CN108588544A - A kind of high-performance gray cast iron with comprehensive high-heat performance and mechanical property - Google Patents

Abstract

The invention discloses a high-performance gray cast iron with comprehensive high thermal performance and mechanical performance, belonging to the technical field of new materials. The composition of the gray cast iron alloy is calculated according to the mass fraction, including C: 3.0%-3.4%, Si: 1.6%-2.1%, Cr: 0.1%-0.6%, Mo: 0.01%-1.2%, Mn: 0.5%-1.3% %, Cu: 0.02 to 0.2%. The remainder is matrix element Fe and impurity elements P<0.05%, S<0.05%, Ni<0.1%, Ti<0.01%, Sn<0.01%, N<0.01%, V<0.01%. The high-performance gray cast iron of the present invention is prepared by a sand casting method, without post-heat treatment, and has a simple process. The high-performance cast iron has a tensile strength of 250-400MPa at room temperature and a thermal conductivity of 52-60W/(m*K) at room temperature. It has comprehensive high thermal conductivity and mechanical properties and is suitable for automobile flywheels, brake discs and other related products. The application field of materials for thermally conductive parts under force.

Description

A high-performance gray cast iron with comprehensive high thermal and mechanical properties

technical field

The invention belongs to the technical field of new materials, and specifically relates to a high-performance gray cast iron with comprehensive high thermal performance and mechanical performance, which is mainly used in automobile flywheels, brake discs, cylinder blocks, cylinder heads and other related components.

Background technique

The development of cast iron technology is one of the important driving forces to promote the "industrial revolution". With the development of science and technology, cast iron has been used in industrial fields such as bridges, rails, pipelines and automobiles, and has become one of the most widely used basic materials in metal materials today. Gray cast iron is widely used in industry due to its good casting performance, wide use space, various achievable mechanical properties and lower cost (20%-40% than steel). According to the results of the 49th World Casting Production Census, in 2014, the total global casting production exceeded 103.6 million tons, of which the output of cast iron accounted for 70.8% of the total casting output, while the output of gray cast iron accounted for 45.8% of the total casting output .

Due to its good performance and low cost, gray cast iron has been widely used in auto parts such as brake discs, flywheels and other auto parts. The gray iron material quickly dissipates excess heat generated in the component, keeping the component cooler, maintaining component dimensional stability and reducing internal stresses. However, with the advancement of manufacturing technology and the development of advanced automobile engines, higher requirements have been placed on the performance of cast iron materials, requiring materials not only to have high strength, but also to have high thermal conductivity, which cannot be met by traditional gray cast iron. requirements of modern automotive applications. Therefore, the development of high-performance cast iron with comprehensive high thermal and mechanical properties will become an important driving force for the development of modern automobiles.

In traditional gray cast iron, thermal conductivity and strength are a pair of contradictory opposites. The main reason is that improving the thermal conductivity of gray cast iron mainly increases the volume fraction of A-type flake graphite in the microstructure of gray cast iron, and increases the size and length of flake graphite, thereby enhancing the heat conduction effect of graphite and making heat energy Conduction along the graphite sheet quickly; while increasing the strength of gray cast iron is bound to reduce the volume fraction of graphite, and reduce the size of graphite, especially the length of graphite sheet, so as to reduce the internal stress of gray cast iron The stress concentration generated on the graphite sheet reduces the generation of crack sources and the channels for their expansion. Therefore, in order to obtain high-performance gray cast iron with comprehensive high thermal conductivity and mechanical properties, it is necessary to balance the volume fraction and size of graphite and optimize the distribution of graphite, while improving the strength of the matrix as much as possible.

Alloying can improve the strength of the matrix, and can also control the graphite fraction and shape, and improve the distribution of good graphite. It is an important way to improve the thermal conductivity and mechanical properties of gray cast iron. The adjustment of the content of C, Si and other elements in the alloy can control the content and shape of graphite in gray cast iron, while the optimization of the content of Cr, Mo, Mn and other elements can improve the distribution of graphite and improve the performance of its matrix.

The carbon content plays a decisive role in the performance of cast iron. In cast iron, carbon element mainly exists in the form of graphite, and the content of carbon element directly affects the level of graphite content in cast iron. The effect of carbon content on the performance of cast iron can usually be expressed together with the content of silicon and phosphorus, expressed in carbon equivalent (Carbon Equivalent, CE), and its calculation formula is as follows:

Studies have shown that when the carbon equivalent increases, it will directly lead to a decrease in the strength and hardness of the casting.

Silicon is one of the important constituent elements in cast iron, which can effectively promote the precipitation of graphite and reduce the tendency of whitening. In the Fe-C alloy phase diagram, under equilibrium conditions, the eutectic temperature of the stable system (Fe-graphite) is 1154°C, and the eutectic temperature of the metastable system (Fe-Fe3C) is 1148°C, which is only 6°C lower than that of the stable system . In the actual solidification process, the supercooling degree and solidification speed of cast iron are generally relatively large, so it is easy to precipitate Fe3C cementite, resulting in white hole. This requires the addition of alloying elements to expand the temperature difference between the stable system and the metastable system, so that carbon elements can be precipitated in the form of graphite. Silicon element plays an indispensable role in it. It can effectively inhibit the formation of cementite between carbon and iron elements, thereby promoting the precipitation of carbon elements in the form of graphite. With the increase of the silicon content, the eutectic temperature of the stable system increases gradually, and the eutectic temperature of the metastable system decreases continuously. It promotes graphitization and inhibits the formation of Fe3C, that is, reduces the tendency of whitening. It has been shown in the literature that when the silicon content is between 1.5% and 2.5%, it has the strongest effect on the graphitization of cast iron; when the silicon content exceeds 3%, the graphitization effect gradually weakens. Although silicon is the main factor that promotes the precipitation of graphite, it is generally believed that silicon is easily dissolved in the austenite or ferrite matrix, which significantly reduces the thermal conductivity of graphite. Studies have pointed out that when other conditions remain unchanged and the silicon content is reduced from 2.5% to 1.5%, the thermal conductivity of cast iron increases by about 10%.

In gray cast iron, most of the alloying elements will hinder the precipitation of graphite, which will reduce the thermal conductivity of cast iron. In previous studies, the addition of molybdenum was mainly used to hinder the precipitation of graphite. This is because molybdenum can refine and improve the distribution of graphite and refine pearlite. The reduction of graphite content and the refinement of size will reduce the chance of crack initiation from graphite flakes, thus improving the mechanical properties of gray cast iron. On the other hand, molybdenum element can change the distribution of carbon element, chromium element and silicon element in gray cast iron, and cause the precipitation of ferrite and molybdenum carbide with high thermal conductivity in the segregation area of molybdenum element. Molybdenum can also refine the size of primary austenite dendrites and eutectic clusters. Refined austenite dendrites will lead to an increase in the number of primary austenite and a decrease in the spacing of austenite dendrites in gray cast iron. A large number of austenite dendrites and a small austenite dendrite spacing will reduce the length of graphite in the eutectic group and make its distribution non-oriented. In summary, the addition of molybdenum will refine the morphology of graphite and decrease the volume fraction in gray cast iron, and the solid solution strengthening of molybdenum will help improve the mechanical properties of gray cast iron. The addition of molybdenum may lead to narrow segregation regions and randomly oriented graphite, while reducing the average distance between adjacent graphite sheets, which will help improve its thermal properties. Molybdenum is an important element to obtain high-performance gray cast iron with comprehensive high thermal and mechanical properties.

Chromium is a strong carbide forming and stabilizing element that can combine with iron carbide to form stronger and harder pearlite, thereby increasing the strength of cast iron. However, on the other hand, the addition of chromium inhibits the precipitation of carbon elements in the form of graphite, which reduces the thermal conductivity of cast iron and also increases the tendency of cast iron to whiten. When the chromium element is added alone, the uniformity of the gray cast iron structure will be reduced, and the pearlite structure will produce uneven microhardness.

Manganese can promote the precipitation of pearlite, which can improve the strength of cast iron. At the same time, manganese can also be combined with sulfur to form MnS, which acts as a non-spontaneous nucleation nucleus for graphite precipitation to promote graphite precipitation. Phosphorus and sulfur are generally regarded as harmful elements in cast iron, but a certain amount of sulfur can improve the cutting performance of cast iron. Sulfur can combine with manganese to form MnS. However, too much MnS will aggregate to form a dense arrangement, and at the same time weaken the alloying effect of manganese and reduce the strength of cast iron. When the phosphorus content in the casting is greater than 0.1%, phosphorus eutectic will appear. Phosphorus eutectic is hard and brittle, which can improve the wear resistance of cast iron, and the phosphorus content of some wear-resistant high-phosphorus cast iron can reach 0.6%. Alloying elements will segregate near the phosphorus eutectic, weakening the effect of the alloy. At the same time, the vicinity of the phosphorus eutectic is solidified in a paste state, which will increase the tendency of casting shrinkage and porosity.

Copper element can promote the formation of graphitization, reduce the whitening tendency of cast iron, and at the same time promote the formation of pearlite, increase the content of pearlite, and at the same time can refine pearlite and strengthen pearlite and ferrite in it, thus increasing the hardness of cast iron and strength.

The purpose of the present invention is to utilize reasonable design of alloying elements to provide a high-performance gray cast iron with comprehensive high thermal and mechanical properties, which can be applied to force heat transfer components such as flywheels and brake discs of modern automobiles. The production process of the high-performance cast iron is simple, low in cost, and has important application value and potential market value.

Contents of the invention

The purpose of the present invention is: the purpose of the present invention is to provide a high-performance gray cast iron with comprehensive high thermal performance and mechanical performance by designing the alloy composition and utilizing the interaction of alloying elements. The gray cast iron has appropriate C and Si content to obtain A-type flake graphite morphology and appropriate graphite content, and optimizes the distribution of graphite through alloying of Cr, Mo, and Mn to increase the thermal conductivity of graphite and the strength of the matrix. At room temperature, the tensile strength of the high-performance cast iron is greater than 250MPa, and its thermal conductivity can reach 52-60W/(m*K).

Technical scheme of the present invention is:

A high-performance gray cast iron material with comprehensive high thermal performance and mechanical performance according to the present invention, its chemical composition is C: 3.0%-3.4%, Si: 1.6%-2.1%, Cr: 0.1%-0.6%, Mo: 0.01%-1.2%, Mn: 0.5%-1.3%, Cu: 0.02%-0.2%, and the balance is matrix element Fe and impurity elements, and the total amount of impurity elements is less than 0.3%.

Further, the mass fractions of impurity elements in the high-performance gray cast iron material are: P<0.05%, S<0.05%, Ni<0.1%, Ti<0.01%, Sn<0.01%, N<0.01% and V<0.01%.

The high-performance gray cast iron with comprehensive high thermal performance and mechanical performance described in the present invention, the graphite form in the gray cast iron microstructure is evenly distributed flake graphite, and its matrix is composed of complete pearlite or pearlite plus a small amount of ferrite , as the addition of molybdenum increases, there is a small amount of eutectic molybdenum carbide precipitates in the gray cast iron matrix.

The preparation method of high-performance gray cast iron with comprehensive high thermal performance and mechanical performance according to the present invention is characterized in that the preparation method of sand casting is adopted, the temperature of the molten iron is 1480°C to 1500°C during pouring, and the pouring temperature is 1300°C to 1500°C. 1360°C, add 0.4-0.6% 75SiFe inoculant by mass percentage during pouring, and air cool to room temperature after pouring.

The invention has the advantages that: the gray cast iron obtains an optimal microstructure through alloying design, so as to achieve comprehensively high mechanical and thermal conductivity properties. The specific performance is as follows: (1) The shape of graphite in its microstructure is uniformly distributed fine and curved A-type flake graphite. This graphite shape reduces the splitting effect on the matrix, which is beneficial to resist the rapid expansion of cracks in the deformation process and increase the strength. ; At the same time, the fine and uniform A-type graphite also reduces the distance between adjacent graphite sheets that conduct heat, thereby effectively increasing the thermal conductivity of gray cast iron. (2) The matrix is composed of complete pearlite or pearlite plus a small amount of ferrite, and the staggered arrangement of pearlite with small layer thickness and sheet spacing will increase the tensile strength of gray iron castings. In particular, the reasonable addition of molybdenum element will lead to the solid solution of molybdenum element in the matrix or the precipitation of eutectic molybdenum carbide to cause strengthening, which further increases the strength of gray cast iron. The room temperature tensile strength of the high-performance cast iron of the present invention is 250-400MPa, and the room temperature thermal conductivity can reach 52-60W/(m*K). It has excellent thermal shock resistance and has important application value in industrial fields such as automobiles.

Description of drawings

Fig. 1 is the typical graphite morphology figure of common gray cast iron embodiment 1 of the present invention;

Fig. 2 is the typical graphite morphology figure of common gray cast iron embodiment 5 of the present invention;

Fig. 3 is a typical matrix microstructure topography figure of high performance gray cast iron embodiment 1 of the present invention;

Fig. 4 is a microstructure topography diagram of a typical matrix of high-performance gray cast iron Example 5 of the present invention.

Detailed ways

The present invention will be described in further detail below.

The present invention is illustrated in more detail through the following examples, so that those skilled in the art can understand the advantages and characteristics of the present invention.

Table 1 shows the alloy composition of the examples. Wherein embodiments 1 to 5 are high-performance gray cast irons within the specified composition range of the present invention, and embodiments 6-9 are all non-patented gray cast irons, wherein C, Mo, Mo, and The contents of Mn and Si elements are respectively outside the scope of the patent rights, and the effects of C, Mo, Mn and Si elements on the properties of cast iron are illustrated by comparison.

The preparation process steps of embodiment 1-9 are:

(1) Weigh high-purity Fe, Si, Cr, Mo, Mn, Cu and other metal materials according to the composition ratio (if necessary, add graphite to balance the carbon content), and the corresponding proportion of cast iron, scrap steel and 75SiFe inoculant, etc. .

(2) Put the metal raw materials, pig iron and scrap steel with the above-mentioned ratio into the intermediate frequency induction furnace until they are completely melted into molten iron. The temperature of the molten iron is controlled at 1480°C to 1500°C, and 0.4-0.6% by mass of 75SiFe inoculant is added in the way of inoculation with flow. The pouring temperature is controlled at 1300°C to 1360°C, and the gray cast iron ingot can be obtained by air cooling in the sand mold to room temperature.

The chemical composition (mass percentage) of the embodiment of table 1

Example C Si Cr Mo mn Cu Example 1 3.05 1.88 0.27 0.03 1.17 0.03 Example 2 3.06 1.64 0.4 0.02 1.06 0.03 Example 3 3.05 1.95 0.14 0.27 1.04 0.028 Example 4 3.15 1.78 0.12 0.55 1.15 0.03 Example 5 3.04 1.88 0.15 1.05 0.99 0.03 Example 6 3.6 1.89 0.14 0.02 1.15 0.03 Example 7 3.07 1.76 0.14 2 0.66 0.03 Example 8 2.98 1.67 0.14 0.02 0.2 0.028 Example 9 3.06 3.0 0.17 0.02 1.09 0.03

Embodiment 1: Metal materials such as high-purity Fe, Si, Cr, Mo, Mn, Cu (adding graphite balance carbon content when necessary) and casting pig iron, steel scrap are weighed according to the composition distribution ratio shown in alloy 1 in table 1 Put it into an intermediate frequency induction furnace until it is completely melted into molten iron. The temperature of the molten iron is controlled at 1480°C, and the 75SiFe inoculant with a mass percentage of 0.6% is added by means of inoculation with flow. The pouring temperature is controlled at 1340°C, and the gray cast iron ingot can be obtained by cooling to room temperature in a sand mold.

Embodiment 2: with high-purity Fe, Si, Cr, Mo, Mn, metal materials such as Cu (adding graphite balance carbon content when needed) with high-purity Fe, Si, Cr, Mo, metal materials such as Mn (when needed Add graphite to balance the carbon content), cast pig iron, and steel scrap are weighed according to the composition ratio shown in alloy 2 in Table 1, and then put into an intermediate frequency induction furnace until completely melted into molten iron. The temperature of the molten iron is controlled at 1480°C, and the 75SiFe inoculant with a mass percentage of 0.5% is added by means of inoculation with flow. The pouring temperature is controlled at 1340°C, and the gray cast iron ingot can be obtained by cooling to room temperature in a sand mold.

Embodiment 3: metal materials such as high-purity Fe, Si, Cr, Mo, Mn, Cu (adding graphite balance carbon content when necessary) and casting pig iron, scrap steel are weighed according to the composition distribution ratio shown in alloy 3 in table 1 Then put it into an intermediate frequency induction furnace until it is completely melted into molten iron. The temperature of the molten iron is controlled at 1480°C, and the 75SiFe inoculant with a mass percentage of 0.4% is added by inoculation with flow. The pouring temperature is controlled at 1350°C, and the gray cast iron ingot can be obtained by cooling to room temperature in a sand mold.

Embodiment 4: Metal materials such as high-purity Fe, Si, Cr, Mo, Mn, Cu (adding graphite balance carbon content when necessary) and casting pig iron, scrap steel are weighed according to the composition distribution ratio shown in alloy 4 in table 1 Put it into an intermediate frequency induction furnace until it is completely melted into molten iron. The temperature of the molten iron is controlled at 1480°C, and the 75SiFe inoculant with a mass percentage of 0.6% is added by means of inoculation with flow. The pouring temperature is controlled at 1350°C, and the gray cast iron ingot can be obtained by cooling to room temperature in a sand mold.

Embodiment 5: Metal materials such as high-purity Fe, Si, Cr, Mo, Mn, Cu (adding graphite balance carbon content when necessary) and casting pig iron, scrap steel are weighed according to the composition distribution ratio shown in alloy 5 in table 1 Put it into an intermediate frequency induction furnace until it is completely melted into molten iron. The temperature of the molten iron is controlled at 1490°C, and the 75SiFe inoculant with a mass percentage of 0.5% is added by means of inoculation with flow. The pouring temperature is controlled at 1360°C, and the gray cast iron ingot can be obtained by cooling to room temperature in a sand mold.

Embodiment 6: Metal materials such as high-purity Fe, Si, Cr, Mo, Mn, Cu (adding graphite balance carbon content when necessary) and casting pig iron, scrap steel are weighed according to the composition distribution ratio shown in alloy 6 in table 1 Then put it into an intermediate frequency induction furnace until it is completely melted into molten iron. The temperature of the molten iron is controlled at 1490°C, and the 75SiFe inoculant with a mass percentage of 0.47% is added by inoculation with flow. The pouring temperature is controlled at 1360°C, and the gray cast iron ingot can be obtained by cooling to room temperature in a sand mold.

Embodiment 7: Metal materials such as high-purity Fe, Si, Cr, Mo, Mn, Cu (adding graphite balance carbon content when necessary) and casting pig iron, scrap steel are weighed according to the composition distribution ratio shown in alloy 7 in table 1 Put it into an intermediate frequency induction furnace until it is completely melted into molten iron. The temperature of the molten iron is controlled at 1500°C, and 75SiFe inoculant with a mass percentage of 0.6% is added by means of inoculation with flow. The pouring temperature is controlled at 1370°C, and the gray cast iron ingot can be obtained by cooling to room temperature in a sand mold.

Embodiment 8: metal materials such as high-purity Fe, Si, Cr, Mo, Mn, Cu (add graphite balance carbon content when necessary) and corresponding proportioning casting pig iron, scrap steel, and casting pig iron, scrap steel according to table 1 The components shown in Alloy 8 are proportionally weighed and put into an intermediate frequency induction furnace until completely melted into molten iron. The temperature of the molten iron is controlled at 1500°C, and the 75SiFe inoculant with a mass percentage of 0.59% is added by means of inoculation with flow. The pouring temperature is controlled at 1380°C, and the gray cast iron ingot can be obtained by cooling to room temperature in a sand mold.

Embodiment 9: metal materials such as high-purity Fe, Si, Cr, Mo, Mn, Cu (add graphite balance carbon content when necessary) and corresponding proportioning casting pig iron, scrap steel, and casting pig iron, scrap steel according to table 1 The components shown in Alloy 8 are proportionally weighed and put into an intermediate frequency induction furnace until completely melted into molten iron. The temperature of the molten iron is controlled at 1500°C, and the 75SiFe inoculant with a mass percentage of 0.59% is added by means of inoculation with flow. The pouring temperature is controlled at 1360°C, and the gray cast iron ingot can be obtained by cooling to room temperature in a sand mold.

Table 2 shows the typical mechanical and thermal conductivity properties of the gray cast iron prepared in the examples. Figures 1 to 4 are typical metallographic microstructures and typical microstructure diagrams of Example 1 and Example 5, respectively.

Typical properties of gray cast iron of the embodiment of table 2

No. Tensile strength at room temperature (MPa) Thermal conductivity at room temperature (W/(m*K))

Claims (2)

1. a kind of high-performance gray cast iron material with comprehensive high-heat performance and mechanical property, chemical composition is according to mass fraction For C：3.0%~3.4%, Si：1.6%~2.1%, Cr：0.1%~0.6%, Mo：0.01%~1.2%, Mn：0.5%~ 1.3%, Cu：0.02%~0.2%, surplus is matrix element Fe and impurity element, and impurity element total amount is less than 0.3%.

2. a kind of high-performance gray cast iron material with comprehensive high-heat performance and mechanical property as described in claim 1, special Sign is：Each composition quality score of impurity element is in the high-performance gray cast iron material：P<0.05%, S<0.05%, Ni< 0.1%, Ti<0.01%, Sn<0.01%, N<0.01% and V<0.01%.