Binary Alloy Design Method For Marine Stress Corrosion-resistant High-strength Low-alloy (hsla) Stress Corrosion-resistant Steel

Abstract

A binary alloy design method for a marine high-strength low-alloy (HSLA) stress corrosion-resistant steel is provided. The binary alloy design method permits synergistic inhibition of anodic dissolution and hydrogen embrittlement by binary alloying to prepare the marine HSLA stress corrosion-resistant steel, the marine HSLA stress corrosion-resistant steel has an increase of more than 50% in stress corrosion resistance in a simulated SO.sub.2 polluted marine atmospheric environment. Microalloying of one element is carried out to improve properties of a rust layer on a surface of a HSLA steel in a marine environment and reduce a electrochemical activity in a local microenvironment to inhibit the anodic dissolution. Microalloying of another element is carried out to reduce a cathodic hydrogen evolution, to increase a hydrogen trap density and to decrease a multiplicative hydrogen diffusion channel density as well as enhance a hydrogen resistance of a structure to inhibit the hydrogen embrittlement.

Description

CROSS REFERENCE TO THE RELATED APPLICATIONS

[0001] This application is based upon and claims priority to Chinese Patent Application No. 202011424195.4, filed on Dec. 8, 2020, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

[0002] The present disclosure belongs to the field of alloy composition design of high-strength low-alloy (HSLA) steels, and in particular, relates to a binary alloy design method for a marine HSLA stress corrosion-resistant steel.

BACKGROUND

[0003] At present, with continuous marine resource development, the service conditions for marine engineering equipment are getting worse and worse. Engineering low-alloy steels are faced with severer stress corrosion which even leads to serious industrial accidents. For example, on Nov. 22, 2013, an explosion occurred in the Huangdao district of Qingdao (a coastal city in China) at the intersection of an urban oil pipeline and a discharge culvert due to corrosion-induced thinning and breakage of the pipeline. The accident caused heavy casualties and huge economic losses. Therefore, stress corrosion has posed a serious threat to the service safety of HSLA steels. However, almost none of the existing protective measures have afforded a special consideration for stress corrosion. Actually, only the toughness and basic corrosion resistance of high-performance HSLA steels are emphasized, while the stress corrosion resistance thereof is neglected.

[0004] It is necessary to get a clear understanding of the mechanisms of stress corrosion first during the research and development of HSLA stress corrosion-resistant steels. Existing studies have shown that the general mechanisms of stress corrosion cracking in the marine environment are anodic dissolution and hydrogen embrittlement, which typically exhibit the characteristics of the composite mechanism of anodic dissolution and hydrogen embrittlement.

[0005] The mechanism of anodic dissolution is related to a local microenvironment. In the marine environment, the enrichment of Cl.sup.- at the bottom of a rust layer leads to acidification of the environment and accelerates the process of local corrosion. In an acidic Cl.sup.--enriched local microenvironment, spot corrosion pits are initiated and developed rapidly under strong self-catalytic action, providing effective nucleation sites for the initiation and propagation of microcracks and resulting in anodic dissolution induced stress corrosion cracking.

[0006] The mechanism of hydrogen embrittlement is related to the diffusion, distribution and concentration of hydrogen atoms in a steel. During a hydrogen evolution reaction of an electrochemical cathode, hydrogen atoms can diffuse into the steel matrix and gather in various defects and stress distortion regions. Once a local hydrogen atom concentration reaches a critical hydrogen concentration, it will lead to the initiation and propagation of cracks and hence hydrogen embrittlement induced stress corrosion cracking.

[0007] Therefore, the stress corrosion cracking in the marine environment is usually caused by the two synergistic mechanisms as described above. It is desirable to prevent the synergistic effect of the two mechanisms by using technical means so as to avoid the stress corrosion cracking in the marine environment.

[0008] In view of this, the stress corrosion resistance of a HSLA steel is improved creatively by alloying against anodic dissolution and hydrogen embrittlement in the present disclosure. In other words, alloying is conducted to render the two corresponding mechanisms inoperative simultaneously with no adverse effect on the toughness and corrosion resistance of the marine HSLA steel.

[0009] Specifically, the following two aspects are involved.

[0010] In one aspect, by alloying, the destructive action of a corrosive element in a rust layer is weakened, accompanied with reduction of local acidification degree, inhibition of the mass transfer or electrochemical process of a corrosive medium, and alleviation of anodic dissolution at the bottom of the rust layer.

[0011] In the other aspect, by alloying, hydrogen evolution is inhibited, while a hydrogen trap density in steel is increased or a multiplicative hydrogen diffusion channel density is decreased, thus allowing for reduction of the total amount of diffusible hydrogen in steel, uniform distribution of hydrogen in steel, reduction of local accumulation of hydrogen, and cooperative inhibition of hydrogen embrittlement.

[0012] Such a binary alloy design method can permit synergistic inhibition of the mechanisms of anodic dissolution and hydrogen embrittlement of HSLA steels in the marine environment, significant improvement of the stress corrosion resistance of HSLA steels, and reduction of the stress corrosion risk. However, the new method of backward design has not yet been proposed.

[0013] Based on the mechanisms of stress corrosion, the present disclosure provides a binary microalloy design method against the mechanisms of anodic dissolution and hydrogen embrittlement. The method can improve the stress corrosion resistance of a HSLA steel in the marine environment by alloying of a plurality of elements.

SUMMARY

[0014] An objective of the present disclosure is to provide a binary alloy design method for a marine HSLA stress corrosion-resistant steel. A HSLA steel designed by this method can have a significant decrease in stress corrosion sensitivity in the marine environment compared with control groups.

[0015] The present disclosure provides a binary alloy design method for a marine HSLA stress corrosion-resistant steel, where synergistic inhibition of anodic dissolution and hydrogen embrittlement is achieved by binary alloying to prepare 690 MPa marine HSLA stress corrosion-resistant steel, so that the 690 MPa marine HSLA steel has an increase of more than 50% in stress corrosion resistance in a simulated SO.sub.2 polluted marine atmospheric environment.

[0016] Preferably, one of two alloying elements used in the binary alloying is one or more alloying elements that are capable of improving enrichment of Cl.sup.- in a rust layer and thus induced acidification in the marine environment while reducing the electrochemical activity of a matrix in an acidic Cl.sup.--containing environment, while the other one is one or more alloying elements that are capable of inhibiting cathodic hydrogen evolution in the marine environment, forming irreversible hydrogen traps and improving a microstructure.

[0017] Preferably, the inhibiting cathodic hydrogen evolution in the marine environment may be achieved by reducing an electric current density for hydrogen evolution; the forming irreversible hydrogen traps may be achieved by increasing a hydrogen trap density in the steel; and the improving a microstructure may be achieved by enhancing hydrogen resistance at special interfaces.

[0018] Preferably, the alloying element for inhibiting the anodic dissolution (anti-corrosion element for short) is selected from the group consisting of P, Sb, Co, Cr, Ni, Cu, Mo, Re, Zr, Ca, Mg, and dispersive oxides thereof, and the alloying element for inhibiting the hydrogen embrittlement is (anti-damage element for short) is selected from the group consisting of Nb, V, Ti, Zr, Re, Mo and W.

[0019] Preferably, the marine HSLA stress corrosion-resistant steel may be composed of the following chemical elements in mass percentage: C: 0.04%-0.08%, Si: 0.2%-0.3%, Mn: 1.45%-1.65%, P.ltoreq.0.015%, S.ltoreq.0.005%, Cr: 0.4%-0.5%, Cu: 0.25%-0.35%, Ni: 0.75%-0.85%, Ti: 0.005%-0.015%, Nb: 0.03%-0.06%, Sb: 0.05%-0.1%, and the balance of Fe.

[0020] Preferably, the HSLA stress corrosion-resistant steel may be prepared specifically by the following process:

[0021] smelting and casting chemical components into billet steel, heating the billet steel to an austenitizing temperature ranging from 1180 to 1220.degree. C., holding the temperature for 1.5-2.5 hours to homogenize the billet steel for hot rolling; controlling an initial rolling temperature within a range of 980-1020.degree. C., carrying out multi-pass rolling until a target steel plate thickness is obtained, and controlling a finishing rolling temperature within a range of 860900.degree. C.; after rolling, cooling in a laminar water flow zone at a cooling rate controlled within a range of 25-30.degree. C./s, thereby ensuring that the billet steel is at a temperature ranging from 420 to 440.degree. C. when taken out of water; and finally, air-cooling to room temperature, thus obtaining the finished marine HSLA stress corrosion-resistant steel.

[0022] Preferably, a slow strain rate tensile test may be conducted on the finished marine HSLA stress corrosion-resistant steel under the following conditions: SO.sub.2 polluted marine atmospheric environment simulated by using 3.5 wt % NaCl+0.05 M NaHSO.sub.3 with 100% humidity; experimental temperature: room temperature; and a slow strain tension rate: 0.5*10.sup.-6 to 1.5*10.sup.-6 S.sup.-1.

[0023] Preferably, the loss of elongation percentage and the loss of section shrinkage percentage of the HSLA steel may be calculated to evaluate the stress corrosion sensitivity of the finished marine HSLA stress corrosion-resistant steel in the simulated SO.sub.2 polluted marine atmospheric environment.

[0024] Preferably, the loss of elongation percentage of the HSLA steel may be 11.05%-15.21%, while the loss of section shrinkage percentage may be 12.1%-14.33%, with a maximum decrease of approximate 60% in the stress corrosion sensitivity compared with a traditional HSLA steel.

[0025] The binary alloy design method of the present disclosure is achieved by the following technical solutions:

[0026] Alloying element design against the mechanism of anodic dissolution: the anodic dissolution is one of the major mechanisms during the stress corrosion cracking of a HSLA steel in the marine environment, which is related to a corrosive microenvironment and the electrochemical activity of a matrix. The enrichment of Cl.sup.- at the bottom of a rust layer in the marine environment can induce spot corrosion. Acidification at the bottom in spot corrosion pits accelerates dissolution and microcracks are initiated under the action of stress, thus resulting in anodic dissolution induced stress corrosion cracking. Therefore, an alloying element against the mechanism of anodic solution is required to be effective in: first, alleviating enrichment of Cl.sup.- in a rust layer and thus induced acidification in the marine environment; and second, reducing the electrochemical activity of a matrix in an acidic Cl.sup.--containing environment. Investigations with respect to the effects in the two aspects revealed that the alloying of trace amount of element Sb could alleviate the enrichment of Cl.sup.- in the rust layer, weaken local acidification and reduce the electrochemical activity of a low-alloy steel in the acidic Cl.sup.--containing environment, with a potential effect of inhibiting the mechanism of anodic solution.

[0027] The microalloying element Sb can improve the corrosion resistance of a low-alloy steel in the acidic Cl.sup.--containing environment, specifically by facilitating the redeposition of element Cu and oxides thereof in the acidic Cl.sup.--containing environment by synergistic action with Cu in steel, thereby enhancing the microalloying effect of Cu. Moreover, Sb can form Sb2O3 and Sb2O5 that are hardly soluble in acidic environment and may gather on the inner side of the rust layer to improve the properties of the rust layer. Under this action, Sb is microalloyed and thus enabled to reduce the electrochemical activity and alleviate the enrichment of Cl.sup.- and acidification in the rust layer, thus achieving the effect of inhibiting the anodic dissolution. In the present disclosure, the inhibiting effect of Sb present in a particular amount on the anodic dissolution has been demonstrated by conducting tests on high-strength steels different in content of Sb in simulated marine atmospheric environment with respect to stress corrosion sensitivity. When the content of Sb was 0.05%, the inhibiting effect of Sb microalloying was not obvious; and when the content of Sb was 0.1%, the inhibiting effect of Sb microalloying was significant.

[0028] Alloying element design against the mechanism of hydrogen embrittlement: the mechanism of hydrogen embrittlement is related to the concentration, diffusion and distribution of hydrogen atoms in steel. Cathodic hydrogen evolution reaction is the main way for hydrogen to enter a steel matrix in the marine environment. A higher electric current density for hydrogen evolution and longer hydrogen evolution reaction time will result in a higher concentration of hydrogen atoms in steel. Hydrogen traps in steel determine the diffusion and distribution of hydrogen atoms, and a higher density and more uniform distribution of hydrogen traps reflect a higher trapping ability of the hydrogen traps, and hence a smaller concentration of diffusible hydrogen in steel, a lower diffusion ability of hydrogen and a lower degree of hydrogen accumulation. Furthermore, the hydrogen resistance at special interfaces in steel such as grain boundaries and phase boundaries have direct influence on the initiation and propagation of hydrogen-induced cracks. Therefore, an alloy element against the mechanism of hydrogen embrittlement is required to be effective in: first, inhibiting the cathodic hydrogen evolution in the marine environment and reducing an electric current density electric current; second, forming irreversible hydrogen traps and increasing a hydrogen trap density in steel; and third, improving a microstructure and enhancing hydrogen resistance at special interfaces. Investigations with respect to the above multiple effects revealed that the alloying of trace amount of element Nb could reduce the cathodic process in an acidic Cl.sup.--containing environment and form dispersively distributed fine precipitated phase in steel to increase a hydrogen trap density in steel, optimize the microstructure and enhance the hydrogen resistance of grain boundaries and phase boundaries, with a potential effect of inhibiting the mechanism of hydrogen embrittlement.

[0029] Nb is an important microalloying element for improving hydrogen behaviors in steel. The microalloying of Nb can reduce the cathodic hydrogen evolution and help to reduce the total hydrogen concentration in steel. Moreover, Nb can form a large amount of stable, fine and dispersed nano-sized NbC precipitated phase with element C in steel. With the NbC precipitated phase, the mechanical properties of steel can be improved by grain refining and precipitation strengthening. Besides, the NbC precipitated phase can serve as high-energy hydrogen traps to trap hydrogen, thereby reducing the concentration of diffusible hydrogen, alleviating local hydrogen enrichment and improving the hydrogen resistance of the structure. These effects enable Nb microalloying to achieve the effect of inhibiting the mechanism of hydrogen embrittlement. In the present disclosure, the inhibiting effect of Nb present in a particular amount on the hydrogen embrittlement has been demonstrated by conducting tests on high-strength steels different in content of Nb in simulated marine atmospheric environment with respect to stress corrosion sensitivity. When the content of Nb was 0.03%, the inhibiting effect of Nb microalloying was not obvious; when the content of Nb was 0.06%, the inhibiting effect of Nb microalloying was good; and when the content of Nb was 0.09%, part of Nb was accumulated in an inclusion, so that the content of the precipitated phase was not significantly increased, and the inhibiting effect of Nb microalloying was not significantly enhanced in this case.

[0030] The above-mentioned technical solutions of the present disclosure have the following advantages:

[0031] The two effects of inhibiting the anodic dissolution and the hydrogen embrittlement by alloying are the core idea of the binary alloy design in the present disclosure, and there are no specific limitations to the number and levels of alloying elements for achieving the effects. The effects can be achieved by an arbitrary combination of an element (such as Sb, Sn, and Mo) for inhibiting the anodic dissolution and an element (such as Nb, V, and Ti) for inhibiting the hydrogen embrittlement. The illustrated elements Sb and Nb are merely representative alloying elements, which means two or more alloying elements can be used in the present disclosure. The elements each in a particular amount can be used for microalloying or in low alloying design and main alloying design. A HSLA designed by the binary alloy method as described above can be used in the marine environment or in other environments in which stress corrosion cracking may occur.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The technical solutions in embodiments of the present disclosure will be further described clearly and completely in conjunction with the accompanying drawings therein.

[0033] FIG. 1A shows a transmission electron microscope (TEM) image of precipitated phases in an example of a binary alloy design method for a marine HSLA stress corrosion-resistant steel of the present disclosure.

[0034] FIG. 1B shows a TEM of precipitated phases in comparative example 1 of a binary alloy design method for a marine HSLA stress corrosion-resistant steel of the present disclosure.

[0035] FIG. 1C shows a TEM image of precipitated phases in comparative example 5 of a binary alloy design method for a marine HSLA stress corrosion-resistant steel of the present disclosure.

[0036] FIG. 2 shows a graph of electrochemical polarization curves in an example and comparative examples 1-5 of a binary alloy design method for a marine HSLA stress corrosion-resistant steel of the present disclosure.

[0037] FIG. 3A shows interface morphology and element distribution images of rust layers in an example of a marine HSLA stress corrosion-resistant steel of the present disclosure.

[0038] FIG. 3B shows interface morphology and element distribution images of rust layers in comparative example 1 of a marine HSLA stress corrosion-resistant steel of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] To make the technical problem to be solved, technical solutions and advantages of the present disclosure clearer, the present disclosure will be described in detail below with reference to the accompanying drawings and specific examples.

[0040] The technical problem to be solved in the present disclosure is how to improve the stress corrosion resistance of a HSLA steel in the marine atmospheric environment.

[0041] To solve the above technical problem, the present disclosure provides a binary alloy design method for a marine HSLA stress corrosion-resistant steel, where synergistic inhibition of anodic dissolution and hydrogen embrittlement is achieved by binary alloying to prepare 690 MPa marine HSLA stress corrosion-resistant steel, so that the 690 MPa marine HSLA steel has an increase of more than 50% in stress corrosion resistance in a simulated SO.sub.2 polluted marine atmospheric environment.

[0042] In particular, one of two alloying elements used in the binary alloying is one or more alloying elements that are capable of alleviating enrichment of Cl.sup.- in a rust layer and thus induced acidification in the marine environment while reducing the electrochemical activity of a matrix in an acidic Cl.sup.--containing environment, while the other one is one or more alloying elements that are capable of inhibiting cathodic hydrogen evolution in the marine environment, forming irreversible hydrogen traps and improving a microstructure.

[0043] In particular, the inhibiting cathodic hydrogen evolution in the marine environment is achieved by reducing an electric current density for hydrogen evolution; the forming irreversible hydrogen traps is achieved by increasing a hydrogen trap density in the steel; and the improving a microstructure is achieved by enhancing hydrogen resistance at special interfaces.

[0044] In particular, the alloying element for inhibiting the anodic dissolution (anti-corrosion element for short) is selected from the group consisting of P, Sb, Co, Cr, Ni, Cu, Mo, Re, Zr, Ca, Mg, and dispersive oxides thereof, and the alloying element for inhibiting the hydrogen embrittlement is (anti-damage element for short) is selected from the group consisting of Nb, V, Ti, Zr, Re, Mo and W.

[0045] In particular, the marine HSLA stress corrosion-resistant steel is composed of the following chemical elements in mass percentage: C: 0.04%-0.08%, Si: 0.2%-0.3%, Mn: 1.45%-1.65%, P.ltoreq.0.015%, S.ltoreq.0.005%, Cr: 0.4%-0.5%, Cu: 0.25%-0.35%, Ni: 0.75%-0.85%, Ti: 0.005%-0.015%, Nb: 0.03%-0.06%, Sb: 0.05%-0.1%, and the balance of Fe.

[0046] In particular, the marine HSLA stress corrosion-resistant steel is prepared specifically by the following process:

[0047] smelt and cast chemical components into billet steel, heat the billet steel to an austenitizing temperature ranging from 1180 to 1220.degree. C., hold the temperature for 1.5-2.5 hours to homogenize the billet steel for hot rolling; control an initial rolling temperature within a range of 980-1020.degree. C., carry out multi-pass rolling until a target steel plate thickness is obtained, and control a finishing rolling temperature within a range of 860-900.degree. C.; after rolling, cool in a laminar water flow zone at a cooling rate controlled within a range of 25-30.degree. C./s, thereby ensuring that the billet steel is at a temperature ranging from 420 to 440.degree. C. when taken out of water; and finally, air-cool to room temperature, thus obtaining the finished marine HSLA stress corrosion-resistant steel.

[0048] In particular, a slow strain rate tensile test is conducted on the finished marine HSLA stress corrosion-resistant steel under the following conditions: SO.sub.2 polluted marine atmospheric environment simulated by using 3.5 wt % NaCl+0.05 M NaHSO.sub.3 with 100% humidity; experimental temperature: room temperature; and a slow strain tension rate: 0.5*10.sup.-6 to 1.5*10.sup.-6 S.sup.-1.

[0049] In particular, the loss of elongation percentage and the loss of section shrinkage percentage of the HSLA steel are calculated to evaluate the stress corrosion sensitivity of the finished marine HSLA stress corrosion-resistant steel in the simulated SO.sub.2 polluted marine atmospheric environment.

[0050] In particular, the loss of elongation percentage of the HSLA steel is 11.05%-15.21%, while the loss of section shrinkage percentage is 12.1%-14.33%, with a maximum decrease of approximate 60% in the stress corrosion sensitivity compared with a traditional HSLA steel.

[0051] The binary alloy design method for a marine HSLA stress corrosion-resistant steel is now specifically described with reference to the following examples and the accompanying drawings.

[0052] 1. Table 1 shows chemical components in weight percentage in an example and comparative examples of HSLA steels obtained by the binary alloy design method of the present disclosure.

[0053] 2. The above chemical components were smelted in a 25 kg vacuum induction furnace to obtain billet steel.

[0054] 3. A steel plate was obtained by a controlled rolling and cooling process. Specifically, the billet steel was heated to an austenitizing temperature of 1200.degree. C., and the temperature was kept for 2 hours to homogenize the billet steel. The billet steel was then cooled in the furnace to an initial rolling temperature of 1000.degree. C. and subjected to 15 passes of reciprocating rolling into a 12 mm steel plate, with a finishing rolling temperature controlled within a range of 860-900.degree. C. After rolling, the steel plate was cooled in a laminar water flow zone at a cooling rate controlled within a range of 25-30.degree. C./s, ensuring that the billet steel was at a temperature ranging from 420 to 440.degree. C. when taken out of water. Subsequently, the steel plate was air-cooled to room temperature.

[0055] 4. Slow strain rate tensile tests were conducted on example 1 and comparative examples 1-5 under the following conditions: SO.sub.2 polluted marine atmospheric environment simulated by using 3.5 wt % NaCl+0.05 M NaHSO.sub.3 with 100% humidity; experimental temperature: room temperature; and a slow strain tension rate: 1*10.sup.-6 S.sup.-1.

[0056] 5. The loss of elongation percentage and the loss of section shrinkage percentage of the HSLA steel were calculated to evaluate the stress corrosion sensitivity of the finished marine HSLA stress corrosion-resistant steel in the simulated SO.sub.2 polluted marine atmospheric environment.

[0057] Table 2 shows the comparison of stress corrosion sensitivity between example 1 and comparative examples 1, 2, 3, 4, and 5 in the simulated SO.sub.2 polluted marine atmospheric environment. As can be seen from the table, the stress corrosion sensitivity of the steel constantly decreased with the addition of elements Nb and Sb. When 0.06% of Nb and 0.10% of Sb were added simultaneously, the HSLA steel had significantly reduced stress corrosion sensitivity in the simulated SO.sub.2 polluted marine atmospheric environment as compared with comparative example 1, with a maximum decrease of approximate 60%.

TABLE-US-00001 TABLE 1 Chemical Components (mass %) of Alloys of Example and Comparative Examples in the Present Disclosure Component C Si Mn P S Cr Cu Ni Ti Nb Sb Example 0.053 0.23 1.52 0.009 0.002 0.47 0.32 0.80 0.008 0.06 0.10 Comparative 0.059 0.24 1.55 0.009 0.002 0.47 0.31 0.81 0.012 / / Example 1 Comparative 0.055 0.21 1.47 0.009 0.003 0.45 0.32 0.80 0.008 0.03 / Example 2 Comparative 0.060 0.25 1.58 0.008 0.002 0.49 0.31 0.78 0.010 0.06 / Example 3 Comparative 0.044 0.24 1.54 0.011 0.002 0.45 0.32 0.83 0.015 / 0.05 Example 4 Comparative 0.060 0.24 1.55 0.009 0.002 0.47 0.32 0.80 0.015 / 0.10 Example 5

TABLE-US-00002 TABLE 2 Comparison of Stress Corrosion Sensitivity Between Example and Comparative Examples in the Present Disclosure Comparative Comparative Comparative Comparative Comparative Example example 1 example 2 example 3 example 4 example 5 Loss of elongation 11.05 26.01 19.18 17.11 26.34 16.33 percentage, % Loss of section 12.1 19.29 16.04 15.19 24.52 16.18 shrinkage percentage, %

[0058] To sum up, the two effects of inhibiting the anodic dissolution and the hydrogen embrittlement by alloying are the core idea of the binary alloy design in the present disclosure, and there are no specific limitations to the number and levels of alloying elements for achieving the effects. The effects can be achieved by an arbitrary combination of an anti-corrosion element (such as Sb, Sn, and Mo) and an anti-corrosion damage element (such as Nb, V, and Ti). The illustrated elements Sb and Nb are merely representative alloying elements, which means two or more alloying elements can be used in the present disclosure. The elements each in a particular amount can be used for microalloying or in low alloying design and main alloying design. A HSLA designed by the binary alloy method as described above can be used in the marine environment or in other environments in which stress corrosion cracking may occur.

[0059] The foregoing are descriptions of preferred embodiments of the present disclosure. It should be noted that a person of ordinary skill in the art can make several improvements and modifications without departing from the principle of the present disclosure, and such improvements and modifications should be deemed as falling within the protection scope of the present disclosure.

Claims

1. A binary alloy design method for a marine high-strength low-alloy (HSLA) stress corrosion-resistant steel, wherein a synergistic inhibition of an anodic dissolution and a hydrogen embrittlement is achieved by a binary alloying to prepare a 690 MPa marine HSLA stress corrosion-resistant steel, wherein the 690 MPa marine HSLA stress corrosion-resistant steel has an increase of more than 50% in a stress corrosion resistance in a simulated SO.sub.2 polluted marine atmospheric environment.

2. The binary alloy design method according to claim 1, wherein a first one of two alloying elements used in the binary alloying is one or more alloying elements for an alleviating enrichment of Cl.sup.- in a rust layer and thus an induced acidification in a marine environment while reducing an electrochemical activity of a matrix in an acidic Cl.sup.--containing environment, while a second one of the two alloying elements is one or more alloying elements for inhibiting a cathodic hydrogen evolution in the marine environment, forming irreversible hydrogen traps and improving a microstructure.

3. The binary alloy design method according to claim 2, wherein the cathodic hydrogen evolution in the marine environment is inhibited by reducing an electric current density for an hydrogen evolution; the irreversible hydrogen traps are formed by increasing a hydrogen trap density in the marine HSLA stress corrosion-resistant steel; and the microstructure is improved by enhancing a hydrogen resistance at special interfaces.

4. The binary alloy design method according to claim 1, wherein an alloying element for inhibiting the anodic dissolution is selected from the group consisting of P, Sb, Co, Cr, Ni, Cu, Mo, Re, Zr, Ca, Mg, and dispersive oxides of P, Sb, Co, Cr, Ni, Cu, Mo, Re, Zr, Ca, and Mg, and the alloying element for inhibiting the anodic dissolution is abbreviated as anti-corrosion element for short; and an alloying element for inhibiting the hydrogen embrittlement is selected from the group consisting of Nb, V, Ti, Zr, Re, Mo and W, and the alloying element for inhibiting the hydrogen embrittlement is abbreviated as anti-damage element for short.

5. The binary alloy design method according to claim 1, wherein the marine HSLA stress corrosion-resistant steel is composed of following chemical elements in a mass percentage: C: 0.04%-0.08%, Si: 0.2%-0.3%, Mn: 1.45%-1.65%, P.ltoreq.0.015%, S.ltoreq.0.005%, Cr: 0.4%-0.5%, Cu: 0.25%-0.35%, Ni: 0.75%-0.85%, Ti: 0.005%-0.015%, Nb: 0.03%-0.06%, Sb: 0.05%-0.1%, and a balance of Fe.

6. The binary alloy design method according to claim 1, wherein the marine HSLA stress corrosion-resistant steel is prepared specifically by the following steps: smelting and casting chemical components into a billet steel, heating the billet steel to an austenitizing temperature ranging from 1180 to 1220.degree. C., holding the austenitizing temperature for 1.5-2.5 hours to homogenize the billet steel for a hot rolling; controlling an initial rolling temperature within a range of 980-1020.degree. C., carrying out a multi-pass rolling until a target steel plate thickness is obtained, and controlling a finishing rolling temperature within a range of 860-900.degree. C.; after rolling, cooling in a laminar water flow zone at a cooling rate controlled within a range of 25-30.degree. C./s to ensure the billet steel is at a temperature ranging from 420 to 440.degree. C. when taken out of water; and air-cooling to a room temperature to obtain a finished marine HSLA stress corrosion-resistant steel.

7. The binary alloy design method according to claim 6, wherein a slow strain rate tensile test is conducted on the finished marine HSLA stress corrosion-resistant steel under following conditions: an SO.sub.2 polluted marine atmospheric environment simulated by using 3.5 wt % NaCl+0.05 M NaHSO.sub.3 with 100% humidity; an experimental temperature of the room temperature; and a slow strain tension rate of 0.5*10.sup.-6 to 1.5*10.sup.-6 S.sup.-1.

8. The binary alloy design method according to claim 6, wherein a loss of an elongation percentage and a loss of a section shrinkage percentage of the finished marine HSLA stress corrosion-resistant steel are calculated to evaluate a stress corrosion sensitivity of the finished marine HSLA stress corrosion-resistant steel in the simulated SO.sub.2 polluted marine atmospheric environment.

9. The binary alloy design method according to claim 8, wherein the loss of the elongation percentage of the finished marine HSLA stress corrosion-resistant steel is 11.05%-15.21%, while the loss of the section shrinkage percentage of the finished marine HSLA stress corrosion-resistant steel is 12.1%-14.33%, with a maximum decrease of approximate 60% in the stress corrosion sensitivity compared with a traditional HSLA stress corrosion-resistant steel.

10. The binary alloy design method according to claim 2, wherein an alloying element for inhibiting the anodic dissolution is selected from the group consisting of P, Sb, Co, Cr, Ni, Cu, Mo, Re, Ca, Mg, and dispersive oxides of P, Sb, Co, Cr, Ni, Cu, Mo, Re, Zr, Ca, and Mg, and the alloying element for inhibiting the anodic dissolution is abbreviated as anti-corrosion element for short; and an alloying element for inhibiting the hydrogen embrittlement is selected from the group consisting of Nb, V, Ti, Zr, Re, Mo and W, and the alloying element for inhibiting the hydrogen embrittlement is abbreviated as anti-damage element for short.

11. The binary alloy design method according to claim 3, wherein an alloying element for inhibiting the anodic dissolution is selected from the group consisting of P, Sb, Co, Cr, Ni, Cu, Mo, Re, Zr, Ca, Mg, and dispersive oxides of P, Sb, Co, Cr, Ni, Cu, Mo, Re, Zr, Ca, and Mg, and the alloying element for inhibiting the anodic dissolution is abbreviated as anti-corrosion element for short; and an alloying element for inhibiting the hydrogen embrittlement is selected from the group consisting of Nb, V, Ti, Zr, Re, Mo and W, and the alloying element for inhibiting the hydrogen embrittlement is abbreviated as anti-damage element for short.