A control method for avoiding breakage of a saw blade steel continuous casting billet

Abstract

The present application relates to the metallurgical saw blade steel production technical field, especially to a kind of control method for avoiding saw blade steel continuous casting billet fracture, and the chemical composition of saw blade steel and weight percentage are as follows: C:0.65%~0.8%, Si:0.17%~0.55%, Mn:0.3%~1.20%, Ca:0.005%~0.010%, P≤0.020%, S≤0.015%, O≤0.003%, H≤0.002%, the balance is Fe and unavoidable impurities, and the total amount of impurity elements is less than 0.05%;The process of the method includes molten steel smelting→off furnace refining, calcium treatment→continuous casting→billet heating;Realize using the continuous casting billet with thickness of 150~200mm to produce saw blade steel plate, and the fracture rate of continuous casting billet is controlled within 1%, which reduces the production cost of saw blade steel and improves the contract delivery cycle.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgical saw blade steel production, in particular to a control method for avoiding saw blade steel continuous casting billet fracture. BACKGROUND

[0002] Saw blade can cut stone, metal and other materials by high-speed rotation, and is widely used in industrial manufacturing, stone and building fields. Its typical grades are 65Mn, 70Mn, DJ100, 75Cr1 and 8CrV, and the carbon mass fraction is generally 0.65% to 0.85%, which has the characteristics of high strength, high hardness and high wear resistance. However, since the production of saw blade steel, the continuous casting billet (thickness 150-200mm) is often prone to transverse fracture during the process of hot delivery after offline, slow cooling after stacking or heating of continuous casting billet waiting for rolling, resulting in low casting billet yield, even causing production stoppage and safety accidents, and also affecting the delivery period. It is found that the casting billet fracture originates from the enrichment of MnS inclusions along the grain boundary, and the thermal stress generated during continuous casting and other factors jointly cause stress concentration, resulting in brittle fracture of the casting billet. At present, the casting billet fracture rate is more than 20%, which seriously affects the contract delivery. Through analysis of the casting billet fracture, the casting billet fracture originates from the proportion of columnar crystal primary dendritic interfacial at a distance of 1 / 4 surface thickness and the formation of inclusions, but after improvement, the casting billet fracture rate still accounts for more than 10%. Therefore, how to solve the casting billet fracture, reduce the rejection rate of steel billet and reduce the production cost is particularly important for the mature and stable development of saw blade steel.

[0003] Comparison with prior art:

[0004] So far, there are few reports on the method for controlling the fracture of saw blade steel continuous casting billet at home and abroad. Before the present application, the application number CN201910337651.2 discloses a saw blade steel plate and a production method thereof, which mainly focuses on producing composite saw blade steel by metallurgical compounding, so that the saw blade steel plate has high durability when subjected to external load impact, thereby having a longer service life. However, the method for controlling the fracture of saw blade steel billet is not analyzed and a solution is not proposed.

[0005] The application number CN202210122541.6 discloses a high-carbon manganese-chromium saw blade steel and a production method thereof. The chemical composition of the steel includes, by mass percentage, C: 0.71-0.82%, Si: 0.20-0.30%, Mn: 0.62-1.21%, Cr: 0.20-0.80%, Al: 0.02-0.08%, O≤0.0015%, P≤0.020%, and S≤0.012%. In the method, a high-basicity refining slag system and an aluminum deoxidation process are used in an LF refining furnace. Finally, a high-carbon manganese-chromium saw blade steel with a tensile strength ≥1000 MPa and an elongation A≥12% is produced, which can be used for cutting wood and marble materials. However, the method does not analyze and propose solutions for the saw blade steel billet cracking, and the produced specifications are coiled plates with a relatively narrow rolling width.

[0006] Although the saw blade steel production methods disclosed in the above patent documents achieve high strength and toughness, they mainly focus on coiled plate or composite plate production processes and do not solve the problem of high-carbon steel billet cracking rate. SUMMARY

[0007] The present application provides a control method for avoiding saw blade steel continuous casting billet cracking, which realizes the production of typical grades 65Mn, 70Mn, DJ100, 75Cr1 and 8CrV saw blade steel plates using continuous casting billets with a thickness of 150-200 mm, and the continuous casting billet cracking rate is controlled within 1%.

[0008] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0009] A control method for avoiding saw blade steel continuous casting billet cracking, the chemical composition of the saw blade steel and the weight percentage are as follows: C: 0.65%-0.8%, Si: 0.17%-0.55%, Mn: 0.3%-1.20%, Ca: 0.005%-0.010%, P≤0.020%, S≤0.015%, O≤0.003%, H≤0.002%, the balance being Fe and unavoidable impurities, and the total amount of impurity elements is less than 0.05%.

[0010] The control method includes the following process: molten steel smelting→off-furnace refining and calcium treatment→continuous casting→billet heating, wherein:

[0011] 1) Molten steel smelting: smelting according to the composition, the raw materials are subjected to KR hot metal pretreatment, the content of S is controlled to be lower than 0.015%, and after slagging, the materials are fed into the converter; a double-slag method is used for P removal in the converter smelting, the content of P is controlled to be ≤0.02%, the content of C at the end of converter smelting is controlled to be 0.65-0.75%, and argon gas is blown for 30-35 min when tapping;

[0012] 2) secondary refining and calcium treatment: LF refining is carried out, and Si-Ca wire is used for secondary refining treatment of molten steel in the secondary refining process;

[0013] 3) continuous casting: the current intensity of electromagnetic stirring in the secondary cooling zone in the continuous casting stage is controlled to be 120-180 A, the secondary cooling water quantity is 1.3 L / kg-1.8 L / kg, heavy pressing is put in the horizontal fan-shaped section, i.e. the solidification end, the pressing amount of the continuous casting billet is 20-30 mm, the billet is put into the pit for slow cooling after being discharged, the temperature of the billet is not lower than 700 ℃, the slow cooling temperature is 700-800 ℃, the slow cooling time is 36-48 h, then the billet is taken out of the pit after the temperature is reduced to below 100 ℃ in the pit, and slow cooling is carried out after the billet is taken out of the pit;

[0014] 4) billet heating: before the billet is put into the furnace, the upper and lower surfaces of the saw blade steel billet are preheated by using other billets at 150-300 ℃, the preheating time is 2-4 h, the length and width of the upper and lower surfaces of the billet are greater than the size of the saw blade steel billet, and after preheating, the continuous casting billet is sent into the walking beam furnace for heating, and the billet is sequentially discharged after passing through the preheating section, the heating section and the soaking section; the preheating section temperature interval is 900-1150 ℃, the heating section temperature interval is 1240-1260 ℃, and the soaking section temperature interval is 1210-1225 ℃, and the heating and soaking time in the furnace is not less than 4.5-5.5 h.

[0015] Further, the thickness of the continuous casting billet is 150-200 mm.

[0016] Further, the superheat of the continuous casting process is 15-20 ℃, and the continuous casting pulling rate is 0.8-1.1 m / min.

[0017] Compared with the prior art, the beneficial effects of the present application are:

[0018] 1) by adopting argon blowing, the inclusions in the molten steel can be removed and the composition uniformity of the molten steel can be improved by argon blowing and setting before continuous casting; the Si-Ca wire is used for secondary refining treatment of molten steel in the secondary refining process, which can effectively reduce the oxygen and sulfur content in the molten steel, change the sulfide and oxide inclusions into calcium-containing spherical inclusions, and reduce the number of inclusions, so as to purify the molten steel, improve the quality of the steel, reduce the local internal stress of the rolled steel plate, control the superheat of the continuous casting, and effectively reduce the quality defects of the billet core and the corner by controlling the current intensity of electromagnetic stirring in the secondary cooling zone and the secondary cooling water quantity, which can reduce the average index of carbon segregation, inhibit segregation, reduce the proportion of columnar crystals, control the proportion of columnar crystals within 10%, limit the secondary cooling intensity, and inhibit the trend of deterioration of the center crack of the billet; the heavy pressing can help to reduce the segregation of the billet, refine the austenite grains, and reduce internal organizational defects; the slow cooling of the billet into the pit can help to reduce the center segregation of the billet and effectively reduce the H content in the billet;

[0019] 2) By preheating the casting blank before entering the furnace, it helps to reduce the temperature difference of the casting blank after entering the furnace, causing excessive internal stress and causing the risk of casting blank fracture; at the same time, it reduces the center segregation, effectively reduces the H content and C, Mn content segregation diffusion in the casting blank, while ensuring the soaking section and heating section in the furnace time, ensuring the high temperature section and total in-furnace time to effectively promote the full diffusion of C, Mn, H and other elements, reduce the composition segregation, reduce the internal stress, and reduce the risk of casting blank fracture;

[0020] 3) By using the above composition and steelmaking continuous casting, slow cooling of the casting blank, and heating scheme, the shortcomings of the prior art are overcome, a control method for avoiding saw blade steel continuous casting blank fracture is realized, and typical grades 65Mn, 70Mn, DJ100, 75Cr1 and 8CrV saw blade steel plates are produced using continuous casting blanks with a thickness of 150-200mm, the continuous casting blank fracture rate is controlled within 1%, the saw blade steel production cost is reduced, and the contract delivery cycle is improved. DETAILED DESCRIPTION

[0021] The specific embodiments of the present application are further described below:

[0022] The present application is a kind of saw blade steel, which is used to manufacture grade 65Mn, 70Mn, DJ100, 75Cr1 and 8CrV saw blade steel plate, and the chemical composition and weight percentage are as follows: C: 0.65%-0.8%, Si: 0.17%-0.55%, Mn: 0.3%-1.20%, Ca: 0.005%-0.010%, P≤0.020%, S≤0.015%, O≤0.003%, H≤0.002%, the balance being Fe and unavoidable impurities, and the total amount of impurity elements is less than 0.05%.

[0023] The functions of each main element in the chemical composition of the steel plate of the present application are as follows:

[0024] C: Carbon is one of the basic elements in steel, and a lower carbon content is beneficial to improving the plasticity of the product, but a too low carbon content is not conducive to the improvement of strength and the subsequent heat treatment; therefore, the carbon content is selected to be 0.65%-0.8%.

[0025] Mn: Manganese is a solid solution strengthening element, and manganese can improve the stability of austenite and increase the strength and plasticity of steel, but a low manganese-sulfur ratio can cause quality problems in continuous casting production of steel; therefore, the manganese content is controlled to be 0.3%-1.20%.

[0026] Si: Silicon is a main element of steel, and the silicon content must reach a certain level to ensure the yield strength of the steel, but a too high silicon content makes it difficult to remove the surface iron oxide scale in the heating furnace, thereby affecting the surface quality of the steel, therefore, the silicon content in the steel is controlled to be 0.17%-0.55%.

[0027] P: phosphorus in steel is a harmful element, the lower the better, but considering the low phosphorus content in steel, the manufacturing cost increases, therefore, P≤0.020% is required.

[0028] S: sulfur in steel is a harmful element, the lower the better, but considering the low sulfur content in steel, the manufacturing cost increases, therefore, S≤0.012% is required.

[0029] O: oxygen in steel is a harmful element, increasing the number of inclusions, therefore, the lower the better, but considering the low oxygen content in steel, the manufacturing cost increases, therefore, O≤0.003% is required.

[0030] H: hydrogen in steel is a harmful element, causing hydrogen embrittlement phenomenon of steel plate, therefore, the lower the better, but considering the low hydrogen content in steel, the manufacturing cost increases, therefore, H≤0.002% is required.

[0031] Ca: trace calcium Ca in steel can be used as a purifying agent for deoxidation and desulfurization, improving the morphology of non-metallic inclusions, and is widely used in calcium-treated clean steel. By adding trace calcium elements to carbon steel, dispersed and thermally stable calcium-containing oxide particles are formed in the steel. Relevant research results show that the dispersed and distributed calcium-containing oxide particles pin the austenite grain boundary migration in the CGHAZ during the welding thermal cycle, limit the growth of austenite grains, and obtain finer welding CGHAZ grain size, thereby improving the strength and toughness of the welding CGHAZ of the micro-calcium steel. However, excessive Ca will segregate at the grain boundary, which will have an adverse effect on the hardenability and impact toughness of the steel. The reasonable range is 0.005-0.010%.

[0032] The application is a control method for avoiding the fracture of saw blade steel continuous casting billets, which realizes the production of typical grades 65Mn, 70Mn, DJ100, 75Cr1 and 8CrV saw blade steel plates using continuous casting billets with a thickness of 150-200 mm, and the fracture rate of the continuous casting billets is controlled within 1%. The process of the method includes the following steps: molten steel smelting, secondary refining and calcium treatment, continuous casting and billet heating.

[0033] 1) Steelmaking and continuous casting: smelt according to the following components, the chemical components are as follows: C: 0.65%~0.8%, Si: 0.17%~0.55%, Mn: 0.3%~1.20%, Ca: 0.005%~0.010%, P≤0.020%, S≤0.015%, O≤0.003%, H≤0.002%, the balance is Fe and inevitable impurities, and the total amount of impurity elements is less than 0.05%; the raw material is pretreated by KR molten iron, the content of S is controlled to be less than 0.015%, and enters the converter after slagging; P is removed by double slag method in the converter smelting, the content of P is controlled to be less than or equal to 0.02%, the content of C is controlled to be 0.65~0.8% at the end of converter smelting, argon blowing is performed for 30~35 min when tapping, the argon blowing and settling before continuous casting can promote the removal of inclusions in the molten steel and improve the composition uniformity of the molten steel; then LF refining is carried out, in the external refining process, Si-Ca wire is used for external refining treatment of molten steel, which can effectively reduce the oxygen and sulfur content in the molten steel, change the sulfide and oxide inclusions into calcium-containing spherical inclusions, and reduce the number of inclusions, so as to purify the molten steel, improve the quality of steel, reduce the local internal stress of the casting blank, and avoid the fracture of the blank; then slab continuous casting is carried out, the overheat degree of continuous casting is 15~20℃, the casting speed is 0.8~1.1m / min, and the control of the overheat degree and the casting speed can effectively reduce the quality defects of the core and the corner of the casting blank; the current intensity of electromagnetic stirring in the secondary cooling zone in the continuous casting stage is controlled to be 120~180A, the secondary cooling water quantity is 1.3L / kg~1.8L / kg, the average index of carbon segregation is reduced, the segregation is inhibited, the secondary cooling intensity is limited, the trend of center crack of the casting blank is inhibited, the proportion of columnar crystal is reduced, and the proportion of columnar crystal is controlled to be within 10%, the heavy pressing is put into the horizontal fan-shaped section, i.e. the solidification end, the pressing amount of the continuous casting blank is 20~30mm, and the heavy pressing can help to reduce the segregation of the blank, refine the original austenite grains, and reduce the internal structure defects; after the blank is taken offline, it is put into the pit for slow cooling, the pit entering temperature is not less than 700℃, the slow cooling temperature is 700~800℃, the slow cooling time is 36~48h, then the blank is taken out after the temperature is reduced to below 100℃ in the pit, and the blank is put into the pit for slow cooling, which helps to reduce the center segregation of the casting blank and effectively reduce the H content in the casting blank.

[0034] 2) Billet heating: before entering the furnace, the saw blade steel billet is preheated on the upper and lower surfaces by using other billets at 150-300°C, the preheating time is 2-4h, the length and width of the upper and lower surface billets are larger than the size of the saw blade steel billet, and the preheating of the billet helps to reduce the risk of billet fracture caused by large temperature difference after the billet enters the furnace, and reduces the center segregation, effectively reduces the H content and C, Mn content segregation diffusion in the billet, and after preheating, the continuous casting billet with a thickness of 150-200mm is sent into the walking beam heating furnace for heating, and the billet is sequentially preheated, heated and soaked, and then discharged from the furnace; the preheating temperature range is 900-1150°C, which promotes the diffusion of C, Mn and H, the heating temperature range is 1240-1260°C, and the soaking temperature range is 1210-1225°C, the heating and soaking time in the furnace is not less than 4.5-5.5h, which further promotes the diffusion of alloy elements Mn, C and H, reduces the composition segregation and internal stress, and reduces the risk of billet fracture.

[0035] The above composition and steelmaking continuous casting, billet slow cooling and heating scheme overcome the shortcomings of the prior art, realize a control method for avoiding saw blade steel continuous casting billet fracture, realize the production of typical grades 65Mn, 70Mn, DJ100, 75Cr1 and 8CrV saw blade steel plates using continuous casting billets with a thickness of 150-200mm, the continuous casting billet fracture rate is controlled within 1%, the saw blade steel production cost is reduced, and the contract delivery cycle is improved.

[0036] The following examples are implemented on the premise of the technical scheme of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0037] Example:

[0038] Table 1 is the chemical composition of the example steel; Table 2 is the smelting process system of the example steel; and Table 3 is the billet preheating process, heating system and fracture rate of the example steel.

[0039] Table 1 Chemical composition of the example of the present application (wt, %)

[0040]

[0041] Note: Impurity elements in steel P≤0.02%, O≤0.003%, S≤0.015%.

[0042] Table 2 Smelting and stacking process system of the example steel

[0043]

[0044] Table 3 Billet preheating process, heating system and fracture rate of the example steel

[0045]

[0046] Therefore, compared with the prior art, the application realizes a control method for avoiding saw blade steel continuous casting billet fracture by optimizing steelmaking continuous casting, billet slow cooling, preheating and heating scheme, realizes production of typical grades 65Mn, 70Mn, DJ100, 75Cr1 and 8CrV saw blade steel plates using continuous casting billets with thickness of 150-200mm, controls the continuous casting billet fracture rate within 1%, reduces the saw blade steel production cost and improves the contract delivery cycle.

[0047] The above examples are only for illustrating the technical concept and characteristics of the application, and the purpose is to enable those skilled in the art to understand the content of the application and implement it, and cannot limit the protection scope of the application. Any equivalent changes or modifications made according to the spirit and principle of the application shall be covered within the protection scope of the application.

Claims

1. A control method for avoiding breakage of a continuous cast billet of saw blade steel, characterized by, The saw blade steel has the following chemical components and weight percentage: C: 0.65-0.8%, Si: 0.17-0.55%, Mn: 0.3-1.20%, Ca: 0.005-0.010%, P≤0.020%, S≤0.015%, O≤0.003%, H≤0.002%, the balance being Fe and inevitable impurities, and the total amount of impurities is less than 0.05%. The control method comprises the following processes: molten steel smelting, secondary refining and calcium treatment, continuous casting and slab heating, wherein: 1) molten steel smelting: smelting according to components, the raw material is subjected to KR molten iron pretreatment, the content of S is controlled to be lower than 0.015%, and after slagging, the molten steel is fed into a converter; double-slag method is used to remove P in the converter smelting, the content of P is controlled to be ≤0.02%, the content of C is controlled to be 0.65-0.75% at the end of the converter smelting, and argon is blown for 30-35 min when the molten steel is tapped; 2) secondary refining and calcium treatment: LF refining is performed, and Si-Ca wire is used to treat the molten steel in the secondary refining process; 3) continuous casting: the current intensity of electromagnetic stirring in the secondary cooling zone in the continuous casting stage is controlled to be 120-180 A, the secondary cooling water quantity is 1.3-1.8 L / kg, heavy pressing is performed at the horizontal fan-shaped section, i.e. the solidification end, the pressing amount of the continuous casting blank is 20-30 mm, the blank is cooled in the pit after being discharged, the temperature when entering the pit is not lower than 700 ℃, the cooling temperature is 700-800 ℃, the cooling time is 36-48 h, and then the blank is discharged from the pit after the temperature in the pit is reduced to below 100 ℃; 4) slab heating: before entering the furnace, the slab is preheated on the upper and lower surfaces by using other slabs at 150-300 ℃, the preheating time is 2-4 h, the length and width of the upper and lower slabs are greater than those of the saw blade steel slab, and after preheating, the continuous casting blank is sent into a walking beam furnace for heating, and the slab is sequentially discharged after passing through a preheating section, a heating section and a soaking section; the temperature interval of the preheating section is 900-1150 ℃, the temperature interval of the heating section is 1240-1260 ℃, the temperature interval of the soaking section is 1210-1225 ℃, and the time in the heating section and the soaking section is 4.5-5.5 h.

2. The control method of claim 1, wherein The thickness of the continuous casting blank is 150-200 mm.

3. The control method of claim 1, wherein the control method is characterized by: In the continuous casting step, the superheat is controlled to be 15-20 ℃, and the continuous casting pulling rate is 0.8-1.1 m / min.

Images