JPH01205058A - Graphite cast steel - Google Patents

Abstract

PURPOSE:To manufacture a graphite cast steel excellent in machinability and mechanical properties in an as-cast state by adding and incorporating specific amounts of rare earth elements to a low-alloy cast steel. CONSTITUTION:This cast steel has a composition containing, by weight, 0.45-2.0% C, 1.0-3.2% Si, 0.01-1.0% rare earth elements, either or both of 0.005-0.400% Ca and 0.005-0.400% Mg, and further one or >=2 kinds among 0.3-2.0% Mn, 0.1-1.0% Cr, 0.01-1.0% Mo, 0.01-0.5% W, 0.01-0.5% V, 0.01-0.5% Nb, and 0.015-0.5% Ti. Since, in this cast steel, contained carbon is precipitated in the form of fine and uniform spheroidal graphite by the increase in Si content and also by the addition of Ca and Mg and superior strength of cast steel is provided by the addition of carbide-forming elements such as Mn and Cr, the cast steel excellent in machinability and mechanical properties in an as-cast state can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to graphite cast steel, and in particular to improvement of the properties of graphite cast steel, which has excellent machinability and mechanical properties as cast.

(Background technology) Conventionally, in order to facilitate plastic working, cutting, etc.
Graphite steel or graphite cast steel in which spheroidal graphite is precipitated inside the cast steel is known. By the way, in order to precipitate such graphite in cast steel, graphite steel can be subjected to graphitization heat treatment, but if you try to precipitate graphite by the same heat treatment in cast steel, the heat treatment takes a long time. Moreover, since the precipitated graphite is coarse and does not have a spherical shape, it is said that it is difficult to achieve the intended purpose by heat treatment. Of course, if cast steel is inoculated with magnesium, calcium, etc. during melting, spheroidal graphite can be generated in the casting as it is, but the distribution of spheroidal graphite is not uniform, and moreover, the precipitated graphite particles Due to the large diameter, the product properties such as machinability were not fully satisfactory.

For this reason, the inventors of the present invention previously applied for patent application No. 61-2482.
No. 84, we proposed an improvement measure to inoculate rare earth elements during melting, and this resulted in fine spheroidal graphite being uniformly precipitated and distributed in the casting, which has excellent machinability and mechanical properties. It became possible to obtain cast steel.

However, as a result of further research by the present inventors, it has been found that free-cutting graphite cast steel, which has superior properties compared to conventional graphite cast steel, is made by adding carbide-forming elements such as manganese and chromium. It has become clear that when attempting to improve its strength, a problem arises in that the precipitated graphite becomes coarse and non-uniform.

(Problem to be solved) Here, the present invention has been made against the background of the above-mentioned circumstances, and the problem to be solved is to impair the excellent properties of the free-cutting graphite cast steel proposed earlier. In other words, the aim is to allow fine and uniform spheroidal graphite to precipitate as it is cast, and to improve the strength of such cast steel.

(Solution Means) In order to solve such problems, the present invention has the following advantages:
J standard, 0.45-2.0% carbon (C), 1.0-2.0%
Contains 3.2% silicon (S i ), 0.01-1.0% rare earth elements (REM), and 0.005-0.4
00% Calcium (Ca) and 0.005-0.40
Contains one or two types of magnesium (Mg) at 0%, and also exceeds 0.3% and 2.0% or less of manganese (Mn), and exceeds 0.1% and 1.0% or less. Chromium (Cr), more than 0.01% and less than 1.0% Molybdenum (Mo), more than 0.01% and less than 0.5% Tungsten (W), more than 0.01% and 0 .5% or less of vanadium (V), more than 0.01% and less than 0.5% niobium (Nb), and more than 0.015% and 0.5%
Containing one or more of the following titanium (Ti), the remainder consisting of iron (Fe) and inevitable impurities,
The gist is graphite cast steel with excellent machinability and mechanical properties.

In this way, in the present invention, in order to precipitate extremely fine and uniform spheroidal graphite as cast, REM
On the other hand, M is added to improve the strength.
The coarsening and non-uniformity of precipitated graphite caused by carbide-forming elements such as n and Cr are prevented by adding Ca and Mg. That is, in graphite cast steel,
The finer and more uniform the precipitated graphite, the better the ductility and machinability when compared at the same tensile strength.Therefore, in the present invention, the carbide-forming element and Ca.

By adding Mg, it was possible to produce graphite cast steel with higher strength, as well as excellent ductility and machinability.

By the way, the action of each alloy component of the free-cutting graphite cast steel according to the present invention and the reason for limiting the content thereof are as follows. Note that all percentages shown below are based on weight.

C: 0.45-2.0% This element is essential for graphite formation in cast steel,
If the content is less than the lower limit (0.45%), the amount of spheroidal graphite precipitated is small, and the machinability improvement effect of graphite is not sufficient. Moreover, if it exceeds the upper limit (2.0%), reticulated graphite will precipitate and the mechanical properties will deteriorate, which is not preferable.

Si:1. O~3.2% St promotes the precipitation of graphite. When the content is less than 1.0%, the effect is small and the amount of graphite precipitated is small. On the other hand, if the content exceeds 3.2%, the hardness of the cast steel increases,
This causes the problem that ductility is significantly reduced.

REM: 0.01-1.0% REV ranges from La with atomic number 57 to 71 with atomic number
REM refers to elements up to Lu, and one or more of these REMs are used, and such REM is an element that promotes the precipitation of graphite. The effect is recognized from a content as low as about 0.01%, and is sufficiently enhanced in a range of 0.1 to 1.0%.

However, if the content exceeds 1.0%, the casting may have large sink marks and cracks may occur.

Ca: 0.005-0.400% MH: 0.005-0. /100% These elements have the effect of preventing the coarsening and non-uniformity of precipitated graphite, which is caused when a carbide-forming element described below is added. In order to achieve its full effect, it is necessary to add at least 0.005% or more of each of these elements, but do not add more than the upper limit of 0.400%. too,
The effect becomes saturated, and it becomes difficult to expect further miniaturization effects.

Mn: More than 0.3%, 2.0% or less Cr: More than 0.1%, 1.0% or less Mo: More than 0.01%, 1.0% or less W: More than 0.01%, 0.5 % or less v: O, ot% or less, 0.5% or less Nb: More than 0.01%, 0.5% or less Ti: More than 0.015%, 0.5% or less All of these elements are carbide forming elements By adding at least one of these elements, carbides are formed in the cast steel to improve mechanical properties, especially strength, but if the addition does not meet the lower limit of each of these elements, The effect of its addition cannot be fully demonstrated.

Moreover, if these elements are contained in excess of their respective upper limit values, problems such as significantly inhibiting the spheroidization of graphite and reducing toughness and ductility occur.

(Examples) Below, some examples of the present invention will be shown to clarify the present invention more specifically, but the present invention is not limited in any way by the description of such examples. Needless to say, it is not something that can be accepted.

In addition to the following examples and the above-mentioned specific description, the present invention includes various changes, modifications, and changes based on the knowledge of those skilled in the art, as long as they do not depart from the spirit of the present invention. It should be understood that improvements and the like may be made.

First, cast steel having a composition consisting of the alloy components shown in Table 1 below was melted in a 50 kg induction furnace, and as shown in Fig. 1 (a) and (
The casting shown in b) was sand-cast, and then the obtained casting was heat-treated at 770° C. for 2 hours, and then air-cooled. The resulting cast products were then subjected to a cutting test and a tensile test, as well as microscopic observation.

Note that Misoshu metal was used as REM.

Further, 1lhl to 13 are cast steels according to the present invention, and further A to D are comparative steels adjusted to have tensile strengths corresponding to the respective steels of the present invention.

By the way, the test method for tensile strength and elongation is shown in Figure 1 (a
) and (b), the broken line portion was taken out from each cast product as a JIS No. d tensile test piece, and each test was conducted. In addition, the test related to cutting efficiency was
A drill life test was conducted on the sound parts of the castings shown in Figures (a) and (b). More specifically, using a 5Kl (51, φ5 straight shank drill) as a tool, feed: 0.1 sm/rev, hole depth: 20 mm, the relationship between tool life and cutting speed for each casting was determined. , the cutting speed at which the tool life of comparative steel A is 1000 mm is 7.1.
(100), the ratio of the cutting speed at which the tool life of each cast product was 1000 u+ was defined as the cutting efficiency.

The obtained results are shown in Table 2 below along with the graphite average particle diameter.

Table 1 Table 2 As is clear from the comparison between Tables 1 and 2, Invention Steel 1 and Comparative Steel A were adjusted to have a tensile strength of 60 kgf/■■2 class. , another invention! II2, 3.
4 and comparison steel B have a tensile strength of 70 kg f /Tsuru 2 class, and inventive steel 5 and comparison @C have a tensile strength of 80 kg
f 712 class tensile strength, and also the invention steel 6~
Comparative steel No. 13 and comparative steel are each adjusted to have a tensile strength of 90 kg f/+u" class, but comparative steel No. 12
Compared to 1A, B, C, and D, in invention steels 1 to 13, the average grain size of precipitated graphite becomes significantly smaller due to the addition effect of Ca and Mg, and the elongation and cutting efficiency are significantly improved. It is being done.

(Effects of the Invention) As is clear from the above description, the graphite cast steel according to the present invention has the strength of free-cutting graphite cast steel in which fine and uniform spheroidal graphite is precipitated as cast due to the effect of rare earth elements.
While adjusting the amount of carbide forming elements such as Mn and Cr,
The addition of Ca and/or Mg improves the precipitation state of graphite (a < grain size 1 distribution) and improves its ductility and machinability. In other words, it improves machinability and mechanical properties. It was possible to effectively increase the strength characteristics while improving the
Therein lies the particularly remarkable technical significance of the present invention.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) respectively show a front view and a side view of a sand-cast casting in an example.

Claims (1)

[Claims] By weight, 0.45-2.0% carbon, 1.0-3
．． Contains 2% silicon, 0.01-1.0% rare earth elements, and 0.005-0.400% calcium and 0.
．． Contains one or two types of magnesium in an amount of 0.005 to 0.400%, and further exceeds 0.3% and contains 2.0%
% or less manganese, more than 0.1% but less than 1.0% chromium, more than 0.01% but less than 1.0% molybdenum,
More than 0.01% and less than 0.5% tungsten, 0.01% and less than 0.5% tungsten.
Vanadium exceeding 0.01% and not exceeding 0.5%, 0.01%
A workpiece containing one or more of the following: more than 0.5% of niobium, and more than 0.015% of titanium, the balance consisting of iron and unavoidable impurities. Graphite cast steel with excellent strength and mechanical properties.