. Thus, the passivation film can cover pores formed on the surface of the stainless steel fastener to thereby prevent the stainless steel fastener from rusting easily, enhance the corrosion resistance properties of the stainless steel fastener, and prolong the service life of the stainless steel fastener.

[0020] To sum up, the method of this invention includes the preparing operation, the annealing operation, the cutting operation, the head forming operation, the thread forming operation, and the heat treating operation. The preparing operation prepares a stainless steel blank containing a molybdenum content, a chromium content, a nickel content, a nitrogen content, a carbon content, an iron content, and an inevitable content. A steel crystalline structure of the stainless steel blank is initially defined as martensite and having a hardness value ranging from 230 HV to 350 HV. The annealing operation executes an annealing treatment of the stainless steel blank whereby a partial crystalline structure of the steel crystalline structure of the stainless steel blank is transformed into ferrite. The hardness value of the stainless steel blank is reduced to a value which is not more than 200 HV. The cutting operation cuts the stainless steel blank according to a length. The head forming operation and the thread forming operation process the stainless steel blank to have a head, a shank extending outwards from the head, a drilling portion connected to the shank and opposite to the head, and a threaded portion formed on shank and located between the head and the drilling portion. The heat treating operation executes a heat treatment of the stainless steel blank through a heat treatment device to thereby transform the partial steel crystalline structure of the stainless steel blank from ferrite into martensite during the heat treatment to thereby complete a stainless steel fastener. A hardness value of the stainless steel fastener is increased when a nitriding effect derived from the nitrogen content and the carbon content is caused during the heat treatment. The hardness value of the stainless steel fastener is increased to be at least 500 HV. The molybdenum content, the chromium content, and the nickel content equip the stainless steel fastener with corrosion resistance properties. Thus, the stainless steel fastener is provided with large strength, large hardness value, and corrosion resistance properties to thereby facilitate a direct drilling effect.

[0021] While the embodiments of this invention are shown and described, it is understood that further variations and modifications may be made without departing from the scope of this invention.