US3700851A

US3700851A - Welding electrode

Info

Publication number: US3700851A
Application number: US156534A
Authority: US
Inventors: Jarl A Bjorkroth
Original assignee: Avesta Jernverks AB
Current assignee: Outokumpu Stainless AB
Priority date: 1967-12-21
Filing date: 1971-06-24
Publication date: 1972-10-24
Anticipated expiration: 1989-10-24
Also published as: NL6818455A; BE725830A; DE1815274A1; AT291708B; FR1597986A; GB1248985A; CH514392A

Abstract

The invention relates to a welding electrode for electric arc welding intended for joint welding and built-up welding stainless steels, particularly steels with a ferrite-martensitic, ferritemartensite-austenitic or martensite-austenitic structure, and is characterized in that the electrode in the shape of a bare wire or a wire with a coating deposits a weld metal whose alloying constituents affecting the structure lie within the following analysis limits: 0.01-0.05 percent carbon, 0.1-0.9 percent silicon, 0.5-4.5 percent manganese, 15.0-18.0 percent chromium, 4.5-7.5 percent nickel, 0.2-2.5 percent molybdenum, 0.02-0.12 percent nitrogen and 0.2-3.5 percent tungsten, the remainder iron apart from the unavoidable impurities. The alloying constituents shall be adapted manually in such a way that the following two equations with the chromium equivalent (Cre) and the nickel equivalent (Nie) are satisfied: Equation 1 Cre + Nie > OR = 26.0 and < OR = 32.0 Equation 2 1.4 X Cre - Nie > OR = 15.0 and < OR = 20.0 WHERE Cre % Cr + % Si + % Si + 0.5 X % W and Nie % Ni + 0.5 X % Mn + (% C + % N - 0.03 ); as a result the structure of the weld metal in a welded or heat treated condition contains martensite, ferrite, and austenite of such a composition that the martensite part lies between 5 and 50 percent and the ferrite plus austenite parts between 50 and 95 percent.

Description

United States Patent Bjiirkroth I 1 WELDING ELECTRODE [72] Inventor: Jarl A. Blllrkmth, Avesta, Sweden [73] Assignee: Avelta Jemverlu Akflebolag,

Avesta, Sweden [22] Filed: June 24, 1971 [21] Appl. No.: 156,534

Related u.s. Application Data [63] Continuation of Ser. No. 786,472, Dec. 23,

1968, abandoned.

[52] US. Cl. ..219/137, 219/145, 29/504, 75/128 [51] Int. Cl. ..B23k 9/00 [58] Field of Search ..75/128, 128 N, 128 W;

,1 9/ 1? 7 r. L i l [56] References Cited UNITED STATES PATENTS 1,991,438 2/ 1938 Wohrman ..75/128 W 2,125,929 8/1938 Krivobok ..75/128 W 2,150,901 3/1939 Amess ..75/128 N 2,214,128 9/1940 Fantana ..75/128 N 2,229,065 l/ 1941 Franks ..75/128 N 2,405,660 8/1946 Norwood ..75/128 N 2,848,323 8/1958 Harris ..75/128 N 3,215,814 11/1965 Dorshu ..75/128W 3,489,551 l/ 1970 Fletcher ..75/128 W 3,123,469 3/1964 Tanczyn ..75/128 W Oct. 24, 1972 [57] ABSTRACT The invention relates to a welding electrode for electric arc welding intended for joint welding and builtup welding stainless steels, particularly steels with a ferrite-martensitic, ferrite-martensite-austenitic or martensite-austenitic structure, and is characterized in that the electrode in the shape of a bare wire or a wire with a coating deposits a weld metal whose alloying constituents affecting the structure lie within the following analysis limits: 0.01-0.05 percent carbon, 0.1-0.9 percent silicon, 0.5-4.5 percent manganese, 15.0-18.0 percent chromium, 4.5-7.5 percent nickel, 0.2-2.5 percent molybdenum, 0.02-0.12 percent nitrogen and 02-35 percent tungsten, the remainder iron apart from the unavoidable impurities. The alloying constituents shall be adapted manually in such a way that the following two equations with the chromium equivalent (Cr,,) and the nickel equivalent (Ni are satisfied:

Equation 1 Cr, +Ni 26.0 and 32.0 Equation 2 1.4 X Cr Ni, 15.0 and where Cr Cr Si Si +0.5 X W and Ni,,=% Ni +0.5 X Mn C N 0.03 as a result the structure of the weld metal in a welded or heat treated condition contains martensite, ferrite, and austenite of such a composition that the martensite part lies between 5 and 50 percent and the ferrite plus austenite parts between 50 and 95 percent.

4 Claims, No Drawings WELDING ELECTRODE This application is a continuation of application Ser. No. 786,472, filed Dec. 23, 1968, now abandoned.

Certain types of stainless steels particularly steels with a ferrite-martensitic, ferrite-martensite-austenitic or martensite-austenitic structure, obtain high mechanical strength characteristics, partly owing to their chemical composition and partly by the heat treatment they undergo prior to being used. Austenitic stainless steels in a heat-treated condition, on the other hand, have a low yield limit, but they may be given a higher yield limit and ultimate strength values by cold work, e.g., by stretching.

In welding stainless steels one aims at obtaining a weld metal with a chemical composition and characteristics which correspond to those of steel both from a corrosion viewpoint and other viewpoints. If one welds ferrite-martensitic, ferrite-martensite-austenitic or martensite-austenitic steels with electrodes having an analysis identical to that of the steel the melted weld metal in an unannealed condition will have a high yield limit and ultimate strength but, on the other hand, a very insignificant elongation and impact value. By a subsequent heat treatment the elongation and impact value of the weld metal may be improved; however it has been very difficult to reach full conformity to he properties of the steel. 3

As regards welding, the elongation value of the weld metal may be regarded as a gauge of the welds cracking resistance. When welding is carried out with electrodes which deposit a weld metal with too low elongation values the risk of contraction cracks in the weld is great. When welding ferrite-martensitic, ferritemartensite-austenitic or martensite-austenitic steel with the corresponding electrodes one has therefore normally applied a method which implies both the preheating of the basic material and the stress-relieving of the welded structure in order to reduce the risk of cracks.

In addition to high strength certain new ferrite-martensite-austenitic steel also possesses an improved weldability, which means that pre-heating has to be applied very seldom. As an example one may mention that a steel with a low carbon content of the type 16 percent chromium, 5 percent nickel and 1 percent molybdenum which after a double heat treatment obtains yield limit values over 80 kp/mm, an elongation of about percent and an impact value over 7 kpm/cm In welding this steel with previously known electrodes it has not been possible to obtain a weld metal which in an unannealed condition possesses the corresponding values. On the other hand the characteristics of the weld metal could be improved by a suitable heat treatment so that they on the whole correspond to those of the steel.

According to the present invention it is possible without subsequent heat treatment to obtain a weld metal with a high yield limit and ultimate strength in combination with very good elongation and impact value by using an electrode which, in the shape of a wire or a wire with a coating deposits a weld metal which contains the following alloying constituents affecting the structure: 0.01-0.05 percent carbon, 0.1-0.9 percent silicon, 0.5-4.5 percent manganese, 15.0-18.0 percent chromium, 4.5-7.5 percent nickel,

0.2-2.5 percent molybdenum, 0.02-0.12 percent nitrogen and 0.2-3.5 percent tungsten the remainder being iron apart from the unavoidable impurities. The content of undesirable impurities, such as sulphur, phosphorus, copper, lead, etc., shall be as low as possible.

The alloying constituents affecting the structure shall be adapted mutually in such a way that the following two equations with the chromium equivalent (Cr and 0 the nickel equivalent (Ni are satisfied:

Equation 1: Cr +Ni 26.0 and S 32.0

Equation 2: 1.4XCr "Ni 15.5 and 20.0 where Cr Cr+% Si Mo +0.5 W; and Ni,,=% Ni+0.5 X% Mn+30 (%C+% N0.03).

A welding electrode which satisfies the pre-requisites indicated above deposits a weld metal with a structure composed of ferrite, martensite and austenite. If these three structure elements are balanced against each other the weld metal, without subsequent heat treatment, obtains yield limit values of about 60 kp/mm and ultimate strength values of about 82 kp/mm while at the same time as the elongation is about 30 percent and the impact value over 10 kpm/cm at room temperature. In addition one obtains a lowered transition temperature, so that the weld metal still at C possessies impact values over 6 kpm/cm and at temperatures about to C meets the impact value requirements which are normally specified for vessels under pressure.

The addition of tungsten to austenitic stainless electrodes is known although the effect achieved has not been described in greater detail. In the present invention tungsten acts as a kind of modulator which in combination with nickel, manganese and nitrogen gives the desired balance to the ratio between the martensite part and the ferrite plus austenite parts. According to the present invention the martensite part of the weld structure shall lie between 5 and 50 percent and the ferrite plus austenite parts between 50 and 95 percent.

Consequently the present invention relates to an electrode or a filler for joint-welding or built-up welding stainless steels, particularly steel with a ferrite-martensite-austenitic structure, e.g., steel of type 16 Cr 5 Ni 1 Mo, as well as steel of a ferrite-martensitic or martensite-austenitic structure, e.g., steel of type 12-14 Cr, 0-3 Ni and 0-2 Mo. In the process of welding with electrodes according to the present invention the weld metal in itself does not require any heat treatment after the welding in order to achieve maximum toughness. In certain cases, on the other hand, the basic material may require stress-relieving in order to eliminate welding stresses or in order to level out the hardness tops which the latter types of steel show in heat-affected zones close to the weld. With the electrode described it is also possible to carry out stress-relieving within the temperature range 550-700C without causing the strength values of the weld material to decrease to any great extent.

In addition the electrode is suitable for welding certain austenitic stainless steels, provided that the corrosion conditions to which the welded object is subjected, suit the weld metal of the electrode. The electrode is particularly suitable suited for joint welding stainless steels of identical or almost identical composition containing at least 13 percent chromium, and 3.5 percent nickel; they are then merged by means of arc welding and melting of a coated or an uncoated electrode whose composition lies within the composition according to claim 1.

By hardfacing or deposit welding the electrode is also very suitable for coating a surface on work-pieces of unalloyed, low-alloyed or stainless steels; the hardfacing then takes place with an electrode which, coated or uncoated, has a composition according to that of claim 1.

The welding electrode according to the present invention may be made in the shape of coated electrodes or uncoated wire for melting in an inert protective gas atmosphere or under a protective blanket of granulated welding powder, so-called flux. The bare wire in its turn may be homogeneous or so-called pipe-wire.

The covering of coated manual-welding electrodes consists of fluxing material, arc-stabilizing, deoxidizing and alloying elements as well as some plasticizer for making the substance ductile. The composition of the covering may be varied and may have a lime-basic, rutile-basic or rutile-acid character all according to the welding properties desired. It is essential for this embodiment within the scope of the invention that the covering should contain a certain amount of one or several of the following alloying elements: chromium, nickel, molybdenum, tungsten, manganese, silicon and nitrogen, partly in order to compensate the loss by burning which normally occurs in connection with the transport of material through the arc and partly in order to provide the weld with that part of the alloying elements which possibly for practical reasons has not been alloyed into the core wire.

According to the second embodiment, i.e., an uncoated filler wire for melting in an inert protective gas or under a protection blanket of granulated welding powder, the composition of the wire in the case mentioned first shall conform as nearly as possible to the desired weld analysis and in the latter case be adapted to the composition of the welding powder.

Examples of some differently coated electrodes and their characteristics are given below in Tables I and II:

Table I chemical analysis The chemical analysis has been made in the manner prescribed in different standards, e.g., DIN 8556, Blatt 2 (Deutsche Industrie Normen), i.e., one makes a weld on plate with a great number of beads and determines the chemical analysis of that part of the weld which is further than 10 mm from the plate. In doing so the effect of the basic material is eliminated. Table II characteristics of strength The values indicated above represent an average of several tests. The welding tests have been carried out with a coated electrode in the manner prescribed in DIN 1913, Blatt 2. For the all-welded tensile tests, test specimens of type 10C50 according to SIS 1121 13 (SIS The Swedish Standard Association) and for the impact tests Charpy V-notch specimen according to SIS 1123 51 have been used. The F2 test indicated above is heat-treated at 600C with subsequent aircooling.

Iclaim:

l. A method of arc welding high strength stainless steels comprising the steps of melting an electrode in an electric are, said electrode having the following composition: 0.01-0.05 percent carbon, 0.l-0.9 percent silicon, 0.5-4.5 percent manganese, 15.0-18.0 percent chromium, 4.5-7.5 percent nickel, 0.2-2.5 percent molybdenum, 0.02-0. 12 percent nitrogen, 02-35 percent tungsten, and the remainder essentially iron, the constituents being adapted so that the chromium equivalent plus the nickel equivalent is not less than 26.0 and not more than 32.0, and 1.4 times the chromium equivalent minus the nickel equivalent is not less than 15.0 and not more than 20.0, the chromium equivalent being the sum of the percent chromium percent molybdenum percent silicon 0.5 times percent tungsten and the nickel equivalent being the sum of the percent nickel 0.5 times percent manganese 30 (percent carbon percent nitrogen 0.03) so as to obtain a weld metal having a microstructure comprising ferrite, martensite, and austenite, the martensite comprising from 5 percent to 50 percent thereof and the sum of the ferrite and austenite comprising from 50 percent to percent thereof.

2. A method according to claim 1 wherein the electrode is bare wire and including the step of melting the electrode in an inert protective gas atmosphere.

3. A method according to claim 1 wherein the electrode is a bare wire and including the step of melting the electrode under a protective blanket of granulated welding flux.

4. A method according to claim 1 wherein the welding electrode is a wire having a coating comprising fluxing material, arc-stabilizing material, deoxidizing material, and at least one material selected from the group of alloying elements consisting of chromium, nickel, molybdenum, tungsten, manganese, silicon and nitrogen.

Po-wso UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,7Q0,85l D t October 24, 1972 lnventofls) Jarl A. Bjorkroth It is certified that'errorappears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

ABSTRACT, line 15, "manually" should read ---mutually--; lines 19 and 20, Equations 1 and 2, after "Ni insert and after "and" insert line 22, Si"

(first occurrence) should be Mo-; line 23, after "MN insert --30--. Column 1, line 28, "he" should read --the-. Column 2, lines ll and 12, Equations 1 and 2, after "Ni insert line 60, "material" should read -metal Column 4, lines 3 and 4, "Table v II characteristics of strength" should appear on a separate line, as a heading.

Signed and sealed this ZZndday of May 1973.

(SEAL) Attest:

EDWARD M .FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents *zgz g UNITED STATES PATENT OFFICE CERTIFICATE OF CQRRECTION Patent N 3,700,851 D t d October 24, 1972 lnventofls) Jarl A. Bjorkroth It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

ABSTRACT, line 15, manually" should read *--mutually--; lines 19 and 20, Equations 1 and 2, after "Ni insert --Z- and after "and" insert line 22,."% Si" (first occurrence) should be Mo-; line 23, after "MN insert --30--. Column 1, line 28, "he" should read --the--. Column 2, lines 11 and 12, Equations 1 and 2, after "Ni insert line 60, "material" should read --metal- Column 4, lines 3 and 4, "Table v II characteristics of strength" should appear on a separate line, as a heading.

Signed and sealed this ZZndday of May 1973.

(SEAL) Attest:

ROBERT GOTTSCHALK Commissioner of Patents EDWARD M.FLETCHER,JR. Attesting Officer

Claims

2. A method according to claim 1 wherein the electrode is bare wire and including the step of melting the electrode in an inert protective gas atmosphere.
3. A method according to claim 1 wherein the electrode is a bare wire and including the step of melting the electrode under a protective blanket of granulated welding flux.
4. A method according to claim 1 wherein the welding electrode is a wire having a coating comprising fluxing material, arc-stabilizing material, deoxidizing material, and at least one material selected from the group of alloying elements consisting of chromium, nickel, molybdenum, tungsten, manganese, silicon and nitrogen.