Production method of mine-used rare earth wear-resistant GN-14A hot-rolled round steel

Abstract

The application discloses a production method of a mining rare-earth wear-resistant GN-14A hot-rolled round steel, and a steelmaking process is as follows: a converter is operated with double-slag, and an end-point basicity is controlled at 2.5; the end-point control target of the converter is C >= 0.08%, and P <= 0.020%; a VD deep vacuum time is >= 15 min, and a soft blowing time is >= 20 min; a superheat degree is <= 25 DEG C, a caster pulling speed is 0.55 m / min <= 0.60 m / min; a casting blank slow cooling time is >= 24 hours; and a rolling process is as follows: 1020 DEG C <= open rolling temperature <= 1050 DEG C; 780 DEG C <= final rolling temperature <= 850 DEG C; 450 DEG C <= entering slow cooling pit temperature <= 550 DEG C; and 50 DEG C <= exiting slow cooling pit temperature <= 150 DEG C. The hot-rolled round steel prepared by the application has a structure of ferrite + pearlite structure, inclusion levels of A class <= 1.5 level, B class <= 1.5 level, C class <= 1.0 level, D class <= 1.5 level, and austenite grain size >= 5 level.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of material metallurgy, in particular to a production method of a mine rare-earth wear-resistant GN-14A hot-rolled round steel. BACKGROUND

[0002] With the large-scale and increasing use of semi-autogenous mills at home and abroad, the demand for large-diameter wear-resistant steel balls is gradually increasing. The forming process of the large-diameter wear-resistant steel balls in the past mainly includes medium-frequency induction heating, air hammer forging or press extrusion forming. However, the heating and forming process has some problems. If the medium-frequency induction heating is adopted, due to the shape characteristics of the round steel, the temperature inside and outside the round steel is not uniform in the rapid heating process, so that the austenitization of the round steel is not uniform, and the product quality uniformity is poor and the quality is unstable. If the air hammer forging is adopted, the process environment temperature is high, the labor intensity is large, the production efficiency is low, and the hourly output of a single machine is about 1 ton, which cannot guarantee the uniformity and stability of the product quality. If the press extrusion is adopted, the compression ratio of the steel ball forming is not satisfied, the steel ball density is poor, and the grain cannot be refined, thereby affecting the product quality of the steel ball.

[0003] Increasing the hardness of the grinding ball is the most effective way to reduce wear. Normal wear of the grinding ball is the wear process of large balls into small balls. Only by maintaining the round shape during the entire wear process and ensuring that the internal and external parts of the grinding ball have sufficient hardness and wear resistance can the normal function of the grinding ball for grinding powder be ensured. If the hardness of the grinding ball is not uniform, the grinding ball will be out of round during the wear process. If the hardness of the internal and external parts of the grinding ball is greatly different, the hardening layer is shallow, and after the hardening layer of the outer part is worn, the wear will increase dramatically. Therefore, a good grinding ball should have a small difference in hardness between the internal and external parts. The industry standard for metallurgical grinding balls stipulates that the difference in hardness between the surface and the core of the grinding ball should not be greater than 3HRC. In addition, the refinement of the structure and grain of the grinding ball is not only beneficial to the improvement of strength and hardness, but also beneficial to the improvement of toughness, which can reduce the risk of cracking of the steel ball.

[0004] The increase of alloy elements is very beneficial to reducing the difference in hardness between the internal and external parts of the steel ball and improving the wear resistance of the steel ball. However, this will first increase the cost of alloy raw materials, and secondly increase the production difficulty and the complexity of the production process, thereby increasing the manufacturing cost. Therefore, it is of great significance to develop a high-quality and low-cost grinding ball steel. SUMMARY

[0005] The purpose of the present application is to provide a production method of a mine rare-earth wear-resistant GN-14A hot-rolled round steel, which has a ferrite + pearlite structure, a inclusion level of A class ≤1.5 level, B class ≤1.5 level, C class ≤1.0 level, D class ≤1.5 level, and an austenite grain size of ≥5 level.

[0006] To solve the above technical problems, the present application adopts the following technical solutions:

[0007] This invention discloses a production method for hot-rolled rare earth wear-resistant GN-14A round steel for mining. The steelmaking process includes: converter—ladle refining—VD vacuum treatment—continuous casting—slow cooling; the rolling process includes: billet heating—high-pressure water descaling—850mm billet mill—700mm×3 + 550mm×4 continuous rolling mill—sawing (sampling)—slow cooling—non-destructive testing (ultrasonic testing + eddy current / infrared / magnetic flux leakage testing)—inspection—grinding—bundling—warehousing—shipment; the key feature is that the technical parameters controlled in the steelmaking process are:

[0008] The converter adopts a dual-slag operation, and the final alkalinity is controlled at 2.5;

[0009] The converter's final control targets are C ≥ 0.08% and P ≤ 0.020%.

[0010] VD deep vacuum time ≥15min, soft blowing time ≥20min;

[0011] Superheat ≤ 25℃, casting speed ≤ 0.55m / min ≤ casting machine speed ≤ 0.60m / min;

[0012] Slow cooling time for cast billets ≥ 24 hours;

[0013] The technical parameters controlled in the steel rolling process are:

[0014] 1020℃≤rolling temperature≤1050℃;

[0015] 780℃≤Final rolling temperature≤850℃;

[0016] 450℃≤Temperature in the slow cooling pit≤550℃;

[0017] 50℃≤Temperature outside the slow cooling pit≤150℃.

[0018] Furthermore, the chemical composition percentage requirements are as follows: C: 0.66-0.68%, Mn: 0.95-1.00%, Si: 0.79-0.89%, Cr: 0.70-0.78%, P: ≤0.025%, S: ≤0.025%, RE: 0.002-0.003%, with the remainder being iron and unavoidable trace amounts of chemical elements.

[0019] Furthermore, the rolled microstructure is a ferrite + pearlite structure.

[0020] Furthermore, the inclusion levels are: Class A ≤ 1.5, Class B ≤ 1.5, Class C ≤ 1.0, Class D ≤ 1.5, and austenite grain size ≥ 5.

[0021] The reasons for limiting the main chemical components are as follows:

[0022] C: C is the most effective element to improve the strength of steel, the increase of C content can improve the tensile strength and yield strength of steel, but the elongation and impact toughness will decrease, the corrosion resistance will also decrease, and the hardening phenomenon will appear in the heat affected zone of steel, which will cause the generation of welding cold cracks. In order to ensure that the round steel has good comprehensive performance, the C content of the steel is designed to be 0.66-0.68%.

[0023] Mn: Mn is an important toughening element, and the cost is low, with the increase of the content of manganese, the strength of the steel is obviously improved, the processing performance of the steel is improved, and the ductile-brittle transition temperature is almost unchanged. However, if the content of manganese is too high, the transformation of ferrite will be inhibited, the yield strength of the steel will be affected, and the control of the yield strength ratio is not conducive. The Mn content of the steel is designed to be 0.95-1.00%.

[0024] Si: Si can improve the strength of the steel, and by increasing the Si element, the strength of the steel can be improved to a certain extent, but with the further increase of the mass percentage of Si, martensite organization is easy to be generated in the steel, therefore, the mass percentage of Si in the production method of the mining rare earth wear-resistant GN-14A hot-rolled round steel is controlled to be 0.79-0.89%.

[0025] Cr: Cr can improve the strength, hardness and atmospheric corrosion resistance of the steel, and the effect is more obvious when other alloy elements are added. Chromium can slow down the decomposition rate of austenite, significantly improve the hardenability of the steel, and has the effect of secondary hardening, but also increases the tendency of temper brittleness of the steel. However, when the content of chromium is too high, the toughness of the base material and the heat affected zone will be reduced. The Cr content of the steel is designed to be 0.70-0.78%.

[0026] RE: RE has the effects of purification and obvious modification in the steel. The cleanliness of the steel is continuously improved, and the micro-alloying effect of rare earth elements is increasingly prominent. The micro-alloying of rare earth includes the solid solution strengthening of trace rare earth elements, the interaction of rare earth elements and other solute elements and compounds, the existence state (atoms, inclusions or compounds), size, shape and distribution of rare earth elements, especially the segregation at grain boundaries and the influence of rare earth on the surface and matrix structure of the steel. Therefore, the mass percentage of RE in the production method of the mining rare earth wear-resistant GN-14A hot-rolled round steel is limited to 0.002-0.003%.

[0027] The innovation of the present application lies in the reasonable control of the content of C and Cr elements and the addition of RE elements, the control of the size of inclusions and the cleanliness of the steel through the steelmaking process, and the control of the organization transformation and grain size of the hot-rolled state through the rolling process, so as to obtain the wear-resistant hot-rolled round steel with matching hardness and toughness.

[0028] Compared with the prior art, the present application has the following beneficial technical effects:

[0029] 1) The rolling structure is ferrite + pearlite structure, which has high strength and toughness and is easy to process the subsequent high wear-resistant steel ball;

[0030] 2) The inclusion size is controlled by the steelmaking process to improve the wear resistance of the steel ball. BRIEF DESCRIPTION OF DRAWINGS

[0031] The application will be further described below in combination with the drawings.

[0032] Figure 1 It is a hot acid macrograph of hot-rolled round steel. DETAILED DESCRIPTION

[0033] The application will be further described below in combination with the drawings.

[0034] The application will be further described below in combination with the drawings.

[0035] Table 1 is a list of chemical composition and weight percentage content of each embodiment of the application;

[0036] Table 2 and 3 are lists of steelmaking and rolling process control parameters of each embodiment of the application;

[0037] Table 4 is the inclusion size of each embodiment of the application.

[0038] Table 1 Chemical composition and weight percentage content (%) of the embodiment

[0039] Embodiments C Si Mn P S Cr RE 1 0.67 0.82 0.98 0.018 0.010 0.73 0.0022 2 0.67 0.82 0.97 0.019 0.009 0.72 0.0025 3 0.68 0.85 0.97 0.018 0.008 0.71 0.0028

[0040] Table 2 Main parameters of the steelmaking process of the embodiment

[0041]

[0042] Table 3 Rolling process parameters of the embodiment

[0043]

[0044]

[0045] Table 4 Inclusion size of each embodiment

[0046] Embodiments Class A Class B Class C Class D 1 1.0 1.0 0.5 1.0 2 1.5 1.0 0.5 1.0 3 1.5 1.0 0.5 1.0

[0047] As can be seen from Table 1, Table 2, Table 3 and Table 4, the mine rare earth wear-resistant GN-14A hot-rolled round steel prepared by the application meets the technical requirements.

[0048] The above described embodiments are only to illustrate the preferred modes of the present application, and are not intended to limit the scope of the present application. Any modification and improvement made by those skilled in the art to the technical solutions of the present application without departing from the design spirit of the present application shall fall within the protection scope of the present application.

Claims

1. A production method for hot-rolled rare earth wear-resistant GN-14A round steel for mining, wherein the steelmaking process is as follows: converter—ladle refining—VD vacuum treatment—continuous casting—slow cooling; the rolling process is as follows: billet heating—high-pressure water descaling—Ф850mm billet mill—Ф700mm×3+Ф550mm×4 continuous rolling mill—sawing—slow cooling—non-destructive testing—inspection—grinding—bundling—warehousing—shipping; characterized in that, The technical parameters controlled in the steelmaking process are: The converter adopts a dual-slag operation, and the final alkalinity is controlled at 2.5; The converter's final control targets are C ≥ 0.08% and P ≤ 0.020%. VD deep vacuum time ≥15min, soft blowing time ≥20min; Superheat ≤ 25℃, casting speed ≤ 0.55m / min ≤ casting machine speed ≤ 0.60m / min; Slow cooling time for cast billets ≥ 24 hours; The technical parameters controlled in the steel rolling process are: 1020℃≤rolling temperature≤1050℃; 780℃≤Final rolling temperature≤850℃; 450℃≤Temperature in the slow cooling pit≤550℃; 50℃≤Temperature outside the slow cooling pit≤150℃; The required chemical composition (by mass percentage) of the hot-rolled round steel is as follows: C: 0.66-0.68%, Mn: 0.95-1.00%, Si: 0.79-0.89%, Cr: 0.70-0.78%, P: ≤0.025%, S: ≤0.025%, RE: 0.002-0.003%, with the remainder being iron and unavoidable trace amounts of chemical elements. The rolled microstructure is ferrite + pearlite.

2. The production method of mining rare earth wear-resistant GN-14A hot-rolled round steel according to claim 1, characterized in that, Inclusion grades: A ≤ 1.5, B ≤ 1.5, C ≤ 1.0, D ≤ 1.5; austenite grain size ≥ 5.

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