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Welded joint
Industrial equipment
Welded joint refers to the contact of two or more parts to be welded together. Or a joint of two or more parts joined by welding method, including
weld
,
Fusion zone
and
Heat affected zone
.
Fusion welding
The welded joint is carried out by a high temperature heat source
Local heating
And form. Welded joint
Weld metal
, fusion zone, heat affected zone and
Base metal
Made of metal.
[1]
- Chinese name
- Welded joint
- Technical term
- Welded joint coefficient
- Influencing factor
- Welding material, welding method and welding process
- Group into
- Weld metal, fusion zone, heat affected zone and Base metal metal
Joint metal and
Filled metal
After melting, it is cooled and solidified at a faster rate. Weld tissue
Liquid metal
crystalline
As-cast structure
,
Coarse grain size
,
Component segregation
The tissue is not dense. However, because
Weld bath
Small, cooling fast,
Chemical composition
Strict control, carbon, sulfur, phosphorus are low, but also through alloying to adjust the chemical composition of the weld, so that it contains a certain
Alloying element
Therefore, the performance of the weld metal is not a big problem and can meet the performance requirements, especially the strength is easy to achieve.
Melting zone
And the transition between the non-melting zone. Chemical composition of the fusion zone
unevenness
The organization is thick, often thick
Superheated structure
Or coarse quench
sclerotissue
. Its performance is often the worst in welded joints. Fusion zone and heat affected zone
Overheated zone
(or quenched zone) is in the welded joint
Mechanical property
The worst weak spot,
It will seriously affect the quality of welded joints.
be
Weld zone
The high temperature heating causes changes in the structure and properties of the area.
Mild steel
The heat affected zone can be divided into superheated zone,
Normalizing zone
Sum part
Phase change zone
.
(1) The area with the highest heating temperature above 1100 ° C in the superheated area has coarse grains and even superheated organization, which is called the superheated area. The plasticity and toughness of the superheated zone decreased significantly, and the mechanical properties of the heat-affected zone were the worst.
(2)
normalizing
The maximum heating temperature of the zone is from Ac3 to 1100℃, and the normalizing structure of the grain is obtained by air cooling after welding, which is called the normalizing zone. The mechanical properties of the normal fire area are better.
(3) Part of the phase transition zone the highest heating temperature from Ac1 to Ac3 in the region, only part
histogenesis
A phase transition is called a partial phase transition region. The grain in this region is not uniform and the performance is poor. During installation welding,
Fusion welding
Welding methods are widely used. Welded joints are high-temperature heat source pairs
Base metal
proceed
Local heating
At the same time, it is formed by melting and solidifying with the molten filler metal
Homogeneous body
. According to the different organization and performance of each part, the welded joint can be divided into three parts. As is shown in Figure 1,
Figure 1 Illustration of welded joint
Welded joint coefficient
Refers to the ratio of the strength of the butt welded joint to the strength of the base material. To reflect
Welding material
,
Weld defect
and
Welding residual stress
The degree to which the strength of welded joints is weakened by such factors is a comprehensive reflection of the mechanical properties of welded joints. (In fact, the welded joint coefficient does not really reflect the weld
Material strength
The degree of weakening is an empirical data indicating how reliable the quality of the weld is.
Coefficient size criteria
Standard: National standard,
American standard
,
Japanese standard
And weld type,
Welding process
And weld
Nondestructive testing
The degree of rigor is relevant. American
ASME
Ⅷ-1, Japan JISB8241, GB150 provisions,
Welded joint coefficient
According to container
Compression element
Welding of welded joints
Process characteristics
(Weld type --
Welding by one side
or
Weld on both sides
; With or without pads), as well as non-destructive testing spot test rates are determined, and only on
Butt weld
Provisions were made.
See Table 1:
Table 1 Welding joint coefficient
|
Form of welded joint
|
Butt joint
|
100% non-destructive testing
|
Local nondestructive testing
|
|
Welding process characteristics
|
Double-sided welding is equivalent to a fully welded joint with double-sided welding
|
1.0
|
0.85
|
|
Single-side welding
|
0.9
|
0.8
|
|
|
JB/T4730 NDT qualified level
|
X-ray inspection (Class AB: Medium sensitivity technology)
|
Level II
|
Level III
|
|
Ultrasonic testing (Class B testing)
|
Level I
|
Level II
|
The mechanical properties of welded joints are determined by their chemical composition and organization. Therefore, the factors that affect the chemical composition of the weld and the structure of the welded joint affect the performance of the welded joint.
Manual arc welding
Of the welding rod,
Submerged arc automatic welding
and
Gas shielded welding
isometric
Welding wire
After melting, it becomes an integral part of the weld metal and directly affects the chemical composition of the weld metal. Flux also affects the chemistry of the weld.
The heat source of different welding methods has different temperature and heat concentration degree. Therefore, the size of the heat affected zone and the thickness of the welded joint are different, and the performance of the joint is different. In addition, different welding methods, mechanical protection effects are also different. Therefore, the purity of the weld metal, that is, the content of harmful impurities, the performance of the weld will be different.
When welding, for assurance
Welding quality
And the chosen ones
Physical quantity
(for example
Welding current
,
Arc voltage
,
Welding speed
,
Linear energy
Etc.) general name, called welding
Process parameter
.
weld
Joint form
There are mainly
Butt joint
,
t-joint
,
Angle joint
,
Lap joint
Four kinds. At times
Welded construction
There are also some other types of joint forms such as
Cross joint
,
End joint
,
Flange joint
,
Casing joint
,
Inclined butt joint
Lock bottom butt joint, etc. It is specified in the national standard GB 985-88.
two
weldment
The relatively parallel joint is called the butt joint, which is the ideal joint form from the mechanical point of view, and the stress condition is better.
Stress concentration
Smaller, can withstand bigger
Static load
or
Live load
It is the most widely used joint form in welding structures.
According to the thickness of the weldment, welding method and
groove
Prepared differently, butt joints can be divided into no
bevelling
Butt joint and open groove butt joint two types. The common joint form is shown in Figure 2.
Figure 2 Butt joint
The end face of one weldment and the surface of another weldment constitute a right Angle or approximately right Angle joint, called a T-joint.
T-joint in
Steel structural parts
As a connection weld, it can withstand forces and moments in all directions. Try to avoid one side when choosing
Fillet weld
Because of the deep notch at the root,
Carrying capacity
It's very low. For welding parts with higher requirements, K-shaped groove can be used to determine whether the root is welded through according to the stress situation, which is larger than without opening the groove
Welding leg
The welds are economical, and the joints
Fatigue strength
High.
