阅读说明：本技术 Cr12冷作模具钢精炼稀土添加方法 (Rare earth adding method for Cr12 cold work die steel refining ) 是由 吴铖川 王洪利 王唐林 杜思敏 于 2020-04-28 设计创作，主要内容包括：本发明涉及Cr12冷作模具钢精炼稀土添加方法,属于模具钢冶金技术领域。本发明解决的技术问题是对于Cr12冷作模具钢目前还没有相适宜的稀土添加方法在提升稀土收得率的同时满足夹杂物要求。本发明的技术方案是采用EF电炉冶炼+LF精炼+VD真空精炼冶炼Cr12冷作模具钢,LF精炼完成脱氧、合金化后添加稀土,VD真空精炼破空后立即添加稀土,出钢,模铸浇注。本发明稀土收得率≥50％,夹杂物按GB/T10561-2005的A法检验与评级,A、B、C、D粗/细系及Ds各类非金属夹杂物级别≤2.0级的达标率≥85％,能开发出各类夹杂物≤1.0级的高端冷作模具钢。(The invention relates to a method for adding Cr12 cold-work die steel refining rare earth, belonging to the technical field of die steel metallurgy. The invention solves the technical problem that no appropriate rare earth adding method for Cr12 cold-work die steel can meet the requirement of inclusions while improving the yield of rare earth. The technical scheme of the invention is that EF electric furnace smelting, LF refining and VD vacuum refining are adopted to smelt Cr12 cold work die steel, rare earth is added after LF refining is performed to deoxidize and alloy, rare earth is immediately added after VD vacuum refining is broken, tapping is performed, and die casting pouring is performed. The yield of the rare earth is more than or equal to 50 percent, the inclusions are inspected and graded according to the GB/T10561-2005 method A, the standard reaching rate of A, B, C, D coarse/fine series and Ds various non-metallic inclusions with the grade less than or equal to 2.0 is more than or equal to 85 percent, and high-end cold-work die steel with various inclusions less than or equal to 1.0 grade can be developed.)

The method for adding rare earth in Cr12 cold-work die steel refining adopts EF electric furnace smelting, LF refining and VD vacuum refining to produce Cr12 cold-work die steel, and is characterized in that: and after the LF refining is finished and deoxidated and alloyed, rare earth is added, after the VD vacuum refining is broken, the rare earth is immediately added, tapping is carried out, and die casting and pouring are carried out.

2. The Cr12 cold work die steel refining rare earth adding method according to claim 1, characterized in that: the chemical components of the LF refined deoxidized and alloyed Al are 0.01-0.04 wt%, S is less than or equal to 0.005 wt%, and O is less than or equal to 0.0020 wt%.

3. The Cr12 cold work die steel refining rare earth adding method according to claim 1 or 2, characterized in that: and rare earth is added in an insertion mode of inserting an inserted rod after the VD vacuum refining is broken.

4. The Cr12 cold work die steel refining rare earth adding method according to any one of claims 1 to 3, characterized in that: after the LF refining is finished, controlling the addition amount of rare earth to be 0.05-0.0.075kg/t steel; the rare earth addition amount after the VD vacuum refining is broken is controlled to be 0.05-0.0.075kg/t steel.

5. The Cr12 cold work die steel refining rare earth adding method according to any one of claims 1 to 4, characterized in that: controlling SiO in the slag after LF refining is finished₂The content of (B) is less than or equal to 10 percent by mass.

6. The Cr12 cold work die steel refining rare earth adding method according to any one of claims 1 to 5, characterized in that: the ultimate vacuum degree of VD vacuum refining is less than or equal to 67Pa, and the holding time under the ultimate vacuum is more than or equal to 15 min.

7. The Cr12 cold work die steel refining rare earth adding method according to any one of claims 1 to 6, characterized in that: and blowing Ar under the VD vacuum refining limit vacuum, wherein the Ar flow is more than or equal to 120L/min, and is adjusted to 20-40L/min about 1-2 min before the air is broken.

8. The Cr12 cold work die steel refining rare earth adding method according to any one of claims 1 to 7, characterized in that: immediately sampling and analyzing after the VD vacuum refining is broken, controlling the [ H ] to be less than or equal to 2.5ppm, and then carrying out soft blowing and adding rare earth.

9. The Cr12 cold work die steel refining rare earth adding method according to any one of claims 1 to 8, characterized in that: and after the VD vacuum refining is broken, the soft argon blowing time is controlled to be 30-50 min.

10. The Cr12 cold work die steel refining rare earth adding method according to any one of claims 1 to 8, characterized in that: and controlling the flow rate of soft blowing after the VD vacuum refining is broken to be 15-30L/min.

Technical Field

The invention belongs to the technical field of die steel metallurgy, and particularly relates to a method for adding rare earth refined by Cr12 cold-work die steel.

Background

The cold-work die steel materials which are most widely applied in the existing market are mainly high-carbon high-chromium cold-work die steels Cr12, Cr12MoV and the like, and have high hardenability, wear resistance and good high-temperature oxidation resistance, so that the cold-work die steel materials are widely applied to manufacturing cold-work dies with various purposes as general cold-work die steel materials, such as punching female dies with complex shapes, cold extrusion dies, rolling threaded wheels, cold shearing knives, precision measuring tools and the like. Therefore, the requirements on the performance of the cold-work die steel are high, and the control of the inclusions in the cold-work die steel also puts forward high requirements, so that the cold-work die steel cannot have hard inclusions with larger sizes, particularly inclusions with sizes larger than 20 mu m, because the inclusions are easy to fall off due to high pressure, abrasion and the like during the use of a product, so that a crack source is formed, the service life of the product is shortened, and even accidents occur.

The inclusion content in the cold-work die steel is high, so that quality problems such as pits, fatigue fracture and the like of a cold-work die steel product in the using process are easily caused, and the service life of the product is seriously influenced. Especially high melting point Al₂O₃Inclusions and sulfide-based inclusions, Al₂O₃The inclusions are easy to dissolve in Cl-containing ionic water to reduce the corrosion resistance of steel, and reduce the plasticity, toughness and fatigue resistance of the steel, if the sulfide content of the steel exceeds a certain standard, casting blank cracks can be caused in the smelting production and rolling processes, and the product quality is seriously influenced. Therefore, the cleanliness of the cold-work die steel is improved, the inclusion content is reduced, and the method plays an important role in improving the quality of the cold-work die steel product.

The rare earth elements have important influence on deoxidation, desulfurization, inclusion modification treatment, solidification structure and steel performance of molten steel. A large number of researches show that the rare earth element is added into the cold-work die steel, so that oxide and sulfide inclusions in molten steel can be subjected to denaturation treatment, and fine and nearly spherical rare earth compounds are generated. Meanwhile, rare earth elements can refine the structure of the as-cast ledeburite, eliminate harmful elements such as sulfur, phosphorus and the like which are partially polymerized along the grain boundary, ensure that carbide is uniformly distributed, refine crystal grains and make the structure more uniform, thereby greatly improving the mechanical property of the steel. The high-end cold-work die steel inside and outside the country mostly adopts the mode of adding trace rare earth elements to improve the cleanliness level and the comprehensive mechanical property of the steel. At present, a lot of patents or articles are provided in the aspect of controlling inclusions in steel smelting or rolling in China, but no suitable rare earth adding method is provided in the steel smelting process, so that the requirement of controlling inclusions can be met while the rare earth yield is improved.

Disclosure of Invention

The invention solves the technical problem that no appropriate rare earth adding method exists for Cr12 cold-work die steel at present, and meets the control requirement of steel inclusion while improving the rare earth yield.

The invention provides a method for adding rare earth in Cr12 cold-work die steel refining, which adopts EF electric furnace smelting, LF refining and VD vacuum refining to produce Cr12 cold-work die steel, wherein the rare earth is added after the LF refining is performed with deoxidation and alloying, the rare earth is immediately added after the VD vacuum refining is broken, tapping is performed, and die casting and pouring are performed.

Wherein, the chemical compositions of the deoxidized and alloyed LF refining are 0.01-0.04 percent of Al, less than or equal to 0.005 percent of S and less than or equal to 0.0020 percent of O in percentage by mass.

Wherein, after VD vacuum refining is broken, rare earth is added in an adding mode of inserting an inserted rod.

Wherein the rare earth addition amount is controlled to be 0.05-0.0.075kg/t steel after LF refining is finished.

Wherein the rare earth addition amount after VD vacuum refining and vacuum breaking is controlled to be 0.05-0.0.075kg/t steel.

Wherein SiO in the slag is controlled after LF refining is finished₂The content of (B) is less than or equal to 10 percent by mass.

Wherein the ultimate vacuum degree of VD vacuum refining is less than or equal to 67Pa, and the holding time under the ultimate vacuum is more than or equal to 15 min.

Wherein, Ar is blown under the VD vacuum refining limit vacuum, the Ar flow is more than or equal to 120L/min, about 1-2 min before the air breaking, and the Ar flow is adjusted to 20-40L/min.

Wherein, VD vacuum refining is carried out, sampling analysis is carried out immediately after breaking the vacuum, H is controlled to be less than or equal to 2.5ppm, and then soft blowing and rare earth addition are carried out.

Wherein the soft argon blowing time is controlled within 30-50 min after the VD vacuum refining is broken.

Wherein the soft blowing flow rate is controlled at 15-30L/min.

The invention has the beneficial effects that:

the rare earth addition method is adopted to produce Cr12MoV cold-work die steel, the yield of rare earth is more than or equal to 50 percent, the inclusions are inspected and graded according to the A method of GB/T10561-2005, the standard reaching rate of A, B, C, D coarse/fine series and Ds various non-metallic inclusions with the grade less than or equal to 2.0 is more than or equal to 85 percent, and high-end cold-work die steel with various inclusions less than or equal to 1.0 grade can be developed;

the addition of the rare earth controls the type and the appearance of inclusions in steel from the original B type (string-shaped and chain-shaped Al)₂O₃) Class A (sulfide inclusion) is converted into class D (round and oval rare earth oxide, rare earth sulfide, rare earth aluminate and rare earth oxysulfide);

the purity of the Cr12 series cold-work die steel produced by the method is greatly improved, the type of inclusions in the steel is optimal, the size distribution is fine and dispersed, the grade of the inclusions is reduced, and the purpose of improving the quality of the cold-work die steel product is finally achieved.

Detailed Description

The invention provides a method for adding rare earth in Cr12 cold-work die steel refining, which adopts EF electric furnace smelting, LF refining and VD vacuum refining to produce Cr12 cold-work die steel, and can be specifically carried out according to the following operation and requirements:

the process flow comprises the following steps: EF → LF → VD → die casting.

The raw material requirements are as follows: the components of various raw materials and steel grades meet the requirements of Cr12MoV in GB/T1299-2014, D2 in American standard ASTMA686/ASTM A681 and SKD11 steel grades in Japanese standard JIS G4401/JIS G4404.

And (3) EF electric furnace smelting:

adding raw materials according to the component requirements of steel types for smelting, after furnace charges are completely melted, when the temperature of molten steel is more than or equal to 1580 ℃, deeply blowing oxygen by a single tube at low pressure, removing Si and Mn from slag, fully stirring, sampling, fully analyzing, tapping after the requirements of the steel types are met, and entering the next procedure;

LF refining:

carrying out the last process, deslagging the steel ladle in time after tapping, refining in an LF (ladle furnace), wherein the LF is put in under the conditions that the temperature is more than or equal to 1550 ℃, the slag thickness is less than or equal to 20mm, measuring the temperature, feeding an Al wire to a 100 m/furnace, adjusting the argon flow, sampling and analyzing after the reduction is completely white, controlling chemical components to meet the standard, and ensuring alloying, wherein [ S ] is]≤0.005％、[O]Less than or equal to 0.0020 percent, adjusting the total Al content to be within the range of 0.01 to 0.04 percent according to the sample return, then adding rare earth according to the addition amount of 0.075 kg/ton steel, and controlling SiO in the slag after LF refining is finished₂The content of (A) is less than or equal to 10 percent;

VD vacuum refining:

carrying out vacuum treatment from 1/2 to VD after the temperature of a ladle is more than or equal to 1560 ℃, evacuating to require that the ultimate vacuum degree is less than or equal to 67Pa, the retention time under the ultimate vacuum is more than or equal to 15min, blowing Ar at a large flow rate under the ultimate vacuum (the flow rate of blowing Ar is more than or equal to 120L/min), about 1-2 min before breaking, adjusting the flow rate of blowing Ar to 20-40L/min, immediately adding rare earth according to the addition amount of 0.075 kg/ton steel after breaking, inserting the rare earth by adopting a special inserted rod, and controlling the soft argon blowing time to be 30-50 min after breaking;

the VD is vacuum refined and then adopts a conventional pouring process, and preferably, the VD can be carried out according to the following operations:

before pouring, argon is introduced into the injection pipe for 3-5 min, Ar gas is used for protection pouring, a water gap and a pouring gate are accurately centered, the height between the water gap and the pouring gate cannot be too high, the height is controlled to be less than or equal to 100mm after visual inspection, and secondary pollution of molten steel is reduced. The height of the used middle pouring pipe is higher than that of the ingot mold by more than 300mm so as to ensure that enough static pressure is generated during molten steel pouring, the liquid level is required to rise stably during ingot body pouring, and the feeding of a cap opening is slow and sufficient.

The rare earth is added in the later stage of LF, and the rare earth is added after the vacuum refining is broken, because the deoxidation and desulfurization capabilities of the rare earth are strong, the rare earth is added in the later stage of LF, so that the molten steel can be deeply desulfurized and deoxidized in advance, and then the molten steel is subjected to the vacuum refining and breaking by VDThe rare earth is directly added, the condition in the molten steel is best, the content of O, S steel grade is low, and the yield of the rare earth is high. Specifically, after the rare earth is added, Al in molten steel is treated₂O₃Performing denaturation treatment on the MnS inclusion; secondly, further deoxidizing and desulfurizing the molten steel; thirdly, some residual rare earth is dissolved in the matrix in the steel grade in a solid way, the structure of the as-cast ledeburite is refined, harmful elements such as sulfur and phosphorus which are partially polymerized along the grain boundary are eliminated, the carbide is uniformly distributed, the crystal grains are refined, the structure is more uniform, and the mechanical property of the steel can be greatly improved.

Except the adding time and condition of rare earth, the rare earth content is low after LF refining is finished, the content of deoxidation, desulfurization and modified inclusion of the rare earth is not enough, the rare earth content is high, the rare earth content is excessive, and SiO (silicon dioxide) in reducing slag can be generated₂The rare earth tends to be continuously oxidized, and the yield of the rare earth is reduced; the rare earth content is low after the VD vacuum refining is broken, the residual rare earth content in steel is low, the beneficial effect of the rare earth is insufficient, the rare earth content is high, the content of residual rare earth inclusions in steel is increased, and the flaw detection and the performance of the finished steel are adversely affected.

In addition, the VD process of the invention adopts an insertion rod insertion adding mode, the yield of the rare earth is higher, the high yield of the rare earth indicates that the rare earth-containing inclusion produced by the rare earth in the steel is less, and both the residual content of the rare earth and the content of the rare earth inclusion in the steel play decisive factors for the performance of the rare earth steel.

The invention is further illustrated and described by the following examples