阅读说明：本技术 一种圆钢的调质工艺及其应用 (Tempering process of round steel and application thereof ) 是由 朱云海 于 2020-05-12 设计创作，主要内容包括：本发明涉及一种圆钢的调质工艺,包括(1)淬火：根据圆钢所属钢种确定淬火温度,采用连续辊底式明火炉进行淬火加热,圆钢进炉前将炉内加热温度设置到淬火温度,待炉内炉气温度到温后,圆钢经辊道步进穿过炉膛,圆钢的在炉时间保持在(0.57—0.63)min/mm<Sup>*</Sup>圆钢直径mm,使得圆钢表面达到淬火温度的同时沿径向存在温度梯度：圆钢表面和圆钢芯部的温度差在200—230℃范围内,出炉后水淬,水淬时间0.1s/mm,淬火至料温≤100℃出水；(2)低温回火：淬火后的圆钢入炉再加热,回火温度280-330℃,保温4小时以上,充分均热,出炉后空冷。采用连续辊底式明火炉,通过控制加热时间在升温过程中让圆钢在其径向形成温度梯度,由此调控圆钢的淬硬层深度,确保芯部韧性。(The invention relates to a round steel quenching and tempering process, which comprises the following steps of (1) quenching: determining the quenching temperature according to the type of the round steel, quenching and heating by using a continuous roller hearth type open-hearth furnace, setting the heating temperature in the furnace to the quenching temperature before the round steel enters the furnace, stepping the round steel through a roller table to pass through a hearth after the temperature of furnace gas in the furnace reaches the temperature, and keeping the in-furnace time of the round steel at (0.57-0.63) min/mm * The diameter of the round steel is mm, so that the surface of the round steel has a temperature gradient along the radial direction when reaching the quenching temperature: surface of round steel andthe temperature difference of the round steel core part is within the range of 200-230 ℃, water quenching is carried out after discharging, the water quenching time is 0.1s/mm, and water is discharged after quenching until the material temperature is less than or equal to 100 ℃; (2) low-temperature tempering: and (3) putting the quenched round steel into a furnace, reheating the round steel at the tempering temperature of 280-330 ℃, preserving heat for more than 4 hours, fully soaking the round steel, and cooling the round steel in air after discharging the round steel out of the furnace. A continuous roller-hearth open-hearth furnace is adopted, and the round steel forms a temperature gradient in the radial direction of the round steel in the temperature rising process by controlling the heating time, so that the depth of a hardening layer of the round steel is regulated and controlled, and the toughness of a core part is ensured.)

1. A quenching and tempering process of round steel is characterized by comprising the following steps: comprises that

(1) Quenching: determining the quenching temperature according to the steel type of the round steel, quenching and heating by adopting a continuous roller hearth open-hearth furnace, setting the heating temperature in the furnace to the quenching temperature before the round steel enters the furnace, and after the temperature of furnace gas in the furnace reaches the temperature, the round steel passes through a hearth step by step through a roller way, keeping the in-furnace time of the round steel at (0.57-0.63) min/mm round steel diameter mm, so that the surface of the round steel reaches the quenching temperature and simultaneously has a temperature gradient along the radial direction: the temperature difference between the surface of the round steel and the core of the round steel is within the range of 200-230 ℃, water quenching is carried out after discharging, the water quenching time is 0.1s/mm, and water is discharged after quenching until the material temperature is less than or equal to 100 ℃;

(2) low-temperature tempering: and (3) putting the quenched round steel into a furnace, reheating the round steel at the tempering temperature of 280-330 ℃, preserving heat for more than 4 hours, fully soaking the round steel, and cooling the round steel in air after discharging the round steel out of the furnace.

2. The round steel tempering process according to claim 1, wherein: the steel grade adopted by the round steel is 65Mn or 70Mn2, and the quenching temperature is 800-.

3. The round steel tempering process according to claim 2, wherein: the tissue hardness within 8mm from the surface of the round steel after tempering is 50-55HRC, and the core hardness of the round steel is 24-28 HRC.

4. Use of the round steel hardening and tempering process according to claim 1, 2 or 3, wherein: used for quenching and tempering of the grinding rod.

Technical Field

The invention relates to a round steel quenching and tempering process, namely a heat treatment process for round steel.

Background

A grinding rod is a grinding medium used in rod mills for grinding material in the mill. The grinding rod is widely applied to rod mills in industries such as metallurgical mines, cement building materials and the like.

At present, round steel (also called bar) steel used for manufacturing grinding rods has 65Mn and 70Mn2, quenching and tempering treatment of quenching and tempering is required in the technological process of reprocessing the round steel into the grinding rods, medium-frequency induction heating is widely adopted to heat the round steel at present, and if the production method of the grinding rods in the grinding machine disclosed in the publication No. CN102703669A is adopted, the material rods are conveyed to a medium-frequency induction heating furnace through a roller way to be continuously heated, the material rods rotate around the axes of the material rods on the roller way to realize more uniform heating, and the quenching is realized in a sequential heating mode.

At present, the round steel quenching and tempering process aiming at the grinding rod production field has no unified standard, and the grinding rods produced by various manufacturing enterprises also show larger performance difference due to quenching and tempering. The hardness at the position 8mm away from the surface of the bar is up to 58HRC and 40HRC, namely the depth of the hardening layer on the surface of the round steel is inconsistent and the difference is large. The hardness of the core of the grinding rod heated by medium-frequency induction is generally high after quenching, the hardness of the core is generally higher than 36HRC, the toughness of the core is poor, and the grinding rod is more easily broken, so that the service life of the product is influenced.

The round steel used as the grinding rod requires that the depth of a hardening layer after quenching and tempering cannot be too large, so that the hardness of the surface of the round steel and the toughness of the core part are ensured.

Disclosure of Invention

Aiming at the quenching and tempering process of round steel which has requirements on the central toughness and is used as a grinding rod, the quenching and heating process is optimally researched and controlled, the round steel is heated by using a continuous roller hearth type open-flame furnace, the temperature difference is generated along the radial direction of the round steel by controlling the furnace temperature and the stepping speed of the round steel in the furnace, namely, the radial quenching temperature of the round steel is changed in a gradient manner, so that the quenching and hardening layer depth of the round steel is controlled, and the round steel with near surface, high hardness and high toughness of a core part is finally obtained. The round steel quenching and tempering process designed by the invention can ensure that the degree of bending per meter of the quenched and tempered steel is less than or equal to 2 mm/m.

The technical scheme adopted by the invention for solving the problems is as follows: a quenching and tempering process for round steel comprises the following steps

(1) Quenching: determining the quenching temperature according to the steel type of the round steel, quenching and heating by adopting a continuous roller hearth open-hearth furnace, setting the heating temperature in the furnace to the quenching temperature before the round steel enters the furnace, stepping the round steel through a roller table to pass through a hearth at a constant speed after the temperature of furnace gas in the furnace reaches the temperature, keeping the in-furnace time of the round steel at (0.57-0.63) min/mm round steel diameter mm, and ensuring that the surface of the round steel has temperature gradient along the radial direction when reaching the quenching temperature: the temperature difference between the surface of the round steel and the core of the round steel is within the range of 200-230 ℃, heat preservation is not carried out, water quenching is carried out after the round steel is directly discharged from a furnace, the water quenching time is 0.1s/mm, and water is discharged when the material temperature is less than or equal to 100 ℃;

(2) low-temperature tempering: and (3) putting the quenched round steel into a furnace, reheating the round steel at the tempering temperature of 280-330 ℃, preserving heat for more than 4 hours, fully soaking the round steel, and cooling the round steel in air after discharging the round steel out of the furnace.

Compared with the prior art, the invention has the advantages that: the key of this application lies in quenching, to the quenching heating of round steel, and the extensive way adopts induction heating, and induction heating's characteristics are that the heating homogeneity is good, and the round steel is heated from the core to the surface is synchronous almost, can obtain great hardening depth of layer like this, even big specification round steel, the hardness of its core can not avoid yet to be higher than the technology ideal value, causes the toughness of core poor. The continuous roller hearth open-fire furnace is adopted, the heating mode is different from that of induction heating, the round steel absorbs heat from the outside to the inside in the open-fire furnace to heat, a temperature gradient is formed in the radial direction of the round steel in the heating process, the heating temperature is high near the surface of the round steel, the core part is heated at a low temperature, the depth of a hardening layer of the round steel is regulated and controlled through the temperature, and the toughness of the core part is ensured.

The grinding rod of the invention can achieve the following mechanical properties after quenching and tempering: the hardness can reach 50-55HRC within 8mm from the surface of the bar, the core part is 24-28HRC, and the bending degree per meter of the steel after hardening and tempering can be ensured to be less than or equal to 2 mm/m.

Drawings

FIG. 1 is a graph of a quenching process of the present invention;

FIG. 2 is a graph of the tempering process of the present invention;

FIG. 3 shows the structure of the invention after tempering at a distance of 5mm from the surface of the round steel;

FIG. 4 shows the structure of the tempered round steel core of the present invention;

FIG. 5 is a variation curve of the round steel along different radial positions and the furnace gas temperature during quenching and heating in the embodiment of the invention;

FIG. 6 shows the macrostructure of a round steel of 120mm diameter in example 1 of the present invention after tempering.

Detailed Description

The present invention will be described in further detail below with reference to the embodiments of the drawings, which are illustrative and intended to be illustrative of the present invention and are not to be construed as limiting the present invention.

The quenching and tempering process of the grinding rod of the embodiment utilizes a continuous roller hearth type open fire quenching and tempering line to carry out quenching and tempering, and utilizes high-temperature furnace gas to comprise the following steps: (1) quenching: the quenching temperature is 800-.

Water quenching the bar for 0.1s/mm until the temperature is less than or equal to 100 ℃ and discharging water; (2) low-temperature tempering: after quenching, the round steel is directly put into a furnace, the tempering temperature is set to be 280-330 ℃, the temperature is kept for 4 hours, the round steel is soaked in heat, and the round steel is discharged from the furnace for air cooling. Specific embodiments of the present invention are described in detail below.