Smelting method of hot working grinding tool steel

Abstract

The invention relates to the technical field of steel and iron smelting, in particular to a smelting method of hot-working grinding tool steel, which comprises the following steps: 1) blowing molten iron through a top-bottom combined blown converter to control the quality parameters of the produced molten steel, and tapping; 2) hoisting the molten steel produced in the step 1) to a refining process, and refining in an LF refining furnace and an RH refining furnace in sequence; (3) the molten steel obtained after LF refining in the step (2) is hoisted to a continuous casting procedure for whole-course protective casting; wherein in the step (3), a weak cooling process is adopted in the continuous casting process. According to the smelting method of the hot-working grinding tool steel, the hot-working grinding tool steel with high cleanliness and high internal quality can be stably and efficiently smelted and obtained, and the problems that hot-working die steel is high in hot crack sensitivity, strict in requirement for indexes such as purity and internal quality, high in alloying difficulty and prone to cracking of a casting blank are solved.

Description

Technical Field

[0001] The invention relates to the technical field of steel smelting, and in particular to a smelting method for hot-working abrasive tool steel. Background Art

[0002] my country's mold industry is large in scale, with high annual output value and huge market potential. However, due to its late start, its products are mainly low-end and medium-end, and large, precise and complex molds are still heavily dependent on imports. Hot forging dies are an important branch of mold steel. The products are mainly divided into three categories: medium-carbon low-alloy hot working die steel, chromium-based medium-alloy hot working die steel and improved hot working die steel. The operating temperature covers the temperature range of 300-700℃ and is widely used in the automotive industry and machinery manufacturing industry.

[0003] Hot working die steel has good cost performance and process performance. It is currently widely used at home and abroad. This type of steel is highly sensitive to hot cracks and has strict requirements on purity, internal quality and other indicators. In addition, this type of steel has a large alloy content, is difficult to alloy, and is prone to cracks in the casting, which seriously affects process control and product quality.

[0004] Based on this, how to accurately control the content of each element in molten steel and avoid cracks in the ingot so as to efficiently smelt and obtain high-quality hot working abrasive steel is a technical problem that needs to be solved urgently. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems of hot working die steel having high sensitivity to thermal cracks, strict requirements on indicators such as purity and internal quality, great difficulty in alloying, and easy cracking of the cast billet, so as to provide a smelting method for hot working mold steel that can stably and efficiently smelt and obtain hot working mold steel with high cleanliness and high internal quality.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a smelting method for hot-working abrasive tool steel, the smelting method comprising: 1) blowing molten iron through a top and bottom double-blown converter to control the quality parameters of the produced molten steel and tap the steel; 2) hoisting the molten steel produced in step 1) to a refining process, and refining it in an LF refining furnace and an RH refining furnace in turn; 3) hoisting the molten steel after LF refining in step 2) to a continuous casting process for full-process protected casting; wherein, in step 3), the continuous casting process adopts a weak cooling process.

[0007] Preferably, in step 1), the blowing is performed by a high-draw supplementary blowing method.

[0008] Preferably, in step 1), the quality parameters of the molten steel produced are controlled to include: controlling the carbon content in the molten steel to ≥0.08wt%, the phosphorus content to <0.008wt%, and the tapping temperature to 1600-1650°C.

[0009] Preferably, in step 1), the conditions for tapping the steel include: when the tapping amount is 1 / 4, firstly adding the alloy into the ladle, and then adding the slag.

[0010] Preferably, the conditions for adding the alloy include: adding ferromolybdenum with the scrap steel bucket, and adding low-titanium ferrosilicon, low-carbon ferrochrome and silicon manganese into the silo.

[0011] More preferably, the amount of ferromolybdenum is 20kg / t, the amount of low-carbon ferrochromium is 24kg / t, the amount of low-titanium ferrosilicon is 12Kg / t, and the amount of silicon manganese is 6Kg / t.

[0012] Further preferably, slag is strictly prohibited during the steel tapping process, and steel should be retained if necessary.

[0013] Preferably, the smelting method further comprises: in step 1), argon is blown from the bottom of the ladle throughout the entire process, and after steel tapping is completed, the flow rate of the bottom-blown argon is adjusted to a bright surface of 300-500 mm.

[0014] Preferably, in step 2), the refining conditions in the LF refining furnace include: first adding the alloy into the molten steel, and then adding slag and slag-reducing agent to produce white slag.

[0015] Preferably, the conditions for adding the alloy include: the amount of ferrovanadium is 17 kg / t, the amount of low-titanium high-carbon ferrochrome is 32 kg / t, and the amount of low-carbon ferrochrome is 26 kg / t.

[0016] More preferably, the conditions for adding slag include: the amount of low-titanium refined synthetic slag is 200 kg / furnace, and the amount of lime is 500-1000 kg.

[0017] Further preferably, the conditions for making white slag include: white slag retention time ≥ 20 min.

[0018] More preferably, the contents of various components in the LF refining final slag satisfy FeO+MnO<1.0wt%, Als / Al≥85%, and basicity R≥3.0.

[0019] Preferably, in step 2), the refining conditions in the RH refining furnace include: RH vacuum refining degassing, and determining hydrogen and oxygen.

[0020] Preferably, the hydrogen and oxygen are determined using a Heraeus hydrogen determiner.

[0021] More preferably, the hydrogen content in the molten steel after refining in the RH refining furnace is ≤2ppm.

[0022] Preferably, in step 2), the soft blowing time of the RH refining satisfies that the first pouring furnace is ≥15min and the continuous pouring furnace is ≥10min.

[0023] Preferably, in step 3), the protective casting adopts a method of argon blowing protection of a large ladle casing and integral nozzle casting.

[0024] Preferably, the protective casting conditions also include: the superheat of the tundish of the first casting furnace is 35-45°C, the superheat of the tundish of the continuous casting furnace is 20-30°C, and the stirring method of crystallizer electromagnetic stirring plus end electromagnetic stirring is adopted during the casting process.

[0025] Preferably, the conditions of the weak cooling process include: after the continuous casting billet comes off the line, it is slowly cooled in the pit for 72 hours, the exit temperature of the pit is ≤200°C, and the exit annealing temperature is 860-900°C.

[0026] Through the above technical scheme, the smelting method of hot working mold steel of the present invention optimizes the operating process of the converter and the refining furnace and the operation of making white slag during the smelting process, accurately controls the composition of molten steel and the content of gaseous hydrogen, and realizes accurate control of the C, Si, Mn, Cr, Mo, and Al components in the molten steel, thereby overcoming the defects that the hot working die steel has an extremely high alloy content, the secondary oxidation of the molten steel easily leads to the deterioration of the cleanliness of the steel, and causes the clogging of the water nozzle to interrupt the casting; at the same time, a weak cooling process is adopted in the continuous casting process, and after the ingot is off the line, it is first put into the pit for slow cooling and then annealed out of the pit, so as to ensure the castability of the molten steel and make the continuous casting ingot weakly cooled to avoid cracks, and successfully develop high-quality hot working die steel.

[0027] Moreover, the smelting method of the hot working mold steel of the present invention adopts a converter, off-furnace refining, and continuous casting steelmaking process flow, and controls the main chemical elements C, Si, Mn, Cr, Mo, and Al in the steel by designing the composition of the hot working die steel, and then adopts RH off-furnace refining vacuum degassing to control the gas hydrogen content in the steel to be ≤2ppm, and finally adjusts the FeO+MnO<1.0wt%, Als / Al≥85wt%, and basicity R≥3.0 in the refined slag after the white slag, thereby improving the cleanliness of the molten steel; the continuous casting adopts a large ladle casing argon blowing protection and an integral water nozzle casting to perform protective casting, and adopts a weak cooling process to prevent cracks in the casting, so that the smelting method is safe and reliable, easy to manufacture, easy to operate, and can be applied to industrial mass production.

[0028] Other features and advantages of the present invention will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0029] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0030] The present invention provides a smelting method for hot-working abrasive tool steel, which comprises: 1) blowing molten iron through a top and bottom double-blowing converter to control the quality parameters of the produced molten steel and tap the steel; 2) hoisting the molten steel produced in step 1) to a refining process, and refining it in an LF refining furnace and an RH refining furnace in sequence; 3) hoisting the molten steel after LF refining in step 2) to a continuous casting process for full-process protected casting; wherein, in step 3), the continuous casting process adopts a weak cooling process.

[0031] The smelting method of the hot working mold steel of the present invention optimizes the operating process of the converter and the refining furnace and the operation of making white slag during the smelting process, accurately controls the composition of molten steel and the content of gaseous hydrogen, and realizes accurate control of the C, Si, Mn, Cr, Mo and Al components in the molten steel, thereby overcoming the defects that the hot working die steel has an extremely high alloy content, the secondary oxidation of the molten steel easily leads to the deterioration of the cleanliness of the steel, and causes the clogging of the water nozzle and the interruption of casting; at the same time, a weak cooling process is adopted in the continuous casting process, and after the ingot is off the line, it is first put into the pit for slow cooling and then annealed out of the pit, so as to ensure the castability of the molten steel and make the continuous casting ingot weakly cooled to avoid cracks, and successfully develop high-quality hot working die steel.

[0032] In a preferred embodiment of the present invention, in order to obtain high-quality hot working die steel through smelting, in step 1), the blowing is performed by a high-drawing supplementary blowing method.

[0033] In a preferred embodiment of the present invention, in order to accurately control the composition of the molten steel and improve the cleanliness of the molten steel, in step 1), the quality parameters of the output molten steel are controlled including: the carbon content in the output molten steel is controlled at ≥0.08wt%, the phosphorus content is controlled at <0.008wt%, and the tapping temperature is controlled at 1600-1650℃.

[0034] In a preferred embodiment of the present invention, in order to accurately control the composition of molten steel and improve the cleanliness of molten steel, in step 1), the conditions for tapping include: when the tapping amount is 1 / 4, first add alloy to the ladle and then add slag.

[0035] In a preferred embodiment of the present invention, in order to accurately control the composition of molten steel and improve the cleanliness of molten steel, the conditions for adding alloys include: adding ferromolybdenum with the scrap steel bucket, and adding low-titanium ferrosilicon, low-carbon ferrochrome and silicon manganese into the silo.

[0036] In a preferred embodiment of the present invention, in order to accurately control the composition in the molten steel and improve the cleanliness of the molten steel, the amount of ferromolybdenum is 20kg / t, the amount of low-carbon ferrochromium is 24kg / t, the amount of low-titanium ferrosilicon is 12Kg / t, and the amount of silicon manganese is 6Kg / t.

[0037] In a preferred embodiment of the present invention, slag is strictly prohibited during the steel tapping process, and steel should be retained if necessary.

[0038] In a preferred embodiment of the present invention, the smelting method further comprises: in step 1), argon is blown from the bottom of the ladle throughout the entire process, and after the steel is tapped, the flow rate of the bottom-blown argon is adjusted to 300-500 mm above the bright surface.

[0039] In a preferred embodiment of the present invention, in order to accurately control the composition of molten steel and improve the cleanliness of molten steel, in step 2), the refining conditions of the LF refining furnace include: first adding alloy to the molten steel, and then adding slag and slag-reducing agent to make white slag.

[0040] In a preferred embodiment of the present invention, in order to accurately control the composition of molten steel and improve the cleanliness of molten steel, the conditions for adding alloys include: the amount of ferrovanadium is 17kg / t, the amount of low-titanium high-carbon ferrochrome is 32kg / t, and the amount of low-carbon ferrochrome is 26kg / t.

[0041] In a preferred embodiment of the present invention, in order to accurately control the composition of molten steel and improve the cleanliness of molten steel, the conditions for adding slag include: the amount of low-titanium refined synthetic slag is 200kg / furnace, and the amount of lime is 500-1000kg.

[0042] In a preferred embodiment of the present invention, in order to accurately control the composition of molten steel and improve the cleanliness of molten steel, the conditions for making white slag include: white slag retention time ≥ 20 min.

[0043] In a preferred embodiment of the present invention, in order to accurately control the composition of molten steel and improve the cleanliness of molten steel, the content of each component in the LF refining final slag satisfies FeO+MnO<1.0wt%, Als / Al≥85%, and basicity R≥3.0.

[0044] In a preferred embodiment of the present invention, in order to accurately control the content of gaseous hydrogen in molten steel and improve the cleanliness of molten steel, in step 2), the refining conditions in the RH refining furnace include: RH vacuum refining degassing and hydrogen and oxygen determination.

[0045] In a preferred embodiment of the present invention, in order to accurately control the content of gaseous hydrogen in molten steel and improve the cleanliness of molten steel, the hydrogen and oxygen determination is performed using a Heraeus hydrogen determination instrument.

[0046] In a preferred embodiment of the present invention, in order to accurately control the content of gaseous hydrogen in molten steel and improve the cleanliness of molten steel, the hydrogen content in the molten steel after refining in the RH refining furnace is ≤2ppm.

[0047] In a preferred embodiment of the present invention, in order to improve the cleanliness of molten steel, in step 2), the soft blowing time of the RH refining satisfies that the first pouring furnace is ≥15min and the continuous pouring furnace is ≥10min.

[0048] In a preferred embodiment of the present invention, in order to improve the cleanliness of the molten steel, in step 3), the protective casting adopts a method of argon blowing protection of a large ladle casing and integral nozzle casting.

[0049] In a preferred embodiment of the present invention, in order to improve the cleanliness of molten steel, the protective casting conditions also include: the superheat of the tundish of the first casting furnace is 35-45°C, the superheat of the tundish of the continuous casting furnace is 20-30°C, and the stirring method of crystallizer electromagnetic stirring plus end electromagnetic stirring is adopted during the casting process.

[0050] In a preferred embodiment of the present invention, in order to avoid cracks in the ingot, the conditions of the weak cooling process include: after the continuous casting ingot comes off the line, slow cooling in the pit for 72 hours, the exit temperature of the pit is ≤200°C, and the exit annealing temperature is 860-900°C.

[0051] The present invention will be described in detail below through examples. In the following examples, the drugs and pharmaceutical agents are all conventional commercial products.

[0052] Example

[0053] The production process route of the smelting method of hot working abrasive steel of the present invention is: hot metal desulfurization → converter smelting → LF refining → RH vacuum degassing → continuous casting → heating → water descaling → rough rolling → 1# flying shear → intermediate rolling → finishing rolling → metal saw → cooling bed → collection → slow cooling → obtaining hot working abrasive steel, wherein:

[0054] (1) Continuous casting and rolling process: Control the superheat of the continuous casting protection casting and the tundish molten steel to 30-40℃, maintain a constant pulling speed of 0.75m / min. Use hot charging process, heating temperature 1110-1150℃, holding time 250-300min, high-pressure water dephosphorization after heating furnace, descaling water pressure ≥10MPa, and rolling temperature 1120±20℃.

[0055] (2) The composition control of each embodiment is shown in Table 1, and the conditions of the continuous casting and rolling process are shown in Table 2.

[0056] Table 1 Composition control (wt%)

[0057] C Si Mn P S Cr Mo V Al N Example 1 0.37 1.10 0.45 0.011 0.002 5.08 1.26 0.937 0.022 0.0077 Example 2 0.37 1.05 0.49 0.009 0.002 5.04 1.26 0.918 0.014 0.0088

[0058] Table 2 Continuous casting and rolling process conditions

[0059]

[0060] Test example

[0061] The actual inclusion detection results of Example 1-2 are shown in Table 3, and the detection standards are shown in Table 4:

[0062] Table 3 Actual inclusion detection results of Example 1-2

[0063]

[0064] Table 4 Standard requirements for non-metallic inclusions:

[0065]

[0066] Among them, the actual inclusions are mainly non-metallic inclusions, which are mainly divided into five categories according to their morphology and distribution characteristics: A, B, C, D and DS. The specific classification is as follows: Category A (sulfide): high ductility, single gray inclusions, rounded ends; Category B (alumina): most of them are not deformed, black or blue particles with corners, distributed in chains along the rolling direction; Category C (silicate): high ductility, smooth boundaries, single black or dark gray inclusions, sharp ends; Category D (spherical oxide): no deformation, angular or round, black or blue, irregularly distributed particles; Category DS (single particle spherical): round inclusions with a diameter of ≥13μm; coarse and fine are measured by comparing the width or diameter of the inclusion with the standard value to determine whether it is coarse or fine.

[0067] It can be seen from the data in Table 3 and Table 4 that the actual inclusion detection results of the hot working abrasive steels prepared by the smelting method of the hot working abrasive steel of the present invention in Example 1-2 meet the standard requirements.

[0068] In summary, the smelting method of hot working mold steel of the present invention adopts a converter, off-furnace refining, and continuous casting steelmaking process, and controls the main chemical elements C, Si, Mn, Cr, Mo, and Al in the steel by designing the composition of the hot working die steel, and then adopts RH off-furnace refining vacuum degassing to control the gas hydrogen content in the steel to be ≤2ppm, and finally adjusts the FeO+MnO<1.0wt%, Als / Al≥85%, and the basicity R≥3.0 in the refined slag after the white slag, thereby improving the cleanliness of the molten steel; the continuous casting adopts a large ladle casing argon blowing protection and an integral water nozzle casting to perform protective casting, and adopts a weak cooling process to prevent cracks in the casting, so that the smelting method is safe and reliable, easy to manufacture, easy to operate, and can be applied to industrial mass production.

[0069] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0070] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0071] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for smelting hot-working abrasive steel, characterized in that: The smelting method comprises: 1) The molten iron is blown through a top and bottom double-blown converter to control the quality parameters of the molten steel produced and to produce steel; 2) the molten steel produced in step 1) is hoisted to the refining process, and refined in the LF refining furnace and the RH refining furnace in sequence; 3) hoisting the molten steel after LF refining in step 2) to the continuous casting process for full-process protection casting; Wherein, in step 3), the continuous casting process adopts a weak cooling process.

2. The smelting method according to claim 1, characterized in that: In step 1), the blowing is performed by a high-draw supplementary blowing method.

3. The smelting method according to claim 1 or 2, characterized in that: In step 1), the quality parameters of the produced molten steel are controlled by controlling the carbon content in the produced molten steel to be ≥0.08wt%, the phosphorus content to be <0.008wt%, and the tapping temperature to be controlled to be 1600-1650°C.

4. The smelting method according to any one of claims 1 to 3, characterized in that: In step 1), the conditions for tapping include: when the tapping amount is 1 / 4, first adding low-carbon ferrochrome, low-titanium ferrosilicon, and silicon-manganese alloy into the ladle, and then adding slag; Preferably, the conditions for adding the alloy include: adding ferromolybdenum with the scrap steel bucket, and adding low-titanium ferrosilicon, low-carbon ferrochrome and silicon manganese to the silo; More preferably, the amount of ferromolybdenum is 20kg / t, the amount of low-carbon ferrochrome is 24kg / t, the amount of low-titanium ferrosilicon is 12Kg / t, and the amount of silicon manganese is 6Kg / t; Further preferably, slag is strictly prohibited during the steel tapping process, and steel should be retained if necessary.

5. The smelting method according to any one of claims 1 to 4, characterized in that: The smelting method further comprises: in step 1), argon is blown from the bottom of the ladle throughout the whole process, and after the steel is tapped, the flow rate of the bottom-blown argon is adjusted to 300-500 mm above the bright surface.

6. The smelting method according to any one of claims 1 to 5, characterized in that: In step 2), the refining conditions of the LF refining furnace include: first adding alloy to molten steel, then adding slag and slag-reducing agent to produce white slag; Preferably, the conditions for adding the alloy include: the amount of ferrovanadium is 17kg / t, the amount of low-titanium high-carbon ferrochrome is 32kg / t, and the amount of low-carbon ferrochrome is 26kg / t; More preferably, the conditions for adding slag materials include: the amount of low-titanium refined synthetic slag is 200 kg / furnace, the amount of lime is 500-1000 kg; Further preferably, the conditions for making white slag include: white slag retention time ≥ 20 min; More preferably, the contents of various components in the LF refining final slag satisfy FeO+MnO<1.0wt%, Als / Al≥85%, and basicity R≥3.

0.

7. The smelting method according to any one of claims 1 to 6, characterized in that: In step 2), the refining conditions in the RH refining furnace include: RH vacuum refining degassing, fixing hydrogen and oxygen; Preferably, the hydrogen and oxygen are determined using a Heraeus hydrogen determination instrument; More preferably, the hydrogen content in the molten steel after refining in the RH refining furnace is ≤2ppm.

8. The smelting method according to any one of claims 1 to 7, characterized in that: In step 2), the soft blowing time of the RH refining satisfies that the first pouring furnace is ≥15min and the continuous pouring furnace is ≥10min.

9. The smelting method according to any one of claims 1 to 8, characterized in that: In step 3), the protective casting adopts a method of argon blowing protection of a large sleeve and integral nozzle casting; Preferably, the protective casting conditions also include: the superheat of the tundish of the first casting furnace is 35-45°C, the superheat of the tundish of the continuous casting furnace is 20-30°C, and the stirring method of crystallizer electromagnetic stirring plus end electromagnetic stirring is adopted during the casting process.

10. The smelting method according to any one of claims 1 to 9, characterized in that: The conditions of the weak cooling process include: after the continuous casting billet comes off the line, it is slowly cooled in the pit for 72 hours, the exit temperature of the pit is ≤200°C, and the exit annealing temperature is 860-900°C.

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