CN114990427B

CN114990427B - Hot-rolled corrosion-resistant round steel and preparation method thereof

Info

Publication number: CN114990427B
Application number: CN202210438359.1A
Authority: CN
Inventors: 郑亚明; 邹钰玺; 刘永军
Original assignee: Jingjiang Special Steel Co Ltd
Current assignee: Jingjiang Special Steel Co Ltd
Priority date: 2022-04-25
Filing date: 2022-04-25
Publication date: 2023-06-30
Anticipated expiration: 2042-04-25
Also published as: CN114990427A

Abstract

The invention relates to a hot-rolled corrosion-resistant round steel and a preparation method thereof, wherein the content of Cu, sb, P, S is strictly controlled according to a set mass percentage when steel is made from a steel billet, so that the corrosion resistance of the steel billet is improved; after austenitizing and reheating, rolling the steel billet in a pipeline mode in four steps: quick descaling; reciprocating cogging with large rolling reduction and fast rolling to obtain middle square billet; cutting the end of the intermediate square billet before entering a continuous rolling mill, and rapidly performing continuous rolling to reduce the possibility of precipitation of copper and antimony in steel at a grain boundary in a high-temperature stage for a long time, reduce rolling cracks, and control the finishing rolling temperature of round steel to be higher than Ar3; after sawing, the material is concentrated on a cooling bed to perform offline temperature control, so that the mechanical performance of the material is improved. The production method organically combines the process requirement and the production requirement, thereby not only meeting the requirement of continuous casting blank on the furnace time, but also guaranteeing the process time requirement of each rolling, guaranteeing the compact production rhythm, guaranteeing the furnace time of the billet, and guaranteeing the rapid rolling at high temperature.

Description

Hot-rolled corrosion-resistant round steel and preparation method thereof

Technical Field

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to hot-rolled corrosion-resistant round steel and a preparation method thereof.

Background

The demand of corrosion-resistant steel is increased frequently along with the development of offshore oil, and meanwhile, in order to reduce the atmospheric corrosion loss, research is conducted on the aspects of adding alloy elements into steel and improving the corrosion resistance of the steel and the service life of the steel, so that the demand of developing various atmospheric corrosion-resistant low alloy steels is met.

The steelmaking difficulty of corrosion-resistant steel is controlled by adding alloy into high-quality low-carbon steel so as to increase the corrosion resistance of the steel. Copper, phosphorus, chromium, molybdenum, nickel and the like are alloy elements with corrosion resistance, and the alloy elements can be enriched in a rust layer to promote the formation of an amorphous rust layer, improve the structure of the rust layer, improve the compactness and the cohesiveness to the surface of steel, and enhance the isolation effect with atmospheric seawater, thereby slowing down the corrosion rate and improving the corrosion resistance of the steel. Among the above alloy elements, copper is the alloy element that improves the atmospheric corrosion resistance of steel best. Steels containing 0.2% to 0.5% copper have exhibited significant corrosion resistance in atmospheric environments. The mechanism is different, and it is considered that cathode contact between the steel and copper secondarily precipitated on the surface of the steel promotes anodization of the steel and forms a rust layer with good protection. Copper is also considered to form a barrier layer having Cu0 as a main component and firmly bonded to the base between the base and the rust layer. It is also believed that the alloying elements such as copper and phosphorus alter the hygroscopicity of the rust layer, thereby increasing the critical humidity. Thereby being beneficial to improving the corrosion resistance of the steel.

The rolling difficulty of corrosion-resistant steel is controlled in that when alloy elements, cu, cr, sb and other elements are added into high-quality low-carbon steel, the reheating temperature and time requirements of a steel billet are strict, and in the plastic deformation process, in order to ensure the quality of finished round steel, rolling cracks need to be prevented, and the deformation temperature needs to be strictly controlled.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a preparation method of hot-rolled corrosion-resistant round steel aiming at the prior art, and the preparation method organically combines the process requirement and the production requirement, thereby not only meeting the requirement of continuous casting blank on the time of a furnace, but also guaranteeing the process time requirement of each rolling, guaranteeing the compact production rhythm, and ensuring the time of the billet in the furnace, and also guaranteeing the rapid rolling at high temperature.

The invention solves the problems by adopting the following technical scheme: a hot rolled corrosion resistant round steel comprising the following chemical components in mass percent: c: less than or equal to 0.12 percent, si:0.20 to 0.40 percent, mn:0.35 to 0.65 percent, 0.70 to 1.10 percent of Cr, S: less than or equal to 0.02 percent, cu:0.25 to 0.45 percent, sb:0.04 to 0.10 percent, P: less than or equal to 0.03 percent, and the balance being Fe and unavoidable impurity elements; the deviation of Sb was +0.02%.

The setting of the ranges of the elements is based on the following:

c: the relation between the carbon content and corrosion resistance of the steel is that the carbon content is high, the corrosion resistance is poor, but the abrasion resistance and hardness are high, and the content of the carbon content is controlled to be 0.12 percent.

Si: is a deoxidizing element in steel, and increases the strength of the steel in a solid solution strengthening form. When the Si content is less than 0.20%, the deoxidizing effect is poor, and when the Si content is high, the toughness is lowered. The Si content of the invention is controlled between 0.20 and 0.40 percent.

Mn: the hardenability of the steel is improved, the strength of the steel is improved through solid solution strengthening, the transformation temperature is reduced, the cementite thickness and lamellar spacing of pearlite are reduced, and the solid solubility of Nb in the steel can be improved. However, mn tends to promote segregation of harmful element P and the like to grain boundaries, and too high Mn can reduce impact toughness of steel, and the Mn content is controlled to be 0.35-0.65%.

Cr: carbide forming elements increase the hardness of the material and prevent the growth of crystal grains, but too high addition of Cr can reduce the toughness and increase the manufacturing cost, so the Cr content is controlled to be 0.7-1.1%.

P, sb: phosphorus and antimony are used as impurity elements, and have a certain effect on improving the tensile strength of carbon steel, but also increase the brittleness of the steel, especially the low-temperature brittleness. The antimony element with higher melting point of the low alloy steel is easy to migrate and aggregate at high temperature, so that the high-temperature tempering brittleness of the low alloy steel is caused. When alloy steel works at high temperature in the growing period of high-temperature tempering heat treatment, antimony element in the alloy steel is easy to migrate and gather at high temperature. Since these elements generally have lower melting points than the alloying elements, they will "fracture" the material matrix, causing the alloy steel to exhibit brittleness at high temperatures. This brittleness of the alloy steel is referred to as red embrittlement because it occurs at red-hot temperatures. In general, low alloy steels are smelted by a higher-grade smelting method (such as electric furnace smelting). The invention controls the Sb content to be 0.04-0.10% and the P content to be below 0.03%.

S: s and Mn form strip sulfide inclusions, so that the cutting performance of the steel is improved. The Cr content is controlled below 0.02%.

Cu: the addition of a small amount of copper into the steel can improve the atmospheric corrosion resistance of the low alloy structural steel and the rail steel, has more remarkable effect when being matched with phosphorus for use, and can slightly improve the high-temperature oxidation resistance of the steel. Can improve the fluidity of molten steel and is beneficial to casting performance. Copper with the mass fraction of 2% -3% is added into the stainless acid-resistant steel, so that the corrosion resistance of the steel to sulfuric acid and hydrochloric acid can be improved. The Cu content is controlled between 0.25 and 0.45 percent.

The invention provides a method for preparing the hot-rolled corrosion-resistant round steel, which comprises the steps of smelting molten steel according to element composition design, casting the molten steel into steel billets, discharging the slowly cooled square billets from a heating furnace, and carrying out pipeline rolling in four steps:

firstly, descaling, removing surface oxide skin, accelerating the temperature drop of a continuous casting billet, and then cogging the continuous casting billet when the temperature of the continuous casting billet reaches 1030-1090 ℃, wherein the retention time is not too long, and the whole process is controlled to be completed within 20 seconds;

step two, reciprocating cogging, namely rolling the intermediate square billet into an intermediate square billet by adopting a reciprocating rolling mill through 9-13 passes, wherein the deformation of each pass is more than or equal to 11%, the total deformation of the continuous casting billet to the intermediate billet is more than or equal to 70.8%, and the whole process is controlled to be completed within 1.5 minutes;

and thirdly, cutting the head and continuously rolling, wherein in the cogging process, the head and the tail of the billet are easy to crack due to the large reduction and the grain boundary segregation influence of Mn, so that the rolled intermediate billet is cut off before entering a continuous rolling mill, and the head and the tail blanks are necessarily cut off. The continuous rolling intermediate billet is directly fed into a continuous rolling mill to be rolled into round steel bars through 6-10 passes after being cut, the deformation of each pass is more than or equal to 12%, the total deformation of the intermediate billet to the round steel is more than or equal to 80%, and the final rolling temperature of the round steel is 900-980 ℃ and is higher than Ar3. The whole process is controlled to be completed within 1 minute;

and fourthly, after the bar is rolled, transferring the bar to a sawing roller way for sawing. And (3) after sawing the bar, the bar is delivered to a cooling bed to control the cooling speed in a concentrated manner, and then delivered to a line for collection and packaging. The round steel after being taken off line can obtain various indexes of strength, extensibility and impact toughness, and can be directly processed into required parts.

Preferably, the molten steel smelting at least comprises primary smelting, LF furnace refining and vacuum degassing treatment. Wherein, the primary smelting is to smelt the alloy raw material block and molten iron in a converter or an electric furnace, and the content of carbon element, copper and antimony metal elements is strictly controlled.

Preferably, a continuous casting square billet is obtained in a continuous casting mode to be used as a billet, the superheat degree of molten steel casting is designed to be 15-30 ℃ during continuous casting, and the continuous casting square billet is put into a pit for slow cooling after being molded.

Preferably, the reheating temperature of the billet is 1150-1210 ℃, the temperature is kept within the temperature range to enable the alloy elements to be fully dissolved in solid and the structure to be fully austenitized, the heating time of the high-temperature section is controlled to be about 2 hours, and the furnace time of the high-temperature section is strictly controlled. Copper and antimony in steel are easy to separate out at grain boundaries at a high temperature stage for a long time, and heavy rolling cracks can be caused.

Preferably, the descaling and cogging are strictly controlled, the rolling is fast, the residence time in the high-temperature stage is reduced as much as possible, the heating time is controlled well, and 4 rolling production links are strictly controlled, so that the quality of round steel finished products is ensured.

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

1. the round steel forming process is finely divided into a plurality of continuous working procedures, the finishing time of each working procedure is limited, batch rolling conditions are provided for the production line of round steel, after a first billet enters a second working procedure, a second billet can enter a first working procedure, after a second billet enters the second working procedure, a third billet can enter the first working procedure, and the like. The production rhythm is compact, and the production efficiency can be obviously improved.

2. The method of forming steel billet to round steel (bar) adopts the modes of high temperature and high pressure, rapid rolling and rapid cooling of finished products, wherein

(1) Before cogging, the billet is descaled and cooled to 1050-1110 ℃, the cogging temperature is lower than that of cogging after traditional reheating, which is beneficial to deferring the recrystallization of deformed austenite grains, enabling the austenite grains to be flattened as much as possible, and further promoting the refinement of the austenite grains after recrystallization.

(2) The continuous rolling stage adopts a large-reduction process, can effectively prevent the recrystallization of austenite grains, obtain large-deformation austenite grains with more deformation bands, and is favorable for obtaining ferrite and pearlite clusters with small sizes in the subsequent cooling phase transformation stage, thereby improving the strength and the plasticity and toughness;

(3) after cogging, the continuous rolling is carried out by fast forward rolling, the temperature is controlled to be higher than 950 ℃, the deformation is realized in a short time, and the precipitation of Cu and Sb elements to grain boundaries is reduced, so that rolling cracks are not generated.

(4) After continuous rolling, the steel is quickly sent to a cooling bed, the temperature is guaranteed to be higher than 700 ℃, meanwhile, the temperature of the lower cooling bed is controlled to be about 500 ℃, the steel is prevented from being cooled extremely fast, the transformation of the structure is more uniform, ferrite is not intensively generated, and the influence on the structure and the performance is large. The control of the cooling time can meet the mechanical performance requirements of clients on yield strength, tensile strength, elongation after break and the like.

Detailed Description

The present invention is described in further detail below with reference to examples.

Example 1

The diameter of the round steel related to the embodiment is 75mm, and the round steel comprises the following chemical components in percentage by mass: c:0.06%, si:0.28%, mn:0.35%, cr 0.7%, S0.012%, P:0.015%, cu 0.27%, sb:0.04%, the balance being iron and unavoidable impurity elements.

Smelting the round steel by an electric furnace and refining the round steel by LF to produce molten steel; the forming process after discharging the furnace is carried out by the following four steps:

(1) the first blank is subjected to primary descaling by high-pressure water on a roller way to remove surface oxide skin; at the moment, the temperature is 1085.3 ℃, then the blank is rolled into an intermediate blank by a reciprocating rolling mill through 9 times, the single-pass deformation is more than or equal to 13%, and the specification of the intermediate blank is 170X175mm ² The process realizes rapid rolling with large rolling reduction, reduces the generation of rolling cracks and the deformation time of a high-temperature section, and is controlled to be completed within 1.5 minutes.

The first intermediate billet is fed into a continuous rolling unit after head cutting at 991.4 ℃, is directly fed into the continuous rolling unit, is rolled into phi 75mm round steel through 8 times, the single-pass deformation is more than or equal to 15%, the finishing temperature is 950.6 ℃, is moved to a sawing roller way for sawing after rolling, the surface temperature is returned to 793 ℃, the upper cooling bed temperature is 769.7 ℃ after sawing, the lower cooling bed temperature is 536.5 ℃, is stacked and cooled in a later line, and is packed and put into storage after straightening and barreling finishing procedures; the round steel is directly processed into parts with required shapes.

Example 2

The diameter of the round steel related to the embodiment is 75mm, and the round steel comprises the following chemical components in percentage by mass: c:0.06%, si:0.3%, mn:0.4%, cr 0.9%, S0.018%, P:0.025%, cu 0.28%, sb:0.03%, the balance being iron and unavoidable impurity elements.

(1) the second blank is subjected to primary descaling by high-pressure water on a roller way to remove surface oxide skin; at the moment, the temperature is 1054.9 ℃, then the blank is rolled into an intermediate blank by a reciprocating rolling mill through 9 times, the single-pass deformation is more than or equal to 13%, and the specification of the intermediate blank is 170X175mm ² The process realizes rapid rolling with large rolling reduction, reduces the generation of rolling cracks and the deformation time of a high-temperature section and is completed within 1.5 minutes.

The second intermediate billet is fed into a continuous rolling unit after head cutting at 995.7 ℃, is directly fed into the continuous rolling unit, is rolled into phi 75mm round steel through 8 times, the single-pass deformation is more than or equal to 15%, the finishing temperature is 982.9 ℃, is moved to a sawing roller way for sawing after rolling, at the moment, the surface temperature is 758.2 ℃, the upper cooling bed temperature is 776.4 ℃ after sawing, the lower cooling bed temperature is 497.7 ℃, is cooled in a stacking mode, and is packaged and put into a warehouse after straightening and barreling finishing procedures; the round steel is directly processed into parts with required shapes.

Example 3

The diameter of the round steel related to the embodiment is 75mm, and the round steel comprises the following chemical components in percentage by mass: c:0.07%, si:0.33%, mn:0.45%, cr 0.85%, S0.016%, P:0.015%, cu 0.25%, sb:0.05%, the balance being iron and unavoidable impurity elements.

(1) the third blank is subjected to primary descaling by high-pressure water on a roller way to remove surface oxide skin; at the moment, the temperature is 1082.8 ℃, then the blank is rolled into an intermediate blank by a reciprocating rolling mill through 9 times, the single-pass deformation is more than or equal to 13%, the specification of the intermediate blank is 170X175mm, and the above process is controlled to be completed within 1.5 minutes.

The third intermediate billet is fed into a continuous rolling unit after head cutting at 995.8 ℃, is directly fed into the continuous rolling unit, is rolled into phi 75mm round steel through 8 times, the single-pass deformation is more than or equal to 15%, the finishing temperature is 879.4 ℃, is moved to a sawing roller way for sawing after rolling, the surface temperature is 799.2 ℃, the upper cooling bed temperature is 753.1 ℃ after sawing, the lower cooling bed temperature is 478.1 ℃, the lower cooling bed temperature is cooled in a stacking mode, and is packaged and put into a warehouse after straightening and barreling finishing procedures; the round steel is directly processed into parts with required shapes.

As a comparison, the inventors of the present application have additionally performed three sets of comparative experiments, in combination with tables 1, 2: the comparative examples 1-3 were each rolled at a conventional speed, which was reduced to 80% of the examples 1-3. Compared with comparative examples 1-3, the embodiment 1-3 adopts faster cogging speed and continuous rolling speed and larger single-pass secondary pressing quantity, and performs concentrated cooling on a cooling bed after rolling, and has obvious advantages in various mechanical performance indexes.

Table 1 comparison of the compositions (wt%) of round steels of examples and comparative examples

Table 2 comparison of the properties of round steels of examples and comparative examples

Table 3 exemplary cogging mill reduction and expansion Meter

Note that: and carrying out one-time steel turning operation in odd number of passes.

While the preferred embodiments of the present invention have been described in detail, it is to be clearly understood that the same may be varied in many ways by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of hot-rolled corrosion-resistant round steel is characterized by comprising the following steps: the round steel comprises the following element components in percentage by mass: less than or equal to 0.12 percent, si:0.20 to 0.40 percent, mn:0.35 to 0.65 percent, 0.70 to 1.10 percent of Cr, S: less than or equal to 0.02 percent, cu:0.25 to 0.45 percent, sb:0.04 to 0.10 percent, P: less than or equal to 0.03 percent, and the balance being Fe and unavoidable impurity elements; the deviation of Sb was according to +0.02%; according to the method, molten steel is smelted according to the element composition design, steel ladle refining and vacuum degassing treatment are carried out to cast molten steel into steel billets, the steel billets are slowly cooled to 200 ℃, and then are rolled in a batch production line mode after being discharged; the batch pipeline rolling method comprises the following steps:

firstly, descaling, namely removing scales on the surface by adopting high-pressure water, and reducing the generation of surface defects for subsequent rolling, wherein the temperature after descaling is 1050-1110 ℃;

step two, reciprocating cogging, namely rolling the intermediate square billet into a middle square billet by adopting a reciprocating rolling mill through 9-13 passes, wherein the deformation of each pass is more than or equal to 11%, the total deformation of the continuous casting billet to the middle square billet is more than or equal to 70.8%, and the total time of the step is controlled to be completed within 2 min;

step three, controlling the time before head cutting and continuous rolling, cutting the head of the intermediate square billet before entering the continuous rolling mill, and entering the continuous rolling mill for rapid rolling at the temperature of 980-1030 ℃, wherein the total time of the step is controlled to be within 1 minute;

step four, continuous rolling, namely rolling the intermediate square billet into round steel bars through 6-10 passes after continuous rolling, wherein the deformation of each pass is more than or equal to 15%, the total deformation of the intermediate square billet to the round steel is more than or equal to 80%, and the final rolling temperature of the round steel is 950 ℃ and higher than Ar3; the whole process is controlled to be completed within 1.5 min;

and fifthly, collecting cooling beds, namely transferring round steel to a sawing roller way for sawing after the fourth step is completed, intensively controlling the cooling speed of the cooling beds after the bar sawing, and then collecting and packing the round steel in a offline manner, wherein the whole process is controlled within 25 minutes.

2. The method for producing hot rolled corrosion resistant round steel according to claim 1, wherein: the round steel has the yield strength of more than or equal to 270MPa, the tensile strength of more than or equal to 430MPa, the elongation after fracture of more than or equal to 35%, the area shrinkage of more than or equal to 75%, the surface hardness of more than or equal to 120HB and the room temperature impact of more than or equal to 260J.

3. The method for producing hot rolled corrosion resistant round steel according to claim 1, wherein: the molten steel smelting at least comprises primary smelting, LF furnace refining and vacuum degassing treatment, wherein the primary smelting is to smelt alloy raw material blocks and molten iron in a converter or an electric furnace, and the carbon element content, copper and antimony metal element content are strictly controlled.

4. The method for producing hot rolled corrosion resistant round steel according to claim 1, wherein: and obtaining a continuous casting square billet serving as a steel billet in a continuous casting mode, wherein the superheat degree of molten steel casting is designed to be 15-30 ℃ during continuous casting, and the continuous casting square billet is formed and then put into a pit for slow cooling.

5. The method for producing hot rolled corrosion resistant round steel according to claim 1, wherein: the reheating temperature of the billet is 1150-1210 ℃, the temperature is kept within the temperature range to ensure that the alloy elements are fully dissolved in solid and the structure is fully austenitized, the heating time of the high-temperature section is controlled to be 2 hours, and the furnace time of the high-temperature section is strictly controlled.

6. The method for producing hot rolled corrosion resistant round steel according to claim 5, wherein: the reheating process of the steel billet comprises the following steps: soaking and heat preserving temperature is 1150-1200 deg.c, initial rolling temperature is 1050-1110 deg.c and continuous rolling temperature is 980-1030 deg.c.