Low alloy cast steel material and its preparation method

Abstract

The present application discloses a novel low-alloy cast steel material and a preparation method thereof, belonging to the technical field of alloy materials. The novel low-alloy cast steel material is composed of the following components in weight percentages: C: 0.17 - 0.25, Si: 0.3 - 0.6, Mn: 0.5 - 0.9, Cr: 1.5 - 2.0, Ni: 0.5 - 0.9, Mo: 0.3 - 0.7, Zr: 0.02 - 0.1, S ≤ 0.02, P ≤ 0.015, and the balance is Fe. On the basis of maintaining other good properties, the novel low-alloy cast steel material provided by the present application also has better tensile strength in a high-temperature environment, especially in a high-temperature environment of 700 °C and above, which can greatly extend the service life of mechanical parts using the novel low-alloy cast steel material and reduce the use cost.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy materials, and particularly to a novel low-alloy cast steel material and a method for preparing the novel low-alloy cast steel. Background Art

[0002] Generally, mechanical parts generate instantaneous high temperatures during operation and then rapidly cool from the high-temperature state to the natural ambient temperature, working in a harsh environment of alternating hot and cold. Such rapid heating and cooling can easily cause fatigue cracks in mechanical parts, thereby reducing their service life.

[0003] Currently, there is a type of heat-resistant steel. Although it has high high-temperature strength, its room-temperature strength is low and it cannot meet the requirements of the working environment.

[0004] In addition, in recent years, most researchers have studied from aspects such as improving the room-temperature tensile strength and impact absorption work of mechanical parts, rather than from the aspect of high-temperature strength. Although the tensile strength of mechanical parts can reach 1200 MPa at room temperature, their strength will rapidly decrease in a high-temperature environment.

[0005] Therefore, most current mechanical parts still have the problem of being vulnerable to high temperatures. Summary of the Invention

[0006] One advantage of the present invention is to provide a novel low-alloy cast steel material and a preparation method thereof. The prepared low-alloy cast steel material has better tensile strength in a high-temperature environment, especially in a high-temperature environment of 700 °C and above, while maintaining other good properties, which can greatly extend the service life of mechanical parts using this novel low-alloy cast steel material, thereby reducing the use cost.

[0007] To achieve at least one of the above advantages of the present invention, in a first aspect, the present invention provides a novel low-alloy cast steel material, which is composed of the following components in weight percentages: C: 0.17 - 0.25, Si: 0.3 - 0.6, Mn: 0.5 - 0.9, Cr: 1.5 - 2.0, Ni: 0.5 - 0.9, Mo: 0.3 - 0.7, Zr: 0.02 - 0.1, S ≤ 0.02, P ≤ 0.015, and the balance is Fe.

[0008] According to an embodiment of the present invention, some components and their weight percentages are as follows: C: 0.20, Si: 0.45, Mn: 0.75, Cr: 1.60, Ni: 0.65, Mo: 0.44, Zr: 0.05.

[0009] According to an embodiment of the present invention, the partial components and their weight percentages are as follows: C: 0.21, Si: 0.44, Mn: 0.74, Cr: 1.65, Ni: 0.63, Mo: 0.46, Zr: 0.04.

[0010] According to an embodiment of the present invention, the partial components and their weight percentages are as follows: C: 0.20, Si: 0.47, Mn: 0.78, Cr: 1.68, Ni: 0.60, Mo: 0.45, Zr: 0.05.

[0011] In a second aspect, the present invention also provides a method for preparing the aforementioned novel low-alloy cast steel material, which successively includes the following steps:

[0012] S10, batching, weighing raw materials according to the ratio of the batching list, where the raw materials include: industrial pure iron, ferrosilicon, ferromanganese, ferrochromium, ferromolybdenum, ferrozirconium, electrolytic nickel, silicon-aluminum alloy, silicon-barium alloy, silicon-calcium alloy, rare earth, graphite carbon agent;

[0013] S20, melting, adding the raw materials in a predetermined order for melting, where the addition order of the raw materials is: industrial pure iron → graphite carbon agent, ferromolybdenum, electrolytic nickel → ferrochromium, industrial pure iron → ferromanganese → ferrosilicon → rare earth → ferrozirconium → silicon-aluminum alloy, silicon-barium alloy, silicon-calcium alloy;

[0014] S30, pouring, pouring at a predetermined speed under natural conditions, where the pouring process ≤ 10 minutes;

[0015] S40, normalizing treatment, heating up to 930°C - 980°C, holding for heat preservation, and then taking it out of the furnace and air-cooling after the heat preservation ends;

[0016] S50, quenching and tempering treatment, including quenching and tempering. Quenching is: heating up to 900°C - 950°C, holding for heat preservation, and then taking it out of the furnace and oil-cooling after the heat preservation ends; Tempering is: heating up to 600°C - 650°C, holding for heat preservation, and then taking it out of the furnace and air-cooling after the heat preservation ends.

[0017] According to an embodiment of the present invention, in step S20, when the temperature of the molten steel reaches 1600°C - 1620°C, add ferromanganese and ferrosilicon, remove the floating slag on the liquid surface, and then add rare earth and ferrozirconium.

[0018] According to an embodiment of the present invention, in step S20, after adding rare earth and ferrozirconium, take a sample for chemical analysis. When the composition is qualified, then heat up the molten steel to 1640°C - 1670°C, and then add silicon-aluminum alloy, silicon-barium alloy, and silicon-calcium alloy for mixed deoxidation, and then take it out of the furnace for pouring.

[0019] According to an embodiment of the present invention, in step S20, the silicon-aluminum alloy, silicon-barium alloy, and silicon-calcium alloy respectively account for 0.08% to 0.15%, 0.15% to 0.23%, and 0.15% to 0.23% of the mass of the molten steel.

[0020] According to an embodiment of the present invention, in step S30, the pouring temperature is 1630°C to 1650°C, and a tundish is used for pouring. The pouring time for each time is ≤ 30 seconds, and the total pouring time is ≤ 10 minutes.

[0021] These and other objects, features, and advantages of the present invention are fully embodied by the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The schematic diagram of the metallographic structure of Specimen NO.1 in the present application after being magnified 100 times is shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments in the following description are only examples, and those skilled in the art can think of other obvious variations. The basic principles defined in the following description can be applied to other implementation schemes, variant schemes, improvement schemes, equivalent schemes, and other technical schemes that do not deviate from the spirit and scope of the present invention.

[0024] Those skilled in the art should understand that in the disclosure of the specification, the orientation or positional relationships indicated by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting the present invention.

[0025] It can be understood that the term "a" should be understood as "at least one" or "one or more". That is, in one embodiment, the number of one element can be one, and in other embodiments, the number of this element can be multiple. The term "a" cannot be construed as limiting the quantity.

[0026] A new type of low-alloy cast steel material according to a preferred embodiment of the present invention will be described in detail below, wherein the new type of low-alloy cast steel material is composed of the following components by weight percentage: C: 0.17 - 0.25, Si: 0.3 - 0.6, Mn: 0.5 - 0.9, Cr: 1.5 - 2.0, Ni: 0.5 - 0.9, Mo: 0.3 - 0.7, Zr: 0.02 - 0.1, S ≤ 0.02, P ≤ 0.015, and the balance is Fe;

[0027] Among them, in one embodiment, some components and their weight percentages are as follows: C: 0.20, Si: 0.45, Mn: 0.75, Cr: 1.60, Ni: 0.65, Mo: 0.44, Zr: 0.05;

[0028] Among them, in another embodiment, some components and their weight percentages are as follows: C: 0.21, Si: 0.44, Mn: 0.74, Cr: 1.65, Ni: 0.63, Mo: 0.46, Zr: 0.04;

[0029] Among them, in the third embodiment, some components and their weight percentages are as follows: C: 0.20, Si: 0.47, Mn: 0.78, Cr: 1.68, Ni: 0.60, Mo: 0.45, Zr: 0.05.

[0030] The new type of low-alloy cast steel material provided by this application adds a small amount of metal elements Zr, Cr, Mo, and Ni to refine the grains in the cast steel. Among them, Zr can improve the oxidation resistance, strength, and low-temperature toughness of the steel, and can also reduce the gas content in the cast steel; among them, Zr, Mo, and C interact with each other to form stable and insoluble carbides, which can improve the high-temperature stability of the cast steel.

[0031] Through computer software simulation, the amount of alloying metal elements is optimized and configured to give full play to their proper role in the performance of alloy steel. After quenching, short bar-shaped low-carbon martensite is formed, and then tempered sorbite (metallographic structure) is formed after high-temperature tempering. Fine alloy carbides are evenly distributed on the matrix, effectively improving the toughness of the alloy steel and increasing the strength of the alloy steel. Stable refractory ZrC and MoC improve the high-temperature stability of the alloy steel, especially the high-temperature strength of the alloy steel, such as tensile strength. Characteristics such as fine grains and low gas content can also improve the tissue density of the alloy steel, enabling the cast low-alloy steel to obtain excellent comprehensive performance.

[0032] The chemical composition (%) of the new type of low-alloy cast steel material provided by this application is shown in the following table:

[0033] C Si Mn Cr Ni Mo Zr S P 0.17～0.25 0.3～0.6 0.5～0.9 1.0～2.0 0.5～0.9 0.3～0.7 0.02～0.1 ≤0.02 ≤0.015

[0034] After corresponding test detections are carried out on the novel low-alloy cast steel material provided by this application, the obtained average mechanical properties are shown in the following table:

[0035]

[0036] After multiple test detections are carried out on the novel low-alloy cast steel material provided by this application, the obtained average high-temperature performance parameters are shown in the following table:

[0037]

[0038] In a second aspect, based on the same principle, the present invention also provides a method for preparing the aforementioned novel low-alloy cast steel material, which is formed by an industrial casting method and obtains the final comprehensive performance through normalizing treatment + quenching and tempering treatment, and successively includes the following steps:

[0039] S10, batching, weighing raw materials according to the ratio of the batching list, wherein the raw materials shall not have impurities such as rust and floating dust, and the surface shall not contain water vapor, and the raw materials include: industrial pure iron, ferrosilicon, ferromanganese, ferrochrome, ferromolybdenum, ferrozirconium, electrolytic nickel, silicon-aluminum alloy, silicobarium alloy, silicocalcium alloy, rare earth, graphite carbon agent;

[0040] S20, melting, using an intermediate frequency induction furnace, adding the raw materials in a predetermined order for melting, wherein the adding order of the raw materials is: industrial pure iron → graphite carbon agent, ferromolybdenum, electrolytic nickel → ferrochrome, industrial pure iron → ferromanganese → ferrosilicon → rare earth → ferrozirconium → silicon-aluminum alloy, silicobarium alloy, silicocalcium alloy;

[0041] S30, pouring, using a tundish to pour at a predetermined speed under natural conditions, wherein the pouring process ≤ 10 minutes, or in other words, not exceeding 10 minutes;

[0042] S40, normalizing treatment, heating up to 930°C - 980°C, holding for heat preservation, and then taking out of the furnace and air cooling after the heat preservation ends;

[0043] S50, quenching and tempering treatment, including quenching and tempering, wherein quenching is: heating up to 900°C - 950°C, holding for heat preservation, and then taking out of the furnace and oil cooling after the heat preservation ends; wherein tempering is: heating up to 600°C - 650°C, holding for heat preservation, and then taking out of the furnace and air cooling after the heat preservation ends.

[0044] Further preferably, in step S20, when the temperature of the molten steel reaches 1600°C - 1620°C, ferromanganese and ferrosilicon are added, the floating slag on the liquid surface is removed, and then rare earth and ferrozirconium are added.

[0045] Further preferably, in step S20, after adding rare earth and ferrozirconium, a sample is taken for chemical analysis. After the composition is qualified, the molten steel is heated to 1640 °C to 1670 °C, and then silicon-aluminum alloy, silicon-barium alloy, and silicon-calcium alloy are added for combined deoxidation, and then the molten steel is tapped for casting.

[0046] Further preferably, in step S20, the silicon-aluminum alloy, silicon-barium alloy, and silicon-calcium alloy respectively account for 0.08% to 0.15%, 0.15% to 0.23%, and 0.15% to 0.23% of the mass of the molten steel.

[0047] It should be noted that in the method for preparing the aforementioned novel low-alloy cast steel material in a preferred embodiment of the present application, rare earth is added first and then ferrozirconium is added because rare earth can remove oxygen in the molten steel, reduce the effect of oxygen on ferrozirconium, so that ferrozirconium can be retained in the largest amount, and further ensure that ferrozirconium can maximize the removal of gases such as nitrogen and hydrogen that are difficult to remove by other methods.

[0048] More specifically, in the present application, the novel low-alloy cast steel material is prepared multiple times according to the same preparation method. Among them, the specimens for testing are prepared and tested according to the regulations of national standards, and relatively advanced test equipment is selected. For example, a German-made OB spectral analyzer is used for chemical composition analysis, and a Tesla force testing machine is used for tensile testing. Specimens prepared from 3 tests are selected for testing, and the test data of 3 specimens are taken each time, and the average value is taken and listed for summary.

[0049] 1. The target element content and addition amount of the materials selected for the test are shown in the following table:

[0050]

[0051] 2. Melting

[0052] Industrial pure iron is added to the crucible and melted. After there is some molten steel in the crucible, graphite carbon agent, ferromolybdenum, and electrolytic nickel are added, and then ferrochromium and the remaining industrial pure iron are added. After all are melted and the temperature reaches 1600 °C to 1620 °C, ferromanganese, ferrosilicon, and rare earth are added, and then slag is removed and ferrozirconium is added. After sampling and chemical analysis and the composition is qualified, the temperature is raised to 1640 °C to 1670 °C, and silicon-aluminum, silicon-barium, and silicon-calcium alloys are added for deoxidation, and then the molten steel is tapped;

[0053] 3. Casting

[0054] The casting temperature is 1630 °C to 1650 °C, and a bottom-pour ladle is used for casting. The casting time for each time is ≤ 30 seconds, and the total casting time is ≤ 10 minutes;

[0055] 4. Normalizing treatment

[0056] After removing the riser from the casting, normalizing treatment is carried out. The treatment temperature is 30°C to 70°C above the Ac3 temperature, and the actual controlled temperature is 930°C to 980°C. Hold for 3 hours and air cool;

[0057] 5. Tempering treatment

[0058] The quenching temperature is controlled at 30°C to 50°C above the Ac3 temperature, and the actual controlled temperature is 900°C to 950°C. Hold for 2.5 hours and oil cool; the tempering temperature is 600°C to 650°C, hold for 3 hours, and air cool after leaving the furnace.

[0059] 6. Three example tests are carried out on the novel low-alloy cast steel material provided by this application. Its chemical composition is shown in the following table:

[0060] Chemical composition of novel low-alloy cast steel (%)

[0061] Instance number C Si Mn Cr Ni Mo Zr NO.1 0.20 0.45 0.75 1.60 0.65 0.44 0.05 NO.2 0.21 0.44 0.74 1.65 0.63 0.46 0.04 NO.3 0.20 0.47 0.78 1.68 0.60 0.45 0.05

[0062] 7. After heat treatment, as Figure 1 is the metallographic structure diagram of the NO.1 specimen magnified 100 times, and the structure is tempered sorbite structure.

[0063] 8. Three example tests are carried out on the novel low-alloy cast steel material provided by this application. Its room-temperature mechanical properties are shown in the following table and are compared with the low-alloy cast steel ZG24CrNiMoV microalloyed with the metal element V:

[0064]

[0065]

[0066] 9. Three example tests are carried out on the novel low-alloy cast steel material provided by this application. Its room-temperature mechanical properties are shown in the following table and are compared with the low-alloy cast steel ZG24CrNiMoV microalloyed with the metal element V:

[0067]

[0068] In the above table, taking 700°C as a reference, for specimens NO.1, NO.2 and NO.3 compared with ZG24CrNiMoV, their tensile strengths are increased by 79.67%, 84.62% and 85.16% respectively; while taking 750°C as a reference, for specimens NO.1, NO.2 and NO.3 compared with ZG24CrNiMoV, their tensile strengths are increased by 93.81%, 109.28% and 103.09% respectively.

[0069] It can be seen from this that on the basis of maintaining other good properties, the novel low-alloy cast steel material provided by this application can achieve a very obvious improvement in tensile strength compared with the prior art in a high-temperature environment, especially in a high-temperature environment of 700 °C and above.

[0070] Those skilled in the art should understand that the embodiments of the present invention described above and shown in the accompanying drawings are only examples and do not limit the present invention. The advantages of the present invention have been fully and effectively realized. The functions and structural principles of the present invention have been shown and described in the embodiments, and the embodiments of the present invention can have any deformation or modification without departing from the above principles.

Claims

1. Low-alloy cast steel material, characterized in that, it is composed of the following components by weight percentage : C: 0.17 - 0.25, Si: 0.3 - 0.6, Mn: 0.5 - 0.9, Cr: 1.5 - 2.0, Ni: 0.5 - 0.9, Mo: 0.3 - 0.7, Zr: 0.02 - 0.1, S ≤ 0.02, P ≤ 0.015, and the balance is Fe; The method for preparing the low-alloy cast steel material successively includes the following steps: S10, batching, weighing raw materials according to the ratio of the batching list, where the raw materials include: industrial pure iron, ferrosilicon, ferromanganese, ferrochrome, ferromolybdenum, ferrozirconium, electrolytic nickel, silicon aluminum alloy, silicon barium alloy, silicon calcium alloy, rare earth, graphite carbon agent; S20, melting, adding the raw materials in a predetermined order for melting, where the addition order of the raw materials is: industrial pure iron → graphite carbon agent, ferromolybdenum, electrolytic nickel → ferrochrome, industrial pure iron → ferromanganese → ferrosilicon → rare earth → ferrozirconium → silicon aluminum alloy, silicon barium alloy, silicon calcium alloy; S30, pouring, pouring at a predetermined speed under natural conditions, where the pouring process ≤ 10 minutes; S40, normalizing treatment, heating up to 930°C - 980°C, holding for heat preservation, and then taking it out of the furnace and air-cooling after the heat preservation ends; S50, quenching and tempering treatment, including quenching and tempering, where quenching is: heating up to 900°C - 950°C, holding for heat preservation, and then taking it out of the furnace and oil-cooling after the heat preservation ends; where tempering is: heating up to 600°C - 650°C, holding for heat preservation, and then taking it out of the furnace and air-cooling after the heat preservation ends; Wherein in step S20, when the temperature of the molten steel reaches 1600°C - 1620°C, ferromanganese and ferrosilicon are added, the floating slag on the liquid surface is removed, and then rare earth and ferrozirconium are added; Wherein after adding rare earth and ferrozirconium, a sample is taken for chemical analysis. After the components are qualified, the molten steel is heated to 1640°C - 1670°C, and then silicon aluminum alloy, silicon barium alloy, and silicon calcium alloy are added for mixed deoxidation, and then taken out of the furnace for pouring.

2. The low-alloy cast steel material according to claim 1, characterized in that, Some components and their weight percentages are as follows: C: 0.20, Si: 0.45, Mn: 0.75, Cr: 1.60, Ni: 0.65, Mo: 0.44, Zr: 0.

05.

3. The low-alloy cast steel material according to claim 1, characterized in that, Some components and their weight percentages are as follows: C: 0.21, Si: 0.44, Mn: 0.74, Cr: 1.65, Ni: 0.63, Mo: 0.46, Zr: 0.

04.

4. The low-alloy cast steel material according to claim 1, characterized in that, Some components and their weight percentages are as follows: C: 0.20, Si: 0.47, Mn: 0.78, Cr: 1.68, Ni: 0.60, Mo: 0.45, Zr: 0.

05.

5. The method for preparing the low-alloy cast steel material according to any one of claims 1 to 4, characterized in that, successively includes the following steps: S10, Batching: Weigh raw materials according to the ratio in the batching list, where the raw materials include: industrial pure iron, ferrosilicon, ferromanganese, ferrochrome, ferromolybdenum, ferrozirconium, electrolytic nickel, silicon-aluminum alloy, silicobarium alloy, silicocalcium alloy, rare earth, and graphite carbon agent; S20, Melting: Add the raw materials in a predetermined order for melting, where the addition order of the raw materials is: industrial pure iron → graphite carbon agent, ferromolybdenum, electrolytic nickel → ferrochrome, industrial pure iron → ferromanganese → ferrosilicon → rare earth → ferrozirconium → silicon-aluminum alloy, silicobarium alloy, silicocalcium alloy; S30, Pouring: Pour at a predetermined speed under natural conditions, where the pouring process ≤ 10 minutes; S40, Normalizing treatment: Heat up to 930°C - 980°C, hold for heat preservation, and then air cool after taking out of the furnace when the heat preservation ends; S50, Quenching and tempering treatment: including quenching and tempering. Quenching is: heat up to 900°C - 950°C, hold for heat preservation, and then oil cool after taking out of the furnace when the heat preservation ends; Tempering is: heat up to 600°C - 650°C, hold for heat preservation, and then air cool after taking out of the furnace when the heat preservation ends.

6. The method for preparing a low-alloy cast steel material as claimed in claim 5, characterized in that, in step S20, the silicon-aluminum alloy, silicobarium alloy, and silicocalcium alloy respectively account for 0.08% - 0.15%, 0.15% - 0.23%, and 0.15% - 0.23% of the mass of the molten steel.

7. The method for preparing a low-alloy cast steel material as claimed in claim 5 or 6, characterized in that, in step S30, the pouring temperature is 1630°C - 1650°C, pouring is carried out using a tundish, the pouring time for each time ≤ 30 seconds, and the total pouring time ≤ 10 minutes.

Images