CN115354207A

CN115354207A - Smelting method of medium-carbon alloy structural steel for high-cleanliness ball screw

Info

Publication number: CN115354207A
Application number: CN202211141946.0A
Authority: CN
Inventors: 谢有; 林俊; 邓向阳; 李仕超; 孟晓玲; 朱飞
Original assignee: Zenith Steel Group Co Ltd; Changzhou Zenith Special Steel Co Ltd
Current assignee: Zenith Steel Group Co Ltd; Changzhou Zenith Special Steel Co Ltd
Priority date: 2022-09-20
Filing date: 2022-09-20
Publication date: 2022-11-18
Anticipated expiration: 2042-09-20
Also published as: CN115354207B

Abstract

The invention relates to the technical field of steel smelting, and particularly discloses a method for smelting medium-carbon alloy structural steel for a high-cleanliness ball screw. By selecting the low-titanium alloy, the oxidizability of slag and molten steel in the LF refining process is improved, the increase of Ti in the molten steel in the refining process is reduced, the Ti content of finished products is less than or equal to 15ppm, and the maximum size of TiN inclusions is less than or equal to 10 mu m.

Description

Smelting method of medium-carbon alloy structural steel for high-cleanliness ball screw

Technical Field

The invention relates to the technical field of steel smelting, and particularly discloses a method for smelting medium-carbon alloy structural steel for a high-cleanliness ball screw.

Background

The machine tool is known as an "industrial master", which is a heart, developing and important base stone in modern manufacturing industry, and its main components include a lathe body, a transmission system, a numerical control device, a servo system and the like, wherein the quality of the transmission system seriously affects the processing precision of the machine tool. An important component of the transmission system is a screw rod, which is used for converting the rotary motion transmitted by the motor into linear motion. The lead screws can be classified into three types according to their frictional characteristics, i.e., a sliding lead screw, a rolling lead screw, and a static pressure lead screw, and can be classified into a trapezoidal lead screw, a ball screw, a roller screw, and the like according to the product structure and the transmission principle. Because the friction coefficient of the ball screw is far smaller than that of a trapezoidal screw (the friction coefficient of the ball screw is between 0.003 and 0.01, and the friction coefficient of the trapezoidal screw is between 0.1 and 0.2), the transmission efficiency is 2-4 times that of the trapezoidal screw, and the ball screw is mainly used in the current high-end numerical control machine tool.

In the machine tool, a ball screw is connected with a driving motor through a coupler, and the other end of the ball screw is connected with a supporting seat; through nut, nut support and workstation connection, consequently it receives crooked, twist reverse, impact and with the atress forms such as friction of ball in the course of the work, corresponding failure mode can be divided into three: surface damage failure, excessive deformation failure and fracture failure, wherein contact fatigue failure among the surface damage failures is the main failure mode of the ball screw pair. Therefore, the ball screw material is required to have high cleanliness, especially titanium nitride type inclusions which are highly harmful to surface fatigue. The medium carbon alloy structural steel for the ball screw is aluminum deoxidized steel, nitrogen with certain content is added to control crystal grains by aluminum nitride, but the control difficulty of titanium nitride is increased by the high nitrogen content, the existence of a large amount of large-size titanium nitride can become a surface failure source in the working process of the ball screw, and the fatigue life of the ball screw is greatly reduced.

There are many researches on the control means of titanium nitride inclusions in steel, and the most effective means at present is to control the content of residual Ti and N in steel. For example, in patent CN 114182056A, the smelting method of titanium nitride inclusion of high carbon chromium bearing steel achieves the purpose of controlling titanium nitride by adopting low titanium raw material and slag removing treatment and controlling nitrogen increase in the smelting process. However, the slag skimming effect in actual production is not well controlled, and slag is left in the subsequent refining more or less after slag skimming, so that Ti in the refining process continues to increase. In order to reduce the influence of large-size titanium nitride on steel products, the content of Ti in steel needs to be controlled to be lower, so that more stable and effective measures are needed. Furthermore, the patent is a high carbon chromium bearing steel, the steel grade requires as low a nitrogen content as possible, as mentioned therein the average nitrogen is 30ppm (more than 70% less than 28 ppm), and the patented method is therefore not suitable for steel grades with higher nitrogen content.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a method for smelting medium-carbon alloy structural steel for a high-cleanliness ball screw, which can ensure that the residual Ti in the steel is less than or equal to 15ppm and greatly reduce the size and the quantity of titanium nitride in the steel by optimizing the structure of raw and auxiliary materials and simultaneously improving the oxidability of molten steel in the refining process aiming at the medium-carbon alloy structural steel for the ball screw containing aluminum, nitrogen and sulfur.

The invention is realized by the following technical scheme:

a smelting method of medium carbon alloy structural steel for a high-cleanliness ball screw comprises the following components in parts by mass: 0.30 to 0.60 percent of C, 0.10 to 0.50 percent of Si, 0.50 to 1.30 percent of Mn, 0.50 to 1.50 percent of Cr, 0.10 to 0.50 percent of Mo, 0.015 to 0.040 percent of Al, 0.0090 to 0.0150 percent of N, 0.005 to 0.025 percent of S, less than or equal to 15ppm of Ti and less than or equal to 10ppm of O, and elements such as Ni, cu and the like can be properly added according to the use requirements of steel grades;

the smelting method comprises the following steps: converter smelting, LF refining, RH vacuum treatment and continuous casting:

the end point temperature of the converter is more than or equal to 1600 ℃, and the end point carbon content is more than or equal to 0.06%; after the smelting of the converter is finished, double-grade steel tapping is carried out by adopting a converter slag stopper and a sliding plate; 1.0kg/t SiC pre-deoxidation is adopted in the tapping process, and then low-titanium alloy (including but not limited to low-titanium low-aluminum silicon iron, low-titanium high-carbon ferrochrome, low-carbon ferromanganese and the like are added to ensure the alloy melting effect in the tapping process), a recarburizing agent, lime and a slagging agent are added.

The low titanium alloy and the slag skimming are common titanium control means in the industry, but the slag skimming operation increases the consumption of manpower and material resources, the slag skimming effect has great correlation with the viscosity of the slag and the level of an operator, and the control effect is unstable.

In the LF refining process, only SiC is adopted for carrying out slag surface deoxidation, lime or fluorite is used for slag regulation, the binary alkalinity (CaO/SiO 2) of slag is controlled to be 1.5-2.5, and the dissolved oxygen of molten steel is controlled to be 20-30ppm; if the chemical composition does not meet the product requirements, common alloy fine adjustment is used, including but not limited to ferrosilicon, high-carbon ferrochrome, silicomanganese and the like; and feeding an aluminum wire at the LF end point to adjust the aluminum content to 0.035-0.045%.

Further, RH adopts nitrogen as lifting gas, the vacuum degree in the vacuum treatment process is less than or equal to 67Pa, and the vacuum treatment time is more than or equal to 10min; and after the blank is broken, a nitrogen-manganese wire is used for adjusting the N content to the required range of the steel grade (N0.0090-0.0150%). And continuously casting and pouring the blank after the soft blowing is more than or equal to 10 min.

The technical scheme principle of the invention is as follows:

(1) The most effective method for controlling titanium nitride inclusions in steel is to control the residual Ti and N contents in the steel, but for steel grades requiring a certain nitrogen content, the requirement for low Ti is further increased. Ti is mainly brought by various raw and auxiliary materials in the steelmaking process, wherein the initial furnace tapping alloying process is brought to the maximum, and then the Ti is increased due to slagging and deoxidizing in the long-time refining process of LF.

(2) The low-alkalinity slag is produced in the refining process, so that the reduction of titanium oxide in the slag can be prevented, the stable control of the sulfur content in the molten steel is facilitated, and the repeated sulfur adjustment during the refining of the high-alkalinity slag is reduced. The oxygen content in the molten steel is controlled by feeding an aluminum wire into the molten steel through an LF end point to directly deoxidize, and the generated inclusions are removed in the subsequent RH high vacuum treatment process, so that the requirements of steel grades on the oxygen content and the inclusion cleanliness are not influenced.

Drawings

Typical morphology of TiN in rolled stock of the embodiment of FIG. 1.

Figure 2 shows typical TiN morphology in a comparative rolled material.

Detailed Description

The present invention is not limited to the following embodiments, and those skilled in the art can implement the present invention in other embodiments according to the disclosure of the present invention, or make simple changes or modifications on the design structure and idea of the present invention, and fall into the protection scope of the present invention. It should be noted that the embodiments and features of the embodiments of the present invention may be combined with each other without conflict.

The invention is described in more detail below with reference to the following examples:

examples

The control effect of the invention on titanium nitride inclusions is illustrated by the smelting process of the structural steel containing the nitrogen-containing medium carbon alloy for the ball screw, and the practical control effect is illustrated by adopting the process in the example 6, wherein the smelting components of the furnace are distributed in the ranges of 0.50 +/-0.02% of C, 0.25 +/-0.03% of Si, 0.90 +/-0.05% of Mn, 0.95 +/-0.03% of Cr, 0.18 +/-0.01% of Mo, 0.020 +/-0.005% of Al, 0.013 +/-0.005% of S and 0.0100% +/-0.0010% of N; repeating six furnaces with the same steel grade and the same process, wherein the production process of one furnace is as follows:

(1) 120kg of SiC is added into the steel discharged from a 120t converter, and then 1820kg of low-titanium high-carbon ferrochrome, 180kg of low-aluminum low-titanium ferrosilicon, 1077kg of low-carbon ferromanganese, 330kg of ferromolybdenum, 400kg of carburant, 500kg of lime and 600kg of slagging agent (the main components are CaO 40 percent and Al2O3 percent), and double-gear steel discharging of a converter slag stopper and a sliding plate are added.

(2) And (4) transferring the ladle to an LF refining furnace for refining, performing slag surface diffusion deoxidation by using 150kg of SiC in the refining process, and supplementing common alloy for adjustment according to detected components. The binary alkalinity of LF refining slag is 1.8, oxygen is determined to be 25ppm before aluminum is fed at the end point, a 300m aluminum wire is fed after oxygen determination to perform molten steel deoxidation, and the Al content is detected to be 0.041 percent after the wire feeding.

(3) RH adopts nitrogen as lifting gas, high vacuum (vacuum degree 20 Pa) is kept for 15min, and 150m nitrogen-manganese line is fed to the target nitrogen content after the vacuum is broken. And performing continuous casting and casting to form a blank after soft blowing for 15 min. Sampling and detecting chemical components of the continuous casting tundish to obtain smelting components.

(4) The rolling specification is phi 80mm.

The Ti content in the smelting components and the TiN distribution in the rolling material are respectively shown in Table 1, and the process can stably control that the Ti content is less than or equal to 15ppm and the maximum size of TiN is less than or equal to 10 mu m. In addition, the total oxygen content of the rolled stock is 6.5-8.2ppm, the oxide non-metal inclusions are graded according to GB/T10561, the B fine is less than or equal to 0.5 grade, the B coarse is less than or equal to 0.5 grade, the C fine is 0 grade, the C coarse is 0 grade, the D fine is less than or equal to 1.0 grade, and the D coarse is less than or equal to 0.5 grade, and compared with a comparative example, the total oxygen content of the rolled stock does not have adverse effects on the oxygen content and the inclusion grade.

Comparative example

Six furnaces are repeated by the same steel grade and the same comparative example process, for example, the production process of 1 furnace is as follows:

(1) After 120kg of Al blocks are added into the steel discharged from a 120t converter, 1810kg of low-titanium high-carbon ferrochrome, 200kg of low-aluminum low-titanium ferrosilicon, 1120kg of low-carbon ferromanganese, 340kg of ferromolybdenum, 400kg of carburant, 500kg of lime, and double-grade steel discharged from a converter slag stopper and a sliding plate.

(2) Transferring the ladle to an LF refining furnace, adding 600kg of lime, using 60kg of aluminum particles and 200kg of SiC for making white slag and strongly deoxidizing in the refining process, wherein the binary alkalinity of the final slag of the slag is 5.0, and the oxygen content is 5.3ppm; and adding common alloy according to the detected components.

(3) In RH, nitrogen is used as lifting gas, high vacuum (the vacuum degree is 15 Pa) is maintained for 15min, and 100m nitrogen-manganese wires are fed to the target nitrogen content after the vacuum is broken. And performing continuous casting and casting to form a blank after soft blowing for 15 min. Sampling and detecting chemical components of the continuous casting tundish to obtain smelting components.

(4) The rolling specification is phi 80mm.

The Ti content in the smelting components and the maximum size of TiN in the rolled stock are shown in Table 1, and the process has large Ti fluctuation and TiN maximum size fluctuation of 10-18 mu m. The total oxygen content of the rolled material is 5.7-9.2ppm, the oxide non-metal inclusions are graded according to GB/T10561, the B fineness is less than or equal to 1.0 grade, the B thickness is less than or equal to 0.5 grade, the C fineness is 0 grade, the C thickness is 0 grade, the D fineness is less than or equal to 1.0 grade, and the D thickness is less than or equal to 1.0 grade.

TABLE 1 examples and comparative examples molten Ti content and maximum size of TiN detection in rolled stock

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered as the technical solutions and their concepts of the present invention within the technical scope of the present invention.

Claims

1. A smelting method of medium carbon alloy structural steel for a high-cleanliness ball screw is characterized by comprising the following steps: the steel comprises the following components in percentage by mass: 0.30-0.60% of C, 0.10-0.50% of Si, 0.50-1.30% of Mn, 0.50-1.50% of Cr, 0.10-0.50% of Mo, 0.015-0.040% of Al, 0.0090-0.0150% of N, 0.005-0.025% of S, less than or equal to 15ppm of Ti, and less than or equal to 10ppm of O;

the end point temperature of the converter is more than or equal to 1600 ℃, and the end point carbon content is more than or equal to 0.06%; after the smelting of the converter is finished, double-grade steel tapping is carried out by adopting a converter slag stopper and a sliding plate; 1.0kg/t SiC pre-deoxidation is adopted in the tapping process, and then low-titanium alloy, carburant, lime and slagging agent are added;

in the LF refining process, siC is adopted for slag surface deoxidation, lime or fluorite is used for slag regulation, and the binary alkalinity CaO/SiO of slag is controlled ₂ The dissolved oxygen of the molten steel is controlled between 1.5 and 2.5 ppm and between 20 and 30ppm; alloy fine adjustment is used to enable the chemical composition to meet the product composition requirement, and an aluminum wire is fed at the LF end point to adjust the aluminum content to 0.035-0.045%.

2. The method of smelting a medium carbon structural alloy steel for a high-cleanliness ball screw according to claim 1, wherein: the low titanium alloy added in the tapping process is any one or more of low-titanium low-aluminum ferrosilicon, low-titanium high-carbon ferrochrome and low-carbon ferromanganese.

3. The method of smelting a medium carbon structural alloy steel for a high-cleanliness ball screw according to claim 1, wherein: the alloy added in the LF refining process comprises any one of ferrosilicon, high-carbon ferrochrome and silicomanganese.

4. The process for controlling titanium nitride inclusions in nitrogen-containing medium carbon alloy structural steel for a ball screw according to claim 1, wherein: RH adopts nitrogen as lifting gas, the vacuum degree in the vacuum treatment process is less than or equal to 67Pa, and the vacuum treatment time is more than or equal to 10min; and after the blank is broken, adjusting the N content to the range required by the steel grade by using a nitrogen-manganese wire, and performing continuous casting and pouring to form a blank after soft blowing is more than or equal to 10 min.