JPS6296614A - Heat treatment of cr-mo steel having excellent hydrogen erosion resistant characteristic - Google Patents

Abstract

PURPOSE:To economically produce a Cr-Mo steel having an excellent hydrogen erosion resistant characteristic by subjecting the Cr-Mo steel having a specific compsn. to hardening and annealing treatments then to tempering or stress relief annealing treatment under adequate conditions. CONSTITUTION:The Cr-Mo steel contg. <=0.20% C, <=0.60% Si, <=1.0% Mn, <=0.020% P, <=0.010% S, 2.0-3.5% Cr, and 0.8-1.6% Mo and the blance substan tially consisting of Fe is subjected to the hardening and annealing treatments. The above-mentioned steel is thereafter subjected to at least one pass of a tempering treatment and/or stress relief annealing treatment within a 600-750 deg.C range under such conditions under which the S value expressed by the formula attains >=810 [where, Ti and ti; temp. deg.C and time h of the 1st tempering treat ment or stress relief annealing treatment, h; number of the tempering treatment and/or stress relief annealing treatment (including n=1)]. The heat treatment of the Cr-Mo steel having the excellent hydrogen erosion resistant characteristic is thus executed.

Description

[Detailed description of the invention] (Industrial application field) This invention uses Cr-M which has excellent hydrogen corrosion resistance.

Regarding heat treatment methods for steel, Cr-M has excellent hydrogen attack resistance and can be suitably used as a material for pressure vessels operated for long periods of time under high temperature and high pressure hydrogen.

This invention relates to a method for heat treatment of steel.

(Prior art) A phenomenon of material deterioration called hydrogen erosion occurs in various pressure vessels in petroleum refineries and petrochemical plants, and in vessels operated for long periods under high temperature and high pressure hydrogen, such as in coal liquefaction and gasification processes. There is. This phenomenon is a phenomenon in which methane bubbles are generated when the carbides in the steel container material react with hydrogen that has entered the steel, and the material deteriorates rapidly after the incubation period unique to the steel material has passed. .

In the past, in order to prevent accidents caused by hydrogen corrosion, a Nern diagram was created that stipulated the upper limits of temperature and hydrogen pressure that would allow safe operation for each steel type of container material, based on the experience of accidents in actual equipment. Based on this, guidelines for the design and operation of pressure vessels have been established. %Cr, heavy oil desulfurization equipment, coal liquefaction equipment, or coal gasification equipment in petroleum refineries have harsh operating conditions.
-IMo steel.

High quality materials are used that are not susceptible to hydrogen attack, such as 3 cr -I Mo steel.

However, in recent years, reaction conditions have tended to become higher in temperature and pressure year by year in order to improve operational efficiency, and it is becoming difficult to cope with such harsh operating conditions using conventional materials.

By the way, a technique is known, for example, as disclosed in Japanese Patent Laid-Open No. 59-219450, etc., in which the hydrogen corrosion resistance of a material is improved by appropriately adjusting the P1 of the constituent elements of the material.

(Problems to be Solved by the Invention) If the chemical composition is changed according to the above-mentioned JP-A-59-219450, etc., the strength, toughness, weldability, manufacturability, etc. will also change. The problem remained that it was not always possible to economically obtain materials with the required material properties.

(Means for Solving the Problems) The present invention aims to provide a method for improving and eliminating the above problems, and by providing the method described in the claims, the above object can be achieved. can be achieved. That is, this invention provides c O, 20% or less,
Si 0.60% or less, Mn 1.0% or less, P0
．． 020% or less, SO, 010% or less, Cr
After quenching or normalizing Cr-Mo14 containing 2.0 to 3.5%, Mo, s to 1.6%, and the remainder substantially consisting of F8, it is subjected to at least one tempering treatment and /or stress relief annealing treatment to 600~
Within the temperature range of 750C and in the case of 1) below, formula (1)
), in the case of 2) below, the present invention relates to a heat treatment method for Cr-Mo steel having excellent hydrogen corrosion resistance, characterized in that the heat treatment is performed under conditions such that the S value derived from formula (2) is 810 or more. It is something.

1) If the tempering treatment and/or straddle stress relief annealing treatment is applied only once, the S value, T + 7! M30g t・・・・・・
(1) In the above formula (1), T: tempering treatment or stress relief annealing treatment temperature (C
), t: Tempering treatment or stress relief annealing treatment time (h
).

2) When tempering treatment and/or stress relief annealing treatment is performed two or more n times, T1: upper opening tempering treatment or stress relief annealing treatment temperature (C), tl: first time Tempering treatment or stress relief annealing treatment time (h).

Next, the present invention will be explained in detail.

Conventional 2% Cr-I Mo steel! 23Cr-I
When manufacturing pressure vessels etc. using Mo steel, after quenching or normalizing treatment, tempering treatment is performed at, for example, 650C for about 6 hours, giving the material enough toughness to withstand machining etc. After that, it is subjected to machining, welding, etc., and finally subjected to tempering treatment or stress relief annealing treatment for 10 to 25 hours at K 650 to 690 t: to form the final product material.

The present invention proposes to modify the conventional tempering treatment or stress relief annealing treatment (hereinafter referred to as PWHT) to impart superior hydrogen attack resistance properties to the material than in conventional heat treatment methods. This is the purpose.

The present inventors have conducted various studies to improve the hydrogen corrosion resistance of conventional Cr-Mo steel, and found that 2y4Cr-I Mo steel or 30r
-I It was newly discovered that the type of carbide present in Mo steel after tempering or PWHT largely depends on the temperature and/or time of the above-mentioned image treatment. By the way, hydrogen attack is a phenomenon in which carbides in steel react with hydrogen, producing methane bubbles and deteriorating the material.The inventors of the present invention have proposed that by precipitating stable carbides, the methane production reaction will be less likely to occur. The present invention was completed as a result of research based on the assumption that material deterioration due to hydrogen erosion would be less likely to occur.

Typical heat treatment conditions when manufacturing pressure vessel materials using conventional Cr-Mo steel, such as quenching or normalizing the material, tempering at 650C for about 6 hours, and then manufacturing the vessel by machining, welding, etc. After that, 22 at 690C
The S value of the final product subjected to PWHT of about h is 793. However, the present inventors have developed a method using normal tempering treatment or P.
It was newly discovered that when the S value is increased to 810 or more by increasing the treatment temperature or the treatment time higher than WHT, hydrogen attack occurs significantly and the chicks become unformed.

Next, the reason for limiting the composition of the 2ACr-xMo steel and 3Gr-IMo steel treated according to the present invention will be explained.

C: C is an element that contributes to improving strength, but 0.20
If it exceeds 0.2%, weldability deteriorates and hydrogen corrosion resistance also deteriorates, so it is necessary to keep C at 0.20% or less.

Si: Si is an element that contributes to deoxidation and improvement of strength, but if the amount of Sl exceeds 0.60, tempering embrittlement occurs.
Sl should be kept below 0.60% because it increases susceptibility to hydrogen attack and reduces creep rupture strength.

Mn: Mn is an element that contributes to improving strength, but if it exceeds 1.0%, it increases the susceptibility to tempering embrittlement, so Mn needs to be 1.0% or less.

P: P segregates at grain boundaries and causes tempering embrittlement, so it is desirable to suppress it to as low a level as possible, but since the dephosphorization operation is performed in actual operation, it does not increase costs and does not cause tempering embrittlement. It is necessary to keep it below the upper limit of 0.02096.

S: When S is contained in excess, it deteriorates toughness and increases SR.
Since it increases cracking susceptibility, S needs to be 0.010- or less.

Cr: Cr is an element that contributes to improving hydrogen corrosion resistance 1 strength and toughness, but if it is less than 2.01, the effect of improving hydrogen corrosion resistance due to PWHT and tempering treatment conditions, which is the objective of the present invention, is not sufficient. On the other hand, if the PWHT is more than 1 and 61 than 3.5 inches, the tempering conditions? Cr is 2.0 to 3 because the change in hydrogen corrosion resistance properties will be less even if the change is made.
．． It must be within the range of 5-.

Mo: Mo is an element that contributes to improving strength, toughness, and creep rupture strength, but if it is less than 0.8%, the effect of improving the above properties cannot be obtained sufficiently, while if it is more than 1.6%, the above Since the effect of improving characteristics is saturated and uneconomical, M
o needs to be within the range of 0.8 to 1.6%.

Next, the reason for limiting the heat treatment conditions of the present invention will be explained.

PWHT or tempering treatment is performed for the purpose of removing thermal stress or improving toughness after welding, but the effect is not sufficient when treated at temperatures below 600C, while ferrite is formed when treated at temperatures higher than 750C. Therefore, the PWHT or tempering temperature must be within the range of 600 to 750C.

Next, increase the above PWHT or tempering temperature to 600-7
The reason why the S value is set within the range of 50C and at least 810 will be explained.

The S value defined by the above formula (1) or (2) is G
It depends on the hydrogen corrosion resistance property of r-Mo#, and the S value is 81
If the S value is less than 0, the hydrogen corrosion resistance will deteriorate when subjected to PWHT or tempering treatment, so when the S value is 810 or more, especially 815 or more, the above characteristics are particularly improved.

Next, the present invention will be explained with reference to examples.

Example 2ACr-IMo steel having the composition shown in Table 1 and 30r-IMo were each heated at 950C for 2.5
After quenching or normalizing treatment of h, 23ACr
-I Table 2 for Mo steel, and 3 Cr -IM
o Steel is tempered and/or treated under the conditions shown in Table 3.
Or PWHT was applied. A Charpy impact test piece was cut out and 2y4Cr-I Mo! 14K vs 600C, hydrogen pressure 300KPf/lL2te, 30r
-IMo Steel K is 600C.

Hydrogen pressure to 500? After performing high-temperature and high-pressure hydrogen treatment for a maximum of 1000 hours using f/cIL2, a 7 yalpy impact test was performed using OC. The dependence of Charpy absorbed energy on hydrogen treatment time is measured, and the time when the absorbed energy begins to decrease is referred to as the incubation period of hydrogen attack.

The S value and hydrogen attack incubation period of the samples subjected to the tempering treatment and/or PWHT are shown in Table 2 for 2y4Cr-IMo steel, and in Table 3 for 3Cr-IMo steel.

@1 Table From these tables, the incubation period of hydrogen erosion depends on the IfiS value,
Tempering treatment or PWHT that results in an S value of 810 or more
It can be seen that when f;

(Effects of the Invention) As shown above, 9Cr-M produced by the present invention
O-steel exhibits excellent hydrogen corrosion resistance, is optimal as a material for pressure vessels operated under high pressure and high water pressure, and has excellent industrial value.

Claims (1)

[Claims] 1 C0.20% or less, Si 0.60% or less, Mn1.
0% or less, P 0.020% or less, S 0.010% or less,
Contains 2.0-3.5% Cr, 0.8-1.6% Mo,
After quenching or normalizing the Cr-Mo steel, the remainder of which is substantially composed of Fe, at least one tempering treatment and/or stress relief annealing treatment is performed at a temperature of 600 to 75
A method for heat treating Cr-Mo steel having excellent hydrogen corrosion resistance, characterized in that the heat treatment is performed within a temperature range of 0° C. and under conditions such that the S value derived from the following formula (1) is 810 or more. S value=Tn+75log(Σ^n_l_=_1ti・1
0^(^T^i^-^T^n^)^/^7^5)...
(1) In the above formula (1), Ti: i-th tempering treatment or stress-relief annealing treatment temperature (°C), ti: i-th tempering treatment or stress-relief annealing treatment time (h), n: Number of times of tempering treatment and/or stress relief annealing treatment (including n=1).