CN114058949B - A kind of hot forming steel pickling plate and method for reducing intergranular oxidation on its surface - Google Patents

Abstract

The invention relates to the technical field of steel rolling, in particular to a hot-formed steel pickling plate and a method for reducing intergranular oxidation on the surface thereof. The chemical composition of the hot-formed steel pickled sheet is measured in mass fraction, including: C: 0.2-0.3%, Si: 0.15-0.25%, Mn: 1-1.5%, Cr: 0.1-0.3%, Nb: 0.02- 0.04%, Sb: 0.03‑0.1%, the balance is Fe and unavoidable impurity elements; the control focus is on the control of Si element in the steel grade and the matching of related processes, such as heating temperature and time; to solve the problem of hot forming steel pickling plate Surface intergranular oxidation can improve the surface quality and formability of pickled sheets.

Description

A kind of hot forming steel pickling plate and method for reducing intergranular oxidation on its surface

technical field

The invention relates to the technical field of steel rolling, in particular to a hot-formed steel pickling plate and a method for reducing intergranular oxidation on the surface thereof.

Background technique

Hot-rolled pickled sheet is a product between cold-rolled sheet and hot-rolled sheet, but the quality requirements are higher than that of hot-rolled sheet, and some hot-rolled pickled sheets need to be produced according to the quality requirements of cold-rolled sheet. In actual production, it is found that the surface quality defects of hot-rolled pickled steel plates mainly include pitting, pits, oxygen spots, scratches, waist folds, under-pickling and over-pickling, etc., mainly due to intergranular oxidation.

Cui Yan et al. found that for high carbon chromium stainless steel 440C quenched in an air furnace, the intergranular oxidation is more serious, and the increase of quenching temperature or the prolongation of holding time will intensify the intergranular oxidation, and the intergranular oxidation is more sensitive to the holding time. Zhao Qian et al. found that the intergranular oxidation behavior of Fe-36Ni Invar alloys with different total oxygen content, the higher the oxidation temperature, the faster the diffusion of reactive species, the greater the thickness of the intergranular oxide layer, the more serious the oxidation, and the total oxygen in the steel. When the content is high, it is favorable for the diffusion of reactive species along the grain boundary, resulting in more serious intragranular oxidation. Fan Yongfei et al. studied the edge band cracks of hot-rolled high-manganese steel sheets and found that high-carbon and high-manganese steels are steels prone to selective oxidation. The exposed columnar grain boundaries during the heating process are the channels for the diffusion of oxygen atoms, and the developed columnar grains It is easier to oxidize, which is the main reason for cracks in hot-rolled high-manganese steel sheets. However, none of the studies involved the generation mechanism and control measures of intergranular oxidation during hot rolling of iron and steel products.

The occurrence of intergranular oxidation causes surface cracking in the stamping process of pickled steel, and at the same time, serious intergranular oxidation can also cause defects such as color difference or rust after pickling.

SUMMARY OF THE INVENTION

The present application provides a hot-formed steel pickling sheet and a method for reducing the intergranular oxidation on the surface thereof, so as to solve the technical problem of easy intergranular oxidation on the surface of the pickling sheet steel in the prior art.

In a first aspect, the present application provides a hot-formed steel pickled sheet, and the chemical composition of the hot-formed steel pickled sheet, in terms of mass fraction, includes: C: 0.2-0.3%, Si: 0.15-0.25%, Mn : 1-1.5%, Cr: 0.1-0.3%, Nb: 0.02-0.04%, Sb: 0.03-0.1%, the balance is Fe and inevitable impurity elements.

Optionally, the metallographic structure of the hot-formed steel pickled sheet, in terms of volume fraction, includes: 10%-20% ferrite and 80-90% pearlite.

Optionally, in the austenite, the diffusion coefficient of austenite elements at 850°C is: DO-γ=2.47×10 ^-12 , DSi-γ=4.06×10 ^-17 , DMn-γ=1.04×10 ^-17 ; In the ferrite, the diffusion coefficient of ferrite element at 850°C is: DO-α=2.00× ^10-11 ; DSi-α=4.27× ^10-15 ; DMn ^- α=2.74×10- ¹⁵ .

In a second aspect, the present application provides a method for reducing intergranular oxidation on the surface of the pickled sheet of hot-formed steel, the method comprising the following steps:

obtaining a cast slab containing the chemical composition;

Measure and obtain the nose tip temperature of the intergranular oxidation depth curve of the slab;

Control the finishing rolling process according to the nose tip temperature;

The slab is successively subjected to multi-stage heating, rough rolling and finish rolling to obtain a rolled slab;

Calculate and obtain the austenite element diffusion coefficient and the ferrite element diffusion coefficient of the hot-formed steel pickled sheet at a certain temperature;

According to the austenite element diffusion coefficient and ferrite element diffusion coefficient of the hot-formed steel pickled sheet, layer cooling and coiling are performed on the rolled slab to obtain a hot-rolled coil;

The hot-rolled coil is sequentially uncoiled and pickled to obtain a hot-formed steel pickled sheet.

Optionally, controlling the finishing rolling process according to the nose tip temperature includes:

The nose tip temperature is 750°C, and the nose tip temperature range is 700-800°C. During the finishing rolling, the nose tip temperature range is avoided, and the influence of low-temperature intergranular oxidation in the finishing rolling is controlled: the opening temperature of the finishing rolling is 1040-1080 °C, The rolling speed of the finishing rolling is controlled to be 8 m/s, and the actual finishing rolling temperature is 880-900°C.

Optionally, performing layer cooling and coiling on the rolled cast slab according to the austenite element diffusion coefficient and ferrite element diffusion coefficient of the hot-formed steel pickled sheet, including:

Determine the diffusion coefficients of Si, Mn, O elements in ferrite and in austenite, determine the ferrite temperature range and austenite temperature range, and gauge the iron during layer cooling and coiling. The temperature of the element body and the temperature range of the austenite are used to control the influence of layer cooling and selective oxidation during the coiling process: the layer cooling uses the ultra-fast cooling mode, and the cooling rate of the layer cooling is controlled to be 70-100℃/ s; control the temperature of the coiling to be 550-600°C.

Optionally, the multi-stage heating includes maintaining the temperature at 1200-1220° C. for 130-160 min.

Optionally, the multi-stage heating sequentially includes: a preheating section, a first-zone heating section, a second-zone heating section and a soaking section, the temperature of the preheating section is ≤800°C, and the temperature of the first-zone heating section is ≤ 1150°C, the temperature of the second-zone heating section is 1200-1220°C, and the temperature of the soaking section is 1200-1220°C.

Optionally, an oxidizing atmosphere is used for the preheating section and the first-zone heating section, and the air-fuel ratio of the oxidative atmosphere is 1.1-1.2; the second-zone heating section and the soaking section use a reducing atmosphere, so The air-fuel ratio of the reducing atmosphere is 0.9-1.0.

Optionally, a descaling process is used in the rough rolling and finishing rolling.

Compared with the prior art, the above-mentioned technical solutions provided in the embodiments of the present application have the following advantages:

The hot-formed steel pickling plate provided in the examples of this application, combined with the chemical composition design, the C content is controlled at 0.2-0.3%; the Si element is controlled at 0.15-0.25%, the Mn element is controlled at 1-1.5%, and the Cr element is controlled at 0.1-0.3%, appropriately increase the Nb content to 0.02-0.04%, and add the Sb element content to 0.03-0.1%, which is beneficial to inhibit the generation of intergranular oxidation during the steel coiling process; because the oxidation potential energy of Sb and Nb is lower than that of iron Instead of being oxidized, it keeps accumulating in the matrix under the iron oxide scale, and the enrichment to a certain extent can limit the diffusion rate of oxygen to the matrix and inhibit intergranular oxidation. The boundary extends to the inside: when the Si element is increased to more than 0.3%, an obvious network iron sheet morphology will be formed, and the network-like Si-rich fayalite phase diffuses to the outer iron sheet grain boundary, and also spreads to the inside of the matrix, which leads to the surface of the substrate. There are defects such as cracks and grain boundaries, and the Si-rich phase is preferentially oxidized, forming an anchor-like embedded morphology of iron sheet, thereby forming a typical morphology of intergranular oxidation at high temperature. The control focus is on the control of Si element in the steel and related processes , such as the heating temperature and time; to solve the intergranular oxidation on the surface of the hot-formed steel pickled sheet, it can improve the surface quality and formability of the pickled sheet.

Description of drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description serve to explain the principles of the invention.

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. In other words, on the premise of no creative labor, other drawings can also be obtained from these drawings.

1 is a schematic flowchart of a method for reducing the intergranular oxidation on the surface of the hot-formed steel pickled plate provided by the embodiment of the application;

Fig. 2 shows the morphology of intergranular oxidation under the condition of oxidizing steel at 1200°C for 30min in the embodiment of the present application;

Fig. 3 intergranular oxidation morphology of steel in the example of the present application under the condition of oxidation at 750°C for 30min;

Fig. 4 changes in the depth of intergranular oxidation under the condition of oxidizing steel in air atmosphere for 30min under different temperature conditions in the embodiment of the present application;

The intergranular oxidation situation in the comparative example of Fig. 5;

FIG. 6 shows the state of intergranular oxidation after the process is implemented in the embodiment of the present application.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments It is a part of the embodiments of this application, but not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present application.

FIG. 1 is a schematic flowchart of a xx method according to an embodiment of the present application.

In an embodiment of the present application, a hot-formed steel pickled sheet, the chemical composition of the hot-formed steel pickled sheet, in terms of mass fraction, includes: C: 0.2-0.3%, Si: 0.15-0.25%, Mn : 1-1.5%, Cr: 0.1-0.3%, Nb: 0.02-0.04%, Sb: 0.03-0.1%, the balance is Fe and inevitable impurity elements.

In the examples of the present application, according to the characteristics of intergranular oxidation under high temperature conditions, as shown in FIG. 2, and the control of the content of preferentially oxidized elements, the temperature and time of the heating furnace are controlled, and the content of relatively preferentially oxidized Si elements is controlled at the same time, so as to achieve control The purpose of the existence of cracks and grain boundaries on the surface of the substrate.

As an optional embodiment, the metallographic structure of the hot-formed steel pickled sheet, in terms of volume fraction, includes: 10%-20% ferrite and 80-90% pearlite.

In the embodiment of the present application, in order to ensure the mechanical properties of the hot-formed steel pickled sheet, the volume fraction of 10%-20% ferrite and 80-90% pearlite can avoid the beneficial effect of austenite coarsening during the heat treatment process . The metallographic structure of the hot rolling process is ferrite and pearlite, and the austenite and martensite will be formed after austenitization and water quenching in the heat treatment process. The metallographic structure during hot rolling is normal ferrite and pearlite.

As an optional embodiment, in the austenite, the diffusion coefficient of austenite at 850°C is: DO-γ=2.47×10 ^-12 , DSi-γ=4.06×10 ^-17 , DMn- γ=1.04×10 ^-17 ; in the ferrite, the diffusion coefficient of ferrite element at 850°C is: DO-d=2.00×10 ^-11 ; DSi-d=4.27×10 ^-15 ; DMn-α =2.74×10 ⁻¹⁵ .

In the embodiment of the present application, a method for reducing the intergranular oxidation on the surface of the hot-formed steel pickled sheet is provided. As shown in FIG. 1 , the method includes the following steps:

S1. Obtain a cast slab containing the chemical composition;

S2. measure and obtain the nose tip temperature of the intergranular oxidation depth curve of the cast slab;

S3. control the finishing rolling process according to the nose tip temperature;

S4. performing multi-stage heating, rough rolling and finishing rolling on the cast slab in turn to obtain the cast slab after rolling;

S5. Calculate and obtain the diffusion coefficient of austenite and ferrite of the hot-formed steel pickled sheet at a certain temperature;

S6. according to the austenite element diffusion coefficient and the ferrite element diffusion coefficient of the hot-formed steel pickled sheet, layer cooling and coiling are performed on the rolled cast slab to obtain a hot-rolled coil;

S7. The hot-rolled coil is sequentially uncoiled and pickled to obtain a hot-formed steel pickled sheet.

In the examples of this application, low-temperature intergranular oxidation is formed in the range of 600-800 °C. As shown in Figure 2, the grain boundary is the weakest place in the metal material, so the oxidation first occurs at the grain boundary, and after the oxidation of the grain boundary, oxygen will The intragranular expansion then oxidizes the entire grain, that is, the surface oxide layer is formed, and the low-temperature intergranular oxidation is controlled by the layer cooling and coiling process.

As an optional embodiment, the control of the finishing rolling process according to the nose tip temperature includes:

The nose tip temperature is 750°C, and the nose tip temperature range is 700-800°C. During the finishing rolling, the nose tip temperature range is avoided, and the influence of low-temperature intergranular oxidation in the finishing rolling is controlled: the opening temperature of the finishing rolling is 1040-1080 °C, The rolling speed of the finishing rolling is controlled to be 8 m/s, and the actual finishing rolling temperature is 880-900°C.

In the examples of the present application, as shown in FIG. 4 , it is the variation of the intergranular oxidation depth of steel seeds under different temperature conditions (600-900° C.) under the condition of air atmosphere oxidation for 30 minutes. The depth of intergranular oxidation exists in the nose tip temperature range around 750 °C, which is related to the competition between internal and external oxidation of steel grades: if the temperature is higher, the diffusion rate of oxygen atoms increases, the external oxidation rate increases significantly, and the intergranular oxidation formed by the selective oxidation of alloy elements The morphological features will be replaced by external oxidation burn loss, and the external iron oxide scale will be formed as a whole, which reduces the intergranular oxidation depth; if the temperature is low, the diffusion rate of oxygen in the low temperature ferrite is slow, and an effective intergranular oxidation depth cannot be formed.

In an optional embodiment, the said rolled cast slab is cooled and coiled according to the diffusion coefficient of austenite elements and the diffusion coefficient of ferrite elements of the hot-formed steel pickled sheet, include:

Determine the diffusion coefficients of Si, Mn, O elements in ferrite and in austenite, determine the ferrite temperature range and austenite temperature range, and avoid the ferrite during layer cooling and coiling. The body temperature range and the austenite temperature range, to control the effect of layer cooling and selective oxidation during coiling: the layer cooling uses the ultra-fast cooling mode, and the cooling rate of the layer cooling is controlled to be 70-100°C/s; The temperature of the coiling is controlled to be 550-600°C.

In the examples of the present application, the intergranular oxidation essentially belongs to the category of selective internal oxidation, and the main intergranular oxidation elements are Si and Mn. The diffusion coefficients of O, Si and Mn are different between ferrite and austenite, so the selective oxidation behavior is different. The diffusion coefficients of Si, Mn, and O elements in α (ferrite) are all 1-2 orders of magnitude higher than those in γ (austenite). In the hot rolling process, the final temperature of finishing rolling is generally set to avoid falling into the temperature range of the two-phase region, so it is higher than the austenitizing temperature. It can be seen that the influence of selective oxidation of elements in the ferrite is mainly controlled. It is the layer cooling and coiling process. Since the occurrence of intergranular oxidation originates from the grain boundary diffusion of alloying elements and oxygen atoms, prolonged heat preservation after coiling provides kinetic and thermodynamic conditions for diffusion. Occurrence of inter-oxidation.

As an optional embodiment, the multi-stage heating includes keeping the temperature at 1200-1220° C. for 130-160 min.

In the examples of the present application, the steel contains a certain amount of silicon. As the temperature exceeds 1150°C, the silicon tends to form a fayalite phase at the interface and undergo a liquefaction reaction, which diffuses into the matrix along the grain boundary, and the diffusion depth of the grain boundary increases with the The temperature and time increase, so on the premise of ensuring that the slab is burned through, control the two addition and soaking temperature, and control the overall oxygen content in the furnace time and high temperature section.

As an optional embodiment, the multi-stage heating sequentially includes: a preheating section, a first-zone heating section, a second-zone heating section and a soaking section. The temperature of the heating section is less than or equal to 1150°C, the temperature of the second-zone heating section is 1200-1220°C, and the temperature of the soaking section is 1200-1220°C.

As an optional embodiment, an oxidizing atmosphere is used for the preheating section and the first-zone heating section, and the air-fuel ratio of the oxidative atmosphere is 1.1-1.2; the second-zone heating section and the soaking section use A reducing atmosphere, the air-fuel ratio of the reducing atmosphere is 0.9-1.0.

As an optional embodiment, a descaling process is used in the rough rolling and finishing rolling.

In the embodiment of the present application, after the slab is released from the furnace, initial descaling is performed to remove the furnace pig iron. The rolling process can adopt a 1+5 rolling mode, and a single pass can be used: 1, 3, and 5 passes to start the rough scale removal; Rolling 2, 4 and 6 double-pass descaling. Through the three-pass descaling process, it is beneficial to effectively remove the outer iron oxide scale. On the one hand, it is beneficial to improve the surface quality of the hot coil. The fayalite phase distributed along the grain boundary of the slab surface layer produced by the heating process is removed.

Detailed explanation of the attached drawings:

The casting billet containing the chemical composition of the embodiment of the present invention is subjected to conventional processing to obtain a hot-formed steel pickling sheet in the prior art. The occurrence of intergranular oxidation results in surface cracking cracks during the stamping process of pickled steel.

The casting billet containing the chemical composition of the embodiment of the present invention is processed by the processing technology of the present application to obtain a hot-formed steel pickled sheet. The situation of the steel pickled sheet is shown in FIG. No surface cracks appear during the steel stamping process, which confirms that the examples of the present application can better control the phenomenon of intergranular oxidation.

It should be noted that, in this document, relational terms such as "first" and "second" etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply these There is no such actual relationship or sequence between entities or operations. Moreover, the terms "comprising", "comprising" or any other variation thereof are intended to encompass a non-exclusive inclusion such that a process, method, article or device that includes a list of elements includes not only those elements, but also includes not explicitly listed or other elements inherent to such a process, method, article or apparatus. Without further limitation, an element qualified by the phrase "comprising a..." does not preclude the presence of additional identical elements in a process, method, article or apparatus that includes the element.

The above descriptions are only specific embodiments of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims (5)

1. A hot-formed steel pickled sheet, characterized in that the chemical composition of the hot-formed steel pickled sheet, in terms of mass fraction, comprises: C: 0.2-0.3%, Si: 0.15-0.25%, Mn: 1 -1.5%, Cr: 0.1-0.3%, Nb: 0.02-0.04%, Sb: 0.03-0.1%, the balance is Fe and inevitable impurity elements; The metallographic structure of the hot-formed steel pickling plate, in terms of volume fraction, is composed of 10%-20% ferrite and 80-90% pearlite; In austenite, the diffusion coefficient of austenite elements at 850℃ is: DO-γ=2.47×10 ^-12 , DSi-γ=4.06×10 ^-17 , DMn-γ=1.04×10 ^-17 ; in iron In the element body, the diffusion coefficient of ferrite element at 850°C is: DO-α=2.00×10 ^-11 ; DSi-α=4.27×10 ^-15 : DMn-α=2.74×10 ^-15 ; The method for intergranular oxidation on the surface of the hot-formed steel pickled plate comprises the following steps: obtaining a cast slab containing the chemical composition; Measure and obtain the nose tip temperature of the intergranular oxidation depth curve of the slab; Control the finishing rolling process according to the nose tip temperature; The slab is successively subjected to multi-stage heating, rough rolling and finish rolling to obtain a rolled slab; Calculate and obtain the austenite element diffusion coefficient and the ferrite element diffusion coefficient of the hot-formed steel pickled sheet at a certain temperature; According to the austenite element diffusion coefficient and ferrite element diffusion coefficient of the hot-formed steel pickled sheet, layer cooling and coiling are performed on the rolled slab to obtain a hot-rolled coil; The hot-rolled coil is sequentially uncoiled and pickled to obtain a hot-formed steel pickled sheet; The described finishing rolling process is controlled according to the nose tip temperature, including: The nose tip temperature is 750°C, and the nose tip temperature range is 700-800°C. During the finishing rolling, the nose tip temperature range is avoided, and the influence of low-temperature intergranular oxidation in the finishing rolling is controlled: the opening temperature of the finishing rolling is 1040-1080 °C, The rolling speed of the finishing rolling is controlled to be 8m/s, and the actual final rolling temperature is 880-900°C; The layer cooling and coiling of the rolled cast slab according to the austenite element diffusion coefficient and the ferrite element diffusion coefficient of the hot-formed steel pickled sheet include: determining the Si, Mn and O elements in the Diffusion coefficient in ferrite and diffusivity in austenite, determination of ferrite temperature range and austenite temperature range, avoidance of the ferrite temperature range and the austenite temperature range during layer cooling and coiling Body temperature range, controlling the effect of layer cooling and selective oxidation in the coiling process: the ultra-fast cooling mode is used for layer cooling, and the cooling rate of the layer cooling is controlled to be 70-100°C/s; the temperature of the coiling is controlled to be 550-600℃. 2 . The hot-formed steel pickling plate according to claim 1 , wherein the multi-stage heating comprises keeping the temperature at 1200-1220° C. for 130-160 min. 3 . 3. The hot-formed steel pickling plate according to claim 1, wherein the multi-stage heating sequentially comprises: a preheating section, a first-zone heating section, a second-zone heating section and a soaking section, the The temperature of the preheating section is ≤800°C, the temperature of the first-zone heating section is ≤1150°C, the temperature of the second-zone heating section is 1200-1220°C, and the temperature of the soaking section is 1200-1220°C. 4. The hot-formed steel pickling plate according to claim 3, wherein the preheating section and the first-zone heating section use an oxidizing atmosphere, and the air-fuel ratio of the oxidizing atmosphere is 1.1-1.2; A reducing atmosphere is used in the second-zone heating section and the soaking section, and the air-fuel ratio of the reducing atmosphere is 0.9-1.0. 5. A kind of hot-formed steel pickling plate according to claim 1, characterized in that, a descaling process is used in the rough rolling and finishing rolling.

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