CN101419139A - Method for preventing steel plate special for flaw detection from generating hydrogen induced cracking - Google Patents

Abstract

The invention provides a method for preventing a special flaw detection plate from producing hydrogen-induced crack. The method is characterized in that under the condition of having no RH or VD vacuum treatment, the moisture of a large ladle covering agent and a middle ladle covering agent is controlled to reduce the hydrogenization of molten steel in the refining and continuous casting process of an LF furnace; a casting blank is subjected to stowing and slow cooling for 48 hours to promote the diffusion of hydrogen to ensure that the hydrogen content of the casting blank is less than 3 ppm; the molten steel is rolled, and is subjected to stowing and slow cooling for 24 to 48 hours; and the hydrogen is fully escaped and the inner stress is removed in order that the H content of the molten steel is less than 1 ppm, thereby avoiding the generation of the hydrogen-induced crack in the core part of the special flaw detection plate. The method does not need to adopt RH/VD vacuum treatment equipment and special hydrogenization equipment, has low production cost and has the advantages of substantially reducing probability for producing the hydrogen-induced crack in the core part of the special flaw detection plate and improving the qualification rate of flaw detection of the special flaw detection plate for a vessel, a bridge, a boiler, pipeline steel, an architectural structure and the like.

Description

A kind of method that prevents steel plate special for flaw detection from generating hydrogen induced cracking

Technical field

The invention belongs to the cut deal manufacturing process, particularly provide a kind of personality board that prevents to detect a flaw to produce the method for hydrogen induced cracking, be applicable to that container, bridge, boiler, pipe line steel, building structure the production of each steel grade flaw detection personality board such as uses.

Background technology

The hot rolled steel plate that container, bridge, boiler, pipe line steel, building structure such as use at important use all requires the UT (Ultrasonic Testing) check, to guarantee the safe reliability of engineering except satisfying dimensions, mechanical property and surface quality etc. require.But because flaw detection qualification rate is low, and fluctuation is very big, has a strong impact on production cycle, contractual delivery phase and production cost, and the flaw detection problem has become the bottleneck of variety steel development.

Influencing the factor that steel plate inspection do not conform to has hydrogen, segregation, snotter etc., but through to a large amount of contrast test of different steel grades, check and analysis, the hydrogen induced cracking of determining steel plate heart portion is the principal element that causes steel plate inspection not conform to.

The ultrasonic testing figure that steel plate inspection does not conform to is seen Fig. 1, and steel plate heart portion hydrogen induced cracking photo is seen Fig. 2～Fig. 4, and the qualified photo of organizing of steel plate inspection is seen Fig. 5.

Steel plate inspection does not conform to dominant mechanism: in smelting and casting process, hydrogen enters molten steel, and in the casting blank solidification process, along with decrease of temperature, the solubleness of hydrogen in steel constantly reduces.When strand cooled off gradually, part hydrogen was gradually to external diffusion, and part hydrogen still with the state of atom supersaturation be solid-solubilized in the steel, subsequent section hydrogen is deposited in the holes such as the shrinkage cavity of strand heart portion, loose and snotter, is combined into molecule hydrogen.When strand is rolling, hole by compression, hole middle part fractionated molecule hydrogen is because volume compression and to the bigger pressure of metal on every side.

Drop to 300 ℃ below the temperature when steel plate cools off fast, oversaturated hydrogen is constantly separated out in the steel, constantly entad gathers in portion's hole, and is combined into the very big hydrogen pressure of hydrogen molecule formation.Under hydrogen pressure and internal stress reciprocation, surpass the metal strength limit, thereby produced heart check, finally cause the UT (Ultrasonic Testing) disqualified upon inspection.

According to the mechanism that above-mentioned flaw detection does not conform to, key is the high problem of hydrogen content that will solve in the steel.

The main method that reduces hydrogen content in the steel both at home and abroad has:

1. adopt RH or VD application of vacuum, reduce hydrogen richness, make hydrogen≤2ppm in the steel.But this method equipment has high input, the cost height.

2. adopt the method for hydrogen DIFFUSION TREATMENT, steel the diffusion heat treatments stove of special use, slow cooling box, etc. equipment carry out the diffusion of hydrogen, this method is limited by the place, and the cost height.

3. adding the method for titanium elements in the employing molten steel, is that the Chinese invention patent of CN101033513A has openly illustrated " a kind of method of manufacturing seamless steel pipe that suppresses hydrogen resulted abscission layer defect " as the patent No..Smelt the back at molten steel and add 0.010～0.030% titanium, its mechanism is to form the TiC precipitated phase, artificially makes irreversible hydrogen trap, catch trap hydrogen molecule on every side, prevent the poly-partially of hydrogen, thereby suppress the generation of inside steel billet hydrogen induced cracking, to solve the problem of steel pipe absciss layer defective.

Container, bridge, boiler, pipe line steel, building structure such as use at variety steel, wherein the part steel grade contains titanium elements, the flaw detection statistics shows that Ti content and steel plate inspection qualification rate do not have corresponding relation, as contain the steel grades such as X60 pipe line steel of Ti0.019～0.021%, before adopting the inventive method, flaw detection qualification rate is lower always.Titanium elements is very little to suppressing the hydrogen induced cracking effect of steel plate heart portion after deliberation.

The method that the present invention controls hydrogen richness by control big covering agent, middle covering agent moisture and slab, the finished product steel plate adopts stacking slow cooling to realize, do not use specialized apparatus to expand hydrogen and handle, so the present invention is different from said method.

Summary of the invention

The purpose of this invention is to provide a kind of method that prevents steel plate special for flaw detection from generating hydrogen induced cracking, particularly under the condition that does not have RH or equipment such as VD vacuum treatment device and special-purpose hydrogen diffusion, or do not use under the vacuum treatment device situation for reducing cost, by reducing hydrogen richness in the steel, prevent the generation of steel plate heart portion hydrogen induced cracking, to solve the low problem of flaw detection personality board flaw detection qualification rate.

Purpose of the present invention can realize by following concrete grammar:

(1) before the LF stove is smelted, big covering agent, middle covering agent auxiliary material are toasted, make big covering agent, middle covering agent moisture≤0.5%.

(2) after the thick 220mm-250mm slab cutting, carry out stacking slow cooling, 800～950 ℃ of stacking slow cooling temperature, make hydrogen richness≤3ppm in the strand at 48 hours stacking slow cooling time.

(3) during thickness 18～70mm finished product steel plate air cooling to 260～500 ℃, fast steel plate is carried out stacking slow cooling in the cold bed zone, during 260～500 ℃ of stacking slow cooling temperature, steel plate stacking piece number 〉=8, thick 〉=30～70mm steel plate stacking slow cooling time is 48 hours, thick 〉=18mm～＜the 30mm steel plate stacking slow cooling time is 24 hours, makes the final hydrogen richness of finished product steel plate less than 1ppm.

Adopt modes such as desulfurizing iron processing, LF refining, full guard casting; control O, S, P content and The amount of inclusions; carry out the Ca degenerative treatments; make that inclusion modification such as MnS and Al2O3 is the near-spherical snotter in the steel; its harmful element control S: P≤0.010% :≤0.022%, lay the first stone for guaranteeing the steel plate inherent quality.

In LF refining and casting process, needing to add auxiliary material has synthetic slag, bauxite, Si-Ca line, Lushan lime, big covering agent, synthetic slag etc., through repeatedly measuring moisture, has only big covering agent and middle covering agent moisture to exceed standard, and sees Table 1.In order to save cost, reduce workload, adopt emphasis to control the method for big covering agent and middle covering agent moisture.Before the LF stove is smelted, big covering agent, middle covering agent are toasted, guarantee≤0.5%.

The main supplementary material determination of moisture result (%) that table 1 is not handled

The Si-Ca line	Synthetic slag	Bauxite	Lushan lime	Two anti-lime	Big covering agent	Middle covering agent	Covering slag	The C powder
									0.21	0.05	0.18	0.07	0.03	0.78	2.03	0.33	0.18
0.34	0.22	0.20	0.15	0.02	1.48	0.80	0.10	0.58
									0.56	0.10	0.21	0.03	0.03	1.94	2.41	0.24	0.57
0.16	0.01	0.12	0.12	0.02	1.57	1.11	-	0.52
									0.13	0.02	0.24	0.05	0.04	-	1.28	0.30	0.36
0.27	0.03	0.10	0.02	0.02	1.18	-	0.32	-
									0.05	0.00	0.12	0.00	0.02	1.04	0.84	0.51	0.66
1.40	0.04	0.08	0.02	0.05	1.57	0.92	0.29	0.47
									0.20	0.02	0.07	0.09	0.02	1.24	0.36	1.31	0.52
0.62	0.03	0.09	0.10	0.00	2.06	1.14	0.46	0.49

After the thick 220mm-250mm slab cutting, slab is carried out stacking slow cooling, 800～950 ℃ of slab stacking temperature, make hydrogen richness≤3ppm in the strand at 48 hours stacking slow cooling time.

Slab is after heating-controlled rolling-control cooling-thermal straightening, during thickness 18～70mm finished product steel plate air cooling to 260～500 ℃, in the cold bed zone fast with the steel plate stacking slow cooling, steel plate stacking piece number 〉=8, thick 〉=30～70mm steel plate stacking slow cooling time is 48 hours, thick 〉=18mm～＜the 30mm steel plate stacking slow cooling time is 24 hours.The slow cooling time that steel plate is taked is determined according to hydrogen diffusion simulations result of calculation.

The present invention has following advantage:

Need not to adopt RH or VD equal vacuum to handle and special-purpose hydrogen diffusion facilities, the inventive method is simple, practical, cost is low.Enforcement by the inventive method, container, bridge, boiler, pipe line steel, building structure such as use to bring up to more than 97% by about 70% at each steel grade flaw detection personality board average of the whole year flaw detection qualification rate, and be implemented under the existing process equipment condition low-cost production high-quality flaw detection personality board product.

Description of drawings

The ultrasound wave figure photo that Fig. 1 does not conform to for thick 40mm steel plate inspection.Flaw detection defect waves height is about 68%, and the position of defective is at the 20mm place, half of steel plate thickness 40mm, the i.e. heart portion of steel plate.

Fig. 2 does not conform to the heart check photo for thick 70mm steel plate inspection.

Fig. 3 does not conform to transcrystalline cracking photo in the heart portion pearlite for thick 48mm steel plate inspection.

Fig. 4 does not pass bainite structure form photo for thick 48mm steel plate inspection conforms to crackle.

Fig. 5 is the qualified tissue morphology photo of thick 48mm steel plate inspection.

Embodiment

The present invention will be described in further detail the method that prevents steel plate special for flaw detection from generating hydrogen induced cracking in conjunction with example:

Embodiment 1:

The X60 pipe line steel adopts two kinds of technologies to produce, and 6C05605 stove adopting process mode is the inventive method, promptly adopts control auxiliary material moisture+48 hours+finished steel of strand slow cooling sheetpile to pile up neatly slow cooling 24 hours.The 6C05606 stove adopts former technology mode, and promptly not controlling auxiliary material moisture+strand does not have slow cooling+finished product steel plate air cooling.Heat (batch) number 6C05605,6C05606 desulfurizing iron, converter smelting, the refining of LF stove, strand heating, controlled rolling and controlled cooling etc. adopt identical production technology.With 220mm * 1600mm * 2800mm slab rolling finished size 20mm * 1875mm * 11800mm X60 pipe line steel.X60 pipe line steel chemical constitution such as table 2, two kinds of technology flaw detection comparing results of X60 pipe line steel such as table 3.As shown in table 3, the 6C05605 stove adopts technology mode flaw detection qualification rate 100% of the present invention, and the 6C05606 stove adopts former technology mode flaw detection qualification rate to have only 39.63%.

Table 2 X60 pipe line steel chemical constitution (wt%)

Heat (batch) number	C	Si	Mn	P	S	Alt	Als	V	Ti	Nb	Mo	Ca
													6C05605	0.06	0.38	1.58	0.010	0.003	0.0426	0.0379	0.065	0.019	0.066	0.079	0.0028
6C05606	0.05	0.39	1.50	0.011	0.002	0.0392	0.0363	0.069	0.021	0.061	0.075	0.0033

Two kinds of technology flaw detections of table 3 X60 pipe line steel comparing result

Embodiment 2:

Table 4 has been listed the flaw detection comparing result that 16MnR, Q345GJCZ15, Q460C steel grade adopt two kinds of technologies.As shown in table 4, the flaw detection qualification rate scope that adopts technology mode steel plate of the present invention is 95.17～100%, and the flaw detection qualification rate scope that adopts former technology mode steel plate is 54.87～79.25%, obviously, after adopting technology mode of the present invention, the steel plate inspection qualification rate is improved significantly.

Two kinds of technology flaw detections of table 4 X60 pipe line steel comparing result

Claims (1)

1, a kind of personality board that prevents to detect a flaw produces the method for hydrogen induced cracking, and it is characterized in that: described method step is as follows:

(1) before the LF stove is smelted, big covering agent, middle covering agent auxiliary material are toasted, make big covering agent, middle covering agent moisture≤0.5%.

(2) after the thick 220mm-250mm slab cutting, carry out stacking slow cooling, 800～950 ℃ of stacking slow cooling temperature, make hydrogen richness≤3ppm in the strand at 48 hours stacking slow cooling time.

(3) during thickness 18～70mm finished product steel plate air cooling to 260～500 ℃, fast steel plate is carried out stacking slow cooling in the cold bed zone, during 260～500 ℃ of stacking slow cooling temperature, steel plate stacking piece number 〉=8, thick 〉=30～70mm steel plate stacking slow cooling time is 48 hours, thick 〉=18mm～＜the 30mm steel plate stacking slow cooling time is 24 hours, makes the final hydrogen richness of finished product steel plate less than 1ppm.

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