CN115570103A - Production method for investment casting of low-carbon low-alloy high-strength structural steel - Google Patents

Production method for investment casting of low-carbon low-alloy high-strength structural steel Download PDF

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CN115570103A
CN115570103A CN202211312490.XA CN202211312490A CN115570103A CN 115570103 A CN115570103 A CN 115570103A CN 202211312490 A CN202211312490 A CN 202211312490A CN 115570103 A CN115570103 A CN 115570103A
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low
percent
casting
temperature
carbon
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马波
邱满元
陈礼年
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Dongfeng Investment Casting Co ltd
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Dongfeng Investment Casting Co ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C9/00—Moulds or cores; Moulding processes
    • B22C9/02—Sand moulds or like moulds for shaped castings
    • B22C9/04—Use of lost patterns
    • 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
    • C21D1/28—Normalising
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C22C33/06—Making ferrous alloys by melting using master alloys
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Continuous Casting (AREA)

Abstract

The invention relates to a production method for investment precision casting of low-carbon low-alloy high-strength cast steel, which comprises the following steps: investment casting shell making and roasting; smelting molten iron; pouring a formwork; and (6) heat treatment. The low-carbon low-alloy high-strength cast steel material prepared by the method has the advantages of yield strength of more than or equal to 750MPa, tensile strength of more than or equal to 800MPa, elongation after fracture of more than or equal to 15 percent and good welding performance.

Description

Production method for investment casting of low-carbon low-alloy high-strength structural steel
Technical Field
The invention relates to a low-alloy carbon structural steel material, which is low-carbon low-alloy high-strength cast steel in consideration of requirements on welding, impact power, fatigue life and the like and is mainly produced by an investment casting process.
Background
The lightweight automobile puts higher requirements on the mechanical properties of automobile part materials, such as static strength, elongation and the like. On the premise that the comprehensive cost is superior to that of aluminum alloy, the iron-based material has a larger use space on an economical vehicle. In addition to some special requirements of heat resistance, wear resistance, impact resistance, shock absorption and the like, the application of the iron-based material on some automobile parts is still indispensable, and further improvement of the performance of the iron-based material is still necessary.
The most used cast iron in the cast iron-based material is various cast irons, and high-performance materials such as austempered ductile iron, high-strength and high-toughness cast iron ductile iron and the like are gradually introduced into parts with higher mechanical property requirements or batch requirements, such as crankshafts, camshafts and the like. However, some of the parts of the automobile have a part of bracket castings which are often used for connecting various assemblies, have higher requirements on strength and toughness, and some parts of the parts also need better weldability. For the parts of the bracket, cast iron is limited by requirements such as weldability and impact toughness, and cast steel is often selected for production. The comprehensive mechanical property of the cast steel parts is improved, and the lightweight automobile is further developed.
At present, low-alloy steel castings or cast carbon steel pieces are generally adopted as automobile part cast steel materials. The higher grade interval specified by GB/T14408 comprises four grades, namely ZGD730-910, ZGD840-1030, ZGD1030-1240 and ZGD1240-1450, but the elongation after fracture standard of the four grades is lower, and the calibration is 8% -4% interval. The elongation rate of the material is more than 12%, the yield strength is lower than 700MPa, and the tensile strength is lower than 900 MPa. The performances of individual grades such as 40Mn2, siMn steel groups, crMo steel groups, 37SiMnMoV, 38CrSi and the like in GB/T699 high-quality carbon structural steel and GB/T3077 alloy structural steel are close to the target mechanical property requirements, but the welding equivalent is overhigh and the weldability is poor, or the steel is different from a more complex heat treatment process of common water quenching and air tempering (such as oil quenching and water or oil tempering cooling), or the casting structural stress is large, cracks easily occur, and the production quality, tempo or cost control requirements of casting enterprises cannot be met.
The invention aims to develop a low-cost cast steel material with yield strength of more than or equal to 750MPa, tensile strength of more than or equal to 800MPa, elongation after fracture of more than or equal to 15 percent and low carbon content (0.25 percent).
Disclosure of Invention
The invention relates to a steel casting component without changing the common low alloy steel quenching and tempering casting blank and the heat treatment production mode of investment casting enterprises and increasing production equipment. The performance of the material can be further improved by optimizing the heat treatment process and the casting process.
The material composition of the invention is:
0.12 to 0.15 percent of C, 0.50 to 0.70 percent of Si, 0.80 to 1.20 percent of Mn, less than or equal to 0.03 percent of S, less than or equal to 0.03 percent of P, 0.60 to 0.70 percent of Cr, 0.10 to 0.15 percent of V, 0.50 to 0.60 percent of Cu and the balance of Fe; the sum of other elements is not more than 0.5%.
The composition designs that Si and Cu mainly play a role in solid solution strengthening of ferrite; part of Mn is dissolved in solid, and part of Mn and iron carbon form complex structure carbide, but the Mn is more prone to dissolving into ferrite when the carbon is low; small amount of V and Cr can easily form VC and Cr carbides 23 C 6 Etc. play a role in refining grains; because the carbon content is low, most Cr atoms enter ferrite to play a role in solid solution strengthening.
The main alloy elements Mn, V, cr, cu and C designed by the composition are elements for reducing Ms point, and Si is used for M S The influence is not obvious, and the design is favorable for the quenching efficiency under the condition of lower C content.
Carbides generated by V, cr and other elements designed by the composition can block the growth speed of austenite grains during normalizing and quenching austenitizing, and are beneficial to refining of a final cooling transformation structure; meanwhile, cr can also increase the tempering temperature during tempering and inhibit the growth of crystal grains.
The main elements Si, mn, V, cr and Cu in the composition design are common elements in the industrial field, are easy to obtain and have low cost. Besides special alloy main materials, other waste materials containing the elements can be adopted for centralized preparation, and the preparation cost is further reduced.
The main smelting materials are low-carbon scrap steel and alloy materials such as ferrosilicon, ferromanganese, ferrochromium, ferrovanadium, copper blocks and the like. The temperature of a smelting furnace is not lower than 1620 ℃, and the casting temperature of a first ladle is not lower than 1580 ℃; the baking temperature of the investment casting shell ranges from 900 ℃ to 950 ℃, the red shell is poured, the temperature of the shell is more than or equal to 750 ℃, and the thickness of the shell can be controlled according to the weight ratio of the shell module to the casting group which is less than or equal to 0.6. The investment shell is beneficial to filling in the early stage of red shell casting, and is fast in heat dissipation due to the fact that the shell is thin in the later stage of solidification and solid phase change, and growth of crystal grains is inhibited.
And normalizing, quenching and tempering the casting blank. Normalizing at 920-940 deg.C, austenitizing at 900-920 deg.C before quenching, and quenching with flowing water at temperature lower than 30 deg.C; tempering at 600-650 deg.C, and cooling in air.
The metallographic structure of the casting after heat treatment is as follows: a tempered sorbite-ferrite mixed structure.
The room temperature mechanical properties of the single cast test block after heat treatment are as follows: the yield strength is more than or equal to 750Mpa, the tensile strength is more than or equal to 800Mpa, the elongation after fracture is more than or equal to 15%, the impact power Akv is more than or equal to 50J, and the surface hardness is 220 to 280HB.
Drawings
FIG. 1 is a metallographic structure diagram (microscopic results at 500 times magnification) of example 1;
fig. 2 is a metallographic structure diagram (microscopic result at 500 times magnification) of example 2.
Detailed Description
The specific implementation comprises molten steel smelting, shell roasting, molten steel pouring and heat treatment.
Example 1
The production method of the investment casting low-carbon low-alloy high-strength cast steel comprises the following steps:
(1) The single-casting GB/T31204 plum blossom test block adopts silica sol and quartz powder as surface layer coating, the mass ratio of the silica sol to the quartz powder is 1.9, the mass ratio of the silica sol to the mullite powder as back layer coating is 1.8, the shell is roasted by using a through type natural gas roasting furnace, the temperature of the roasting furnace is controlled to be 900-950 ℃, and the roasting time is 2.5 hours;
(2) Smelting molten iron: smelting by adopting a 750 kg medium-frequency induction furnace, wherein the furnace burden comprises, by mass, 96.59% of 08# scrap steel, 0.60% of ferrosilicon (FeSi 75), 1.0% of ferromanganese (FeMn78C2.0), 1.05% of ferrochrome (FeCr60C0.06), 0.20% of ferrovanadium (50V), 0.52% of copper block (electrolytic copper), 0.04% of carburant (C98), and iron liquid components in percentage by mass: c:0.13, si:0.56, mn: 0.98, S:0.019, P:0.024, V: 0.61, cu: 0.53, and the balance Fe;
(3) Casting a formwork: and taking the investment shell out of the roasting furnace, and pouring. The tapping temperature of the molten steel is 1635 ℃, the temperature of the investment shell is 780 ℃, the temperature of the first ladle pouring is 1603 ℃, and the molten steel is naturally cooled after pouring;
(4) And (3) heat treatment: and normalizing, quenching and tempering the casting blank. Normalizing at 930 + -5 deg.C for 1.5h, with the temperature before quenching being 914 deg.C, the quenching medium being flowing water, the temperature of the flowing water being 25 deg.C, and quenching being completed within 5 min; controlling the tempering temperature at 630 +/-5 ℃, preserving the heat for 1h, and cooling in the air.
The low-carbon low-alloy high-strength cast steel prepared by the method has a metallographic phase of tempered sorbite and ferrite, a metallographic phase diagram is detailed in the attached figure 1 of the specification, and the mechanical properties are shown in the table 1:
table 1 example 1 mechanical properties of single-cast plum blossom test block
Test bar Tensile strength/MPa Yield strength/Mpa Elongation/percent hardness/HB Impact work Akv/J
1-1 887 828 16.0 235 64
1-2 844 831 18.5 240 63
1-3 822 809 19.0 226 71
Example 2
The production method of the investment casting low-carbon low-alloy high-strength cast steel comprises the following steps:
(1) The single-casting GB/T31204 base test block adopts silica sol and quartz powder as surface layer coating, the mass ratio of the silica sol to the quartz powder is 1.9, the mass ratio of the silica sol to the mullite powder as back layer coating is 1.8, a shell is roasted by using a through natural gas roasting furnace, the temperature of the roasting furnace is controlled to be 900-950 ℃, and the roasting time is 3.5h;
(2) Smelting molten iron: smelting by adopting a 500 kg medium frequency induction furnace, wherein according to the mass percentage, the furnace burden is selected from 08# scrap steel 96.21%, ferrosilicon (FeSi 75) 0.70%, ferromanganese (FeMn78C2.0) 1.1%, ferrochromium (specification FeCr60C0.06) 1.1%, ferrovanadium (50V) 0.25%, copper block (electrolytic copper) 0.58%, carburant (C98) 0.06%, and iron liquid components in percentage by mass: 0.14 percent of C, 0.62 percent of Si, 0.022 percent of P, 0.67 percent of Cr, 0.14 percent of V, and the balance of Fe;
(3) Casting a formwork: and taking the investment shell out of the roasting furnace, and pouring. Through measurement: the tapping temperature of the molten steel is 1628 ℃, the temperature of the investment shell is 755 ℃, the casting temperature of the first ladle is 1591 ℃, and the molten steel is naturally cooled after casting;
(4) And (3) heat treatment: and normalizing, quenching and tempering the casting blank. Controlling the normalizing temperature to be 930 +/-5 ℃, preserving the heat for 1.5h, controlling the temperature before quenching to be 907 ℃, controlling the temperature of quenching medium to be flowing water, controlling the temperature of the flowing water to be 20 ℃, and completing the quenching within 5 min; controlling the tempering temperature at 630 +/-5 ℃, preserving the heat for 1h, and cooling in the air.
The low-carbon low-alloy high-strength cast steel prepared by the method has a metallographic phase of tempered sorbite and ferrite, a metallographic phase diagram is detailed in an attached figure 2 of the specification, and the mechanical properties are shown in a table 2:
table 2 example 2 mechanical properties of single cast kir test block
Test bar Tensile strength/MPa Yield strength/Mpa Elongation/percent hardness/HB Impact work Akv/J
2-1 919 850 18.0 255 62
2-2 956 898 17.5 264 58
2-3 957 902 16.0 269 53
The results of the two experimental cases show that the low-carbon low-alloy high-strength cast steel material can be produced by the method, the yield strength is more than or equal to 750MPa, the tensile strength is more than or equal to 800MPa, and the elongation after fracture is more than or equal to 15%.
The above description is intended to be illustrative of some embodiments of the invention, and should not be taken as limiting the invention, and any modifications, equivalents, improvements and the like that are within the spirit and scope of the invention should be included.

Claims (3)

1. A production method of investment casting low-carbon low-alloy high-strength cast steel is characterized by comprising the following steps:
(1) Investment casting shell making and roasting: silica sol and quartz powder are adopted as surface layer coating, and silica sol and mullite powder are adopted as back layer coating;
(2) Smelting molten steel: the smelting material is low-carbon scrap steel and alloy materials such as ferrosilicon, ferromanganese, ferrochromium, ferrovanadium, copper blocks and the like, and the iron liquid comprises the following components in percentage by mass: 0.12 to 0.15 percent of C, 0.50 to 0.70 percent of Si, 0.80 to 1.20 percent of Mn, less than or equal to 0.03 percent of S, less than or equal to 0.03 percent of P, 0.60 to 0.70 percent of Cr, 0.10 to 0.15 percent of V, 0.50 to 0.60 percent of Cu and the balance of Fe; the sum of other elements is not more than 0.5%;
(3) Roasting and pouring the mould shell: roasting the dewaxed shell by using a through type natural gas roasting furnace, taking out the fired mold shell from the roasting furnace before casting, casting and cooling;
(4) And (3) heat treatment: and normalizing, quenching and high-temperature tempering the casting blank.
2. The method for producing investment casting low-carbon low-alloy high-strength cast steel according to claim 1, wherein: in the step 3, the tapping temperature of molten steel is not lower than 1620 ℃, and the pouring temperature is not lower than 1580 ℃; the temperature of the shell is more than or equal to 750 ℃ during casting.
3. The method for producing investment casting low-carbon low-alloy high-strength cast steel according to claim 1, wherein: in the step (4), the normalizing temperature is 920-940 ℃, the austenitizing temperature before quenching is 900-920 ℃, the quenching medium is running water, and the temperature of the running water is lower than 30 ℃; the tempering temperature is 600-650 ℃, the casting is cooled in air, and the metallographic structure of the casting after heat treatment is as follows: a tempered sorbite-ferrite mixed structure.
CN202211312490.XA 2022-10-25 2022-10-25 Production method for investment casting of low-carbon low-alloy high-strength structural steel Pending CN115570103A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117026068A (en) * 2023-10-08 2023-11-10 中北大学 Investment precision casting ferrite stainless steel and preparation method and application thereof

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117026068A (en) * 2023-10-08 2023-11-10 中北大学 Investment precision casting ferrite stainless steel and preparation method and application thereof
CN117026068B (en) * 2023-10-08 2023-12-22 中北大学 Investment precision casting ferrite stainless steel and preparation method and application thereof

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