CN113462971A

CN113462971A - Hot-working die large round billet and preparation method thereof

Info

Publication number: CN113462971A
Application number: CN202110685175.0A
Authority: CN
Inventors: 张海霞; 韩蕾蕾; 陈良; 梁建国; 马传庆; 范斌; 张利平; 李金浩
Original assignee: Shandong Iron and Steel Co Ltd
Current assignee: Shandong Iron and Steel Co Ltd
Priority date: 2021-06-21
Filing date: 2021-06-21
Publication date: 2021-10-01

Abstract

The invention belongs to the technical field of metallurgy, and particularly relates to a hot-working die large round billet and a preparation method thereof. The hot working die round billet comprises the following chemical components in percentage by weight: c: 0.45-0.55%, Si: 0.80-1.20%, Mn: 0.2-0.4%, P: less than or equal to 0.015%, S: less than or equal to 0.003 percent, Cr: 4.5% -5.5%, Mo: 1.2-1.5%, V: 0.8% -1.2%, Ti: less than or equal to 0.010 percent, Al: less than or equal to 0.030 percent, and the balance of Fe and inevitable impurities. The hot work die round billet prepared by the invention has good macroscopic structure, and the hardness after annealing meets the requirements of users.

Description

Hot-working die large round billet and preparation method thereof

Technical Field

The invention belongs to the technical field of metallurgy, and particularly relates to a hot-working die large round billet and a preparation method thereof.

Background

The hot die steel has high alloy content of about 10%, good toughness, heat strength, thermal fatigue performance, high wear resistance, small heat treatment deformation and other advantages, and is used widely in making die casting mold, hot extruding mold, punching tool, etc. and in making die casting mold of aluminum, copper and its alloy. Because the alloy content of the steel is high, the amount of the alloy to be added is large, the hardness is high, the head of the steel is easy to warp in continuous casting, die casting is mostly adopted in China, and the production difficulty is high.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a hot-working die large round billet and a preparation method thereof. The invention adopts continuous casting to produce large-size continuous casting round billets with the specifications of phi 500mm, phi 600mm, phi 650mm, phi 700mm, phi 750mm and phi 800 mm.

The invention relates to a hot-working die large round billet which comprises the following chemical components in percentage by weight: c: 0.45-0.55%, Si: 0.80-1.20%, Mn: 0.2-0.4%, P: less than or equal to 0.015%, S: less than or equal to 0.003 percent, Cr: 4.5% -5.5%, Mo: 1.2-1.5%, V: 0.8% -1.2%, Ti: less than or equal to 0.010 percent, Al: less than or equal to 0.030 percent, and the balance of Fe and inevitable impurities.

The invention provides a production method of a hot-working die large round billet, which comprises the following steps:

1) electric furnace smelting: the method is characterized in that a 100-ton electric furnace is adopted, molten iron and scrap steel are used as raw materials, and a fine material policy is adopted to ensure that the molten iron is not less than 80 tons. The whole process of electric furnace smelting is used for making foamed slag, the low-oxygen mode is used for blowing oxygen in the early stage, slag is fully melted, carbon powder is blown, and the thickness of the foamed slag is more than or equal to 200 mm. The molten carbon content is more than or equal to 0.30 percent, the uniform decarburization is realized, the good oxidation boiling is ensured, the floating of inclusions and gas in the steel is promoted, the end point [ C ] is controlled to be more than or equal to 0.13 percent, the P is less than or equal to 0.007 percent, and the content of residual elements meets the standard requirement. The tapping temperature of molten steel is 1630-1660 ℃, steel and slag are left during tapping, slag is strictly forbidden to be discharged, and alloy is added according to the lower component limit during ladle alloying; and adding steel core aluminum along with the tapping flow in the electric furnace tapping process for pre-deoxidation.

2) Refining in an LF furnace: and (3) refining the molten steel smelted by the electric furnace in the step 1) in an LF furnace to enhance the refining of desulfurization operation. White slag is produced in the whole process, the white slag holding time is more than or equal to 20 minutes, the refining period is more than or equal to 60 minutes, and the refining argon blowing is carried out according to the principle of promoting the floating of inclusions and reducing secondary oxidation. Before LF tapping, the components and the temperature are finely adjusted, so that the stable performance of the steel and the temperature requirement of the continuous casting process are ensured. Feeding calcium wire according to the steel of 0.8-2.0 m/t, and soft blowing for more than or equal to 3 min. And taking the refining slag for analysis.

3) Vacuum refining in a VD furnace: slagging off the molten steel refined by the LF furnace in the step 2), vacuum degassing the molten steel, wherein the vacuum treatment time is more than or equal to 27 minutes, soft argon blowing is more than or equal to 20 minutes, and the stirring and cooling of the bare molten steel and the large amount of argon are strictly forbidden during the soft argon blowing. After the VD breaks the air, a covering agent is added, hydrogen is determined, the target [ H ] is less than or equal to 1.5PPM, oxygen is determined, and the target [ O ] is less than or equal to 4.0 PPM.

4) Continuous casting: and 3) continuously casting the molten steel treated in the step 3) by adopting an integral tundish, adopting full-process protection casting, using a double-layer tundish covering agent, using a low-titanium alkaline tundish covering agent at the lower layer, using a low-titanium covering agent at the upper layer, and preventing the slag surface from being covered red. The special covering slag for hot-work die steel is adopted, the addition principle of 'adding frequently, adding less frequently and adding evenly' means that the slag surface can not be seen red visually, and the covering of blue flame on the slag surface is the best to prevent the secondary oxidation of molten steel. The fluctuation of the liquid level of the crystallizer is within +/-3 mm; pouring with low superheat degree is adopted, the superheat degree of the tundish molten steel is controlled to be 15-30 ℃, a weak cooling mode is adopted for secondary cooling water distribution, electromagnetic stirring is adopted for a crystallizer and a solidification tail end, the structure defects such as segregation and the like are reduced, and the quality of a casting blank is improved. The pouring adopts three constant operations of constant liquid level, constant temperature and constant pulling speed, the temperature of the casting blank in the pulling and straightening machine is more than or equal to 920 ℃, and the slow cooling of the casting blank is more than or equal to 24 hours. As the hardness required by the steel grade is less than or equal to 280HBW, the steel grade needs to be collected into an annealing pit in time for annealing. Wherein, Ti0 in the low titanium alkaline tundish covering agent₂The content of (A) is less than or equal to 0.50 percent and is not equal to 0, and the content of C in the low-carbon covering agent is less than or equal to 2 percent and is not equal to 0; in the prior art, C is more than or equal to 25 percent.

The processes not mentioned in the present invention can all adopt the prior art.

Compared with the prior art, the invention has the following beneficial effects:

1) according to the technical scheme provided by the invention, through reasonable component design, medium-high carbon steel is adopted as a matrix, Si, Mn, Cr, Mo and V are added, and the content of Ti is controlled to be less than or equal to 100ppm, so that the material has the advantages of high toughness, heat strength, thermal fatigue performance, wear resistance, small heat treatment deformation and the like, and is used for die-casting dies, hot extrusion dies, plastic dies and the like.

2) Ti can preferentially form strong carbonitride with C, N to play a role of refining grains, but if the content is too high, the primary carbonitride formed during the material solidification is too much and has larger size, which is not beneficial to improving the impact toughness and fatigue performance of hot-work die steel, therefore, the content of Ti is controlled to be less than or equal to 100ppm, so that low-titanium synthetic slag and low-titanium alloy are selected when the alloy is added.

3) The alloy content of the invention is about 10 percent, about 18 tons of alloy is added, and the bending is easy to occur in the continuous casting process due to different expansion coefficients of phase change structures, so that the continuous casting process needs to be optimized.

4) The alloy content of the invention is about 10 percent, so the hardness of the large round billet is higher, and in order to meet the requirement of a user for saw cutting, the hardness is required to be less than or equal to 280HBW, so high-temperature collection is needed, and a proper annealing and slow cooling process is formulated.

5) The hot work die round billet prepared by the invention has good macroscopic structure, and the hardness after annealing meets the requirements of users.

Drawings

FIG. 1 is a macroscopic structure of a round billet of a hot working die obtained by the invention;

FIG. 2 shows the situation after annealing of a large round blank of a hot work die.

Detailed Description

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

The embodiment of the invention adopts UHP ultrahigh power electric furnace smelting, LF furnace refining, VD vacuum degassing treatment process smelting and continuous casting to pour the large round billet. The present invention will be further described with reference to examples.

The production method of the hot-working die large round billet comprises the following steps:

1) electric furnace smelting: the method is characterized in that a 100-ton electric furnace is adopted, raw materials of molten iron and scrap steel are fed into the electric furnace, a fine material policy is adopted, the molten iron is ensured to be not less than 80 tons, and the optimal molten iron ratio is more than 65%, so that harmful elements in the scrap steel are diluted. The whole process of electric furnace smelting is used for making foamed slag, the low-oxygen mode is used for blowing oxygen in the early stage, slag is fully melted, carbon powder is properly blown, and the thickness of the foamed slag is more than or equal to 200 mm. The molten carbon content is more than or equal to 0.30 percent, the uniform decarburization is realized, the good oxidation boiling is ensured, the floating of inclusions and gas in the steel is promoted, the end point [ C ] is controlled to be more than or equal to 0.13 percent, the P is less than or equal to 0.007 percent, and the content of residual elements meets the standard requirement. The tapping temperature of molten steel is 1630-1660 ℃, steel and slag are left during tapping, slag is strictly forbidden to be discharged, and alloy is added according to the lower component limit during ladle alloying; and adding steel core aluminum along with the tapping flow in the electric furnace tapping process for pre-deoxidation. The alloy amount is preferably large, so that the alloy can be added on an electric furnace to avoid influencing the production rhythm.

2) Refining in an LF furnace: and (3) refining the molten steel smelted by the electric furnace in the step 1) in an LF furnace to enhance the refining of desulfurization operation. White slag is manufactured in the whole process, the white slag holding time is more than or equal to 20 minutes, the refining period is more than or equal to 60 minutes, the preferable white slag holding time is more than or equal to 25 minutes, the refining period is more than or equal to 75 minutes, and the refining argon blowing is carried out according to the principle of promoting the floating of inclusions and reducing secondary oxidation. Before LF tapping, the components and the temperature are finely adjusted, so that the stable performance of the steel and the temperature requirement of the continuous casting process are ensured. Feeding calcium wire according to the steel of 0.8-2.0 m/t, and soft blowing for more than or equal to 3 min. And taking the refining slag for analysis.

3) Vacuum refining in a VD furnace: slagging off the molten steel refined by the LF furnace in the step 2), vacuum degassing the molten steel, wherein the vacuum treatment time is more than or equal to 27 minutes, the soft argon blowing time is more than or equal to 20 minutes, the preferred vacuum treatment time is more than or equal to 35 minutes, the soft argon blowing time is more than or equal to 25 minutes, and the stirring and cooling of the bare molten steel and the large argon amount are strictly forbidden during the soft argon blowing. After the VD breaks the air, a covering agent is added, hydrogen is determined, the target [ H ] is less than or equal to 1.5PPM, oxygen is determined, and the target [ O ] is less than or equal to 4.0 PPM.

4) Continuous casting: and 3) continuously casting the molten steel treated in the step 3) by adopting an integral tundish, adopting full-process protection casting, using a double-layer tundish covering agent, using a low-titanium alkaline tundish covering agent at the lower layer, using a low-titanium covering agent at the upper layer, and preventing the slag surface from being covered red. The special covering slag for hot-work die steel is adopted, the addition principle of 'adding frequently, adding less frequently and adding evenly' means that the slag surface can not be seen red visually, and the covering of blue flame on the slag surface is the best to prevent the secondary oxidation of molten steel. The fluctuation of the liquid level of the crystallizer is within +/-2 mm; pouring with low superheat degree is adopted, the superheat degree of the tundish molten steel is controlled to be 15-30 ℃, a weak cooling mode is adopted for secondary cooling water distribution, electromagnetic stirring is adopted for a crystallizer and a solidification tail end, the structure defects such as segregation and the like are reduced, and the quality of a casting blank is improved. The pouring adopts three constant operations of constant liquid level, constant temperature and constant pulling speed, the temperature of the casting blank in the pulling and straightening machine is more than or equal to 920 ℃, and the slow cooling of the casting blank is more than or equal to 24 hours. As the hardness required by the steel grade is less than or equal to 280HBW, the steel grade needs to be collected into an annealing pit in time for annealing.

Examples 1 to 6

Examples 1-6 provide a method of producing a hot work die round billet having the chemical composition shown in table 1.

Table 1 examples 1-6 chemical composition table of hot work die round billet

Require that	C	Si	Mn	P	S	Cr	Mo	V	Ca	Al	Ti
												Example 1	0.50	0.95	0.27	0.014	0.002	4.90	1.33	0.98	0.0026	0.018	0.003
Example 2	0.49	0.95	0.28	0.012	0.001	4.89	1.34	0.97	0.0019	0.021	0.003
												Example 3	0.51	0.96	0.28	0.015	0.001	4.94	1.39	0.96	0.0061	0.023	0.004
Example 4	0.51	0.99	0.27	0.013	0.003	4.94	1.34	0.97	0.0058	0.018	0.003
												Example 5	0.51	0.98	0.27	0.011	0.002	4.93	1.34	0.96	0.0021	0.019	0.004
Example 6	0.50	0.98	0.28	0.014	0.002	4.90	1.36	0.95	0.0015	0.019	0.003

Examples 1 to 6 alkalinity of refining slag of hot work die large round billet is shown in table 2.

TABLE 2 examples 1-6 basicity of refining slag of large round billet of hot-working die

Require that	R
		Example 1	4.79
Example 2	4.47
		Example 3	4.37
Example 4	3.87
		Example 5	4.00
Example 6	3.71

The macrostructures of a hot work die round billet prepared in examples 1 to 6 described above (see FIG. 1).

Examples 1-6 macrostructures of hot-work die round billets are shown in table 3. The center is loose by 1 grade, the shrinkage cavity is 0 grade, the center crack is 0.5-1 grade, and the middle crack, the subcutaneous bubble and the subcutaneous crack are all 3 grades, thereby excellently meeting the technical requirements of the macroscopic structure of the hot-work die steel.

Table 3 examples 1-6 macrostructures (grades) of round hot-work die blanks

The hardness value of the hot work die round billet prepared in the above embodiments 1-6 is 216-280 HBW, the hardness after annealing is uniform, and the requirement of a user for sawing and blanking is met.

TABLE 4 hardness of hot work die round billets of examples 1-6

Conventional technical knowledge in the art can be used for the details which are not described in the present invention.

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 hot work die large round billet is characterized by comprising the following chemical components in percentage by weight: c: 0.45-0.55%, Si: 0.80-1.20%, Mn: 0.2-0.4%, P: less than or equal to 0.015%, S: less than or equal to 0.003 percent, Cr: 4.5% -5.5%, Mo: 1.2-1.5%, V: 0.8% -1.2%, Ti: less than or equal to 0.010 percent, Al: less than or equal to 0.030 percent, and the balance of Fe and inevitable impurities.

2. The method of claim 1, wherein the hot work die round billet hardness is 280HBW or less.

3. A preparation method of a hot-working die large round blank comprises the following steps:

1) electric furnace smelting: the raw materials of the furnace are molten iron and scrap steel, and the molten iron is not less than 80 tons; making foamed slag in the electric furnace smelting process, wherein the thickness of the foamed slag is more than or equal to 200 mm; the molten carbon is more than or equal to 0.30 percent, the control end point [ C ] is more than or equal to 0.13 percent, and P is less than or equal to 0.007 percent;

2) refining in an LF furnace: carrying out LF furnace refining on the molten steel smelted in the step 1) to produce white slag in the whole process, wherein the white slag retention time is more than or equal to 20 minutes, the refining period is more than or equal to 60 minutes, and feeding a calcium wire according to 0.8-2.0 m/t of steel for soft blowing;

3) vacuum refining in a VD furnace: slagging off the molten steel refined in the LF furnace in the step 2), vacuum degassing the molten steel, blowing soft argon for more than or equal to 20 minutes, breaking the vacuum by VD, adding a covering agent, and fixing hydrogen, wherein the target [ H ] is less than or equal to 1.5PPM, and oxygen is fixed, and the target [ O ] is less than or equal to 4.0 PPM;

4) continuous casting: the molten steel treated in the step 3) is continuously cast by adopting an integral tundish, the whole-process protective pouring is adopted, a double-layer tundish covering agent is used, and the fluctuation of the liquid level of the crystallizer is within +/-3 mm; the temperature of the casting blank in the tension leveler is more than or equal to 920 ℃, and the casting blank is slowly cooled.

4. The method according to claim 3, wherein in the step 1), a 100 ton electric furnace is used, and oxygen is blown by using an oxygen lance; the tapping temperature of the molten steel is 1630-1660 ℃; when the steel ladle is alloyed, the alloy is added according to the lower limit of the components; and adding steel core aluminum along with the tapping flow in the electric furnace tapping process for pre-deoxidation.

5. The preparation method according to claim 3, wherein the soft blowing time in the step 2) is not less than 3 min.

6. The preparation method according to claim 3, wherein the step 3) vacuum treatment time is not less than 27 minutes.

7. The method according to claim 3, wherein the step 4) employs a double-layer tundishThe covering agent is: the lower layer uses low-titanium alkaline tundish covering agent, the upper layer uses low-carbon covering agent, and the slag surface cannot be covered red; ti0 in low-titanium alkaline tundish covering agent₂The content of (A) is less than or equal to 0.50 percent, and the content of C in the low-carbon covering agent is less than or equal to 2 percent;

pouring with low superheat degree, controlling the superheat degree of the tundish molten steel at 15-30 ℃, adopting a weak cooling mode for secondary cooling water distribution, electromagnetically stirring the crystallizer and the solidification tail end, and slowly cooling the casting blank for more than or equal to 24 hours.