JP2741872B2 - Heat treatment method for corrosion-resistant iron-based metal articles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention contains Fe ₂ SiO ₄ on the surface of an iron-based metal article containing 0.5% by weight or more of Si and containing iron as a main component. Corrosion-resistant iron-based metal articles provided with corrosion resistance by forming an oxide film, for example, stopper metal fittings and pushes used for insertion connection parts of pipes such as water pipes and gas pipes arranged in a corrosive environment. The present invention relates to a method for performing a heat treatment for imparting a predetermined mechanical strength to a bolt or the like.

[Conventional technology]

The structure shown in FIG. 5 is adopted as a structure for preventing the pipe from being pulled out at the insertion connection portion of the pipe such as the water pipe or the gas pipe. That is, the stopper (5) on the receiving pipe (1) side and the sealing material (6) are attached to the receiving pipe (1).
A plurality of wedge pieces or a C-shaped ring-shaped stopper metal fitting (7) extending substantially all around the axis of the tube between the insertion tube (2) inserted and connected via A plurality of push bolts (8) in the circumferential direction for pressing the retaining fitting (7) to the retaining portion (5) and pressing the retaining fitting (7) against the outer peripheral surface of the insertion tube (2) are attached, and the retaining fitting (7) is provided. Formed on the outer peripheral surface of the insertion tube (2) by being pressed by the push bolt (8), the retaining protrusion (9) being formed on the outer peripheral surface of the insertion tube (2). The contact surface (10) pressed by the push bolt (8) is positioned in an inclined position closer to the outer peripheral surface of the insertion tube (2) as the insertion tube (2) is closer to the drawing direction from the receiving tube (1). When a pull-out force acts on the receiving pipe (1) and the insertion pipe (2), the pull-out force causes the above-mentioned stopper (7) to be inserted into the insertion pipe ( Structure component force that presses the outer peripheral surface is formed on the cam surface causing the are employed).

By the way, ductile cast iron pipes are generally used as the pipe itself including the receiving pipe (1), the insertion pipe (2), and the like, but the retaining part (5) and the retaining fitting (7) used for the insertion connection part are used. Also, as a connection article such as (1), an iron-based metal article containing 0.5% by weight or more of Si, which is equivalent to ductile cast iron, and made of an iron-based metal mainly composed of iron is used.

Since the connection article is particularly required to have corrosion resistance, the article is heated in an oxidizing atmosphere at 700 to 950 ° C. to form an oxide film containing Fe ₂ SiO ₄ on its surface. . This is a technique for imparting corrosion resistance to the article by focusing on the generation of Fe ₂ SiO ₄ by Si contained in the material of the article at 0.5% by weight or more (Japanese Patent Publication No. 46-19843).

By the way, a retaining fitting (7) is included in the connection article.
There are also articles that require a predetermined mechanical strength, such as a bolt and a push bolt (8). In order to obtain a connection article that also requires such a predetermined mechanical strength, the article is heated and the structure is austenitic. after reduction, quenching the article is immersed into M _S point following an oil bath, by a so-called oil quenching, was the fact that the tissue was martensite and to obtain a predetermined mechanical strength.

[Problems to be solved by the invention]

However, according to such a conventional method, although a predetermined mechanical strength is imparted to the article, Fe ₂ SiO already formed on the surface of the article before quenching in the oil quenching process.
There was a problem that the oxide film containing ₄ peeled off and the article had insufficient corrosion resistance.

The present invention has been made in view of such circumstances, and has as its object to provide a heat treatment method capable of imparting a predetermined mechanical strength to the corrosion-resistant iron-based metal article without impairing the corrosion resistance of the article.

[Means for solving the problem]

The heat treatment method for a corrosion-resistant iron-based metal article according to the present invention may be performed by using Si
By forming an oxide film containing Fe ₂ SiO ₄ on the surface of an iron-based metal article containing iron as a main component and containing iron by 0.5% by weight or more. contrast, in the heat treatment method for corrosion resistant ferrous metal article is subjected to a heat treatment for improving mechanical strength, after the tissue is austenitizing the heating said corrosion resistant ferrous metal article, immediately the article, M _S point The heat treatment is performed by immersing the structure in a bath maintained at a higher temperature than that of the bath and transforming the structure at a constant temperature.

(Operation)

According to the method of the present invention, the corrosion-resistant iron alloy article is heated to a temperature at which its structure is austenitized, and then rapidly cooled to change its structure as in the case of the conventional method. Although strength is imparted, since the article is not quenched to a temperature below the _MS point as in the case of the conventional method, its structural change is not due to martensitic transformation accompanied by a significant volume change, It is due to relatively gradual transformation such as bainite transformation. Therefore, it is possible to prevent the oxide film already formed on the surface of the article from peeling off in the process of imparting the predetermined mechanical strength to the article.

〔The invention's effect〕

Therefore, according to the present invention, a predetermined mechanical strength can be imparted to the corrosion-resistant iron-based metal article without impairing the corrosion resistance of the article.

〔Example〕

Hereinafter, the method of the present invention will be specifically described while comparing the embodiment with the embodiment of the conventional method. The articles to be individually subjected to the heat treatment of the present invention and the conventional heat treatment in order to perform the comparison include articles made of a corrosion-resistant iron-based metal manufactured in the following manner, specifically,
The retaining fitting (7) shown in the figure was selected.

First, a material having the chemical composition shown in Table 1 (equivalent to ductile cast iron FCD45) is melted and cast into a shape suitable for the metal fittings while performing an appropriate treatment for spheroidizing graphite as-cast. Thus, an article (a stopper metal fitting) before forming an oxide film was obtained.

Then, the article is heated in an oxidizing atmosphere at 700 to 950 ° C. for 1 to 2 hours, and an oxide film having a thickness of 0.02 to 0.04 mm is formed on the surface thereof, thereby giving an article having corrosion resistance (prevention metal fitting). I got As a result of analyzing the oxide film, 4.0 to
5.5% by weight of Si was observed, and 30
It was confirmed that Fe ₂ SiO ₄ was mainly used in the thickness of about 40%.

Next, the heat treatment of the present invention and the conventional heat treatment shown in the following bullet points were individually applied to the articles (retainer fittings) manufactured as described above. In addition, a plurality of articles were examined in consideration of the occurrence of variations in quality after heat treatment.

(I) After the heat treatment the article of the present invention were heated to austenitizing temperatures T ₁ as shown by a dashed line in FIG. 1, a higher appropriate temperatures than M _S point T ₂
In a bath maintained at a constant temperature (specifically, in a salt bath), the structure was subjected to a constant temperature transformation (specifically, bainite transformation).

(Ii) After heating the conventional heat treatment the article to austenitizing temperatures T ₁ as shown by two-dot chain line in FIG. 1, and oil quenching by immersing the M _S point following oil bath Martensite the tissue I made it a site.

As a result of comparing the article subjected to the heat treatment of the present invention as described above with that of the conventional article, the oxide film on the article surface was peeled off by the conventional heat treatment, whereas the oxide film on the article surface was removed by the heat treatment of the present invention. No peeling of the film was observed.

Also, as a result of comparing the mechanical strengths, the Brinell hardness of the surface of the article shown in FIG. 2, the amount of deflection when the article was broken by the universal testing machine shown in FIG. 3, and the article by the Amsler testing machine shown in FIG. In all of the loads at the time of breaking, the present invention shows superior numerical values (black circles indicate the present invention, white circles indicate the conventional), and it was possible to confirm the excellent effects of the method of the present invention. .

In the above-described embodiment of the present invention, the heat treatment for obtaining the bainite structure by the isothermal transformation is performed. However, in the case where the mechanical strength of the article is slightly low, the temperature of the isothermal transformation ( In other words, an embodiment in which the temperature of the salt bath in which the article is immersed) is set slightly higher and the structure obtained by the isothermal transformation is made more solvitic can be considered.

Further, the heat treatment according to the present invention can be performed directly from the process of forming an oxide film on the surface of the article (heated to a predetermined temperature). In this case, the energy required for heating the article can be reduced. However, in this case, there is a limitation that the quality of the oxide film formed on the surface of the article treated under the conditions must satisfy desired conditions.

Further, the article on which the method of the present invention can be carried out is, of course, not limited to one made of ductile cast iron as in the above-described embodiment, and contains Si in an amount of 0.5% by weight or more, and contains iron as a main component. What is necessary is just to consist of ferrous metals.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing the heat treatment conditions of the present invention and the conventional heat treatment conditions. FIGS. 2 to 4 show the comparison of the mechanical strength between the heat-treated article of the present invention and the conventional heat-treated article. FIG. 5 is a sectional view showing an example of the article to be subjected to the heat treatment of the present invention.

Claims (1)

(57) [Claims] (1) Corrosion resistance is imparted by forming an oxide film containing Fe ₂ SiO ₄ on the surface of an iron-based metal article containing Si in an amount of 0.5% by weight or more and iron as a main component. In a heat treatment method for a corrosion-resistant iron-based metal article that performs a heat treatment for improving mechanical strength on the corrosion-resistant iron-based metal article,
After the tissue was austenitized by heating the corrosion-resistant iron-based metal article, quickly the article, possible to isothermal transformation the tissue was immersed in a constant temperature retained bath to a temperature higher than M _S point A heat treatment method for a corrosion-resistant iron-based metal article.