CN101509861A - Judgement method for protective capability of weathering steel rust layer - Google Patents

Abstract

The invention relates to a judging method for the degree of protecting capacity of a weather-proof steel rust layer, belonging to the corrosion of the steel material in atmosphere environment. The method proposes that a method of combining weight loss and weight increment is adopted to judge the conditions of gaining and loss of the water in corrosion products; dehydration test and water absorption test are adopted; the dehydration test and water absorption test are carried out through the way of circulating alternation till the water absorption rate and dehydration rate are not changeable; and then the difficulty level of dehydration and water absorption of the corrosion products is judged, thus judging the degree of the protecting capacity of the weather-proof steel rust layer. The method overcomes the defect that the existing detection means for judging the weatherability of steel neglect the important role of the water, and not only reflects the protecting capacity of the weather-proof steel rust layer actually, leading the judging result to be more actual and reliable, but also has more simple and easy process.

Description

A kind of decision method of weathering steel rusty scale protective capability size

Technical field

The invention belongs to the corrosion of ferrous materials in atmospheric environment, particularly the judgement of weathering steel rusty scale protection.

Background technology

Naked steel corrosion resistance under naval air environment mainly is to rely on the corrosion product layer of the stable densification of surface formation that the obstruction of corroding progress is realized.People mainly contain weight-loss method, corrosion product analysis and electrochemical process to the evaluation of this inhibition of corrosion product layer at present.

Weight-loss method is to weigh the corrosion progress of steel under certain environment with attenuate amount on the weight per unit area loss of steel behind the removing surface corrosion product or the unit area.This is the simplest and effective macroanalysis method of a kind of assessment metal atmospheric corrosion, can truly reflect the atmospheric corrosion dynamics of metal.Document " corrosion research of ULCB plow-steel " (Wuhan University Of Technology's journal (natural science edition) [J] for example, 2008,31 (2): the employing weight-loss method of report provides evidence for " the seawater corrosion resistance ability of ULCB plow-steel is higher than Seawate-corrosive-resisting steel CrMoAl commonly used " this experimental result 127-131); By observing weightlessness or attenuate slope of a curve, can judge the speed of steel a certain moment corrosion progress in this environment.When curve and time shaft were approximate parallel, stable fine and close rusty scale formed in the corrosion product, and the corrosion process of steel slowly takes place.This method is widely used, and various countries have also all formulated the standard that corrosion product is removed, as the standard GB/T 16545-1996 of China.

The corrosion product analysis method be by the composition of a series of means analysis corrosion products and performance reflect its steel anticorrosive aspect the method for effect.General people adopt scanning electron microscope or metaloscope to observe the structure and the pattern of the corrosion product layer of close matrix, with the content of thermodynamics stable state material in XRD or the spectral analysis corrosion product, reflect the compactness of rusty scale etc. indirectly with nitrogen absorption investigation corrosion product grain size.For example, document " decay resistance of the weather-proof steel of low-alloy in the chloride ion-containing environment " (material heat treatment journal [J], 2008,29 (4): report adopts means such as metallography microscope sem observation and XRD material phase analysis to investigate the decay resistance of the weather-proof steel of low-alloy in the chloride ion-containing environment 171-175); Document " exposes carbon steel and the rusty scale analysis of weathering steel surface in 2 years ", and (corrosion and protection [J], 2002,23 (3): 97-98,101) middle report has been analyzed carbon steel and the weathering steel surface rusty scale that exposes 2 years with infra-red sepectrometry.

Because the corrosion of steel under atmospheric environment is galvanic corrosion, so electrochemical method also has its distinctive feature on research steel corrosion product property.People often adopt AC impedence method to calculate the internal resistance size of steel corrosion product layer in particular etch solution, judge steel rusty scale resistance to corrosion from the ability aspect that hinders charge exchange.The research of anti-Hou Gang in the atmosphere of coastal waters and carbon steel corrosion resistance being carried out as document " research of anti-Hou Gang and carbon steel corrosion resistance in the atmosphere of coastal waters " (Materials Science and Engineering [J], 2001,19 (2): 12-15,25) report.

Yet these methods tend to ignore the effect of moisture in the corrosion product resistance to corrosion.This moisture is not a large amount of, complete macroscopical aqueous solution of submergence matrix, but in atmospheric environment, small water droplet or even hydrone in the steel surface corrosion product layer.Many means in the corrosion product analysis method are all carried out after to corrosion product drying or vaccum dewatering, and purpose is to get rid of the interference of moisture; And electrochemical method will be measured in the complete submergence etchant solution of material.From the angle that reduces error is correct, but does not reflect the truth that steel surface corrosion product combines with micro-moisture under the atmospheric environment.

Summary of the invention

The deficiency of all having ignored the vital role of moisture for the detection means that overcomes existing judgement steel weatherability in the above-mentioned analysis; propose to adopt the weightless method that combines with weightening finish to judge the gain and loss situation of moisture in the corrosion product; the protective capability that not only reflects the weathering steel rusty scale truly; make result of determination more true and reliable, and process is more simple.

The step of this method is as follows:

(1) dehydration test

To after the moistening different steel grade corrosion more than 12 hours of moist environment, weigh and be recorded as m by sample _jAfter the test of dewatering, promptly in 50～95 ℃ thermostatic drying chamber or drying basin, carry out drying, sampling in per 1～12 hour is once weighed and is recorded as m according to grade of steel _Ji, i is the sampling number of times, and j is the steel grade numbering, and footnote is down together; Adopt formula:

$M_{\mathrm{ji}}=\frac{m_j-m_{\mathrm{ji}}}{S_j}$

Calculate the dehydrating amount M of each unit area corrosion product _Ji, wherein, S is the surface area of each original steel sample; Make the M of each steel sample respectively _JiThe curve map of-t (time) is judged the difficulty or ease that corrosion product dewaters by slope of a curve, works as M _JiWhen-t curve and time shaft almost parallel or curve are enough to distinguish each steel grade, the dehydration end of test (EOT).

(2) water absorption test

With used steel sample of above test or the drying that from 50～95 ℃ dry environment, obtains corrosion sample, be recorded as n after weighing _j, j is the steel grade sequence number, is put in relative humidity greater than absorbing water in 50% the constant moist environment, sampling in per 0.5～2 hour is once measured weight, is recorded as n _Ji, i is the sampling number of times; Use following formula to calculate water absorbing capacity N _Ji:

$N_{\mathrm{ji}}=\frac{n_{\mathrm{ji}}-n_j}{S_j}$

Wherein, S is the surface area of each original steel sample; Make each steel N _JiThe curve map of-t (time) is judged the difficulty or ease that corrosion product absorbs water by slope of a curve; Work as N _JiWhen-t curve and time shaft almost parallel or curve were enough to distinguish each steel grade, water absorption test finished.

In addition, produce new corrosion product in order to prevent sample in the drying and wetting, or need more illustration in the reality, other two additional tests also will be carried out, promptly pure corrosion product take off water absorption test and repeatedly round-robin take off water absorption test.

Pure corrosion product take off the protective value that water absorption test is judged corrosion product when not having matrix to participate in; its step is roughly the same with band rust bloom; do not exist together for investigated to as if the corrosion product that scrapes off from steel; and characterize the physical quantity take off absorption speed and should be and take off suction number percent, it is as follows respectively to take off the suction formula:

$M_{\mathrm{ji}}=\frac{m_j-m_{\mathrm{ji}}}{m_j}\×100\%$ $N_{\mathrm{ji}}=\frac{n_{\mathrm{ji}}-n_j}{n_j}\×100\%$

Repeatedly round-robin is done the stability that wet test is used for judging rusty scale, and its step is that dehydration, two testing procedure cycle alternations of suction are carried out, till sample suction, rate of water loss no longer change.

The beneficial effect of this method:

This method has more comprehensively been considered the effect of moisture.Exposed steel are because the cathode reactant regenerative response under the drying condition: 2{FeOHOH}+1/2O corroding easily under the atmospheric environment of alternation of wetting and drying ₂----〉2 γ-FeOOH+H ₂O.This reaction impels the formation of γ-FeOOH, causes the oxidation of Fe atom under moist environment subsequently.Under the wet condition in the atmospheric environment water of trace and the water of crystallization that combines with corrosion product can fill up in the hole in the porous corrosion product.When environmental baseline is dry, there are some to be not easy to vapor away than water in the small holes and most water of crystallization, they can stop up hole, prevent the invasion of oxygen molecule in the atmosphere, reduce the generation of cathode reactant, the cathode reaction in the corrosion of finally slowing down.These rely on the surface tension of water and surfactivity to pass through wick water than small holes under the moist environment, and water of crystallization forms by crystallization reaction, so their formation speed is faster than the water than macroscopic void.This method is exactly to inhale the size of dewatering speed and characterize and wherein have this than small holes and crystalline hydrate quantity what by investigating the corrosion product layer, thereby judges that the corrosion product layer hinders the size of corrosive power.

Simultaneously, under the alternation of wetting and drying condition, the corrosion product of steel also can change to thermodynamics stable state, and stable material not only can reduce the oxidation to matrix, and can also form the less fine and close rusty scale of composition particle, and the protection matrix is not subjected to the invasion of extraneous ion.So this method also can be replenished to taking off the suction rate variations by test corrosion product moisture in drying and wetting repeatedly, judges its stability size, reflects erosion-resisting ability indirectly.

In addition, this method is easy to use, need not very accurate instrument, and only need a precision balance and some experimental facilitiess that are seen everywhere just can finish.Test process is simple, can draw data very soon.

Description of drawings

Fig. 1 is a histogram of judging steel corrosion product resistance to corrosion size with electrochemical method.

Fig. 2 is to use the nitrogen adsorption method to judge the histogram of steel corrosion product resistance to corrosion size.

Fig. 3 is for inhaling the corrosion product water desorption curve that carries out according to embodiment 1 in the dehydration test.

Fig. 4 is for inhaling the corrosion product water suction curves that carries out according to embodiment 1 in the dehydration test.

Fig. 5 is for inhaling the corrosion product water desorption curve that carries out according to embodiment 2 in the dehydration test.

Fig. 6 is for inhaling the corrosion product water suction curves that carries out according to embodiment 2 in the dehydration test.

Fig. 7 is for inhaling the corrosion product dehydration number percent curve that carries out according to embodiment 3 in the dehydration test.

Fig. 8 is for inhaling the corrosion product suction number percent curve that carries out according to embodiment 3 in the dehydration test.

Fig. 9 is for inhaling the corrosion product suction number percent curve that carries out according to embodiment 4 in the dehydration test.

Figure 10 is for inhaling the corrosion product dehydration number percent curve that carries out according to embodiment 4 in the dehydration test.

Embodiment

Before detection was carried out, the steel grade that will investigate was cut into the coupon of same size earlier, and the surface is with sand papering to No. 1000, and cleaning is deoiled, and measuring to render to behind the length of sample needs to corrode under the naval air environment investigated or the simulated environment.True naval air environment corroded 4 months down or the lab simulation environment can be taken a sample after following 15 days, takes off water absorption test.Used key instrument has: precision balance (precision reaches 100 μ g), and the thermostatic drying chamber drying basin of new drying agent (or be equipped with), psychrometer, Water Tank with Temp.-controlled with cover, simple rack and double dish and vial are some.

Test material and previous experiments:

Two kinds of steel are selected in test for use, and a kind of is the old-fashioned homemade weathering steel 09CuPCrNi that has been extensive use of for many years, and a kind of is the high strength bainite weathering resistant steel with excellent weather resistance energy that new development is got up.Two kinds of steel line-transects cut out each 4 of the coupons of 60 * 40 * 5cm, they are carried out indoor salt fog accelerated corrosion experiment, the salt fog cabinet model is ATLAS CCX, corrosive liquid is that mass concentration is 0.5% sodium-chloride water solution, setting the dried wetted perimeter phase is 24 hours, and wherein salt fog is 6 hours, dries 18 hours, the temperature inside the box is controlled at 40 ℃, and relative humidity is 97%.For guaranteeing uniform corrosion, each cycle is turned over sample one time.Every sampling in four days once, band rust sample is carried out ac impedance measurement, and use computer simulation, gained rusty scale internal resistance value as shown in Figure 1, wherein B-S is a bainitic steel, down together.

As seen, the rusty scale resistance of bainitic steel shows that it can better stop the charge exchange in the electrochemical reaction, thereby reduces corrosion rate greater than 09CuPCrNi; In addition, scrape off the corrosion product of specimen surface during respectively at corrosion 4 days and 16 days, specific surface area with the determination of nitrogen adsorption particle, the result as shown in Figure 2, the specific surface area of the corrosion product particle of bainitic steel is bigger, shows that its particle size is less, and smaller particles has bigger surface energy, can form fine and close more rusty scale, thereby stop corrosion reaction.In summary, bainitic steel weather resistance be higher than 09CuPCrNi.

Embodiment 1:

With two kinds of steel samples each 3 of coupons of line cutting 60 * 40 * 5cm once more, do same processing and corrosion with previous experiments, corrode and close salt fog after 16 days and spray, keep that the interior humidity of case was progressively taken off after 24 hours, water absorption test, step is as follows:

The dehydration test:

1) will put into the dry double dish of suitable size after the sample taking-up, weigh is recorded as m _a, m _b, footnote a, b represent 09CuPCrNi and bainitic steel respectively.

2) it is dry the sample of band double dish to be put into the drying basin that new drying agent is housed, and drying agent is selected discolour silica gel for use.

3) set sampling in per 12 hours once, weigh, be recorded as m _Ai, m _Bi, i is the sampling number of times.

4) calculate the dehydrating amount M of sample unit area corrosion product respectively with following formula _AiAnd M _BiAnd run a curve as Fig. 3.

$M_{\mathrm{ai}}=\frac{m_a-m_{\mathrm{ai}}}{S_a}$ $M_{\mathrm{bi}}=\frac{m_b-m_{\mathrm{bi}}}{S_b}$

S is the surface area of each original steel sample.

5) as seen from Figure 3, after dewatering time reached 60 hours, curve was almost parallel with time shaft, and this moment, the dehydration test can finish.

Water absorption test:

1) sample is put in the baking oven into dry 2 hours of constant temperature 95 ℃ (temperature can not be too high, otherwise the oxyhydroxide in the rusty scale can decompose), weighing is recorded as n _a, n _b, the footnote implication as above, and is together following.

2) wet environment of suction use is provided by Water Tank with Temp.-controlled.Tank is placed in the experiment closet, and heating is also partly covered sink cover, with near the ambient humidity psychrometer mensuration sink cover, regulates heating-up temperature and makes humidity reach 97%.

3) sample being placed on relative humidity is to absorb water in the environment near 97% the tank.Every 1 hour sampling one-shot measurement weight, be recorded as n _Ai, n _Bi

4) calculate the water absorbing capacity N of sample unit area corrosion product according to formula _AiAnd N _Bi, and run a curve as Fig. 4.

5) as shown in Figure 4, after test was carried out 9 hours, the difference of two kinds of steel was fairly obvious, can finish test.

$N_{\mathrm{ai}}=\frac{n_{\mathrm{ai}}-n_a}{S_a}$ $N_{\mathrm{bi}}=\frac{n_{\mathrm{bi}}-n_b}{S_b}$

Find out according to above dehydration suction analysis, the dehydration of the corrosion product of 09CuPCrNi steel is comparatively fast more in two kinds of steel, and suction is more less, show that its inner hole is bigger, a little less than stoping ability to the oxygen in the atmosphere under the drying condition, resistance to corrosion than bainite weathering resistant steel a little less than, this also just in time meets the test result of measuring with classic method.

Embodiment 2:

With the coupon of 60 * 40 * 5cm, do same processing and corrosion with previous experiments, corrode and close salt fog after 16 days and spray, reduce in the case humidity reach 50% and keep progressively taking off after 48 hours, water absorption test.

The dehydration test:

1) will put into the dry double dish of suitable size after the sample taking-up, weigh is recorded as m _a, m _b, footnote a, b represent 09CuPCrNi and bainitic steel respectively.

2) sample is packed in 50 ℃ the thermostatic drying chamber, got once, weigh, be recorded as m every 12 hours _Ai, m _Bi, i is the sampling number of times.

3) calculate the dehydrating amount M of sample unit area corrosion product according to formula _AiAnd M _Bi, and run a curve as Fig. 5.

$M_{\mathrm{ai}}=\frac{m_a-m_{\mathrm{ai}}}{S_a}$ $M_{\mathrm{bi}}=\frac{m_b-m_{\mathrm{bi}}}{S_b}$

S is the surface area of each original steel sample.

4) as seen from Figure 5, after dewatering time reached 60 hours, curve was almost parallel with time shaft, and this moment, the dehydration test can finish.

Water absorption test:

1) sample was put in the baking oven into 50 ℃ of dryings of constant temperature 60 hours, weighing is recorded as n _a, n _b, the footnote implication as above, and is together following.

2) wet environment of suction use is provided by Water Tank with Temp.-controlled.Tank is placed in the experiment closet, and heating is also partly covered sink cover, with near the ambient humidity psychrometer mensuration sink cover, regulates heating-up temperature and makes humidity reach 50%.

3) sample being placed on relative humidity is to absorb water in the environment near 50% the tank.Every 2 hours sampling one-shot measurement weight, be recorded as n _Ai, n _Bi

4) calculate the water absorbing capacity N of sample unit area corrosion product according to formula _AiAnd N _Bi, and run a curve as Fig. 5.

$N_{\mathrm{ai}}=\frac{n_{\mathrm{ai}}-n_a}{S_a}$ $N_{\mathrm{bi}}=\frac{n_{\mathrm{bi}}-n_b}{S_b}$

5) as shown in Figure 6, after test was carried out 10 hours, the difference of two kinds of steel was apparent in view, can finish test.

By this test as seen, when test condition changes to some extent, decrease though the corrosion product layer is inhaled dehydrating amount, but still can judge the steel atmospheric corrosion resistance by this character.

Embodiment 3:

This test is to prove the availability of this method for pure corrosion product.

The dehydration test:

1) 16 days sample corrosion products of salt air corrosion are scraped off, in the vial of packing into, the relative humidity that putting into Water Tank with Temp.-controlled provides is environment suction taking-up after 12 hours of 80%, and weigh is recorded as m _a, m _b, footnote a, b represent 09CuPCrNi and bainitic steel respectively.

2) it is dry sample to be put into the drying basin that new drying agent is housed, and drying agent is selected discolour silica gel for use.Set sampling in per 12 hours once, weigh, be recorded as m _Ai, m _Bi, i is the sampling number of times.

3) calculate the dehydration number percent M of corrosion product according to formula _AiAnd M _Bi, and run a curve as Fig. 7.

$M_{\mathrm{ai}}=\frac{m_a-m_{\mathrm{ai}}}{m_a}\×100\%$ $M_{\mathrm{bi}}=\frac{m_b-m_{\mathrm{bi}}}{m_b}\×100\%$

4) as seen, after dewatering time reached 60 hours, curve was basically parallel to time shaft, the dehydration end of test (EOT).Water absorption test:

1) sample was put in the baking oven into 95 ℃ of dryings of constant temperature 2 hours, weighing is recorded as n _a, n _b, the footnote implication as above, and is together following.

2) wet environment is provided by Water Tank with Temp.-controlled, and setting relative humidity with preceding method is 60%.Every 1 hour sampling one-shot measurement weight, be recorded as n _Ai, n _Bi

3) calculate the suction number percent N of corrosion product according to formula _AiAnd N _Bi, and run a curve as Fig. 8.

$N_{\mathrm{ai}}=\frac{n_{\mathrm{ai}}-n_a}{n_a}\×100\%$ $N_{\mathrm{bi}}=\frac{n_{\mathrm{bi}}-n_b}{n_b}\×100\%$

4) as shown in Figure 8, after absorbent time reached 8 hours, curvilinear motion was small, and test stops.

In view of this, pure corrosion product also can adopt and take off the quality that the suction method is judged the steel decay resistance.

Embodiment 4:

The corrosion product on the steel surface of indoor salt air corrosion after 36 days is scraped off bottling.

Water absorption test:

1) sample is placed in the drying basin that new drying agent is housed after 96 hours, weighing is recorded as n _a, n _b, the footnote implication as above, and is together following.

2) use Water Tank with Temp.-controlled according to precedent, setting relative humidity is 97%, and sampling in each 0.5 hour is once weighed and is recorded as n _Ai, n _Bi

3) calculate the suction number percent N of sample corrosion product according to formula _AiAnd N _Bi, and run a curve as Fig. 9.

$N_{\mathrm{ai}}=\frac{n_{\mathrm{ai}}-n_a}{n_a}\×100\%$ $N_{\mathrm{bi}}=\frac{n_{\mathrm{bi}}-n_b}{n_b}\×100\%$

4) as seen from the figure, when the suction ambient humidity was bigger, the pure corrosion product suction of two kinds of steel was all very fast, but this does not influence the judgement to the rusty scale corrosion resistance.By contrast, the corrosion product of bainite weathering resistant steel absorbs water comparatively fast in earlier stage, show the more small holes that the quick planar water of capillary action can take place is wherein arranged, and after 3 hours, both number percent that absorbs water is basic identical, proof can judge that the hole of corrosion product resistance to corrosion size is filled up by water among both at this moment, and later suction is by finishing than the water of macroscopic void.

The dehydration test:

1) sample after the last end of test (EOT) is weighed is recorded as m _a, m _b, directly put into the drying basin that discolour silica gel the is housed test of dewatering.

2) set sampling in per 6 hours once, weigh, be recorded as m _Ai, m _Bi, i is the sampling number of times.

3) calculate the dehydration number percent M of corrosion product according to following formula _AiAnd M _Bi, and run a curve as Figure 10.

$M_{\mathrm{ai}}=\frac{m_a-m_{\mathrm{ai}}}{m_a}\×100\%$ $M_{\mathrm{bi}}=\frac{m_b-m_{\mathrm{bi}}}{m_b}\×100\%$

4) as seen, the dewatering speed of bainitic steel corrosion product proves that less than the 09CuPCrNi steel ability of its opposing corrosion is stronger relatively, meets the test result in early stage.

Claims (3)

1, a kind of decision method of weathering steel rusty scale protective capability size is characterized in that concrete steps are as follows:

(1) dehydration test

To after the moistening different steel grade corrosion of moist environment, weigh and be recorded as m by sample _jAfter the test of dewatering, promptly in 50～95 ℃ thermostatic drying chamber or drying basin, carry out drying, sampling in per 1～12 hour is once weighed and is recorded as m according to grade of steel _Ji, i is the sampling number of times, and j is the steel grade numbering, and footnote is down together; Adopt formula:

$\mathrm{Mji}=\frac{m_j-m_{\mathrm{ji}}}{S_j}$

Calculate the dehydrating amount M of each unit area corrosion product _Ji, wherein, S is the surface area of each original steel sample; Make the dehydrating amount and the time M of each steel sample respectively _JiThe curve map of-t is judged the difficulty or ease that corrosion product dewaters by slope of a curve, works as M _JiWhen-t curve and time shaft almost parallel or curve are enough to distinguish each steel grade, the dehydration end of test (EOT);

(2) water absorption test

With used steel sample of above test or the drying that from 50～95 ℃ dry environment, obtains corrosion sample, be recorded as n after weighing _j, j is the steel grade sequence number, is put in relative humidity greater than absorbing water in 50% the constant moist environment, sampling in per 0.5～2 hour is once measured weight, is recorded as n _Ji, i is the sampling number of times; Use following formula to calculate water absorbing capacity N _Ji:

$\mathrm{Nji}=\frac{n_{\mathrm{ji}}-n_j}{S_j}$

Wherein, S is the surface area of each original steel sample; Make each steel water absorbing capacity and time N _JiThe curve map of-t is judged the difficulty or ease that corrosion product absorbs water by slope of a curve, works as N _JiWhen-t curve and time shaft almost parallel or curve were enough to distinguish each steel grade, water absorption test finished.

2, the decision method of weathering steel rusty scale protective capability size as claimed in claim 1; it is characterized in that; adopt above-mentioned dehydration test and water absorption test once to circulate or two repeatedly circulations that the testing procedure cycle alternation carries out, till sample suction, rate of water loss no longer change.

3, the decision method of weathering steel rusty scale protective capability size as claimed in claim 1 is characterized in that, when carrying out the dehydration test of pure corrosion product and water absorption test, the dehydration formula is as follows:

$\mathrm{Mji}=\frac{m_j-m_{\mathrm{ji}}}{m_j}\×100\%$

The suction formula is as follows:

$\mathrm{Nji}=\frac{n_{\mathrm{ji}}-n_j}{n_j}\×100\%.$

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