A method for preparing D2 steel bars and wires by arc continuous casting and rolling process

Abstract

The present invention provides a method for preparing D2 steel bars and wires by an arc continuous casting and rolling process, and belongs to the technical field of continuous casting and rolling of cold working die steel. The present invention melts, refines and degasses the raw materials for preparing D2 steel to obtain molten steel; the molten steel enters the continuous casting tundish, and a covering agent is added to the molten steel; the molten steel in the continuous casting tundish enters the crystallizer for solidification, and a continuous casting billet is continuously pulled out by continuous casting; the continuous casting billet is sequentially subjected to a first annealing, a continuous rolling and a second annealing to obtain D2 steel bars and wires. The present invention adopts a continuous casting + continuous rolling process to refine the thickness of the eutectic carbide network and improve the uneven distribution of eutectic carbides; at the same time, the macroscopic segregation of the steel billet is reduced, and the uniformity of the organization is improved. The obtained D2 steel bars and wires have an excellent low-magnification organization level, and have good service performance and service life. At the same time, the present invention adopts a continuous casting + continuous rolling process to prepare D2 steel bars and wires with a short production process, which can save production procedures, save energy and reduce consumption, and reduce costs and increase efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of continuous casting and rolling of cold working die steel, and in particular to a method for preparing D2 steel bars and wires by an arc-shaped continuous casting and rolling process. Background Art

[0002] Cold working die steel is widely used in various cold punching, cold heading, cold extrusion, wire drawing and other large and medium-sized precision, complex, long-life, heavy-load cold processing dies, and is an important basic material for modern machinery manufacturing. Among them, D2 steel is a representative high-carbon high-chromium cold working die steel, the matrix structure is ledeburite, and there are a large number of eutectic carbides, the size, quantity, structure and morphology of which determine the service performance and service life of D2 steel.

[0003] The conventional D2 steel bar and wire preparation process is to use an ingot mold casting process, the ingot is forged or rolled into blanks, and then rolled into different sizes. However, the D2 steel obtained by this method has uneven distribution of eutectic carbides, poor service performance and service life. Summary of the invention

[0004] In view of this, the present invention aims to provide a method for preparing D2 steel bars and wires by arc continuous casting and rolling process. The D2 steel bars and wires prepared by the present invention by continuous casting + continuous rolling process have small eutectic carbides and high uniformity, and excellent macrostructure level.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing D2 steel bars and wires by arc continuous casting and rolling process, comprising the following steps:

[0007] The raw materials for preparing D2 steel are melted, refined and degassed to obtain molten steel;

[0008] The molten steel enters the continuous casting tundish, and a covering agent is added to the molten steel;

[0009] The molten steel in the continuous casting tundish enters the crystallizer to solidify, and the continuous casting billet is continuously pulled out by continuous casting;

[0010] The continuous casting billet is subjected to first annealing, continuous rolling and second annealing in sequence to obtain D2 steel bars and wires.

[0011] Preferably, in terms of mass percentage, the chemical composition of the D2 steel includes:

[0012] C=1.40~1.60%, Si≤0.60%, Mn≤0.60%, Cr=11.00~13.00%, Mo=0.70~1.20%, V=0.50~1.10%, Co≤1.00%, and the balance is Fe and unavoidable impurities.

[0013] Preferably, the tapping temperature of the molten steel is 1450-1600°C.

[0014] Preferably, before the molten steel enters the continuous casting tundish, the continuous casting tundish is preheated, and the preheating temperature is 1440-1450°C.

[0015] Preferably, the temperature difference of the crystallizer is 6-8°C, and the water flow rate of the crystallizer is 90-95 / h.

[0016] Preferably, the continuous casting is arc continuous casting, and the speed of pulling out the continuous casting billet is 0.8-1.4 m / min.

[0017] Preferably, the temperature of the first annealing is 860-880° C., and the holding time is 4-8 hours.

[0018] Preferably, the continuous rolling includes rough rolling and finish rolling, the start rolling temperature of the continuous rolling is 1050-1150°C, the final rolling temperature of the rough rolling is ≥950°C, the final rolling temperature of the finish rolling is ≥880°C, and the deformation amount of a single pass is 10-15%.

[0019] Preferably, the temperature of the second annealing is 860-880° C., and the holding time is 1-4 hours.

[0020] Preferably, the continuous casting also includes vibrating the crystallizer and / or stirring the molten steel in the crystallizer.

[0021] The present invention provides a method for preparing D2 steel bars and wires by an arc continuous casting and rolling process, comprising the following steps: melting, refining and degassing the raw materials for preparing D2 steel to obtain molten steel; the molten steel enters a continuous casting tundish, and a covering agent is added to the molten steel; the molten steel in the continuous casting tundish enters a crystallizer for solidification, and a continuous casting billet is continuously pulled out by continuous casting; the continuous casting billet is subjected to a first annealing, a continuous rolling and a second annealing in sequence to obtain D2 steel bars and wires. The present invention adopts a continuous casting + continuous rolling process to refine the thickness of the eutectic carbide network and improve the uneven distribution of eutectic carbides; at the same time, the macrosegregation of the steel billet is reduced, and the uniformity of the organization is improved. The obtained D2 steel bars and wires have an excellent macrostructure level, good service performance and service life. At the same time, the present invention adopts a continuous casting + continuous rolling process to prepare D2 steel bars and wires with a short production process, which can save production procedures, save energy and reduce consumption, and reduce costs and increase efficiency.

[0022] Furthermore, the present invention controls the cooling water flow of the crystallizer and the pulling speed of the continuous casting billet to 1.05-1.10 m / min, controls the secondary cooling intensity and the pulling speed to control the straightening temperature of the continuous production of the casting billet, while ensuring the internal quality and surface quality of the casting billet. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the eutectic carbide morphology of the D2 steel rod and wire obtained in Example 1. DETAILED DESCRIPTION

[0024] The present invention provides a method for preparing D2 steel bars and wires by arc continuous casting and rolling process, comprising the following steps:

[0025] The raw materials for preparing D2 steel are melted, refined and degassed to obtain molten steel;

[0026] The molten steel enters the continuous casting tundish, and a covering agent is added to the molten steel;

[0027] The molten steel in the continuous casting tundish enters the crystallizer to solidify, and the continuous casting billet is continuously pulled out by continuous casting;

[0028] The continuous casting billet is subjected to first annealing, continuous rolling and second annealing in sequence to obtain D2 steel bars and wires.

[0029] The present invention melts, refines and degasses the raw materials for preparing D2 steel to obtain molten steel. In the present invention, the chemical composition of the D2 steel preferably includes, by weight percentage:

[0030] C = 1.40-1.60%, more preferably 1.46-1.55%;

[0031] Si≤0.60%, more preferably 0.40-0.60%;

[0032] Mn≤0.60%, more preferably 0.40-0.06%;

[0033] Cr = 11.00-13.00%, more preferably 11.50-12.50%;

[0034] Mo = 0.70-1.20%, more preferably 0.80-1.0%;

[0035] V = 0.50-1.10%, more preferably 0.70-1.10%;

[0036] Co≤1.00%, more preferably 0.80-1.0%;

[0037] The balance is Fe and inevitable impurities.

[0038] In the present invention, the raw materials for preparing D2 steel preferably include ferromolybdenum, ferrovanadium and high carbon ferrochromium.

[0039] In the present invention, the smelting is preferably electric arc furnace smelting or industrial frequency induction smelting furnace smelting. In the present invention, when the smelting is electric arc furnace smelting, the electric arc furnace uses furnace door oxygen lance and furnace wall multifunctional oxygen lance to blow oxygen to assist melting, and foam slag is made throughout the process, oxygen blowing decarburization, low-temperature dephosphorization, and 30 tons to 40 tons of steel are retained when the electric arc furnace is tapped.

[0040] In the present invention, the refining is preferably LF refining, and during the refining, the present invention preferably feeds aluminum wire and adds a refining slag-forming agent. In the present invention, the LF refining preferably adopts precipitation deoxidation and diffusion deoxidation, and performs submerged arc operation, and the white slag control time is ≥30min.

[0041] In the present invention, the degassing is preferably vacuum degassing. The present invention preferably uses a VD furnace for the vacuum degassing. In the present invention, during the vacuum degassing, when the ultimate vacuum is less than 67Pa, the present invention preferably increases the argon flow rate to ensure the degassing effect. In the present invention, during the vacuum degassing, the holding time under the ultimate vacuum is not less than 20 minutes, and the soft blowing time of argon after vacuum is not less than 20 minutes.

[0042] In the present invention, the tapping temperature of the molten steel is preferably 1450-1600°C, more preferably 1455°C.

[0043] In the present invention, the molten steel enters the continuous casting tundish, and a covering agent is added to the molten steel. The present invention has no special requirements on the type of the covering agent, and a covering agent well known to those skilled in the art can be used. The present invention has no special requirements on the amount of the covering agent added, and an amount well known to those skilled in the art can be used.

[0044] In the present invention, before the molten steel enters the continuous casting tundish, the present invention preferably preheats the continuous casting tundish, and the preheating temperature is 1440-1450° C. In the present invention, the preheating method is preferably baking, and the baking time is preferably 5 hours.

[0045] In the present invention, the molten steel in the continuous casting ladle enters the crystallizer for solidification, and the continuous casting billet is continuously pulled out by continuous casting. In the present invention, the solidifier is preferably a continuous casting crystallizer. In the present invention, the molten steel preferably enters the continuous casting crystallizer through an immersed water nozzle. In the present invention, the temperature difference of the crystallizer is 6 to 8°C, more preferably 7°C, and the water flow rate of the crystallizer is preferably 90 to 95t / h, more preferably 94t / h. In the present invention, the cooling method of the crystallizer is preferably water cooling.

[0046] In the present invention, after the molten steel enters the crystallizer, the present invention preferably adds mold powder into the crystallizer. The present invention has no special requirements on the type of the mold powder, and the mold powder well known to those skilled in the art can be used. By adding the mold powder, the present invention can enhance the lubrication effect of the continuous casting billet and the inner wall of the crystallizer.

[0047] In the present invention, the continuous casting is arc continuous casting. In the present invention, the pulling speed of the continuous casting billet during the continuous casting is preferably 0.8 to 1.4 m / min, more preferably 1 to 1.2 m / min.

[0048] In the present invention, the cross section of the continuous casting billet is preferably square or rectangular. In the present invention, the cross section size of the continuous casting billet is preferably 100 mm×100 mm to 200 mm×200 mm.

[0049] In the present invention, the continuous casting preferably further includes vibrating the crystallizer and / or stirring the molten steel in the crystallizer.

[0050] The present invention sequentially performs first annealing, continuous rolling and second annealing on the continuous casting billet to obtain D2 steel bar wire. In the present invention, the first annealing method is preferably slow cooling and then annealing or direct hot delivery annealing. In the present invention, the temperature of the first annealing is preferably 860-880°C, more preferably 870°C, and the holding time is preferably 4-8h, more preferably 5-6h. In the present invention, the heating rate to the first annealing temperature is preferably 30°C / h. After the first annealing, the present invention preferably cools the obtained continuous casting billet to 200°C and takes it out of the furnace, and the cooling method is preferably furnace cooling.

[0051] The present invention preferably performs a hot rolling of the continuous casting billet after the first annealing to the finished product size on a bar or wire rolling mill. In the present invention, the continuous rolling preferably includes rough rolling and finish rolling; the start rolling temperature of the continuous rolling is preferably 1050-1150°C, more preferably 1100°C; the rough rolling final rolling temperature is preferably ≥950°C, more preferably 950-980°C; the finish rolling final rolling temperature is preferably ≥880°C, more preferably 880-900°C; the single-pass deformation is preferably 10-15%, more preferably 12-14%. In the present invention, the diameter of the steel bar wire obtained after the continuous rolling is preferably φ10-50mm, more preferably φ20-40mm.

[0052] In the present invention, the second annealing method is preferably slow cooling annealing or direct hot delivery annealing. In the present invention, the temperature of the first annealing is preferably 860-880°C, more preferably 870°C, and the holding time is preferably 1-4h, more preferably 2h. In the present invention, the heating rate to the second annealing temperature is preferably 30°C / h. After the second annealing, the present invention preferably cools the obtained steel bar wire to 200°C and takes it out of the furnace, and the cooling method is preferably furnace cooling.

[0053] The method for preparing D2 steel bars and wires by the arc continuous casting and rolling process provided by the present invention is described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0054] Example 1

[0055] A D2 steel bar wire prepared by an arc continuous casting and rolling process, wherein the chemical composition, by mass percentage, includes: C=1.46wt.%, Si=0.52wt.%, Mn=0.34wt.%, Cr=11.75wt.%, Mo=0.84wt.%, V=0.91wt.%, Co=0.82wt.%, and the remainder is Fe and unavoidable impurities.

[0056] A method for preparing D2 steel bars and wires by the above-mentioned arc continuous casting + continuous rolling process comprises the following steps:

[0057] (1) Prepare the raw materials according to the chemical composition ratio of the above-mentioned D2 steel.

[0058] (2) The raw materials are put into an electric arc furnace and smelted through external refining and vacuum degassing until the liquid state meets the quality control target and the smelting composition is qualified, and then enter the arc continuous casting process, and the tapping temperature of the molten steel is 1550±5°C.

[0059] (3) Before the start of the arc continuous casting process, the continuous casting tundish is baked for 5 hours. The temperature of the tundish reaches 1445±5°C. The molten steel enters the continuous casting tundish, and the tundish covering agent is added to the molten steel. The molten steel in the continuous casting tundish flows into the continuous casting crystallizer through an immersion nozzle. The temperature difference of the crystallizer is 7±1°C, and the crystallizer protective slag is added for control. The R9m arc continuous casting machine is used to continuously produce and pull out the continuous casting square billet at a speed of 1.10m / min. The size of the billet is 150mm×150mm. At the same time, the crystallizer vibration is turned on. The water flow rate of the crystallizer is 94t / h, and the secondary cooling water is automatically controlled (the specific water volume is 7L / kg).

[0060] (4) After the continuous casting square billet cut to a predetermined length is slowly cooled, it is placed in an annealing furnace for a first annealing process at a temperature of 870° C. and a heating rate of 30° C. / h. After being kept at this temperature for 6 hours, it is cooled along with the furnace until it is cooled to 200° C. and then taken out of the furnace.

[0061] (5) The continuous casting square billet after high temperature annealing is fed into a rolling mill, the starting rolling temperature is 1100±10°C, the rough rolling and final rolling temperature is 980±10°C, the fine rolling and final rolling temperature is 900±10°C, the single-pass deformation is 10%, and the billet is rolled to φ30mm.

[0062] (6) The D2 steel bars and wires after hot continuous rolling are directly sent to a hood-type protective atmosphere annealing furnace for a second annealing process at a temperature of 870±10° C. After being kept at this temperature for 2 hours, they are cooled along with the furnace until they are cooled to 200° C. and then taken out of the furnace.

[0063] The eutectic carbide morphology of D2 steel bar and wire is as follows Figure 1 As shown. The eutectic carbide size of the D2 steel bar and wire prepared by the arc continuous casting + continuous rolling process in this embodiment is refined and evenly distributed. The macrostructure of the D2 steel bar and wire prepared by the arc continuous casting + continuous rolling process is excellent: the center is loose, the grade is 0.5; the center is segregated, the grade is 0.5; and no shrinkage cavity is found.

[0064] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing D2 steel bars and wires by arc continuous casting and rolling process, comprising the following steps: The raw materials for preparing D2 steel are melted, refined and degassed to obtain molten steel; the chemical composition of the D2 steel comprises, by mass percentage, C=1.40-1.60%, Si≤0.60%, Mn≤0.60%, Cr=11.00-13.00%, Mo=0.70-1.20%, V=0.50-1.10%, Co≤1.00%, and the balance is Fe and unavoidable impurities; The molten steel enters the continuous casting tundish, and a covering agent is added to the molten steel; The molten steel in the continuous casting tundish enters the crystallizer for solidification, and the continuous casting billet is continuously pulled out by continuous casting; the continuous casting is arc continuous casting, and the speed of pulling out the continuous casting billet is 0.8-1.4 m / min; the temperature difference of the crystallizer is 6-8°C, and the water flow rate of the crystallizer is 90-95t / h; the cross-sectional size of the continuous casting billet is 100mm×100mm~200mm×200mm; The continuous casting billet is subjected to first annealing, continuous rolling and second annealing in sequence to obtain D2 steel bars and wires; The first annealing temperature is 860-880°C, and the holding time is 4-8h; The continuous rolling includes rough rolling and finish rolling, the start rolling temperature of the continuous rolling is 1050-1150°C, the final rolling temperature of the rough rolling is ≥950°C, the final rolling temperature of the finish rolling is ≥880°C, and the deformation amount of a single pass is 10-15%; the diameter of the D2 steel bar wire obtained after the continuous rolling is 10-50mm; The second annealing temperature is 860-880° C., and the holding time is 1-4 hours.

2. The method according to claim 1, characterized in that The tapping temperature of the molten steel is 1450-1600°C.

3. The method according to claim 1, characterized in that Before the molten steel enters the continuous casting tundish, the continuous casting tundish is preheated, and the preheating temperature is 1440-1450°C.

4. The method according to claim 1, characterized in that: The continuous casting also includes vibrating the crystallizer and / or stirring the molten steel in the crystallizer.

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