Non-magnetic steel ZYNM7 smelting and continuous casting production process

Abstract

The present application relates to a kind of non-magnetic steel ZYNM7 smelting and continuous casting production process, by optimizing pouring method on the basis of original mold casting production process, develop the process flow using IF induction furnace batching→IF induction furnace preliminary refining→AOD furnace smelting→LF refining homogenization purification treatment→CC vertical continuous casting pouring→air cooling, change pouring mode from mold casting to continuous casting pouring, shorten smelting time by optimizing material type ratio in process, ensure continuous casting billet quality by using special protective slag in continuous casting, process control two cooling zone parameters, superheat and constant speed, simultaneously solve the problem of mold casting electrode billet specification limited production scheduling difficulty, improve the production efficiency of non-magnetic product.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a smelting and continuous casting production process for non-magnetic steel ZYNM7. Background Technology

[0002] ZYNM7 steel is a non-magnetic steel used to manufacture high-strength non-magnetic drill collars and pressure-bearing drill pipes. It has very low magnetic permeability, high strength, hardness, and wear resistance, and has strict requirements for intergranular corrosion and both the A and E processes. Currently, the smelting of this steel grade suffers from problems such as long overall smelting time, low production efficiency, and difficulties in production scheduling due to the limitation on electrode billet specifications caused by the inability to perform alternating electroslag processes. These problems urgently need to be solved. Summary of the Invention

[0003] The purpose of this invention is to optimize the existing smelting and casting technology of non-magnetic steel ZYNM7, thereby designing and developing a smelting and continuous casting production process for non-magnetic steel ZYNM7 with high production efficiency and strong ingot shape selectivity.

[0004] The objective of this invention is achieved as follows:

[0005] A smelting and continuous casting process for non-magnetic steel ZYNM7 is characterized by the following steps: IF induction furnace batching → IF induction furnace primary smelting → AOD furnace smelting → LF refining, homogenization and purification treatment → CC vertical continuous casting → air cooling.

[0006] Step 1) The induction furnace feed includes 240-360 kg / t of Cr13 scrap or steel chips and 240-360 kg / t of Cr16 scrap or steel chips, 100-150 kg / t of high-carbon ferrochrome, 4-7 kg / t of ferromolybdenum, and 12-16 kg / t of nickel plate material. In the feed, the high-carbon ferrochrome P≤0.035%, Si≤4.0%, and scrap or steel chips P≤0.025% are controlled according to the mass percentage. After the induction furnace is cleaned, samples are taken at 1580-1620℃. When the temperature of the molten steel is 1620-1660℃, the steel is tapped into a clean ladle.

[0007] Step 2) The molten steel treated in Step 1) is sent to the AOD furnace for steelmaking. The temperature inside the AOD furnace is maintained at ≥1000℃ before steelmaking. 1000kg of lime is added to the furnace. After steelmaking, nitrogen is blown in, controlling the temperature at 1650~1680℃. 2000~4000kg of lime and 70~120kg / t of high-carbon ferrochrome are added in batches, with each batch ≤2000kg. The carbon content is ≤0.015%. Then, 20~25kg / t of ferrosilicon is added for pre-reduction. After the initial process, 220-240 kg / t of electrolytic manganese and 10-16 kg / t of aluminum blocks were added to the aluminum to raise the temperature. Argon was blown and stirred for 30 seconds, then nitrogen was blown and stirred. The Si content was controlled at 0.30%-0.50% by mass, and the temperature was 1640-1700℃. The slag was skimmed off, and 100-300 kg of lime with CaO ≥ 92% and 100-200 kg of fluorite were added by mass. The mixture was stirred with nitrogen until the temperature reached 1480-1550℃ before tapping the steel.

[0008] Step 3) The molten steel treated in Step 2) is hoisted back to the refining plant, stirred with nitrogen, and 0.5-1.5 kg / t of silicon-calcium powder is added in batches for continuous reduction and purification. After deep deoxidation by feeding 2-4 m / t of silicon-calcium wire, the steel is stirred weakly for ≥15 min at a temperature of 1460-1475℃ and then hoisted to the continuous casting plant.

[0009] Step 4) The molten steel treated in Step 3) is hoisted to the continuous casting station and injected into the tundish through a long nozzle. Argon protection is applied to the long nozzle, followed by argon purging inside the tundish, covering with a covering agent, and overall immersion nozzle protection during casting. ST-SP protective slag, specifically for non-magnetic steel continuous casting, is used. The slag's basicity R (CaO / SiO2) is controlled at 1.0±0.1, melting point temperature at 1146±50℃, and viscosity at 1300℃ at 5.74±1.00P. Moisture content is controlled to not exceed 0.5%. The casting speed is 0.35~0.40m / min, the molten steel superheat in the tundish is 25~45℃, the crystallizer electromagnetic stirring parameters are 500A, 2HZ, and the end electromagnetic stirring parameters are 400A, 2Hz. The secondary cooling zone water flow rate is 35, 46, and 36L / min in three zones. The casting process maintains a stable casting speed and molten steel level, resulting in a continuously cast billet.

[0010] Step 5) Stack the billets produced in Step 4) on a dry ground without venting air, and do not allow any metal objects to be placed underneath them. During air cooling, prevent venting air from blowing directly onto the continuous casting billets.

[0011] The positive effects of this invention are as follows:

[0012] 1. By optimizing the combination and matching ratio of furnace charge types, the first-pass yield of AOD components is improved, the smelting time is shortened, and the production efficiency is increased;

[0013] 2. After AOD, the steel is returned to LF for refining and homogenization purification. Before tapping, it is fed into a silicon-calcium wire for deep deoxidation to reduce the oxygen content of the molten steel and improve its purity.

[0014] 3. Vertical continuous casting uses low casting speed and special protective slag. The process is carried out through three-stage electromagnetic stirring to ensure the surface quality and internal composition uniformity of the continuously cast billet. At the same time, it solves the problem of limited specifications and production scheduling difficulties of in-mold electrode billets, and improves the production efficiency of non-magnetic products. Detailed Implementation

[0015] Example: A smelting and continuous casting process for non-magnetic steel ZYNM7. The smelting process flow is as follows: IF induction furnace charging → IF induction furnace primary smelting → AOD furnace smelting → LF refining, homogenization and purification treatment → CC vertical continuous casting → air cooling. To ensure the requirements of inclusions, performance, and continuous casting production, the smelting and continuous casting process includes the following steps:

[0016] Step 1) The batching consists of 240-360 kg / t Cr13 scrap (steel chips) and 240-360 kg / t Cr16 scrap (steel chips), 100-150 kg / t high-carbon ferrochrome, 4-7 kg / t ferromolybdenum, and 12-16 kg / t nickel plate material. The batching is controlled with high-carbon ferrochrome P≤0.035%, Si≤4.0%, and scrap (steel chips) P≤0.025%. After melting and cleaning in the induction furnace, samples are taken at 1580-1620℃. When the molten steel temperature is 1620-1660℃, the steel is tapped into a clean ladle.

[0017] Step 2) The molten steel treated in Step 1) is sent to the AOD furnace for steelmaking. The temperature inside the AOD furnace is maintained at ≥1000℃ before steelmaking. 1000kg of lime is added to the furnace. After steelmaking, nitrogen blowing is performed, and the temperature is controlled at 1650~1680℃. 2000~4000kg of lime and 70~120kg / t of high-carbon ferrochrome are added in batches, with each batch ≤2000kg. After the carbon content is ≤0.015%, 20~25kg of special ferrosilicon is added. / t pre-reduction, after the pre-reduction is completed, add 220-240 kg / t of electrolytic manganese metal and 10-16 kg / t of aluminum blocks to burn aluminum and raise the temperature. After stirring with argon for 30 seconds, switch to stirring with nitrogen. Control Si: 0.30%-0.50% and temperature 1640-1700℃. Remove slag and add 100-300 kg of lime with CaO≥92% and 100-200 kg of fluorite. Stir with nitrogen until the temperature reaches 1480-1550℃ and then tap the steel.

[0018] Step 3) The molten steel treated in Step 2) is hoisted back to the refining plant, stirred with nitrogen, and 0.5-1.5 kg / t of silicon-calcium powder is added in batches for continuous reduction and purification. After deep deoxidation by feeding 2-4 m / t of silicon-calcium wire, the steel is stirred weakly for ≥15 min at a temperature of 1460-1475℃ and then hoisted to the continuous casting plant.

[0019] Step 4) After the molten steel treated in Step 3) is hoisted to the continuous casting platform for temperature measurement, it is then placed on the ladle turret. The molten steel from the ladle is injected into the tundish through a long nozzle. Argon gas is used for protection between the upper and lower nozzles. An argon-blowing plug is used in the tundish, with the argon flow rate controlled at 3-5 L / min. A carbon-free covering agent is used in the tundish. After the last heat sampling, carbonized rice husks are added to reduce heat radiation loss from the molten steel and to protect it from secondary oxidation. During continuous casting, the superheat of the molten steel in the tundish is controlled at 25-45℃. The molten steel in the tundish is injected into the crystallizer through an integral submersible nozzle with an insertion depth of 100-150 mm. ST-SP, a special protective slag for non-magnetic steel continuous casting billets, is used and added evenly. The molten steel in the crystallizer is electromagnetically stirred by an external crystallizer electromagnetic stirrer with stirring parameters of 500A current and 2HZ. The crystallizer is cooled by a cold water source. The electromagnetic stirring of the molten steel in the crystallizer is used to form equiaxed crystals. The billet pulling machine operates at 0. The billet is drawn at a speed of 35–0.40 m / min, maintaining a constant speed. A three-roll clamp is used in the drawing machine to eliminate clamping stress. The billet travels perpendicular to the casting platform. The secondary cooling zone employs a three-stage spray system for intensive cooling, with the water flow rates controlled at 35, 46, and 36 L / min for each zone. At the upper part of the solidification end of the liquid phase cavity in the lower part of the secondary cooling chamber, an external electromagnetic stirrer is used to electromagnetically stir the molten steel, with a stirring current of 50 A. 12HZ, reducing segregation at half the radius of the billet; an external end electromagnetic stirrer at the bottom of the billet mill electromagnetically stirs the liquid core of the billet, with stirring parameters of 400A current and 4HZ, improving the quality of the billet core; the billet is cut into fixed-length billets vertically by a flame cutter synchronized with the billet pulling speed, tilted onto a horizontal roller conveyor, and then lifted onto the billet discharge roller conveyor by a steel hook machine; after discharge, the end face is cleaned and marked, and then sent to a sand pit for air cooling.

[0020] Step 5) Stack the billets produced in Step 4) on a dry ground without venting air, and do not allow any metal objects to be placed underneath them. During air cooling, prevent venting air from blowing directly onto the continuous casting billets.

Claims

1. A non-magnetic steel ZYNM7 smelting and continuous casting production process, characterized in that: The process flow is as follows: adopting IF induction furnace charging→IF induction furnace initial smelting→AOD furnace smelting→LF refining homogenizing purification treatment→CC vertical continuous casting steel pouring→air cooling, and the smelting and continuous casting process comprises the following steps: Step 1), the induction furnace charging comprises 240-360 kg / t Cr13 scrap or steel scrap, 240-360 kg / t Cr16 scrap or steel scrap, 100-150 kg / t high-carbon chromium iron, 4-7 kg / t molybdenum iron and 12-16 kg / t nickel plate material, wherein the high-carbon chromium iron is controlled to have P≤0.035%, Si≤4.0% according to the mass percentage, the scrap or steel scrap is controlled to have P≤0.025%, and the induction furnace is sampled at 1580-1620 ℃ after being cleaned, and the molten steel is poured into a cleaned ladle at 1620-1660 ℃; Step 2), the molten steel treated in step 1) is sent to the AOD furnace for steel mixing, the temperature in the AOD furnace is kept at ≥1000 ℃ before the steel mixing, 1000 kg of lime is added in the furnace, nitrogen blowing is carried out after the steel mixing, 2000-4000 kg of lime is added in batches at the temperature of 1650-1680 ℃, 70-120 kg / t of high-carbon chromium iron is added, each batch of addition is ≤2000 kg, 20-25 kg / t of ferrosilicon is added for pre-reduction after the carbon content is ≤0.015%, 220-240 kg / t of electrolytic manganese and 10-16 kg / t of aluminum block are added for burning aluminum to increase the temperature, argon stirring is changed to nitrogen stirring after 30 s of blowing argon, Si is controlled to be 0.30%-0.50% according to the mass percentage, the temperature is 1640-1700 ℃, slag is poured, 100-300 kg of lime with CaO≥92% and 100-200 kg of fluorite are added according to the mass percentage, and the molten steel is poured at the temperature of 1480-1550 ℃ under nitrogen stirring; Step 3), the molten steel treated in step 2) is hoisted back to the refining position, nitrogen stirring is carried out, and 0.5-1.5 kg / t of silicon calcium powder is added in batches for continuous reduction and purification treatment, 2-4 m / t of silicon calcium wire is fed for deep deoxidization, the weak stirring time is ≥15 min, and the ladle is hoisted to the continuous casting position at the temperature of 1460-1475 ℃; Step 4), the molten steel treated in step 3) is hoisted to the continuous casting position, is injected into the tundish through a long nozzle, is protected by long nozzle argon protection, tundish internal argon filling, covering agent covering and whole immersion type nozzle, uses ST-SP special protection slag for non-magnetic steel continuous casting, controls the basicity R (CaO / SiO2) of the protection slag to be 1.0±0.1, the melting point temperature of the protection slag is 1146±50 ℃, the viscosity at 1300 ℃ is 5.74±1.00 P, the water content is controlled to be not more than 0.5%, the casting speed is 0.35-0.40 m / min during the continuous casting process, the superheat degree of the molten steel in the tundish is 25-45 ℃, the electromagnetic stirring parameters of the crystallizer are 500 A, 2 Hz, the electromagnetic stirring parameters at the end are 400 A, 2 Hz, the water flow of the secondary cooling zone is 35, 46 and 36 L / min respectively, the casting speed and the molten steel surface are kept stable during the pouring process, and the continuous casting billet is obtained. Step 5) The cast slab produced in Step 4) is stacked on a dry floor without through-air and is not allowed to have a metal object under it, and the through-air is prevented from directly blowing on the continuous cast slab during air cooling.