Corrosion Research by B.I.S.R.A RESISTANCE OF LOWALLOY STEELS STUDIED

doi:10.1108/eb018933

1954-04-01 00:00:00

Corrosion Research by B.I.S.R.A RESISTANCE OF LOW-ALLOY STEELS STUDIED Research by the Corrosion Section of the British Iron and Steel Research Association during the past year has shown that the corrosion-resistance of low-alloy steels is considerably greater than that of ordinary mild steel. This is reported briefly in the 1953 annual report of B.I.S.R.A. which was published last month. Other work, summarised below, has been concerned with protective coatings, thickness meters, corrosion inhibitors and the mechanism of resistance of wrought iron. Rust study RESEARCH into the corrosion resis alloy steels were not more resistant to tance of low-alloy steels has been corrosion than mild steel. Some of the A seasonal character of rust—which completed and a report is to be published specimens remain exposed and will be becomes favourable for paint application in the Journal of the Iron and Steel Institute. examined later. in the summer months but unfavourable in The principal conclusion is that, under Tests have been completed to find a the winter—has been detected. The pos conditions of atmospheric exposure, the suitable maintenance anti-corrosive com sibility that this behaviour is due to varying corrosion rate of steels containing small position for application to ships' bottoms amounts of electrolyte in the rust is to be percentage additions of chromium, copper when in dry dock. Specimens were given examined. and nickel is not more than one-third of a first coat of paint, currently in use for Although the combined action of cal that of ordinary mild steel. When im new construction and allowed to dry cium compounds and condensed phos mersed in sea water, small additions of thoroughly before receiving an anti-fouling phates inhibits the corrosion of steel in alloying elements are not so beneficial; coat; they were then immersed in the sea. water containing chlorides, their protective the corrosion rate is halved by the addition The tests continued for two years, the action is not long-lasting. This appears to of 3 % chromium and there are indications specimens being removed at six-monthly be due to a breaking down of the protective that aluminium and beryllium additions intervals, brushed down and coated with film formed initially. may be of value. Differences in carbon one of four experimental paints, suitably content had little effect on the measured formulated for application in dry dock, and Wrough t iron's corrosion resistance corrosion rate and there was a negligible re-immersed after brief drying. All the Experiments have been carried out to effect due to heat treatment. Cast iron maintenance paints proved suitable, but decide whether the special resistance of corroded less rapidly than unalloyed low- one was much better than the others. wrought iron could be attributed to the carbon steel in the atmosphere, but at Service trials are now envisaged on ocean formation of phosphate film during ex about the same rate when immersed in sea going vessels. The surface preparation posure to air. Electron diffraction studies water. Some graphitisation occurred in before painting was found to have a marked of films stripped from polished specimens cast iron under the latter condition. It effect on the behaviour of all the painting do not support the view that wrought iron proved impossible to correlate the results schemes. Those specimens which were is a 'self-phosphating' material. The of accelerated laboratory tests with those pickled to remove all mill scale, weathered behaviour of wrought iron towards cor of outdoor exposures. for 2-¾ years and wire-brushed before rosion may be attributed to its lamellar painting were far superior to those which Tests in the B.I.S.R.A. rotor apparatus structure which in general consists of had been pickled and weathered for a on nodular cast iron have shown that, in quickly corroding, relatively resistant and short period or to those which had retained both distilled water and sea water, some very resistant zones. The degree of attack various amounts of mill scale after weather specimens are liable to severe graphitisation in any environment will depend upon the ing for short periods. and erosion. Further specimens, together orientation of these zones to the surface. with samples of pipes protected with bitu Tests are being undertaken to determine A sample of lap-welded wrought iron tube mens and tars—both hot-dipped and the resistance to corrosion of hot-dipped from a marine boiler, which had given 25 sprayed—have been buried at three sites; aluminium and of electrodeposited man years' satisfactory life, was found to have they will be removed in due course. ganese coatings on steel. The specimens continuous, very resistant zones on both were prepared at Sketty Hall and the the outside and inside faces. Fulmer Research Institute, respectively. Protective coatings A research has been commenced which All the specimens in a research on the is intended primarily to compare the protective value of priming paints have accuracies of available coating thickness been removed from the Derby exposure meters when used for sprayed coatings of site after seven years' exposure, and a non-ferrous metals on steel. It is hoped to report on them will be prepared shortly. develop a more reliable thickness tester A new Joint Technical Panel (J/P4) has for use on curved surfaces and a prototype been formed in collaboration with the paint is being designed. industry to study the protective properties Microanalytical methods have been de of various paints applied to metallic coat vised for determining the weight of phos ings on structural and light-gauge steel phate coatings on small areas of steel and when exposed to the atmosphere, water reproducibility tests are being conducted and soil. at a number of laboratories. Sets of specimens, which have been Fundamental research work has con exposed inside factories and dwelling- tinued at Cambridge University. houses for one year, have been examined. It has been found that the true inhibitors The corrosivities of the sites chosen varied present in red-lead oil paints are not the widely and the results have shown that soaps contained in them but salts of dibasic coatings of sprayed zinc were superior to acid and other degradation products of those of sprayed aluminium, but that low- these soaps. 118 CORROSION TECHNOLOGY, June 1954

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$Corrosion Research by B.I.S.R.A RESISTANCE OF LOW-ALLOY STEELS STUDIED Research by the Corrosion Section of the British Iron and Steel Research Association during the past year has shown that the corrosion-resistance of low-alloy steels is considerably greater than that of ordinary mild steel. This is reported briefly in the 1953 annual report of B.I.S.R.A. which was published last month. Other work, summarised below, has been concerned with protective coatings, thickness meters, corrosion inhibitors and the mechanism of resistance of wrought iron. Rust study RESEARCH into the corrosion resis alloy steels were not more resistant to tance of low-alloy steels has been corrosion than mild steel. Some of the A seasonal character of rust—which completed and a report is to be published specimens remain exposed and will be becomes favourable for paint application in the Journal of the Iron and Steel Institute. examined later. in the summer months but unfavourable in The principal conclusion is that, under Tests have been completed to find a the winter—has been detected. The pos conditions of atmospheric exposure, the suitable maintenance anti-corrosive com sibility that this behaviour is due to varying corrosion rate of steels containing small position for application to ships' bottoms amounts of electrolyte in the rust is to be percentage additions of chromium, copper when in dry dock. Specimens were given examined. and nickel is not more than one-third of a first coat of paint, currently in use for Although the combined action of cal that of ordinary mild steel. When im new construction and allowed to dry cium compounds and condensed phos mersed in sea water, small additions of thoroughly before receiving an anti-fouling phates inhibits the corrosion of steel in alloying elements are not so beneficial; coat; they were then immersed in the sea. water containing chlorides, their protective the corrosion rate is halved by the addition The tests continued for two years, the action is not long-lasting. This appears to of 3 % chromium and there are indications specimens being removed at six-monthly be due to a breaking down of the protective that aluminium and beryllium additions intervals, brushed down and coated with film formed initially. may be of value. Differences in carbon one of four experimental paints, suitably content had little effect on the measured formulated for application in dry dock, and Wrough t iron's corrosion resistance corrosion rate and there was a negligible re-immersed after brief drying. All the Experiments have been carried out to effect due to heat treatment. Cast iron maintenance paints proved suitable, but decide whether the special resistance of corroded less rapidly than unalloyed low- one was much better than the others. wrought iron could be attributed to the carbon steel in the atmosphere, but at Service trials are now envisaged on ocean formation of phosphate film during ex about the same rate when immersed in sea going vessels. The surface preparation posure to air. Electron diffraction studies water. Some graphitisation occurred in before painting was found to have a marked of films stripped from polished specimens cast iron under the latter condition. It effect on the behaviour of all the painting do not support the view that wrought iron proved impossible to correlate the results schemes. Those specimens which were is a 'self-phosphating' material. The of accelerated laboratory tests with those pickled to remove all mill scale, weathered behaviour of wrought iron towards cor of outdoor exposures. for 2-¾ years and wire-brushed before rosion may be attributed to its lamellar painting were far superior to those which Tests in the B.I.S.R.A. rotor apparatus structure which in general consists of had been pickled and weathered for a on nodular cast iron have shown that, in quickly corroding, relatively resistant and short period or to those which had retained both distilled water and sea water, some very resistant zones. The degree of attack various amounts of mill scale after weather specimens are liable to severe graphitisation in any environment will depend upon the ing for short periods. and erosion. Further specimens, together orientation of these zones to the surface. with samples of pipes protected with bitu Tests are being undertaken to determine A sample of lap-welded wrought iron tube mens and tars—both hot-dipped and the resistance to corrosion of hot-dipped from a marine boiler, which had given 25 sprayed—have been buried at three sites; aluminium and of electrodeposited man years' satisfactory life, was found to have they will be removed in due course. ganese coatings on steel. The specimens continuous, very resistant zones on both were prepared at Sketty Hall and the the outside and inside faces. Fulmer Research Institute, respectively. Protective coatings A research has been commenced which All the specimens in a research on the is intended primarily to compare the protective value of priming paints have accuracies of available coating thickness been removed from the Derby exposure meters when used for sprayed coatings of site after seven years' exposure, and a non-ferrous metals on steel. It is hoped to report on them will be prepared shortly. develop a more reliable thickness tester A new Joint Technical Panel (J/P4) has for use on curved surfaces and a prototype been formed in collaboration with the paint is being designed. industry to study the protective properties Microanalytical methods have been de of various paints applied to metallic coat vised for determining the weight of phos ings on structural and light-gauge steel phate coatings on small areas of steel and when exposed to the atmosphere, water reproducibility tests are being conducted and soil. at a number of laboratories. Sets of specimens, which have been Fundamental research work has con exposed inside factories and dwelling- tinued at Cambridge University. houses for one year, have been examined. It has been found that the true inhibitors The corrosivities of the sites chosen varied present in red-lead oil paints are not the widely and the results have shown that soaps contained in them but salts of dibasic coatings of sprayed zinc were superior to acid and other degradation products of those of sprayed aluminium, but that low- these soaps. 118 CORROSION TECHNOLOGY, June 1954$

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Corrosion Research by B.I.S.R.A RESISTANCE OF LOWALLOY STEELS STUDIED

Corrosion Research by B.I.S.R.A RESISTANCE OF LOWALLOY STEELS STUDIED

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Corrosion Research by B.I.S.R.A RESISTANCE OF LOWALLOY STEELS STUDIED

Corrosion Research by B.I.S.R.A RESISTANCE OF LOWALLOY STEELS STUDIED

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