JP6313097B2 - Cast iron member and method for producing cast iron member - Google Patents

Description

  The technology of the present disclosure relates to a cast iron member and a method for manufacturing the cast iron member.

  Steel materials are roughly classified into three types, iron, carbon steel, cast iron, according to the carbon content in the steel material. Of these, cast iron is used as a material for engine cylinder blocks and cylinder liners in automobiles. Cast iron members such as cylinder blocks and cylinder liners wear as the piston ring slides. Such cast iron members are required to have low wear, that is, excellent wear resistance that is durability against sliding. Moreover, in recent years, a small engine with high output is sometimes mounted on a vehicle for the purpose of improving fuel efficiency, and a cast iron member excellent in wear resistance has been desired. Such a demand is not limited to a cylinder block or a cylinder liner, but is common to cast iron members used in parts where wear occurs. As a cast iron member with improved wear resistance, for example, a cast iron member described in Patent Document 1 can be cited.

JP 2012-188719 A

  The cast iron member described in Patent Document 1 has improved wear resistance by narrowing the lamellar interval, which is the precipitation interval between ferrite and cementite in pearlite, to a predetermined interval, and the lamellar interval is increased depending on the content of copper and tin. It has been adjusted. However, there remains room for improvement in increasing the wear resistance of cast iron members.

  The technique of this indication aims at providing the manufacturing method of the cast iron member excellent in abrasion resistance and corrosion resistance, and a cast iron member.

  The cast iron member that solves the above problems is 3.0 mass% to 3.7 mass% carbon, 1.5 mass% to 2.5 mass% silicon, 0.5 mass% to 1.0 mass%. The following manganese, 0.1 mass% or more and 0.5 mass% or less phosphorus, 0.12 mass% or less sulfur, greater than 1.0 mass% and 2.0 mass% or less copper, and 0.6 mass % Is a cast iron member containing 1.0% by mass or less chromium and the balance is composed of iron and inevitable impurities, and has a pearlite that is a layered structure of ferrite and cementite as a metal structure of the cast iron member The cementite precipitation interval in the pearlite is a lamella interval, and the ratio of the portion where the lamella interval is 0.7 μm or less to the area of the pearlite in the cast iron member is 70% or more.

The cast iron member may further contain at least one of 0.1% by mass to 1.0% by mass of molybdenum and 0.02% by mass to 0.11% by mass of boron.
In the cast iron member, the ratio of the portion where the lamella spacing is 0.5 μm or less to the area of the pearlite in the cast iron member is preferably 70% or more.

The cast iron member can be embodied as a member having a cylindrical shape.
The cast iron member can be embodied in a cylinder liner.
The cast iron member is preferably cast by a sand casting method.
The cast iron member is preferably cooled at a cooling rate of 2 to 10 ° C./sec between 1080 ° C. and 1140 ° C. in the sand casting method.

  According to each said structure, the abrasion resistance of a cast iron member and corrosion resistance increase.

It is a figure which shows an example of the image which image | photographed the metal structure of the cast iron member with the laser microscope with respect to one Example of the cast iron member in the technique of this indication. It is a figure which shows an example of the picked-up image of the metal structure of a comparative example. It is a graph which shows an example of the measurement result of a lamella space | interval, Comprising: It is a graph which shows the range of the measured lamella space | interval. It is a figure which shows the outline | summary of an abrasion test typically. It is a graph which shows an example of the result of an abrasion test. It is a scatter diagram which shows an example of the result of a hardness test. It is a graph which shows the result of a corrosion resistance test.

With reference to FIGS. 1-7, one Embodiment of the manufacturing method of the cast iron member and cast iron member in this indication is described.
The cast iron member is embodied in, for example, a cylinder block or a cylinder liner in an automobile. The cast iron member is composed of 3.0% by mass to 3.7% by mass of carbon, 1.5% by mass to 2.5% by mass of silicon, 0.5% by mass to 1.0% by mass of manganese, 0% .1% by mass or more and 0.5% by mass or less of phosphorus, 0.12% by mass or less of sulfur, 1.0% by mass to 2.0% by mass of copper, and 0.6% by mass or more. This is a cast iron member containing 0% by mass or less of chromium and the balance being composed of iron and inevitable impurities.

The cast iron member preferably contains at least one of molybdenum of 0.1% by mass to 1.0% by mass and boron of 0.02% by mass to 0.11% by mass.
Copper contained in the cast iron member enhances the tensile strength, impact resistance, and wear resistance of the cast iron member within the above-mentioned content range. Chromium contained in the cast iron member increases the stability of cementite and increases the tensile strength, heat resistance, corrosion resistance, and wear resistance within the above-mentioned content range. Boron contained in the cast iron member enhances corrosion resistance and wear resistance within the above-mentioned content range. Molybdenum contained in the cast iron member increases the tensile strength by strengthening the base within the above-mentioned content range.

  The metal structure of the cast iron member has pearlite which is a layered structure of ferrite and cementite. The portion where the lamellar interval, which is the cementite precipitation interval, in the pearlite of the cast iron member is 0.7 μm or less is a narrow portion.

The ratio of the narrow portion to the pearlite area in the cast iron member is 70% or more. In the narrow portion, the lamella interval is preferably 0.5 μm or less.
The ratio of the narrow part to the pearlite area in the cast iron member means not the ratio of the narrow part to the entire area of the cast iron member but the ratio of the narrow part in the pearlite. However, when all of the pearlite is a narrow width portion, it becomes 100%.

  The above ratio is obtained by taking an image of an arbitrary 10 locations of a cast iron member at a magnification of 2000 times using a laser microscope with a range of 65 μm × 50 μm as a measurement visual field, and narrowing the average value of the area of pearlite obtained by analysis of the captured images It is a value calculated based on the average value of the area of the width portion.

The cast iron member described above is preferably cast by a sand mold casting method. An example of the manufacturing method of the cast iron member by the sand mold casting method will be described.
First, an alloy calculated from the target chemical composition is weighed using the pig iron for casting, steel scrap, and return material as the main raw materials, and put into a cupola melting furnace together with coal coke. Then, the molten metal is poured into a molten metal holding furnace at 1520 ° C. to 1600 ° C. and then poured into a ladle container. At that time, as an inoculation treatment, 0.3 mass% of ferrosilicon alloy with respect to the tapping weight is added. The inoculated molten metal is transported in a pan, poured into a sand mold at 1350 ° C. to 1450 ° C., and naturally cooled in the mold. In the cooling step, the cooling rate between 1080 ° C and 1140 ° C is preferably 2 to 10 ° C / sec.

  3.0 mass% to 3.7 mass% carbon, 1.5 mass% to 2.5 mass% silicon, 0.5 mass% to 1.0 mass% manganese, 0.1 mass% More than 0.5% by mass of phosphorus, 0.12% by mass or less of sulfur, based on containing these, by changing the content of copper and chromium, a plurality of different chemical compositions in the manufacturing method described above A cylinder liner was obtained as the cast iron member of the example. Moreover, the several cylinder liner from which the chemical composition of copper and chromium differs from an Example with the manufacturing method mentioned above was obtained as a cast iron member of a comparative example. In addition to the above, a cylinder liner containing at least one of molybdenum and boron was obtained as the cast iron member of the example. In addition to the above, a cylinder liner containing both molybdenum and boron was obtained as a cast iron member of a comparative example.

  Next, the chemical composition of the cast iron member was quantitatively analyzed for each of the cast iron members of the plurality of examples and the cast iron members of the plurality of comparative examples. Further, for each of the cast iron members of the plurality of examples and the cast iron members of the plurality of comparative examples, the metallographic structure was imaged at a magnification of 2000 using a laser microscope, and the lamella interval was measured.

(Quantitative analysis results)
In each of the cast iron members of the plurality of examples, in addition to iron and inevitable impurities, carbon of 3.0% by mass to 3.7% by mass, silicon of 1.5% by mass to 2.5% by mass, 5% by mass or more and 1.0% by mass or less of manganese, 0.1% by mass or more and 0.5% by mass or less of phosphorus, 0.12% by mass or less of sulfur, 1.0% by mass or more and 2.0% by mass or less Of copper, and was found to contain greater than 0.6 wt% and less than 1.0 wt% chromium. On the other hand, in each of the cast iron members of the comparative examples, it was recognized that at least one of the copper content and the chromium content was different from the content range of the cast iron members of the above examples.

Table 1 shows the results of quantitative analysis in Examples and Comparative Examples. Table 1 shows the chemical composition in mass%.

(Observation result of metal structure)
About the cast iron member of each Example and the cast iron member of each comparative example, the arbitrary 10 places which set the range of 65 micrometers x 50 micrometers as a measurement visual field were imaged by the magnification 2000 times using the laser microscope. FIG. 1 is an example of a captured image of the metal structure of the cast iron member of the example, and an example of the captured image of the example 4. FIG. 2 is an example of a captured image of the metal structure of the cast iron member of the comparative example, and an example of the captured image of the comparative example 4.

  As shown in FIGS. 1 and 2, the lamellar structure in which the black thin portion and the black dark portion are repeated is pearlite, the black thin portion is ferrite, and the black dark portion is cementite. When Example 4 and Comparative Example 4 were compared based on FIG. 1 and FIG. 2, it was confirmed that Example 4 had a narrower cementite precipitation interval and a pearlite structure was denser than Comparative Example 4. . Moreover, when observing the metal structure of Examples other than Example 4 and Comparative Examples other than Comparative Example 4, in each Example, the structure of pearlite is denser than any Comparative Example. Was confirmed.

(Measurement result of lamella spacing)
One of the indexes indicating the degree of compactness of the structure in pearlite is a lamellar interval λ which is a cementite precipitation interval in pearlite. In each of the cast iron members of the plurality of examples and the cast iron members of the plurality of comparative examples, the lamella interval λ was measured for a portion where the lamella interval λ was determined to be average in the captured image. As a part of the measurement results of the lamella interval λ, the measurement results of Example 4 and Comparative Example 4 are shown in Table 2, and the range of the lamella interval λ measured in Example 4 and Comparative Example 4 is shown in FIG.

  The measured value was obtained in the range of 0.7 μm or less for the lamella interval λ of Example 4, and the average value was 0.5 μm. On the other hand, as for the lamella interval λ of Comparative Example 4, a measured value was obtained in a range larger than 0.78 μm, and the average value was 1.0 μm. Regarding the lamella interval λ, it was confirmed that the minimum value of the comparative example was larger than the maximum value of the example, and the average value of the example was smaller than the average value of the comparative example.

  Further, in other examples other than Example 4, when the lamella interval λ was measured by the same measurement method, it was confirmed that the same measurement result as in Example 4 was obtained. Further, when the lamella interval λ was measured by the same measurement method for other comparative examples other than the comparative example 4, it was recognized that the same measurement result as that of the comparative example 4 was obtained.

  Images taken of the cast iron member of Example 4 and the cast iron member of Comparative Example 4 were analyzed. As a result, in the cast iron member of Example 4, the ratio of the pearlite to the surface area of the cast iron member is 80 to 90%, and the ratio of the narrow portion in which the lamella spacing is 0.7 μm or less in the pearlite. It was found to be 70% or more. On the other hand, in the cast iron member of Comparative Example 4, it was recognized that the ratio of the narrow portion having a lamellar spacing of 0.7 μm or less in pearlite was 10% or less.

  Moreover, also about other examples other than Example 4, it was recognized that the ratio for which the narrow part whose lamella space | interval is 0.7 micrometer or less in pearlite is 70% or more. Similarly, in Comparative Examples 1 and 2, it was recognized that the ratio of the narrow portion having a lamellar spacing of 0.7 μm or less in pearlite was 10% or less. Moreover, about the comparative example 3, it was recognized that the ratio for which the narrow width part whose lamella space | interval is 0.7 micrometer or less in pearlite is less than 70%.

  It should be noted that the relationship between the lamellar interval λ and the added amount of copper, and between the lamellar interval λ and the added amount of chromium, the larger the added amount, the smaller the lamellar interval λ is recognized in the above-mentioned range of added amounts. It was. Therefore, it is possible to derive the addition amount of copper and the addition amount of chromium so that a desired lamella interval λ can be obtained.

(Abrasion test)
In the wear test, a plurality of blocks having a rectangular parallelepiped shape of 15 mm × 35 mm × 160 mm are produced by changing the contents of copper and chromium based on the above-described manufacturing method and the chemical composition of carbon, silicon, manganese, phosphorus, and sulfur. Obtained as a cast iron member of the example. Moreover, the addition amount of copper and chromium was changed from the Example, and the block which has a rectangular parallelepiped shape of 15 mm x 35 mm x 160 mm was obtained as a cast iron member of a comparative example.

  As a result of quantitative analysis of the chemical composition of the blocks of the plurality of examples, the chemical composition in the same range as the cylinder liner of the above examples was found in the blocks of the examples. Moreover, as a result of measuring the lamella spacing of the blocks of the plurality of examples, the lamella spacing in the same range as the cylinder liner of the above examples was recognized.

  Similarly, as a result of quantitative analysis of the chemical composition of the block of the comparative example, the chemical composition similar to that of the cylinder liner of the comparative example 4 was recognized in the block of the comparative example. Moreover, as a result of measuring the lamella spacing of the block of the comparative example, a lamella spacing in the same range as the cylinder liner of the comparative example 4 was recognized.

A friction test was performed using the blocks of the above-described examples and the block of the comparative example. First, the outline of the wear test will be described with reference to FIG.
As shown in FIG. 4, in the wear test, the block of each example and the block of the comparative example are used as test pieces 11, and the mating material 12 for the test pieces 11 is PVD (physical vapor deposition) on a SUS304 material having a cylindrical shape. Method), a Cr-N-based thin film having a thickness of 30 μm was formed. Then, while pressing the bottom surface of the mating member 12 against the test piece 11 with a load of 14 kgf, the test piece 11 is reciprocated with respect to the mating material 12 at a frequency of 8.3 Hz, a stroke ± 50 mm, and a feed rate of 2.6 m / s. It was. And the frequency | count of the reciprocation required until the downward displacement amount of the other party material 12 which is the abrasion amount of the test piece 11 reaches | attains a predetermined value was obtained as evaluation value.

  As an example of the result of the wear test performed on each test piece 11, the result of the wear test performed on the test piece 11 having a chemical composition corresponding to Example 4 shown in Table 1 is shown in FIG. In FIG. 5, the evaluation value obtained from the block of the comparative example is 200,000 times, and the evaluation value of the block of the example when this evaluation value is 1.0 is shown.

  As shown in FIG. 5, it was confirmed that the block of the example was superior in wear resistance to the block of the comparative example, and the amount of wear was about 1/10 of that of the comparative example. In addition, the same abrasion resistance was recognized in each of the cast iron member of several Example.

(Hardness test)
The micro Vickers hardness test based on the Vickers hardness test specified in JISZ2244 was performed on the surface of each of the blocks of the above-described examples and the block of the comparative example. In this hardness test, the test load was set to 100 gf, and the impression by the testing machine was observed with an electron microscope. And the average value of the lamella space | interval in several cementite contained in an indentation was calculated | required, and the average value was made into the lamella space | interval (lambda) of the part in which the indentation was formed. As an example of the results of the hardness test, Table 3 and FIG. 6 show the results of the hardness test performed on the block of the example having the chemical composition corresponding to Example 4 shown in Table 1. In Table 3, the lamella interval λ is divided into a plurality of ranges, and the micro Vickers hardness MHV for each lamella interval λ is shown.

  As shown in Table 3 and FIG. 6, it was confirmed that the micro Vickers hardness MHV tends to increase as the lamella interval λ decreases. In particular, in the range where the lamella interval λ is 0.5 μm or less, the micro Vickers hardness MHV is particularly high compared to the range where the lamella interval λ is larger than 0.5 μm. The ratio of the increase in the micro Vickers hardness MHV with respect to the decrease in the lamella interval λ is greatly different between a range where the lamella interval λ is 0.5 μm or less and a range where the lamella interval λ is greater than 0.5 μm. Therefore, even if the pearlite structure is denser, the hardness is higher, and even if the lamella interval λ of the cast iron member varies, it is recognized that such an effect is particularly great in the range where the lamella interval λ is 0.5 μm or less. It was.

In addition, the following formula | equation (1) was obtained as an example of the regression equation which shows the relationship between micro Vickers hardness MHV and lamella space | interval (lambda) (micrometer).
MHV = −127 × ln (λ) +271.42 (1)
The regression curve represented by Equation (1) is a logarithmic function having a negative coefficient. Therefore, in the range where the lamella interval λ is smaller than 1 μm, the calculation result of the formula (1) increases exponentially as the lamella interval λ decreases. The lamella interval λ from which the desired micro Vickers hardness MHV can be obtained can be roughly grasped by the equation (1). In particular, if the lamella interval λ is 0.5 μm or less, the desired micro Vickers hardness MHV is obtained. Higher micro Vickers hardness MHV is obtained.

(Corrosion resistance test)
In the corrosion resistance test, each of the cylinder liners of Examples 1 to 9 shown in Table 1 was cut into blocks having a rectangular parallelepiped shape of 5 mm × 5 mm × 70 mm, and the cut blocks were obtained as cast iron members of Examples 1 to 9. It was. Further, each of the cylinder liners of Comparative Examples 1 to 4 shown in Table 1 was cut into blocks having a rectangular parallelepiped shape of 5 mm × 5 mm × 70 mm, and the cut blocks were obtained as cast iron members of Comparative Examples 1 to 4. .

An outline of the corrosion resistance test will be described. In the corrosion resistance test, each of the blocks of Examples 1 to 9 and each of the blocks of Comparative Examples 1 to 4 were used as test pieces and immersed in a corrosive solution under the following conditions.
・ Corrosive liquid: 2.5 mass% sulfuric acid ・ Liquid temperature: 70 ° C ± 0.5 ° C
・ Liquid volume: 2L
・ Immersion time: 25 minutes

  And the difference of the weight before immersion and the weight after immersion was computed as corrosion weight loss. FIG. 7 shows an example of the results of the corrosion resistance test. In addition, in FIG. 7, the ratio of the corrosion weight loss of each Example 1-9 and each Comparative Example 1-4 with respect to the corrosion weight loss in the block of the comparative example 1 is shown as a corrosion weight loss ratio.

  As shown in FIG. 7, the corrosion weight loss of the blocks of Examples 1 to 9 was found to be 30% or less less than the corrosion weight loss of Comparative Example 1. On the other hand, although the corrosion weight loss of the blocks of Comparative Examples 2 to 4 was smaller than the corrosion weight loss of Comparative Example 1, it was recognized that the reduction amount was less than 30% with respect to the corrosion weight loss of Comparative Example 1. .

  In addition, Examples 2, 3, 4, and 9 containing at least one of 0.1% by mass or more and 1.0% by mass or less of molybdenum and 0.02% by mass or more and 0.11% by mass or less of boron, It was found that there was less corrosion weight loss than Examples 1, 5, 6, 7, and 8 which did not contain boron and molybdenum.

Hereafter, it enumerates about the effect of the said embodiment.
(1) The wear resistance and corrosion resistance of the cast iron member are increased by setting the ratio of the narrow width portion in the pearlite, that is, the portion where the lamellar interval λ is 0.7 μm or less to 70% or more.

  (2) In the range where the lamellar interval λ is 0.5 μm or less, the micro Vickers hardness MHV is significantly higher than the other ranges. Therefore, by setting the lamella interval λ in the narrow width portion to 0.5 μm or less, the wear resistance and corrosion resistance of the cast iron member are enhanced.

(3) The wear resistance of the cast iron member is increased only by changing the addition amount of copper and chromium. As a result, an increase in cost for improving the wear resistance of the cast iron member can be suppressed.
(4) Corrosion resistance of the cast iron member by further including in the chemical composition at least one of 0.1% by mass to 1.0% by mass of molybdenum and 0.02% by mass to 0.11% by mass of boron. Will increase.

(5) When the lamellar interval λ in the narrow width portion is 0.5 μm or less, the wear resistance and corrosion resistance of the cast iron member are more reliably increased.
(6) Although the cooling rate is likely to increase in a high alloy cast iron member containing copper, chromium, or the like, the cooling rate is higher than that of other casting methods, for example, a mold centrifugal casting method, by producing the cast iron member by a sand casting method. Can slow down. As a result, chilling of the cast iron member is suppressed, and a cast iron member having a metal structure excellent in wear resistance and corrosion resistance can be obtained.

  (7) By setting the cooling rate between 1080 ° C. and 1140 ° C. to 2 to 10 ° C./sec, chilling of the cast iron member is more reliably suppressed, and the cast iron member has a metal structure with excellent wear resistance and corrosion resistance. Can be obtained.

  (8) Since the cylinder liner that is required to have a higher level of wear resistance and corrosion resistance is manufactured by the cast iron member described above, the reliability related to the durability of the cylinder liner is increased.

(9) The lamella interval λ for obtaining the desired micro Vickers hardness MHV can be estimated from the above equation (1).
In addition, the said embodiment can also be suitably changed and implemented as follows.
The cast iron member is not limited to a cylinder liner or cylinder block, but may be a crankshaft, an exhaust manifold, or a brake rotor.

  The cast iron member is not limited to the sand mold casting method, and may be manufactured by other casting methods such as a mold centrifugal casting method.

  11 ... test piece, 12 ... mating material.

Claims (6)

3.0 mass% to 3.7 mass% carbon, 1.5 mass% to 2.5 mass% silicon, 0.5 mass% to 1.0 mass% manganese, 0.1 mass% More than 0.5 mass% phosphorus, less than 0.12 mass% sulfur, more than 1.0 mass% and less than 2.0 mass% copper, and more than 0.6 mass% and less than 1.0 mass%. Is a cast iron member that contains chromium and the balance is composed of iron and inevitable impurities,
As the metal structure of the cast iron member, it has pearlite that is a layered structure of ferrite and cementite, and the precipitation interval of the cementite in the pearlite is a lamellar interval,
The ratio of the portion where the lamella interval is 0.7 μm or less to the area of the pearlite in the cast iron member is 70% or more. The cast iron member contains at least one of molybdenum of 0.1% by mass or more and 1.0% by mass or less and boron of 0.02% by mass or more and 0.11% by mass or less. Cast iron member. The cast iron member according to claim 1 or 2, wherein a ratio of a portion where the lamella interval is 0.5 µm or less to the area of the pearlite in the cast iron member is 70% or more.   The cast iron member according to claim 1, wherein the cast iron member has a cylindrical shape.   The cast iron member according to claim 4, wherein the cast iron member is a cylinder liner. A cast iron member manufacturing method for casting the cast iron member according to any one of claims 1 to 5 by a sand casting method ,
A cooling rate of 2 to 10 is between 1080 ° C and 1140 ° C in the step of cooling the molten metal in the sand mold.
A method for producing a cast iron member that is cooled at a temperature of ° C / sec.