Treatment method of cast steel molten steel V-N, Ti-Nb-Y two-step complex inoculation

Abstract

A kind of cast steel liquid V-N, Ti-Nb-Y two-step compound inoculation treatment method, V-N inoculant and Nb-Ti-Y inoculant are prepared by FeV50, FeTi30, FeNb50, FeY60, FeSiN30 alloy, and are made into cored wire.After liquid deoxidation, V-N cored wire inoculant is inserted to carry out first inoculation, to create conditions for forming a large number of dispersed V(C,N) in liquid, and then Ti-Nb-Y cored wire inoculant is inserted to carry out second inoculation, using residual N in liquid, to form a large number of dispersed Ti(C,N) and Nb(C,N) in liquid, to provide a large number of nucleation core for δ-Fe phase precipitation, at the same time, to shorten the primary dendrite of δ-Fe phase, so as to achieve the purpose of refining δ-Fe phase and inhibiting austenite grain growth.The process is simple, easy to operate and realize, the effect of refining cast steel grain is obvious, and as-cast austenite grain is refined by 64-89%.

Description

Technical Field

[0001] This invention belongs to the field of refining the grain size of cast steel parts, and specifically relates to a two-step composite inoculation method of VN and Ti-Nb-Y in molten cast steel to achieve microstructure control of high-strength and tough cast steel parts. Background Technology

[0002] As modern equipment develops towards larger size, lighter weight, and higher reliability, the demand for high strength and toughness in cast steel components is increasing. This is especially true in strategic fields such as aerospace and deep-sea exploration, where the demand for strength and toughness directly targets technological high ground; the performance consistency requirements for large cross-sections in major energy and power equipment are extremely stringent; the trade-off between lightweighting and safety in transportation and engineering machinery is fierce; and high toughness is essential in marine engineering and extremely cold environments. Therefore, achieving a balance of strength and toughness in cast steel components has become a crucial development trend in cast steel component manufacturing.

[0003] In order to obtain high strength and toughness cast steel parts, people often use the following methods: (1) Alloying: improve strength and toughness by adding alloying elements such as nickel, chromium, and molybdenum; adopt multi-element micro-alloying method, add elements such as Nb, V, and Ce to low alloy steel, and use fine grain strengthening and nano-precipitation phase strengthening to improve strength without damaging or even improving toughness; (2) Inoculation treatment: for the problem of coarse structure that is prone to occur in thick cross sections, special rare earth composite refining inoculant is used, which has the effect of effectively improving the morphology of inclusions and eliminating coarse grains; (3) Adopting microstructure control technology: adopt multi-phase composite microstructure such as austenite, bainite, and martensite, and use the TRIP / TWIP effect to dynamically strengthen the material; (4) Improve purity and density: strictly control the content of impurities such as P and S. Traditional electric arc furnace smelting can no longer meet the high-end demand, and the industry is popularizing the "smelting + ladle refining" process. (5) Improve density: Predict the location of shrinkage cavities and porosity through digital simulation (CAE), and design a gating system that can establish a positive temperature gradient field to ensure "sequential solidification". Use an intelligent gating system. For castings of hundreds of tons, the technology has been developed into a double ladle and double gate bottom pouring design. Combined with honeycomb ceramic filtration and 3-minute ultra-fast filling, turbulence and slag inclusions can be completely avoided. Use "hot rolling" technology. After the casting solidifies, use large-diameter rolls to perform deep micro-compression on hot nodes such as rounded corners (e.g., compression amount of 3mm, influence depth of 20mm). The micro-shrinkage cavities are "welded" by hydrostatic pressure stress, so that the fatigue strength of the cast steel is close to that of forgings. Apply an electromagnetic field during the solidification process of the billet to precisely control the flow of molten steel, effectively solve the segregation problem in the center of large steel ingots, and achieve fine grain homogenization.

[0004] Good progress has been made in the above five aspects. However, there is relatively little research on the inoculation treatment of molten steel for cast steel, the application is not widespread, and the effect is not stable. Summary of the Invention

[0005] This invention aims to solve the problem of coarse and uneven grains in cast steel parts by providing a two-step composite inoculation treatment method of VN and Ti-Nb-Y in molten cast steel. The method is simple, easy to operate and implement, and has a significant effect on refining the grains of cast steel parts.

[0006] To achieve the objectives of this invention, the technical solution adopted is: A two-step composite inoculation method for cast steel molten steel using VN and Ti-Nb-Y processes, the specific steps of which are as follows: (1) Preparation of VN inoculant Using FeV50 alloy powder and FeSiN30 alloy powder as raw materials, a VN inoculant with a FeV50 mass content of 70% and a FeSiN30 mass content of 30% was prepared; the prepared VN inoculant was then used to make VN inoculant cored wire. (2) Preparation of Nb-Ti-Y inoculant Using FeNb50 alloy powder, FeTi30 alloy powder, and FeY60 alloy powder as raw materials, an Nb-Ti-Y inoculant with a FeNb50 mass content of 50%, a FeTi30 mass content of 30%, and a FeY60 mass content of 20% was prepared; the prepared Nb-Ti-Y inoculant was then used to make Nb-Ti-Y inoculant cored wire. (3) After the steel is deoxidized, the VN cored wire inoculant obtained in step (1) is first inserted into the steel for primary inoculation, and then the Ti-Nb-Y cored wire inoculant is inserted into the steel for secondary inoculation, and then the steel is tapped.

[0007] Furthermore, the time interval between the first and second pregnancies is 2 minutes.

[0008] Furthermore, the processing method refines the as-cast austenite grains by 64-89%.

[0009] Furthermore, before tapping the steel, pure aluminum is inserted to perform a second final deoxidation of the aluminum.

[0010] Furthermore, the particle size of the FeV50 alloy powder, FeSiN30 alloy powder, FeNb50 alloy powder, FeTi30 alloy powder, and FeY60 alloy powder is -200 mesh.

[0011] Furthermore, the diameter of the VN inoculant cored wire is 10 mm.

[0012] Furthermore, the diameter of the Nb-Ti-Y inoculant cored wire is 10 mm.

[0013] This invention relates to the formulation of a VN inoculant (70%) using FeV50, FeTi30, FeNb50, FeY60, and FeSiN30 alloy powder with a particle size of -200 mesh as raw materials. w FeV50 -30% w FeSiN30 ) and Nb-Ti-Y probiotic (50%) w FeNb50 -30% w FeTi30 -20% w FeY60 The prepared inoculant is used to make cored wire with a diameter of 10 mm. After deoxidation of the molten steel, the VN cored wire inoculant is first inserted into the molten steel for primary inoculation, and then the Ti-Nb-Y cored wire inoculant is inserted into the molten steel for secondary inoculation. The beneficial effects are: (1) V, Ti and Nb in the inoculant form a large number of dispersed V(C,N), Ti(C,N) and Nb(C,N) in the molten steel, which serve as non-spontaneous nucleation nuclei when the δ-Fe phase precipitates, thereby refining the δ-Fe phase; Y shortens the primary dendrite length of the δ-Fe phase, reduces the dendrite spacing, and purifies the grain boundaries.

[0014] (2) After deoxidation of molten steel, VN cored wire inoculant is first inserted into molten steel for primary inoculation, creating conditions for the formation of a large amount of dispersed V(C,N) in molten steel. Then, Ti-Nb-Y cored wire inoculant is inserted into molten steel for secondary inoculation. The residual N in molten steel is used to form a large amount of dispersed Ti(C,N) and Nb(C,N) in molten steel, which increases the number of nucleation cores for the precipitation of δ-Fe phase, thereby achieving the purpose of refining δ-Fe phase and inhibiting the growth of austenite grains.

[0015] (3) The process is simple, easy to operate and easy to implement. It has a significant effect on refining the grain size of cast steel parts, and the as-cast austenite grain size is refined by 64-89%. Detailed Implementation

[0016] Example 1 Using FeV50, FeTi30, FeNb50, FeY60, and FeSiN30 alloy powders with a particle size of -200 mesh as raw materials, specifically FeV50 and FeSiN30 alloy powders with a particle size of -200 mesh, a VN inoculant (70%) was formulated with a FeV50 mass content of 70% and a FeSiN30 mass content of 30%. w FeV50 -30% w FeSiN30Using FeNb50, FeTi30, and FeY60 alloy powders with a particle size of -200 mesh as raw materials, an Nb-Ti-Y inoculant (50%) was prepared, comprising 50% FeNb50, 30% FeTi30, and 20% FeY60 by mass. w FeNb50 -30% w FeTi30 -20% w FeY60 The prepared VN inoculant and Nb-Ti-Y inoculant were used to make cored wires with a diameter of 10 mm. For ZG35, after pre-deoxidation of ferrosilicon and ferromanganese and adjustment of composition, pure aluminum was inserted for the first final deoxidation. When the N in the molten steel was less than 80 ppm, 0.2% of VN cored wire inoculant (by mass of the molten steel) was first inserted for the first inoculation. Two minutes later, 0.2% of Ti-Nb-Y cored wire inoculant (by mass of the molten steel) was inserted for the second inoculation. Pure aluminum was then inserted for the second final deoxidation of the aluminum, and the steel was tapped. When a sample with a wall thickness of 60 mm was prepared, the as-cast austenite grains were refined from 126-179 μm (without VN cored wire inoculant or Ti-Nb-Y cored wire inoculant, and other parallel tests as in Example 1) to 34-43 μm, a refinement of 66-81%.

[0017] Example 2 A VN inoculant (70%) was prepared using FeV50, FeTi30, FeNb50, FeY60, and FeSiN30 alloy powders with a particle size of -200 mesh as raw materials. w FeV50 -30% w FeSiN30 ) and Nb-Ti-Y probiotic (50%) w FeNb50 -30% w FeTi30 -20% w FeY60 The prepared VN inoculant and Nb-Ti-Y inoculant were respectively made into VN cored wire inoculant and Nb-Ti-Y cored wire inoculant with a diameter of 10 mm; For ZG35, after pre-deoxidation and composition adjustment of ferrosilicon and ferromanganese steel, pure aluminum was inserted for the first final deoxidation. When the N in the molten steel was >80 ppm, 0.2% of VN cored wire inoculant (by mass of the molten steel) was first inserted into the molten steel for the first inoculation. Two minutes later, 0.1% of Ti-Nb-Y cored wire inoculant (by mass of the molten steel) was inserted into the molten steel for the second inoculation. Pure aluminum was then inserted for the second final deoxidation of the aluminum, and the steel was tapped. When a sample with a wall thickness of 30 mm was made, the as-cast austenite grains were refined from 84-153 μm (without VN cored wire inoculant or Ti-Nb-Y cored wire inoculant, and other aspects were the same as in parallel tests of Example 2) to 16-22 μm, a refinement of 64-89%.

[0018] Example 3 A VN inoculant (70%) was prepared using FeV50, FeTi30, FeNb50, FeY60, and FeSiN30 alloy powders with a particle size of -200 mesh as raw materials. w FeV50 -30% w FeSiN30 ) and Nb-Ti-Y probiotic (50%) w FeNb50 -30% w FeTi30 -20% w FeY60 The prepared VN inoculant and Nb-Ti-Y inoculant were respectively made into VN cored wire inoculant and Nb-Ti-Y cored wire inoculant with a diameter of 10 mm; For ZG35, after pre-deoxidation and composition adjustment of ferrosilicon and ferromanganese steel, pure aluminum was inserted for the first final deoxidation. When the N content of the molten steel was less than 80 ppm, 0.4% of VN cored wire inoculant (by mass of the molten steel) was first inserted into the molten steel for a first inoculation. Two minutes later, 0.4% of Ti-Nb-Y cored wire inoculant (by mass of the molten steel) was inserted into the molten steel for a second inoculation, and then the steel was tapped. When a sample with a wall thickness of 150 mm was produced, the as-cast austenite grains were refined from 256-341 μm (without VN cored wire inoculant or Ti-Nb-Y cored wire inoculant, and other aspects were the same as in parallel tests of Example 3) to 58-82 μm, a refinement of 69-83%.

[0019] Example 4 A VN inoculant (70%) was prepared using FeV50, FeTi30, FeNb50, FeY60, and FeSiN30 alloy powders with a particle size of -200 mesh as raw materials. w FeV50 -30% w FeSiN30 ) and Nb-Ti-Y probiotic (50%) w FeNb50 -30%w FeTi30 -20% w FeY60 The prepared VN inoculant and Nb-Ti-Y inoculant were respectively made into VN cored wire inoculant and Nb-Ti-Y cored wire inoculant with a diameter of 10 mm; For ZG35, after pre-deoxidation and composition adjustment of ferrosilicon and ferromanganese steel, pure aluminum was inserted for the first final deoxidation. When the N content of the molten steel was greater than 80 ppm, 0.4% of VN cored wire inoculant (by mass of the molten steel) was first inserted into the molten steel for a first inoculation. One minute later, 0.3% of Ti-Nb-Y cored wire inoculant (by mass of the molten steel) was inserted into the molten steel for a second inoculation, and then the steel was tapped. When a sample with a wall thickness of 100 mm was produced, the as-cast austenite grains were refined from 188-261 μm (without VN cored wire inoculant or Ti-Nb-Y cored wire inoculant, and other aspects were the same as in parallel experiments of Example 4) to 51-68 μm, a refinement of 64-81%.

[0020] Example 5 A VN inoculant (70%) was prepared using FeV50, FeTi30, FeNb50, FeY60, and FeSiN30 alloy powders with a particle size of -200 mesh as raw materials. w FeV50 -30% w FeSiN30 ) and Nb-Ti-Y probiotic (50%) w FeNb50 -30% w FeTi30 -20% w FeY60 The prepared VN inoculant and Nb-Ti-Y inoculant were respectively made into VN cored wire inoculant and Nb-Ti-Y cored wire inoculant with a diameter of 10 mm; For ZG35MnSiCr, after pre-deoxidation and composition adjustment of ferrosilicon and ferromanganese steel and alloying, pure aluminum was inserted for the first final deoxidation. When the N in the molten steel was less than 80 ppm, 0.4% of VN cored wire inoculant (by mass of the molten steel) was first inserted into the molten steel for the first inoculation. Two minutes later, 0.4% of Ti-Nb-Y cored wire inoculant (by mass of the molten steel) was inserted into the molten steel for the second inoculation. Pure aluminum was then inserted for the second final deoxidation of the aluminum, and the steel was tapped. When a sample with a wall thickness of 100 mm was produced, the as-cast austenite grains were refined from 179-253 μm (without VN cored wire inoculant or Ti-Nb-Y cored wire inoculant, and other parallel tests as in Example 5) to 47-62 μm, a refinement of 65-81%.

[0021] Example 6 A VN inoculant (70%) was prepared using FeV50, FeTi30, FeNb50, FeY60, and FeSiN30 alloy powders with a particle size of -200 mesh as raw materials. w FeV50 -30% w FeSiN30 ) and Nb-Ti-Y probiotic (50%) w FeNb50 -30% w FeTi30 -20% w FeY60 The prepared VN inoculant and Nb-Ti-Y inoculant were respectively made into VN cored wire inoculant and Nb-Ti-Y cored wire inoculant with a diameter of 10 mm; For ZG35MnSiCr, after pre-deoxidation and composition adjustment of ferrosilicon and ferromanganese steel and alloying, pure aluminum was inserted for the first final deoxidation. When the N in the molten steel was >80ppm, 0.4% of VN cored wire inoculant (by mass of the molten steel) was first inserted into the molten steel for the first inoculation. Two minutes later, 0.3% of Ti-Nb-Y cored wire inoculant (by mass of the molten steel) was inserted into the molten steel for the second inoculation. Pure aluminum was then inserted for the second final deoxidation of the aluminum, and the steel was tapped. When a 60mm thick sample was made, the as-cast austenite grains were refined from 118-170μm (without VN cored wire inoculant or Ti-Nb-Y cored wire inoculant, and other aspects were the same as in the parallel test of Example 6) to 31-41μm, a refinement of 65-82%.

[0022] Example 7 A VN inoculant (70%) was prepared using FeV50, FeTi30, FeNb50, FeY60, and FeSiN30 alloy powders with a particle size of -200 mesh as raw materials. w FeV50 -30% w FeSiN30 ) and Nb-Ti-Y probiotic (50%) w FeNb50 -30% w FeTi30 -20% w FeY60 The prepared VN inoculant and Nb-Ti-Y inoculant were respectively made into VN cored wire inoculant and Nb-Ti-Y cored wire inoculant with a diameter of 10 mm; For ZG35MnSiCr, after pre-deoxidation and composition adjustment of ferrosilicon and ferromanganese steel and alloying, pure aluminum was inserted for the first final deoxidation. When the N in the molten steel was <80ppm, 0.6% of VN cored wire inoculant (by mass of the molten steel) was first inserted into the molten steel for a first inoculation. Two minutes later, 0.6% of Ti-Nb-Y cored wire inoculant (by mass of the molten steel) was inserted into the molten steel for a second inoculation, and then the steel was tapped. When a sample with a wall thickness of 150 mm was produced, the as-cast austenite grains were refined from 249-329 μm (without VN cored wire inoculant or Ti-Nb-Y cored wire inoculant, and other aspects were the same as in parallel tests of Example 7) to 51-71 μm, a refinement of 72-85%.

[0023] Example 8 A VN inoculant (70%) was prepared using FeV50, FeTi30, FeNb50, FeY60, and FeSiN30 alloy powders with a particle size of -200 mesh as raw materials. w FeV50 -30% w FeSiN30 ) and Nb-Ti-Y probiotic (50%) w FeNb50 -30% w FeTi30 -20% w FeY60 The prepared VN inoculant and Nb-Ti-Y inoculant were respectively made into VN cored wire inoculant and Nb-Ti-Y cored wire inoculant with a diameter of 10 mm; For ZG35MnSiCr, after pre-deoxidation and composition adjustment of ferrosilicon and ferromanganese steel and alloying, pure aluminum was inserted for the first final deoxidation. When the N in the molten steel was >80ppm, 0.6% of VN cored wire inoculant (by mass of the molten steel) was first inserted into the molten steel for a first inoculation. Two minutes later, 0.5% of Ti-Nb-Y cored wire inoculant (by mass of the molten steel) was inserted into the molten steel for a second inoculation, and then the steel was tapped. When a sample with a wall thickness of 100 mm was made, the as-cast austenite grains were refined from 179-253 μm (without VN cored wire inoculant or Ti-Nb-Y cored wire inoculant, and other aspects were the same as in parallel tests of Example 8) to 44-61 μm, a refinement of 66-83%.

Claims

1. A method for two-step composite inoculation of VN and Ti-Nb-Y in molten cast steel, characterized by: The specific steps are as follows: (1) Preparation of VN inoculant Using FeV50 alloy powder and FeSiN30 alloy powder as raw materials, a VN inoculant with a FeV50 mass content of 70% and a FeSiN30 mass content of 30% was prepared; the prepared VN inoculant was then used to make VN inoculant cored wire. (2) Preparation of Nb-Ti-Y inoculant Using FeNb50 alloy powder, FeTi30 alloy powder, and FeY60 alloy powder as raw materials, an Nb-Ti-Y inoculant with a FeNb50 mass content of 50%, a FeTi30 mass content of 30%, and a FeY60 mass content of 20% was prepared; the prepared Nb-Ti-Y inoculant was then used to make Nb-Ti-Y inoculant cored wire. (3) After the steel is deoxidized, the VN cored wire inoculant obtained in step (1) is first inserted into the steel for primary inoculation, and then the Ti-Nb-Y cored wire inoculant is inserted into the steel for secondary inoculation, and then the steel is tapped.

2. The treatment method for two-step composite inoculation of VN and Ti-Nb-Y in molten cast steel according to claim 1, characterized in that: The treatment method refines the as-cast austenite grains by 64-89%.

3. The method for two-step composite inoculation of VN and Ti-Nb-Y in molten cast steel according to claim 1, characterized in that: The time interval between the first and second pregnancies is 2 minutes.

4. The treatment method for two-step composite inoculation of cast steel molten steel with VN and Ti-Nb-Y as described in claim 1, characterized in that: The particle size of the FeV50 alloy powder, FeSiN30 alloy powder, FeNb50 alloy powder, FeTi30 alloy powder, and FeY60 alloy powder is -200 mesh.

5. The treatment method for two-step composite inoculation of VN and Ti-Nb-Y in molten cast steel according to claim 1, characterized in that: The diameter of the VN inoculant cored wire is 10 mm.

6. The treatment method for two-step composite inoculation of VN and Ti-Nb-Y in molten cast steel according to claim 1, characterized in that: The diameter of the Nb-Ti-Y inoculant cored wire is 10 mm.