JPS61136622A - Manufacture of high strength low alloy ultrathick steel material - Google Patents

Abstract

PURPOSE:To obtain the titled steel material superior in toughness, by adding V, Nb, Ti, etc. to Mn-Cr-Mo steel, hot rolling it at a specified temp. range, then quenching and tempering said plate. CONSTITUTION:Steel contg. 0.05-0.20wt% C, <=0.80% Si, 0.2-1.5% Mn, <=5.0% Cr, 0.4-1.5% Mo, <=0.35% V, 0.01-0.12% total of >=one kind of Nb, Ti, 0.01-0.1% sol Al, further 0.0003-0.002% B, while restricting N to <=0.005% is melted. Steel ingot or slab of the compsn. is heated to 1,100-1,280 deg.C, then hot rolled at 800-1,050 deg.C by >=1.2 draft, to refine crystal grains up to center part in thickness of ultrathick steel plate. Next, the plate is immediately quenched directly from >=800 deg.C, temperated to obtain the titled steel material having superior toughness.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application)
High-temperature strength of ultra-thick steel (49% creep strength f)
This relates to a manufacturing method for increasing the

(Prior art and problems) Mo-based and Or-Mo-based low alloy heat-resistant steels are widely used in high-temperature, high-pressure reaction vessels such as chemical industry, petrochemical industry, and petroleum refining industry due to their excellent high-temperature strength and hydrogen corrosion resistance. It is used.

By the way, what about recent high-temperature reaction vessels?

There is a movement toward larger sizes, higher temperatures, and higher pressures to improve efficiency.
Along with this, there is a tendency for devices to become increasingly thick. A place to make things with monoblocks.

Extreme thickness leads to a decrease in the cooling rate at the center of the plate thickness, resulting in zero strength.

Increasing the wall thickness, which leads to a decrease in toughness, requires a longer stress relief annealing time, which also leads to a decrease in strength.

For these reasons, we have developed a new component system that has improved high-temperature strength without causing an extreme increase in wall thickness, as well as high toughness and fire resistance to prevent brittle fracture caused by pressure tests during periodic inspections. New consideration will be required from the viewpoint of strength and toughness, including embrittlement.

In addition, the trend toward higher temperatures to increase reaction efficiency compared to conventional operating temperatures requires steels with higher hydrogen attack resistance and higher creep strength than conventional steel weights. As a steel that can cope with such high temperatures, for example, 30r-I Mo steel is said to be able to withstand hydrogen attack up to 538°C, but it has the drawback of low high-temperature strength.

That is, conventionally known Or-Mo based low alloy steels include those disclosed in JP-A-50-130621 or JP-A-5
5-41961: There are some known steels, but none of these can guarantee sufficient surface strength at high temperatures;
It has not yet been possible to solve all of the above-mentioned problems with steel components alone.

c) Means for Solving Problems 1 Effect) The inventors of the present invention have repeatedly conducted various experiments in order to achieve a further increase in strength compared to the conventional low metal content heat-resistant steels as described above.
We obtained the knowledge that the strength and toughness of steel added with strengthening elements such as Ti, hot worked in a specific temperature range, and then offline quenched and tempered are improved.

A patent was granted as Japanese Patent Application No. 59-207763.

As they continued their research, they discovered that it was possible to manufacture low-metallic steel with high strength and toughness equivalent to or better than the recent invention at a low cost, and thus completed the invention. .

That is, in the present invention, o o, o s ~ 0.20% in terms of 1 weight
.

sto, sos or less, Mn 0.2-1.5
'1k, Or 5.0% or less. Mo0.4-1.
5%, VO, 35'4 or less, Nb, Ti (
7) 0.01 to 0.12' fk for type 1 or type 2 in total
, 8o1. After heating to 11,100 to 1,280 tl, steel ingots or slabs containing 0.01 to 0.1% of VC and VC of 80,0003 to 0.002% are added and ICN is limited to 0.008% or less. , 800-10
A high-strength low alloy characterized by hot working such that the ratio (pre-processing material/finish thickness) is 1.2 or higher at 50°C, then directly quenching at a temperature of 800°C or higher, and then tempering. This is a method for manufacturing thick steel material.

The present invention will be explained in detail below.

First, in the present invention, the term "extremely thick steel" refers to a steel with a thickness of more than 100 mm. This #i, as mentioned earlier, in applications such as chemical industry 1 petroleum refining, equipment is becoming larger due to higher pressure, and the thickness is increasing compared to the conventional thickness of 100 + n + or less, so the plate thickness as above is increasing. It is aimed at a range of items.

Next, each component of the steel to be subjected to the method of the present invention is defined as described above, and the reason for the limitations will be described.

It is necessary to maintain oFi strength, but if it exceeds 0.201 Th, it will impair weldability and toughness, so the upper limit is set to 0.20 Th, and the lower limit is less than this when using a high ten-no-9 meter when heated after Fi welding. A friend who has difficulty maintaining strength o, o
I made it s s. Here, Tennozo-nozoramata (T,
P, ) is determined by T, P, = T(20+Iogt). However, T: temperature (K), t: time (hour
).

Although 8i is added as a deoxidizing agent, it is also an element that is effective in improving strength. However, if it is too much, it will have a negative effect on weldability and toughness, so it should be less than o, s o s.

Mn is a necessary component not only for defrosting but also for maintaining one strength. However, if it exceeds 1.5 degrees, it is not preferable from the point of view of toughness, so the upper limit was set at 1.51, and the lower limit was set at 0.2 from the point of view of guaranteeing the strength of extremely thick materials.

Or is necessary from the viewpoint of oxidation resistance, hydrogen corrosion resistance, and strength, but if it is added in excess of 5%, problems will occur with weldability, so the upper limit is set at 5%.

Mo is an element that significantly increases high temperature strength.

If it is less than 0.41, the effect is extremely reduced, and even if it exceeds 1.5, there is almost no increase in effect. Upper limit as it does not have a negative effect on l-contact property! -1.5chi, the lower limit was set to 0.41.

■ is a friend'a M that significantly increases resistance to tempering and softening.

Similarly, it is an element that has a remarkable effect on improving high-temperature strength, but if it is added in an amount exceeding 0.35%, it will have a decisive adverse effect on weldability, so the upper limit was set at 0.351.

Next, Nb and Ti are elements that make crystal grains finer and improve strength, but their t#'' can be reduced to 0.
If it is less than 0.01 width, it will not be effective, and if it exceeds 0.12 width, the creep strength will actually decrease, so set the upper limit! -0.12 Unfortunately, the lower limit is set to 0.01.

5o and At are effective elements for improving toughness.

The effect is weak when the 0.01 ratio is unfinished, and if it exceeds 0.1096 gold, it has a negative effect on hot workability, so the upper limit is 0.10 ratio for all
The lower limit was set to 0.011.

The above is the basic content of the steel according to the present invention, but when the plate thickness becomes extremely thick, a composition system that takes hardenability into consideration is required.

B is an effective element for preventing the precipitation of eK7 elite, which is an extremely thick material and requires an extremely slow cooling rate during quenching, and for ensuring a 4-inite structure.

If it is less than 0.00031, no matter how large the amount of S is or how much the amount of N, which will be described later, is lowered, there is no effect on hardenability. Also, if it exceeds 0.00201, it will be difficult to work due to segregation.

Since it has a negative effect on weldability, the upper limit is set at 0.002Q%.

Lower limit t? o, o003*tL-7t.

N is a very small amount of 8 mentioned above, and At is the ninth to ensure hardenability.
It is effective to keep the amount of B low while adding B, but the effect of the trace amount of B only becomes apparent when it is reduced to 0.00896 or less.

It was decided to keep it below o, o o s%.

The above are the steels to which the manufacturing method using VC of the present invention is applied,
Nine manufacturing methods for increasing high-temperature strength and ensuring toughness at the same time using this steel will be described below.

First, a steel ingot or slab is melted using normal steelmaking methods.
It is made into an ingot by continuous casting or ordinary ingot making.

After that, heating prior to hot rolling is performed using NbO, TiOt
In order to expect strengthening by solid solution in austenite and subsequent precipitation, it is necessary to heat it to 1100° C. or higher. However, if heated above 1280°C, the crystal grains will begin to coarsen, which will have a negative effect on the toughness of the final product, so the upper limit of the heating temperature should be set to 1280°C and the lower limit to 110°C.
The temperature was 0°C.

Next, hot working refers to forging and ring rolling in this case.

Refers to roll rolling, etc.

In this hot working, the reason why hot working is carried out at a temperature range of 80 () to 1050°C and a reduction ratio (unprocessed thickness/finished thickness) of 1.2 or more is because the center of the thickness of the extra-thick steel plate This process has been thoroughly processed to refine the crystal grains down to the center, improving toughness.

The lower limit temperature for hot working is set to 800°C or higher to ensure a later cooling start temperature of 800°C. Moreover, at 1050° C. or higher, the grain refining effect due to high-temperature hot working is lost.

If the reduction ratio (unprocessed thickness/finished thickness) is less than 1.2, sufficient processing will not be performed to the center of the plate thickness, grain refinement will be insufficient, and no improvement in toughness can be expected.
The number of hot workings at 50° C. and the measured reduction ratio may be sufficient, and it is preferable that the ratio is as large as possible for grain refinement.

Immediately after the above-mentioned hot working, direct quenching at a temperature of 800°C or higher takes advantage of the steel composition processing and hot working conditions described above to achieve high strength and toughness equivalent to or higher than that of the prior invention. This is the key point of the present invention in manufacturing extremely thick steel materials. However, in the case where the quenching start temperature is less than 800℃, the hardness is 7? : Strengthening elements such as V, Nb, and Ti are partially precipitated.

Since it no longer contributes to strengthening, the temperature was set at 800°C or higher.

Next, tempering is carried out to obtain homogeneous and excellent strength and toughness, and is carried out in the same manner as ordinary Or-Mo steel (e.g., 625 to 700 cm x 30 minutes or more).

All embodiments of the effects of the present invention will be described in more detail below.

C Example〉 Table 1 shows the chemical composition WIt of the test steel.The test steel was melted and ingot-formed in a high frequency furnace, and then forged to 60tX100w.
The material has a shape of X200t. Second, second
The table shows the hot working and cooling conditions and cooling rate, the equivalent plate thickness of the actual steel plate corresponding to the cooling rate, the T (Tennozo-) parameter calculated by 20 + TOG, and the various properties, namely room temperature and high temperature tensile properties. .

Creep rupture properties, impact value Tri(lt") at 0°C.

In addition, room temperature tension is JI84 high temperature tension 1. Creep rupture tests are performed using JI8 standard test pieces.

In Table 2, No, 1.3, 6, 7, 8, 11゜1
2.14.15Fi, Comparative Example, NO, 2, 4, 5, 9
, 10.

No. 13 is an example of the present invention.

No. 1 to No. 0.7 are related to 30r-I Mo-based steel, and No. 1 is a normal process material, that is, after hot working, it is cooled to room temperature, then reheated and quenched from 950 ° C. In the case of t-type steel, sufficient strength was not obtained in both 1 strength and creep rupture strength.

No. 013 has a heating temperature that does not violate the requirements of the present invention.

The crystal grains become coarser and the toughness deteriorates significantly. No. 006 has a hot working reduction ratio that does not meet the requirements of the present invention.

Toughness value is low. In No. 7, the direct quenching temperature after hot working was too low, so the strength and creep rupture strength at both room temperature and high temperature were low.

On the other hand, NO, 2, 4, and 5 were manufactured within the range that met the requirements of the present invention, and all exhibited high creep rupture strength, high strength, and high toughness, making them excellent materials.

Next, NO, 8~No, 11 is 1 ・1/40'r
-1/2 This relates to Mo steel. N018 is a normal process material, that is, after hot processing, it is cooled to room temperature and then reheated to 9301:! It is hardened and does not have sufficient strength. No. 11 does not have sufficient strength because the direct quenching temperature after hot working is low.

N029 was manufactured within a range that satisfies the requirements of the present invention, and has high levels of both strength and toughness, as well as high creep rupture strength. No. 10 was also manufactured within the range that satisfied the requirements of the present invention, and the rolling ratio was just at the lower limit, so the toughness value was a little low, but the 1 strength and creep rupture strength were high values.

Next, NO.12 to NO.15 are related to Mn-Mo steel. NO, 12#i is a conventionally worked material, that is, after hot working, it is cooled to room temperature, reheated to 900°C, and quenched, and does not have sufficient strength. In N0114, the heating temperature does not meet the requirements of the present invention, grain refinement is insufficient, and the toughness value is low. No. 15 did not have sufficient strength because the direct quenching temperature after hot working did not meet the requirements of the present invention.

On the other hand, No. 13 was manufactured within the range that satisfied the requirements of the present invention, and had good strength and toughness.

Creep rupture strength is also at a high level.

(Effects of the Invention) As described above, according to the manufacturing method of the present invention, a steel material with higher creep rupture strength, higher high temperature strength, and a better balance with toughness than the conventional manufacturing method can be obtained. Therefore, this method is not only suitable for larger and higher temperature high-temperature and high-pressure equipment and is advantageous for reducing the weight of the equipment, but also allows direct quenching after hot working.

Since there is no need to cool the product to room temperature and then reheat it to the quenching temperature after hot working as in the conventional method, this invention has great industrial effects, such as being able to reduce costs and shorten the manufacturing period.

Agent Patent Attorney Masaaki Aki Sawa 2 believers

Claims (1)

[Claims] (1) 0:0.05-0.20% by weight, Si:0.
80% or less, Mn: 0.2 to 1.5%, Cr: 5.0% or less, Mo: 0.4 to 1.5%, V: 0.35% or less, one or two of Nb and Ti Total species 0.01-0.12%, Sol. Steel ingots or slabs containing Al: 0.01-0.1%, or further adding B: 0.0003-0.002% and limiting N: 0.005% or less to 1100-1280 After heating to ℃, hot working is performed at 800 to 1050℃ so that the reduction ratio (unprocessed thickness/finished thickness) is 1.2 or more, then immediately quenched directly at a temperature of 800℃ or higher, and then tempered. A method for producing high-strength, low-alloy steel and extra-thick steel.