KR19980035768A - Manufacturing method of steel with excellent hydrogen organic cracking resistance - Google Patents

Abstract

The present invention relates to a method for manufacturing a steel having excellent hydrogen organic crack resistance, which minimizes the influence of carbide generation, segregation of the center and non-metallic inclusions, suppresses the increase in hardness of the base metal and the welded portion, excellent weldability and water resistance An object of the present invention is to provide a method for manufacturing steel having excellent cracking properties.

The present invention for achieving the above object by weight% C: 0.20% or less, Si: 0.1 ~ 0.4%, Mn: 0.6 ~ 1.8%, P: 0.005 ~ 0.010%, S: 0.005% or less, Cu: 0.10 ~ 0.50 %, Ni: 0.10 ~ 1.00%, Ca: 0.0010 ~ 0.0040%, Cr: 0.20 ~ 1.00%, Ti: 0.01 ~ 0.05%, Nb: 0.01 ~ 0.1%, V: 0.01 ~ 0.05%, Co: hot-rolling the steel containing one or two or more selected from 0.1 to 0.8% of the component elements at a hot rolling finish temperature of 850 ° C. or higher; Subjecting the hot rolled steel to a range of 850 to 950 ° C .; And it relates to a method for producing a steel material having excellent hydrogen resistance to organic cracking, including the step of soaking the cast-treated steel in the 600 ~ 680 ℃ range.

Description

Manufacturing method of steel with excellent hydrogen organic cracking resistance

The present invention relates to a method for producing steels used for storage containers such as natural gas and crude oil, and more particularly, to a method for producing steels having excellent hydrogen organic crack resistance.

In recent years, the production of natural gas and crude oil containing a large amount of sulfur gas has been increasing, and accordingly, demand for hydrogen-organic cracking resistance having crack resistance in a wet sour gas atmosphere has increased. The cracks began to be problematic due to the formation of blisters that swell the surface due to the action of hydrogen in pressure vessel steels with relatively low strength, but it was concluded that non-metallic inclusions were involved as the cause of the cracks. By doing so, we have reached the point where we have almost solved the problem. However, in steel with a tensile strength of 60kg / mm2 or more, through cracks connected stepwise in the thickness direction without accompanying blisters occur, so that oil leakage frequently occurs. Many efforts are being made to develop a method for manufacturing steel having excellent hydrogen organic crack resistance.

The control of production manufacturing conditions to improve the hydrogen organic crack resistance should be carried out to understand the composition composition, rolling conditions, heat treatment, etc. in detail, and also to consider the effect on weldability.

Conventionally, clean steel was manufactured by adding only Ca to spheroidized or reducing non-metallic inclusions, C, P, S, etc. in order to manufacture steel having excellent hydrogen organic crack resistance. However, this conventional method does not suppress the occurrence of cracking by hydrogen by increasing the C equivalent by increasing the content of C in the high-strength steel to increase the hardness of the weld.

The present invention has been proposed to solve the above problems to minimize the effects of carbide production, segregation of the center and non-metallic inclusions, and to suppress the increase in hardness of the base metal and the welded portion, to provide a good weldability and excellent hydrogen organic crack resistance The purpose is to provide a method for manufacturing.

By weight% C: 0.20% or less, Si: 0.1 ~ 0.4%, Mn: 0.6 ~ 1.8%, P: 0.005 ~ 0.010%, S: 0.005% or less, Cu: 0.10 ~ 0.50%, Ni: 0.10 ~ 1.00%, Ca: 0.0010 ~ 0.0040%, Cr: 0.20 ~ 1.00%, Ti: 0.01 ~ 0.05%, Nb: 0.01 ~ 0.1%, V: 0.01 ~ 0.05%, Co: 0.1 ~ 0.8 Hot-rolling a steel material containing one or two or more selected from the components of% at a hot rolling finishing temperature of 850 ° C. or higher; Subjecting the hot rolled steel to a range of 850 to 950 ° C .; And it relates to a method of producing a steel having excellent hydrogen resistance to organic cracking, including the step of soaking the cast-treated steel in the 600 ~ 680 ℃ range.

EMBODIMENT OF THE INVENTION Hereinafter, the reason for limitation of the component value of this invention is demonstrated.

As C decreases, the hydrogen organic crack resistance and weldability are improved, and as C increases, the hardness of the weld portion increases and the hydrogen organic crack and weldability deteriorate due to the increase of carbide and pearlite band structure. Therefore, in the present invention, the content of C was limited to 0.20% or less in order to prevent a sharp increase in the hydrogen organic crack resistance.

The Si is an element deoxidizing in steelmaking, and should be added at least 0.10% in order to obtain a deoxidizing effect. When the content is more than 0.40%, Si acts as a non-metallic inclusion in steel to impair hydrogen organic cracking resistance. Therefore, in the present invention, the content of Si is limited to 0.10 to 0.40%.

The Mn is an effective element for deoxidizing in steel and improving weldability, hot workability and strength in place of C, but it should be added at least 0.6% to obtain the effect, but when the content is more than 1.8%, impact toughness, weldability and cleanliness Is lowered. Therefore, in the present invention, the content of Mn is limited to 0.6-1.8%.

If the P is present in a large amount, segregation at the grain boundary causes cracks in the weld zone, and therefore, the smaller the P value is, the better the content is. In addition, since dephosphorization (P) in steelmaking is a very difficult process, it is difficult to control to 0.005% or less industrially. Therefore, in the present invention, the content of P was limited to 0.005 to 0.010%.

Since S is an element which is very detrimental to corrosion resistance, the smaller the content is, the more effective but impossible to completely remove. Therefore, in the present invention, the content is limited to 0.005% or less, so that non-metallic inclusions such as MnS are not present in a large amount in the steel so that the corrosion resistance of the welded portion is not lowered.

The addition of Cu and Ni reduces the hydrogen uptake of the matrix structure and helps to improve the hydrogen-organic cracking resistance, and in particular, the rapid increase of the hydrogen-organic cracking resistance in the state immediately after hot rolling and after the heat treatment after the annealing and welding. To help.

Cu is an element that improves the corrosion resistance in the welded part and the base metal part. If the content is less than 0.10%, the effect of improving corrosion resistance is small. If the content is more than 0.50%, surface defects are easily generated during hot rolling. Harm weldability. Therefore, in the present invention, the content of Cu is limited to 0.10 to 0.50%.

Ni has the effect of suppressing the high temperature cracking of the steel sheet due to the addition of Cu in steel, and it is added because it greatly improves the hydrogen-organic crack resistance and low temperature toughness without significantly increasing the strength and hardness of the welded part and the base material after hot rolling. . However, if the content is more than 1.0%, the effect is saturated, and it is not necessary to add any more economically. If the content is less than 0.10%, the effect is not. Therefore, in the present invention, the content of Ni was limited to 0.10 to 1.0%.

The Ca addition is added because it increases the cleanliness of the steel and makes the spherical MnS inclusions elongated to improve hydrogen-hydrogen organic crack resistance. However, if the content is less than 0.0010%, the effect is not, and if more than 0.004% damages the refractory, further addition is impossible industrially. Therefore, the content was limited to 0.0010 to 0.0040%.

The Ti, Nb and V are elements that increase the strength by miniaturizing the crystal grains and forming fine precipitates without increasing the carbon equivalent, and the effect is very significant even by the addition of a small amount. However, when Ti is contained 0.05% or more, Nb: 0.05% or more, and V: 0.10% or more, micronization no longer occurs and coarse precipitates appear and the quality characteristics are no longer improved.

In addition, when the content of each of Ti, Nb, V is contained at 0.01% or less, there is no effect of improving the quality characteristics. Therefore, in the present invention, it is limited to Ti: 0.01% to 0.05%, Nb: 0.01% to 0.05%, and V: 0.10% to 0.01%.

The Co is a component that greatly improves the hydrogen organic crack resistance, and helps to improve the hydrogen organic cracking resistance without increasing the hardness of the weld portion, the hydrogen organic cracking rapidly due to the subarray heat treatment and the sour heat treatment Improve. If the content is 0.80% or more, the effect is saturated and uneconomical, and if the content is 0.10% or less, the effect is not shown. Therefore, in the present invention, the Co content is limited to 0.10 to 0.8%.

Hereinafter, the heat treatment conditions of the steel material configured as described above will be described in detail.

First, the present invention undergoes a step of hot rolling the steel material configured as described above to a hot finishing temperature of 850 ℃ or more.

In order to suppress the adverse effect of the pearlite band, which is the cause of cracking defects, and to increase the grain size and to improve the hydrogen organic cracking resistance, it is most preferable to set the rolling finish temperature at 850 ° C or higher during hot rolling. It was limited to the above.

Next, the hot rolled steel is subjected to a step of sintering in the range of 850 ~ 950 ℃.

The roughing heat treatment removes the internal stresses generated by hot rolling and reduces the pearlite bands caused by the internal defects which are most likely to generate hydrogen organic cracks.

When the annealing temperature is below 850 ℃, the internal stress generated by hot rolling is completely eliminated, so it does not form a uniform structure, so hydrogen does not completely escape from the inside of the steel, and above 950 ℃, the grains become coarse and the hardness drops sharply. In the invention, it was limited to a temperature range of 850 ~ 950 ℃.

Next, go through the step of considering the annealed steel in the 600 ~ 680 ℃ range.

Sorrow heat treatment plays a role to remove the thermal stress generated by the semi-thermal treatment, and especially after welding because it plays a decisive role to improve the hydrogen-organic crack resistance by removing the thermal stress generated by welding during welding. Effective heat treatment In the heat treatment temperature, the internal thermal stress is not sufficiently removed at 600 ° C. or lower, and at 680 ° C. or higher, tensile strength and impact value are simultaneously dropped, thereby degrading the quality characteristics.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

In order to evaluate the hydrogen cracking resistance and quality characteristics of the inventive steels and the comparative steels according to the component elements, rolling conditions and heat treatments, 25 kg single ingots were prepared by hot melting and hot rolled to prepare test pieces. At this time, the chemical composition of the prepared comparative steel and the present invention steel was as Table 1 below.

In order to measure hydrogen organic cracking according to the addition of alloying element, hot rolling temperature, roughening heat treatment and sorrow heat treatment, a small sized test specimen for internal HIC having a length of 10 mm, a width of 15 mm, and a thickness of 14 mm was prepared. . Hydrogen organic crack susceptibility was measured by immersing in NACE solution (Standard TM-02-84, 5% NaCl-0.5% acetic acid (CH ₃ COOH), pH = 3) for 96 hours according to NACE TM-02-84. It was. According to the degree of occurrence of the steel surface crack (○ no crack generation), △ (small crack generation), × (marked crack generation) is shown in Table 2 below.

As can be seen in Table 2, the hot rolling finish temperature was more excellent in the hydrogen-organic crack resistance at high temperature (900 ℃) than at low temperature (750 ℃) regardless of the post-weld heat treatment. In particular, it was confirmed that the hydrogen-organic crack resistance was greatly increased by the subarray heat treatment at 890 ° C and the heat treatment at 625 ° C. Comparative steels A and B, despite the inclusion of Ca, P content of more than 0.010% or C content of more than 0.20% was found to be poor hydrogen cracking resistance.

In addition, it was found that the hydrogen-organic crack resistance was poor even when the subarranged heat treatment and / or the soaked heat treatment were not performed (see Table 2).

As described above, the present invention adjusts the components of the steel and heat treatment at an appropriate temperature range, thereby reducing the growth of pearlite bands that cause cracking defects, suppressing the absorption of hydrogen as much as possible to excellent hydrogen-organic crack resistance It is effective to provide a method for producing steel.

Claims (1)

By weight% C: 0.20% or less, Si: 0.1 ~ 0.4%, Mn: 0.6 ~ 1.8%, P: 0.005 ~ 0.010%, S: 0.005% or less, Cu: 0.10 ~ 0.50%, Ni: 0.10 ~ 1.00%, Ca: 0.0010 ~ 0.0040%, Cr: 0.20 ~ 1.00%, Ti: 0.01 ~ 0.05%, Nb: 0.01 ~ 0.1%, V: 0.01 ~ 0.05%, Co: 0.1 ~ 0.8 Hot-rolling a steel material containing one or two or more selected from the components of% at a hot rolling finishing temperature of 850 ° C. or higher; Subjecting the hot rolled steel to a range of 850 to 950 ° C .; And The method of producing a steel having excellent hydrogen resistance to organic cracking, characterized in that it comprises the step of soaking the cast-treated steel in the 600 ~ 680 ℃ range.