Welding Method of Martensitic Stainless Steel and Duplex Stainless Steel

1. What is martensitic stainless steel?

It refers to stainless steel whose microstructure is martensite at room temperature and whose mechanical properties can be adjusted by heat treatment.

Generally speaking, it is a kind of hardenable stainless steel.

The steel grades of martensitic stainless steel include 1Cr13, 2Cr13, 3Cr13, 4Cr13, 3Cr13Mo, 1Cr17Ni2, 2Cr13Ni2, 9Cr18, 9Cr18MoV, etc.

Related reading: Stainless Steel Grades

Welding Method of Martensitic Stainless Steel and Duplex Stainless Steel 1

2. Common welding methods

Martensitic stainless steel can be welded by various electric arc welding methods.

At present, welding rod arc welding is still the main method, while carbon dioxide gas shielded welding or argon carbon dioxide mixed gas shielded welding can greatly reduce the hydrogen content in the weld, thus reducing the sensitivity of cold cracking of the weld.

3. Common welding materials

(1) Cr13 martensitic stainless steel electrode and wire

Generally, when the weld has higher strength requirements, Cr13 martensitic stainless steel welding rod and wire are used to make the chemical composition of the weld metal similar to that of the base metal, but the cold cracking tendency of the weld is large.

Matters needing attention:

a. Preheating is required before welding, and the preheating temperature shall not exceed 450 ℃ to prevent 475 ℃ embrittlement.

The post welding heat treatment is carried out.

When the temperature is cooled to 150-200 ℃, the post welding heat treatment is carried out for 2h, so that all parts of austenite can be transformed into martensite, and then the high temperature tempering is carried out immediately, and the temperature is heated to 730-790 ℃.

The holding time is 10min for every 1mm of plate thickness, but not less than 2h, and finally the air cooling is carried out.

b. In order to prevent cracks, the content of S and P in welding rods and wires shall be less than 0.015%, and the content of Si shall not be greater than 0.3%.

The increase of Si content promotes the formation of coarse primary ferrite, leading to the decrease of the plasticity of the joint.

The carbon content should generally be lower than that of the base metal, which can reduce the hardenability.

(2) Cr Ni austenitic stainless steel electrode and wire

The weld metal of Cr Ni austenitic steel has good plasticity, which can ease the stress generated during martensitic transformation in the heat affected zone.

In addition, Cr Ni austenitic stainless steel type welds have a large solubility of hydrogen, which can reduce the diffusion of hydrogen from the weld metal to the heat affected zone and effectively prevent cold cracks, so preheating is not required.

However, the strength of the weld is low and cannot be improved by post weld heat treatment.

Welding Method of Martensitic Stainless Steel and Duplex Stainless Steel 2

4. Common welding problems

(1) Welding cold crack

Martensitic stainless steel has high chromium content, which greatly improves its hardenability.

Regardless of the original state before welding, welding will always produce martensite near the seam.

With the increase of hardening tendency, the joint is more sensitive to cold cracking, especially in the presence of hydrogen, martensitic stainless steel will also produce more dangerous hydrogen induced delayed cracking.

Measures:

1) The welding current with large wire energy can slow down the cooling speed;

2) For different steel grades, the interpass temperature is different, which is generally not lower than the preheating temperature;

3) Slow cooling after welding to 150~200 ℃, and post welding heat treatment to eliminate welding residual stress, remove diffusible hydrogen in the joint, and also improve the structure and properties of the joint.

(2) Embrittlement of heat affected zone

Martensitic stainless steels, especially those with higher ferrite forming elements, have a greater tendency of grain growth.

When the cooling rate is low, coarse ferrite and carbide are easily produced in the welding heat affected zone;

When the cooling rate is high, the heat affected zone will harden and form coarse martensite.

These coarse structures reduce the plasticity and toughness of the welding heat affected zone (HAZ) of martensitic stainless steel and embrittle it.

Measures:

1) Control reasonable cooling rate;

2) The preheating temperature shall be reasonably selected. The preheating temperature shall not exceed 450 ℃, otherwise the joint may be embrittled at 475 ℃ if it is under high temperature for a long time;

3) The welding materials shall be selected reasonably to adjust the composition of the weld, and the coarse ferrite in the weld shall be avoided as far as possible.

5. Welding process

Welding Method of Martensitic Stainless Steel and Duplex Stainless Steel 3

1) Preheating before welding

Preheating before welding is the main technological measure to prevent cold cracks.

When the mass fraction of C is 0.1% ~ 0.2%, the preheating temperature is 200 ~ 260 ℃, and the high rigid weldment can be preheated to 400 ~ 450 ℃.

2) Cooling after welding

After welding, the weldment shall not be directly heated from the welding temperature for tempering treatment, because the austenite may not be completely transformed during welding.

If it is heated and tempered immediately after welding, carbides will precipitate along the austenite grain boundary and austenite will transform to pearlite, resulting in coarse grain structure, which will seriously reduce the toughness.

Therefore, the weldment shall be cooled before tempering, and the austenite in the weld and heat affected zone shall be basically decomposed.

For weldments with small rigidity, they can be cooled to room temperature and then tempered;

For weldments with large thickness, more complex processes are required;

After welding, cool it to 100~150 ℃, keep it warm for 0.5~1h, and then heat it to the tempering temperature.

3) Post weld heat treatment

The purpose is to reduce the hardness of weld and heat affected zone, improve plasticity and toughness, and reduce welding residual stress.

Post weld heat treatment includes tempering and full annealing. Tempering temperature is 650~750 ℃, heat preservation for 1h, air cooling;

If the weldment needs to be machined after welding, in order to obtain the minimum hardness, it can be fully annealed.

The annealing temperature is 830~880 ℃, and the furnace is cooled to 595 ℃ after holding for 2h, and then air cooled.

4) Selection of welding rod

Electrodes for welding martensitic stainless steel are divided into chromium stainless steel electrode and chromium nickel austenitic stainless steel electrode.

Common chrome stainless steel electrodes include E1-13-16 (G202) and E1-13-15 (G207);

Common chromium nickel austenitic stainless steel electrodes include E0-19-10-16 (A102), E0-19-10-15 (A107), E0-18-12Mo2-16 (A202), E0-18-12Mo2-15 (A207), etc.

6. Welding of Duplex Stainless Steel

Welding Method of Martensitic Stainless Steel and Duplex Stainless Steel 4

1. Weldability of duplex stainless steel

The weldability of duplex stainless steel has both the advantages of austenitic steel and ferritic steel, and reduces their shortcomings.

(1) The sensitivity of hot cracking is much smaller than that of austenitic steel;

(2) The sensitivity of cold cracking is much smaller than that of ordinary low alloy high strength steel;

(3) After cooling in the heat affected zone, more ferrite is always retained, which increases the corrosion tendency and the sensitivity of hydrogen induced cracking (embrittlement);

(4) The welded joint of duplex stainless steel is likely to precipitate δ phase, which is an intermetallic compound of Cr and Fe.

Its formation temperature ranges from 600 ℃ to 1000 ℃.

The formation temperature of δ phase is different for different steel grades;

Table 1 Temperature Range of Solution Treatment, Phase δ and 475 ℃ Brittleness of Duplex Stainless Steel

Content2205 dual phase steel and 2507, etcSuper duplex steel00Cr25Ni7Mo3CuN
Solid solution temperature/℃10401025~1100
Peeling temperature when heated in air/℃10001000
Phase δ formation temperature/℃600~1000600~1000
475 ° C embrittlement temperature/℃300~525300~525

2. Selection of welding methods

The welding method of dual phase steel is TIG welding first, followed by electrode arc welding.

When submerged arc welding is adopted, the heat input and interpass temperature shall be strictly controlled, and large dilution rate shall be avoided.

Note:

When TIG welding is used, 1-2% nitrogen should be added to the shielding gas (if N exceeds 2%, the porosity will increase, and the arc is unstable) to absorb nitrogen from the weld metal (prevent nitrogen loss due to diffusion in the weld surface area), which is conducive to stabilizing the austenite phase in the welded joint.

3. Selection of welding materials

Welding materials with higher austenitic forming elements (Ni, N, etc.) are selected to promote the transformation of ferrite in the weld to austenite.

22.8.3L electrode or welding wire is mostly used for 2205 steel, and 25.10.4L electrode or 25.10.4R electrode is mostly used for 2507 steel.

Table 2 Welding materials and FN of Typical duplex stainless steel

Base metal

Welding Material

Chemical composition

Name

FN(%)

C

Si

Mn

Cr

Ni

Mo

N

Cu

W

2507

Welding wire

0.02

0.3

0.5

25

10

4

0.25

2507/P100

40~100

0.02

 

 

25

10

4

0.25

Sandivick 25.10.4L

Welding core

0.03

0.5

1

25

9.5

3.6

0.22

Avesta 2507/p100

0.04

 

 

25

10.5

4

0.25

Sandivick 25.10.4L

Zeron

100

Welding wire

Welding core

0.04

1.2

2.5

25

10

4

0.22

1

1

22.9.4CuWL

22.9.4CuWLB

40~60

2205

Welding wire

0.02

0.5

1.6

22.5

8

3

0.14

Sandivick 22.8.3L

40~60

Welding core

0.03

1.0

0.8

22.5

9.5

3

0.14

Sandivick 22.8.3R

4. Welding points

(1) During welding thermal process, the control of welding line energy, interpass temperature, preheating and material thickness will affect the cooling rate during welding, thus affecting the structure and properties of weld and heat affected zone.

In order to obtain the best weld metal properties, it is recommended that the maximum interpass temperature be controlled at 100 ℃.

When post weld heat treatment is required, the interpass temperature may not be limited.

(2) Post weld heat treatment It is better not to conduct heat treatment for duplex stainless steel after welding.

When post welding heat treatment is required, the heat treatment method used is water quenching.

During heat treatment, the heating shall be as fast as possible, and the holding time at the heat treatment temperature shall be 5~30min, which shall be sufficient to restore the phase balance.

The oxidation of metal is very serious during heat treatment, so inert gas protection should be considered.

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