WO2011140823A1

WO2011140823A1 - Smelting method for medium carbon steel j55

Info

Publication number: WO2011140823A1
Application number: PCT/CN2011/000748
Authority: WO
Inventors: 宋维兆; 王新成; 吾塔; 陈勇; 张建新; 孙学刚
Original assignee: Song Weizhao; Wang Xincheng; Wu Ta; Chen Yong; Zhang Jianxin; Sun Xuegang
Priority date: 2010-05-11
Filing date: 2011-04-27
Publication date: 2011-11-17
Also published as: CN102010925A

Abstract

A method for smelting medium carbon steel J55 comprises the following steps: pre-treating molten iron, smelting in a converter, refining in a ladle furnace (LF), continuous casting to obtain slab, cleaning and reheating the slab, rolling and cooling the slab and examining the end product. In the smelting step, reblowing is forbidden, tapping temperature of the converter is 1620-1670℃, and the content of [C], [P] and [N] during tapping is 0.09％, lower than 0.008％ and lower than 0.002％ respectively. In the refining step, Al-Ca is added as a refining agent by 2.5kg/ton•steel, and Ar₂ is blown into from the bottom of the ladle to provide weak agitation for 15-20min. The content of [N] and the non-metallic impurities of A-type and B-type in the molten steel after refinement is respectively lower than 0.004％ and 1.0 grade, and the content of Al₂O₃in the refining slag is 29-31％. In the continuous casting step, the continuous casting temperature is controlled at 1528～1542℃, and the casting is protected by sealing the extended nozzle of the ladle with Ar₂ and sealing ring. The increment of [N] in the molten steel is lower than 0.001% during continuous casting. The steel with the contents of [S] and [N] respectively being lower than 0.003％ and 0.005％ is thus obtained.

Description

- a medium carbon J55 steel smelting method

Technical field

The invention relates to the smelting of medium carbon J55 steel, which is especially suitable for the manufacture of new medium carbon J55 steel. Background technique

In recent years, with the continuous exploration and exploitation of oil fields, the demand for oil casings has increased year by year. Compared with commercially available petroleum ERW pipes with the same specifications and performance, the price of welded pipes will be about 20% cheaper. Therefore, more and more straight seam welded pipe units need to be hot rolled steel coil raw materials have become a real need. According to the statistics of ERW welded pipe units under construction and construction in China, the demand for hot-rolled raw materials for welded pipes is more than 400,000 tons per year. Domestic Baosteel and Wuhan Iron and Steel are both in production and supply, but they still cannot meet the demand. In the past, in the API 5CT standard, the J55 steel grade has only performance requirements and no composition requirements. Although the J55 performance requirements specified in the enterprise standard are the same as those of the API 5CT, the design principle is low carbon (the carbon in the steel is less than 0.0012%). Microalloyed steel. At present, the low-carbon microalloy J55 steel is commercially available. First, the inherent quality of the steel is unstable, and the band structure is serious. A and B non-metallic inclusions appear during the flaw detection of the steel pipe, and Nb and Ti are often enriched in the vicinity of the A-type inclusion. (C, N) compound, which affects the impact toughness of steel; second, it is not conducive to the threading of the pipe end thread.

The invention relates to a smelting method of a novel medium carbon J55 steel, which adopts the nitrogen absorption of the molten steel in the production process, reduces the enrichment of the slab TiN and the formation of Nb, Ti (C _x , N _y ), and adopts AL- in the LF furnace refining. The control of key technical steps such as the treatment of Ca refining agent, and then controlled rolling and controlled cold-pressing, to obtain medium carbon J55 steel coil, not only has the high strength and good impact toughness unique to J55 steel, but also the steel pipe is beneficial to the tube. The thread of the end thread is laid out. Summary of the invention

The object of the invention is: the new medium carbon J55 steel provided, adopting medium carbon, low manganese, and adding a small amount of Nb, Ti microalloying elements, the design scheme is scientific and reasonable, the smelting method is simple and easy, and the cost is increased and the cost is increased. The quality is very significant.

The object of the present invention is to achieve a new medium carbon J55 steel smelting method, including hot metal pretreatment ~ converter blowing → LF refining → slab continuous casting → slab cleaning → slab reheating - controlled rolling Process flow with cooling→finished product inspection; especially for the control of nitrogen removal in non-metallic inclusions in steel and the key technical steps for steel segregation control;

The removal of non-metallic inclusions and the control of nitrogen elements:

1 002%; The content of the [N] is less than 0. 002%;

2 至 0. 6Nm ³ /t The strength of the oxygen is 0. 8 ~ 0. 85MPa, the flow rate is 32000 ~ 33000m ³ / h, the strength is 0. 4 ~ 0. 6Nm ³ /t In, oxygen blowing time l1⁄2in; The bottom blowing argon stirring gas supply intensity is 0. 05 ~ 0. 08Nm ³ oct. min, the pressure is 1. 0 ~ 1. 2Mpa; the converter tapping temperature is 1620-1670 °C, at this time the [C] content is 0. 09%, [P] content is less than 0. 008%;

3 LF refining and slagging, desulfurization, need to add AL-Ca refining agent, and then the bottom of the ladle is weakly stirred by argon, the control time is 15-20 minutes; the content of refining final slag A1 ₂ 0 ₃ is 29 ~ 31%; 0级; The metal [A] content of less than 0. 004%, A, 8 metal inclusions in the steel is less than 1. 0;

4 Continuous casting protection casting, the long water inlet of the large bag is protected by a seal 圏 + argon seal; the increase of molten steel [N] during continuous casting is less than 0. 001%.

Among them, steel segregation control:

The sulphide segregation and the Nb (C _x , N _y ) formation, the steel [S] content is less than 0. 0030%, [N] content is less than 0. 0050%;

2 In order to prevent segregation of the slab, the temperature of the continuous casting tundish can be controlled at 1528 ~ 1542 °C.

The smelting method of the medium carbon J55 steel, the amount of the AL-Ca refining agent is 2. 5 kg / ton of steel; wherein the content of the metal aluminum powder is 35-38%, the content of the silicon powder is 10%, A1 ₂ 0 The content of ₃ is 50%, the content of the binder is 5%, and the binder is light burnt dolomite.

In the smelting method of the medium carbon J55 steel, the continuous casting sealing ring is made of fiber shield aluminum silicate cotton, and the sealing is made of high temperature binder, and the binder is refractory clay.

In the smelting method of the medium carbon J55 steel, the tensile strength of the finished steel is greater than 520 Mpa, the yield strength is 420 ~ 530 MPa, the impact energy at - 10 °C is greater than 30 J, and the hardness is less than 170 HV10.

In the smelting method of the medium carbon J55 steel, when the hot-rolled steel coil is used in longitudinal section, the steel tube degradation rate is controlled to be less than 0.05%, which is the best index of similar products in China.

The smelting method of the medium carbon J 55 steel and the material selection for smelting are all commercially available products.

The method of the invention adopts medium carbon, low manganese, and adds a small amount of Nb, Ti microalloying element strengthening component design to ensure the cold workability of the steel under the premise of ensuring the strength and toughness of the steel, and is beneficial to the end thread processing of the steel pipe. The affinity of N and Ti in steel is greater than that of Nb, and the addition of Ti reduces the formation of Nb (C _x , N _y ). Ti, which increases the strength of TiN, improves the toughness of steel. At the same time, it is beneficial to improve the surface quality of continuous casting slab; control the production process of molten steel to reduce nitrogen content, reduce the enrichment of slab TiN, LF furnace refining adopts AL-Ca treatment to spheroidize A1 ₂ 0 ₃ inclusions to improve steel Resilience and so on are unique.

The method of the invention is fully embodied:

The first is to add AL-Ca refining agent to LF refining, which makes it deeply deoxidize, increases the yield of calcium, increases the collision probability of A1 ₂ 0 ₃ and CaO, and improves the low melting point of VIII ₂ 0 ₃ and CaO. The kinetic conditions of the formation and growth of the composite inclusions increase the spheroidization removal effect and the modification effect of the A1 ₂ 0 ₃ inclusions (the brittle inclusions of small size are plastic inclusions). The second is to add AL-Ca refining agent after the tapping of the converter, so that the ratio of LF refining slag has strong adsorption and removal ability to the non-metallic inclusions in the molten steel, and the weakening of the argon blowing at the bottom of the ladle is added to make the steel people , Class B non-metallic inclusions are removed or the content level is reduced.

The third is to carry out calcium treatment on the small and difficult to float AL ₂ 0 ₃ inclusions, which can purify the molten steel to improve the toughness of the steel.

Ming's medium carbon steel J55 steel smelting composition control range has reached the performance design requirements, see Table 1.

Note: The impact test conditions, the direction is transverse, the notch is the Xia V type, the standard GB/T229-2007 "Metal Charpy Impact Test Method" is implemented, and the temperature is - 10 °C.

The above table description: The composition design must ensure the strength, toughness, hardness and end of the steel to facilitate the processing of the wire, and ensure the quality of the slab, avoid surface quality defects in the steel bead and reduce the inherent band structure of the steel.

The method is scientific and reasonable. Strictly grasp the important smelting methods and steps of steel segregation and inclusion control when smelting J55 steel, and obtain the new medium carbon steel J55, which meets the requirements of original design performance and demonstrates technological progress. detailed description

Example

The process route is: hot metal pretreatment → converter blowing - LF refining (low sulfur, low bismuth, micro titanium, calcium treatment) - slab continuous casting → slab cleaning → slab reheating → controlled rolling cooling - finished product sampling inspection Ex-factory; the purpose is to reduce or eliminate the transverse crack of the slab corner by controlling the molten steel nitrogen content in the production process.

Among them, the removal of non-metallic inclusions in steel and the control of nitrogen elements:

(002) The content of the molten iron [N] is less than 0. 002%;

(2) The control parameters of the converter smelting are as follows: the amount of the molten iron is 120 tons, the oxygen supply pressure is 0. 8 - 0. 85MPa, the oxygen flow rate is 32000m7h, and the gas supply intensity before and after the smelting of the molten steel is 0. 6NmV t. Oxygen time 14min; bottom blowing argon stirring gas supply intensity adjustment range is 0. 08NmV t. min, working pressure is L 2Mpa, Ensure that the converter has a pass rate of 100%. Due to the re-blowing, it is easy to cause the molten steel to increase nitrogen. At this time, due to the post-mixing period, the slag level is low, the molten steel surface is blown open again, causing the molten steel to increase nitrogen, and once again, the nitrogen can be increased by more than 7 ppm, and then blown twice. Nitrogen increase of 20PPm), thereby increasing the nitrogen content of the steel in the steel; strengthening the maintenance of the taphole, the tapping of the steel tapping during tapping, preventing the molten steel from spreading; the tapping of the converter increases the temperature of the molten steel, and the tapping temperature of the converter is controlled at 1620 °C 008%。 The content of the converter [C] is controlled at 0. 09%, [P] content <0. 008%.

(3) LF slagging, desulfurization to remove inclusions

5公斤/吨钢。 After the converter, the amount of 2. 5kg / ton of steel. The main components of AL-Ca refining agent: aluminum powder 35%, silicon calcium powder 10%, Α1 ₂ Ο ₃ 50%, added 5% binder (light burnt dolomite) cold consolidation. The ratio of LF refining slag has a strong adsorption capacity for non-metallic inclusions in the molten steel. After the LF is energized, the argon gas is blown into the bottom of the ladle to weakly stir, and the acceleration of the inclusion collision is increased and floated. 0级。 The A and B non-metallic inclusions in the steel is less than 1. 0. Calcium treatment is applied to the fine and difficult-to-float AL ₂ 0 ₃ inclusions to further purify the molten steel to improve the toughness of the steel.

The LF refining final slag A1 ₂ 0 ₃ content is controlled at 29 ~ 32%, the CaO content is controlled at 50 ~ 55%, the electrification time is controlled within 15min, and the LF treatment time is 45 minutes, effectively controlling the LF treatment process. 00«。 The molten steel [N] content is less than 0. 00«.

(4) Continuous casting protection casting, continuous casting large bag long nozzle with sealing ring + argon seal protection, the material is fibrous aluminosilicate cotton and high temperature binder high temperature refractory clay. 008以上。 The continuous casting process molten steel [N] is less than 0. 008%.

Among them, the control of steel segregation:

(1) The steel [S] content is less than 0.004%, and the steel [N] content is less than 0.005% to reduce the sulphide segregation of the slab and the Nb (C _x , N _y ) enrichment.

(2) The superheat of tundish steel is the main factor affecting the segregation of slab. Therefore, the temperature of the tundish steel in continuous casting is controlled at 1528 °C ~ 1542 °C, and the superheat of molten steel is controlled at 11. C ~ 25 °C.

Implementation Effect:

The tensile strength of the finished steel is greater than 520 Mpa, the yield strength is 420 ~ 530Mpa, the impact energy at -10 °C is greater than 30J, and the hardness is less than 170 HV10.

When the hot-rolled steel coil is used in longitudinal section, the steel tube degradation rate is controlled to below 0.55%, which is the best indicator of similar products in China.

Claims

1. A new medium carbon J55 steel smelting method, which comprises: hot metal pretreatment→ converter blowing→ LF refining→ slab continuous casting→ slab cleaning→ slab reheating→ controlled rolling and cooling→finished product Process flow for inspection; especially for the control of nitrogen removal in non-metallic inclusions in steel and the key technical steps for steel segregation control;

The removal of non-metallic inclusions and the control of nitrogen elements:

1 002%; The content of the [N] is less than 0. 002%;

② When the converter blowing, blowing up is prohibited to prevent the molten steel by nitrogen, oxygen pressure which the control parameter is 0. 8 ~ 0. 85MPa, Flow 32000 ~ 33000m ³ / h, the intensity of 0. 4 ~ 0. 6Nm ³ / t -min, the oxygen blowing time is 14 min; the bottom blowing argon stirring gas supply strength is 0. 05 - 0. 08Nm7 t. min, the pressure is 1. 0 ~ 1. 2Mpa; the converter tapping temperature is 1620-1670 ° C, at this time 008%; [C] content is 0. 09%, [P] content is less than 0. 008%;

3 LF refining and slagging, desulfurization, need to add AL-Ca refining agent, and then the bottom of the ladle is weakly stirred by argon. The control time is 15-20 minutes; the final residue of refining A1 ₂ 0 ₃ is 29 ~ 31% The grade of the non-metallic inclusions in the steel is less than 1. 0 grade;

4 Continuous casting protection casting, large bag long nozzle with seal ring + argon seal protection; continuous casting molten steel [N] increase is less than 0. 001%.

Among them, steel segregation control:

① In order to reduce the slab and segregation sulfide Nb (C _x, N _y) generates, steel [S] content of less than 0. 003%, [N] content is less than 0.005%;

The smelting method of the medium carbon J55 steel according to claim 1, wherein the amount of the AL-Ca refining agent is 2. 5 kg / ton of steel; wherein the content of the metal aluminum powder is 35 - 38%, silicon The content of 4 丐 powder is 10 ° /. The content of A1 ₂ 0 ₃ is 50%, the content of the binder is 5%, and the binder is light burnt dolomite.

3. The method for smelting medium carbon J55 steel according to claim 1, characterized in that: the continuous casting sealing slag is made of fibrous aluminosilicate cotton, the sealing is a high temperature binder, and the binder is refractory clay.

4. The method for smelting medium carbon J55 steel according to claim 1, wherein: the tensile strength of the finished steel is greater than 520 Mpa, the yield strength is 420 to 530 MPa, the impact energy at -10 ° C is greater than 30 J, and the hardness is less than 170 HV10.

The smelting method of the medium carbon J55 steel according to claim 1, wherein: the hot-rolled steel coil is controlled by a longitudinal section, and the steel tube degradation rate is controlled to be less than 0.05%, which is the best indicator of similar products in China. .

6. The method for smelting medium carbon J55 steel according to claim 1, wherein the smelting materials are all commercially available products.