A method for corrosion fatigue regulation of low-alloy high-strength steel used in marine environment

Abstract

The application provides a low-alloy high-strength steel corrosion fatigue regulation method for a marine environment, and steps include: using TMCP process to obtain a finished steel, and each component in the finished steel is as follows: according to mass percentage, C accounts for 0.08% to 0.12%, Si accounts for 0.2% to 0.25%, Mn accounts for 1.6% to 1.8%, S accounts for less than or equal to 0.01%, Cr accounts for 0.55% to 0.6%, Ni accounts for 1.15% to 1.2%, Mo accounts for 0.15% to 0.2%, Nb accounts for 0.02% to 0.15%, and the rest is Fe and inevitable impurities; and the obtained finished steel is sequentially subjected to homogenization treatment, cold rolling treatment, solid solution treatment and aging treatment. By using the scheme of the application, the corrosion fatigue of the low-alloy high-strength steel can be significantly regulated on the basis of fine adjustment of element content, and in particular, on the basis of fine adjustment of C, Si, Mn and Nb, the regulation of process parameters realizes that the fatigue number variation of the low-alloy high-strength steel is up to about 60,000 times; the high-strength steel component design in the application is simple, the workpiece is short, easy to regulate, and the manufacturing cost is low.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-strength steel performance regulation, and particularly relates to a low-alloy high-strength steel corrosion fatigue regulation method for marine environment. BACKGROUND

[0002] Research shows that the strengthening and toughening mechanism of the nanometer precipitated phase in the steel and the mechanism of improving the fatigue performance mainly lie in the dispersion strengthening and grain refinement of the nanometer precipitated phase. Taking Nb as an example, in the high-temperature rolling process, Nb(C, N) is induced to precipitate on the dislocation line due to strain, and the Nb atoms dissolved in the austenite matrix tend to segregate to the grain boundary due to the size effect, thereby hindering the movement of the new grain boundary after the austenite recrystallization. The combination of this precipitate pinning and solute drag effect hinders the recrystallization and grain growth of the austenite, effectively refines the austenite grains, and generates fine ferrite grains after phase transformation; on the other hand, the Nb dissolved in the matrix can hinder the gamma to alpha phase transformation, delay the phase transformation to a lower temperature, refine the grains, and hinder the formation of ferrite, which is beneficial to the formation of high-strength and high-toughness acicular ferrite and bainite ferrite, thereby improving the mechanical properties of the steel.

[0003] The low-alloy high-strength marine engineering steel represented by E690 steel has a typical structure of bainite. The dispersion strengthening and grain refinement mechanisms of the C, N compounds nanometer precipitated phase of the micro-alloying elements such as Nb can further strengthen and toughen. However, the influence rule and mechanism of the nanometer Nb(C, N) precipitated phase in the E690 steel on the marine environment corrosion, especially the corrosion fatigue, are still unclear.

[0004] For the low-alloy high-strength steel used in marine environment, the corrosion fatigue condition is directly related to the service life of the steel, therefore, it is necessary to clarify the corrosion fatigue mechanism of the low-alloy high-strength steel, and in particular, how to accurately regulate the corrosion fatigue condition of the low-alloy high-strength steel in the case of adding Nb is a problem to be solved. SUMMARY

[0005] At least to solve the technical problems mentioned in the background, the present application aims to provide a low-alloy high-strength steel corrosion fatigue regulation method for marine environment.

[0006] The present application adopts the following technical scheme.

[0007] A low-alloy high-strength steel corrosion fatigue regulation method for marine environment, the steps comprising:

[0008] Step 1, using TMCP process to obtain finished steel,

[0009] The components of the finished steel are as follows: C accounts for 0.08% to 0.12%, Si accounts for 0.2% to 0.25%, Mn accounts for 1.6% to 1.8%, S accounts for ≤0.01%, Cr accounts for 0.55% to 0.6%, Ni accounts for 1.15% to 1.2%, Mo accounts for 0.15% to 0.2%, Nb accounts for 0.02% to 0.15%, and the rest is Fe and inevitable impurities;

[0010] Step 2, the obtained finished steel is sequentially subjected to homogenization treatment, cold rolling treatment, solid solution treatment and aging treatment.

[0011] Further, the finished steel is homogenized at 1200℃ and then water-cooled to room temperature, and then cold-rolled, with a deformation of 50% to 80%.

[0012] Further, the temperature of the solid solution treatment is controlled at 800℃ to 950℃, and the holding time is 15 to 60 minutes.

[0013] Further, the temperature of the aging treatment is controlled at 480℃, and the time is controlled at 6 hours, and then water-cooled.

[0014] As preferred, when the C accounts for 0.11% in the finished steel, Si accounts for 0.21%, Mn accounts for 1.65%, S accounts for ≤0.01%, Cr accounts for 0.6%, Ni accounts for 1.2%, Mo accounts for 0.18%, and Nb accounts for 0.071%;

[0015] The temperature of the TMCP process is controlled at 1200℃, and the time is controlled at 24 hours; the cold rolling deformation after quenching is 72%; the temperature of the solid solution treatment is controlled at 880℃, and the holding time is 30 minutes.

[0016] As preferred, when the C accounts for 0.10% in the finished steel, Si accounts for 0.22%, Mn accounts for 1.66%, S accounts for ≤0.01%, Cr accounts for 0.57%, Ni accounts for 1.16%, Mo accounts for 0.18%, and Nb accounts for 0.088%;

[0017] The temperature of the TMCP process is controlled at 1200℃, and the time is controlled at 24 hours; the cold rolling deformation after quenching is 77%; the temperature of the solid solution treatment is controlled at 900℃, and the holding time is 45 minutes.

[0018] In the application, on the basis of "C accounts for 0.11%, Si accounts for 0.21%, Mn accounts for 1.65%, S accounts for <=0.01%, Cr accounts for 0.6%, Ni accounts for 1.2%, Mo accounts for 0.18%, Nb accounts for 0.071%", and corresponding process parameters thereof, when it is needed to adjust the corrosion fatigue performance of the low-alloy high-strength steel to meet the lower requirement of corrosion fatigue resistance, one is to control the decrease of C content, the increase of Si content, the increase of Mn content, the decrease of Cr content, the decrease of Ni content, the increase of Mo content, and the decrease of Nb content; the other is to control the decrease of the cold rolling deformation after quenching and the decrease of the temperature of solid solution treatment.

[0019] In the application, on the basis of "C accounts for 0.1%, Si accounts for 0.22%, Mn accounts for 1.66%, S accounts for <=0.01%, Cr accounts for 0.57%, Ni accounts for 1.16%, Mo accounts for 0.18%, Nb accounts for 0.088%", and corresponding process parameters thereof, when it is needed to adjust the corrosion fatigue performance of the low-alloy high-strength steel to meet the higher requirement of corrosion fatigue resistance, one is to control the increase of C content, the increase of Si content, the increase of Mn content, the increase of Cr content, the increase of Ni content, the increase of Mo content, and the increase of Nb content; the other is to control the decrease of the cold rolling deformation after quenching and the increase of the temperature of solid solution treatment.

[0020] In the application, the variable control of other elements in the regulation process is 0.01% except Fe, S and Nb.

[0021] Beneficial effects: by adopting the scheme of the application, the corrosion fatigue of the low-alloy high-strength steel can be significantly regulated on the basis of the micro-adjustment of the element content, especially on the basis of the micro-adjustment of C, Si, Mn and Nb, and the regulation of the process parameters, so that the fatigue resistance of the low-alloy high-strength steel is changed by about 60,000 times; the component design of the high-strength steel in the application is simple, the workpiece is short, easy to regulate, and the manufacturing cost is low. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is the process flowchart in the embodiment.

[0023] Figure 2 It is the metallographic graph of the low-alloy high-strength steel (E690) with NbC precipitated phase in the embodiment 4;

[0024] Figure 3 It is the metallographic graph of the low-alloy high-strength steel (E690) with NbC precipitated phase in the embodiment 5;

[0025] Figure 4 It is the metallographic graph of the low-alloy high-strength steel (E690) with NbC precipitated phase in the embodiment 2. DETAILED DESCRIPTION

[0026] The technical solutions in the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0027] Embodiment 1

[0028] A low-alloy high-strength steel corrosion fatigue regulation method for marine environment, comprising the following steps:

[0029] Step 1, using TMCP process (temperature control at 1200℃ after heating, holding time control at 24 hours, and then quenching) to prepare E690 finished steel,

[0030] In this embodiment, the components in the E690 finished steel are as follows: C accounts for 0.1%, Si accounts for 0.22%, Mn accounts for 1.7%, S accounts for 0.01%, Cr accounts for 0.58%, Ni accounts for 1.18%, Mo accounts for 0.2%, Nb accounts for 0.021%, and the rest is Fe and inevitable impurities;

[0031] Step 2, sequentially performing cold rolling treatment, solid solution treatment and aging treatment on the obtained E690 finished steel; wherein the E690 finished steel is uniformly treated at 1200℃, and then water-cooled to room temperature, and then cold-rolled with a deformation of 60%; the solid solution treatment is controlled at a temperature of 830℃ for 15 minutes; the aging treatment is controlled at a temperature of 480℃ for 6 hours, and then water-cooled to obtain E690 low-alloy high-strength steel.

[0032] Embodiment 2

[0033] A low-alloy high-strength steel corrosion fatigue regulation method for marine environment, comprising the following steps based on the embodiment 1:

[0034] Step 1, using TMCP process (temperature control at 1200℃ after heating, holding time control at 24 hours, and then quenching) to prepare E690 finished steel,

[0035] In this embodiment, the components in the E690 finished steel are as follows: C accounts for 0.09%, Si accounts for 0.23%, Mn accounts for 1.68%, S accounts for 0.01%, Cr accounts for 0.59%, Ni accounts for 1.19%, Mo accounts for 0.19%, Nb accounts for 0.045%, and the rest is Fe and inevitable impurities;

[0036] Step 2, the obtained E690 finished steel is sequentially subjected to cold rolling treatment, solid solution treatment and aging treatment; the E690 finished steel is subjected to homogenization treatment at 1200 DEG C and then water cooled to room temperature, and then cold rolled with a deformation of 65%; the solid solution treatment is controlled at a temperature of 850 DEG C for 20 minutes; the aging treatment is controlled at a temperature of 480 DEG C for 6 hours, and then water cooled to obtain the E690 low alloy high strength steel.

[0037] Example 3

[0038] A low alloy high strength steel corrosion fatigue regulation method for marine environment, when it is needed to adjust the corrosion fatigue resistance of E690 high strength steel to meet higher corrosion fatigue resistance requirements (relative to the corrosion fatigue resistance of E690 high strength steel in Example 2), the element content and process parameters are regulated on the basis of Example 2, and the steps include:

[0039] Step 1, the TMCP process (temperature control at 1200 DEG C after heating, holding time control at 24 hours, and then quenching) is used to prepare E690 finished steel,

[0040] In this embodiment, the components in the E690 finished steel are as follows: C accounts for 0.11%, Si accounts for 0.21%, Mn accounts for 1.65%, S accounts for 0.009%, Cr accounts for 0.6%, Ni accounts for 1.2%, Mo accounts for 0.18%, Nb accounts for 0.071%, and the rest is Fe and inevitable impurities;

[0041] Step 2, the obtained E690 finished steel is sequentially subjected to cold rolling treatment, solid solution treatment and aging treatment; wherein the E690 finished steel is subjected to homogenization treatment at 1200 DEG C and then water cooled to room temperature, and then cold rolled with a deformation of 72%; the solid solution treatment is controlled at a temperature of 880 DEG C for 30 minutes; the aging treatment is controlled at a temperature of 480 DEG C for 6 hours, and then water cooled to obtain the E690 low alloy high strength steel.

[0042] Example 4

[0043] A low alloy high strength steel corrosion fatigue regulation method for marine environment, when it is needed to adjust the corrosion fatigue resistance of E690 high strength steel to meet lower corrosion fatigue resistance requirements (relative to the corrosion fatigue resistance of E690 high strength steel in Example 3), the element content and process parameters are regulated on the basis of Example 3, and the steps include:

[0044] Step 1, the TMCP process (temperature control at 1200 DEG C after heating, holding time control at 24 hours, and then quenching) is used to prepare E690 finished steel,

[0045] In the embodiment, the components of the E690 finished steel are as follows: C accounts for 0.1%, Si accounts for 0.22%, Mn accounts for 1.66%, S accounts for 0.008%, Cr accounts for 0.57%, Ni accounts for 1.16%, Mo accounts for 0.18%, Nb accounts for 0.088%, and the rest is Fe and inevitable impurities;

[0046] Step 2, sequentially performing cold rolling treatment, solid solution treatment and aging treatment on the obtained E690 finished steel; wherein the E690 finished steel is uniformly treated at 1200℃ and then water-cooled to room temperature, and then cold-rolled, with a deformation of 77%; the temperature of the solid solution treatment is controlled at 900℃, and the holding time is 45 minutes; the temperature of the aging treatment is controlled at 480℃, and the time is controlled at 6 hours, and then water-cooled to obtain the E690 low-alloy high-strength steel.

[0047] Embodiment 5

[0048] A method for regulating the corrosion fatigue resistance of a low-alloy high-strength steel used in a marine environment, which regulates the content of each element and the process parameters on the basis of Embodiment 4, and the steps include:

[0049] Step 1, using a TMCP process (temperature control at 1200℃ after heating, holding time control at 24 hours, and then quenching) to prepare an E690 finished steel,

[0050] In the embodiment, the components of the E690 finished steel are as follows: C accounts for 0.11%, Si accounts for 0.24%, Mn accounts for 1.74%, S accounts for 0.01%, Cr accounts for 0.58%, Ni accounts for 1.19%, Mo accounts for 0.17%, Nb accounts for 0.124%, and the rest is Fe and inevitable impurities;

[0051] Step 2, sequentially performing cold rolling treatment, solid solution treatment and aging treatment on the obtained E690 finished steel; wherein the E690 finished steel is uniformly treated at 1200℃ and then water-cooled to room temperature, and then cold-rolled, with a deformation of 78%; the temperature of the solid solution treatment is controlled at 930℃, and the holding time is 50 minutes; the temperature of the aging treatment is controlled at 480℃, and the time is controlled at 6 hours, and then water-cooled to obtain the E690 low-alloy high-strength steel.

[0052] Comparative Embodiment 1

[0053] A method for regulating the corrosion fatigue resistance of a low-alloy high-strength steel used in a marine environment, which regulates the content of each element and the process parameters on the basis of Embodiment 4, and the steps include:

[0054] Step 1, using a TMCP process (temperature control at 1200℃ after heating, holding time control at 24 hours, and then quenching) to prepare an E690 finished steel,

[0055] In the embodiment, the components of the E690 finished steel are as follows: C accounts for 0.98%, Si accounts for 0.2%, Mn accounts for 1.77%, S accounts for 0.011%, Cr accounts for 0.59%, Ni accounts for 1.2%, Mo accounts for 0.2%, and the rest is Fe and inevitable impurities;

[0056] Step 2, sequentially performing cold rolling treatment, solid solution treatment and aging treatment on the obtained E690 finished steel; wherein the E690 finished steel is uniformly treated at 1200 DEG C and then water-cooled to room temperature, and then cold-rolled with a deformation of 70%; the temperature of the solid solution treatment is controlled at 900 DEG C with 40 minutes of heat preservation; the temperature of the aging treatment is controlled at 480 DEG C with 6 hours of time control, and then water-cooled to obtain the E690 steel.

[0057] Comparative Example 2

[0058] A low-alloy high-strength steel corrosion fatigue regulation method for marine environment, on the basis of the embodiment 5, the element content and process parameters are regulated, and the steps comprise:

[0059] Step 1, using TMCP process (temperature control at 1200 DEG C after heating, heat preservation time control at 24 hours, and then quenching) to prepare E690 finished steel,

[0060] In the embodiment, the components of the E690 finished steel are as follows: C accounts for 0.98%, Si accounts for 0.2%, Mn accounts for 1.77%, S accounts for 0.011%, Cr accounts for 0.59%, Ni accounts for 1.2%, Mo accounts for 0.2%, and the rest is Fe and inevitable impurities;

[0061] Step 2, sequentially performing cold rolling treatment, solid solution treatment and aging treatment on the obtained E690 finished steel; wherein the E690 finished steel is uniformly treated at 1200 DEG C and then water-cooled to room temperature, and then cold-rolled with a deformation of 70%; the temperature of the solid solution treatment is controlled at 900 DEG C with 40 minutes of heat preservation; the temperature of the aging treatment is controlled at 480 DEG C with 6 hours of time control, and then water-cooled to obtain the E690 steel.

[0062] Comparative Example 3

[0063] A low-alloy high-strength steel corrosion fatigue regulation method for marine environment, on the basis of the embodiment 3, the element content and process parameters are regulated, and the steps comprise:

[0064] Step 1, using TMCP process (temperature control at 1200 DEG C after heating, heat preservation time control at 24 hours, and then quenching) to prepare E690 finished steel,

[0065] In the embodiment, the components of the E690 finished steel are as follows: C accounts for 0.96%, Si accounts for 0.22%, Mn accounts for 1.78%, S accounts for 0.01%, Cr accounts for 0.57%, Ni accounts for 1.17%, Mo accounts for 0.18%, and the rest is Fe and inevitable impurities;

[0066] Step 2, the obtained E690 finished steel is sequentially subjected to cold rolling treatment, solid solution treatment and aging treatment; wherein the E690 finished steel is uniformly treated at 1200℃ and then water-cooled to room temperature, and then cold-rolled, with a deformation of 70%; the temperature of the solid solution treatment is controlled at 880℃, and the holding time is 50 minutes; the temperature of the aging treatment is controlled at 480℃, and the time is controlled at 6 hours, and then water-cooled to obtain the E690 steel.

[0067] The E690 high-strength steel in the embodiment and the E690 steel in the comparative embodiment are subjected to corrosion fatigue experiments. The mechanical parameters are selected as follows: a corrosion fatigue experiment machine with adjustable stress ratio, loading frequency and waveform is used to perform seawater corrosion fatigue experiments. Since the stress ratio is related to the overall corrosion or pitting corrosion of the steel surface, the transgranular or intergranular cracking, according to the previous experimental results in the laboratory, two kinds of typical fixed cyclic stress parameters (R=0.75 and 0.95, f=1Hz, the stress peak value is 80% of the yield strength, and the loading waveform is a sine wave, and the loading direction is axial) are selected to obtain two different surface corrosion and cracking types. Environmental factors are simulated as follows: artificial seawater is used, and the experimental temperature, seawater dissolved oxygen content, hydrostatic pressure, pH value and the like are simultaneously adjusted to simulate the changes with the depth of seawater.

[0068] The experimental results are shown in Table 1,

[0069] Table 1 is the corrosion fatigue of the E690 high-strength steel in the embodiment and the E690 steel in the comparative embodiment

[0070]

[0071] As can be seen from Table 1, the E690 high-strength steel in Example 3 and Example 4 can withstand a larger number of fatigue loads than the steels in the other examples and the comparative example, which indicates that the E690 high-strength steel after adding Nb can significantly prevent corrosion fatigue, and the process parameters of cold rolling and solid solution also significantly affect the corrosion fatigue of the E690 high-strength steel, and Example 3 and Example 4 correspond to the best combination of Nb content, cold rolling deformation and solid solution process parameters.

[0072] In this invention, Nb carbon and nitrogen compounds form a large number of dispersed nano-precipitates in E690 steel. These Nb(C) nano-precipitates in E690 steel not only improve the mechanical properties of high-strength low-alloy steel but also enhance its corrosion resistance in marine environments, particularly significantly improving its resistance to stress corrosion and hydrogen-induced cracking under hydrogen-containing conditions. The nano-precipitates improve corrosion resistance by improving the steel's microstructure (including improving microstructure uniformity and phase homogeneity, refining grains, reducing dislocation density, increasing the proportion of small-angle grain boundaries, and adjusting the number and distribution of different types of solid lattice grain boundaries), reducing C supersaturation, and decreasing internal stress. The nanoscale size of the precipitates makes their influence as a cathode phase negligible. Due to the dispersed distribution of the nano-precipitates, a large number of high-energy hydrogen traps are formed, trapping hydrogen atoms, reducing the hydrogen content in the crystal lattice, and inhibiting matrix activation, thus improving corrosion resistance. Simultaneously, the dispersed hydrogen traps inhibit hydrogen migration and accumulation, reducing the steel's tendency for hydrogen-induced cracking and hydrogen-induced stress corrosion.

[0073] Observation of the microstructure of the E690 high-strength steel prepared in the examples revealed that coarse NbC precipitates appeared in the metallographic image of Example 2. Figure 4 As indicated by the middle arrow, coarse (highlighted) particles appear in the metallographic image of Example 4. Figure 3 The metallographic image in Example 5 shows only a small amount of NbC precipitates, while the circled image shows a large number of fine NbC precipitates. This indicates that the simultaneous presence of relatively large and fine NbC precipitates in the alloy steel demonstrates excellent corrosion fatigue resistance. The solution in this invention can significantly control the corrosion fatigue of E690 high-strength steel by finely adjusting the element content. In particular, by finely adjusting C, Si, Mn, and Nb (with a single adjustment amount of only 0.01%) in conjunction with process parameter control, the fatigue resistance of E690 high-strength steel can be varied up to approximately 60,000 cycles. The high-strength steel composition design in this invention is simple, the workpiece is short, easy to control, and the manufacturing cost is low.

Claims

1. A method for controlling corrosion fatigue resistance of low-alloy high-strength steel for marine environments, characterized by the following steps: include: Step 1: The finished steel is produced by the TMCP process. The temperature in the TMCP process is controlled at 1200℃ and the time is controlled at 24 hours. The components of the finished steel, by mass percentage, are: C 0.11%, Si 0.21%, Mn 1.65%, S 0.009%, Cr 0.6%, Ni 1.2%, Mo 0.18%, Nb 0.071%, with the remainder being Fe and unavoidable impurities; Step 2: The resulting finished steel is subjected to homogenization treatment, cold rolling treatment, solution treatment and aging treatment in sequence; The cold rolling deformation is 72%; the solution treatment temperature is controlled at 880℃ and held for 30 minutes. The aging treatment temperature was controlled at 480℃, the time was controlled at 6 hours, and then water cooling was performed. When it is necessary to adjust the corrosion fatigue resistance of low-alloy high-strength steel to meet the requirements of lower corrosion fatigue resistance, the following measures should be taken: First, control the C content to decrease, the Si content to increase, the Mn content to increase, the Cr content to decrease, the Ni content to decrease, the Mo content to increase, and the Nb content to decrease; second, control the cold rolling deformation after quenching to reduce, and lower the solution treatment temperature.

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