WO2022267173A1 - High-strength, low-temperature-resistant h-shaped steel for marine engineering tempering treatment and preparation method thereoffor - Google Patents

Abstract

High-strength, low-temperature-resistant H-shaped steel for marine engineering tempering treatment and a preparation method therefor. The chemical components of the H-shaped steel comprise according to percentage by weight: C: 0.09-0.15, Si≤0.5, Mn: 1.0-1.6, V: 0.04-0.59, Nb: 0.01-0.03, Ni: 0.51-0.7, P≤0.02, S≤0.005, Cr: 0.51-0.7, B: 0.001-0.002, Al: 0.02-0.05, N≤0.014, O≤0.004, and the remainder is Fe and inevitable impurities. The H-shaped steel for marine engineering has a yield strength which is greater than 610 MPa, a tensile strength which is greater than 700 MPa, and in particular longitudinal impact power which is greater than 50 J at -40°C.

Description

A quenched and tempered high-strength low-temperature-resistant H-shaped steel for marine engineering and its preparation method

Cross References to Related Applications

This application claims priority to Chinese Patent Application No. 202110686708.7 filed on June 21, 2021, which is hereby incorporated by reference in its entirety.

technical field

The invention belongs to the technical field of metallurgy and heat treatment, and in particular relates to a quenched and tempered high-strength low-temperature-resistant H-shaped steel for marine engineering and a preparation method thereof.

Background technique

With the increasing demand for oil and natural gas, oil and gas exploitation has shown a situation where land and sea are advancing side by side. Offshore engineering equipment has broad prospects and a rapid development momentum. With the increasing development of polar oil and gas resources in many countries, the number of oil platforms in polar regions has gradually increased. The low temperature environment also puts forward more stringent requirements for steel used in offshore oil platforms. On the one hand, transportation costs need to be reduced, and on the other hand, the polar -50°C environment also raises the requirements for the low-temperature performance of steel materials. Therefore, the low temperature toughness must also be satisfied while ensuring the strength of the steel used in polar ocean engineering. H-beams with complex sections can play an important role in reducing weight, prolonging service life, increasing speed, increasing freight volume and reducing logistics costs. Especially with the rapid development of marine engineering to deeper and colder regions, there is an urgent need for high-strength, high-toughness H-shaped steel. The yield strength of traditional low-alloy ferritic + pearlitic H-beams is generally below 500MPa. Although microalloying technology can break through the strength to a certain extent, it is very difficult to ensure other properties, such as welding performance. With the growing demand for strength grade H-beams, how to develop high-strength H-beams above 600MPa over 345MPa, 420MPa and other lower-grade H-beams has become a common technical problem faced by the industry.

At present, my country's H-beam manufacturers have developed yield strength to ensure that the strength and other indicators of the steel meet the standard requirements, and they are all produced by hot rolling with the addition of higher content alloy elements Nb, V, and Mn. Different companies prepare steel products for marine engineering with different grades and comprehensive properties according to their equipment levels.

The Chinese patent application with the application number 201810341054.2 discloses a high-strength and toughness hot-rolled H-shaped steel for low temperature and its preparation method. The chemical composition of the steel is: C: 0.05-0.17%, Si: 0.15-0.35%, Mn: 1.0～2.0%, P: 0.005～0.015%, S: 0.005～0.015%, N: 0.003～0.007%, O: 0.002～0.005%, Ti: 0.01～0.02%, Al: 0.005～0.015%, Mg: 0.001 ～0.005%, B: 0.001～0.002%, Cr: 0～0.5%, Mo: 0～0.5%, and the balance is Fe and impurity elements. The high-strength and toughness hot-rolled H-shaped steel for low temperature is adopted by oxide metallurgy technology , Refining inclusions, after rolling and two-stage rapid cooling after rolling, the yield strength of this kind of H-beam is below 600MPa.

Publication No. CN 102644032B patent relates to a cooling method after rolling of high weather resistance hot-rolled H-shaped steel with yield strength of 550MPa. : 0.30～0.60, Mn: 1.25～1.50, P: 0.010～0.030, S: 0.001～0.015, Cu: 0.20～0.35, Cr: 0.20～0.40, Ni: 0.15～0.30, V: 0.10～0.12, N: 0.008 ～0.014, Als: 0.003～0.030, and the rest are iron and residual trace impurities; the H-beam adopts two-stage rapid cooling after rolling; by adopting two-stage rapid cooling method after H-beam hot rolling, the fine-grain strengthening, The mechanism of precipitation strengthening and phase transformation strengthening results in a multi-phase structure dominated by bainite.

Both of the above two high-strength H-shaped steels and their preparation technologies adopt micro-alloying and on-line controlled cooling to achieve increased strength. However, due to the limitation of equipment capabilities, under the condition of ensuring low temperature toughness, the strength level cannot achieve a higher level of breakthrough, and at the same time, there is a defect of uneven distribution of the overall structure.

Contents of the invention

In order to meet the needs of marine engineering in the complex environment of polar and extremely cold regions, the present invention provides a quenched and tempered high-strength low-temperature-resistant H-shaped steel for marine engineering and its preparation method, that is, high-strength H-shaped steel for marine engineering, which is hot-rolled and used offline Quenching and tempering treatment method to achieve a yield strength of 610MPa and above.

The chemical composition of the H-shaped steel is as follows: C: 0.09～0.15; Si: ≤0.5; Mn: 1.0～1.6; V: 0.04～0.59; Nb: 0.01～0.03; Ni: 0.51～0.7; P≤0.02 ; S≤0.005; Cr: 0.51～0.7; B: 0.001～0.002; Al: 0.02～0.05; N≤0.014; O≤0.004; the rest are iron Fe and unavoidable impurities.

Preferably, C: 0.10-0.13; Si: 0.2-0.3; Mn: 1.2-1.4; V: 0.045-0.55; Nb: 0.02-0.03; Ni: 0.55-0.65; P≤0.015; S≤0.005; Cr:0.50 ～0.6; B: 0.001～0.0015; Al: 0.03～0.04; N≤0.012; O≤0.004; the rest are iron Fe and unavoidable impurities.

The invention provides a method for preparing high-strength and low-temperature-resistant H-shaped steel for marine engineering. The production and preparation process mainly includes converter smelting, LF refining, continuous casting and hot rolling forming. The specific steps are as follows:

1) Pre-desulfurization of molten iron:

After desulfurization, the sulfur content in the molten iron is guaranteed to be ≤0.019wt%; the As content is controlled below 0.008wt%.

2) Smelting:

The slag must be added 3 minutes before the end point, and the basicity of the final slag should be controlled within the range of 2.4 to 3.2. The tapping process with double slag blocking is adopted, the steel putting time is not less than 2min, and the amount of slag lowered by the converter is controlled to be less than 85mm. Ferro-Al-Mn is used for deoxidation, and the amount of Ferro-Al-Mn added is 1.6-3.8kg/t steel, which can be added according to the situation before the furnace; ferrochrome and vanadium nitrogen are used for alloying. Among them, the addition amount of medium-carbon ferrochromium is 10.1-11.8kg/t, and the addition amount of vanadium nitrogen is 0.6-1.1kg/t. Bottom blowing argon and stirring throughout the refining process to ensure soft argon blowing for more than 15 minutes in refining. In order to ensure smooth production, feed calcium line 80-160m/furnace before refining out of the station.

3) Continuous casting:

The liquid level of the tundish in the continuous casting process is ≥800mm, and the full protection pouring process is adopted; the casting speed is controlled at 0.9-1.1m/min.

4) Hot rolling:

During the rolling process, the soaking temperature of the heating furnace is 1150-1230°C, and the billet stays in the furnace for 110-180 minutes; the starting temperature of the rough rolling is 1050-1130°C, and the finish rolling is carried out on the TM three-stand continuous rolling mill , the water cooling between the stands is fully turned on, and the final rolling temperature is 800-850°C; the precision and size control is strictly carried out during the rolling process, and the cooling bed air cooling method is adopted after rolling.

5) Offline heat treatment:

In order to obtain the ultra-fine structure, the hot-rolled H-beam is first subjected to off-line normalizing treatment, the normalizing temperature is controlled at 890-950°C, and the holding time is controlled at 30-100min according to the thickness of the flange, and air-cooled cooling treatment is carried out after being released from the furnace; The rolled H-shaped steel is quenched off-line, the quenching temperature is controlled at 850-900°C, and then high-temperature tempering and straightening are performed. According to different sizes, the quenching process controls the amount of water sprayed on the flange and web, and the quenching is uniform. The tempering temperature is controlled at 450-600° C., and the holding time is 25-60 minutes, so as to finally obtain an ultrafine tempered sorbite structure with a martensite morphology. During the tempering process, the precipitation of microalloy carbonitrides such as V(C,N) plays a role in precipitation strengthening, compensating for the weakening of the dislocation strengthening effect caused by dislocation recovery, and improving the tempering stability of the steel.

6) Straightening process

Straighten the heat-treated steel at a temperature below 200°C to avoid bending problems, ensure the size is qualified, and finally pack it into bundles.

The invention adopts low-carbon micro-alloying process design, combined with the heat treatment process control of section steel pass on-line rolling + off-line normalizing + quenching + medium temperature tempering, and through phase transformation strengthening + precipitation strengthening, the yield strength for marine engineering is obtained above 610MPa Industrialized production of large and medium-sized H-beam products. The invention mainly obtains fine tempered sorbite structure to realize phase transformation strengthening, and at the same time cooperates with fine second phase particles such as V(C,N) to realize precipitation strengthening.

The operation that the present invention does not mention all can adopt prior art.

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

1) The present invention is suitable for preparing composite microalloying composition design of ultra-fine micron-scale tempered sorbite structure + nano-scale second phase particles, so as to obtain high-strength hot-rolled H-shaped steel for marine engineering with yield strength above 610MPa.

2) The structure uniformity of the H-shaped steel for marine engineering prepared by the present invention using the quenching and tempering treatment of off-line normalizing + quenching + medium temperature tempering is high. Compared with the H-shaped steel web prepared by other methods, the flange strength and toughness tend to be more uniform. The strength difference between the edge and the web is within 20MPa;

3) The present invention adopts V microalloying, the heating temperature is reduced, the rolling force is reduced, the rolling load of the equipment is reduced, and the precipitation strengthening effect in the later stage is remarkable;

4) The present invention relates to H-shaped steel products for marine engineering, which have good mechanical properties, yield strength greater than 610MPa, tensile strength greater than 700MPa, especially the longitudinal impact energy at -40°C greater than 50J, realizing lightweight preparation of offshore oil platforms, suitable for polar alpine regions use.

Description of drawings

Fig. 1 is the tissue diagram obtained in Example 2 of the present invention.

detailed description

The present invention will be further described below in conjunction with specific examples.

Example

The invention provides a preparation method of quenched and tempered high-strength and low-temperature-resistant H-shaped steel for marine engineering. The preparation method includes desulfurization, converter smelting, LF refining, full-protection continuous casting, rolling process and off-line quenching+tempering heat treatment process.

The continuous casting slabs in the following examples are all prepared according to the following process flow: according to the set chemical composition range (Table 1), the chemical composition C, Si, Mn, S, P and Fe are used as raw materials for converter smelting and refining , Continuous casting, billet heating or soaking directly. The preparation steps of embodiment 1-3 are as follows:

1. Pre-desulfurization of molten iron:

After desulfurization, the sulfur content in the molten iron is guaranteed to be ≤0.019wt%; the As content is controlled below 0.008%.

2. Smelting:

The basicity of the final slag is controlled within the range of 2.4 to 3.2. The tapping process with double slag blocking is adopted, the steel putting time is not less than 2min, and the amount of slag lowered by the converter is controlled to be less than 85mm. Al-Mn-Fe is added in an amount of 1.6-3.8kg/t steel for deoxidation; metal manganese and vanadium nitrogen are used for alloying. Bottom-blown argon gas is stirred throughout the refining process to ensure soft argon blowing for 15-20 minutes during refining, and 80-160m/furnace of calcium wire is fed before refining out of the station.

3. Continuous casting:

The casting speed in the continuous casting process is controlled at 0.9-1.0m/min.

4. Hot rolling and quenching and tempering heat treatment:

The hot rolling process is controlled according to different specifications. The whole process is mainly based on temperature control. The final rolling temperature is detected on the outside of the flange, and the rolled material is naturally cooled in the cooling bed after rolling. The chemical composition and concrete technology of embodiment 1-3 are shown in the table below.

Table 1 chemical composition (wt%, balance iron)

The hot rolling process conditions of Examples 1-3 are shown in Table 2. According to the standard GB/T 2975-2018 "Mechanical Properties Test Sampling Location and Sample Preparation of Steel and Steel Products"; the test methods for yield strength, tensile strength and elongation refer to the standard GB/T228-2002 "Metal Materials Tensile at Room Temperature Test method"; the impact energy test method refers to the standard ISO 148-1 "Charpy pendulum impact test of metal materials", the results are shown in Table 2.

Table 2 Section Steel Rolling Process

It can be seen from the table that the yield strength of Examples 1-3 of the present invention maintains the level of 610MPa, and its -40°C impact energy is relatively high, which can meet the requirements for the preparation of low-temperature resistant marine steel, and is suitable for the production of offshore oil platforms and other structures with high low-temperature toughness requirements. Supporting structural members. As shown in Figure 1 is the microstructure diagram of Example 2.

Table 3 mechanical properties

The conventional technical knowledge in this field can be used for the contents not described in detail in the present invention.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limit them. Although the present invention has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that modifications or equivalent replacements to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all should be covered by the present invention. within the scope of the claims.

Claims (7)

1. A quenched and tempered high-strength low-temperature-resistant H-shaped steel for marine engineering, characterized in that the chemical composition of the H-shaped steel is calculated by weight percentage, including: C: 0.09-0.15; Si: ≤0.5; Mn: 1.0-1.6 ; V: 0.04～0.59; Nb: 0.01～0.03; Ni: 0.51～0.7; P≤0.02; ≤0.004; the rest are iron Fe and unavoidable impurities.
2. According to claim 1, the quenched and tempered high-strength and low-temperature-resistant H-shaped steel for marine engineering is characterized in that the yield strength of the H-shaped steel is greater than 610MPa, the tensile strength is greater than 700MPa, and the longitudinal impact energy at -40°C is greater than 50J.
3. A method for preparing high-strength and low-temperature-resistant H-shaped steel for quenching and tempering treatment for marine engineering, comprising the following steps:

   1) Pre-desulfurization of molten iron: the sulfur content in the molten iron is ≤0.019wt%; the As content is controlled below 0.008wt%;

   2) Smelting:

   The slag material must be added 3 minutes before the end point, and the final slag basicity is controlled within the range of 2.4 to 3.2; the double-block slag tapping process is adopted, the steel discharge time is not less than 2 minutes, and the amount of slag lowered by the converter is controlled <85mm;

   3) Continuous casting:

   The liquid level of the tundish in the continuous casting process is ≥800mm, and the full protection pouring process is adopted; the casting speed is controlled at 0.9-1.1m/min;

   4) Hot rolling:

   During the rolling process, the soaking temperature of the heating furnace is 1150-1230°C, and the billet stays in the furnace for 110-180 minutes; the starting temperature of rough rolling is 1050-1130°C, and the finish rolling temperature is 800-850°C; Cooling bed air cooling is adopted after rolling;

   5) Offline heat treatment:

   First, the hot-rolled H-beam is subjected to off-line normalizing treatment, the normalizing temperature is controlled at 890-950°C, the holding time is controlled at 30-100min, and air-cooling is performed after being released from the furnace;

   Then the hot-rolled H-shaped steel undergoes off-line quenching treatment, the quenching temperature is controlled at 850-900°C, and then high-temperature tempering and straightening treatment is performed; the tempering temperature is controlled at 450-600°C, and the holding time is 25-60min;

   6) Straightening process

   The heat-treated steel is straightened at a temperature below 200°C, and finally bundled and packaged.
4. The preparation method according to claim 3, characterized in that, said step 2) also includes the use of Almanganese Ferrodeoxidation, the addition of Almanganese Ferromanganese is 1.6-3.8kg/t steel, and alloying is carried out by using Ferrochromium and Vanadium Nitrogen , the amount of medium-carbon ferrochromium added is 10.1-11.8kg/t, and the amount of vanadium nitrogen added is 0.6-1.1kg/t.
5. The preparation method according to claim 3, characterized in that, in the step 2), argon gas is blown at the bottom and argon is stirred throughout the refining process, and argon is blown softly for more than 15 minutes; before refining, 80-160m/furnace of calcium wire is fed.
6. The preparation method according to claim 3, characterized in that, in the step 4), the finish rolling is carried out on the TM three-stand continuous rolling mill, and the water cooling between the stands is all opened; the rolling process is strictly controlled for accuracy and size, and after rolling Adopt cooling bed air cooling method.
7. The preparation method according to claim 3, characterized in that the strength difference between the flange and the web of the H-shaped steel in the step 5) is within 20 MPa.

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