CN1240866C - Refractory steel and manufacturing method thereof - Google Patents

Abstract

The present invention provides refractory steel and a manufacturing method thereof. The steel is characterized in that C, Si, Mn, Cr and Mo are used as main alloy elements, Cu, Nb, V, Ni, Ti, Al, B and RE are appended as trace elements, a controlled rolling technology and a controlled cooling technology are adopted, and carbon equivalent, alloy content and yield ratio are controlled to make the steel have low value and good welding performance. Process control and refractory alloy proportion are used to realize Q235 grade and Q345 grade high performance refractory steel to satisfy the requirements of the material used for national safe fireproof buildings, wherein the steel has the characteristics of atmospheric corrosion resistance and easy welding.

Description

Refractory steel and method for its manufacture

technical field

The invention belongs to the field of metal materials, in particular to refractory low-alloy steel for construction and a manufacturing method thereof.

Background technique

Fire-resistant steel for construction is a kind of low-alloy steel with fire-resistant properties developed in recent years. It plays a decisive role in building structural buildings with their own fire-preventing effects. According to new searches, the fire-resistant steels currently developed internationally, such as the Japanese patent "Fireproof Weldable Weathering Steel" with the patent No. It reaches 600°C within 1-3 hours, and the yield strength drops no less than 2/3 of its normal temperature, and even reaches 700°C, and within 1-3 hours, the yield strength drops no less than 2/3 of its normal temperature, but its resistance to 600°C High-temperature refractory steel does not control the production process and yield ratio, has high alloy content, is expensive, and is not easy to weld. Although the production process of fire-resistant steel resistant to 700°C is controlled, the carbon equivalent and yield strength ratio are not controlled. The cost is expensive, and it belongs to 58kg class fire-resistant steel, which is not suitable for the domestic construction steel market.

Domestic construction steel generally adopts Q235 steel specified in GB700 and Q345 steel specified in GB/T1591. The disadvantage of this type of steel is that it softens when the temperature reaches 350°C and does not have fire resistance.

Wuhan Iron and Steel provides a fire-resistant steel with patent application number 011335629. Although the yield strength of this steel reaches 600°C within 1-3 hours, the drop is not less than 2/3 of its normal temperature, but there is also the problem of not controlling the carbon equivalent and yield strength ratio. However, the disadvantages of high alloy content and high price cannot meet the needs of the domestic structural steel market.

Invention content:

In order to overcome the deficiencies of the prior art, the present invention provides a low-priced fire-resistant steel with excellent welding performance. The steel adopts an appropriate rolling process to control the carbon equivalent, alloy content, and yield ratio to optimize its composition. Q235 and Q345 high-performance refractory steels with excellent performance, which are resistant to atmospheric corrosion and easy to weld by using process control and refractory alloy ratio, can meet the domestic demand for safe and fire-resistant building structural materials.

The fire-resistant steel provided by the invention is mainly composed of C, Si, Mn, Cr, Cr, Cu, Nb, V alloy elements, and Ni, Ti, Al, B, RE trace elements are added. Its chemical composition content (by weight): C 0.01-0.12, Si 0.05-0.55, Mn0.30-1.20, P≤0.030, S≤0.015, Cr 0.30-0.60, Mo 0.20-0.50, Cu0.25-0.50, Nb 0.01-0.04, V O.02-0.05, Ni≤0.20, Ti≤0.015, Al≤0.045, B≤0.0035, RE 0.02-0.20, and the rest is Fe. In the present invention, the main effect of each alloying element is:

C: In order to ensure that the refractory steel can be welded and meet the strength requirements of Q235 steel specified in GB700 and Q345 steel specified in GB/T1591, the C content is required to be 0.01%-0.12%;

Si: Also in order to ensure the weldability and strength requirements of refractory steel, Si is required to be no more than 0.55%, but Si less than 0.05% reduces the conventional strength of refractory steel, so its lower limit is not less than 0.05%.

Mn: Mn content higher than 1.2% is not conducive to welding, but too low Mn has no effect on the control of rear rolling, so the Mn content is controlled at 0.3%-1.2%.

P and S are harmful elements in steel, the lower the better, usually P≤0.030%, S≤0.015%.

Cr: Cr contributes to the improvement of the high temperature performance of steel. When the Cr content exceeds 0.30%, the refractory steel has the effect of atmospheric corrosion resistance, especially when added with Mo, it not only improves the high temperature performance of the steel, but also improves the salt spray resistance of the steel The ability to corrode makes fire-resistant steel more suitable for coastal areas; Cr content higher than 0.60% is meaningless, and increases the cost and carbon equivalent; due to the addition of Cr and Mo, the yield strength of 600 ° C for 1-3 hours can be achieved The amount of Mo added that is not lower than 2/3 of the normal temperature is reduced to less than 0.40%, so as to meet the index requirements of fire-resistant steel, and the price is low. In order to realize that the yield strength of fire-resistant steel at 600°C for 1-3 hours is not lower than 2/3 of its normal temperature, the optimum alloy ratio is: 0.40%≤Cr+Mo+Nb+V≤1.00%.

Mo: Mo is an element that must be added to fire-resistant steel to achieve fire resistance. When it is required that the yield strength at 600 ° C for 1-3 hours is not lower than 2/3 of its normal temperature, the Mo content must be greater than 0.20%; when it is added at the same time as Cr, the upper limit of Mo exceeding 0.40% is meaningless. When Mo is not added simultaneously with Cr, the upper limit of Mo should be increased to 0.50%.

Cu: The addition of Cu in refractory steel is to further improve the strength and atmospheric corrosion resistance of the steel. If fire-resistant steel is considered to be used in coastal areas or the atmospheric corrosion resistance is not emphasized, Cu and Ni may not be added. A Cu content exceeding 0.50% will lead to adverse consequences such as cracks on the steel surface, an increase in carbon equivalent, and an increase in cost; if it is less than 0.25%, the effect of resisting atmospheric corrosion will be reduced.

Ni: Adding Cu must add Ni. Ni is added to alleviate the steel surface cracks caused by adding Cu, and Ni also has a certain ability to resist atmospheric corrosion. There is a 1:3 correspondence between the addition of Ni and Cu. Its maximum content does not exceed 0.20%.

The addition of Nb, V, Ti, B, Als, and RE is to control the grain growth of the steel during heating, and to obtain finer grains during rolling, so as to obtain a fire-resistant steel with good comprehensive properties. Composite precipitates also contribute to high temperature performance. In addition, the addition of Ti is beneficial to improve the aging resistance of steel; the addition of V is beneficial to improve the yield strength of steel under the effect of controlled cooling process. For steel over a certain thickness specification, adding an appropriate amount of B and cooperating with the rolling process can achieve the conventional performance and high temperature performance of refractory steel. When the refractory steel is further required to improve the performance at room temperature and high temperature, purify the steel quality, increase the negative temperature impact energy and further improve the corrosion resistance of the steel, RE alloys can be added to the steel. In the production of refractory steel, at least two or more of Nb, V, Ti, B, Als, and RE should be added at the same time. Among them, the addition of Nb and V should be controlled at 0.01%-0.04% and 0.02%-0.05%, Ti≤0.015%, B≤0.0035%, Al≤0.045%, and RE (addition) 0.02%-0.20%.

Ceq: For steel plates below 40mm, Ceq≤0.43% is required, while for steel plates above 40mm, Ceq≤0.45% is defined in consideration of the characteristics of refractory steel site welding, and the carbon equivalent is in accordance with: Ceq＝C+Mn/6+ (Cr+Mo+v)/5+(Ni+Cu)/15(%) calculation, so this fire-resistant steel is suitable for manual welding and automatic welding.

To realize the present invention, a controlled rolling + controlled cooling process is adopted in the manufacturing process, and the steel billet is heated to 1100°C-1300°C for controlled rolling, that is: above 1000°C, the reduction is ≥ 40%, and the remaining rolling amount is at It is completed below 930°C, and the final rolling temperature is controlled at 840°C-890°C. The controlled cooling process is as follows: thin steel plates below 16mm are hot-rolled and air-cooled; thick steel plates above 16mm are rolled and cooled at a speed of 4°C-20°C/S from 800°C-830°C to 650°C, and then air-cooled.

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

1. The fire-resistant steel provided by the present invention forms Q235～Q345 strength series, and Mn-Mo, Cr-Mo-Nb series Q235 grade and Mo-Nb, Cr-Mo-Nb-Cu, Cr-Mo-Nb-V The series of Q345 grade fire-resistant steel achieves low cost and meets the multi-level requirements of the construction market.

2. The present invention strictly controls the carbon equivalent (Ceq), and can meet the requirements of welding in construction steel structures such as manual and automatic welding.

3. The present invention has good comprehensive performance. Negative temperature shock can reach C, D, E grade quality. The Z-direction performance meets the requirements of Z35.

4. The present invention improves the fire resistance limit of steel. Welded refractory H-beams equivalent to 36b steel beams and Q345 steel girders are loaded with 142KN under the condition of bare steel firing, and the fire-resistant limit of refractory H-beams reaches 36 minutes (870°C), which meets the IV class fire protection stipulated in the national building design fire protection code Meet the 30-minute requirement. The Q345 steel beam only reaches 28 minutes (827°C), which is difficult to meet the specification requirements

5. The present invention comes with atmospheric corrosion resistance, by adding Cr, Mo, Cu, Ni, RE and other elements that can improve the atmospheric corrosion resistance of steel, especially when these elements are added in combination, the atmospheric corrosion resistance can be further improved .

6. The present invention also has anti-seismic performance, and the test proves that the yield strength ratio of steel plates over 16mm is not greater than 0.80. Made into a steel structure, it has the function of absorbing earthquake energy, so the seismic performance of the steel structure is improved.

Detailed ways

According to the formula and manufacturing process provided by the present invention to produce fire-resistant steel, its chemical composition is listed in Table 1, and the corresponding mechanical properties are listed in Table 2.

Table 1 Implementation of the chemical composition of the fire-resistant steel (%) Example C Si mn P S Cr Mo Nb V Cu Re Ceq 1 0.095 0.30 0.78 0.008 0.004 0.058 0.40 0.32 2 0.06 0.25 0.48 0.005 0.003 0.38 0.24 0.033 0.26 3 0.08 0.22 0.86 0.01 0.003 0.47 0.30 0.022 0.02 0.38 4 0.052 0.15 0.82 0.015 0.015 0.51 0.32 0.035 0.36 5 0.045 0.22 0.93 0.021 0.011 0.53 0.34 0.022 0.33 0.40 6 0.066 0.30 1.05 0.011 0.007 0.49 0.34 0.29 0.02 0.43

※RE is based on the amount added

Table 2 The mechanical properties of this fire-resistant steel Example Rp _0.2 MPa RmMPa Rp _0.2 /Rm A% Rel600℃MPa AKV-20°CJ state 1 270 390 0.6923 34 176 82, 86, 74 hot rolled 2 325 415 0.7831 39 173 100, 106, 82 hot rolled 3 430 550 0.78 26 260 270, 242, 262 hot rolled 4 430～455 545～555 0.789～0.82 24～26 345～350 100, 107 Hot rolling + controlled cooling 5 370～375 535～570 0.658～0.69 26～31 255～275 34, 53 hot rolled 6 325～370 530～565 0.6132～0.6549 12～33 255 82,88 hot rolled

Claims (2)

1. A fire-resistant steel for construction, which is mainly composed of C, Si, Mn, Cr, Mo, Cu, Nb, and V alloy elements, with Ni, Ti, Al, B, and RE trace elements added, and the chemical composition content (according to Weight percent) is: C 0.01～0.12, Si 0.05～0.55, Mn 0.30～1.20, P≤0.030, S≤0.015, Cr 0.30～0.60, Mo 0.20～0.50, Cu 0.25～0.50, Nb 0.01～0.04, V 0.02 ～0.05, Ni≤0.20, Ti≤0.015, Al≤0.045, B≤0.0035, RE 0.02～0.20, and the rest is Fe; it is characterized in that: the carbon equivalent in steel is calculated according to Ceq=C+Mn/6+(Cr+Mo +V)/5+(Ni+Cu)/15(%) formula, Ceq≤0.43% for steel plates with a thickness of less than 40mm; Ceq≤0.45% for steel plates with a thickness of more than 40mm; the ratio of alloy content is 0.4%≤ Cr+Mo+Nb+V≤1.00% control. 2. A method for manufacturing fire-resistant steel for construction as claimed in claim 1, characterized in that: it is produced by controlled rolling + controlled cooling process, the steel is rolled above 1000°C, the reduction is ≥ 40%, and the rest is rolled The production volume is completed below 930°C, the final rolling temperature is 840°C~890°C, and the controlled cooling process after rolling is: air cooling for thin steel plates below 16mm after rolling; Speed, cooling from 800°C-830°C to 650°C, then air cooling.