WO2021208181A1 - 一种低温高韧高温高强及高淬透性热模钢及制备技术 - Google Patents

一种低温高韧高温高强及高淬透性热模钢及制备技术 Download PDF

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WO2021208181A1
WO2021208181A1 PCT/CN2020/091212 CN2020091212W WO2021208181A1 WO 2021208181 A1 WO2021208181 A1 WO 2021208181A1 CN 2020091212 W CN2020091212 W CN 2020091212W WO 2021208181 A1 WO2021208181 A1 WO 2021208181A1
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temperature
forging
steel
low
toughness
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French (fr)
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黄进峰
张津
赵超
张�诚
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北京科技大学
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron

Definitions

  • the invention belongs to the technical field of die steel, and in particular relates to a low temperature, high toughness, high temperature, high strength and high hardenability hot die steel and preparation technology.
  • Hot work die steel is mainly divided into hot forming die, hot extrusion die and pressure casting die. In actual working conditions, these molds will not only withstand high temperature and high load, but also withstand rapid cold and hot temperature changes, so it is easy to cause thermal fatigue cracks.
  • the level of thermal fatigue resistance directly affects the service life of hot work die steel [1].
  • Literature studies have shown [2] that increasing the high-temperature strength and toughness of materials can increase the fatigue resistance of the material and thus increase the fatigue life. This is because high strength can reduce the plastic strain amplitude of each thermal cycle and better toughness makes local The stress concentration is relaxed; there are studies [3] that high strength can delay the fatigue crack initiation of die steel and high plastic toughness can delay the growth of thermal fatigue cracks.
  • the temperature in winter in many areas can be as low as -40°C, and the -40°C low-temperature toughness of the material needs to be improved to ensure that the mold material is safer in service.
  • many large-scale hot-work die products are large in size, so hot-work die steel requires high hardenability to ensure consistent microstructure and performance inside and outside the mold.
  • 700°C high temperature strength needs to be increased to 350MPa
  • -40°C V-shaped hole impact energy needs to reach 30J or more
  • hardenability reaches the current traditional Hot work die steel level.
  • Hot traditional die steel is mainly divided into three categories: high alloy hot die steel, medium alloy hot die steel and low alloy hot die steel.
  • Literature [4] reported that high-alloy hot work die steel 3Cr2W8V, 700°C high temperature tensile strength 415MPa; medium-high alloy hot work die steel H13, 700°C high temperature tensile strength of 292MPa; low alloy hot work die steel 5CrMnMoSiV steel, its 700 °C high temperature tensile strength is 137MPa.
  • the room temperature impact toughness of 3Cr2W8V and H13 are 13J and 21J, respectively, and the room temperature impact toughness of 5CrMnMoSiV steel is 34.7J.
  • the low-temperature impact toughness of the three materials at -40°C is lower than that at room temperature, generally only 1/2-1/3 of room temperature. To sum up, it shows that the existing hot work die steel cannot meet the requirements of low temperature high toughness and high temperature high strength at the same time.
  • Literature 1 Xia Pengcheng, Chen Yunbo, Ge Xueyuan, et al. Research status and development trend of thermal fatigue properties of hot work die steels[J]. Heat Treatment of Metals. 2008(12):1-6.
  • Literature 2 Feng Xiaozeng, Liu Jianhong. Thermal fatigue mechanism and thermal fatigue resistance difference of 3Cr2W8V and 4Cr5MoSiVl steel[J].Journal of Anhui Institute of Technology.1988(2):1-9.
  • Literature 3 Liu Jianhong. Research on the thermal fatigue mechanism of hot work die steel 3Cr2W8V4Cr5MoSiV1[D].1987.
  • Literature 4 Zhu Zongyuan. Performance Data Collection of Hot Work Die Steel in China (Continued II)[J].Materials for Mechanical Engineering,2001(3).
  • the present invention adopts the principle of multiple composite strengthening to provide a low-temperature, high-toughness, high-temperature, high-strength, and high-hardenability hot die steel. Its advantage lies in the use of low carbon
  • the structure control technology of design and preparation of medium and low alloy composition makes it have low temperature, high toughness, high temperature, high strength and high hardenability.
  • the present invention proposes a low-carbon, low-alloy hot mold steel with low temperature, high toughness, high temperature, high strength, and high hardenability.
  • the hot mold steel includes the following components: C: 0.15-0.35%, Si : 0.40-0.90%, Mn: ⁇ 0.80%, Cr: 1.50-2.40%, Ni: 2.50-4.50%, Mo: 1.00-1.60%, V: 0.10-0.40%, W: 0.20-0.90%, P: ⁇ 0.02%, S ⁇ 0.02%, the rest is the matrix Fe and inevitable impurities, the above% is the mass percentage.
  • One embodiment is to add 0.01-0.03% Zr, 0.10-0.50% Co, 0.001-0.005% B, 0.01-0.05% Nb, or 0.01-0.10% in addition to the above main components based on the mass ratio. Re.
  • a method for preparing the above-mentioned hot die steel which includes the following steps: (1) a smelting process; (2) a homogenization annealing and forging process; (3) a post-forging annealing process; (4) Quenching and tempering process.
  • the smelting process is carried out through the electric furnace + external refining + vacuum degassing (EAF+LF+VD) plus electroslag remelting (ESR) process.
  • EAF+LF+VD electric furnace + external refining + vacuum degassing
  • ESR electroslag remelting
  • the mass percentage content of each component is as claimed The content of each ingredient in 1 or 2.
  • One embodiment is that during the smelting process, the burned rare earths still need to be supplemented during the electroslag remelting process, and the content is guaranteed to be above 0.01%.
  • One embodiment is that in the homogenization annealing and forging process, the steel ingot of step (1) is heated for at least 5h to 1200-1250°C, kept for 15-25h, and then lowered to the heating temperature of 1130-1200°C, and kept 2- 3h; when forging billet, the forging temperature of forging and drawing is 1050-1130°C, the final forging temperature is ⁇ 850°C, the upsetting is 1-3 times longer, and the upsetting ratio is greater than 2.
  • One embodiment is that in the homogenization annealing and forging processes, GFM precision forging or other forging methods are performed as needed.
  • the heating temperature for precision forging is 900-1050°C, the initial forging temperature is 850-950°C, and the final forging temperature is ⁇ 800°C;
  • the heating temperature for hydraulic hammer or hydraulic press is 1150-1200°C, the initial forging temperature is 1130-1160°C, and the final Forging temperature ⁇ 850°C.
  • step (2) is immediately put into the furnace, heated to 850-900°C at a heating rate of not more than 100°C/h, and then kept for 6-8h, and then the furnace is cooled to The preforms are obtained from the furnace and pile cooling below 500°C.
  • the preform of step (3) is quenched and tempered, and the quenching process is to heat the preform to 920-980°C and keep it for 1-6 hours, and then water or oil cooling to ensure the temperature of the preform It is about 50-150°C, and then immediately tempered.
  • the tempering can be divided into two times, the temperature is selected according to the required mechanical properties of the final product, and then the product performance parameters are tested, and the second tempering temperature and time are determined according to the test results.
  • the material of the present invention adopts low-carbon and low-alloy components, and its high temperature strength reaches the high temperature strength of medium and high carbon hot mold steel, and the low temperature toughness of -40°C reaches the low temperature toughness of low carbon hot mold steel. Hardenability is also very excellent.
  • Figure 1 is the structure and carbide analysis of the quenched and tempered steel of the present invention: (a) structure morphology; (b) carbide morphology; (c) carbide diffraction pattern; (d) carbide high-resolution morphology .
  • composition design of the present invention adopts the chemical composition of low-carbon and low-alloy elements, relying on alloying elements such as Cr, Mo, W, V and C to form dispersed carbides, and the formed alloy carbides and maintaining a good orientation relationship with the matrix can be guaranteed
  • alloying elements such as Cr, Mo, W, V and C
  • the high temperature strength of the material, and its strength depends on the joint strengthening of W/Mo.
  • the specific high temperature strength of the material of the present invention is shown in Table 2.
  • the structure after quenching and tempering is lath martensite instead of acicular martensite, so the low temperature toughness is better.
  • rare earth, Mn, Si and other alloying elements are added to improve the purity of the material, thereby improving the toughness of the material.
  • the specific -40°C low temperature toughness data is shown in Table 3.
  • Carbon is the most basic element in steel, which determines the hardness and strength of martensite after quenching.
  • the quenched structure of low carbon steel is dislocation martensite, which not only has high toughness, but also has certain plastic deformation ability, which can reduce the formation of quenching cracks.
  • the carbon content needs to be controlled to exceed 0.15%.
  • the carbon content exceeds 0.35%, acicular martensite will be formed after quenching, which will cause high stress and reduce low temperature toughness , So the carbon content is designed as: 0.15-0.35%.
  • Ni Nickel can improve the hardenability and low-temperature toughness of steel. When Ni is combined with Cr, W, and Mo, the hardenability can be increased, which can ensure that the large section steel obtains better strength and plasticity after quenching and quenching and tempering treatment. Cooperate. When the Ni content is less than 2.5%, the material has insufficient low-temperature toughness at -40°C, but adding more than 4.5% of Ni content will cause carbides to precipitate along the austenite grain boundaries during quenching, which will adversely affect the corrosion resistance of the steel. Therefore, the Ni content is designed to be 2.50-4.50%.
  • Chromium is a medium carbide forming element. Among all kinds of carbides, chromium carbide is the smallest one. It can be evenly distributed in the volume of steel, so it has high strength, hardness, yield point and high The abrasion resistance. When Cr is greater than 2.4%, it will have an adverse effect on toughness and precipitation, especially low temperature toughness; when the content of Cr is less than 1.5%, it will affect the corrosion resistance and oxidation resistance of the material, so the Cr in this steel: 1.50-2.40% .
  • Mo has a good effect of refining grains, increasing the strength of steel without reducing plasticity, and can improve the impact toughness of steel. And the combination with Cr and Ni can significantly improve the hardenability. However, when the Mo content is less than 1.0%, the grain size will be larger. When the Mo content is higher than 1.6%, ferrite delta phase or other brittle phases are likely to appear, making the -40°C low temperature toughness less than 30J, so the Mo content choose 1.00-1.60%.
  • V Vanadium is a strong carbide forming element, which can improve the stability of its carbides, effectively prevent the growth of austenite grains, obtain a refined martensite structure after quenching, and improve temper toughness. Studies have shown that V A content exceeding 1% will have an adverse effect on toughness, while a too high V content is detrimental to hardenability, and the depth of the quenched layer in the end quenching test cannot reach 200mm. In order to ensure the toughness and hardenability of the material, the V content is designed to be 0.10-0.40%.
  • W Tungsten not only improves the hardenability of the material, but also improves the thermal strength, thermal stability and high temperature strength of steel.
  • the first method is to improve the red hardness of the steel matrix by solid solution, and the second is to form special carbides (M 2 C, MC) for secondary hardening.
  • M 2 C, MC special carbides
  • the combination of tungsten and molybdenum can improve the thermal stability of steel.
  • Mo is an alloy element that is easy to oxidize.
  • the addition of tungsten can inhibit the oxidation and volatilization of Mo, but when the tungsten content exceeds 1.0%, the thermal strength will not be significantly improved.
  • the low-temperature toughness of the steel will decrease. Therefore, the content of W in the steel of the present invention is controlled to 0.20-0.90%.
  • Zr Zirconium is a powerful deoxidizing and denitrifying element in the steelmaking process. Adding a small amount of Zr can combine with oxygen and nitrogen during the smelting process to form fine and dispersed oxides and nitrides in the matrix, which is beneficial to refine the grain structure. Zr element can also combine with impurity element S to form sulfide, preventing the hot brittleness of steel. Therefore, in order to obtain a finer and purer steel, the Zr content can be controlled as follows: 0.01-0.04%.
  • Si It can be used as a reducing agent and a deoxidizer in the steelmaking process, which can increase the annealing, normalizing and quenching temperature, and improve the hardenability in the hypoeutectoid steel. Moreover, silicon can significantly increase the elastic limit, yield point and tensile strength of steel, and at the same time, increase the content of Si so that the structure can be transformed into lath ferrite and the retained austenite film between the laths. Carbide bainite structure, the structure not only has high strength, high hardness, but also has high low temperature impact toughness, so the Si content is 0.40-0.90%.
  • Mn In an appropriate amount, an increase in manganese content can increase the strength and hardness of steel, have the effects of deoxidation and desulfurization, and can replace part of nickel to improve material hardenability and reduce material costs. However, if the Mn content is too high, the corrosion ability and welding performance will be deteriorated, so the Mn content does not exceed 0.80%.
  • Re Rare earth can control the form of sulfide in steel, deoxidize and desulfurize at the same time, improve transverse performance and low temperature toughness. There is also a dispersion hardening effect in low-sulfur steel. Therefore, in order to deoxidize and desulfurize steel to purify molten steel and improve the strength and toughness of steel, 0.01-0.03% Re can be added.
  • Co Like nickel and manganese, cobalt can form a continuous solid solution with iron, which can hinder and delay the precipitation and aggregation of carbides in other alloys during the tempering process, and can significantly improve the thermal strength of the material, but the cobalt element reduces the quenching of martensitic steel Permeability, it is not advisable to add too much, so the design amount is: 0.10-0.50%.
  • B In a certain range, boron has a very strong ability to improve hardenability, but it does not improve hardenability much after more than 0.005%; it plays a role in strengthening the grain boundary in steel and can significantly improve the high-temperature strength of the material. Therefore, the design amount is: 0.001-0.005%.
  • S and P As impurity elements, both have a large adverse effect on the toughness of the material. Therefore, the content of S and P should be reduced, so the content of S and P should be controlled to less than 0.02%.
  • Scrap steel and pure iron can be selected according to the specific working conditions and purity requirements of the barrel.
  • the present invention has made key improvements in composition content and technology.
  • composition through the compound action of Cr, Mo, W, V and other elements, MC type alloy carbides are formed, so that they can maintain a coherent orientation relationship with the matrix to a high temperature. So as to obtain high temperature and high strength; low carbon and high Ni design to form lath martensite/sortenite structure to obtain low temperature and high toughness, while adding rare earth, Mn, Si and other alloying elements to improve the purity of the material, which can further improve the material
  • the toughness through the right amount of W, Mo, Ni, Cr, Mn and other elements to ensure hardenability.
  • Process According to the characteristics of the large-size steel ingot of the present invention, the post-forging annealing and quenching and tempering processes (temperature, time) are adjusted to achieve the best performance matching.
  • the existing technology has solved the problem that it is difficult to have both the low-temperature high-impact toughness and high-temperature high-strength of hot mold steel, and the hardenability can reach the level of H13 steel, which is suitable for the preparation of large-scale molds. .
  • the present invention provides a low-carbon, low-alloy hot mold steel with low temperature, high toughness, high temperature, high strength and high hardenability.
  • the specific preparation process includes the following steps:
  • step (1) Heat the steel ingot of step (1) for at least 5h to 1200-1250°C, keep it for 15-25h, then lower the temperature to the heating temperature of 1130-1200°C, keep it for 2-3h, and perform forging with a hydraulic press.
  • the forging temperature is 1050-1130°C.
  • the heating temperature for precision forging is 900-1050°C, the initial forging temperature is 850-950°C, and the final forging temperature is ⁇ 800°C; the heating temperature for hydraulic hammer or hydraulic press is 1150-1200°C, the initial forging temperature is 1130-1160°C, and the final Forging temperature ⁇ 850°C.
  • Post-forging annealing process Put the precision forging steel ingot of step (2) into the furnace immediately, heat it to 850 ⁇ 870°C at a heating rate of not more than 100°C/h, then keep it for 6 ⁇ 8h, and then cool it to 500°C. The pile is cold from the furnace below °C.
  • the prefabricated steel ingot of step (3) is quenched and tempered.
  • the quenching process is to heat the material to 920-980°C and keep it for 1-6h, and then water or oil cooling to ensure that the material temperature is 50-150°C
  • immediately perform one or two tempering and select the tempering temperature according to the required mechanical properties of the final product, such as 580°C, 4-10 hours tempering, and then test the hardness and toughness, etc., and determine the second tempering temperature based on the test results With time.
  • a preparation method of low temperature, high toughness, high temperature, high strength and high hardenability hot mold steel the specific steps are:
  • step (3) The electroslag ingot obtained in step (2) is heated for at least 5h to 1260°C, kept for 8h, and then cooled to 1200°C for billet forging.
  • the billet is opened by hydraulic press, the initial forging temperature is 1200°C, and the final forging The temperature is 850°C, the upsetting is repeated once and the upsetting ratio is greater than 2.
  • the material is returned to the furnace and heated to 1160 ⁇ 850°C at 100°C/h and then kept for 1h. Then the material is formed using a precision forging machine, the initial forging temperature is 1160°C, and the final forging temperature is 800°C.
  • step (4) Put the steel ingot of step (4) into the furnace immediately after the precision forging, heat it to 860°C at a heating rate of not more than 100°C/h, and then heat it for 6 hours, and then cool the furnace to below 500°C and release it from the furnace.
  • step (5) The prefabricated steel ingot of step (5) is quenched and tempered.
  • the quenching process is to heat the material to 930-980°C and hold for 1 hour, then water or oil cooling to ensure that the material temperature is about 200°C, and then at 520-620°C It is tempered within the range, and the hardness after tempering is 45HRC.
  • Fig. 1 shows the structure and carbide morphology of Example 5 of the steel of the present invention after quenching at 980°C and tempering at 620°C for 4 hours. It can be seen from Figure (a) that it is a lath tempered sorbite structure, and Figures (b) and (c) show that there are flaky MC carbides dispersed in the lath. From the high-resolution morphology of Figure (d), it can be seen that the formed MC-type carbide maintains a good coherent relationship with the matrix, so its coherent relationship can be maintained to a high temperature to obtain high temperature and high strength.
  • Performance test The mechanical properties and hardenability tests of the low temperature, high toughness, high temperature, high strength and high hardenability hot mold steels of Examples 1-6.
  • the materials of Comparative Examples 1, 2 and 3 are H13 steel, 5CrMnMoSiV and 3Cr2W8V steel, respectively. Among them, the hardenability was tested in Example 1 and Example 4 and compared with H13 steel.
  • the relevant test standards and specific test data are shown in Table 3-4:
  • the high temperature strength of the material of the present invention at 700°C is higher than H13 and 5CrMnMoSiV hot work die steel, and some examples are even higher than the high alloy hot work die steel 3Cr2W8V steel, indicating that the steel of the present invention has excellent high temperature strength.
  • the impact toughness at room temperature of the material of the present invention is higher than that of Comparative Examples 1, 2 and 3.
  • the impact toughness at -40°C of the material of the present invention in Examples 1-3 is even higher than the room temperature toughness of the hot mold steels of the three comparative examples. Usually much lower than normal temperature toughness, so the low temperature toughness of the material of the present invention is much higher than the comparative steel.
  • the room temperature tensile strength of the steel of the present invention can be adjusted in the range of 1200 MPa to 1600 MPa by adjusting the heat treatment process according to the requirements of the working conditions, while ensuring that the high temperature strength is basically stable.
  • Example 1 and Example 2 compare the upper and lower limits of the composition of the material of the present invention.
  • Example 3 Example 4 and Example 5 were compared and studied the Cr, Mo and Ni elements of the material of the present invention.
  • Example 2 Example 3 and Example 5 were compared and studied the V and W elements of the materials of the present invention.
  • Example 2 and Example 6 were compared to study the trace elements Re, Nb, Zr, Co and B elements added in the material of the present invention.
  • the material of the present invention can be applied to special working conditions requiring low temperature, high toughness, high temperature, high strength, and high hardenability, and has good industrial applicability.

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Abstract

一种低温低韧高温高强及高淬透性热模钢，所述热模钢包括以下组分：C：0.15-0.35％，Si：0.40-0.90％，Mn≤0.80％，Cr：1.50-2.40％，Ni：2.50-4.50％，Mo:1.00-1.60％，V:0.10-0.40％，W:0.20-0.90％，P≤0.02％，S≤0.02％，其余为基体Fe和不可避免的杂质，以上％为质量百分比。经调质处理后材料的-40℃的V型孔低温冲击功可达到30J以上，其700℃高温强度可达到380MPa以上，淬透性可达200mm以上，保证其组织内外均匀。该材料可适用于要求低温高韧性高温高强度以及高淬透性的特殊工况的热作模具。

Description

一种低温高韧高温高强及高淬透性热模钢及制备技术 技术领域
本发明属于模具钢技术领域，尤其涉及一种低温高韧高温高强及高淬透性热模钢及制备技术。
背景技术
热作模具钢主要分为热成形模、热挤压模和压力铸造模具，这些模具在实际工况下除了承受高温高载荷外，还会承受急冷急热的温度变化，因此容易引起热疲劳裂纹，热疲劳抗力的高低直接影响热作模具钢的使用寿命[1]。文献研究表明[2]，提高材料的高温强度和韧性可以提高材料的疲劳抗力从而提高疲劳寿命，这是由于高的强度可减少每一热循环的塑性应变幅和较好的韧性则使局部的应力集中得到松弛；还有研究认为[3]，高的强度可以延缓模具钢的疲劳裂纹萌生和高的塑韧性可以延缓热疲劳裂纹的扩展。而且，许多地区冬天温度可低至-40℃，需提高材料的-40℃低温韧性保证模具材料服役更加安全。另外，很多大型热作模具产品尺寸较大，因此热作模具钢需要高淬透性保证模具内外组织性能一致。综上所述，为提高热作模具钢使用寿命而提出以下新的要求：700℃高温强度需提高至350MPa，-40℃的V形孔冲击功需达到30J以上，淬透性达到现用传统热作模具钢水平。
热传统作模具钢主要分为三类：高合金热模钢、中合金热模钢和低合金热模钢。文献[4]报道，高合金热作模具钢3Cr2W8V，700℃高温抗拉强度415MPa；中高合金热作模具钢H13，700℃高温抗拉强度为292MPa；低合金热作模具钢5CrMnMoSiV钢，其700℃高温抗拉强度为137MPa。3Cr2W8V和H13两种材料的常温冲击韧性分别为13J和21J，5CrMnMoSiV钢的室温冲击韧性34.7J。因此，三种材料-40℃低温冲击韧性与其室温相比会更低，一般仅室温的1/2-1/3。综上说明现有热作模具钢不能同时满足低温高韧性和高温高强度的要求。
随着经济和工业的发展，模具服役条件日益苛刻，同时为使该热作模具钢可以在极冷地区的安全使用，现代制造业对模具的高温强度、低温韧性和淬透 性提出更高的要求。因此，需同时具有低温高韧、高温高强及高淬透性的热模钢。
文献1：夏鹏成，陈蕴博，葛学元，等.热作模具钢热疲劳性能的研究现状与发展趋势[J].金属热处理.2008(12):1-6.
文献2：冯晓曾，刘剑虹.3Cr2W8V、4Cr5MoSiVl钢热疲劳机理及热疲劳抗力的差异[J].安徽工学院学报.1988(2):1-9.
文献3：刘剑虹.热作模具钢3Cr2W8V4Cr5MoSiV1热疲劳机理的研究[D].1987.
文献4：朱宗元.我国热作模具钢性能数据集(续Ⅱ)[J].机械工程材料,2001(3).
发明内容
发明要解决的技术问题
本发明针对现有技术不足，热作模具钢在低温环境服役的安全性，采用多元复合强化原理，提供一种低温高韧高温高强及高淬透性热模钢，其优势在于，采用低碳和中低合金成分设计与制备的组织调控技术，使之具有低温高韧性、高温高强度和高淬透性。
用于解决技术问题的方法
针对上述问题，本发明提出了一种具有低温高韧性、高温高强度及高淬透性的低碳低合金热模钢，所述热模钢包括以下组分：C：0.15-0.35％，Si：0.40-0.90％，Mn：≤0.80％，Cr：1.50-2.40％，Ni：2.50-4.50％，Mo:1.00-1.60％，V:0.10-0.40％，W:0.20-0.90％，P:≤0.02％，S≤0.02％，其余为基体Fe和不可避免的杂质，以上％为质量百分比。
一种实施方式为，以质量比计，除以上主要成分以外还可添加0.01-0.03％的Zr、0.10-0.50％的Co、0.001-0.005％的B、0.01-0.05％Nb或0.01-0.10％的Re。
根据本发明的第二方面，提供一种上述的热模钢的制备方法，其包括以下 步骤：(1)冶炼工序；(2)均质化退火及锻造工序；(3)锻后退火工序；(4)调质工序。
一种实施方式为，冶炼工序中，通过电炉+炉外精炼+真空脱气(EAF+LF+VD)加电渣重熔(ESR)工艺冶炼，冶炼工序中，各成分质量百分比含量如权利要求1或2中各成分含量。
一种实施方式为，冶炼工序中，在电渣重熔过程中仍需补充烧损的稀土，保证含量0.01％以上。
一种实施方式为，均质化退火及锻造工序中，将步骤(1)的钢锭加热至少5h升温至1200-1250℃，保温15-25h，随后降温到加热温度1130-1200℃，保温2-3h；锻造开坯时，锻拔的开锻温度1050-1130℃，终锻温度≥850℃，镦粗拔长1-3次，镦粗比大于2。
一种实施方式为，均质化退火及锻造工序中，根据需要，进行GFM精锻或其它锻造方式成型。精锻加热温度为900-1050℃，始锻温度为850-950℃，终锻温度≥800℃；液压锤或油压机成型的加热温度为1150-1200℃，始锻温度为1130-1160℃，终锻温度≥850℃。
一种实施方式为，锻后退火工序中，将步骤(2)的锻件立即入炉，以不大于100℃/h的加热速率加热到850～900℃后进行保温6-8h，然后炉冷至500℃以下出炉堆冷，得到预制件。
一种实施方式为，调质工序中，将步骤(3)的预制件进行调质，淬火工艺为将预制件加热到920-980℃后保温1-6h，随后水冷或油冷确保预制件温度为50-150℃左右，然后立即进行回火。
一种实施方式为，回火可分两次，根据最终产品需要的力学性能选择温度，然后测试产品性能参数，根据测试结果，确定第二次回火温度与时间。
本发明的有益效果
与现有热模钢相比，本发明材料采用低碳低合金成分，其高温强度达到了中高碳热模钢的高温强度，-40℃低温韧性达到了低碳热模钢的低温韧性，其淬 透性也非常优异。
从以下示例性实施方案的描述中，本发明的进一步特征将变得显而易见。
附图说明
图1是本发明钢调质态的组织形貌与碳化物分析：(a)组织形貌；(b)碳化物形貌；(c)碳化物衍射花样；(d)碳化物高分辨形貌。
具体实施方式
以下对本公开的一个实施方式具体地说明，但本公开并非限定于此。
具体原理如下：
1、本发明成分设计上采用低碳低合金元素化学成分，依靠Cr、Mo、W、V等合金元素与C元素形成弥散碳化物，形成的合金碳化物和与基体保持良好位向关系可以保证材料的高温强度，而其强度取决于W/Mo的共同强化。具体本发明材料高温强度如表2所示。
2、由于本发明材料的碳含量低和Ni含量较高，调质处理后的组织是板条状马氏体而非针状马氏体，因此低温韧性较好。同时加入稀土、Mn、Si等合金元素来提高材料纯净化，从而提高材料的韧性，具体-40℃低温韧性数据如表3所示。
3、本发明材料中加入适量的W、Mo、Ni、Cr、Mn等合金元素可以显著提高材料的淬透性，具体淬透性数据如表4所示。
下面对本发明钢各构成元素作用及含量范围的选择进一步说明，在以下的说明中，元素的添加量以质量比(％)表示：
C：碳是钢中最基础的元素，决定着淬火后马氏体的硬度和强度。低碳钢淬火组织为位错马氏体，不仅韧性高，还有一定塑性变形能力，可以减轻淬火裂纹的形成。当碳含量较低时会导致淬透性差和强度不足，因此需要碳含量控制超过0.15％，当碳含量超过0.35％上时，淬火后会形成针状马氏体，应力大且导致低温韧性降低，故含碳量设计为：0.15-0.35％。
Ni：镍能提高钢的淬透性和低温韧性，Ni同Cr、W、Mo元素相结合时，淬透性可增高，可保证大截面钢淬火和调质处理后获得较好的强度和塑性配合。当Ni含量低于2.5％时，材料-40℃低温韧性不足，但加入超过4.5％的Ni含量会导致碳化物在淬火时沿奥氏体晶界析出，对钢的耐蚀性产生不利影响。故Ni含量设计为：2.50-4.50％。
Cr：铬是中等碳化物形成元素，在所有各种碳化物中，铬碳化物是最细小的一种，它可均匀地分布在钢体积中，所以具有高的强度、硬度、屈服点和高的耐磨性。Cr大于2.4％以后对韧性和析出相会有不利影响，尤其是低温韧性；当Cr含量低于1.5％时会影响材料的耐腐蚀性和抗氧化性能，故本钢中Cr：1.50-2.40％。
Mo：钼具有良好的细化晶粒作用，提高钢的强度而塑性不降低，且可提高钢的冲击韧性。且与Cr、Ni相结合可显著提高淬透性。但Mo含量低于1.0％时，晶粒度会较大，当Mo含量高于1.6％时容易出现铁素体δ相或其它脆性相而使-40℃低温韧性达不到30J，故Mo含量选择1.00-1.60％。
V：钒为强碳化物形成元素，可提高其碳化物的稳定性，有效地阻止奥氏体晶粒长大，淬火后得到细化的马氏体组织，改善回火韧性，有研究表明V含量超过1％会对韧性产生不利影响，而V含量太高对淬透性有不利，其端淬试验的淬透层深度达不到200mm。为了保证材料的韧性和淬透性，故V含量设计为：0.10-0.40％。
W：钨不仅提高材料的淬透性，更能提高钢的热强性、热稳定性和高温强度。其方式一是通过固溶提高钢的基体红硬性，二是形成特殊碳化物(M 2C，MC)起二次硬化作用。钨与钼配合可提高钢的热稳定性，Mo是易于氧化的合金元素，钨的加入可以抑制Mo的氧化与挥发，但当钨含量超过1.0％时，热强性不会再有明显提高，而钢的低温韧性会有所下降，因此，本发明钢中W含量控制为0.20-0.90％。
Zr：锆在炼钢过程中强有力的脱氧和脱氮元素，加入少量Zr能在冶炼过程中与氧氮结合形成基体中细小弥散分布的氧化物与氮化物，有利于细化晶粒组织。Zr元素还能与杂质元素S结合生成硫化物，防止钢材的热脆性。因此，为获得组织细小且更为纯净的钢，故Zr含量可控制为：0.01-0.04％。
Si：在炼钢过程中可作为还原剂和脱氧剂存在，可提高退火、正火和淬火温度，在亚共析钢中提高淬透性。而且，硅能够显著提高钢的弹性极限，屈服点和抗拉强度，同时提高Si含量可使组织在转变过程中得到由板条状铁素体及其板条间残余奥氏体膜组成的无碳化物贝氏体组织,该组织既具有高强度、高硬度,又具有较高的低温冲击韧性，因此Si含量在0.40-0.90％。
Mn：在适量下，锰含量增加可提高钢的强度和硬度，有脱氧及脱硫的功效，并且可以代替一部分镍提高材料淬透性，降低材料成本。但是Mn含量太高，腐蚀能力和焊接性能会变差，因此Mn含量不超过0.80％。
Re：稀土在钢中可以控制硫化物的形态，同时脱氧，脱硫，提高横向性能及低温韧性。在低硫钢中还有弥散硬化作用。因此，为使钢脱氧脱硫净化钢液，提高钢的强韧性，可加入0.01-0.03％Re。
Co：钴同镍锰一样和铁能形成连续固溶体，可以在回火过程中阻碍、延缓其它合金碳化物的析出和聚集，可显著提高材料的热强性，但钴元素降低马氏体钢淬透性，故不宜添加过量，故设计量为：0.10-0.50％。
B：在一定范围内，硼提高淬透性的能力极强，但超过0.005％后对淬透性的提高不大；在钢中起到强化晶界的作用，可显著提高材料的高温强度，故设计量为：0.001-0.005％。
S、P:作为杂质元素，均对材料韧性产生较大的不利影响。因此应降低S、P含量，故S、P含量控制在小于0.02％。
Fe：为基体元素，可根据身管的具体使用工况以及纯净度等要求来确定选择采用废钢和纯铁。
本发明从成分含量和工艺上进行了关键改进，成分上：通过Cr、Mo、W、V等元素复合作用，形成MC型合金碳化物，使其可与基体保持共格位向关系至高温，从而获得高温高强度；通过低碳高Ni设计以形成板条马氏体/索氏体组织以获得低温高韧性，同时加入稀土、Mn、Si等合金元素来提高材料纯净化，可进一步提高材料的韧性；通过适量的W、Mo、Ni、Cr、Mn等元素以保证淬透性。工艺上：针对本发明钢大尺寸钢锭的特点，对锻后退火和调质工艺(温度、时间)进行了调整，使之获得最佳性能匹配。
通过上述关键改进，解决了现有技术中对于热模钢的低温高冲击韧性和高温高强度二者难以兼具的问题，且淬透性可达H13钢的水平，可适用于大型模具的制备。
本发明提供了一种低温高韧高温高强及高淬透性的低碳低合金热模钢，具体制备工艺包括以下步骤：
(1)通过电炉+炉外精炼+真空脱气(EAF+LF+VD)加电渣重熔(ESR)等工艺冶炼，按成分质量百分比：
C：0.15-0.35％，Si：0.40-0.90％，，Mn：≤0.80％，Cr：1.50-2.450％，Ni：2.50-4.50％，Mo:1.00-1.60％，V:0.10-0.40％，W:0.20-0.90％，P:≤0.02％，S≤0.02％，除以上主要成分以外还可根据性能要求的不同适当添加Zr：0.01-0.03％，Co:0.10-0.50％，B:0.001-0.005％，Nb:0.01-0.03％,Re：0.01-0.10％，其余为基体Fe。在电渣重熔过程中仍需补充烧损的稀土，保证含量0.01％以上，因为稀土在电渣重熔过程中容易挥发。
(2)均质化退火+锻造工艺：
将步骤(1)的钢锭加热至少5h升温至1200-1250℃，保温15-25h，随后降温到加热温度1130-1200℃，保温2-3h油压机进行锻拔，开锻温度1050-1130℃，终锻温度≥850℃，镦粗拔长1-3次，镦粗比大于2。随后根据需要，进行GFM精锻或其它锻造方式成型。精锻加热温度为900-1050℃，始锻温度为850-950℃， 终锻温度≥800℃；液压锤或油压机成型的加热温度为1150-1200℃，始锻温度为1130-1160℃，终锻温度≥850℃。
(3)锻后退火工艺：将步骤(2)的精锻后钢锭立即入炉，以不大于100℃/h的加热速率加热到850～870℃后进行保温6～8h，然后炉冷至500℃以下出炉堆冷。
(4)调质工艺：将步骤(3)的预制钢锭进行调质，淬火工艺为将材料加热到920-980℃后进行保温1-6h，随后水冷或油冷确保材料温度为50-150℃左右，然后立即进行一到两次回火，根据最终产品需要的力学性能选择回火温度，如580℃、4-10小时回火，然后测试硬度韧性等，根据测试结果，确定第二次回火温度与时间。
实施例
通过实施例更详细地描述本发明，但本发明不限于下述实施例。需要说明的是，只要不特别声明，“份”表示“质量份”。
实施例1-6的具体合金元素成分如表1所示。
一种低温高韧高温高强及高淬透性热模钢的制备方法，具体步骤为：
(1)按照表1中实施例1-6的化学成分进行配料。成分
(2)将配料(1)所配物料进行电炉-精炼(LF+VD)加电渣重熔等工艺冶炼。
(3)将步骤(2)中的到的电渣锭加热至少5h升温至1260℃，保温8h，随后冷到1200℃进行开坯锻造，开坯采用油压机，始锻温度采用1200℃，终锻温度850℃，反复镦粗拔长1次，镦粗比大于2。开坯后材料回炉以100℃/h升温至1160～850℃然后保温1h，然后材料成型采用精锻机，始锻温度1160℃，终锻温度800℃。
(5)将步骤(4)的精锻后钢锭立即入炉，以不大于100℃/h的加热速率加热到860℃后进行保温6h，然后炉冷至500℃以下出炉堆冷。
(6)将步骤(5)的预制钢锭进行调质，淬火工艺为将材料加热到930-980℃后进行保温1h，随后水冷或油冷确保材料温度为200℃左右，然后在520-620℃范围内进行回火，回火后硬度为45HRC。
本发明钢实施例5在980℃淬火，620℃回火4小时后的组织与碳化物形貌如图1所示。由图(a)可知，其为板条状回火索氏体组织，由图(b)和(c)可知，板条内弥散分布着片状MC型碳化物。由图(d)的高分辨形貌可知，形成的MC型碳化物与基体保持良好的共格关系，因此其共格关系可保持至高温从而获得高温高强度。
性能测试：实施例1-6的低温高韧高温高强及高淬透性热模钢力学性能和淬透性测试，对比例1、2和3的材料分别为H13钢、5CrMnMoSiV和3Cr2W8V钢。其中淬透性采用实施例1和实施例4进行测试并与H13钢进行对比。相关测试标准和具体测试数据如下表3-4所示：
(1)根据HB 5278-1984《金属低温冲击韧性试验方法》对以下各实施例及对比例进行试验，测定-40℃的V型冲击韧功。
(2)高温拉伸力学性能试验方法参考GB/T4338-2006，测试700℃抗拉强度及屈服强度。室温拉伸力学性能试验方法参考GB/T 228.1-2010。
(3)淬透性参考端淬试验方法ASTM A255-02。
从表3-4进行对比可以得出以下结论：
(1)通过表3可以看出本发明材料700℃高温强度均高于H13和5CrMnMoSiV热作模具钢，部分实施例甚至高于高合金热作模具钢3Cr2W8V钢，表明本发明钢具有优异的高温强度。本发明材料的常温冲击韧性均高于对比例1、2和3，本发明材料实施例1-3的-40℃冲击韧性甚至高于三种对比例热模钢的常温韧性，由于材料低温韧性通常远低于常温韧性，因此本发明材料的低温韧性远高于对比例钢。本发明钢的室温抗拉强度可根据工况要求通过调整热处理工艺实现1200MPa～1600MPa范围可调，同时保证高温强度基本保持稳定。
(2)通过表4可以看出本专利的上下限成分材料随着距端淬面的距离增加，其硬度下降程度相当，说明本发明材料的淬透性可达到H13钢的水平。
表1 各实施例具体成分表
Figure PCTCN2020091212-appb-000001
注：(1)实施例1和实施例2对比研究本发明材料的成分的上下限。
(2)实施例3、实施例4和实施例5对比研究本发明材料的Cr、Mo和Ni元素。
(3)实施例2、实施例3和实施例5对比研究本发明材料的V和W元素。
(4)实施例2和实施例6对比研究本发明材料添加的微量元素Re、Nb、Zr、Co和B元素。
表2 本发明钢的热处理工艺
Figure PCTCN2020091212-appb-000002
Figure PCTCN2020091212-appb-000003
表3 各实施例和对比例的高温拉伸强度和低温冲击功表
Figure PCTCN2020091212-appb-000004
注：未查到对比例1、2和3的-40℃低温冲击韧性数据，但其常温韧性均低于本发明材料常温韧性。
表4 各实施例和对比例的端淬硬度表
Figure PCTCN2020091212-appb-000005
注：随着距端淬面距离增加，本发明材料硬度下降幅度与H13钢相当。
工业实用性
本发明的材料可适用于要求低温高韧性高温高强度以及高淬透性的特殊工 况，具有良好的工业实用性。
此实施例仅为本发明较佳的具体实施方式，但本发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的技术范围内，可轻易想到的变化或替换，都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应该以权利要求的保护范围为准。

Claims (10)

  1. 一种具有低温高韧性、高温高强度及高淬透性的低碳低合金热模钢，其特征在于：所述热模钢包括以下组分：C：0.15-0.35％，Si：0.40-0.90％，Mn：≤0.80％，Cr：1.50-2.40％，Ni：2.50-4.50％，Mo:1.00-1.60％，V:0.10-0.40％，W:0.20-0.90％，P:≤0.02％，S≤0.02％，其余为基体Fe和不可避免的杂质，以上％为质量百分比。
  2. 如权利要求1所述的热模钢，其中，以质量比计，除以上主要成分以外还可添加0.01-0.03％的Zr、0.10-0.50％的Co、0.001-0.005％的B、0.01-0.05％Nb或0.01-0.10％的Re。
  3. 如权利要求1-2所述的热模钢的制备方法，其特征在于，包括以下步骤：
    (1)冶炼工序；
    (2)均质化退火及锻造工序；
    (3)锻后退火工序；
    (4)调质工序。
  4. 如权利要求3所述的制备方法，其中，冶炼工序中，通过电炉，炉外精炼，真空脱气加电渣重熔(EAF+LF+VD+ESR)工艺冶炼，冶炼工序中，各成分质量百分比含量如权利要求1或2中各成分含量。
  5. 如权利要求4所述的制备方法，其中，冶炼工序中，在电渣重熔过程中仍需补充烧损的稀土，保证含量0.01％以上。
  6. 如权利要求3所述的制备方法，其中，均质化退火及锻造工序中，将步骤(1)的钢锭加热至少5h升温至1200-1250℃，保温15-25h，随后降温到加热温度1130-1200℃，保温2-3h；锻造开坯时，锻拔的开锻温度1050-1130，终锻温度≥850℃，镦粗拔长1-3次，镦粗比大于2。
  7. 如权利要求3所述的制备方法，其中，均质化退火及锻造工序中，根据需要，进行GFM精锻或其它锻造方式成型；精锻加热温度为900-1050℃，始锻温度为850-950，终锻温度≥800℃；液压锤或油压机成型的加热温度为1150-1200℃，始锻温度为1130-1160℃，终锻温度≥850℃。
  8. 如权利要求3所述的热模钢的制备方法，其中，锻后退火工序中，将步骤(2)的锻件立即入炉，以不大于100℃/h的加热速率加热到850～900℃后进行保温6-8h，然后炉冷至500℃以下出炉堆冷，得到预制件。
  9. 如权利要求3所述的热模钢的制备方法，其中，调质工序中，将步骤(3)的预制件进行调质，淬火工艺为将预制件加热到920-980℃后保温1-6h，随后水冷或油冷确保预制件温度为50-150℃左右，然后立即进行回火。
  10. 如权利要求9所述的热模钢的制备方法，其中，回火可分两次，根据最终产品需要的力学性能选择温度，然后测试产品性能参数，根据测试结果，确定第二次回火温度与时间。
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