CAST IRON, PARTICULARLY FOR DISC BRAKE COMPONENTS

Abstract

The invention consists of a gray cast iron comprising carbon, silicon, vanadium, manganese, nickel, chromium, molybdenum, copper, sulfur, phosphorus, tin, and titanium, wherein: the weight percentage of carbon is 3.70 to 3.90%; the weight percentage of silicon is 1.30 to 2.10%; the weight percentage of vanadium is 0.10 to 0.15%; the weight percentage of manganese is 0.60 to 0.90%; the weight percentage of nickel is 0.05 to 0.50%; the weight percentage of chromium is 0.20 to 0.35%; the weight percentage of molybdenum is not more than 0.10%; the weight percentage of copper is not more than 0.35%; the weight percentage of sulfur is less than 0.10%; and the weight percentage of phosphorus is less than 0.10%. The weight percentage of tin is less than 0.10%; the weight percentage of titanium is no more than 0.01%; where the remainder by weight is iron.

Description

CAST IRON, PARTICULARLY FOR DISC BRAKE COMPONENTS FIELD OF INVENTION The present invention relates to cast iron, in particular for making a brake disc, and to a brake disc for a disc brake made from said cast iron. BACKGROUND OF THE INVENTION As is well known, brake discs made of gray cast iron are subject to wear on the braking surfaces over time. Inevitably, this affects the lifespan of the discs. Therefore, the need to manufacture brake discs made of cast iron, which have high wear resistance, is very noticeable in the automotive field and, in particular, for high-performance vehicles. Thus, increased wear resistance results in a reduction of metal dust released into the environment. However, the increased wear resistance of discs made of gray cast iron must be achieved while taking into account the high-intensity mechanical and thermal stresses to which the brake discs are subjected. These stresses result in high temperatures in the braking surfaces, which can lead to decreased braking performance and even cracking of the braking surface. This need also exists for iron brake discs to have high corrosion resistance to increase their lifespan. Therefore, increased wear resistance should not negatively impact corrosion resistance. In the art, there are no known cast iron solutions capable of simultaneously combining high wear resistance with high performance in terms of mechanical strength, thermal resistance, and corrosion resistance. BRIEF DESCRIPTION OF THE INVENTION The objective of the present invention is to provide a gray cast iron that overcomes the disadvantages listed with reference to the prior art. It overcomes such disadvantages with a gray cast iron in accordance with claim 1. Other forms of cast iron according to the invention are described in the following claims. Additional features and advantages of the present invention will become more apparent from the description of preferred, but not limiting, embodiments that follows. DETAILED DESCRIPTION OF THE INVENTION According to a general embodiment, the gray cast iron of the present invention comprises in the alloy: carbon, silicon, vanadium, manganese, nickel, chromium, molybdenum, copper, sulfur, phosphorus, tin, and titanium. These alloying elements are contained in cast iron with the following weight percentage intervals of the total weight of cast iron: - carbon content of 3.70 to 3.90% by weight, - silicon from 1.30 to 2.10% by weight, - vanadium from 0.10 to 0.15% by weight, - manganese from 0.60 to 0.90% by weight, - nickel from 0.05 to 0.50% by weight, - chromium from 0.20 to 0.35% by weight, - molybdenum not more than 0.10% by weight, - copper not more than 0.35% by weight, - sulfur less than 0.10% by weight, - phosphorus less than 0.10% by weight, - tin less than 0.10% by weight, - titanium no more than 0.01% by weight, where the remainder of the weight is iron. Preferably, and Preferably, and Preferably, and Preferably, and Preferably, and Preferably, and Preferably, and Preferably, and Ideally, the percentage by weight of carbon is 3.70 to 3.86%. The weight percentage of silicon is 1.40 to 2.08%. The percentage by weight of vanadium is 0.12 to 0.14%. The percentage by weight of manganese is 0.63 to 0.85%. The weight percentage of nickel is 0.06 to 0.47%. The weight percentage of chromium is 0.21 to 0.35%. The percentage by weight of copper is 0.19 to 0.35%. The percentage by weight of tin is no more than 0.09%. The weight percentage of titanium is 0.0079 to 0.01%. According to a first preferred embodiment, gray cast iron has the following composition: - 3.86% carbon by weight; - 1.85% silicon by weight; - 0.12% by weight of vanadium; - 0.63% by weight of manganese; - 0.06% by weight of nickel; - 0.21% by weight of chromium; - 0.002% by weight of molybdenum; - 0.19% by weight of copper; - 0.065% by weight of sulfur; - 0.04% by weight of phosphorus; - 0.023% by weight of tin; - 0.0079% by weight of titanium; where the rest of the weight is iron. According to a second preferred embodiment, gray cast iron has the following composition: - 3.70% carbon by weight; - 2.08% silicon by weight; - 0.12% by weight of vanadium; - 0.658% by weight of manganese; - 0.47% by weight of nickel; - 0.255% by weight of chromium; - 0.0312% by weight of molybdenum; - 0.238% by weight of copper; - 0.0463% by weight of sulfur; - 0.031% by weight of phosphorus; - 0.038% by weight of tin; - 0.01% by weight of titanium; where the rest of the weight is iron. Advantageously, gray cast iron may also comprise tungsten, with a weight percentage of 0.10 to 0.14% and, preferably, equal to 0.12%. According to a third preferred embodiment, gray cast iron has the following composition: - 3.75% carbon by weight, - 1.40% silicon by weight, - 0.14% by weight of vanadium; - 0.12% by weight of tungsten, - 0.85% by weight of manganese, - 0.1% by weight of nickel, - 0.35% by weight of chromium, - 0.1% by weight of molybdenum, - 0.35% by weight of copper, - <0.1% by weight of sulfur, - <0.1% by weight of phosphorus, - 0.09% by weight of tin, - 0.01% by weight of titanium where the rest of the weight is iron. Ideally, the ferrous matrix of the cast steel is of the pearlite or fine lamellar type. In particular, the weight percentage of pearlite relative to the weight of the ferrous matrix is ​​not less than 95%. Preferably, gray cast iron comprises ferrite with a weight percentage of less than 5% of the ferrous matrix weight. Even more preferably, the weight percentage of ferrite relative to the ferrous matrix weight is equal to or less than 1%. In particular, gray cast iron comprises cementite and free carbides with a weight percentage of no more than 1% of the weight of the ferrous matrix. Advantageously, the cast iron of the present invention can be used to produce disc brake components. For example, cast iron can be used to produce at least one brake band for a brake disc of any type. Experimental wear tests have been carried out, comparing a brake disc made of gray cast iron of a standard composition to three brake discs made of three cast irons having different compositions that fall within the present invention. COMPARATIVE EXAMPLE A brake disc was obtained from gray cast iron having the following composition: 3.74 wt% carbon; 1.65 wt% silicon; 0.55 wt% manganese; 0.1 wt% nickel; 0.15 wt% chromium; 0.1 wt% molybdenum; 0.2 wt% copper; <0.1 wt% sulfur; <0.08 wt% phosphorus; 0.023 wt% tin; 0.09 wt% titanium; where the remainder of the weight is iron. The ferrous matrix consists of 1% by weight of ferrite, 98.5% by weight of pearlite and 0.5% by weight of carbides. The brake disc made of such gray cast iron will be referred to as the COMPARATIVE DISC hereafter. EXAMPLE 1 A first brake disc was obtained, identical to the comparator disc, but using a gray cast iron in accordance with the invention, having the following initial first composition: 3.86 wt% carbon; 1.85 wt% silicon; 0.12 wt% vanadium; 0.63 wt% manganese; 0.06 wt% nickel; 0.21 wt% chromium; 0.002 wt% molybdenum; 0.19 wt% copper; 0.065 wt% sulfur; 0.04 wt% phosphorus; 0.023 wt% tin; 0.0079 wt% titanium; wherein the remainder of the weight is iron. The ferrous matrix consists of 1% by weight of ferrite, 98% by weight of pearlite and 1% by weight of carbides. The brake disc made of such gray cast iron will be referred to as DISC 1 hereafter. EXAMPLE 2 A second brake disc was obtained, identical to the comparator disc, but using a gray cast iron in accordance with the invention, having the following second initial composition: 3.70 wt% carbon; 2.08 wt% silicon; 0.12 wt% vanadium; 0.658 wt% manganese; 0.47 wt% nickel; 0.255 wt% chromium; 0.0312 wt% molybdenum; 0.238 wt% copper; 0.0463 wt% sulfur; 0.031 wt% phosphorus; 0.038 wt% tin; 0.01 wt% titanium; wherein the remainder of the weight is iron. The ferrous matrix consists of 1% by weight of ferrite, 98% by weight of pearlite and 1% by weight of carbides. The brake disc made of such gray cast iron will be referred to as DISC 2 hereafter. EXAMPLE 3 A third brake disc was obtained, identical to the comparator disc, but using a gray cast iron in accordance with the invention, having the following third initial composition: 3.75 wt% carbon; 1.40 wt% silicon; 0.14 wt% vanadium; 0.12 wt% tungsten; 0.85 wt% manganese; 0.1 wt% nickel; 0.35 wt% chromium; 0.1 wt% molybdenum; 0.35 wt% copper; <0.1 wt% sulfur; <0.1 wt% phosphorus; 0.09 wt% tin; 0.01 wt% titanium; wherein the remainder of the weight is iron. The ferrous matrix consists of approximately 1% by weight of ferrite, 97.5% by weight of pearlite and < 1% by weight of carbides. The brake disc made of such gray cast iron will be referred to as DISC 3 hereafter. EXPERIMENTAL TESTS The comparative brake disc and the three brake discs according to the invention (DISC 1, 2, and 3) were subjected to five repetitions of a well-known test in the field of braking systems. At the end of this test, it was found that the weight reduction of the three discs is 50–55% compared to the reference disc. Tests show that, under identical conditions, the brake discs according to the invention (discs 1, 2, and 3) experienced significantly less weight loss than the comparator disc. On average, the brake discs according to the invention (discs 1, 2, and 3) have a weight loss of less than 50% compared to the comparator disc. This means that gray cast irons according to the invention offer greater wear resistance than standard gray cast iron taken as a reference. Analysis of the test results also reveals that disc 3 exhibits a more significant reduction in weight loss than the comparator disc. This suggests that the gray cast iron used to manufacture disc 3 provides greater wear resistance. The same brake discs (comparative disc, disc 1, disc 2, and disc 3) are further characterized from a mechanical and functional parameter point of view. The results are shown in Table 1: TABLE 1 COMPARATIVE DISC DISC 1 DISC 2 DISC 3 Tensile strength Rm [MPa] 190 182 165 273 Hardness [HBW] 180-186 187-190 183-185 234 Density [kg / dm3] 7.1 7.1 7.1 7.3 Corrosion [percentage weight loss] 0.29 0.21 0.23 0.17 Based on a comparison of the data shown in Table 1, it appears that, in terms of mechanical strength, thermal resistance and corrosion resistance, the performance of discs 1, 2 and 3 is that of a brake disc created using standard cast iron. All this is indirectly confirmed by the fact that, with respect to the standard gray cast iron used to make the comparison disc, the gray cast iron according to the invention does not involve any significant change in the weight percentages of carbon (graphite), silicon and in the sum of the weight percentages of chromium and molybdenum. The high carbon (graphite) content ensures that the cast iron according to the invention has high thermal conductivity, allowing for high heat exchange during braking shocks. This significantly reduces the risk of cracking due to thermal stress, even after heavy use of the braking system. The cast iron of the present invention also has high damping capacity, which contributes to increased resistance to crack formation and spread. Due to the percentage of silicon included in the molten iron of the present invention, a gratifying effect is achieved, preventing the formation of cementite and carbides. What's more, chromium and molybdenum stabilize the formation of lamellar pearlite in the metallic matrix. At the end of the five repetitions of the standard test using during the design of brake discs suitable for the braking system, the weight losses of the pads used in association with the comparator disc and with discs 1, 2 and 3 were also measured. A comparison of the data shows that discs 1, 2, and 3 cause wear on the pads that is substantially comparable to that caused by the comparator disc. Thus, the increase in wear resistance does not cause an increase in pad wear associated with the disc made using cast iron according to the invention. As can be seen from the description, the gray cast iron of the present invention allows overcoming the disadvantages presented in the prior art. In particular, the cast iron of the present invention and the related brake discs made from said cast iron offer significantly greater wear resistance than standard gray cast iron, taken as a reference. Such an increase does not result in a deterioration of mechanical strength, thermal resistance, and corrosion resistance. In fact, the performance of brake discs made of gray cast iron according to the invention is comparable to that of a brake disc made of standard gray cast iron, in terms of mechanical strength, thermal resistance and corrosion resistance. It also emerged that the increased wear resistance ensured by the gray cast iron according to the invention does not significantly alter the wear of the pads. In fact, based on the weight loss data, it appears that the pads associated with discs 1, 2, and 3 wore substantially similarly (in terms of weight loss) to those associated with the comparator disc. In particular, compared to the comparator disc, there is actually a reduction in pad wear for disc 3. To meet specific and contingent needs, those skilled in the art may make various changes and variations to the cast irons and brake disc described above, all contained within the scope of the invention as defined by the following claims.

Claims

CLAIMS 1. A gray cast iron, characterized in that it comprises carbon, silicon, vanadium, manganese, nickel, chromium, molybdenum, copper, sulfur, phosphorus, tin, and titanium, wherein the weight percentage of carbon is from 3.70 to 3.90%, the weight percentage of silicon is from 1.30 to 2.10%, the weight percentage of vanadium is from 0.10 to 0.15%, the weight percentage of manganese is from 0.60 to 0.90%, the weight percentage of nickel is from 0.05 to 0.50%, the weight percentage of chromium is from 0.20 to 0.35%, the weight percentage of molybdenum is not more than 0.10%, the weight percentage of copper is not more than 0.35%, the weight percentage of sulfur is less than 0.10%, the weight percentage of phosphorus is not more than 0.10%, the weight percentage of The weight of tin is less than 0.10%, the weight percentage of titanium is less than 0.01%, where the remainder of the weight is made up of iron.

2. Cast iron according to claim 1 or 2, further characterized in that the percentage by weight of carbon is from 3.70 to 3.86%.

3. Cast iron according to claim 1, 2 or 3, further characterized in that the weight percentage of silicon is from 1.40 to 2.08%.

4. Cast iron according to one or more of the preceding claims, further characterized in that the weight percentage of vanadium is between 0.12 and 0.14%.

5. Cast iron according to one or more of the preceding claims, further characterized in that the percentage by weight of manganese is from 0.63 to 0.85%.

6. Cast iron according to one or more of the preceding claims, further characterized in that the weight percentage of nickel is between 0.06 and 0.47%.

7. Cast iron according to one or more of the preceding claims, further characterized in that the weight percentage of chromium is between 0.21 and 0.35%.

8. Cast iron in accordance with one or more of the preceding claims, further characterized in that the weight percentage of copper is between 0.19 and 0.35%.

9. Cast iron in accordance with one or more of the preceding claims, further characterized in that the percentage by weight of tin is not greater than 0.09%.

10. Cast iron according to one or more of the preceding claims, further characterized in that the weight percentage of titanium is between 0.0079 and 0.01%.

11. Cast iron according to one or more of the preceding claims, further characterized in that it consists of 3.86% by weight of carbon, 1.85% by weight of silicon, 0.12% by weight of vanadium, 0.63% by weight of manganese, 0.06% by weight of nickel, 0.21% by weight of chromium, 0.002% by weight of molybdenum, 0.19% by weight of copper, 0.065% by weight of sulfur, 0.04% by weight of phosphorus, 0.023% by weight of tin and 0.0079% by weight of titanium, wherein the remainder by weight is iron.

12. Cast iron according to one or more of claims 1 to 10, further characterized in that it consists of 3.70% by weight of carbon, 2.08% by weight of silicon, 0.12% by weight of vanadium, 0.658% by weight of manganese, 0.47% by weight of nickel, 0.255% by weight of chromium, 0.0312% by weight of molybdenum, 0.238% by weight of copper, 0.0463% by weight of sulfur, 0.031% by weight of phosphorus, 0.038% by weight of tin and 0.01% by weight of titanium, wherein the remainder by weight is iron.

13. Cast iron according to one or more of claims 1 to 10, further characterized in that it comprises tungsten, wherein the weight percentage of tungsten is between 0.10 and 0.14%, and preferably 0.12%.

14. Cast iron according to claim 13, further characterized in that it consists of 3.75% by weight of carbon, 1.40% by weight of silicon, 0.14% by weight of vanadium, 0.12% by weight of tungsten, 0.85% by weight of manganese, 0.1% by weight of nickel, 0.35% by weight of chromium, 0.1% by weight of molybdenum, 0.35% by weight of copper, <0.1% by weight of sulfur, <0.1% by weight of phosphorus, 0.09% by weight of tin and 0.01% by weight of titanium, wherein the remainder by weight is iron.

15. Cast iron according to one or more of the preceding claims, further characterized in that the matrix of said cast iron is pearlitic, or fine lamellar, wherein, preferably, the percentage by weight of pearlite in relation to the weight of the ferrous matrix is ​​not less than 95%. 16 - Cast iron according to one or more of the preceding claims, further characterized in that it comprises ferrite in a percentage by weight less than 5% relative to the weight of the ferrous matrix and, preferably, equal to 1%.

17. Cast iron according to one or more of the preceding claims, further characterized in that it comprises cementite and free carbides in a percentage by weight not greater than 1% in relation to the weight of the ferrous matrix. 18.- A brake disc for a disc brake, characterized in that it comprises a braking surface made of cast iron in accordance with any of the preceding claims.