JP2009155728A - Wear resistant cast iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide wear resistant cast iron which satisfies a balance between costs and various properties while maintaining excellent hardenability by controlling Mo content and incorporating at least one element among W, Nb and Ti in a well-balanced manner. <P>SOLUTION: This cast iron has a chemical composition which is composed of, by mass, 2.5 to 3.7% C, 0.2 to 1.0% Si, 0.4 to 0.8% Mn, 0.13 to 5.0% Ni, 10.0 to 23.0% Cr, 0.5 to 4.0% Mo, 0 to 3.9% W, 0 to 2.1% Nb, 0 to 1.0% Ti, 0 to 0.7% V and the balance Fe with inevitable impurities and in which, when P is represented by equation P=1.72[Mo%]+0.51[W%]+0.23[Nb%]+5.29[Ti%]+12.2[C%]-0.59[Cr%]+2.23[Ni%], P≥32 is satisfied. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention suppresses the Mo content and balances cost and performance while maintaining good hardenability by containing C, Si, Mn, Ni, Cr, W, Nb, and Ti in a balanced manner. The present invention relates to compatible wear-resistant cast iron.

In equipment such as roller tires, pulverized coal machines such as table segments, crushed stone machines, mining machines, power-related equipment, construction machines, and industrial machines, the wear of members is significant due to contact with raw materials and materials handled, etc. In addition to the physical strength, wear resistance is an important condition. In this type of application, wear-resistant cast iron in which a large amount of carbide is dispersed is known as a general-purpose material that is resistant to scratch wear and erosion.
As a general strengthening method of cast iron, surface treatment techniques such as carburizing and nitriding are widely known, but as a large wear-resistant cast iron without surface treatment, a composition type cast iron with a large amount of Mo added is known. In the cast iron of the composition system to which a large amount of is added, the high hardness of the cast iron is maintained by utilizing the precipitation mechanism of M7C3 carbide.

  As a conventional example of this type of wear-resistant cast iron, the chemical composition is C: 2.7 to 3.5 wt%, Cr: 16 to 22 wt%, Mo: 6 to 12 wt%, Si: 0.4 to 0.00. A wear-resistant cast iron comprising 8 wt%, Mn: 0.4 to 1.0 wt%, Ni: 0.5 to 1.2 wt%, V: 0.2 to 3.5 wt%, the balance being Fe and inevitable impurities Are known. (See Patent Document 1)

  As one conventional example of other wear-resistant cast iron, the chemical component is C2.7 to 3.5% by weight, Si 0.2 to 1.0%, Mn 0.5 to 1.5%, Cr 27 to 34%, Mo 0.5-2.0%, W 0.5-2.0%, B 0.1% or less, obtained by quenching and tempering high chromium cast iron with the balance being substantially Fe and inevitable impurities Also known are wear-resistant alloy cast irons. (See Patent Document 2)

Further, as another example of the wear-resistant cast iron, the high Cr cast iron containing C, Cr and Mo contains Nb: 2 to 5% by mass and satisfies the following formula (1). A feature of wear-resistant high Cr cast iron is known.
7.5 ≦ [Nb] / ([C] −2.8) ≦ 9 (1)
However, [Nb] and [C] indicate the contents (% by mass) of Nb and C, respectively. (See Patent Document 3)
Japanese Patent Laid-Open No. 11-199963 Japanese Patent Laid-Open No. 3-150334 Japanese Patent Laid-Open No. 11-229070

In each of the wear-resistant cast irons disclosed in the above-mentioned patent publications and other known wear-resistant cast irons, M7C3 carbide having a high hardness at the quenching temperature is precipitated in the austenite matrix. The wear resistance is enhanced by adopting a structure in which M7C3 carbide is finely dispersed in the structure at the tempering temperature.
This M7C3 carbide is known as one of the types of carbides deposited on steel materials, has a hardness (Hv): 1800-2800, and can be expressed as (Cr, Fe) 7C3, and is a high Cr steel material It is easily used for strengthening wear-resistant cast iron because it is likely to precipitate in the steel, hardly dissolves in the substrate even when heated to the quenching temperature, and remains in the structure.
However, Mo is an important additive element in producing high-hardness wear-resistant cast iron. Currently, Mo relies on imports from regions such as North America, Latin America, and China. In recent years, the price of molybdenum has begun to rise due to tight demand on a global scale. For this reason, the present inventor conducted research on an additive element in place of Mo as an additive element necessary for wear-resistant cast iron, and obtained a good result this time, thus reaching the present invention.

  In order to solve the above-mentioned problems, the present invention reduces the Mo content and maintains good hardenability by containing C, Si, Mn, Ni, Cr, W, Nb, and Ti in a balanced manner. The object is to provide wear-resistant cast iron that balances cost and performance.

  In order to achieve the above object, the present inventor, as an alternative element of Mo, among the group elements in the vicinity of Mo that is Group 6A of the periodic table, Ti, V, Cr, Zr, Nb, Ta, Hf, Focusing on W, research and development were conducted. Among these elements, Hf was a rare element and was excluded from the study because it was extremely expensive.

Next, when Zr is added to cast iron, it becomes very easy to oxidize. When melting the alloy, it is wasted as it is wasted, so it is excluded from the research object, and when Ta is added, the base tends to become a ferrite structure and softens. It was excluded from the study because it was easy to do.
Among the remaining elements, the analysis of Ti, V, Cr, Nb, and W and the correlation with other elements such as Si, Mn, and Ni as elements contained in cast iron are obtained according to the content of each element. As a result of various test studies on what characteristics cast iron has, the present invention has been achieved.

(1) The wear-resistant cast iron of the present invention is in mass% as a chemical composition, C: 2.5-3.7%, Si: 0.2-1.0%, Mn: 0.4-0.8 %, Ni: 0.13-5.0%, Cr: 10.0-23.0%, Mo: 0.5-4.0%, W: 0-3.9%, Nb: 0-2. 1%, Ti: 0 to 1.0%, V: 0 to 0.7%, the balance being Fe and inevitable impurities, and when P is represented by the following formula, P = 1.72 [Mo% ] +0.51 [W%] + 0.23 [Nb%] + 5.29 [Ti%] + 12.2 [C%] − 0.59 [Cr%] + 2.23 [Ni%], satisfying P ≧ 32. It has a composition.
(2) The wear-resistant cast iron of the present invention is in mass% as a chemical composition, C: 2.5 to 3.7%, Si: 0.2 to 1.0%, Mn: 0.4 to 0.8 %, Ni: 0.13-5.0%, Cr: 10.0-23.0%, Mo: 0.5-4.0%, W: 0-3.9%, Nb: 0-2. 1%, Ti: 0 to 1.0%, V: 0 to 0.7%, the balance being Fe and inevitable impurities, and when P is represented by the following formula, P * = 1.72 [Mo %] + 0.51 [W%] + 0.23 [Nb%] + 2.23 [V%] + 5.29 [Ti%] + 12.2 [C%] − 0.59 [Cr%] + 2.23 [Ni %],
It has the composition which satisfy | fills P> = 32.

(3) The wear-resistant cast iron of the present invention has the chemical composition of the wear-resistant cast iron described in (1) or (2), C: 2.88 to 3.7%, Si: 0.55 to 1. 0%, Mn: 0.6 to 0.8%, Ni: 0.13 to 5.0%, Cr: 10.0 to 22.56%, Mo: 0.5 to 3.94% Features.
(4) The wear-resistant cast iron of the present invention has a chemical composition of mass%, C: 2.88 to 3.22%, Si: 0.55 to 0.66%, Mn: 0.60 to 0.72. %, Ni: 0.13 to 1.55%, Cr: 16.51 to 22.56%, Mo: 0.50 to 3.94%, W: 0 to 3.86%, V: 0 to 0.0. 7%, Nb: 0 to 2.1%, Ti: 0 to 0.27%, and remaining Fe and inevitable impurities.

(5) The wear-resistant cast iron of the present invention has the chemical composition described in (3), C: 3.07 to 3.15%, Ni: 1.0 to 1.55%, Cr: 17.76 to 18.18%, Mo: 1.5 to 3.94%, W: 0 to 2.38%.
(6) The wear-resistant cast iron of the present invention is composed of any one of M7C3 carbide represented by (Cr, Fe) 7C3 and MoC, TiC, NbC in the metal structure described in (1) to (5). MC carbide and M23C6 carbide represented by (Cr, Fe) 23C6 are precipitated.
(7) In the wear-resistant cast iron of the present invention, the amount ratio of M7C3 carbide to M23C6 carbide in the metal structure described in (6) is M7C3 carbide (at%) ÷ M23C6 amount (at%) <3.4. It is characterized by becoming.
(8) In the wear-resistant cast iron of the present invention, the amount ratio of M7C3 carbide to M23C6 carbide in the metal structure described in (6) is M7C3 carbide (at%) ÷ M23C6 amount (at%) <2.5. It is characterized by becoming.
(9) The wear-resistant cast iron of the present invention has P = 1.72 [Mo%] + 0.51 [W%] + 0.23 [Nb] according to any one of (1) and (3) to (8). %] + 5.29 [Ti%] + 12.2 [C%] − 0.59 [Cr%] + 2.23 [Ni%], and has a composition satisfying P ≧ 33.7. .

According to the present invention, the content of Mo can be suppressed and made inexpensive, while maintaining good hardenability by making the content of C, Si, Mn, Ni, Cr, and Mo within an appropriate range. It is possible to provide a wear-resistant cast iron that balances various performances such as cost and high hardness.
Furthermore, in addition to the addition of these elements, even if at least one of W, Nb, Ti, and V is contained in a well-balanced manner, the balance between various performances such as cost and high hardness is further maintained while maintaining good hardenability. A wear-resistant cast iron that is compatible at a high level can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments described below.
The wear-resistant cast iron according to the present invention is in mass% as a chemical composition, C: 2.5 to 3.7%, Si: 0.2 to 1.0%, Mn: 0.4 to 0.8%, Ni: 0.13-5.0%, Cr: 10.0-23.0%, Mo: 0.5-4.0%, W: 0-3.9%, Nb: 0-2.1% Ti: 0 to 1.0%, V: 0 to 0.7%, and the balance is Fe and inevitable impurities.
Instead of the chemical composition, C: 2.88-3.7%, Si: 0.55-1.0%, Mn: 0.6-0.8%, Ni: 0.13- It may be 5.0%, Cr: 10.0 to 22.56%, Mo: 0.5 to 3.94%.

Further, the wear-resistant cast iron of the present invention has a chemical composition of mass%, C: 2.88 to 3.22%, Si: 0.55 to 0.66%, Mn: 0.60 to 0.72%, Ni: 0.13 to 1.55%, Cr: 16.51 to 22.56%, Mo: 0.50 to 3.94%, W: 0 to 3.9%, V: 0 to 0.5% Nb: 0 to 2.1%, Ti: 0 to 0.27%, and may be characterized by being composed of the remaining Fe and inevitable impurities.
In the chemical composition described above, C: 3.07 to 3.15%, Ni: 1.0 to 1.55%, Cr: 17.76 to 18.18%, Mo: 1.5 to 3 0.94%, W: 0 to 2.38%.

Further, the wear-resistant cast iron of the present invention has one of the above-mentioned compositions, and when P is represented by the following formula, P = 1.72 [Mo%] + 0.51 [W%] + 0.23 [Nb%] + 5.29 [Ti%] + 12.2 [C%] − 0.59 [Cr%] + 2.23 [Ni%]
It is required to have a composition that satisfies P ≧ 32.
The value of P is more preferably 32.8 or more, and most preferably 33.7 or more.
In the wear-resistant cast iron according to the present invention, a wear-resistant cast iron exceeding HRC62.5 can be obtained by setting the P value to 32.8 or more, and HRC63.5 by setting the P value to 33.7 or more. It is possible to obtain a wear-resistant cast iron exceeding.
Next, the wear-resistant cast iron of the present invention has one of the above-mentioned compositions, and when P is represented by the following formula, P * = 1.72 [Mo%] + 0.51 [W%] + 0 .23 [Nb%] + 2.23 [V%] + 5.29 [Ti%] + 12.2 [C%] − 0.59 [Cr%] + 2.23 [Ni%]
It is required to have a composition that satisfies P ≧ 32.
The value of P is more preferably 32.8 or more, and most preferably 33.7 or more.

The reasons for limiting the components of the wear-resistant cast iron of the present invention will be described below. In the following description, the unit of each component is mass%.
C: 2.5-3.7%
C is one of the main constituent elements of carbide effective for wear resistance, and the amount of precipitate increases as the amount added increases. If the C content is less than 2.5%, the amount of precipitation is not sufficient. Conversely, if the C content is more than 3.7%, a large amount of coarse carbides and graphite are dispersed. This range was selected because it became brittle. Among them, the C content range is preferably 2.88 to 3.7%, 2.88 to 3.22%, and 3.07 to 3.15% in this order.

Si: 0.2-1.0%, Mn: 0.4-0.8%,
Si and Mn are elements necessary for deoxygenation in the melting of cast iron, and 0.2 to 1.0% is added for Si and 0.4 to 0.8% is added for Mn. Addition of a large amount leads to deterioration of wear resistance. Among these, the range of 0.55 to 1.0% and 0.55 to 0.66% in the Si content is a more preferable range in this order. Further, in the Mn content, 0.6 to 0.8% and 0.5 to 0.72% are more preferable ranges in this order.
Ni: 0.13-5.0%
Ni is an element added in a small amount in the base material in order to improve the hardenability, and it is desirable to add in such a range. Ni addition contributes to the production | generation of M23C6 carbide | carbonized_material, and contributes to the improvement of hardness. In the Ni content, 0.13 to 1.55% and 1.0 to 1.55% are more preferable ranges in this order.
Cr: 10.0-23.0%,
Cr is an inexpensive material element and is combined with Fe to form M23C6 carbide represented by (Cr, Fe) 23C6. Note that Cr also contributes to the formation of M7C3 carbide represented by (Cr, Fe) 7C3. However, since the present inventor believes that M7C3 carbide does not contribute to improving the hardness of cast iron, it is not desirable to contain more Cr than necessary.
In the Cr content, 10 to 22.56%, 16.51 to 22.56%, and 17.76 to 18.18% are more preferable ranges in this order.

Mo: 0.5-4.0%
Mo is added to the base material in order to improve hardenability, improve hardness, and improve wear resistance, and contributes to the formation of M23C6 carbide, but with a small Mo content It is difficult to obtain an effect, and if the content is large, the balance between cost and wear resistance is deteriorated (particularly, the cost is significantly increased).
Here, in order to improve the wear resistance, it is preferable to increase the addition amount of Mo. However, in the present invention, the addition amount of Mo is suppressed, and the wear resistance is compensated by adding an appropriate amount of other elements. It may be in the range of .5 to 4.0%. In the Mo content, 0.5 to 3.94% and 1.5 to 3.94% are more preferable ranges in this order.

W: 0 to 3.9%
W is useful as a substitute element for Mo, and can be added in the range of (3.9% or less) in consideration of the amount of (Mo + W). W contributes to the improvement of hardness and precipitates W6C as M6C carbide. If W is added, the range of 0 to 2.38%, that is, 2.38% or less is preferable.
Nb: 0 to 2.1%
Nb is useful as a substitute element for Mo, and can be added in a range of (2.1% or less) in consideration of the amount of (Mo + Nb). Nb has the effect of precipitating NbC carbide (MC carbide) and contributes to the improvement of wear resistance.
Ti: 0 to 1.0%
Ti is useful as a substitute element for Mo and can be added in the range of (1.0% or less) in consideration of the amount of (Mo + Ti). Ti greatly contributes to the improvement of hardness and has an effect of generating TiC. The range of 0 to 0.27% is preferable as the range of Ti.
V: 0 to 0.7%
V has the effect of precipitating VC (MC type carbide), and even if added in a small amount, it has an effect of improving wear resistance. In the V content, a range of 0 to 0.5%, that is, a content of 0.5% or less is more preferable. V is also an element effective for temper softening resistance and secondary hardening.

Further, the wear-resistant cast iron according to the present invention has the above-described chemical composition, and in the metal structure, consists of M7C3 carbide represented by (Cr, Fe) 7C3 and MoC, TiC, NbC. It is preferable that MC carbide and M23C6 carbide represented by (Cr, Fe) 23C6 are precipitated.
Further, the amount ratio of M7C3 carbide to M23C6 carbide in the metal structure is preferably M7C3 carbide (at%) ÷ M23C6 amount (at%) <3.4, and M7C3 carbide (at%) ÷ M23C6 amount. More preferably, (at%) <2.5.

  In the wear-resistant cast iron of the present invention, for example, M7C3 carbide is precipitated as flake carbide having a cross-sectional thickness of 10 μm to several tens of μm and a cross-sectional length of several tens to several hundreds of μm, and MC carbide is about 2 to 10 μm in cross section. The M23C6 carbide is precipitated as a granular carbide of about 3 μm or less, and presents a metal structure in which these carbides are mixed and precipitated in the parent phase mainly composed of the austenite phase. Usually, the M7C3 carbide is dispersed in the mother phase mainly composed of the austenite phase, the MC carbide is precipitated so as to be unevenly distributed between them, and the metal structure is formed in which the M23C6 carbide is dispersed and precipitated in the mother phase.

  In order to manufacture the wear-resistant cast iron of the present invention, as an example, the materials are mixed so as to have the composition ratio, cast into a melting furnace, and the cast sample is allowed to cool. Next, the sample is quenched. When the temperature is raised from room temperature during quenching, the matrix changes from ferrite (bcc: αFe) to austenite (fcc: γFe) from around 500 ° C. Further, when the temperature is raised, it is heated at a temperature in the range of about 1000 ° C. to 1100 ° C., for example, 1070 ° C. for several tens of minutes to several hours (6 hours), and then quenching is performed for rapid cooling. The condition is that the quenching temperature is higher than the M23C6 disappearance temperature and lower than the phase transition temperature to the liquid phase. Next, each sample can be manufactured by heating to a temperature of 450 ° C. to 550 ° C., for example, 500 ° C. for about several tens of minutes to several hours (4 hours), followed by tempering in a furnace.

By the manufacturing method described above, it is possible to obtain wear-resistant cast iron having a target structure in which each carbide is dispersed and precipitated in a metal structure mainly composed of an austenite phase as described above.
For example, M7C3 carbide having a high hardness is precipitated by a quenching treatment under the above conditions in a mother phase mainly composed of an austenite phase, and M7C3 carbide is precipitated as finely as possible by a tempering treatment under the above conditions.
The wear-resistant cast iron obtained as described above can be obtained at a lower cost than conventional products containing a large amount of Mo, and can have high hardness and good wear resistance.

By the way, the inventor believes that in the wear-resistant cast iron of the present invention, the hardness is improved with the decrease of M7C3 carbide, and the wear amount is increased with the increase of M7C3 carbide. This is opposite to the action of M7C3 carbide, which is generally considered to contribute to wear resistance. In this wear-resistant cast iron, the phenomenon that M7C3 carbide becomes a foreign material on the cast iron surface and the surface is scraped off is dominant. It is estimated that the wear resistance is hindered. That is, since the M7C3 carbide is hard but brittle, the M7C3 carbide itself is not a parent phase in terms of wear resistance, and there is a possibility that the M7C3 carbide itself may be lost, so that it is preferable to disperse and precipitate as finely as possible.
In the wear-resistant cast iron of the present invention, the hardness of M23C6 carbide increases with the increase, and the wear amount increases with the decrease. In the wear-resistant cast iron according to the present invention, M23C6 carbide contributes to wear resistance. It can be estimated that this is because M23C6 carbide precipitates finely in the matrix and contributes to hardness and wear resistance.
In the wear-resistant cast iron of the present invention, the MC carbide is considered to increase in hardness and increase in wear amount with the increase. Moreover, it is thought that M6C carbide has the same tendency as M7C3 carbide.

Based on these findings, the present inventor ascertains the tendency of each carbide and further analyzes the content of each element in the examples described below. As a result, P = 1.72 [Mo%] + 0. 51 [W%] + 0.23 [Nb%] + 5.29 [Ti%] + 12.2 [C%] − 0.59 [Cr%] + 2.23 [Ni%] In the formula of P ≧ 32 It has been found that having a composition is important.
If the content of each element satisfying this equation is set, it is possible to provide a wear-resistant cast iron having a balance between wear resistance, hardness and cost.
In terms of cost conversion, C is extremely cheap, Cr is the standard unit price 1, and according to the relative price conversion of current metal prices, Ti is 8.7 times, Ni is 9.5 times, Nb is 11.6 times, and V is Since 17.6 times, W is 21 times, and Mo is 33.2 times, it is clear that the cost can be reduced by reducing the amount of Mo used and allocating it to other elements.

In addition, although the influence of V is not considered in said Formula, when the influence of V is also considered, it is preferable to set it as the following formula | equation.
That is, when P * is represented by the following equation, P * = 1.72 [Mo%] + 0.51 [W%] + 0.23 [Nb%] + 2.23 [V%] + 5.29 [Ti%] +12.2 [C%] − 0.59 [Cr%] + 2.23 [Ni%] and a relationship satisfying P ≧ 32 are preferable.
If the content of each element satisfying this equation is taken into account, it is possible to provide a wear-resistant cast iron with a balance between wear resistance, hardness and cost in consideration of the influence of V more accurately.

  Among the above conditions, in order to improve the hardenability, the carbon equivalent is preferably 1.8 or more, and the M7C3 amount at the tempering temperature is preferably 0.25% or more. The amount of M23C6 at the tempering temperature is desirably 0.15% or more. This is a carbide that dissolves in the matrix, and its hardness is lower than that of M7C3. However, since it dissolves in the matrix, it is considered that it is preferably precipitated.

Hereinafter, specific examples of the wear-resistant cast iron according to the present invention will be described.
In producing the wear-resistant cast iron according to the present invention, it was cast into a melting furnace so as to have the compositions shown in Sample No. 1 to No. 19 in Table 1, and the cast sample was allowed to cool for 8 hours to room temperature. The casting sample was manufactured under conditions simulating a large sand mold casting.
Next, a quenching treatment was performed in which the sample was allowed to cool after heating at about 1070 ° C. for 6 hours, and then each sample was subjected to a heat treatment in which the sample was heated to about 500 ° C. for 4 hours and then cooled in a furnace and tempered.
The obtained sample was polished, the structure was observed, and the tempering hardness was measured.
The measurement results of the composition ratio, P value, and hardness (HRC) of each sample obtained as a result are shown in Table 1 below.

From the results shown in Table 1, the chemical composition is in mass%, C: 2.88 to 3.22%, Si: 0.55 to 0.66%, Mn: 0.60 to 0.72%, Ni: 0 .13 to 1.55%, Cr: 16.51 to 22.56%, Mo: 0.50 to 3.94%, W: 0 to 3.86%, V: 0 to 0.7%, Nb: It is apparent that wear resistant cast iron in the range of 62.18 to 64.55 can be obtained in the Vickers hardness HRC by selecting the ranges of 0 to 2.1% and Ti: 0 to 0.27%. became.
In addition, as a chemical composition by mass%, C: 2.88 to 3.22%, Si: 0.55 to 0.66%, Mn: 0.60 to 0.72%, Ni: 1 to 1.55% , Cr: 16.51 to 22.56%, Mo: 1.50 to 3.94%, W: 0 to 2.38%, V: 0 to 0.7%, Nb: 0 to 2.1%, By selecting a range of Ti: 0 to 0.27%, it became clear that 62.5 or more wear-resistant cast iron can be obtained in the Vickers hardness HRC.

In the sample according to the present invention, it can be presumed that adopting the composition according to the present invention effectively worked in terms of achieving HRC61 in hardness even when cast using a sand-only mold. When deviating from the composition according to the present invention, it is not easy to achieve the previous hardness in a sand-only casting mold. In addition, since the hardness is high but easily brittle when quenched, there is a feature that the toughness can be increased although the hardness is somewhat reduced by tempering under the above-mentioned conditions.
Next, with respect to the samples shown in Table 1, multiple regression analysis was performed and the results of calculating the regression equation are shown in FIG.
From this multiple regression analysis result, P = 1.72 [Mo%] + 0.51 [W%] + 0.23 [Nb%] + 5.29 [Ti%] + 12.2 [C%] − 0.59 [Cr %] + 2.23 [Ni%], it was confirmed that the calculated value HRC (predicted HRC) was very close to the actually measured HRC. The multiple correlation R is R = 0.97, which is a numerical value very close to 1. Therefore, as shown in FIG. 1, the predicted hardness based on the previous regression equation and the measured hardness tend to substantially coincide with each other. The effectiveness of the equation shown can be confirmed.
Using the above equation, it has been found that the hardness can be predicted when changing the composition. Looking at this regression equation, it is C (12.2)> Ti (5.29)> Ni (2.23)> Mo (1.72)> W (5.1) that contributes to the hardness. ) Nb (0.23). Note that Cr is a negative value, and a smaller value is considered to be better in terms of hardness.

Next, the structure photograph (SEM photograph) of the sample No. 13 shown in Table 1 is shown in FIG. 2 (magnification 500 times, white spot scale 60 μm in the figure), FIG. 3 (magnification 1000 times, white spot scale 30 μm in the figure). ), FIG. 4 (5000 times magnification, white point scale 6 μm in the figure).
From the metallographic photographs shown in FIGS. 2 (A) to (C), M7C3 carbide precipitates relatively large, MC carbide precipitates with a size of about 10 μm, and M23C6 carbide has a particle size of 3 μm or less in the matrix. It turns out that it has precipitated. In addition, since M23C6 carbide | carbonized_material melt | dissolves in a mother phase easily by heat processing, it is thought that the particle | grains analyzed finely in a mother phase are M23C6 carbide | carbonized_material.

Next, FIG. 3 shows the EDX (energy dispersive X-ray) analysis result of MC carbide, FIG. 4 shows the EDX analysis result of M7C3 carbide, FIG. 5 shows the EDX analysis result of M23C6 carbide, and FIG. The results of EDX analysis of the phases are shown, and all clearly show the characteristics of each carbide and the parent phase. Although precipitation of carbides such as MoC and TiC is also conceivable, it can be estimated that the main component is NbC from the analysis result of MC carbide in this analysis sample.

  Next, in order to investigate the relationship between the amount of precipitated carbide and each characteristic, the results of calculating the amount of carbide that can be calculated from the tempering temperature using the thermodynamic calculation software (JMatPro Ver.4.1) are shown in Table 2 below.

The results shown in Table 2 are summarized and shown in comparison with FIGS. 7 (a) and 7 (b). FIG. 7A shows the calculated data of the carbide amount and the comparison data of the hardness HRC, and FIG. 7B shows the calculated data of the carbide amount and the comparison data of the wear amount. The amount of wear was determined by a rubber wheel test.
The test conditions were as follows: load: 10 kg, test time: 1 hour, rubber material: chlorobutyl rubber, rotation speed: 70 rpm, grinding powder: mullite ball 0.8 mm, drop speed: 300 g / min.

From the results shown in FIGS. 7 (a) and 7 (b), the hardness increases as the M7C3 carbide content decreases, but the wear amount tends to increase as the M7C3 carbide content increases. It can be presumed that this is because the M7C3 carbide precipitated coarsely as compared with the carbides of No. 1 tends to crack during the wear test. In addition, it seems that M23C6 carbide has an effect of improving both hardness and wear resistance by increasing. Thus, although M7C3 is hard and can improve abrasion resistance by being finely dispersed, it is considered that it has a feature of being brittle.
This is a novel finding contrary to the action of M7C3 carbide, which is generally considered to contribute to wear resistance. The inventor has found a relationship of M7C3 amount (at%) = − 2.6266 × [HRC] +197.97 and M23C6 amount (at%) = 2.8526 × [HRC] −168.25. From these, in order to obtain wear-resistant cast iron having a hardness HRC exceeding 62.5, the amount ratio of M7C3 carbide to M23C6 carbide should satisfy M7C3 amount (at%) ÷ M23C6 amount (at%) <3.4. I understand that. In order to obtain wear-resistant cast iron having a hardness HRC exceeding 63.5, the amount ratio of M7C3 carbide to M23C6 carbide should satisfy M7C3 amount (at%) ÷ M23C6 amount (at%) <2.5. Recognize.

FIG. 8 is a diagram showing the correlation between the P value of each sample and the hardness HRC for the samples No. 1 to 19 shown in Table 1 above.
From the results of FIG. 8, by setting the P value to 32.8 or higher, it is possible to obtain wear-resistant cast iron having a hardness HRC exceeding 62.5, and by setting the P value to 33.7 or higher, It can be seen that a wear-resistant cast iron exceeding 63.5 in HRC can be obtained.

  Further, from the results of FIG. 8, the hardness increases as the M7C3 carbide decreases, the wear amount tends to increase as the M7C3 carbide increases, the hardness increases as the M23C6 carbide increases, and the wear amount increases as the decrease increases. It has been found that there is a tendency, hardness increases with increasing MC carbide, wear amount also improves, and M6C carbide has the same tendency as M7C3 carbide.

Next, for the samples A to D having the respective compositions shown in Table 3 below, the calculated value HRC (predicted HRC) and the P value were obtained in the same manner as the sample shown in Table 2 above.
Further, in order to further examine a sample having a composition containing V, P = 1.72 [Mo%] + 0.51 [W%] + 0.23 [Nb%] + 5.29 [ Instead of the regression equation of Ti%] + 12.2 [C%] − 0.59 [Cr%] + 2.23 [Ni%], P * = 1.72 [Mo%] + 0.51 [W%] + 0 Predictive HRC using a regression equation of .23 [Nb%] + 2.23 [V%] + 5.29 [Ti%] + 12.2 [C%] − 0.59 [Cr%] + 2.23 [Ni%] * Values and P * values were determined.
The results are summarized in Table 3.

  From the results shown in Table 3, P = 1.72 [Mo%] + 0.51 [W%] + 0.23 [Nb%] + 5.29 [Ti%] + 12.2 [C%] − 0.59 [Cr%] + 2.23 [Ni%] regression equation and P = 1.72 [Mo%] + 0.51 [W%] + 0.23 [Nb%] + 2.23 [V%] + 5.29 [Ti %] + 12.2 [C%] − 0.59 [Cr%] + 2.23 [Ni%] in any of the regression equations, the predicted hardness and the measured hardness tend to almost coincide, in addition to the value of P, The effectiveness of the formula indicated by P * could also be confirmed.

FIG. 1 is a graph showing a result of performing multiple regression analysis on the test results of the wear-resistant cast iron sample according to the present invention and comparing the predicted hardness and the measured hardness in the result of calculating the regression equation. FIG. 2 shows a photograph of a part of the metal structure in a wear-resistant cast iron sample according to the present invention. FIG. 2 (A) is an SEM photograph magnified 500 times, and FIG. 2 (B) is magnified 1000 times. SEM photograph, FIG. 2 (C) is an SEM photograph magnified 500 times. FIG. 3 is a diagram showing an EDX analysis result of MC carbide in a wear-resistant cast iron sample according to the present invention. FIG. 4 is a diagram showing an EDX analysis result of M7C3 carbide in a wear-resistant cast iron sample according to the present invention. FIG. 5 is a diagram showing an EDX analysis result of M23C6 carbide in a wear-resistant cast iron sample according to the present invention. FIG. 6 is a view showing an EDX analysis result of a parent phase in a wear-resistant cast iron sample according to the present invention. FIG. 7 shows the relationship between the amount of carbide, the hardness, and the amount of wear in the wear-resistant cast iron sample according to the present invention, and FIG. 7A shows the relationship between the amount of carbide and the hardness (HRC). (B) is a diagram showing the relationship between the amount of carbide and the amount of wear. FIG. 8 is a diagram showing the relationship between P value and hardness in a wear-resistant cast iron sample according to the present invention.

Claims (9)

The chemical composition is mass%, C: 2.5-3.7%, Si: 0.2-1.0%, Mn: 0.4-0.8%, Ni: 0.13-5.0% Cr: 10.0-23.0%, Mo: 0.5-4.0%, W: 0-3.9%, Nb: 0-2.1%, Ti: 0-1.0%, V: 0 to 0.7%, the balance consisting of Fe and inevitable impurities, and when P is represented by the following formula:
P = 1.72 [Mo%] + 0.51 [W%] + 0.23 [Nb%] + 5.29 [Ti%] + 12.2 [C%] − 0.59 [Cr%] + 2.23 [Ni %],
A wear-resistant cast iron having a composition satisfying P ≧ 32. The chemical composition is mass%, C: 2.5-3.7%, Si: 0.2-1.0%, Mn: 0.4-0.8%, Ni: 0.13-5.0% Cr: 10.0-23.0%, Mo: 0.5-4.0%, W: 0-3.9%, Nb: 0-2.1%, Ti: 0-1.0%, V: 0 to 0.7%, the balance consisting of Fe and inevitable impurities, and when P is represented by the following formula:
P * = 1.72 [Mo%] + 0.51 [W%] + 0.23 [Nb%] + 2.23 [V%] + 5.29 [Ti%] + 12.2 [C%] − 0.59 [ Cr%] + 2.23 [Ni%],
A wear-resistant cast iron having a composition satisfying P ≧ 32.   In the chemical composition, C: 2.88 to 3.7%, Si: 0.55 to 1.0%, Mn: 0.6 to 0.8%, Ni: 0.13 to 5.0%, Cr The wear-resistant cast iron according to claim 1 or 2, wherein: 10.0 to 22.56%, Mo: 0.5 to 3.94%.   The chemical composition is mass%, C: 2.88 to 3.22%, Si: 0.55 to 0.66%, Mn: 0.60 to 0.72%, Ni: 0.13 to 1.55% , Cr: 16.51 to 22.56%, Mo: 0.50 to 3.94%, W: 0 to 3.86%, V: 0 to 0.7%, Nb: 0 to 2.1%, The wear-resistant cast iron according to claim 1 or 2, characterized by comprising Ti: 0 to 0.27%, and comprising balance Fe and inevitable impurities.   In the chemical composition, C: 3.07 to 3.15%, Ni: 1.0 to 1.55%, Cr: 17.76 to 18.18%, Mo: 1.5 to 3.94%, W The wear-resistant cast iron according to claim 4, wherein the wear-resistant cast iron is 0 to 2.38%.   M7C3 carbide represented by (Cr, Fe) 7C3, MC carbide composed of any of MoC, TiC, and NbC, and M23C6 carbide represented by (Cr, Fe) 23C6 in the metal structure. The wear-resistant cast iron according to any one of claims 1 to 5, wherein   7. The wear-resistant cast iron according to claim 6, wherein the amount ratio of M7C3 carbide to M23C6 carbide in the metal structure is M7C3 carbide (at%) ÷ M23C6 amount (at%) <3.4. .   7. The wear-resistant cast iron according to claim 6, wherein an amount ratio of M7C3 carbide to M23C6 carbide in the metal structure is M7C3 carbide (at%) ÷ M23C6 amount (at%) <2.5. .   P = 1.72 [Mo%] + 0.51 [W%] + 0.23 [Nb%] + 5.29 [Ti%] + 12.2 [C%] − 0.59 [Cr%] + 2.23 [ The wear-resistant cast iron according to any one of claims 1 and 3 to 8, which has a composition satisfying P ≧ 33.7 in the formula of “Ni%”.

Images