Welding, Assignment,

1. 1
2.4 Welding of stainless steels
[Q2.4-1]
Answer to the following questions on the austenitic stainless steel.
(1) Describe simply the reasons for using the austenitic stainless steel in structure used at cryogenic
temperature.
(2) Pick out two (2) important items on selection of the welding materials to prevent occurrence of hot
cracking in the arc welding of austenitic stainless steel.
[Q2 .4-2]
Answer the following regarding hot cracking in the weld metal of austenitic stainless steel.
(1) Give three factors causing the cracking
(2) Name more than two impurity elements that accelerate hot cracking
(3) Describe the cautions to be taken in selecting welding consumables to prevent hot cracking.
[Q2 .4-3]
Choose an appropriate factor from the factors listed in group B that causes each defect listed in group A in
the welding of a stainless steel and fill in the parenthesis with its symbol. Also choose a method for
generally preventing the defect from those listed in group C and fill in the parenthesis with its symbol.
Answer column
[Group A] (Factor causing defect) (Method for preventing defect)
(1) Hot cracking of SUS310 steel ( ) [ ]
(2) Grain boundary corrosion of SUS 304steel ( ) [ ]
(Weld decay)
(3) SCC of SUS316L steel ( ) [ ]
(Stress corrosion cracking)
(4) Sigma embrittlement ( ) [ ]
(5) Deformation of SUS304 steel sheet ( ) [ ]
[Group B]
(a)High thermal expansion rate
(b)Decrease in Cr concentration near the grain boundary caused by the precipitation of Cr carbides
(c)Segregation of elements such as P, S and Si in the grain boundary
(d)Tensile stress applied to the welded structure in service
(e)A long time heating at a temperature ranging from 600 to 800°C
[Group C]
1. Use of an austenitic stainless steel containing low carbon
2. Lowering heat input and increasing constraint
3. Welding so that 5 to 10% delta-ferrite is made
4. Heating to the temperature higher than 900 C followed by rapid cooling
5. Reduction of residual stress by PWHT

2. 2
[Q2 .4-4]
When an austenitic stainless steel is welded, corrosion resistance might be deteriorated at a welded heat
affected zone left a little from fusion line. What this phenomenon is called?
Describe the cause, and give three prevention measures. Moreover, what is the corrosion caused by this
phenomenon called?
[Q2 .4-5]
Answer the following questions related to austenitic stainless steels and their welded joints:
(1) Describe the reason why austenitic stainless steels are used as structural materials even at cryogenic
temperatures.
(2) The heat affected zone of an austenitic stainless steel made by arc welding is so sensitized that
intergranular corrosion is liable to occur. Describe two measures for preventing sensitization.
(3) Many wires or electrodes for arc welding of austenitic stainless steels contain alloying composition that
causes the precipitation of a small amount of δ (delta)ferrites. What is the purpose of precipitating δ
(delta) ferrites?
[Q2 .4-6]
The following sentences are describing the phenomena observed in arc welding of austenitic stainless steel
such as type 304. Choose the relevant one circle its alphabet.
(1) The main elements which enhance the susceptibility to hot cracking in arc welding are;
(a) C and P
(b) C and S
(c) P and S
(d) P and Cr
(2) Hot cracking susceptibility of weld metal is reduced by the existence of;
(a) martensite
(b) pearlite
(c) austenite
(d) ferrite (δ ferrite)
(3) Weld decay (Intergranular corrosion) is prone to form in the heat affected zone which is heated to
the temperature range of;
(a) from 100 °C to 300 °C
(b) from 300 °C to 500 °C
(c) from 500 °C to 850 °C
(d) from 1000 °C to 1300 °C
(4) Weld decay (Intergranular corrosion) is caused by the formation of the precipitate in grain
boundaries such as;
(a) Titanium carbide
(b) Molybdenum nitride
(c) Chromium carbide
(d) Chromium nitride

3. 3
(5) Weld decay (Intergranular corrosion) can be prevented by using the austenitic stainless steel which
contains;
(a)a larger amount of nickel
(b)a larger amount of molybdenum
(c)a smaller amount of nitrogen
(d)a smaller amount of carbon
[Q2 .4-7]
The following sentences describe the arc welding of stainless steels. Choose the relevant one and circle
its alphabet.
(1) In general, among ferritic, martensitic, and austenitic stainless steels;
(a) ferritic
(b) martensitic
(c) austenitic
stainless steel is highest in strength at room temperature, and
(a) ferritic
(b) martensitic
(c) a u s t e n i t i c stainless steel is highest in
strength at 500 ºC or higher.
(a) Ferritic
(b) Martensitic
(c) Austeni ti c stainless steel is used as structural materials at
cryogenic temperatures.
(2) For prevention of;
(a) cold crack
(b) solidification crack
(c) intergranular corrosion crack
that can occur at the heat-affected zone of austenitic stainless steel welds, the welding procedure in
which the cooling rate is;
(a) high
(b) low
(c) constant
should be used.