阅读说明：本技术 铌微合金化hrb400e热轧带肋钢筋无屈服现象的控制方法 (Control method for non-yield phenomenon of niobium microalloyed HRB400E hot-rolled ribbed steel bar ) 是由 钱学海 黄伟忠 何维 周博文 樊雷 周从锐 胡鳌全 唐锡明 李西德 于 2019-10-24 设计创作，主要内容包括：本发明涉及一种铌微合金化HRB400E热轧带肋钢筋无屈服现象的控制方法,其特征在于：控制铌微合金化HRB400E热轧带肋钢筋合理的成分：低锰Mn含量高硅Si含量,控制氮N含量和铬Cr含量；碳C：0.19Wt％～0.25Wt％,锰Mn：1.25Wt％～1.40Wt％,硅Si：0.50Wt％～0.70Wt％,氮N≤0.009Wt％,铬Cr≤0.10Wt％；控制铌微合金化HRB400E热轧带肋钢筋低开轧温度：1000～1060℃；控制铌微合金化HRB400E热轧带肋钢筋进精轧温度：850～950℃。(The invention relates to a control method for non-yield phenomenon of niobium microalloyed HRB400E hot-rolled ribbed steel bars, which is characterized by comprising the following steps: controlling reasonable components of niobium microalloyed HRB400E hot-rolled ribbed steel bars: the low manganese Mn content and the high silicon Si content are controlled, and the nitrogen N content and the chromium Cr content are controlled; c, carbon C: 0.19 Wt% -0.25 Wt%, Mn: 1.25 Wt% -1.40 Wt%, Si: 0.50 Wt% -0.70 Wt%, nitrogen N is less than or equal to 0.009 Wt%, chromium Cr is less than or equal to 0.10 Wt%; controlling the low initial rolling temperature of the niobium microalloying HRB400E hot-rolled ribbed steel bar: 1000 to 1060 ℃; controlling the finish rolling temperature of the niobium microalloying HRB400E hot-rolled ribbed steel bar: 850-950 ℃.)

1. A control method for non-yield phenomenon of niobium microalloyed HRB400E hot-rolled ribbed steel bars is characterized by comprising the following steps:

the process route of the control method for the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar is as follows: smelting blast furnace molten iron, desulfurizing and pretreating the molten iron, smelting converter molten steel, continuously casting square billets, continuously rolling bars and cutting the bars to length; wherein:

controlling reasonable components of niobium microalloyed HRB400E hot-rolled ribbed steel bars: the low manganese Mn content and the high silicon Si content are controlled, and the nitrogen N content and the chromium Cr content are controlled; c, carbon C: 0.19 Wt% -0.25 Wt%, Mn: 1.25 Wt% -1.40 Wt%, Si: 0.50 Wt% -0.70 Wt%, nitrogen N is less than or equal to 0.009 Wt%, chromium Cr is less than or equal to 0.10 Wt%, phosphorus P: less than or equal to 0.040 Wt%;

controlling the low initial rolling temperature of the niobium microalloying HRB400E hot-rolled ribbed steel bar: 1000 to 1060 ℃;

controlling the finish rolling temperature of the niobium microalloying HRB400E hot-rolled ribbed steel bar: 850-950 ℃.

2. The method for controlling the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar as claimed in claim 1, wherein:

smelting molten steel in the converter: s is required to be less than or equal to 0.040 Wt% when the molten iron enters the furnace; argon is blown from the bottom in the whole process of smelting, the gas flow is increased in the later stage of blowing, and the stirring of a molten pool is enhanced; the end point of the converter is controlled to be less than or equal to 0.15 Wt% C and less than or equal to 0.037 Wt% P.

3. The method for controlling the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar as claimed in claim 1, wherein:

and (3) continuous casting of the square billet: and (3) ladle slag discharging detection control is adopted, the pouring temperature of the tundish is 1525-1545 ℃, the tundish uses a common covering agent and common square billet covering slag, and the single flow pulling speed of the casting blank is 2.5-3.2 m/min.

4. The method for controlling the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar as claimed in claim 1, wherein:

and (3) hot continuous rolling of the bar: controlling the heating temperature of a casting blank to 1150-1200 ℃, the heating time of a billet to 60-90 minutes, the initial rolling temperature to 1000-1060 ℃, adopting an 18-frame hot continuous rolling unit, using a cooling control device before finish rolling, and controlling the finish rolling temperature to 850-950 ℃.

5. The method for controlling the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar as claimed in claim 1, wherein:

the square billet continuous casting process protects the pouring requirement: a protective sleeve is adopted from the ladle to the tundish, the liquid level of molten steel in the tundish is fully covered by a covering agent, and a drain port with a sealing gasket is used from the tundish to the crystallizer, so that the nitrogen increase N of the molten steel is reduced.

6. The method for controlling the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar as claimed in claim 1, wherein:

in the control method for the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar, the initial rolling temperature is 1010 ℃, and the finish rolling temperature is 928 ℃.

7. The method for controlling the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar as claimed in claim 1, wherein:

the control method for the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar has the advantages that the initial rolling temperature is 1033 ℃, and the finish rolling temperature is 933 ℃.

8. The method for controlling the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar as claimed in claim 1, wherein:

in the control method for the yield-free niobium microalloying HRB400E hot-rolled ribbed steel bar, the initial rolling temperature is 1045 ℃, and the finish rolling temperature is 938 ℃.

9. The method for controlling the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar as claimed in claim 1, wherein:

in the control method for the yield-free niobium microalloying HRB400E hot-rolled ribbed steel bar, the initial rolling temperature is 1040 ℃, and the finish rolling temperature is 919 ℃.

10. The method for controlling the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar as claimed in claim 1, wherein:

in the control method for the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar, the initial rolling temperature is 1028 ℃, and the finish rolling temperature is 942 ℃.

Technical Field

The invention belongs to the field of steel production and manufacturing, and particularly relates to a control method for enabling niobium microalloyed HRB400E hot-rolled ribbed steel bars (hereinafter referred to as steel bars) with the specification of phi 12-25 mm to have no yield phenomenon.

Background

HRB400E steel bar domestic steel mills are mostly produced by adopting a vanadium microalloying process, and in the next half year of 2018, along with GB/T1499.2-2018 part 2 of steel for reinforced concrete: the implementation of hot rolling ribbed steel bars, the price of vanadium series alloy such as vanadium-nitrogen alloy is expanded, and the cost for producing HRB400E steel bars by using a vanadium micro-alloying process is too high. Meanwhile, the niobium-iron alloy price keeps stable, and the cost for producing the HRB400E steel bar by the niobium microalloying process has more advantages. However, when the niobium microalloying process is used for producing the HRB400E steel bar, the phenomenon that the mechanical curve does not have a yield platform easily occurs on a small-sized product, so that the yield strength of the steel bar is too low and the performance is not good. Therefore, when the niobium microalloying process is used for producing the HRB400E hot-rolled ribbed steel bar, the niobium microalloying HRB400E hot-rolled ribbed steel bar without yield phenomenon is urgently needed, and the production and quality requirements are met.

In the process of implementing the invention, the applicant finds that at least the following problems exist in the prior art: the prior niobium microalloyed HRB400E hot-rolled ribbed steel bar has the problems of no yield phenomenon, incapability of meeting production requirements and quality requirements and the like.

Disclosure of Invention

The embodiment of the invention provides a control method for the yield-free phenomenon of niobium microalloyed HRB400E hot-rolled ribbed steel bars, and aims to solve the problem that the yield-free phenomenon of HRB400E hot-rolled ribbed steel bars is solved. The invention aims to produce the niobium microalloyed HRB400E hot-rolled ribbed steel bar with the yield strength of phi 12-25 mm by applying a specific component design, a reasonable steel rolling initial rolling temperature and a low finishing mill feeding temperature through a niobium microalloying process.

To achieve the above object, an embodiment of the present invention provides a method for controlling yield-free phenomenon of niobium microalloyed HRB400E hot-rolled ribbed steel bar, comprising:

the process route of the control method for the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar is as follows: smelting blast furnace molten iron, desulfurizing and pretreating the molten iron, smelting converter molten steel, continuously casting square billets, continuously rolling bars and cutting the bars to length; wherein:

controlling reasonable components of niobium microalloyed HRB400E hot-rolled ribbed steel bars: the low manganese Mn content and the high silicon Si content are controlled, and the nitrogen N content and the chromium Cr content are controlled; c, carbon C: 0.19 Wt% -0.25 Wt%, Mn: 1.25 Wt% -1.40 Wt%, Si: 0.50 Wt% -0.70 Wt%, nitrogen N is less than or equal to 0.009 Wt%, chromium Cr is less than or equal to 0.10 Wt%;

controlling the low initial rolling temperature of the niobium microalloying HRB400E hot-rolled ribbed steel bar: 1000 to 1060 ℃;

controlling the finish rolling temperature of the niobium microalloying HRB400E hot-rolled ribbed steel bar: 850-950 ℃.

Further, smelting molten steel in the converter: s is required to be less than or equal to 0.040 Wt% when the molten iron enters the furnace; argon is blown from the bottom in the whole process of smelting, the gas flow is increased in the later stage of blowing, and the stirring of a molten pool is enhanced; the end point of the converter is controlled to be less than or equal to 0.15 Wt% C and less than or equal to 0.037 Wt% P.

Further, the billet continuous casting comprises the following steps: and (3) ladle slag discharging detection control is adopted, the pouring temperature of the tundish is 1525-1545 ℃, the tundish uses a common covering agent and common square billet covering slag, and the single flow pulling speed of the casting blank is 2.5-3.2 m/min.

Further, the bar is hot continuous rolled: controlling the heating temperature of a casting blank to 1150-1200 ℃, the heating time of a billet to 60-90 minutes, the initial rolling temperature to 1000-1060 ℃, adopting an 18-frame hot continuous rolling unit, using a cooling control device before finish rolling, and controlling the finish rolling temperature to 850-950 ℃.

Further, the steel scrap condition of the converter molten steel smelting is as follows: the common steel scraps must not use high-chromium Cr steel scraps.

Further, the billet continuous casting process protects the pouring requirements: a protective sleeve is adopted from the ladle to the tundish, the liquid level of molten steel in the tundish is fully covered by a covering agent, and a drain port with a sealing gasket is used from the tundish to the crystallizer, so that the nitrogen increase N of the molten steel is reduced.

Furthermore, the control method for the niobium microalloying HRB400E hot-rolled ribbed steel bar non-yielding phenomenon has the advantages that the initial rolling temperature is 1010 ℃, and the finish rolling temperature is 928 ℃.

Furthermore, the control method for the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar has the advantages that the initial rolling temperature is 1045 ℃, and the finish rolling temperature is 938 ℃.

Furthermore, the control method for the niobium microalloying HRB400E hot-rolled ribbed steel bar yield-free phenomenon has the advantages that the initial rolling temperature is 1040 ℃, and the finish rolling temperature is 919 ℃.

Furthermore, in the control method for the niobium microalloying HRB400E hot-rolled ribbed steel bar yield-free phenomenon, the initial rolling temperature is 1028 ℃, and the finish rolling temperature is 942 ℃.

The technical scheme has the following beneficial effects: the invention can control the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar with the diameter of 12-25 mm to be below 0.1 percent.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The embodiment of the invention provides a method for controlling yield-free phenomenon of niobium microalloyed HRB400E hot-rolled ribbed steel bars, which comprises the following steps:

the process route of the control method for the yield-free phenomenon of the niobium microalloyed HRB400E hot-rolled ribbed steel bar is as follows: smelting blast furnace molten iron, desulfurizing and pretreating the molten iron, smelting converter molten steel, continuously casting square billets, continuously rolling bars and cutting the bars to length; wherein:

controlling reasonable components of niobium microalloyed HRB400E hot-rolled ribbed steel bars: the low manganese Mn content and the high silicon Si content are controlled, and the nitrogen N content and the chromium Cr content are controlled; c, carbon C: 0.19 Wt% -0.25 Wt%, Si: 0.50 Wt% -0.70 Wt%, Mn: 1.25 Wt% -1.40 Wt%, phosphorus P: less than or equal to 0.040 Wt%, S: less than or equal to 0.035 Wt%, Nb: 0.020-0.035 Wt%, nitrogen N is less than or equal to 0.009 Wt%, chromium Cr is less than or equal to 0.10 Wt%;

controlling the low initial rolling temperature of the niobium microalloying HRB400E hot-rolled ribbed steel bar: 1000 to 1060 ℃;

controlling the finish rolling temperature of the niobium microalloying HRB400E hot-rolled ribbed steel bar: 850-950 ℃.

The reason why the steel bar has no yield phenomenon is that the bainite content in the steel is too high; the principle of the invention is that according to the influence of each component in Nb microalloyed steel on bainite, the Mn content in the steel is properly reduced, the Si content is improved, Cr brought by scrap steel is controlled, and the increase of N in molten steel is reduced; the low-temperature rolling ensures that the amount of the solid-solution niobium is in a reasonable interval and austenite grains of the billet are not grown; before finish rolling, controlled cooling equipment is used, the finish rolling temperature is controlled, solid solution niobium is reduced, the finish rolling temperature is reduced, austenite crystal grain growth after rolling is controlled, and bainite tissue formation is reduced. The final rolling temperature can be controlled to be about 1045 ℃ by controlling the initial rolling temperature without controlled cooling equipment between the rolling mill frames; meanwhile, on the premise of meeting the requirements of a new national standard metallographic phase, the cooling can be slightly controlled after rolling, the growth of austenite grains after rolling is controlled, and the formation of a bainite structure is inhibited; therefore, the phenomenon that the reinforcing steel bar is not subjected to yielding can be effectively controlled.

The invention discloses a control method of niobium microalloying HRB400E hot-rolled ribbed steel bar without yield phenomenon, which comprises the following process routes: blast furnace molten iron smelting → molten iron desulphurization pretreatment → converter molten steel smelting → square billet continuous casting → hot continuous rolling → fixed-length shearing → inspection, packaging and warehousing; wherein, the process characteristics of each stage are as follows:

smelting molten steel in a converter: s is required to be less than or equal to 0.040 Wt% when the molten iron enters the furnace; argon is blown from the bottom in the whole process of smelting, the gas flow is increased in the later stage of blowing, and the stirring of a molten pool is enhanced; controlling the end point of the converter to be less than or equal to 0.15 Wt% C and less than or equal to 0.037 Wt% P;

and (3) square billet continuous casting, wherein ladle deslagging detection control is adopted, the pouring temperature of a tundish is 1525-1545 ℃, the tundish uses a common covering agent and common square billet covering slag, and the single flow pulling speed of a casting blank is 2.5-3.2 m/min.

Hot continuous rolling of bars: controlling the heating temperature of a casting blank to 1150-1200 ℃, the heating time of a billet to 60-90 minutes, the initial rolling temperature to 1000-1060 ℃, adopting an 18-frame hot continuous rolling unit, using a cooling control device before finish rolling, and controlling the finish rolling temperature to 850-950 ℃.

In the invention, the following measures are also adopted:

the steel scrap condition of converter molten steel smelting is as follows: the common steel scraps must not use high-chromium Cr steel scraps (such as stainless steel scraps).

The continuous casting process protects the pouring requirement: a protective sleeve is adopted from the ladle to the tundish, the liquid level of molten steel in the tundish is fully covered by a covering agent, and a drain port with a sealing gasket is used from the tundish to the crystallizer, so that the nitrogen increase N of the molten steel is reduced.

Based on the principle, the niobium microalloyed HRB400E hot-rolled ribbed steel bar has the following specific technical measures:

1. reasonable components:

(1) the manganese content. Manganese is dissolved in ferrite and cementite in steel, plays a role in solid solution strengthening, and improves the stability of the undercooled austenite. The excessively high manganese content significantly shifts the pearlite transformation curve to the right in the supercooled austenite isothermal transformation diagram, and as a result, the bainite structure can be obtained when the steel is continuously cooled after austenitizing. Therefore, an excessively high manganese content in the steel is a main cause of the formation of granular bainite.

(2) Nitrogen content. Nitrogen is a strong austenite forming and stabilizing element that is about 20 times as effective as nickel, and it increases austenite stability so that at certain cooling rates, the normal transformation from austenite to the "ferrite + pearlite" structure is incomplete and a portion of the austenite is transformed to granular bainite.

(3) The Cr content. The diffusion speed of Cr in austenite is relatively low, and the diffusion of carbon can be hindered, so that the stability of austenite can be improved, the C curve can be shifted to the right, the critical cooling speed is reduced, the hardenability is improved, and the bainite can be formed.

Properly reducing the Mn content in the steel and improving the Si content according to the influence of each component in the niobium microalloyed steel on bainite; controlling Cr brought by scrap steel; molten steel covering and continuous casting protection pouring after the converter is finished, and the increase of N in the molten steel is reduced; the formation of bainite in steel can be controlled, and the steel bar is controlled not to yield. The weight percentage ranges of the chemical components of the niobium microalloyed HRB400E hot rolled ribbed steel bar are shown in Table 1.

Table 1: niobium microalloying HRB400E hot-rolled ribbed steel bar chemical composition weight percentage range (wt%)

2. And (5) low-temperature rolling. The initial rolling temperature of the niobium microalloyed steel bar is set to be 1000-1060 ℃. For Nb microalloyed steel, the higher initial rolling temperature can increase the amount of niobium dissolved in the steel, and is more favorable for the formation of bainite tissues in the steel during cooling after rolling; meanwhile, the original austenite crystals of the steel billet are coarse due to the higher initial rolling temperature, the larger the austenite grains are, the less the nucleation and the more difficult the phase transformation are when the austenite is transformed into the ferrite and the pearlite in the cooling process after rolling, and more austenite enters the bainite transformation region to form a bainite structure. Therefore, the niobium microalloyed steel bar is different from the conventional microalloyed steel bar, partial dissolution of carbonitride in the steel is not needed when the steel billet is heated and is rolled, and the proper rolling temperature ensures that the solid-solution niobium amount is in a reasonable interval and the austenite grains of the steel billet are not grown.

3. And the finish rolling temperature is lowered. The finish rolling temperature of the niobium microalloyed steel bar is set to 850-950 ℃. The temperature rise is more in the finish rolling process of the deformed steel bar, the controlled cooling equipment is installed before finish rolling, the finish rolling temperature is controlled, the niobium dissolved in the steel is reduced, the finish rolling temperature and the temperature of an upper cooling bed are reduced, the austenite grain growth after rolling is controlled, and the bainite tissue formation is reduced.

The invention discloses a method for controlling the yield-free phenomenon of niobium microalloyed HRB400E hot-rolled ribbed steel bars with the diameter of 12-25 mm by adopting the following component proportions and specific processes. Wherein, table 2 is the composition (in weight percent) of the steels of the respective examples. Table 3 shows the production specifications, process parameters and mechanical properties corresponding to the steels of the examples described in Table 2.

Table 2: examples Steel product chemistry (wt%)

Examples of the invention	C	Si	Mn	P	S	Nb	N	Cr
									Example 1	0.23	0.61	1.305	0.028	0.019	0.025	0.005	0.03
Example 2	0.21	0.60	1.305	0.029	0.020	0.030	0.003	0.05
									Example 3	0.24	0.55	1.291	0.027	0.018	0.022	0.006	0.06
Example 4	0.23	0.58	1.291	0.035	0.022	0.027	0.005	0.07
									Example 5	0.25	0.65	1.291	0.040	0.015	0.020	0.008	0.03

Table 3: production specification, process parameters and mechanical properties corresponding to each embodiment

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. To those skilled in the art; various modifications to these embodiments will be readily apparent, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.