Electroslag oxygen control slag system suitable for chromium-molybdenum hot work die steel and use method of electroslag oxygen control slag system

Abstract

The invention discloses an electroslag oxygen control slag system suitable for chromium-molybdenum hot work die steel and a use method of the electroslag oxygen control slag system. The electroslag oxygen control slag system comprises the following components: 48-53% of CaF2, 22-27% of Al2O3, 15-20% of CaO, 3-5% of SiO2, 3-5% of MgO, 1-3% of Li2O, 1-3% of BaO and the balance of inevitable impurities. The alkalinity is controlled between 1.2 and 1.65; the using method comprises the following steps: (1) pre-heating the electroslag oxygen control slag system slag in an early stage; (2) the preheated hot slag is added into an electroslag furnace crystallizer; and (3) smelting in an electroslag furnace. According to the slag system provided by the invention, the oxygen content in the chromium-molybdenum hot work die steel can be effectively reduced, B-class and D-class oxygen-containing inclusions are reduced, the purity of steel is improved, and the performance requirements of customers on high polishing and high cold and hot fatigue resistance of the die steel are met.

Description

Technical Field

[0001] The present invention relates to the technical field of electroslag special metallurgy, and specifically relates to an electroslag oxygen-controlled slag system suitable for chromium-molybdenum hot working die steel and a use method thereof. Background Art

[0002] Hot working die steel is an important component of tool steel, with an annual demand of 250,000 to 300,000 tons. It is widely used in non-ferrous alloy die-casting molds, hot extrusion molds, hot forging molds, hot rolling mandrels and various types of cutting tools. Chromium-molybdenum hot working die steel accounts for the largest proportion and is the most widely used in hot working die steel due to its good comprehensive mechanical properties, economy and production operability.

[0003] With the rapid development of high-end manufacturing industries such as automobiles and rail transit in my country, higher requirements have been placed on the quality stability and service life of mold steel. Among them, steel purity and inclusion level are important indicators. Oxide inclusions are the most difficult to remove among the four types of non-metallic inclusions. Therefore, how to further reduce the oxygen content of steel and reduce oxide inclusions through electroslag remelting has always been an important research direction for the production and preparation of high-quality mold steel.

[0004] At present, the commonly used electroslag remelting slag systems in the electroslag remelting process of chromium-molybdenum hot working die steel include 7-3 slag system, 6-2-2 slag system and 4-3-3 slag system. These three types of slag systems have insufficient ability to remove oxide inclusions and do not meet the use requirements of producing ultra-low oxygen ([O] ≤ 0.001%) die steel. Summary of the invention

[0005] The object of the present invention is to provide an electroslag oxygen-controlled slag system suitable for chromium-molybdenum hot working die steel and a method of using the same, so as to solve the problem of insufficient deoxidation capacity of the existing mature electroslag remelting slag system.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] An electroslag oxygen-controlled slag system suitable for chromium-molybdenum hot-working die steel consists of the following components in weight percentage: CaF2: 48-53%, Al2O3: 22-27%, CaO: 15-20%, SiO2: 3-5%, MgO: 3-5%, Li2O: 1-3%, BaO: 1-3%, and the rest is inevitable impurity content; its basicity (CaO+MgO+0.5Li2O+BaO) / (SiO2+0.5Al2O3) is controlled between 1.2 and 1.65.

[0008] The functions of the components in the electroslag oxygen-controlled slag system of the present invention are as follows:

[0009] CaF2: CaF2 can reduce the melting point, viscosity and surface tension of slag, improve the electrical conductivity of slag and promote rapid slag formation. It is the main component of electroslag slag.

[0010] Al2O3: Al2O3 can increase the viscosity of slag, regulate the basicity of slag, significantly reduce the electrical conductivity of slag, reduce power consumption, and improve the efficiency of removing inclusions.

[0011] CaO: CaO can increase the basicity of slag, reduce the viscosity of slag, and has a significant effect on removing sulfide inclusions and oxide inclusions. However, since CaO easily absorbs moisture and increases the risk of electroslag oxygen and hydrogenation, the composition is set at 15-20%.

[0012] SiO2: SiO2 can increase the heat transfer of slag and have a deoxidation effect. Since SiO2 is an unstable oxide, its content should be controlled when designing the oxygen-controlled slag system to prevent the burning of easily oxidizable elements in the molten steel.

[0013] MgO: MgO can reduce the viscosity of slag and form a semi-solidified film on the surface of the slag pool, which can prevent the slag pool from absorbing oxygen and nitrogen and reduce the heat loss from the slag pool to the atmosphere.

[0014] Li2O, BaO: Li2O and BaO can reduce the viscosity of slag, improve the fluidity of slag, and increase the deoxidation capacity of slag. At the same time, they can modify the inclusions, promote the aggregation of Al2O3 inclusions, and make them easy to float and remove.

[0015] The present invention controls the slag basicity (CaO+MgO+0.5Li2O+BaO) / (SiO2+0.5Al2O3) to be 1.2-1.65; its purpose is to form weak alkaline slag to ensure the electroslag desulfurization ability and at the same time ensure the stability of easily oxidized elements in the electroslag process.

[0016] The method for using the electroslag oxygen-controlled slag system for chromium-molybdenum hot working die steel of the present invention comprises the following steps:

[0017] (1) preheating the electroslag oxygen-controlled slag system slag material;

[0018] (2) adding the preheated hot slag into the electroslag furnace crystallizer;

[0019] (3) Electroslag furnace smelting.

[0020] Furthermore, in the method for using the electroslag oxygen-controlled slag system of the present invention, the slag material is preheated at a temperature of 650 to 700° C. in step (1) and the preheating time is more than 4 hours.

[0021] Furthermore, in the method for using the electroslag oxygen-controlled slag system of the present invention, the hot slag in step (2) is added in a slow-first-fast-later manner, the total amount added is controlled at 30-40 kg / ton of steel, and the total slag adding time is controlled at 30 min-2 h. Before forming the slag pool, the slag should be added slowly to avoid the slag from accumulating at the bottom of the crystallizer, causing difficulty in melting the slag and arc extinguishing, and promoting the gas discharge in the bottom range of the crystallizer.

[0022] Furthermore, in the method for using the electroslag oxygen-controlled slag system of the present invention, the electroslag furnace smelting in step (3) is entirely carried out under argon atmosphere protection conditions.

[0023] Furthermore, in the method for using the electroslag oxygen-controlled slag system of the present invention, the electrode melting rate in the electroslag furnace smelting process of step (3) is 3.5-15 kg / min, and the shrinkage compensation time is controlled at 30-150 min.

[0024] Furthermore, in the method for using the electroslag oxygen-controlled slag system of the present invention, no aluminum particles are used for deoxidation during the electroslag furnace smelting process in step (3).

[0025] Furthermore, in the method for using the electroslag oxygen-controlled slag system of the present invention, the slag material of the electroslag oxygen-controlled slag system includes pre-melted slag and premixed slag.

[0026] The electroslag oxygen-controlled slag system of the present invention is used to produce chromium-molybdenum hot working die steel mainly composed of Cr, Mo and V, and the sum of the mass fractions of chromium, molybdenum and vanadium (Cr+Mo+V)% is in the range of 7% to 10%.

[0027] The electroslag oxygen-controlled slag system of the present invention can control the oxygen content of the chromium-molybdenum hot working die steel to [O] ≤ 0.001%; ​​and the inclusion level of the produced chromium-molybdenum hot working die steel is B 细 ≤0.5 level, D 细 ≤1 level, D 粗 ≤0.5 level.

[0028] The beneficial effects of the above technical solution are as follows: adding lithium and barium oxides to the slag to partially replace Al2O3 can, on the one hand, improve the deoxidation ability of the slag and reduce the risk of Class B inclusions caused by excessive Al2O3; on the other hand, lithium-barium oxides can modify the inclusions. After modification, the inclusions are easy to aggregate to form large particle inclusions, which are more conducive to floating removal and meet the strong deoxidation requirements of chromium-molybdenum hot working die steel. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present invention are described in detail below with reference to examples. The embodiments of the present invention are used to illustrate the principles of the present invention and are not used to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] 4Cr5MoSiV1 is selected as the consumable electrode, the sum of the mass percentages of Cr+Mo+V is 7.6%, the consumable electrode diameter is Φ420mm, the electrode weight is 3 tons, [O]: 0.0019%, [Al]: 0.035%.

[0032] The electroslag oxygen-control slag system used in this embodiment is composed of the following components in weight percentage: CaF2: 48.8%, Al2O3: 27%, CaO: 15.6%, SiO2: 3%, MgO: 3.2%, Li2O: 1.30%, BaO: 1.10%; its basicity (CaO+MgO+0.5Li2O+BaO) / (SiO2+0.5Al2O3) is 1.25; the method for using the electroslag oxygen-control slag system comprises the following steps:

[0033] (1) preheating the oxygen-controlled slag premixed slag of the above composition at a preheating temperature of 680° C. for a holding time of 6 hours;

[0034] (2) 110 kg of preheated slag was added to the electroslag furnace crystallizer in a slow and fast rhythm, and the slag adding time was 44 minutes;

[0035] (3) The electroslag furnace smelting was carried out under argon atmosphere protection conditions, the electrode melting rate in the steady state period was 6-8 kg / min, and the shrinkage compensation time was 52 min.

[0036] The 4Cr5MoSiV1 electroslag ingot smelted by the electroslag oxygen-controlled slag system described in this embodiment was sampled at the tail and riser end of the electroslag ingot after annealing. The oxygen content and aluminum content at the tail and riser end of the electroslag ingot were [O]: 0.0007% and 0.0009%, [Al]: 0.038% and 0.034%, respectively. Forged to Φ240mm round steel, the inclusion level is B 细 0.5 level, D 细 0.5 level, D 粗 Level 0.5.

[0037] Example 2

[0038] 4Cr5Mo2V is selected as the consumable electrode, the sum of the mass percentages of Cr+Mo+V is 8.3%, the consumable electrode diameter is Φ520mm, the electrode weight is 5 tons, [O]: 0.0022%, [Al]: 0.032%.

[0039] The electroslag oxygen-control slag system used in this embodiment is composed of the following components in weight percentage: CaF2: 53%, Al2O3: 22.9%, CaO: 15.2%, SiO2: 3.3%, MgO: 3.0%, Li2O: 1.30%, BaO: 1.3%; its basicity (CaO+MgO+0.5Li2O+BaO) / (SiO2+0.5Al2O3) is 1.37; the method for using the electroslag oxygen-control slag system comprises the following steps:

[0040] (1) preheating the oxygen-controlled slag premixed slag of the above composition at a preheating temperature of 700° C. for a holding time of 6.5 h;

[0041] (2) 170 kg of preheated slag was selected and added to the electroslag furnace crystallizer in a rhythm of first slow and then fast, and the slag adding time was 87 minutes;

[0042] (3) Electroslag smelting was carried out under argon atmosphere protection conditions, with an electrode melting rate of 8 to 10 kg / min in the steady state and a shrinkage compensation time of 86 min.

[0043] The 4Cr5Mo2V electroslag ingot smelted by the electroslag oxygen-controlled slag system was sampled at the tail and riser end of the electroslag ingot after annealing. The oxygen content and aluminum content at the tail and riser end of the electroslag ingot were [O]: 0.0008% and 0.0010%, [Al]: 0.034% and 0.035%, respectively. Forged to Φ270mm round steel, its inclusion level is B 细 0.5 level, D 细 Level 1.0, D 粗 Level 0.5.

[0044] Example 3

[0045] 4Cr5Mo3V is selected as the consumable electrode, the sum of the mass percentages of Cr+Mo+V is 8.6%, the consumable electrode diameter is Φ640mm, the electrode weight is 6 tons, of which [O]: 0.0023%, [Al]: 0.030%.

[0046] The electroslag oxygen-controlled slag system used in this embodiment is composed of the following components in weight percentage: CaF2: 48.0%, Al2O3: 25.8%, CaO: 15.0%, SiO2: 3.9%, MgO: 3.3%, Li2O: 1.0%, BaO: 3.0%, and its basicity (CaO+MgO+0.5Li2O+BaO) / (SiO2+0.5Al2O3) is 1.30; the method for using the electroslag oxygen-controlled slag system comprises the following steps:

[0047] (1) preheating the oxygen-controlled slag premixed slag of the above-mentioned composition at a preheating temperature of 700° C. for a holding time of 5 hours;

[0048] (2) 210 kg of preheated slag was added to the electroslag furnace crystallizer in a slow and fast rhythm, and the slag adding time was 105 min;

[0049] (3) Electroslag smelting was carried out under argon atmosphere protection conditions, with an electrode melting rate of 8 to 10 kg / min in the steady state and a shrinkage compensation time of 98 min.

[0050] The 4Cr5Mo3V electroslag ingot smelted by the electroslag oxygen-controlled slag system was sampled at the tail and riser end of the electroslag ingot after annealing. The oxygen content and aluminum content at the tail and riser end of the electroslag ingot were [O]: 0.0007% and 0.0008%, [Al]: 0.034% and 0.033%, respectively. Forged to Φ330mm round steel, the inclusion level is B 细 0.5 level, D 细 Level 1.0, D 粗 Level 0.5.

[0051] Example 4

[0052] 4Cr5MoSiV1 is selected as the consumable electrode, the sum of the mass percentages of Cr+Mo+V is 7.4%, the consumable electrode diameter is Φ640mm, the electrode weight is 6 tons, of which [O]: 0.0018%, [Al]: 0.029%.

[0053] The electroslag oxygen-controlled slag system used in this embodiment is composed of the following components in weight percentage: CaF2: 50.1%, Al2O3: 22.0%, CaO: 15.6%, SiO2: 3.9%, MgO: 5.0%, Li2O: 2.4%, BaO: 1.0%, and its basicity (CaO+MgO+0.5Li2O+BaO) / (SiO2+0.5Al2O3) is 1.53; the method for using the electroslag oxygen-controlled slag system comprises the following steps:

[0054] (1) preheating the oxygen-controlled slag premixed slag of the above-mentioned composition at a preheating temperature of 700° C. for a holding time of 5 hours;

[0055] (2) 180 kg of preheated slag was selected and added to the electroslag furnace crystallizer in a rhythm of first slow and then fast, and the slag adding time was 90 minutes;

[0056] (3) Electroslag smelting was carried out under argon atmosphere protection conditions, with an electrode melting rate of 8 to 10 kg / min in the steady state and a shrinkage compensation time of 110 min.

[0057] The 4Cr5MoSiV1 electroslag ingot smelted by the electroslag oxygen-controlled slag system was sampled at the tail and riser end of the electroslag ingot after annealing. The oxygen content and aluminum content at the tail and riser end of the electroslag ingot were [O]: 0.0007% and 0.0008%, [Al]: 0.030% and 0.032%, respectively. Forged to Φ330mm round steel, its inclusion level is B 细 0.5 level, D 细 0.5 level, D 粗 Level 0.5.

[0058] Example 5

[0059] 4Cr5Mo2V is selected as the consumable electrode, the sum of the mass percentages of Cr+Mo+V is 8.1%, the consumable electrode diameter is Φ640mm, the electrode weight is 6 tons, [O]: 0.0021%, [Al]: 0.028%.

[0060] The electroslag oxygen-control slag system used in this embodiment is composed of the following components in weight percentage: CaF2: 48.2%, Al2O3: 22.2%, CaO: 20.0%, SiO2: 4.0%, MgO: 3.1%, Li2O: 1.4%, BaO: 1.1%, and its basicity (CaO+MgO+0.5Li2O+BaO) / (SiO2+0.5Al2O3) is 1.65; the method for using the electroslag oxygen-control slag system comprises the following steps:

[0061] (1) preheating the oxygen-controlled slag premixed slag of the above composition at a temperature of 650° C. for a holding time of 6 h;

[0062] (2) 220 kg of preheated slag was added to the electroslag furnace crystallizer in a slow and fast rhythm, and the slag adding time was 100 min;

[0063] (3) Electroslag smelting is carried out under argon atmosphere protection conditions, the electrode melting rate in the steady state period is 6-8 kg / min, and the shrinkage compensation time is 120 min.

[0064] The 4Cr5Mo2V electroslag ingot smelted by the electroslag oxygen-controlled slag system was sampled at the tail and riser end of the electroslag ingot after annealing. The oxygen content and aluminum content at the tail and riser end of the electroslag ingot were [O]: 0.007% and 0.007%, [Al]: 0.028% and 0.029%, respectively. Forged to Φ330mm round steel, the inclusion level is B 细 0.5 level, D 细 0.5 level, D 粗 Level 0.5.

[0065] Example 6

[0066] 4Cr5Mo3V is selected as the consumable electrode, the sum of the mass percentages of Cr+Mo+V is 8.7%, the consumable electrode diameter is Φ520mm, the electrode weight is 5 tons, [O]: 0.0022%, [Al]: 0.031%.

[0067] The electroslag oxygen-controlled slag system used in this embodiment is composed of the following components in weight percentage: CaF2: 48.8%, Al2O3: 23.1%, CaO: 15.4%, SiO2: 5.0%, MgO: 3.5%, Li2O: 3.0%, BaO: 1.2%, and its basicity (CaO+MgO+0.5Li2O+BaO) / (SiO2+0.5Al2O3) is 1.31; the method for using the electroslag oxygen-controlled slag system comprises the following steps:

[0068] (1) preheating the oxygen-controlled slag premixed slag of the above-mentioned composition at a preheating temperature of 680° C. for a holding time of 5 h;

[0069] (2) 190 kg of preheated slag was selected and added to the electroslag furnace crystallizer in a rhythm of first slow and then fast, and the slag adding time was 90 minutes;

[0070] (3) Electroslag smelting is carried out under argon atmosphere protection conditions, the electrode melting rate in the steady state period is 6-8 kg / min, and the shrinkage compensation time is 120 min.

[0071] The 4Cr5Mo3V electroslag ingot smelted by the electroslag oxygen-controlled slag system was sampled at the tail and riser end of the electroslag ingot after annealing. The oxygen content and aluminum content at the tail and riser end of the electroslag ingot were [O]: 0.008% and 0.009%, [Al]: 0.030% and 0.029%, respectively. Forged to Φ270mm round steel, the inclusion level is B 细 0.5 level, D 细 Level 1.0, D 粗 Level 0.

[0072] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. An electroslag oxygen-controlled slag system suitable for chromium-molybdenum hot working die steel, characterized in that: It is composed of the following components in weight percentage: CaF2: 48-53%, Al2O3: 22-27%, CaO: 15-20%, SiO2: 3-5%, MgO: 3-5%, Li2O: 1-3%, BaO: 1-3%, and the rest are inevitable impurities; the basicity of the slag system (CaO+MgO+0.5Li2O+BaO) / (SiO2+0.5Al2O3) is controlled between 1.2 and 1.

65.

2. The electroslag oxygen-controlled slag system suitable for chromium-molybdenum hot working die steel according to claim 1, characterized in that: The sum of the mass fractions of chromium, molybdenum and vanadium (Cr+Mo+V)% in the chromium-molybdenum hot working die steel is in the range of 7% to 10%.

3. The method for using the electroslag oxygen-controlled slag system suitable for chromium-molybdenum hot working die steel according to claim 1, characterized in that: The steps include: (1) preheating the electroslag oxygen-controlled slag system slag material; (2) adding the preheated hot slag into the electroslag furnace crystallizer; (3) Electroslag furnace smelting.

4. The method for using the electroslag oxygen-controlled slag system suitable for chromium-molybdenum hot working die steel according to claim 3, characterized in that: In step (1), the slag is preheated at a temperature of 650-700°C for a preheating time of more than 4 hours.

5. The method for using the electroslag oxygen-controlled slag system suitable for chromium-molybdenum hot working die steel according to claim 3, characterized in that: The hot slag in step (2) is added in a slow-first-fast-then manner, with the total amount added controlled at 30-40 kg / ton of steel, and the total slag adding time controlled at 30 min-2 h.

6. The method for using the electroslag oxygen-controlled slag system suitable for chromium-molybdenum hot working die steel according to claim 3, characterized in that: The electroslag furnace smelting in step (3) is carried out entirely under argon atmosphere protection conditions.

7. The method for using the electroslag oxygen-controlled slag system suitable for chromium-molybdenum hot working die steel according to claim 3, characterized in that: In step (3), the electrode melting rate during the electroslag furnace smelting process is 3.5-15 kg / min, and the shrinkage compensation time is controlled at 30-150 min.

8. The method for using the electroslag oxygen-controlled slag system suitable for chromium-molybdenum hot working die steel according to claim 3, characterized in that: In step (3), no aluminum pellet deoxidation is used during the electroslag furnace smelting process.

9. The method for using the electroslag oxygen-controlled slag system suitable for chromium-molybdenum hot working die steel according to claim 3, characterized in that: The slag material of the electroslag oxygen-controlled slag system includes pre-melted slag and pre-mixed slag.