CN117488191A - Medium carbon cold heading steel with high fatigue performance for 10.9-grade automobile engine fastener - Google Patents

Medium carbon cold heading steel with high fatigue performance for 10.9-grade automobile engine fastener Download PDF

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CN117488191A
CN117488191A CN202311502088.2A CN202311502088A CN117488191A CN 117488191 A CN117488191 A CN 117488191A CN 202311502088 A CN202311502088 A CN 202311502088A CN 117488191 A CN117488191 A CN 117488191A
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percent
medium carbon
carbon cold
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王杨
周蕾
邓伟
谷亮
王国柱
成建兵
董瀚
陆恒昌
赵秀明
张波
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Nanjing Iron and Steel Co Ltd
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Nanjing Iron and Steel Co Ltd
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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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • 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
    • C21D1/32—Soft annealing, e.g. spheroidising
    • 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
    • C21D11/00—Process control or regulation for heat treatments
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
    • 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
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • 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
    • 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
    • C21D2211/008—Martensite

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

The invention discloses medium carbon cold heading steel for a 10.9-grade automobile engine fastener with high fatigue performance, which comprises the following components in percentage by mass: c:0.32 to 0.38 percent; si:0.1 to 0.3 percent; mn:0.6 to 0.9 percent; p: less than or equal to 0.02 percent; s: less than or equal to 0.005%; cr:0.9 to 1.2 percent; mo:0.15 to 0.25 percent; n: less than or equal to 0.004%; o: less than or equal to 0.002%; the balance being Fe and unavoidable impurities. The invention adopts a brand new component formula, reduces adverse effects of micro defects and the like caused by brittle inclusions after thread rolling through good inclusion size and quantity control, and improves fatigue performance.

Description

Medium carbon cold heading steel with high fatigue performance for 10.9-grade automobile engine fastener
Technical Field
The invention relates to the field of medium carbon cold forging steel for fasteners, in particular to medium carbon cold forging steel for a 10.9-grade automobile engine fastener with high fatigue performance.
Background
At present, the quality and performance stability of the high-strength fastener steel for the engine of 10.9 grade or above at home and abroad still have defects, and the fatigue performance still cannot better meet the use requirements.
The fatigue failure stress of the fastener is often far lower than the strength limit under the static load, belongs to brittle fracture, has no obvious fracture sign and is the most common and most harmful failure mode of the fastener. The fatigue limit of the fastening piece for the engine directly influences the service life of the engine and the safe running of the automobile. In view of the harsh operating environment of engine structural members and high reliability requirements, it is necessary to conduct fatigue performance tests on high strength fasteners. The fatigue performance of the steel for the fastener is researched, measures for improving the fatigue life of the material are found, and the method has great significance for the development of structural parts of automobile engines.
Application numbers CN201510972039.4 and CN201510972010.6 disclose a steel for fasteners for 10.9 grade rail transit mobile equipment containing niobium and a heat treatment process thereof, and a steel for fasteners for 10.9 grade rail transit mobile equipment containing vanadium and a heat treatment process thereof, respectively. However, the fatigue life is more than or equal to 1000 ten thousand times under the condition of 550MPa cyclic stress, expensive Ni, nb or V elements are added to increase the cost, the structure is tempered sorbite, and the fatigue life is applied to rail transit mobile equipment, and the service environment and an automobile engine are greatly different.
Disclosure of Invention
The invention aims to: aiming at the defects and the shortcomings of the prior art, the invention provides the medium carbon cold heading steel for the 10.9-grade automobile engine fastener with high fatigue performance, which adopts a brand-new component formula, reduces adverse effects such as micro defects caused by brittle inclusions after thread rolling and improves the fatigue performance through good inclusion size and quantity control.
The technical scheme is as follows: the invention discloses a medium carbon cold heading steel for a 10.9-grade automobile engine fastener with high fatigue performance, which is characterized in that: comprises the following components in percentage by mass: c:0.32 to 0.38 percent; si:0.1 to 0.3 percent; mn:0.6 to 0.9 percent; p: less than or equal to 0.02 percent; s: less than or equal to 0.005%; cr:0.9 to 1.2 percent; mo:0.15 to 0.25 percent; n: less than or equal to 0.004%; o: less than or equal to 0.002%; the balance being Fe and unavoidable impurities.
The invention discloses a preparation method of medium carbon cold heading steel for a 10.9-grade automobile engine fastener with high fatigue performance, which is characterized by comprising the following steps of: comprises the working procedures of smelting, rolling, primary drawing, spheroidizing annealing, secondary drawing, cold heading, thread rolling, quenching and tempering and surface treatment.
Wherein, the smelting process comprises the following steps: comprises refining, vacuum degassing, and controlling the ingot casting N: less than or equal to 0.004%; o: less than or equal to 0.002%; s is less than or equal to 0.005%; the depth of the total decarburized layer at the edge is less than or equal to 1mm; center segregation is less than or equal to 0.5 level.
Wherein, in the side total decarburized layer, total carbon amount=total decarburized amount+partial decarburized amount.
Wherein, the rolling procedure is as follows: the hot rolled wire rod is obtained through controlled rolling and controlled cooling, the strength is controlled to be 950 MPa-1050 MPa, and the ferrite content is less than or equal to 35%.
Wherein, the primary drawing procedure: the drawing reduction rate is controlled to be 15-25 percent; in the spheroidizing annealing stage, the spheroidizing grade is controlled to be more than or equal to 5 grades; the secondary drawing control drawing reduction ratio is 5-10%.
Wherein, the cold heading process: the temperature rise caused by deformation is controlled to be less than or equal to 60 ℃.
Wherein, the quenching and tempering process comprises the following steps: controlling the quenching heating temperature to 840-870 ℃ by using a mesh belt furnace, and tempering, wherein the total heating time is more than or equal to 6min/mm, and the tempered martensite of the tempered structure accounts for more than 95%, and the proportion of the tempered martensite of the core part is more than 93%; and controlling the thread rolling to form compressive stress on the surface.
Wherein, after the thread rolling control, the inclusion on the secondary surface rises to the surface to form micro defects.
Wherein the inclusions comprise strip-shaped inclusions and spherical inclusions, more than 98 percent of the strip-shaped inclusions are less than or equal to 6 mu m in size, and more than 98 percent of the spherical inclusions are less than or equal to 5 mu m in size.
The beneficial effects are that: compared with the prior art, the invention has the following remarkable advantages: compared with the prior art, the quality level and reliability of the bolt steel are improved, the toughness, plasticity and fatigue resistance of the bolt steel are greatly improved by improving the purity of the steel and reducing the content and size of nonmetallic inclusions in the steel, and the manufactured automobile key fastener has higher reliability and stability, meets the requirement of obtaining stable clamping force during assembly, and has positive effects of ensuring the stability and higher consistency of the service performance of the steel and improving the safety of automobiles.
The invention reduces adverse effects of micro defects and the like caused by brittle inclusions after thread rolling and improves fatigue performance through good inclusion size and quantity control. The finished product 10.9-grade automobile engine bolt specification M12 is manufactured, and the average stress is sigma in fatigue test m =618 MPa, change stress amplitude σ a Loading, the cycle times are 1000 ten thousand times, and the fatigue limit sigma a50 And more than or equal to 90MPa. Under the condition of 618MPa cyclic stress, the fatigue life is more than or equal to 1000 ten thousand times, and the method is superior to the prior art and the existing product, and has lower cost.
Detailed Description
The technical scheme of the invention is further described below with reference to the specific embodiments.
The invention relates to medium carbon cold heading steel with high fatigue performance for a 10.9-grade automobile engine fastener, which is characterized in that: comprises the following components in percentage by mass: c:0.32 to 0.38 percent; si:0.1 to 0.3 percent; mn:0.6 to 0.9 percent; p: less than or equal to 0.02 percent; s: less than or equal to 0.005%; cr:0.9 to 1.2 percent; mo:0.15 to 0.25 percent; n: less than or equal to 0.004%; o: less than or equal to 0.002%; the balance being Fe and unavoidable impurities.
In the matrix structure of the medium carbon cold forging steel, the following components are formed: (a) tempered martensite as a main body in a proportion exceeding 95%; (b) The core tempered martensite accounts for more than 93% of the core structure. The inclusions comprise strip-shaped inclusions and spherical inclusions, wherein more than 98% of the strip-shaped inclusions are less than or equal to 6 mu m in size, and more than 98% of the spherical inclusions are less than or equal to 5 mu m in size.
The influence factors of fatigue life are divided into three types according to a fatigue mechanism, namely chemical components, inclusions and surface conditions, wherein the first two types are related to the quality of materials, and the surface conditions are mainly related to the machining precision:
the chemical components are as follows: different materials, components and tissue structures are different, so that the mechanical properties are different, and the fatigue properties are also changed. Tempered martensite has higher fatigue resistance than pearlite + martensite + bainite + martensite.
Inclusions: when the steel is acted by external force, the non-metallic inclusion in the steel is different from the matrix, the inclusion is uncoordinated with the matrix, and stress concentration is easy to occur in the matrix around the inclusion, so the inclusion is often used as a fatigue crack source to have obvious adverse effect on the fatigue performance of the steel. The effect of inclusions in steel on fatigue properties is mainly dependent on factors such as type, size, number, shape and distribution. The most common of steel are oxide and sulfide inclusions, of which hard and brittle oxides and TiN inclusions are the most detrimental to the fatigue properties of the steel and sulfide is relatively less detrimental. In addition, the deformation rate of nonmetallic inclusions also affects the fatigue performance of the material, and the inclusions at crack sources during fatigue fracture are mostly Al with lower deformation rate 2 O 3 And TiN inclusions, which are different in expansion amount from the steel matrix,the stress existing in the matrix cannot be transferred, resulting in stress concentration. In addition, an increase in the inclusion content in the steel results in a great decrease in the fatigue strength of the steel. Among the many inclusion characteristics, the inclusion size has the most pronounced effect on fatigue performance. As the average size of oxide inclusions in the steel increases, the fatigue limit decreases significantly.
Thus, controlling the content of O and N is critical to controlling the inclusion content, and the inventors have found that when N: less than or equal to 0.004 percent, O: when S is less than or equal to 0.002 percent and S is less than or equal to 0.005 percent, the shape of the inclusions in the medium carbon cold forging steel is mainly strip-shaped and spherical, wherein the size of the strip-shaped inclusions is less than or equal to 6 mu m, the size of the spherical inclusions is less than or equal to 5 mu m and the ratio exceeds 98 percent, and the inclusions are mainly sulfide inclusions (MnS) and oxide inclusions (Al) when combined with the component surface scanning distribution of the inclusions 2 O 3 ) The material has higher fatigue property.
Example 1:
a method for manufacturing medium carbon cold heading steel for a 10.9-grade automobile engine fastener with excellent fatigue performance mainly comprises the following technological processes of smelting, rolling, primary drawing, spheroidizing annealing, secondary drawing, cold heading, thread rolling, quenching and tempering and surface treatment. The depth of a total decarburized layer (total decarburization and partial decarburization) of a casting blank obtained by smelting is 0.8mm, the center segregation is 0.5 grade, and the chemical components in percentage by mass are as follows: c:0.35% of Si;0.21%, mn:0.79%, P:0.012%, S:0.004%, cr:1.05%, mo:0.21%, N:0.004%, O:0.0011%, the balance being Fe and unavoidable impurities. Rolling into a wire rod with the diameter phi 11mm, wherein the tensile strength is 988MPa, and the ferrite content is 19%; the primary drawing reduction rate is 16%, the spheroidizing annealing grade is 5, the secondary drawing reduction rate is 6%, and the temperature rise caused by deformation is less than or equal to 60 ℃ in the cold heading and thread rolling stages; in the quenching and tempering stage, the quenching heating temperature is controlled to 870 ℃, the austenitizing heating time is controlled to 8min/mm, the proportion of tempered martensite in the structure after quenching and tempering is over 95%, and the proportion of tempered martensite in the core is over 93%.
The finished product 10.9-grade automobile engine bolt specification M10 is manufactured, and the average stress is sigma in fatigue test m =618 MPa, change stress amplitude σ a Loading, the cycle times are 1000 ten thousand times, and the fatigue limit sigma a50 ＝95.7Mpa。
Example 2:
a method for manufacturing medium carbon cold heading steel for a 10.9-grade automobile engine fastener with excellent fatigue performance mainly comprises the following technological processes of smelting, rolling, primary drawing, spheroidizing annealing, secondary drawing, cold heading, thread rolling, quenching and tempering and surface treatment. The depth of a total decarburized layer (total decarburization and partial decarburization) of a casting blank obtained by smelting is 1.0mm, the center segregation is 0 grade, and the chemical components in percentage by mass are as follows: c:0.38% of Si;0.29%, mn:0.6%, P:0.012%, S:0.003%, cr:1.02%, mo:0.25%, N:0.0035%, O:0.0012% and the balance of Fe and unavoidable impurities. Rolling into a wire rod with the diameter phi of 14mm, wherein the tensile strength is 930MPa, and the ferrite content is 35%; the primary drawing reduction rate is 27%, the spheroidizing annealing grade is 5%, the secondary drawing reduction rate is 5%, and the temperature rise caused by deformation is less than or equal to 60 ℃ in the cold heading and thread rolling stages; in the quenching and tempering stage, the quenching heating temperature is controlled to 860 ℃, the austenitizing heating time is 7min/mm, the proportion of tempered martensite in the structure after quenching and tempering exceeds 95%, and the proportion of tempered martensite in the core is more than 93%.
The finished product 10.9-grade automobile engine bolt specification M12 is manufactured, and the average stress is sigma in fatigue test m =618 MPa, change stress amplitude σ a Loading, the cycle times are 1000 ten thousand times, and the fatigue limit sigma a50 ＝96.3Mpa。
Example 3:
a method for manufacturing medium carbon cold heading steel for a 10.9-grade automobile engine fastener with excellent fatigue performance mainly comprises the following technological processes of smelting, rolling, primary drawing, spheroidizing annealing, secondary drawing, cold heading, thread rolling, quenching and tempering and surface treatment. The depth of a total decarburized layer (total decarburization and partial decarburization) of a casting blank obtained by smelting is 1.0mm, the center segregation is 0 grade, and the chemical components in percentage by mass are as follows: c:0.32% of Si;0.12%, mn:0.89%, P:0.019%, S:0.002%, cr:1.19%, mo:0.16%, N:0.0033%, O:0.002%, the balance being Fe and unavoidable impurities. Rolling into a wire rod with the diameter phi of 10mm, wherein the tensile strength is 920MPa, and the ferrite content is 30%; the primary drawing reduction rate is 33%, the spheroidizing annealing grade is 6, the secondary drawing reduction rate is 9.5%, and the temperature rise caused by deformation is less than or equal to 60 ℃ in the cold heading and thread rolling stages; in the quenching and tempering stage, the quenching heating temperature is controlled to 840 ℃, the austenitizing heating time is 9.5min/mm, the proportion of tempered martensite in the structure after quenching and tempering is over 95%, and the proportion of tempered martensite in the core is over 93%.
The finished product 10.9-grade automobile engine bolt specification M8 is manufactured, and the average stress is sigma in fatigue test m =618 MPa, change stress amplitude σ a Loading, the cycle times are 1000 ten thousand times, and the fatigue limit sigma a50 ＝97.3MPa。
Example 4:
a method for manufacturing medium carbon cold heading steel for a 10.9-grade automobile engine fastener with excellent fatigue performance mainly comprises the following technological processes of smelting, rolling, primary drawing, spheroidizing annealing, secondary drawing, cold heading, thread rolling, quenching and tempering and surface treatment. The depth of a total decarburized layer (total decarburization and partial decarburization) of a casting blank obtained by smelting is 0.5mm, the center segregation is 0.5 grade, and the chemical components in percentage by mass are as follows: c:0.36% of Si;0.17%, mn:0.80%, P:0.011%, S:0.003%, cr:0.9%, mo:0.23%, N:0.0037%, O:0.001%, the balance being Fe and unavoidable impurities. Rolling into a wire rod with the diameter phi 11mm, wherein the tensile strength is 1030MPa, and the ferrite content is 17%; the primary drawing reduction rate is 15%, the spheroidizing annealing grade is 5, the secondary drawing reduction rate is 7%, and the temperature rise caused by deformation is less than or equal to 60 ℃ in the cold heading and thread rolling stages; in the quenching and tempering stage, the quenching heating temperature is controlled to 840 ℃, the austenitizing heating time is 9.5min/mm, the proportion of tempered martensite in the structure after quenching and tempering is over 95%, and the proportion of tempered martensite in the core is over 93%.
The finished product 10.9-grade automobile engine bolt specification M10 is manufactured, and the average stress is sigma in fatigue test m =618 MPa, change stress amplitude σ a Loading, the cycle times are 1000 ten thousand times, and the fatigue limit sigma a50 ＝98.4MPa。
Example 5:
a method for manufacturing medium carbon cold heading steel for a 10.9-grade automobile engine fastener with excellent fatigue performance mainly comprises the following technological processes of smelting, rolling, primary drawing, spheroidizing annealing, secondary drawing, cold heading, thread rolling, quenching and tempering and surface treatment. The depth of a total decarburized layer (total decarburization and partial decarburization) of a casting blank obtained by smelting is 0.7mm, the center segregation is 0.5 grade, and the chemical components in percentage by mass are as follows: c:0.36% of Si;0.12%, mn:0.89%, P:0.019%, S:0.001%, cr:0.9%, mo:0.23%, N:0.0033%, O:0.0015% and the balance of Fe and unavoidable impurities. Rolling into a wire rod with the diameter phi 11mm, wherein the tensile strength is 1030MPa, and the ferrite content is 17%; the primary drawing reduction rate is 15%, the spheroidizing annealing grade is 5, the secondary drawing reduction rate is 7%, and the temperature rise caused by deformation is less than or equal to 60 ℃ in the cold heading and thread rolling stages; in the quenching and tempering stage, the quenching heating temperature is controlled to 850 ℃, the austenitizing heating time is 9min/mm, the proportion of tempered martensite in the structure after quenching and tempering is over 95%, and the proportion of tempered martensite in the core is over 93%.
The finished product 10.9-grade automobile engine bolt specification M10 is manufactured, and the average stress is sigma in fatigue test m =618 MPa, change stress amplitude σ a Loading, the cycle times are 1000 ten thousand times, and the fatigue limit sigma a50 ＝98.4Mpa。
Comparative example 1:
a method for manufacturing medium carbon cold heading steel for a 10.9-grade automobile engine fastener with excellent fatigue performance mainly comprises the following technological processes of smelting, rolling, primary drawing, spheroidizing annealing, secondary drawing, cold heading, thread rolling, quenching and tempering and surface treatment. The depth of a total decarburized layer (total decarburization and partial decarburization) of a casting blank obtained by smelting is 0.8mm, the center segregation is 0.5 grade, and the chemical components in percentage by mass are as follows: c:0.36% of Si;0.21%, mn:0.78%, P:0.012%, S:0.01%, cr:1.03%, mo:0.22%, N:0.0032%, O:0.0015% and the balance of Fe and unavoidable impurities. Rolling into a wire rod with the diameter phi 11mm, wherein the tensile strength is 980MPa, and the ferrite content is 27%; the primary drawing reduction rate is 15%, the spheroidizing annealing grade is 5, the secondary drawing reduction rate is 7%, and the temperature rise caused by deformation is less than or equal to 60 ℃ in the cold heading and thread rolling stages; in the quenching and tempering stage, the quenching heating temperature is controlled to 860 ℃, the austenitizing heating time is 8min/mm, the proportion of tempered martensite in the structure after quenching and tempering exceeds 95%, and the proportion of tempered martensite in the core is more than 93%. The shape of the inclusions in the steel is mainly strip-shaped and spherical, wherein the size of the strip-shaped inclusions is less than or equal to 6 mu m, the size of the spherical inclusions is less than or equal to 5 mu m and accounts for 90%, and the size of the strip-shaped inclusions more than 6 mu m accounts for more than 3%.
The finished product 10.9-grade automobile engine bolt specification M10 is manufactured, and the average stress is sigma in fatigue test m =618 MPa, change stress amplitude σ a Loading, the cycle times are 1000 ten thousand times, and the fatigue limit sigma a50 ＝85.4MPa。
Comparative example 2:
a method for manufacturing medium carbon cold heading steel for a 10.9-grade automobile engine fastener with excellent fatigue performance mainly comprises the following technological processes of smelting, rolling, primary drawing, spheroidizing annealing, secondary drawing, cold heading, thread rolling, quenching and tempering and surface treatment. The depth of a total decarburized layer (total decarburization and partial decarburization) of a casting blank obtained by smelting is 0.9mm, the center segregation is 0 level, and the chemical components in percentage by mass are as follows: c:0.34% of Si;0.19%, mn:0.76%, P:0.012%, S:0.001%, cr:1.01%, mo:0.20%, N:0.0061%, O:0.0035% and the balance of Fe and unavoidable impurities. Rolling into a wire rod with the diameter phi 11mm, wherein the tensile strength is 990MPa, and the ferrite content is 25%; the primary drawing reduction rate is 16%, the spheroidizing annealing grade is 5, the secondary drawing reduction rate is 6%, and the temperature rise caused by deformation is less than or equal to 60 ℃ in the cold heading and thread rolling stages; and in the quenching and tempering stage, the quenching heating temperature is controlled to 870 ℃, and the austenitizing heating time is 6.5min/mm. The shape of the inclusions in the steel is mainly strip-shaped and spherical, wherein the size of the strip-shaped inclusions is less than or equal to 6 mu m, the size of the spherical inclusions is less than or equal to 5 mu m and accounts for 96%, and the size of the spherical inclusions more than 5 mu m accounts for 2.3%.
The finished product 10.9-grade automobile engine bolt specification M10 is manufactured, and the average stress is sigma in fatigue test m =618 MPa, change stress amplitude σ a Loading, the cycle times are 1000 ten thousand times, and the fatigue limit sigma a50 ＝82.3Mpa。
The invention reduces adverse effects of micro defects and the like caused by brittle inclusions after thread rolling and improves fatigue performance through good inclusion size and quantity control. The finished product 10.9-grade automobile engine bolt specification M12 is manufactured, and the average stress is sigma in fatigue test m =618 MPa, change stress amplitude σ a LoadingThe cycle times are 1000 ten thousand times, and the fatigue limit sigma is the same as that of the prior art a50 And more than or equal to 90MPa. Under the condition of 618MPa cyclic stress, the fatigue life is more than or equal to 1000 ten thousand times, and the method is superior to the prior art and the existing product, and has lower cost.

Claims (10)

1. A high fatigue performance's 10.9 grades of automobile engine fastener are with well carbon cold heading steel which characterized in that: comprises the following components in percentage by mass: c:0.32 to 0.38 percent; si:0.1 to 0.3 percent; mn:0.6 to 0.9 percent; p: less than or equal to 0.02 percent; s: less than or equal to 0.005%; cr:0.9 to 1.2 percent; mo:0.15 to 0.25 percent; n: less than or equal to 0.004%; o: less than or equal to 0.002%; the balance being Fe and unavoidable impurities.
2. The method for preparing the medium carbon cold forging steel according to claim 1, wherein: comprises the working procedures of smelting, rolling, primary drawing, spheroidizing annealing, secondary drawing, cold heading, thread rolling, quenching and tempering and surface treatment.
3. The method for preparing the medium carbon cold forging steel according to claim 2, wherein: the smelting process comprises the following steps: comprises refining, vacuum degassing, and controlling the ingot casting N: less than or equal to 0.004%; o: less than or equal to 0.002%; s is less than or equal to 0.005%; the depth of the total decarburized layer at the edge is less than or equal to 1mm; center segregation is less than or equal to 0.5 level.
4. The method for preparing the medium carbon cold forging steel according to claim 3, wherein: in the side total decarburized layer, total carbon amount=total decarburized amount+partial decarburized amount.
5. The method for preparing the medium carbon cold forging steel according to claim 2, wherein: the rolling procedure comprises the following steps: the hot rolled wire rod is obtained through controlled rolling and controlled cooling, the strength is controlled to be 950 MPa-1050 MPa, and the ferrite content is less than or equal to 35%.
6. The method for preparing the medium carbon cold forging steel according to claim 2, wherein: the primary drawing process comprises the following steps: the drawing reduction rate is controlled to be 15-25 percent; in the spheroidizing annealing stage, the spheroidizing grade is controlled to be more than or equal to 5 grades; the secondary drawing control drawing reduction ratio is 5-10%.
7. The method for preparing the medium carbon cold forging steel according to claim 2, wherein: the cold heading procedure comprises the following steps: the temperature rise caused by deformation is controlled to be less than or equal to 60 ℃.
8. The method for preparing the medium carbon cold forging steel according to claim 2, wherein: the quenching and tempering process comprises the following steps: controlling the quenching heating temperature to 840-870 ℃ by using a mesh belt furnace, and tempering, wherein the total heating time is more than or equal to 6min/mm, and the tempered martensite of the tempered structure accounts for more than 95%, and the proportion of the tempered martensite of the core part is more than 93%; and controlling the thread rolling to form compressive stress on the surface.
9. The method for preparing the medium carbon cold forging steel according to claim 8, wherein: after the thread rolling control, inclusions on the secondary surface rise to the surface to form micro defects.
10. The method for preparing the medium carbon cold forging steel according to claim 9, wherein: the inclusions comprise strip-shaped inclusions and spherical inclusions, wherein more than 98% of the strip-shaped inclusions are less than or equal to 6 mu m in size, and more than 98% of the spherical inclusions are less than or equal to 5 mu m in size.
CN202311502088.2A 2023-11-13 2023-11-13 Medium carbon cold heading steel with high fatigue performance for 10.9-grade automobile engine fastener Pending CN117488191A (en)

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