JPS641529B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a high-pressure type electric resistance welded steel pipe for oil wells. In recent years, gas and oil wells have tended to become deeper and deeper, and the demand for high collapse type oil country tubular goods has been increasing year by year. ERW steel pipes have higher dimensional accuracy than seamless steel pipes, so they are suitable for high crush type oil country tubular goods. However, since the processes of forming ERW steel pipes, sizing the pipes to a constant diameter and perfect circle, and straightening the pipes to make them straight are performed cold, it is impossible to avoid the generation of compressive residual stress on the inner surface of the pipes. Can not. This residual stress acts to reduce the crushing strength of the electric resistance welded steel pipe. It has been known for a long time that residual stress can be reduced by heat treatment, but heat treatment requires a large amount of cost. Further, in some cases, the yield stress of the tube decreases due to heat treatment, thereby causing a problem in that the crushing strength decreases. Therefore, in order to manufacture high-strength oil country tubular goods without heat treatment, it is necessary to use a composition that contains a large amount of C and Mn, and as a result, the yield ratio decreases due to the increase in Ceq, and the crushing strength becomes lower than the tensile strength. The current situation is that it has to be relatively low. This invention was made in order to solve the above-mentioned problems in manufacturing high-pressure crush type ERW oil country tubular goods, and an object of the present invention is to provide a method for manufacturing ERW steel pipes with high crushing strength without applying heat treatment. . In the manufacturing method of the electric resistance welded steel pipe of this invention, C: 0.01~
0.18%, Si: 0.05~0.25%, Mn: 1.00~2.00%,
A steel whose basic components are Al: 0.01 to 0.10%, Nb: 0.050% or less, and the balance is Fe and unavoidable impurities is hot rolled at a temperature of 740 to 830°C, and 1 second from the end temperature of the hot rolling. For the above 15 seconds, cool without water injection, and then increase the average cooling rate to 15 seconds until winding.
°C/sec to 25 °C/sec, winding at 400 °C to 600 °C, or V: 0.070 or less to the above components,
Or Ti: 0.030% or less is added. This invention will be explained in detail below. It has long been well known that increasing the yield strength is sufficient to improve the crushing pressure, but simply increasing the yield strength will not satisfy the upper limit of hardness because the tensile strength will also increase accordingly. It disappears. Therefore, the yield ratio (yield strength/
It is important to increase the tensile strength x 100 (%). Furthermore, by reducing the variation as much as possible, the crushing strength can be increased. Therefore, in the present invention, by limiting the component composition of the material and the hot rolling and cooling conditions, the crushing strength is improved by controlling the variation to be extremely small while maintaining a high yield ratio. First, regarding the ingredients of the material, C is important for ensuring the necessary tensile strength, but as C increases, the yield ratio decreases, so it is desirable to have as low C as possible. The reason for this is that C does not contribute much to the strength of ferrite, which controls yield strength, but mainly strengthens the second phase, such as pearlite, which controls tensile strength, so it becomes an element that lowers the yield ratio. Furthermore, generally speaking, as C increases, bainite is more likely to occur, which also causes a decrease in yield ratio. Therefore, C is set at 0.18% or less, but on the other hand, 0.01%
If it is less than 0.01% to 0.18%, the cost will increase. Mn is also necessary to ensure the necessary strength,
Furthermore, in order to make the ferrite grains finer, it is better to add as much as possible to 1.0% or more. but
If it exceeds 2.0%, an intermediate structure will occur and the yield ratio will decrease.
Therefore, Mn is set in the range of 1.0 to 2.0%. Although Si is necessary to ensure the necessary strength,
It should be in the range of 0.05 to 0.25% from the point of view of electric resistance weldability. Nb is necessary to ensure the necessary strength,
Yield strength can be significantly improved due to precipitation strengthening within ferrite grains. Furthermore, it is an extremely effective element that can improve the yield strength by making the ferrite grains finer, but if it exceeds 0.050%, it cannot be dissolved in solid form at normal heating temperatures, so it does not play the above-mentioned effective role. Therefore
Nb should be 0.050% or less. V is added to the basic components of C, Si, Mn, Al, and Nb mentioned above.
Alternatively, it is more advantageous to add Ti. Like Nb, V is an element that improves yield strength and is an effective element, and its effect becomes even greater when added in combination with Nb. If it exceeds 0.070%, it becomes difficult to increase the strength and it becomes difficult to play an effective role. Therefore, V is set to 0.070% or less. Ti is an element for refining ferrite grains and is effective for achieving a high yield ratio. But Ti is solN
Be careful as the strength may decrease due to merging with other materials. However, too much Ti deteriorates the toughness, so the Ti content was set to 0.03% or less. Molten steel with the above-mentioned basic components is produced in a converter.
Any killed steel from an open hearth or electric furnace is fine, but it should be an Al killed steel containing 0.01 to 0.10% Al.If the Al content is less than 0.01%, the deoxidizing effect will be insufficient, and if it exceeds 0.10%, the deoxidizing effect will be insufficient. does not change, and therefore 0.01~
The range was set at 0.10%. The steel billets may be manufactured by either ingot-blushing rolling or continuous casting, but the continuous casting method is more advantageous. Next, regarding the hot rolling conditions, it is desirable that the hot rolling end temperature be as low as possible. The reason is that intermediate structures are less likely to occur when the γ grains are refined by low-temperature rolling. This intermediate structure lowers the yield ratio, so it is better to prevent it. Furthermore, rolling at a lower temperature makes the ferrite grains finer and increases the yield ratio. Therefore, the hot rolling finish temperature was set to 830°C or lower. However, if the temperature is lower than 740°C, the yield ratio decreases due to coarsening of the ferrite grains, and the crushing strength decreases, which is undesirable. Next, the cooling conditions will be described. If the ferrite is rapidly cooled immediately after hot rolling, solid solution C and N may remain in the ferrite and the yield ratio may increase, but on the other hand, bainite may be generated, significantly increasing the variation in the yield strength and increasing the yield ratio. Since this may lower the ratio, it is preferable to allow cooling without pouring water after hot rolling. Therefore, the cooling time is allowed to cool for more than 1 second and less than 15 seconds without pouring water. In other words, after hot rolling, if you let it cool for 1 to 15 seconds,
Bainite generation areas can be avoided. Again 1
If the cooling rate exceeds 25°C/sec after cooling for 15 seconds to 15 seconds, it will enter the bainite generation region and
A winding temperature of .degree. C. to 600.degree. C. or less is undesirable because it causes bainitic transformation and lowers the yield ratio. For cooling after cooling, the average cooling rate is 15% until winding up.
Rapid cooling at ℃/sec or higher. This is because the bainite transformation is completed by cooling immediately after hot rolling, and this rapid cooling causes the precipitation of fine pearlite, which increases the tensile strength and decreases the C content by that amount, which lowers the yield ratio. can rise. Further, the upper limit of the cooling rate is 25°C/sec.
The reason for this is that when the temperature exceeds 25° C./sec, the yield ratio decreases due to the generation of bainite structure, and the crushing strength decreases, which is not preferable. Next, regarding the winding temperature, as shown in FIG. 1, by winding at a temperature of 600° C. or lower, the strength and crushing strength increase. This is because the self-annealing effect during winding becomes smaller below 600°C, resulting in less strength loss.

[Table] As described above, according to the present invention, it is possible to manufacture high-strength ERW oil country tubular goods without the need for heat treatment such as quenching, tempering, and normalizing, and it has extremely excellent crushing strength. It is extremely advantageous as it is inexpensive.

[Brief explanation of drawings]

FIG. 1 is a chart showing the relationship between crushing strength and winding temperature.

Claims (1)

[Claims] 1% by weight: C: 0.01-0.18%, Si: 0.05-0.25%, Mn:
1.00~2.00%, Nb: 0.050% or less, Al: 0.01~0.10
%, with the remainder being Fe and unavoidable impurities, hot rolled at a temperature of 740 to 830°C, and allowed to cool without pouring water for 1 to 15 seconds from the end temperature of the hot rolling. , the average cooling rate until the subsequent winding is 15℃/sec to 25℃/sec, and the temperature is 400℃ or more.
A method for producing a high crush type electric resistance welded steel pipe for oil wells that does not undergo heat treatment and is characterized by being wound at a temperature of 600°C or less. 2% by weight: C: 0.01-0.18%, Si: 0.05-0.25%, Mn:
1.00~2.00%, Nb: 0.050% or less, Al: 0.01~0.10
% as the basic component, V: 0.070% or less, or Ti:
Steel containing 0.03% or less of Fe and unavoidable impurities is hot-rolled at a temperature of 740 to 830°C, and allowed to cool without pouring water for at least 1 second and within 15 seconds from the end temperature of the hot rolling. , the average cooling rate until the subsequent winding is 15℃/sec to 25℃/sec, and the temperature is 400℃ or more.
A method for producing a high crush type electric resistance welded steel pipe for oil wells that does not undergo heat treatment and is characterized by being wound at a temperature of 600°C or less.