CN111254359A

CN111254359A - Corrosion-resistant rare earth bearing steel and preparation method thereof

Info

Publication number: CN111254359A
Application number: CN202010217278.XA
Authority: CN
Inventors: 刘春伟; 许荣昌; 王中学; 杜显彬; 刘茂文; 何毅; 陈良; 刘成宝; 董丙成; 杨旭; 李传振
Original assignee: Shandong Iron and Steel Co Ltd
Current assignee: Shandong Iron and Steel Co Ltd
Priority date: 2020-03-25
Filing date: 2020-03-25
Publication date: 2020-06-09

Abstract

The invention relates to corrosion-resistant rare earth bearing steel and a preparation method thereof, wherein the corrosion-resistant rare earth bearing steel comprises the following components in percentage by mass: c0.90‑1.10、Si 0.20‑0.40、Mn 0.20‑0.50、Cr 1.35‑1.70、Cu 0.12‑0.26、Al_t0.015-0.035%, P is less than or equal to 0.020%, S is less than or equal to 0.010%, rare earth alloy: 0.003 to 0.005, and the balance of Fe and inevitable impurities. The addition of trace rare earth refines the size of inclusions, reduces the number of inclusions, and obviously prolongs the fatigue life of the bearing steel, while the addition of Cu element obviously improves the surface quality of the bearing steel while improving the corrosion resistance of the bearing steel.

Description

Corrosion-resistant rare earth bearing steel and preparation method thereof

Technical Field

The invention belongs to the field of metallurgical engineering, and relates to corrosion-resistant rare earth bearing steel and a preparation method thereof.

Background

The purification effect of rare earth in steel is mainly shown in that the content of oxygen and sulfur can be deeply reduced, and the harmful effects of elements such as phosphorus, low melting point and the like are reduced. Today, the cleanliness of steel is continuously improved, and the effect of rare earth elements in steel is more focused on the functions of metamorphism and powerful microalloying. Besides the function of modifying and modifying the inclusion, the rare earth also has the function of deforming the inclusion, so that the harmful nonmetallic inclusions in molten steel, such as chain, cusp and strip shapes, can be deformed into equiaxial or close to spindle and spherical RE complex compounds, thereby obviously improving the toughness, plasticity, high-temperature oxidation resistance and other properties of the steel, particularly the impact toughness and anisotropy of the steel. As the rare earth element RE in the molten steel can well control the shape and distribution of inclusions such as oxygen, sulfur and the like, can play a role in purifying the molten steel and the like, and can also refine crystal grains, microalloy and the like in the solidification process of the molten steel, the comprehensive performance of the RE steel is obviously improved.

Although the performance and quality of steel products can be obviously improved by treating the steel by using the RE element, at present, China still has a plurality of problems in the aspect of treating the steel by using the RE element, and the production of the RE steel is directly influenced. 1) The RE addition process and equipment fall behind; 2) aiming at the production of different RE new steel grades, the relation among the RE adding method, the adding amount and the performance needs to be further optimized, and the application field of the RE treated steel grade is obviously limited due to the fact that the steel grade treated by RE in China is single at present; 3) the RE treated steel is easy to generate nozzle nodulation during casting, and the continuous large-scale production of the RE steel is influenced.

Disclosure of Invention

The invention aims to overcome the problems and provides corrosion-resistant rare earth bearing steel and a preparation method thereof.

In order to achieve the above object, the present invention provides a corrosion resistant rare earth bearing steel.

The bearing steel comprises the following chemical components in percentage by weight: c: 0.90-1.10, Si: 0.20-0.40, Mn: 0.20-0.50, Cr: 1.35-1.70, Cu: 0.12-0.26 of Al_t: 0.015-0.035, P is less than or equal to 0.020, S is less than or equal to 0.010, rare earth alloy: 0.003-0.005 and the balance of Fe and inevitable impurities, wherein the rare earth alloy comprises lanthanum and cerium.

The invention provides a preparation method of corrosion-resistant rare earth bearing steel, which comprises the following steps:

1) electric furnace smelting: the bearing steel comprises the following chemical components in percentage by weight: 0.90-1.10% of C, 0.20-0.40% of Si, 0.20-0.50% of Mn, 1.35-1.70% of Cr, 0.12-0.26% of Cu, 0.015-0.035% of Alt, less than or equal to 0.020% of P, less than or equal to 0.010% of S, 0.003-0.005% of rare earth alloy and the balance of Fe and inevitable impurities, wherein the rare earth alloy comprises lanthanum and cerium. The molten steel which is designed and smelted according to the chemical components is cast into a square billet with the section of 180mm multiplied by 220 mm. In order to ensure optimum furnace conditions and to reduce the increase in gas content in the steel due to furnace factors, the use of new ladles is not permitted. The foam slag is manufactured and evenly decarburized in the smelting process, and the P and Ti removal operation is enhanced by adopting large-slag-amount deep decarburizing. The end point control target C is more than or equal to 0.20 percent, P is less than or equal to 0.012 percent, and the content of other residual elements meets the standard requirement; the tapping temperature is 1630-1670 ℃. Adding steel core aluminum along with steel flow in the electric furnace tapping process, and then adding other alloys and slag making materials;

2) refining in an LF furnace: argon is blown at the bottom in the whole process for stirring, the pressure of the argon can be properly increased in the early stage according to the condition, and the inclusion floating is ensured by adopting small-pressure soft blowing before leaving the station. Controlling the alkalinity of the slag to be not less than 3.1, feeding an aluminum wire before sampling for the first time, sampling under white slag and carrying out full analysis, wherein the white slag retention time in the refining process is not less than 15 min. According to the analysis result of the primary sample, adjusting the contents of C, Si, Mn, Cr and other components according to the internal control requirement; before LF tapping, controlling the total aluminum content in steel to be 0.015-0.035%;

3) adding rare earth alloy wires after LF refining; ensuring that the argon blowing stirring time is not less than 25min (controlled at 25-30 min) after entering VD;

4) vacuum degassing in a VD furnace: argon blowing and stirring time is not less than 25min, slag is removed before the steel ladle is put into a VD furnace, the vacuum degree is not more than 60Pa, and the holding time is not less than 18 min;

5) continuous casting: the special continuous casting covering slag for bearing steel is adopted, a covering agent is coated in the use process, and the temperature of a casting blank entering a tension leveler is more than or equal to 880 ℃; .

6) Entering a pit for slow cooling: putting the casting blank after continuous casting in the step 5) into a pit in time for slow cooling;

7) rolling: slowly heating and preheating a blank at the temperature of below 600 ℃, and after the steel blank is completely austenitized, increasing the heating speed, ensuring that the steel blank is uniformly heated, preventing decarburization and furnace sticking, ensuring that the initial rolling temperature of rough rolling is 1060-1130 ℃ and ensuring the final rolling temperature of finish rolling is 920-980 ℃;

8) slow cooling: and (4) slowly cooling after rolling, wherein the slowly cooling time is 18-24 hours, and the temperature after slowly cooling is not more than 100 ℃.

Preferably, the amount of steel core aluminum added along with steel flow in the electric furnace tapping process in the step 1) is 1.5-3.5 kg/t steel.

Preferably, the aluminum wire is fed in the step 2), the feeding amount of the aluminum wire is 10-50 m, and the total aluminum content in the steel is controlled to be 0.015-0.035 wt%.

Preferably, the alkalinity of the slag in the step 2) is controlled to be 3.1-3.4, and the white slag holding time in the refining process is controlled to be 15-18 min.

Preferably, the amount of the rare earth alloy wire added in the step 3) is 0.03-0.05 kg/ton of steel, and more preferably 0.04 kg/ton of steel, and after the addition amount of the rare earth alloy wire exceeds 0.05 kg/ton of steel, a water gap of a crystallizer starts to be blocked, so that smooth production is seriously affected, wherein the rare earth alloy wire comprises lanthanum and cerium, and the ratio of the lanthanum to the cerium is 1: 1-2: 1.

Preferably, the argon blowing and stirring time in the step 4) is 25-30 min, the vacuum degree is controlled to be 50-60 Pa, and the holding time is 18-23 min.

Preferably, after the vacuum degassing treatment of the VD furnace in the step 4), the soft argon blowing time is not less than 12-18 min, the steel feeding temperature is controlled to be 1505-1535 ℃, and further preferably, the soft argon blowing time is 12-18 min.

Preferably, the temperature of a liquid phase line of the steel in the continuous casting in the step 5) is 1445-1455 ℃, the temperature of a superheat degree of a tundish is controlled to be 20-30 ℃, the drawing speed of a billet with the thickness of 180mm multiplied by 220mm is controlled to be 0.95 +/-0.02 m/min, and the tail end of a crystallizer is electromagnetically stirred.

Preferably, the pit entry temperature in the step 6) is not lower than 560 ℃, and the slow cooling time is not less than 24 hours, so as to ensure that the pit exit temperature is not more than 200 ℃; preferably, the pit entering temperature in the step 6) is 560-650 ℃, and the slow cooling time is 24-30 hours, so as to ensure that the pit discharging temperature is not more than 200 DEG C

Preferably, the steel bar is rolled into a bar material with the diameter of 30-55 mm in the step 7).

The invention adds trace rare earth and a small amount of Cu, obviously improves the internal quality and the external quality of steel, purifies molten steel by adding the rare earth, improves the corrosion resistance of the steel by adding the Cu, does not greatly increase the production cost, has little difficulty increase of the technical process compared with the prior art, but has obvious effect of improving the quality of the steel.

Compared with the prior art, the invention has the advantages that:

1) the invention adds rare earth in a wire feeding mode, fully ensures the argon stirring time, accurately controls the adding amount, effectively solves the problem of nodulation of a molten rare earth steel opening, reduces the quantity and size of impurities and obviously prolongs the fatigue-resistant service life.

2) The proper amount of copper is added into the steel, so that the corrosion resistance of the steel can be improved, the corrosion resistance is obviously enhanced, and the surface quality of the steel is improved. Copper plays the effect of activation negative pole in the atmospheric corrosion process, makes the steel produce the anodic passivation to slowed down atmospheric corrosion, copper can also improve the structure of rust layer in addition, forms the inner layer of bilayer structure rust layer, hugs closely the steel matrix, makes its tissue more even compact.

Drawings

FIG. 1 is a statistical view of the scanning of inclusion planes according to the present invention;

FIG. 2 is a graph of the weight loss ratio of the salt spray test of the present invention.

Detailed Description

The present invention will be further described with reference to the following specific examples.

The preparation process of the invention comprises the following steps: the method comprises the following steps of electric furnace smelting → LF furnace refining + VD vacuum degassing treatment → continuous casting (electromagnetic stirring) → slow cooling → rolling into a material → slow cooling process.

1. Electric furnace smelting: smelting in an electric furnace, then LF refining, VD vacuum degassing, wherein the smelting billet comprises the following chemical components in percentage by weight: 0.90-1.10 percent of C, 0.20-0.40 percent of Si, 0.20-0.50 percent of Mn, 1.35-1.70 percent of Cr, 0.12-0.26 percent of Cu, and Al_t0.015-0.035 wt%, P less than or equal to 0.020 wt%, S less than or equal to 0.010 wt%, La + Ce 0.003-0.005 wt%, and Fe and inevitable impurity for the rest. The actual electric furnace smelting components are shown in Table 1, the furnace No. 1 is not added with rare earth and copper, the furnace Nos. 2 and 3 are added with rare earth and copper, and three furnaces are used for performance comparison experiments. Controlling the alkalinity of the final slag to be 3.2, and carrying out VD vacuum degassing for 20 minutes. Then, a three-machine three-flow small billet caster is adopted to cast the molten steel into a billet with the section of 165mm multiplied by 200 mm.

TABLE 1 actual electric furnace smelting composition (wt/%)

Furnace number	C	Si	Mn	P	S	Cr	Al_t	Cu
									1	0.97	0.21	0.31	0.013	0.002	1.5	0.028
2	0.96	0.22	0.32	0.011	0.002	1.5	0.026	0.18
									3	0.98	0.2	0.31	0.014	0.002	1.5	0.028	0.19

The contents of rare earth in the steels of furnace No. 2 and furnace No. 3 are actually measured to be 11ppm and 12ppm respectively, and the yield of the rare earth elements is calculated to be about 30 percent according to the addition of 0.04 kg/ton steel.

2. Heating: the temperature of the heating furnace is 1100 ℃, the heating time is 5 hours, and then the steel is taken out of the furnace for rolling.

3. Rolling and cooling: the initial rolling temperature is 1090 ℃, the final rolling temperature is 950 ℃, and finally, the steel bar with the diameter of 35mm is rolled. And (3) collecting the rolled steel plates in time, putting the rolled steel plates into a pit for slow cooling for 24 hours, and ensuring that the temperature is not more than 100 ℃ after slow cooling.

4. And (3) performance test:

(1) inclusion plane scanning statistics

Sampling and detecting the three-furnace steel, wherein the detection area is 100mm²The statistics of the number change of the inclusions with different sizes is shown in table 2, the number of the inclusions is obviously reduced after the rare earth is added, and particularly, the number 2 of the inclusion with the size of more than 10um is reduced by 74 percent, and the number III of the inclusion is reduced by 78 percent. More intuitively as shown in fig. 1.

TABLE 2 inclusion surface scanning statistical table

	Total number of inclusions	5～10um	10um～30um	＞30um
					Furnace number 1	389	266	99	24
Furnace number 2	222	190	30	2
					Furnace number 3	232	205	24	3

(2) Fatigue life detection

The Rolling Contact Fatigue (RCF) life of the three-furnace steels was measured, and the results are shown in Table 3, in which the fatigue life of the rare earth steels was doubled.

TABLE 3L of three-furnace test steels₁₀Life span

Lifetime (. times.10)⁶r)	Furnace number 1	Furnace number 2	Furnace number 3
				L₁₀	5.15	10.04	10.10

(3) Salt spray test

A salt spray experiment is used as an indoor accelerated corrosion experiment, the outdoor atmospheric corrosion condition can be rapidly simulated, a chemical pure sodium chloride reagent is adopted in the experiment, the chemical pure sodium chloride reagent is dissolved in deionized water, a 5% sodium chloride solution is prepared, the pH is adjusted to be 6.5-7.2, a neutral salt spray experiment is carried out by using continuous spraying, the experiment periods are respectively 7 days, 14 days, 21 days and 28 days, the rust removal weight loss analysis is carried out, the result is shown in figure 2, the weight loss rate is reduced after copper elements are added into furnace numbers 2 and 3, and the corrosion resistance is enhanced.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. The corrosion-resistant rare earth bearing steel is characterized by comprising the following chemical components in percentage by weight: c: 0.90-1.10, Si: 0.20-0.40, Mn: 0.20-0.50, Cr: 1.35-1.70, Cu: 0.12-0.26 of Al_t: 0.015-0.035, P is less than or equal to 0.020, S is less than or equal to 0.010, rare earth alloy: 0.003-0.005 and the balance of Fe and inevitable impurities, wherein the rare earth alloy comprises lanthanum and cerium.

2. A method for producing the corrosion-resistant rare earth bearing steel of claim 1, comprising the steps of:

1) electric furnace smelting: the end point control target C is more than or equal to 0.20 percent, the P is less than or equal to 0.012 percent, and the tapping temperature is 1630-1670 ℃;

2) refining in an LF furnace: controlling the alkalinity of the slag to be not less than 3.1 and keeping the white slag for not less than 15 min;

3) adding rare earth alloy wires after LF refining;

4) vacuum degassing in a VD furnace: argon blowing and stirring time is not less than 25min, vacuum degree is not more than 60Pa, and holding time is not less than 18 min;

5) continuous casting: the temperature of the casting blank entering a tension leveler is more than or equal to 880 ℃;

6) entering a pit for slow cooling: putting the casting blank after continuous casting in the step 5) into a pit for slow cooling;

7) rolling: slowly raising the temperature of the blank below 600 ℃ for preheating, wherein the rough rolling starting temperature is 1060-1130 ℃, and the finish rolling finishing temperature is 920-980 ℃;

3. The method of claim 2, wherein the steel-cored aluminum is added along with the steel stream during the tapping of the electric furnace in the step 1), and the amount of the added steel-cored aluminum is 1.5 to 3.5kg/t steel.

4. The method as claimed in claim 2, wherein the aluminum wire is fed in the step 2), the amount of the fed aluminum wire is 10-50 m, and the total aluminum content in the steel is controlled to be 0.015-0.035 wt%.

5. The method according to claim 2, wherein the amount of the rare earth alloy wire added in the step 3) is 0.03-0.05 kg/ton of steel, wherein the rare earth alloy wire comprises lanthanum and cerium, and the ratio of lanthanum to cerium is 1: 1-2: 1.

6. The method as claimed in claim 2, wherein after the vacuum degassing treatment of the VD furnace in the step 4), the soft argon blowing time is not less than 12 minutes, and the steel feeding temperature is controlled to be 1505-1535 ℃.

7. The method as claimed in claim 2, wherein the liquidus temperature of the steel in the step 5) is 1445-1455 ℃, the superheat temperature of the tundish is controlled to be 20-30 ℃, the casting speed of the 180mm x 220mm billet is controlled to be 0.95 +/-0.02 m/min, and the tail end of the crystallizer is stirred by using electromagnetism.

8. The method of claim 2, wherein the pit entry temperature in the step 6) is not lower than 560 ℃, the slow cooling time is not less than 24 hours, and the pit exit temperature is not more than 200 ℃.

9. The method of claim 2, wherein step 7) is performed by rolling into a bar with a diameter of 30-55 mm.