A cored wire for nitrogen addition to molten steel and its preparation and use method

Abstract

The present invention belongs to the technical field of cored wires used in the steelmaking process, and in particular, relates to a cored wire for nitrogen enhancement of molten steel and a preparation and use method thereof. In the prior art, the core powder of the cored wire for nitrogen enhancement of molten steel is mostly nitrogen-containing alloys and has a high cost. In order to solve the above problems, the cored wire provided by the present invention uses nitrogen-containing organic matter urea, diphenylamine, and nitrogen-containing inorganic compounds lime nitrogen and boron nitride as core powders; the cored wire structure is iron sheet coated nitrogen-containing organic matter as the core wire, nitrogen-containing inorganic core powder layer is coated on the outer periphery of the core wire, and then the nitrogen-containing inorganic core powder layer is coated with the outer iron sheet layer. This structure allows lime nitrogen and boron nitride powders to contact and react with molten steel first, and urea and diphenylamine powders to react later, so as to alleviate the decomposition of urea and diphenylamine at high temperature, and also avoid the reaction of the two at high temperature after mixing, thereby reducing the loss of nitrogen elements. Feeding the cored wire into the molten steel in a back-and-forth swinging manner can reduce the segregation of elements inside the molten steel and improve the nitrogen enhancement effect.

Description

Technical Field

[0001] The invention belongs to the technical field of cored wires used in a steelmaking process, and in particular relates to a cored wire for nitrogen addition to molten steel and a preparation and use method thereof. Background Art

[0002] Nitrogen is generally considered a harmful element in steel, but previous studies have found that as long as the nitrogen mass fraction in steel is controlled to about 170 mg / kg, the mechanical properties of steel can be improved without affecting toughness. Due to its good mechanical properties and corrosion resistance, oxidation resistance, and wear resistance, high nitrogen steel is increasingly widely used in energy, chemical, petrochemical, transportation and other fields. Since the 1970s, the development of low-alloy high-strength steel in the world has entered a new era, and micro-alloyed steel varieties have emerged.

[0003] Compared with ordinary low alloy steel, microalloyed steel has improved mechanical properties and process performance, and can meet various special performance requirements. Nitrogen can combine with three microalloy elements, niobium, vanadium and titanium, in steel, and precipitate fine second phase particles during solidification and rolling to hinder dislocation movement, thus greatly improving the yield strength of steel under low niobium, vanadium and titanium conditions. Using nitrogen to strengthen steel is economical and environmentally friendly.

[0004] The ability of nitrogen to stabilize austenite is second only to carbon. In addition, nitrogen can also effectively expand the range of the austenite phase region in the phase diagram. As an austenite-forming element, it is a substitute for nickel. The strengthening effect of nitrogen on steel is much higher than other elements. In addition to being able to replace part of the metallic nickel, the role of nitrogen is mainly to improve the strength of austenitic steel without significantly affecting the plasticity and toughness of the steel. In addition, as an interstitial solid solution strengthening element, nitrogen has a stronger ability to improve the strength of steel than carbon and other alloying elements. At the same time, nitrogen can also effectively reduce the close-packed incomplete dislocations in austenite and limit the movement of splintered dislocations containing interstitial impurity atom groups.

[0005] According to the research results, microalloyed steel is an important type of steel, in which nitrogen plays a vital role. Nitrogen is a very beneficial and inexpensive alloying element, which can achieve fine grain strengthening and precipitation strengthening by forming carbonitrides. This alloying element can play an important role in vanadium-containing microalloyed steel and improve the performance of steel. From the existing technology, in the alloying technology of nitrogen microalloyed steel, more nitrogen is generally added to the steel to save the amount of microalloying elements, and the strength of the steel is improved by optimizing the design of alloy composition and improving the rolling process, so as to achieve the purpose of reducing alloy costs.

[0006] The Chinese patent with publication number CN107937662 A discloses a silicon nitride manganese titanium alloy cored wire, which is composed of a steel belt sheath and a core layer structure wrapped therein, wherein the core layer is silicon nitride manganese titanium powder with a particle size of less than 3 mm, and the mass percentage element composition of the silicon nitride manganese titanium alloy powder is: Mn≥75%, N≥5%, Si≤10%, C≤0.5%, P≤0.3%, S≤0.2%Ti≥5%, and the balance is iron. The silicon nitride manganese titanium alloy cored wire can be added to microalloyed steel to not only solve the problem of low recovery rate, but also save the use of ferrosilicon and ferromanganese. Chinese patent publication number CN114231696 A discloses a method for preparing an alloy cored wire, wherein the core layer is a mixture of vanadium-iron alloy, silicon ferronitride and microalloy. The cored wire can replace the relatively expensive vanadium-nitrogen alloy for steelmaking production. The V / N ratio can be adjusted according to the composition of the steel grade, and the nitrogen content can be increased as needed without affecting the vanadium content. The nitrogen recovery rate is high and stable.

[0007] In addition, the Chinese patent with publication number CN 112280934 A also discloses a cored wire containing vanadium and nitrogen and its application, wherein the core powder of the cored wire is made of nano-scale vanadium nitride powder, and the size of the vanadium nitride powder is less than 100 nm. The cored wire is used for microalloying of molten steel, and almost all vanadium elements in the steel exist in the form of precipitated particles, and the size of the precipitated particles is all less than 100 nm, the precipitation rate of vanadium element precipitated particles is ≥98%, and the proportion of precipitated particles with a size less than 100 nm is ≥99%. However, the core powder components of these cored wires all use nitrogen-containing alloys as the main raw materials to achieve the purpose of adding nitrogen to the molten steel, which results in a high production cost of the cored wire. Summary of the invention

[0008] In view of the above problems, the primary purpose of the present invention is to provide a core powder formula for a cored wire for nitrogen enrichment of molten steel, the second purpose of the present invention is to provide a structure of the cored wire, and the third purpose of the present invention is to provide a preparation method and a use method of the cored wire.

[0009] The cored wire for nitrogen enhancement of molten steel of the present invention comprises a core powder comprising nitrogen-containing organic matter and nitrogen-containing inorganic compound, wherein the nitrogen-containing organic matter comprises urea and diphenylamine, and the nitrogen-containing inorganic compound comprises lime nitrogen and boron nitride;

[0010] The mass proportions of the materials in the core powder are as follows: lime nitrogen (20-30) parts, diphenylamine (10-30) parts, urea (30-40) parts, and boron nitride (10-20) parts;

[0011] In order to speed up the reaction between the core powder and the molten steel after wire feeding, the above four materials are all powders, and the powder particle size can pass through a 150-mesh sieve to a 200-mesh sieve.

[0012] The cored wire for nitrogen enhancement of molten steel of the present invention is composed of a nitrogen-containing organic core wire, a nitrogen-containing inorganic core powder layer, and an outer iron sheet layer; the nitrogen-containing inorganic core powder layer covers the nitrogen-containing organic core wire, and the outer iron sheet layer covers the nitrogen-containing inorganic core powder layer; the nitrogen-containing organic core wire is composed of a core part and a core wire iron sheet layer covering the core part, and the core part is composed of nitrogen-containing organic powder;

[0013] The nitrogen-containing organic core wire comprises a urea core wire, the core of which comprises urea powder;

[0014] The nitrogen-containing organic core wire comprises a diphenylamine core wire, the core of which comprises diphenylamine powder;

[0015] The core mass of each nitrogen-containing organic core wire accounts for 10% to 20% of the total mass of the cored wire;

[0016] The cored wire contains a plurality of nitrogen-containing organic core wires;

[0017] The nitrogen-containing inorganic core powder layer comprises lime nitrogen powder and boron nitride powder.

[0018] By adding high-nitrogen organic matter urea and inorganic compound lime nitrogen to the cored wire instead of nitrogen-containing alloy as the core powder composition, not only can the nitrogen recovery rate be improved, but also the amount of nitrogen-containing alloy used during deoxidation alloying can be reduced, saving costs while also having a better use effect.

[0019] Furthermore, since urea and diphenylamine will decompose into ammonia at high temperature, and ammonia will decompose into nitrogen and hydrogen at high temperature, and lime nitrogen and boron nitride have low reactivity, urea powder and diphenylamine powder are first coated with iron sheets to form small-sized urea core wires and diphenylamine core wires respectively, and then the urea core wires and diphenylamine core wires are wrapped with mixed powders of lime nitrogen and boron nitride, so that the lime nitrogen and boron nitride powders are first contacted with the molten steel to react, and the urea and diphenylamine powders react later, so as to alleviate the decomposition of urea and diphenylamine at high temperature and affect the nitrogen-enhancing effect of the molten steel, and also avoid the reaction of the two at high temperature after mixing, further reduce the loss of nitrogen in urea and diphenylamine, and improve the nitrogen-enhancing effect.

[0020] Furthermore, in addition to its high nitrogen content, urea also has an oxygen content of about 27%. In addition to about 20% nitrogen, lime nitrogen also contains about 40% calcium and a small amount of sulfur. In addition to about 8% nitrogen, diphenylamine also contains about 86% carbon. The addition of compounds such as lime nitrogen and diphenylamine not only adds nitrogen to the molten steel, but also has the effects of deoxidation and desulfurization, which can effectively avoid the problem of excessive oxygen content in molten steel due to the high oxygen content in urea.

[0021] Furthermore, boron nitride can not only be used as a nitrogen-increasing agent, but also has good thermal conductivity, which can improve the fluidity of molten steel and reduce the impact of powders such as lime nitrogen, urea, and diphenylamine on the fluidity of molten steel.

[0022] The method for preparing the cored wire for nitrogen addition to molten steel of the present invention comprises the following contents:

[0023] Step 1: First, use iron sheets to coat urea powder and diphenylamine powder into small-diameter urea core wires and diphenylamine core wires respectively. Under unit length, the core mass of each core wire accounts for about 10% to 20% of the total mass of the core wire, which is convenient for controlling the amount of urea and diphenylamine added;

[0024] Step 2: Spread half of the lime nitrogen and boron nitride mixed powder on another iron sheet;

[0025] Step 3: placing the urea core wire and the diphenylamine core wire prepared in step 1 on the mixed powder in step 2;

[0026] Step 4: Lay the other half of the lime nitrogen and boron nitride mixed powder on the core wire of step 3 to bury it, and then encapsulate the lime nitrogen, boron nitride, diphenylamine core wire and urea core wire to obtain the cored wire of the present invention.

[0027] The above-mentioned preparation method includes the following specific contents: first, the iron sheet is spread flat on the cored wire machine, and then the core powder is spread on the iron sheet by the spreading device. The iron sheet moves forward along the conveying device below, and the sealing device at the end of the cored wire machine will automatically curl, wrap and seal the iron sheet covered with the core powder.

[0028] The present invention also provides a method for using the cored wire, which specifically includes the following contents: feeding the prepared cored wire into the molten steel in a ladle or a refining furnace in a back-and-forth swinging manner; controlling the wire feeding speed to be 1 m / s to 2 m / s; and using nitrogen instead of argon to perform bottom blowing on the ladle while feeding the wire.

[0029] When feeding the cored wire into the molten steel in the ladle through the wire feeder, the feeding method of swinging back and forth is adopted to make the elements in the molten steel evenly distributed, reduce element segregation, and further improve the nitrogen-increasing effect of the molten steel. This is because the nitrogen content of the core powder in the cored wire is high, and the saturated solubility of nitrogen in the molten steel is limited. Feeding all the cored wires in the same position is likely to cause the nitrogen content in this part to be saturated, thereby reducing the nitrogen-increasing effect. Therefore, when feeding the wire, an arm that swings up and down can be set at the feeding position of the wire feeder, and the cored wire is placed above the arm. The feeding position of the cored wire is adjusted by raising and lowering the height of the arm. When the swing arm is raised, the feeding position will become farther, and when the swing arm is lowered, the feeding position will become closer. Feeding the wire by swinging back and forth can make the alloy elements in the molten steel more evenly distributed, thereby reducing element segregation.

[0030] While feeding the wire, nitrogen can be used instead of argon to blow the bottom of the ladle, which can improve the fluidity of the slag on the surface of the ladle, effectively ensure the rapid feeding of the cored wire, and prevent the cored wire from getting stuck or broken. At the same time, it can better add nitrogen to the molten steel and promote the nitrogen micro-alloying reaction.

[0031] The steel liquid nitrogen-enhanced cored wire provided by the present invention directly reacts with the microalloying elements in the steel liquid after being fed into the steel liquid, and forms a large amount of molten precipitation phase in the steel liquid, which can play the role of precipitation strengthening and fine grain strengthening during subsequent rolling. The wire has wide applicability and can be applied to microalloyed steel varieties such as high-strength steel bars, steel sections, plates, special steels and cast steels, and has good promotion and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a structural schematic diagram of the cored wire for nitrogen addition to molten steel according to the present invention;

[0033] Among them, 1-outer iron sheet layer, 2-core iron sheet layer, 3-nitrogen-containing inorganic core powder layer, 4-nitrogen-containing organic powder core. DETAILED DESCRIPTION

[0034] The above contents of the present invention are further described in detail below through embodiments, but this should not be understood as limiting the scope of the above subject matter of the present invention. All technologies realized based on the above contents of the present invention belong to the protection scope of the present invention.

[0035] It should be noted that the lime nitrogen, diphenylamine, boron nitride and urea in the present invention are all powders. Before preparing the cored wire, it is necessary to use a crushing device to crush the above four raw materials respectively, and the crushed powders can pass through a 150-mesh sieve to a 200-mesh sieve. The structural schematic diagram of the cored wire for nitrogen enrichment of molten steel according to the present invention is as follows Figure 1 shown.

[0036] Example 1 The core powder of the cored wire for nitrogen enhancement of molten steel is composed of the following parts by mass: 25 parts of lime nitrogen powder, 30 parts of urea powder, 30 parts of diphenylamine powder, 10 parts of boron nitride powder; 5 parts of iron sheet (the total mass of the outer iron sheet layer and the core wire iron sheet layer).

[0037] The preparation method is as follows:

[0038] Step 1: First, use iron sheets to coat urea powder and diphenylamine powder into urea core wires and diphenylamine core wires of small diameters, respectively. Under unit length, the mass of urea powder and diphenylamine powder in each urea core wire and diphenylamine core wire accounts for 15% of the total mass of the coated core wires;

[0039] Step 2: Spread half of the lime nitrogen and boron nitride mixed powder evenly on another iron sheet;

[0040] Step 3: Place two urea core wires and two diphenylamine core wires on the mixed powder in step 2 respectively;

[0041] Step 4: Lay the other half of the lime nitrogen and boron nitride mixed powder on the core wire of step 3 to bury it, and then package the lime nitrogen and boron nitride mixed powder, diphenylamine wire and urea wire to obtain the core wire of the present invention.

[0042] Example 2 The core powder for nitrogen enhancement of molten steel is composed of the following parts by mass: 25 parts of lime nitrogen powder, 30 parts of urea powder, 20 parts of diphenylamine powder, 15 parts of boron nitride powder; and 10 parts of iron sheet.

[0043] In step 1, the mass of urea powder and diphenylamine powder in each urea core wire and diphenylamine core wire respectively accounts for 10% of the total mass of the cored wire. In step 3, 3 urea core wires and 2 diphenylamine core wires are used, and the rest of the method is the same as in Example 1.

[0044] Example 3 The core powder of the cored wire for nitrogen enhancement of molten steel is composed of the following parts by mass: 20 parts of lime nitrogen powder, 40 parts of urea powder, 20 parts of diphenylamine powder, 15 parts of boron nitride powder; and 5 parts of iron sheet.

[0045] In step 1, the mass of urea powder and diphenylamine powder in each urea core wire and diphenylamine core wire respectively accounts for 10% of the total mass of the cored wire. In step 3, 4 urea core wires and 2 diphenylamine core wires are used, and the rest of the method is the same as in Example 1.

[0046] Example 4 The core powder for nitrogen enhancement of molten steel is composed of the following parts by mass: 30 parts of lime nitrogen powder, 30 parts of urea powder, 10 parts of diphenylamine powder, 20 parts of boron nitride powder; and 10 parts of iron sheet.

[0047] In step 1, the mass of urea powder and diphenylamine powder in each urea core wire and diphenylamine core wire respectively accounts for 10% of the total mass of the cored wire. In step 3, 3 urea core wires and 1 diphenylamine core wire are used, and the rest of the method is the same as in Example 1.

[0048] Example 5 The core powder of the cored wire for nitrogen enhancement of molten steel is composed of the following parts by mass: 30 parts of lime nitrogen powder, 40 parts of urea powder, 10 parts of diphenylamine powder, 10 parts of boron nitride powder; and 10 parts of iron sheet.

[0049] In step 1, the urea powder in each urea core wire accounts for 20% of the total mass of the core wire, and the diphenylamine powder in each diphenylamine core wire accounts for 10% of the total mass of the core wire. In step 3, 2 urea core wires and 1 diphenylamine core wire are used, and the rest of the method is the same as in Example 1.

[0050] The above embodiments are merely illustrative of the basic principles of the present invention and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A cored wire for nitrogen addition to molten steel, characterized in that: The core powder of the cored wire includes nitrogen-containing organic matter and nitrogen-containing inorganic compound; The cored wire is composed of a nitrogen-containing organic core wire, a nitrogen-containing inorganic core powder layer, and an outer iron sheet layer; the nitrogen-containing inorganic core powder layer is composed of nitrogen-containing inorganic compound powder and covers the nitrogen-containing organic core wire, and the outer iron sheet layer covers the nitrogen-containing inorganic core powder layer; the nitrogen-containing organic core wire is composed of a core and a core wire iron sheet layer covering the core, and the core is composed of nitrogen-containing organic powder; The nitrogen-containing organic matter includes urea and diphenylamine, and the nitrogen-containing inorganic compound includes lime nitrogen and boron nitride.

2. The cored wire for nitrogen enrichment of molten steel according to claim 1, characterized in that: The mass proportions of the materials in the core powder are as follows: 20-30 parts of lime nitrogen, 10-30 parts of diphenylamine, 30-40 parts of urea, and 10-20 parts of boron nitride; the core powder is sieved through a 150-mesh sieve to a 200-mesh sieve.

3. The cored wire for nitrogen enrichment of molten steel according to claim 1 or 2, characterized in that: The nitrogen-containing organic core wire comprises a urea core wire, the core of which comprises urea powder.

4. The cored wire for nitrogen enrichment of molten steel according to claim 1 or 2, characterized in that: The nitrogen-containing organic core wire comprises a diphenylamine core wire, and the core portion of the core wire comprises diphenylamine powder.

5. The cored wire for nitrogen enrichment of molten steel according to claim 1 or 2, characterized in that: The mass of nitrogen-containing organic powder in each nitrogen-containing organic core wire accounts for 10% to 20% of the total mass of the core wire, and the core wire contains a plurality of nitrogen-containing organic core wires.

6. The cored wire for nitrogen enrichment of molten steel according to claim 1 or 2, characterized in that: The nitrogen-containing inorganic core powder layer comprises lime nitrogen powder and boron nitride powder.

7. The method for using the cored wire for nitrogenation of molten steel according to claim 1 or 2, characterized in that: The cored wire is fed into the molten steel in a forward and backward swinging manner; the wire feeding speed is 1m / s to 2m / s; and nitrogen is used to blow the bottom of the ladle while feeding the wire.

8. The method for preparing the cored wire according to claim 1, characterized in that: Includes the following: Step 1: First, use iron sheets to coat urea powder and diphenylamine powder into urea core wire and diphenylamine core wire respectively, and the mass of nitrogen-containing organic matter in each core wire accounts for 10% to 20% of the total mass of the core wire; Step 2: Spread half of the lime nitrogen and boron nitride mixed powder on another iron sheet; Step 3: placing the urea core wire and the diphenylamine core wire prepared in step 1 on the mixed powder in step 2; Step 4: Lay the other half of the lime nitrogen and boron nitride mixed powder on the core wire of step 3 to bury it, and then encapsulate the lime nitrogen, boron nitride, diphenylamine core wire and urea core wire to obtain the core wire for nitrogen enhancement of molten steel according to the present invention.

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