CN104190740B - The production method of hot rolled seamless steel tube pipe - Google Patents

Abstract

The invention discloses a production method of a hot-rolled seamless steel pipe billet, which is characterized in that the method comprises the following steps: (1) steelmaking; (2) continuous casting; (3) pipe rolling and on-line heat treatment. The method of the present invention has simple steps and is easy to operate. In the steelmaking process, the present invention converts brittle inclusions in steel into plastic inclusions by using specially designed low-alkalinity acidic synthetic refining slag in the steelmaking process, so that the oil cylinder can use heat Rolled seamless steel pipe blanks are not easy to be cracked during the cold drawing process and the surface of the steel pipe after machining is not easy to appear defects that affect product quality such as "white spots and pits" caused by brittle inclusions, so it can improve the quality of the products produced by the present invention. The quality of the seamless steel pipe blank is suitable for promotion and use.

Description

Production method of hot-rolled seamless steel pipe billet

technical field

The invention relates to a production method of a seamless steel tube blank, in particular to a production method of a hot-rolled seamless steel tube blank.

Background technique

The production process of cold-drawn seamless steel pipes for oil tanks is generally: hot-rolled seamless steel pipe blanks—annealing heat treatment—pickling, phosphating, saponification—cold drawing into finished steel pipes. Among them, the function of annealing heat treatment process is to improve the finished product quality of cold-drawn seamless steel pipe by reducing the yield strength and residual stress of hot-rolled seamless steel pipe billet, improving its plasticity and uniformity of structure.

At present, many manufacturers of cold-drawn seamless steel pipes omit the annealing heat treatment process of the tube blank when producing cold-drawn seamless steel pipes for medium and low carbon oil tanks, and adopt the production process of direct cold drawing after pickling, phosphating and saponification . Although after using this production process, cold drawn seamless steel pipe manufacturers have improved production efficiency, saved equipment purchase costs, and reduced production costs. However, the yield of cold-drawn seamless steel pipes has dropped significantly.

The reason for the waste cold drawn seamless steel pipe is mainly related to the physical quality of the hot-rolled seamless steel pipe billet. Although the hot-rolled seamless steel pipe billet meets the requirements of the relevant national standard - GB/T8162, it cannot be used for direct cold drawing The use requirements of the production process. This is mainly reflected in the following aspects:

1. The delivery state of the hot-rolled seamless steel pipe billet for medium and low-carbon oil cylinders is generally hot-rolled, and its grain size is relatively coarse, the structure is disordered, the residual structure stress is large, and the elongation is low, which can easily lead to cold drawing defects. produce.

2. The wall thickness tolerance of the hot-rolled seamless steel pipe billet for medium and low carbon oil cylinders is ±12.5%, and the tolerance range is relatively large. In the case of large wall thickness tolerance and low elongation, it is easy to cause cold drawing defects.

3. GB/T8162 has no clear requirements on the content of non-metallic inclusions in the hot-rolled seamless steel pipe blanks for medium and low carbon oil cylinders. When there are a large number of brittle inclusions distributed in the hot-rolled seamless steel pipe billet for medium and low carbon oil cylinders, not only defects are easily formed at the brittle inclusions during cold drawing, but also the brittle inclusions are easy to fall off after machining and form "white spot, concave "Pits" and other defects that affect product quality.

Therefore, in order to fully meet the requirements of the direct cold drawing production process of hot-rolled seamless steel pipe blanks for medium and low carbon oil cylinders, the hot-rolled seamless steel pipe blanks must meet the following technical conditions: 1. Good elongation; 2. High wall thickness accuracy 3. The content of brittle inclusions in steel is less.

Contents of the invention

One of the purposes of the present invention is to provide a production method of hot-rolled seamless steel pipe blanks for the above-mentioned shortcomings, in order to solve the problem that the hot-rolled seamless steel pipe blanks for medium and low carbon oil cylinders produced in the prior art cannot meet the requirements of direct cooling. The problem of pulling out the requirements of the production process.

The purpose of the invention is achieved through the following technical solutions:

A method for producing a hot-rolled seamless steel pipe billet, the method comprising the following steps:

(1) Steelmaking

(1a) Pre-desulfurization of molten iron, control the S content of the molten iron entering the converter ≤ 0.015%;

(1b) Converter smelting, when the converter is tapping, the carbon content is C≥0.10%, the phosphorus content is P≤0.008%, the tapping temperature is 1620°C to 1660°C, and then the tapping is deoxidized and alloyed;

(1c) Refining in an LF refining furnace, using low-basic acidic synthetic refining slag for refining, the low-basic acidic synthetic refining slag is composed of 35-55 parts by weight of SiO ₂ , 25-40 parts of CaO, and 10-20 parts of Al Composed of ₂ O ₃ ;

(1d) carrying out alloying operation to obtain molten steel;

(2) Continuous casting

(2a) Adopting the protection pouring method of continuous casting shroud combined with blowing Ar protection and protection pad to carry out continuous casting to the molten steel that step (1d) makes;

(2b) Control the liquid level of the tundish. The opening liquid level of the continuous casting tundish is 550-650mm, the pouring liquid level is 750-850mm, and continuous pouring is prohibited when the continuous pouring liquid level is lower than 450mm;

(2c) Control the degree of superheat of molten steel, and the temperature of the tundish is 1520°C to 1545°C;

(2d) making a continuous casting slab;

(3) Tube rolling and on-line heat treatment

The continuous casting slab obtained by the hot rolling step (2d) of the continuous rolling mill is pierced, and rolled by the continuous rolling mill. After the rolling, the blank pipe is air-cooled to below 500°C and then heated. The amount of deformation is controlled at 10% to 15%, and the wall thickness tolerance of the finished steel pipe is -10% to +10%. After sizing, it is piled in the air and cooled to room temperature.

According to an embodiment of the present invention, in the step (1b), the deoxidation and alloying of tapping adopts an Al-free deoxidation process, and 2.5-3.5 Kg/t of Si—Mn alloy is added for deoxidation.

According to one embodiment of the present invention, when the LF refining furnace finishes refining and tapping in step (1c), the temperature before static blowing is 1595°C to 1605°C, and the static blowing time after tapping is ≥15min, and the intensity of argon blowing is controlled to keep the steel Liquid peristalsis and molten steel must not be exposed.

According to one embodiment of the present invention, the chemical composition of the molten steel obtained in step (1d) is calculated by weight percentage: C: 0.23% to 0.28%, Si: 0.17% to 0.37%, Mn: 0.70% to 1.00%, P≤0.035%, S≤0.035%, Cr≤0.25%, Ni≤0.30%, Cu≤0.25%, and the balance is Fe and other impurities.

According to an embodiment of the present invention, when the continuous casting slab is hot-rolled by the continuous rolling mill in step (3), the temperature of the exit tube of the annular furnace is 1230°C-1270°C.

According to an embodiment of the present invention, in step (3), a two-roll cross-rolling tapered roll piercer is used for piercing.

According to an embodiment of the present invention, the finish rolling temperature during rolling in step (3) is 860°C-900°C.

According to an embodiment of the present invention, three rolls are used for sizing in step (3).

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) The method of the present invention has simple steps and is easy to operate. In the steelmaking process, the present invention converts brittle inclusions in steel into plastic inclusions by adopting specially designed low-alkalinity acidic synthetic refining slag for refining, thereby making The hot-rolled seamless steel pipe blanks for oil cylinders are not easy to be cracked during the cold drawing process, and the surface of the steel pipe after machining is not easy to appear defects that affect product quality such as "white spots and pits" caused by brittle inclusions, so the invention can be improved. The quality of the seamless steel pipe blanks produced.

(2) The present invention adopts the continuous rolling mill to roll the steel pipe, which ensures that the wall thickness tolerance of the steel pipe is controlled at ±10%, so that the produced hot-rolled seamless steel pipe billet for the oil cylinder is not easy to be pulled out during the cold drawing process.

(3) The present invention controls the finish rolling temperature at 860-900 degrees, refines the grain size of the finished product and improves the elongation of the finished product by refining the grain size of the hot-rolled seamless blank tube for the oil cylinder.

(4) The on-line heat treatment process of the present invention adopts the process of sizing the blank pipe at a temperature range of 10-30 degrees above AC3, compared with the commonly used process of on-line heat treatment in the two-phase region, the on-line heat treatment process of the present invention not only maintains The normalizing process in the two-phase region has the characteristics of refining grains, and because the sizing temperature is above AC3, the banded structure in the metallographic structure of the steel pipe is significantly improved, so the steel pipe after heat treatment also has low yield strength and low longitudinal elongation. Advantages of higher, especially significantly higher transverse elongation.

(5) In the on-line heat treatment process of the present invention, the cooling method of stack cooling is adopted after sizing; because the cooling rate of stack cooling is relatively slow, the elongation of the steel pipe after heat treatment is increased and the internal stress is significantly reduced.

(6) The production cost of on-line heat treatment process of the present invention is equivalent to general on-line heat treatment process, but the properties such as yield strength, elongation of steel pipe after heat treatment are obviously better than the latter; The production cost of on-line heat treatment process of the present invention is obviously lower than The general off-line heat treatment process, and the yield strength, elongation and other properties of the steel pipe after heat treatment are slightly better than the latter. Therefore, the online heat treatment process of the present invention has the advantages of lower production cost and better product quality.

detailed description

Below in conjunction with embodiment the present invention is described in further detail:

Example 1

The production method of the hot-rolled seamless steel pipe billet of the present invention mainly includes the steps of steelmaking, continuous casting, pipe rolling and on-line heat treatment, and the seamless steel pipe billet produced by the hot-rolled seamless steel pipe billet production method is mainly used for production cylinder.

The production specifications are 159*17 hot-rolled seamless steel pipe blanks for oil cylinders. The chemical composition of the hot-rolled seamless steel pipe blanks for oil cylinders is shown in Table 1 by weight percentage (%), and the balance is Fe and other impurities.

C Si mn P S Cr Ni Cu

0.24 0.28 0.76 0.013 0.014 0.03 0.03 0.06

Table I

In the steelmaking step, the step of pre-desulfurizing molten iron is firstly carried out, and then the molten steel is initially smelted in a 70T converter, and the molten iron is fed into the converter for pre-desulfurization treatment, and the S content of the molten iron entering the converter is controlled to be ≤0.015%, and low-alkali is used for the subsequent LF furnace To create conditions for the slag, and then proceed to the following steps:

For converter smelting, the carbon content and phosphorus content are controlled when the converter is tapping, and the carbon content is 0.10%, and the phosphorus content is 0.008%. At the same time, the tapping temperature is controlled, and the tapping temperature is 1620° C. to 1660° C.

Pre-deoxidation and preliminary alloying control the total oxygen content in the steel to reduce the inclusions produced by the deoxidation products and create favorable conditions for subsequent deoxidation and the removal of inclusions in the steel. Control the types of inclusions in the steel, adopt Al-free deoxidation process for deoxidation and alloying of converter tapping, and add Si-Mn alloy 2.5-3.5Kg/t for deoxidation, and the Si-Mn alloy 2.5-3.5Kg/t means per ton Add 2.5-3.5 kg of Si-Mn alloy into molten steel.

Refining in LF refining furnace. In the refining process of LF refining furnace, in order to strictly control the type, quantity, size and shape of inclusions in molten steel, the present invention uses low-basic acidic synthetic refining slag for refining. The low-alkalinity acidic synthetic refining slag is composed of 35-55 parts of SiO ₂ , 25-40 parts of CaO and 10-20 parts of Al ₂ O ₃ in parts by weight. No addition of Al in the refining process of molten steel can reduce the content of Al ₂ O ₃ in the slag. At the end of refining, the content of Al ₂ O ₃ in the slag is controlled at about 10%. The ultimate purpose of refining is to control the Al ₂ O ₃ in inclusions Around 20%. Appropriately increase the tapping temperature, increase the fluidity of molten steel, keep the bottom blowing Ar unblocked, control the intensity of blowing Ar, and avoid tumbling and suction of molten steel. Strong deoxidation operation, rapid foaming of white slag, keeping white slag out of steel, and prolonging the time of static blowing of molten steel to promote the floating of inclusions in steel.

Then carry out the alloying operation. Since the hot-rolled seamless steel pipe blanks for oil cylinders of different specifications have different chemical element components, the alloying operation can adjust the content of each chemical element component in the molten steel to achieve different output. Specifications of hot-rolled seamless steel pipe blanks for oil cylinders. In all hot-rolled seamless steel pipe blanks for oil cylinders of different specifications, the chemical components are all within the following content ranges by weight percentage: C: 0.23% ~ 0.28%, Si: 0.17% ~ 0.37%, Mn: 0.70% ~1.00%, P≤0.035%, S≤0.035%, Cr≤0.25%, Ni≤0.30%, Cu≤0.25%, the balance is Fe and other impurities. In this embodiment, the hot-rolled seamless steel pipe blanks for oil cylinders with a specification of 159*17 can be adjusted to the chemical components of the molten steel by weight percentage: C: 0.24%, Si: 0.28% by alloying operation , Mn: 0.76%, P: 0.013%, S: 0.014%, Cr: 0.03%, Ni: 0.03%, Cu: 0.06%, and the balance is Fe and other impurities. At the end of refining and tapping, the temperature control range before static blowing is: 1595 ° C ~ 1605 ° C, and the static blowing time after refining and tapping is 15 minutes, and the blowing Ar intensity is controlled to keep the molten steel peristaltic and the molten steel must not be exposed. Through the above steelmaking The steps can make molten steel.

In the continuous casting step, the molten steel obtained in the steelmaking step is continuously casted by using a continuous casting long nozzle combined with Ar blowing protection and a protection casting method of a protective pad to prevent nitrogen absorption and secondary oxidation of the molten steel. In order to prevent tundish slag from being brought into inclusions, the liquid level of the tundish is strictly controlled. The opening liquid level of the continuous casting tundish is 550-650mm, and the pouring liquid level is 750-850mm. to pour. Control the superheat degree of molten steel, adopt low superheat degree pouring, the tundish temperature is 1520～1545℃. The continuous casting mold slag adopts special mold slag, the casting speed control is stable during the pouring process, and the continuous casting secondary cooling water is automatically distributed throughout the process. Finally, a continuous casting slab with uniform chemical composition and low content of inclusions in steel, especially brittle inclusions, is produced.

In the tube rolling and on-line heat treatment steps, the continuous casting slab produced by the continuous rolling mill is used for hot rolling and continuous casting. When the continuous rolling mill is used for hot rolling the continuous casting slab, the temperature of the tube coming out of the ring furnace is 1230°C-1270°C. Then use a two-roll skew rolling tapered roll piercer to perforate, and use a continuous rolling mill to roll. The rolling step is carried out by hot rolling, and the final rolling temperature is controlled at 860-900°C. After rolling, the blank pipe is air-cooled to below 500°C, and then enters a walking heating furnace for reheating at a temperature of 835-865°C. After heat preservation and out of the furnace, three-rollers are used for sizing, and the deformation of sizing is controlled at 10-15 %. The wall thickness tolerance control range of the finished steel pipe is: -10% to +10%. After sizing, it is stacked and cooled in the air to room temperature. After flaw detection and inspection, it is packaged and put into storage.

After the metallographic and mechanical inspections of the finished steel pipes prepared in this embodiment, the content of non-metallic inclusions and mechanical properties meet the design requirements. Among them, the test data of some mechanical properties of the finished steel pipes are shown in Table 2, and the test data of non-metallic inclusions are shown in Table 3.

Table II

Table three

Example 2

The production method of this embodiment is exactly the same as that of Example 1, the only difference is that the specifications of the hot-rolled seamless steel pipe blanks for oil cylinders produced in this embodiment are 168*15 hot-rolled seamless steel pipe blanks for oil cylinders. The chemical composition of the hot-rolled seamless steel pipe blanks for oil cylinders is shown in Table 4 by weight percentage (%), and the balance is Fe and other impurities.

C Si mn P S Cr Ni Cu 0.25 0.28 0.80 0.012 0.013 0.03 0.03 0.07

Table four

In this embodiment, during converter smelting, the carbon content and phosphorus content are controlled during converter tapping, the carbon content is 0.13%, and the phosphorus content is 0.007%. During the alloying operation, the content of each chemical component in the molten steel is adjusted according to the content of each chemical component in the hot-rolled seamless steel pipe billet for oil cylinders with a specification of 168*15, that is, the chemical components in the molten steel are adjusted by weight percentage to : C: 0.25%, Si: 0.28%, Mn: 0.80%, P: 0.012%, S: 0.013%, Cr: 0.03%, Ni: 0.03%, Cu: 0.07%, and the balance is Fe and other impurities.

After metallographic and mechanical inspections, the content of non-metallic inclusions and mechanical properties of the finished steel pipes prepared in this embodiment meet the design requirements. Among them, the test data of some mechanical properties of the finished steel pipes are shown in Table 5, and the test data of non-metallic inclusions are shown in Table 6.

Table five

Table six

Example 3

The production method of this embodiment is exactly the same as that of Example 1, the only difference is that the specification of the hot-rolled seamless steel pipe blank for oil cylinders produced in this embodiment is 139.7*17 hot-rolled seamless steel pipe blanks for oil cylinders, the specification The chemical composition of the hot-rolled seamless steel pipe blanks for oil cylinders is shown in Table 7 by weight percentage (%), and the balance is Fe and other impurities.

C Si mn P S Cr Ni Cu 0.25 0.30 0.83 0.015 0.014 0.03 0.02 0.06

Table seven

In this embodiment, during converter smelting, the carbon content and phosphorus content are controlled when the converter is tapping, and the carbon content is 0.14%, and the phosphorus content is 0.008%. During the alloying operation, adjust the content of each chemical component in the molten steel according to the content of each chemical component in the hot-rolled seamless steel pipe billet for oil cylinders with a specification of 139.7*17, that is, adjust the chemical components in the molten steel by weight percentage to : C: 0.25%, Si: 0.30%, Mn: 0.83%, P: 0.015%, S: 0.014%, Cr: 0.03%, Ni: 0.02%, Cu: 0.06%, and the balance is Fe and other impurities.

After metallographic and mechanical inspections, the content of non-metallic inclusions and mechanical properties of the finished steel pipes prepared in this embodiment meet the design requirements. Among them, the test data of some mechanical properties of the finished steel pipes are shown in Table 8, and the test data of non-metallic inclusions are shown in Table 9.

table eight

Table nine

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (7)

1. the production method of hot rolled seamless steel tube pipe, is characterized in that the method comprises the following steps:

(1) make steel

(1a) molten iron pre-desulfurization, controls into converter molten iron S content≤0.015%;

(1b) converter smelting, during converter tapping, carbon content is C >=0.10%, and phosphorus content is P≤0.008%, and tapping temperature is 1620 DEG C ~ 1660 DEG C, then tapping deoxidization; Tapping deoxidization adopts without Al deoxidization technique, and adds Si-Mn alloy 2.5 ~ 3.5Kg/t and carry out deoxidation;

(1c) LF refining furnace refining, adopts the acid lab-prepared refining slag refining of low alkalinity, and the acid lab-prepared refining slag of described low alkalinity is by parts by weight 35 ~ 55 parts of SiO ₂, 25 ~ 40 parts of CaO, 10 ~ 20 parts of Al ₂o ₃composition;

(1d) alloying operation is carried out, obtained molten steel;

(2) continuous casting

(2a) the molding casting mode adopting continuous casting long gate combination to blow Ar protection and neonychium carries out continuous casting to molten steel;

(2b) control tundish liquid level, continuous casting production is opened and watered liquid level is 550-650mm, and cast liquid level is 750-850mm, even waters liquid level and waters lower than forbidding during 450mm connecting;

(2c) control the degree of superheat of molten steel, tundish temperature is 1520 DEG C ~ 1545 DEG C;

(2d) obtained continuous casting billet;

(3) tube rolling and burning optimization on line

Use Continuous mill train hot rolling continuous casting billet, perforation, adopt continuous rolling-tube unit rolling, heat again below hollow forging air cooling to 500 after to be rolled DEG C, be incubated sizing after coming out of the stove, sizing deformation amount controlling is 10% ~ 15%, and the wall thickness tolerance of steel pipe finished product is-10% ~+10%, and after sizing, heap is cooled to room temperature in atmosphere.

2. according to the production method of hot rolled seamless steel tube pipe according to claim 1, when it is characterized in that in step (1c), LF refining furnace terminates refining tapping, it is quiet that to blow front temperature be 1595 DEG C ~ 1605 DEG C, tapping after the quiet time of blowing >=15min, and control Argon intensity with keeps molten steel wriggling and molten steel must not be exposed.

3., according to the production method of hot rolled seamless steel tube pipe according to claim 1, it is characterized in that the chemical composition of obtained molten steel in step (1d) is by weight percentage: C:0.23% ~ 0.28%, Si:0.17% ~ 0.37%, Mn:0.70% ~ 1.00%, P≤0.035%, S≤0.035%, Cr≤0.25%, Ni≤0.30%, Cu≤0.025%, surplus are Fe and other impurity.

4., according to the production method of hot rolled seamless steel tube pipe according to claim 1, when it is characterized in that using Continuous mill train hot rolling continuous casting billet in step (3), annular furnace goes out the temperature of boiler tube is 1230 DEG C-1270 DEG C.

5., according to the production method of hot rolled seamless steel tube pipe according to claim 1, it is characterized in that in step (3), adopting the perforation of two-roller skew-rolling cone type piercer.

6., according to the production method of hot rolled seamless steel tube pipe according to claim 1, when it is characterized in that rolling in step (3), finishing temperature is 860 DEG C-900 DEG C.

7., according to the production method of hot rolled seamless steel tube pipe according to claim 1, it is characterized in that adopting three roller sizings in step (3).