Production method of free-cutting non-modulated hot-rolled round steel with tensile strength of 900MPa

Abstract

The invention discloses a production method of free-cutting non-modulated hot-rolled round steel with tensile strength of 900MPa. The production method comprises the following steps: controlling chemical components of an obtained casting blank in a steelmaking process, wherein the chemical components comprise the following components in percentage by mass: 0.44%-0.47% of C, 1.30%-1.40% of Mn, 0.36%-0.44% of Si, less than or equal to 0.020% of P, 0.035%-0.050% of S, 0.02%-0.04% of V, 0.02%-0.04% of B, 0.015%-0.025% of Al, 0.010%-0.015% of N, 0.0035%-0.0040% of RE and the balance of Fe and inevitable impurities; and the pulling speed of the casting machine is controlled to meet the condition that the pulling speed of the casting machine is larger than or equal to 0.52 m / min and smaller than or equal to 0.55 m / The strength performance of the hot-rolled round steel meets the conditions that the yield strength is larger than or equal to 570 MPa, and the tensile strength is larger than or equal to 910 MPa.

Description

Technical Field

[0001] The invention belongs to the field of metallurgical materials, and in particular relates to a production method of free-cutting non-modulated hot-rolled round steel with a tensile strength of 900 MPa. Background Art

[0002] Rare earth elements have the effects of spheroidizing inclusions and refining grains in steel. Adding rare earth elements to free-cutting non-quenched and tempered steel can effectively improve the cutting performance and impact toughness of free-cutting non-quenched and tempered steel. For example, patent document CN113293336A (hereinafter referred to as document 1) discloses a method for preparing a rare earth non-quenched and tempered free-cutting hot-rolled round steel with a yield strength of 500MPa, and patent document CN116590596A (hereinafter referred to as document 2) discloses a method for preparing a non-quenched and tempered free-cutting F35VSRE hot-rolled round steel. Both of them use the effects of rare earth elements in steel with spheroidizing inclusions and refining grains to obtain a non-quenched and tempered free-cutting hot-rolled round steel with good plastic toughness and higher strength. However, the tensile strength of the rare earth non-quenched and tempered free-cutting hot-rolled round steel with a yield strength of 500MPa obtained in document 1 can only reach about 780MPa at most, and the tensile strength of the non-quenched and tempered free-cutting F35VSRE hot-rolled round steel obtained in document 2 can only reach about 650MPa at most. With the development of automobile lightweight technology, the development of higher-strength steel plates will be more conducive to the lightweight design and development of automobiles. Summary of the invention

[0003] The present invention aims to provide a method for producing free-cutting non-modulated hot-rolled round steel with high strength, especially tensile strength up to 900 MPa, and provides hot-rolled round steel produced by the method. The specific technical scheme is as follows.

[0004] One aspect of the present invention provides a method for producing free-cutting non-modulated hot-rolled round steel with a tensile strength of 900 MPa, the production method comprising a steelmaking process and a steel rolling process, wherein:

[0005] In the steelmaking process, the chemical composition of the obtained ingot is controlled to be calculated by mass percentage as follows: C: 0.44%-0.47%, Mn: 1.30%-1.40%, Si: 0.36%-0.44%, P≤0.020%, S: 0.035%-0.050%, V: 0.02%-0.04%, B: 0.02-0.04%, Al: 0.015%-0.025%, N: 0.010%-0.015%, RE: 0.0035%-0.0040%, and the rest are iron and inevitable trace chemical elements, and the casting machine pulling speed is controlled to meet the following conditions: 0.52m / min≤casting machine pulling speed≤0.55m / min;

[0006] In the steel rolling process, the starting rolling temperature is controlled to be ≤1050°C and the final rolling temperature is controlled to be ≤850°C;

[0007] The strength properties of the 900MPa-grade free-cutting non-modulated hot-rolled round steel meet the following requirements: yield strength ≥570MPa, and tensile strength ≥910MPa.

[0008] In some embodiments, the properties of the 900 MPa grade free-cutting non-modulated hot-rolled round steel also meet the following requirements: elongation ≥ 19%, area reduction ≥ 45%, and room temperature impact energy KU 2 ≥70J.

[0009] In some embodiments, the steelmaking process includes the following steps: converter—refining outside the furnace—VD vacuum treatment—continuous casting—slow cooling.

[0010] In some embodiments, in the converter process, double slag operation is adopted, the endpoint basicity is controlled at 4.0, and the converter endpoint control target C≥0.10%, P≤0.020%.

[0011] In some embodiments, in the VD vacuum treatment process, the VD deep vacuum time is ≥13 min, and the soft blowing time is ≥13 min.

[0012] In some embodiments, during the continuous casting process, the superheat is controlled to be ≤30°C.

[0013] In some embodiments, the steel rolling process includes the following steps: heating of ingot - high-pressure water dephosphorization - Ф850mm ingot opening machine - Ф700mm×3+Ф550mm×4 continuous rolling mill - sawing (sampling) - non-destructive testing (ultrasonic flaw detection + eddy current / infrared / leakage magnetic flaw detection) - inspection - grinding - bundling - warehousing - delivery.

[0014] In some embodiments, in the casting billet heating step, the heating temperature is controlled to be ≤1220°C and the heating time is controlled to be ≥3 hours.

[0015] In some embodiments, in the steelmaking process, the chemical composition of the obtained ingot is controlled to be calculated by mass percentage as follows: C: 0.44%-0.46%, Mn: 1.34%-1.37%, Si: 0.36%-0.38%, P≤0.020%, S: 0.040%-0.050%, V: 0.02%-0.04%, B: 0.02-0.04%, Al: 0.020%-0.022%, N: 0.012%-0.015%, RE: 0.0035%-0.0038%, and the rest are iron and inevitable trace chemical elements.

[0016] Another aspect of the present invention provides free-cutting non-modulated hot-rolled round steel with a tensile strength of 900 MPa, which is obtained by the above production method.

[0017] The beneficial effects of the present invention are as follows: the method provided by the present invention reasonably regulates the contents of C, Si, Mn, etc. in the steelmaking process, adds an appropriate amount of B element, and controls the process parameters, so that the strength performance of the easy-to-cut non-modulated hot-rolled round steel modified by rare earth can be further improved, and the yield strength of the obtained hot-rolled round steel can reach more than 570MPa, and the tensile strength can reach more than 910MPa, which can improve the application field of the hot-rolled round steel and is conducive to the design and development of lightweight automobiles. DETAILED DESCRIPTION

[0018] The present invention is described in detail below through specific examples. The examples are intended to help understand the present invention but are not intended to limit the present invention.

[0019] The present invention provides a production method of free-cutting non-modulated hot-rolled round steel with a tensile strength of 900 MPa, which comprises a steelmaking process: a converter - refining outside the furnace - VD vacuum treatment - continuous casting - slow cooling, and a steel rolling process: heating of the cast billet - high-pressure water dephosphorization - Ф850mm billet opening machine - rolling of Ф700mm×3+Ф550mm×4 continuous rolling mill group - sawing (sampling) - non-destructive testing (ultrasonic flaw detection + eddy current / infrared / magnetic leakage flaw detection) - inspection - grinding - bundling - warehousing - delivery; wherein:

[0020] In the steelmaking process, the converter adopts double slag operation, the end point basicity is controlled at 4.0, the converter end point control target C ≥ 0.10%, P ≤ 0.020%, VD deep vacuum time ≥ 13min, soft blowing time ≥ 13min, superheat ≤ 30℃, and the casting machine pulling speed is controlled at 0.52m / min ≤ 0.55m / min. By fine-tuning the chemical composition, the chemical composition of the obtained ingot is calculated by mass percentage as follows: C: 0.44%-0.47 %, Mn: 1.30%-1.40%, Si: 0.36%-0.44%, P≤0.020%, S: 0.035%-0.050%, V: 0.02%-0.04%, B: 0.02-0.04%, Al: 0.015%-0.025%, N: 0.010%-0.015%, RE: 0.0035%-0.0040%, the rest are iron and inevitable trace chemical elements;

[0021] In the steel rolling process, the heating temperature is controlled to be ≤1220℃; the heating time is ≥3 hours; the starting rolling temperature is ≤1050℃; and the final rolling temperature is ≤860℃.

[0022] Table 1 below lists the chemical compositions and weight percentages of various embodiments and comparative examples of the present invention.

[0023] Tables 2 and 3 below list the steelmaking and rolling process control parameters of the embodiments of the present invention and the comparative examples respectively.

[0024] Table 4 below lists the properties of the hot-rolled round steels obtained in various embodiments of the present invention and comparative examples.

[0025] Table 1: Chemical composition and weight percentage of each embodiment and comparative example.

[0026] Example C Si Mn P S Al V B RE N 1 0.45 0.38 1.36 0.015 0.045 0.022 0.02 0.03 0.0036 0.012 2 0.44 0.36 1.37 0.017 0.043 0.021 0.03 0.02 0.0038 0.015 3 0.46 0.37 1.34 0.014 0.047 0.020 0.04 0.04 0.0035 0.014 Comparative Example 1 0.46 0.37 1.34 0.014 0.047 0.020 0.04 - 0.0035 0.014 Comparative Example 2 0.35 0.34 0.74 0.018 0.057 0.015 0.10 - 0.0022 0.012 Comparative Example 3 0.45 0.38 1.36 0.015 0.045 0.022 0.02 0.03 0.0036 0.012

[0027] Table 2: List of steelmaking and steel rolling process control parameters for various embodiments of the present invention.

[0028]

[0029] Table 3: Steel rolling process control parameters of various embodiments of the present invention and comparative examples.

[0030] Example Heating temperature(℃) Heating time (h) Rolling temperature (℃) Finishing rolling temperature(℃) 1 1210 3h 37min 1043 850 2 1218 3h 35min 1045 845 3 1215 3h 42min 1039 847 Comparative Example 1 1215 3h 42min 1039 847 Comparative Example 2 1215 3h 42min 1039 847 Comparative Example 3 1210 3h 37min 1056 864

[0031] Table 4: Mechanical properties of various embodiments of the present invention.

[0032]

[0033] It can be seen from Table 1, Table 2, Table 3 and Table 4 that by rationally controlling the microalloying elements and their percentages, and controlling the steelmaking process and steel rolling process parameters, a free-cutting non-quenched and tempered hot-rolled round steel with significantly improved strength based on rare earth modification can be obtained. Moreover, the method provided by the present invention also has the advantages of simple control, low manufacturing cost and strong operability, and is suitable for large-scale production.

[0034] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for producing free-cutting non-modulated hot-rolled round steel with a tensile strength of 900 MPa, the method comprising a steelmaking process and a steel rolling process, wherein: In the steelmaking process, the chemical composition of the obtained ingot is controlled to be calculated by mass percentage as follows: C: 0.44%-0.47%, Mn: 1.30%-1.40%, Si: 0.36%-0.44%, P≤0.020%, S: 0.035%-0.050%, V: 0.02%-0.04%, B: 0.02-0.04%, Al: 0.015%-0.025%, N: 0.010%-0.015%, RE: 0.0035%-0.0040%, and the rest are iron and inevitable trace chemical elements, and the casting machine pulling speed is controlled to meet the following conditions: 0.52m / min≤casting machine pulling speed≤0.55m / min; In the steel rolling process, the starting rolling temperature is controlled to be ≤1050°C and the final rolling temperature is controlled to be ≤850°C; The strength properties of the 900MPa-grade free-cutting non-modulated hot-rolled round steel meet the following requirements: yield strength ≥570MPa, and tensile strength ≥910MPa.

2. The production method according to claim 1, wherein the properties of the free-cutting non-modulated hot-rolled round steel with a tensile strength of 900 MPa also meet the following requirements: elongation ≥ 19%, area reduction ≥ 45%, and normal temperature impact energy KU2 ≥ 70 J.

3. According to the production method of claim 1 or 2, the steelmaking process includes the following steps: converter - refining outside the furnace - VD vacuum treatment - continuous casting - slow cooling.

4. The production method according to claim 3, wherein: In the converter process, double slag operation is adopted, the end point basicity is controlled at 4.0, and the converter end point control target C ≥ 0.10%, P ≤ 0.020%; In the VD vacuum treatment process, the VD deep vacuum time is ≥13 min, and the soft blowing time is ≥13 min; and In the continuous casting process, the superheat is controlled to be ≤30°C.

5. The production method according to any one of claims 1-3, wherein the steel rolling process comprises the following steps: heating of the ingot - high-pressure water dephosphorization - Ф850mm ingot opening machine - rolling by Ф700mm×3+Ф550mm×4 continuous rolling mill group.

6. The production method according to claim 5, wherein: In the casting heating process, the heating temperature is controlled to be ≤1220°C and the heating time is controlled to be ≥3 hours.

7. The production method according to any one of claims 1 to 6, wherein in the steelmaking process, the chemical composition of the resulting ingot is controlled to be, in percentage by mass: C: 0.44%-0.46%, Mn: 1.34%-1.37%, Si: 0.36%-0.38%, P≤0.020%, S: 0.040%-0.050%, V: 0.02%-0.04%, B: 0.02-0.04%, Al: 0.020%-0.022%, N: 0.012%-0.015%, RE: 0.0035%-0.0038%, and the rest are iron and inevitable trace chemical elements.

8. A free-cutting non-modulated hot-rolled round steel with a tensile strength of 900 MPa, obtained by the production method according to any one of claims 1 to 7.

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