Laser Welding Machine For Sale

Laser welding is a new welding method, mainly for the welding of thin-walled materials and precision parts, and can realize spot welding, butt welding, overlap welding, seal welding, etc. It features high aspect ratio, small weld width, small heat affected zone, small deformation, fast welding speed, flat and beautiful weld.

Handheld Laser Welding Machine

Handheld Laser Welding Machine

It has the advantages of simple structure, fast operation, flexible welding and strong welding penetration, and can be competent for welding at various complex angles

Automatic Laser Welding Machine

Automatic Laser Welding Machine

It has high working efficiency, faster speed than general laser welding machine, with good welding effect and stable performance

Robotic Laser Welding Machine

The combination of industrial robot and welding laser for three-dimensional laser welding greatly meets the market demand.

Key Points Of Weldability Of Metal Materials

Weldability Of Metal Materials

Weldability Of Metal Materials

1. Metal weldability: 

It refers to the ability of homogeneous or heterogeneous materials to form a complete joint and meet the expected use requirements under the manufacturing process conditions. Including (process weldability and service weldability).

2. Process weldability:

Under certain welding process conditions, whether the metal or material can obtain high-quality, dense, defect free and service performance welded joints.

3. Weldability:

Refers to the degree to which the welded joint and the overall welded structure meet various properties, including conventional mechanical properties.

4. Factors affecting metal weldability:

  1. Material factor
  2. Design factor
  3. Process factor
  4. Service environment

5. Principles for evaluating weldability:

(1) evaluate the tendency of process defects in welded joints, so as to provide basis for formulating reasonable welding process;

(2) Evaluate whether the welded joint can meet the requirements of structural performance.

6. Principles that the experimental method should meet:

  • comparability
  • pertinence
  • reproducibility
  • economy

7. Common weldability test methods:

A: Oblique y groove welding crack test method: this method is mainly used to evaluate the sensitivity of welding heat affected zone of carbon steel and low alloy high strength steel to cold crack.

B: Pin test

C: Test method for butt welding crack of pressing plate

D: Adjustable restraint crack test method

I. Q & A:

1. What is the purpose of the experiment and what occasion is it applicable to?

Understand the main experimental steps and analyze the factors affecting the stability of the experimental results.

Answer:

The purpose is to evaluate the sensitivity of welding heat-affected zone of carbon steel and low alloy high strength steel to cold crack.

When evaluating the sensitivity of welding heat-affected zone of carbon steel and low alloy high strength steel to cold crack, the factors affecting the stability of the results are restraint of welded joint, preheating temperature, angular deformation and incomplete penetration.

(it is generally considered that when the surface crack rate of low alloy steel is less than 20%, it is safe for general welded structures)

2. What are the main factors affecting process weldability?

Answer: influencing factors:

(1) Material factors

It includes the base metal itself and the welding materials used, such as welding rod for electrode arc welding, welding wire and flux for submerged arc welding, welding wire and shielding gas for gas shielded welding, etc.

(2) Design factors

The structural design of welded joints will affect the stress state, thus affecting the weldability.

(3) Process factors

For the same base metal, different welding methods and process measures show great differences in weldability.

(4) Service environment

The service environment of welded structure is various, such as working temperature, working medium type, load property and so on.

3. Sometimes, metal materials with good process weldability may not have good use weldability.

Answer:

The use and welding performance of metal materials refers to the various use properties specified by the technical conditions of the welded joint or overall welded structure, mainly including the conventional mechanical properties or the use properties under specific working conditions, such as low-temperature toughness, fracture toughness, high-temperature creep strength, long-term strength, fatigue performance, corrosion resistance, wear resistance, etc.

Process weldability refers to the ability of metal or material to obtain high-quality, dense, defect free and service-oriented welded joints under certain welding process conditions.

For example, low carbon steel has good weldability, but its strength and hardness are not as good as high carbon steel.

4. Why can the highest hardness of heat affected zone be used to evaluate the welding cold crack sensitivity of iron and steel materials? What is the effect of welding process conditions on the maximum hardness of heat affected zone?

Answer:

(1) Cold cracks mainly occur in the heat affected zone;

(2) It directly evaluates the most important of the three elements of cold crack generation, the hardened structure of the joint, so it can be approximately used to evaluate cold crack.

Generally speaking, the welded joint includes the heat affected zone. The higher its hardness value relative to the base metal hardness value, the worse the toughness of the welded joint and the worse the comprehensive mechanical properties, which is prone to embrittlement, fracture and other hazards.

Reasonable welding process conditions are to reduce the difference of hardness value and ensure the service performance of welded joints.

When the carbon equivalent increases, the hardening tendency of heat affected zone increases, but it does not always maintain a linear relationship.

2. Welding of alloy structural steel

1. Weldability analysis of low carbon quenched and tempered steel

Low carbon quenched and tempered steel is mainly used as high-strength welded structural steel, so the carbon content limit is low.

The weldability requirements are considered in the design of alloy composition.

The mass fraction of carbon in low carbon quenched and tempered steel is less than 0.18%, and the welding performance is much better than that of medium carbon quenched and tempered steel.

Because the welding heat affected zone of this kind of steel is low-carbon martensite, the martensite transformation temperature MS is high, and the formed martensite has the characteristics of “self tempering”, the tendency of welding cold crack is smaller than that of medium carbon quenched and tempered steel.

When fine low carbon martensite (ML) or lower bainite (B) structure is obtained in the heat affected zone of low carbon quenched and tempered steel, the toughness is good.

The microstructure with the best toughness is the mixed structure of ML and low temperature transformed bainite (B), and the crystal position between bainite laths is quite different.

The effective grain diameter depends on the strip width, which is fine and has good toughness. When ml and BL are mixed, the original austenite grains are effectively divided by the first precipitated B, which promotes ml to have more nucleation positions and limits the growth of ml. Therefore, the effective grains of ML + B mixed structure are the smallest.

Ni is an important element in the development of low temperature steel.

In order to improve the low temperature properties of steel, Ni element can be added to form ferritic low temperature steel containing Ni.

For example, while increasing Ni, 1.5Ni steel should reduce carbon content and strictly limit the contents of S, P and N, H and O to prevent aging brittleness and tempering brittleness.

The heat treatment conditions of this kind of steel are normalizing, normalizing + tempering and quenching + tempering.

In low temperature steel, because the carbon content and the content of impurities s and P are strictly controlled, the liquefaction crack is not very obvious in this kind of steel.

Another problem is temper brittleness. It is necessary to control the temper temperature and cooling rate after welding.

Process characteristics of low-temperature steel welding:

In addition to preventing cracks, the key is to ensure the low-temperature toughness of the weld and heat affected zone, which is a fundamental starting point for developing the welding process of low-temperature steel.

9Ni steel has excellent low temperature toughness, but the toughness of the weld is very poor when ferritic welding materials similar to 9Ni steel are used.

In addition to the microstructure of as cast weld, it is mainly related to the oxygen content in the weld.

11ni ferritic welding material, which is the same as 9Ni steel, can obtain good low temperature toughness only when TIG welding.

Because the mass fraction of oxygen in the weld metal can be reduced to less than 0.05% of the base metal.

2. Weldability analysis of medium carbon quenched and tempered steel

  • In the hot cracks in the weld, the carbon content and alloy element content of carbon quenched and tempered steel are high, so the liquid-solid interval is large, the segregation is more serious, and has a large tendency of hot cracks.
  • Cold cracked medium carbon quenched and tempered steel has an obvious hardening tendency due to high carbon content and more alloy elements;

Due to the low MS point, the martensite formed at low temperature is generally difficult to produce self tempering effect, and the cold crack tendency is serious.

  • Reheat crack (IV) performance change of heat-affected zone.

Embrittlement in superheated zone

1) Medium carbon quenched and tempered steel is easy to produce hard and brittle high carbon martensite in the welding superheated zone because of its high carbon content, many alloy elements and considerable hardenability.

The greater the cooling rate, the more high carbon martensite will be generated, and the more serious the embrittlement tendency will be.

2) Even with large linear energy, it is difficult to avoid the occurrence of high carbon m, which will make m coarser and more brittle.

3) Generally, small line energy, preheating, slow cooling and post heating measures are adopted to improve the performance of superheated zone.

Heat affected zone softening

When quenching and tempering treatment cannot be carried out after welding, the softening of heat affected zone needs to be considered.

The higher the strength grade of quenched and tempered steel is, the more serious the softening problem is.

The softening degree and width of softening zone are closely related to welding line energy and welding method.

3. Welding process characteristics of medium carbon quenched and tempered steel

(1) In the hot cracks in the weld, the carbon content and alloy element content of carbon quenched and tempered steel are high, so the liquid-solid interval is large, the segregation is more serious, and has a large tendency of hot cracks.

(2) Cold cracked medium carbon quenched and tempered steel has obvious hardening tendency due to high carbon content and more alloy elements;

Due to the low MS point, the martensite formed at low temperature is generally difficult to produce self tempering effect, and the cold crack tendency is serious.

(3) Reheat crack

(4)Performance change of heat affected zone

Embrittlement in superheated zone

(1) Medium carbon quenched and tempered steel is easy to produce hard and brittle high carbon martensite in the welding superheated zone because of its high carbon content, many alloy elements and considerable hardenability.

The greater the cooling rate, the more high carbon martensite will be generated, and the more serious the embrittlement tendency will be.

(2) Even with large linear energy, it is difficult to avoid the occurrence of high carbon m, which will make m coarser and more brittle.

(3) Generally, small line energy, preheating, slow cooling and post heating measures are adopted to improve the performance of superheated zone.

Heat affected zone softening

When quenching and tempering treatment cannot be carried out after welding, the softening of heat affected zone needs to be considered.

The higher the strength grade of quenched and tempered steel is, the more serious the softening problem is.

The softening degree and width of softening zone are closely related to welding line energy and welding method.

The welding method with more concentrated heat source is more favorable to reduce softening.

4. Welding process characteristics of medium carbon quenched and tempered steel

(1) Medium carbon quenched and tempered steel is generally welded in annealed state.

After welding, uniform welded joints with satisfactory properties can be obtained through overall quenching and tempering treatment.

(2) When welding must be carried out after quenching and tempering, the deterioration of heat affected zone performance is often difficult to solve.

(3) The state before welding determines the nature of problems and process measures.

The weldability characteristics of Q345 steel are analyzed, and the corresponding welding materials and welding process requirements are given.

Answer: Q345 steel is a hot rolled steel with carbon equivalent less than 0.4% and good weldability. Generally, preheating and strict control of welding heat input are not required.

In terms of brittle and hard tendency, when Q345 steel is continuously cooled, the pearlite transformation moves to the right, which precipitates ferrite under rapid cooling, leaving carbon rich austenite too late to transform into pearlite.

The transformation into bainite and martensite with high carbon content has a hardening tendency, Q345 steel has low carbon content and high manganese content, and has good hot crack resistance.

Adding V and Nb to Q345 steel to achieve precipitation strengthening can eliminate the stress crack in the welded joint. Coarse grain embrittlement may occur in the superheated zone of the heat affected zone heated above 1200 ℃, and the toughness is significantly reduced.

Q345 steel passes through 600 ℃ × After annealing for 1h, the toughness was greatly improved and the tendency of thermal strain embrittlement was significantly reduced.

Welding material: selection of butt welding electrode and arc welding electrode: E5 series.

Submerged arc welding: flux sj501, welding wire H08A / H08MnA

Electroslag welding: flux HJ431, hj360, welding wire H08MnMoA.

CO2 gas shielded welding: H08 series and yj5 series.

Preheating temperature: 100 ~ 150 ℃.

Post weld heat treatment: arc welding is generally not conducted or tempered at 600 ~ 650 ℃.

Electroslag welding 900 ~ 930 ℃ normalizing and 600 ~ 650 ℃ tempering

What is the difference in weldability between Q345 and Q390? Is the welding process of Q345 applicable to the welding of Q390 and why?

Answer: Q345 and Q390 are hot rolled steels with basically the same chemical composition.

Only the Mn content of Q390 is higher than Q345, so that the carbon equivalent of Q390 is greater than Q345.

Therefore, the hardenability and cold crack tendency of Q390 are greater than Q345, and the other weldability are basically the same.

The welding process of Q345 is not necessarily applicable to the welding of Q390, because the carbon equivalent of Q390 is large and the heat input of primary Q345 is wide, which may lead to the intensification of overheating in the joint area due to excessive heat input of Q390, or the tendency of cold cracks and serious embrittlement in the overheating area due to too small heat input.

What is the principle of selecting welding materials when welding low alloy high strength steel? What is the effect of post weld heat treatment on welding materials?

Answer: selection principle: consider the influence of the microstructure of the weld and heat affected zone on the strength and toughness of the welded joint.

Since post weld heat treatment is generally not carried out, it is required that the weld metal should be close to the mechanical properties of the base metal in the as welded state.

For medium carbon quenched and tempered steel, the welding materials shall be selected according to the stress conditions of the weld, performance requirements and post weld heat treatment.

For the components to be treated after welding, the chemical composition of the weld metal shall be similar to that of the base metal.

Analyze the possible problems during welding of low carbon quenched and tempered steel?

This post briefly describes the key points of the welding process of low-carbon quenched and tempered steel.

What range should the welding heat input of typical low-carbon quenched and tempered steel such as (14mnmonib, HQ70, HQ80) be controlled?

When preheating measures are adopted, why there are minimum preheating temperature requirements, and how to determine the maximum preheating temperature.

Answer: embrittlement is easy to occur during welding. During welding, the strength and toughness of heat affected zone are reduced due to thermal cycle.

Welding process features: generally, heat treatment is not required after welding, multi-layer process is adopted, and narrow weld bead is adopted instead of transverse swing strip transportation technology.

The welding heat input of typical low-carbon quenched and tempered steel shall be controlled at WC › 0.18%, and the cooling speed shall not be increased.

The cooling speed can be increased (reduce the heat input) when WC ≯ 0.18%.

The welding heat input shall be controlled at less than 481kj / cm.

When the welding heat input is increased to the maximum allowable value and cracks can not be avoided, preheating measures must be taken.

When the preheating temperature is too high, it is not necessary to prevent cold cracks.

On the contrary, the cooling rate of 800 ~ 500 ℃ will be lower than the critical cooling rate of brittle mixed structure, and the toughness of heat affected zone will be reduced.

Therefore, it is necessary to avoid unnecessarily increasing the preheating temperature, including room temperature.

Therefore, there is a minimum preheating temperature.

Determine the maximum allowable value of welding heat input of steel after the experiment, and then consider whether preheating and preheating temperature, including the maximum preheating temperature, are required according to the cold crack tendency during the maximum heat input.

What is the difference in welding process between quenched and tempered and annealed medium carbon quenched and tempered steel of the same brand? Why are medium carbon quenched and tempered steels generally not welded in the annealed state?

Welding in quenched and tempered state: preheating, interpass temperature control, intermediate heat treatment and timely tempering after welding must be adopted in order to eliminate the hardened structure of the hardened zone in the heat affected zone and prevent delayed cracks.

In order to reduce the softening of heat effect, the method of heat concentration and higher energy density shall be adopted, and the smaller the welding heat input, the better.

Welding in annealed state: common welding methods can be used.

When selecting materials, the quenching and tempering treatment specification of weld metal shall be consistent with that of base metal, and the main alloy shall also be consistent with that of base metal.

In the case of quenching and tempering, high preheating temperature and interlayer temperature can be used to ensure that there is no crack before quenching and tempering.

Due to the high hardenability and hardenability of medium carbon quenched and tempered steel, improper welding treatment in annealing state is easy to produce delayed cracks.

Generally, complex welding process is required. Auxiliary processes such as preheating, post heating, tempering and post weld heat treatment can ensure the service performance of the joint.

Is there any difference in welding process and material selection when low temperature steel is used at – 40 ℃ and normal temperature? Why?

Answer: in order to ensure the low-temperature embrittlement of welded joints and the generation of thermal cracks, the materials of low-temperature steel require less impurity elements. Select appropriate welding materials to control the weld composition and structure to form fine acicular ferrite and a small amount of alloy carbide, which can ensure certain AK requirements at low temperature.

For the welding process at low temperature, when SMAW is used, small linear energy welding is used to prevent overheating of heat affected zone, resulting in WF and coarse M. fast multi pass welding is used to reduce weld bead overheating. When saw is used, the vibration arc welding method can be used to prevent the formation of columnar crystals.

What are the differences in strengthening methods and main strengthening elements between hot rolled steel and normalized steel, and what are the differences in weldability between them? What problems should be paid attention to when formulating welding process?

Answer: the strengthening methods of hot rolled steel are:

(1) Solid solution strengthening, main strengthening elements: Mn, Si.

(2) Fine grain strengthening, main strengthening elements: Nb, V.

(3) Precipitation strengthening, main strengthening elements: Nb, V;

Strengthening mode of normalized steel:

Weldability: hot rolled steel contains a small amount of alloy elements, with low carbon equivalent and little tendency to cold crack.

Normalized steel contains more alloy elements, with increased hardenability, low carbon equivalent and little tendency to cold crack.

The HAZ of hot rolled steel heated above 1200 ℃ may produce coarse grain embrittlement and significantly reduce the toughness.

However, under this condition, the V precipitate in the coarse grain region of normalized steel is basically solid solution, and the effect of inhibiting a growth and microstructure refinement is weakened.

Coarse grains, upper bainite and M-A are easy to appear in the coarse grain region, resulting in the decrease of toughness and the increase of aging sensitivity.

When formulating the welding process, the welding method shall be selected according to the material structure, plate thickness, service performance requirements and production conditions.

Low carbon quenched and tempered steel and medium carbon quenched and tempered steel belong to quenched and tempered steel. Are their embrittlement mechanisms in welding heat affected zone the same?

Why can welding of low carbon steel in quenched and tempered state ensure welding quality, while medium carbon quenched and tempered steel generally requires post weld heat treatment?

Answer: low carbon quenched and tempered steel: under the cyclic action, when T8 / 5 continues to increase, the embrittlement of low carbon quenched and tempered steel occurs, which is due to the coarsening of austenite and the formation of upper bainite and M-A components.

Medium carbon quenched and tempered steel: due to high carbon content and many alloying elements, it has considerable hardening tendency, low martensitic transformation temperature and no self tempering process. Therefore, it is easy to produce a large amount of M structure and approximate embrittlement in the welding heat affected zone.

Low carbon quenched and tempered steel generally uses the effect of medium and low heat on the base metal, while medium carbon steel can obtain the best performance welded joint by heating input welding and timely heat treatment after welding

What is the difference between the weldability characteristics of Pearlite Heat-resistant Steel and low-carbon quenched and tempered steel? What is the difference between the principle of selecting welding materials for Pearlite Heat-resistant Steel and strength steel? why?

Answer: cold cracks exist in Pearlite Heat-resistant Steel and low-carbon quenched and tempered steel.

Hardening and embrittlement of heat affected zone and reheat cracks during heat treatment or long-term use at high temperature.

However, in low-carbon quenched and tempered steel, there is a certain tendency of hot cracks for high nickel and low manganese steel, while Pearlite Heat-resistant Steel may often produce hot cracks when the material is not selected properly.

Pearlitic heat-resistant steel not only has certain strength in the selection of materials, but also considers the principle of using the joint at high temperature.

Pay special attention to the dryness of welding materials, because Pearlite Heat-resistant steel is used at high temperature and has certain strength requirements.

Welding of stainless steel and heat resistant steel

Stainless steel: refers to steel used in atmospheric environment and aggressive chemical medium.

Heat resistant steel: including oxidation resistant steel and thermal strength steel. Oxidation resistant steel refers to the steel with oxidation resistance at high temperature, which has low requirements for high temperature strength.

Hot strength steel: it means that it not only has oxidation resistance at high temperature, but also has high temperature strength.

Thermal strength: refers to the resistance to fracture (lasting strength) when working at high temperature for a long time.

Or the ability to resist plastic deformation (creep resistance) when working at high temperature for a long time.

Some concepts:

  1. Chromium equivalent:in the diagram of the relationship between the composition and structure of stainless steel, the elements forming ferrite are converted into the sum of Cr elements (the action coefficient of Cr is 1) according to their action degree, which is called CR equivalent.
  2. Nickel equivalent:in the diagram of the relationship between stainless steel composition and structure, the elements forming austenite are converted into the sum of Ni elements (the action coefficient of Ni is 1) according to their action degree, which is called Ni equivalent.
  3. 4750 C embrittlement:This embrittlement occurs when high chromium ferritic stainless steel is heated for a long time in the range of 400 ~ 540 degrees.

Because its most sensitive temperature is around 475 degrees, it is called 475 degrees brittleness. At this time, the strength and hardness of the steel increase, while the plasticity and toughness decrease significantly.

  1. Solidification mode:which primary phase does the solidification mode first refer to( γ or δ) The solidification process begins with crystallization, followed by which phase completes the solidification process.

Solidification mode: which primary phase does the solidification mode first refer to( γ or δ) The solidification process begins with crystallization, followed by which phase completes the solidification process.

  1. Stress corrosion crack:it refers to the crack form that occurs in the weak corrosive medium below the material yield point under the joint action of stress and corrosive medium
  2. σ Phase embrittlement: σ Phase is a kind of brittle, hard and non-magnetic intermetallic compound phase with compositional and complex crystal structure.
  3. Intergranular corrosion: selective corrosion near the grain boundary.
  4. Chromium deficiency mechanism:the supersaturated solid solution carbon diffuses to the grain boundary.

Chromium carbide cr23c16 or (Fe, Cr) C6 is formed with chromium near the boundary and precipitated at the grain boundary.

Because carbon diffuses much faster than chromium, it is too late for chromium to supplement from within the crystal to near the grain boundary, so that the mass fraction of Cr in the grain peripheral layer adjacent to the grain boundary is less than 12%, that is, the so-called “chromium deficiency” phenomenon.

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