JPH0116283B2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) Large industrial machines, welded steel pipes and others, marine structures,
The technical content described in this specification regarding the advantageous production of high-strength steel materials for shear welded structures that are suitable for uses such as bridges, etc. The aim is to propose the results of research to meet the demands for sexual compatibility. In order to improve weldability, lowering C is effective, but on the other hand, the requirement for higher strength is impaired. For this reason, when lowering C, it is necessary to supplement the strength by other methods. One method is to utilize the precipitation hardening effect of Cu. (Prior art) Regarding the use of precipitation hardening of Cu, for example, ASTM
Examples can be found in A710 and US Pat. No. 3,692,514. However, when trying to increase strength by utilizing Cu precipitation hardening, low-temperature toughness is impaired. One way to ensure low-temperature toughness in Cu-containing steel is to set the Cu precipitation temperature higher (e.g., 670°C) than the maximum hardening condition (e.g., 550°C), but this would result in a lower temperature due to Cu precipitation. The effect of increasing strength is lost and the original purpose cannot be achieved. (Problem to be solved by the invention) High tensile strength steel with YP: 49Kgf/mm ² or higher, which has excellent low-temperature toughness and weldability by significantly improving low-temperature toughness without impairing the precipitation hardening effect of Cu. The purpose of the development research described here is to secure an advantageous manufacturing method for. (Means to solve the problem) (1) Increase the amount of C from 0.01 to 0.10wt to improve weldability.
Reduce to %. (2) To increase strength, 0.7 to 1.5 wt% of Cu is included. (3) Controlled rolling is performed in order to prevent toughness deterioration resulting from precipitation hardening treatment and improve low-temperature toughness under the presence of Cu. The above are the basic factors for solving the above problem, and after this rolling, the object of the present invention is to achieve C. : 0.0-0.10wt%, Si: 0.40wt% or less Mn: 0.5-2.0wt%, Cu: 0.7-1.5wt% Ni: 0.5-2.0wt%, Nb: 0.005-0.06wt% and Al: 0.01-0.10wt Composition containing % or further Cr and/or Mo:
The process of forming these steels into a composition containing 1.0wt% or less and applying a reduction of 30% or more at temperatures below 900°C and above 700°C until rolling is completed is common; Apply Cu precipitation treatment in the range of A _C3 ~ After finishing the rolling and cooling it once.
A _C3 After reheating to +30℃, cooling with water and then performing Cu precipitation treatment in the range of 500℃ to 650℃, or immediately after finishing rolling at an average cooling rate of 2.5
Cool to room temperature at ℃/s or more, then 500℃
This is achieved by either performing Cu precipitation treatment in the temperature range of 650°C to 650°C, allowing stable production of high-strength steel for welded structures with excellent low-temperature toughness and weldability. It becomes possible. (Function) The amount of C is 0.01wt% or more and 0.10wt% or less, which is one of the characteristics of each invention. If the C content is less than 0.01wt%, the required strength cannot be obtained, and if it exceeds 0.10wt%,
This is because weldability is impaired. Si is an essential element for deoxidizing during steel refining, and is also an inexpensive steel-strengthening element, but if it exceeds 0.60 wt%, the cleanliness of the steel will be impaired, resulting in a decrease in weldability and toughness. On the other hand, if it is less than 0.02wt%, the above effects cannot be obtained. Therefore, the range of Si is 0.02wt%~
It was set to 0.6wt%. Mn is an element that increases strength without reducing toughness, and for this purpose it is necessary to add 0.5 wt% or more. However, if it exceeds 2.0wt%, weldability will be impaired. Therefore, the addition range of Mn should be 0.5~
It was set to 2.0wt%. The inclusion of Cu is also one of the characteristics of each invention.
High strength is achieved by utilizing its precipitation hardening effect.
Here, if Cu is less than 0.7 wt%, there is no precipitation hardening effect, while if it exceeds 1.5 wt%, low temperature toughness is impaired. Therefore, the Cu content was limited to 0.7wt% to 1.5wt%. Ni has the effect of preventing the deterioration of hot workability due to Cu content, and has the effect of improving low-temperature toughness at 0.5% or more, but the effect is not enhanced by excessive addition exceeding 2.0wt%. Therefore, it is not economical. Nb is an element that brings about the atomization effect by controlled rolling. However, if it is less than 0.005wt%, its effect is insufficient, and if it exceeds 0.06wt%, low temperature toughness is impaired. Al is an element necessary for deoxidation and austenite atomization, and for this purpose 0.010wt%
Although more than 0.10wt% is necessary, the cleanliness of the steel will be impaired. In addition to the above elements, in order to further increase the strength
One or both of Cr and Mo can be added. These elements increase strength by increasing solid solution hardening, precipitation hardening, or hardenability. However, if each exceeds 1.0wt%, the toughness will be impaired, so upper limits were regulated. For strength increase as these other ingredients
Addition of V0.001~0.10wt%, B0.0005~0.0025wt%, Ti0.003~0.05wt% to improve weldability, Ca, REM0.05~0.10% to control inclusion shape, etc. However, the effect remains unchanged. P and S are impurity elements that seriously damage the base metal and the weld zone dust, but their unavoidable contamination is unavoidable, so each should be kept within the limits that do not cause actual damage.
It is acceptable if it is 0.015wt% or less, 0.010wt% or less. Next, the rolling conditions will be described. The rolling finishing temperature shall be 900℃ or less. At temperatures exceeding 900℃, the grains become coarse and toughness deteriorates. Furthermore, if the finishing rolling temperature is lower than 700°C, the toughness will be impaired, so the lower limit was set at 700°C. The reduction in this temperature range requires a reduction of 30% or more, and if it is less than 30%, a sufficient fine grain structure cannot be obtained. Cu precipitation treatment is carried out at a temperature of 500℃~650℃, 500℃
The reason why we limited it to ℃~600℃ is that outside this temperature range,
This is because the precipitation hardening effect of Cu is impaired. Prior to this Cu precipitation treatment, when reheating and quenching is performed after controlled rolling, the reheating temperature is A _C3
~A _C3 It is necessary to perform water cooling at +30°C in order to refine the structure after quenching. Also, when direct quenching is performed after controlled rolling, the cooling rate is
2.5℃/sec or more. The reason is that high strength cannot be obtained with cooling slower than 2.5/sec. (Example) Example 1 The chemical composition of the test steel is shown in Table 1. [Table] [Table] Each sample steel was heated to the austenite region, rolled to 25 mm at a finishing temperature of 800°C (reduction ratio of 75%), and then subjected to Cu precipitation treatment at 600°C for 1 hour. The strength and toughness at that time are shown in Table 2. Table 2 also includes data when the rolling was finished at 920°C. [Table] It can be seen that excellent strength and low temperature toughness can be obtained by each of the first and second inventions. Next, the rolling end temperature of the test steel (E) was set to 650.
The effect on the toughness value vE-60 after the Cu precipitation treatment was investigated at various temperatures in the range of ~950°C, and the results shown in Figure 1 were obtained. Furthermore, the rolling end temperature is
Regarding the case of 850℃, Cu precipitation treatment is 450 to 675
The results shown in Figure 2 were obtained by changing the temperature to various conditions and investigating the effects on YS. Example 2 The chemical composition of the test steel is shown in Table 3 along with comparative examples. [Table] RI, (S), and (T) steel are examples of components for comparison.
Each test steel was heated to the austenite region, rolled to 25 mm at a finishing temperature of 800°C (reduction ratio of 75%), cooled in air, and then heated to 900°C for quenching. then 550℃
Cu precipitation treatment was performed for 1 hour. The strength and toughness at that time are shown in Table 4, with the results according to the third and fourth inventions being shown separately, surrounded by thick line sections. Table 4 also includes data when rolling was completed at 920°C and the quenching temperature was 960°C. [Table] [Table] It can be seen that excellent strength and low-temperature toughness can be obtained by each of the third and fourth inventions. Next, for sample steel J, only the quenching temperature was set to 800℃.
above at various temperatures ranging from ~1000°C.
Figure 3 shows the relationship with low temperature toughness after Cu precipitation treatment. Furthermore, Figure 4 shows the effect of the Cu precipitation treatment temperature on YS when the quenching temperature was 900°C. Example 3 Next, each test steel whose chemical composition is shown in Table 3 was heated to the austenite region, rolled to 25 mm at a finishing temperature of 800° C. (reduction ratio of 75%), and then immediately water quenched. Thereafter, Cu precipitation treatment was performed at 550°C for 1 hour. Table 5 shows the strength and toughness at that time. Table 5 also includes comparative data when rolling was completed at 920°C and direct quenching was performed. [Table] It can be seen that the fifth and sixth inventions provide excellent strength and low-temperature toughness. Figures 5 and 6 show the dependence of YS and TS on Cu content and the influence of Ni content on vTrs.
Figure 7 shows the Cu precipitation treatment temperature for sample steel P.
The effect on YS when changing the temperature from 400 to 700℃ was shown. (Effect of the invention) In any of the first to sixth inventions, C is 0.01 or more.
After rolling a steel with a specified composition range based on the characteristics of reducing Cu to 0.10wt% and adding 0.7 to 1.5wt% Cu at a finishing temperature of 900 to 700℃,
After Cu precipitation treatment or rolling, A _C3
~A _C3 After being reheated to +30℃ and quenched, Cu precipitation treatment is performed at 500 to 650℃, or immediately after rolling, quenching is performed and then quenched at a temperature of 500 to 650℃.
By either Cu precipitation treatment, it was possible to stably produce steel with excellent strength and low-temperature toughness without impairing weldability.

[Brief explanation of drawings]

Figure 1 is a diagram showing the effect of rolling end temperature on low-temperature toughness, and Figure 2 is a diagram showing the effect of rolling finish temperature on low-temperature toughness.
Figure 3 is a diagram showing the relationship between reheating and quenching temperature after rolling and low temperature toughness, and Figure 4 is a diagram showing the relationship between Cu precipitation treatment temperature and YS in this case. , Fig. 5 is a graph of the relationship between Cu content and strength in the case of direct quenching, Fig. 6 is a graph of the relationship between Ni content and toughness, and Fig. 7 is a graph of the relationship between Cu content and toughness in the case of direct quenching.
It is a graph showing the relationship between precipitation temperature and strength.

Claims (1)

[Claims] 1 C: 0.01 to 0.10wt%, Si: 0.40wt% or less,
Mn: 0.5-2.0wt%, Cu: 0.7-1.5wt%, Ni: 0.5
~2.0wt%, Nb: 0.005~0.06wt%, and Al:
Steel with a composition containing 0.01 to 0.10 wt% is rolled by applying a reduction of 30% or more at temperatures below 900°C and above 700°C, and then subjected to Cu precipitation treatment in the range of 500°C to 650°C. A method for manufacturing high-strength steel for welded structures, which is characterized by excellent low-temperature toughness and weldability. 2 C: 0.01 to 0.10wt%, Si: 0.40wt% or less,
Mn: 0.5-2.0wt%, Cu: 0.7-1.5wt%, Ni: 0.5
~2.0wt%, Nb: 0.005~0.06wt%, and Al:
0.01~0.10wt% and further Cr: 1.0wt% or less, Mo:
Steel with a composition containing one or more of the following: 1.0wt% or less is rolled by applying a reduction of 30% or more at temperatures below 900°C and above 700°C, and then subjected to Cu precipitation treatment in the range of 500°C to 650°C. A method for producing high-strength steel for welded structures having excellent low-temperature toughness and weldability, characterized by: 3 C: 0.01 to 0.10wt%, Si: 0.40wt% or less,
Mn: 0.5-2.0wt%, Cu: 0.7-1.5wt%, Ni: 0.5
~2.0wt%, Nb: 0.005~0.06wt%, and Al:
Steel with a composition containing 0.01 to 0.10wt% is rolled by applying a reduction of 30% or more at temperatures below 900℃ and above 700℃, cooled once, and then reheated to a temperature range of A _C3 to A _C3 +30℃. A method for producing high-strength steel for welded structures with excellent low-temperature toughness and weldability, which comprises heating, water-cooling, and then performing Cu precipitation treatment at a temperature in the range of 500°C to 650°C. 4 C: 0.01 to 0.10wt%, Si: 0.40wt% or less,
Mn: 0.5-2.0wt%, Cu: 0.7-1.5wt%, Ni: 0.5
~2.0wt%, Nb: 0.005~0.06wt%, and Al:
0.01~0.10wt% and further Cr: 1.0wt% or less, Mo:
Steel with a composition containing one or more of 1.0wt% or less is rolled by applying a reduction of 30% or more at temperatures below 900℃ and above 700℃, and after cooling once, A _C3 ~ A _C3 +30 A method for manufacturing high-strength steel for welded structures with excellent low-temperature toughness and weldability, characterized by reheating the steel to a temperature range of 100°C, cooling it with water, and then subjecting it to Cu precipitation treatment at a temperature of 500°C to 650°C. . 5 C: 0.01 to 0.10wt%, Si: 0.40wt% or less,
Mn: 0.5-2.0wt%, Cu: 0.7-1.5wt%, Ni: 0.5
~2.0wt%, Nb: 0.005~0.06wt%, and Al:
Steel with a composition containing 0.01 to 0.10wt% is rolled by applying a reduction of 30% or more at a temperature of 900℃ or lower and 700℃ or higher, immediately cooled to room temperature at an average cooling rate of 2.5℃/s or higher, and then 500℃ A method for producing high-strength steel for welded structures with excellent low-temperature toughness and weldability, characterized by performing Cu precipitation treatment in the range of ℃ to 650℃. 6 C: 0.01 to 0.10wt%, Si: 0.40wt% or less,
Mn: 0.5-2.0wt%, Cu: 0.7-1.5wt%, Ni: 0.5
~2.0wt%, Nb: 0.005~0.06wt%, and Al:
0.01~0.10wt% and further Cr: 1.0wt% or less, Mo:
Steel with a composition containing one or more of the following: 1.0 wt% or less is rolled by applying a reduction of 30% or more at a temperature of 900°C or lower and 700°C or higher, and then immediately cooled to room temperature at an average cooling rate of 2.5°C/s or higher. A method for producing high-strength steel for welded structures with excellent low-temperature toughness and weldability, characterized by cooling and then subjecting it to Cu precipitation treatment at a temperature of 500°C to 650°C.