DE2413161A1 - Corrosion-resistant clad steel prodn - by applying a stainless steel cladding and a heat treatment - Google Patents

Abstract

A high strength and corrosion resistant clad steel is obtained by (a) forming a low alloy C steel sheet to the required shape, (b) applying a coating of stainless steel by welding or cladding to the normalised or rolled and tempered base sheet, (c) heating the composite to a temp. 800-1000 degrees C over a period of not less than 2 h, (d) cooling at a controlled rate, and (e) heating the composite to a temp. 450-700 degrees C for a period of not less than 4 h. The steel may be given the required shape after the stainless steel coating has been applied. This coating is pref. applied by weld-cladding.

Description

Process for the production of against mechanical stresses and Corrosion-resistant composite steel products.

The invention relates to composite steel products which are @ resistant to mechanical stresses and corrosion occur at one and the same time. It relates to the problem of obtaining these results by having two Layers of steel of different Zu @@ mmenzetzune and different structure are superimposed on each other.

D @ s problem @@ to make a steel ore @@ @ both good ones Resistance to mechanical breakdowns and corrosion. occurs in the construction of pressure vessels in general and reactors for the chemical industry Industry in b @@ onderen. In di @@@ n P @ llen there are two requirements that w @ nig @ tens @@@ Toil contradicts @ chem. @@ is of course necessary, in the by @ @ iden one welded @@ (g @@ ch @ olz @@@@) stainless @@ Stahl @ berzug @ a gewi @@@@ share @iner P @@@@ to @@ z @ ugen, which at Z @@@@@ * @ rh @ lt @ n @ n surface @ chicht temperature is metastable (# ferrite) to avoid the risk of cracking during the To avoid cooling of the stainless steel and on the other hand this percentage To keep the share within minimum values in order to avoid its negative influences on the To reduce the corrosion resistance of the product.

Heretofore, the problem has been solved by having a cylindrical structure made of low-alloy carbon steel (base) has been subjected to a process, which essentially consisted of the following phases: - Ausonitisierung at temperatures around 9000C; -Cooling in air or in a hardening medium; - Blackening to a temperature of about 6000C, ui the stresses induced by the drastic cooling eliminate; - the inner wall of the cylinder with a layer of rustproof To pre-cut steel by build-up welding or by die-casting; - heat treatment, to eliminate the stresses exerted on the lining during cooling Boundary between this and the base metal occur.

It should be noted that while the molten stainless steel of different phases, which are metastable at room temperature are to occur. A subsequent heat treatment ensures that it is metastable Phase is transformed into compounds, which in turn are metastable even at room temperature are. All of this has the effect that the interface between the austenitic Structure of the deposit and the peuen setastabileln compounds formed here the seat or starting point is noticeably corroded if the surface of Article traded in contact with the liii finished reaction vessel Chemicals is coming.

The invention is thus based on a heat treatment process, by completely and irreversibly the said metastable phase in a compound which is stable at room temperature, the trend is corrosion resistance of the article is retained even if it is exposed to heat treatment which can then become necessary.

The method of the invention is characterized by the following Steps: a) Hot working and welding of a normalized low alloy Carbon heavy plate or a rolled, tempered or tempered heavy plate (Base); b) depositing thereon a layer of stainless steel (coating); c) Heating the composite metal thus obtained at a temperature between 800 and 1000 ° C for periods of not less than 2 hours, such that the austenitization of the base steel and the irreversible deformation of the metastable phase of the steel lining becomes possible in a stable phase; d) cooling the composite metal followed by annealing at temperatures between 400 and 7000C for periods not less than 4 Hours, so that the best mechanical properties in the base steel can be obtained.

This final heat treatment does not affect the corrosion resistance the steel lining.

It should be pointed out that low-alloy carbon steel sheets can be subjected to hot deformation and, if necessary, welding, even after which the steel lining has been pre-applied by order.

It should be relied on that low-alloyed carbon steel heavy plates can be subjected to hot deformation and, if necessary, welding, even after they have been provided with the steel lining as an order.

The measure according to the invention is therefore based on the principle of the composite metal some heat treatment to get the component parts you want Properties with regard to mechanical loads or

To give corrosion.

The following example explains the invention without limiting it: Example: A 50 mm thick steel sheet that complies with ASTM A 201 GrB-2usemmensetzung, was subjected to the following process steps by thermoforming and for Production of a cylinder was welded: melt deposition or build-up welding the inner wall of the cylinder lit a stainless steel band of the following percentages Composition by weight, under plating; C Si mm Cr Ni Mo Nb Ti Cu Fe 0.03 0.85 X, 47 17.74 11.73 2.70 0.01 0.01 0.07 remainder% heating the composite metal to 910 ° C for 2 hours; Cooling the composite metal to room temperature by means of Air; Heating the composite metal to 610 ° C for 6 hours; To the corrosion behavior the steel lining or

To predict steel order, was related to the profile of the anodic Polarization curve obtained by placing the material in a 20% strength H2SO4-USsuug was brought, which was vented with N2 and its electrochemical Behavior towards a saturated mercury (I) sulfate electrode (E t + 645 mV) was applied.

The most striking properties that emerge from the anodic polarization curve The following can be derived: a) the maximum critical current density for passivation of the steel b) the passivation current density (Ip) These quantities are inversely proportional the corrosion resistance of the steel.

The following were obtained for the steel treated according to the invention Value: IC 75mA IP 7.5 For the same composite metal, which by Weld-cladding with cladding of the already heated to 910 ° C and base material cooled in air was obtained with a curtain Usual procedures for 2 hours at 700 ° C after the single liner deposition the following values were obtained: IC 265µ A IP 15µ A.

d. H. significantly poorer corrosion resistance properties.

Expectations

Claims (5)

CLAIMS 1. Process for the production of composite steel products, consisting of a steel base layer that is resistant to mechanical loads and a deposited layer of corrosion-resistant steel through the following process steps: - Forming a low-alloy carbon steel sheet in the permit desired for the intended use; - Deposition of a layer made of overlay welded or melted stainless steel, possibly under Plating on normalized or rolled and tempered sheet; - warming up of the composite metal thus obtained after solidification of the lining to a temperature between 800 and 1000 ° C for periods of not less than 2 hours0 - cooling of the composite metal at a controlled speed; - heating the composite metal to a temperature between 450 and 700 ° C for periods not less than 4 Hours. 2. The method according to claim 1, characterized in that the Blchformungsvorgang is carried out, after which the lining is made of molten stainless Steel was deposited. 3. The method according to claim 1 or 2, characterized in that the Deposition is a lining that is created by build-up welding or plating Base with a ribbon is obtained from stainless steel. (bp weld-cladding) 4. Manufactured articles, characterized in that they have a layer of corrosion-resistant gea Steel and a layer of resistant to mechanical stress. stole comprising, these products being obtained by the process of: - Deposition a layer of molten stainless steel on a normalized base low alloy carbon steel or rolled and tempered steel; - Warm up of the composite metal thus obtained after solidification of the lining to a temperature between 850 and 9500C for periods of not less than 2 hours; - Cool of the vertebral metal at a controlled speed; and expansion of the composite metal to a temperature between 400 and 700 ° C for periods not less than 4th Hours. 5. A process for the manufacture of composite metal products, consisting of from a base layer made of steel resistant to Varqebean stresses and a Layer of corrosion-resistant steel as well as manufactured objects obtained in this way, as explained, described and claimed by the example above.