Metal macrostructure defect inspection

Metal macrostructure defect inspection is also referred to as a macroscopic examination.It is with the naked eye or is not more than 10 times the magnifying glass to check the metal surface, fracture or macroscopic organization method and its defects.Macroscopic examination on the metal ingot casting, casting, forging, welding, rolling, heat treatment process, the commonly used inspection method is a kind of important.This test method is simple, rapid, can reflect the metal macro morphology and distribution characteristics of regional organizations and defects.Enable people to correct and comprehensive judge the quality of the metal material, in order to guide the production, the rational use of materials science.For the analysis of the optical microscopy and electron metallographic basic work.Macroscopic examination including macrostructure and defect inspection (including acid corrosion, sulphur print, tower turning and non-destructive methods such as damage) and fracture analysis, etc. TitaniumCN
1. The typical macroscopic defects
The typical macroscopic defects have segregation, porosity, shrinkage cavity, bubble, crack, low power inclusion, coarse grain ring, etc.
(1) the uneven phenomenon called segregation of alloy chemical composition segregation.Based on the characteristics of the range size and position of the segregation, generally can be divided into three kinds.The intracrystalline partial and segregation, regional segregation, gravity segregation.Coring and segregation as after solid solution alloy casting in the condensation process, due to the solid phase liquid ingredients in constant change, therefore, even within the same crystal, first part of the solidification after solidification of the part and its chemical composition is not the same.The intracrystalline chemicals called coring uneven phenomenon.
(2) the shrinkage and loose in the ingot head, middle, grain boundary and interdendritic, often have some of the macroscopic and microscopic shrinkage holes, collectively known as the shrinkage cavity.Large volume and concentration of shrinkage cavity called on shrinkage cavity;Small and dispersed shrinkage cavity called osteoporosis.Which appear in the grain boundary and interdendritic porosity is also called microporosity.Shrinkage cavity and loose irregular shape, the surface is not smooth, easily distinguished from the more pliable porosity.Ingot casting box segregation four years the national registered construction engineer examination in terms of construction project cost management of construction engineering construction project cost case analysis construction engineering technology and measuring shrinkage and loose the direct cause, is solidified body contraction of the liquid metal solidification occurs.Residual shrinkage cavity in the metal material of axial position of the transverse specimens acid leaching, easy to recognize.
(3) the hole according to the position of porosity in ingot casting, it can be divided into three classes of surface porosity, subcutaneous blowhole and internal porosity.Can be divided into the precipitation type according to the cause of porosity, porosity and reactive pores.
(4) the most complicated composition of crack or higher amount of impurities or have a small amount of non-equilibrium eutectic alloy, there are larger crack tendency.Especially large ingot casting.Under the condition of the cooling strength of continuous casting, the tendency of crack is bigger.Produced in the process of solidification crack is called hot crack.After solidification cracks occurring in the process of cooling is called cold crack.More hot cracking along the grain boundary extension, twists and turns and irregular, often for transgranular crack, cold crack in a straight line extension.
(5) low power inclusions
On the acid leaching at low sample, some naked eye can see fire-proof material, slag and other non-metallic inclusions, these relatively bulky inclusions are called macroscopic inclusions.Them on acid leaching test plate in the form of Mosaic, and maintain its inherent in all sorts of color, common are gray, beige and dark gray, etc.Some low power inclusions may fall off during production, and surface is empty.Empty characteristics different from the edge of the bubble is that it is not neat, spongy.
(6) streamline is the low melting point metal composition and banded structure segregation when rolling or extrusion stretch.At the same time, also in the process of rolling ingot casting grain in elongated into strips.After recrystallization heating process can restore the elongated grain into equiaxed grain, but due to the low melting point elements and the elongation of banded structure is formed by the distribution of stripe still exist.In steel on the longitudinal section after polishing and acid leaching, with the naked eye can see the line of the stripes.The macroscopic organization called fibrous tissue, also known as the streamline.
(7) coarse grain ring is one of the main defects of aluminium alloy extrusion products.Aluminum alloy extrusion in the subsequent heating of the outer coarse grains, according to the phenomenon of coarse grain rings.Its characterization features are: for single-hole extrusion bar, bulky zone, a symmetric circular.The porous squeeze rod eccentric crescent shaped.The presence of coarse grain ring could sharply reduce the mechanical properties.Coarse grain ring also has a "genetic" organization.With coarse grain ring blank after moulding, still keep original coarse grain area, causing uneven and affect the surface quality of molded parts.Even in the heat treatment process is easy to cause crack.Study shows that the formation of coarse grain ring is driven by extrusion deformation caused by uneven friends.
2. The organization and the defect is etching method
Macrostructure etching method is divided into hot acid etching method, cold acid etching method and three kinds of electrochemical corrosion method.Experiments using cold acid etching.Cold acid etching operation main points are as follows:
(1) according to the appropriate material selection type and a certain proportion of etching solution.
(2) on the surface of the sample inspection should finish in 7 above, acid corrosion tests should be surface wipe, remove the oil pollution.
(3) with the method of corrosion, pour acid slowly in the basin of land acid sample again, then acid brush divide evenly with a brush,
(4) etching, water rushs acid, and alkaline neutralization, then use hot water to rinse, blow dry immediately.
3. The fracture analysis of metal fracture according to the fracture methods can be divided into brittle fracture
And thus reduce the grain boundary strength.Transgranular fracture is due to the strength of the grain itself is not high, or along the grain in the process of crystallization of some crystal clip into the impurities.See the shape of the fracture physical objects.Ductile fracture rupture occurred plastic deformation before.Distorted the original grain (spin or broken), no longer keep the original size, shape, and can't study from these fracture metal internal organization.See the shape of the fracture physical objects.

Titanium Phase transition temperature of testing

GR2 industrial pure titanium with good corrosion resistance, mechanical property and welding performance, in ship, chemical industry, and many other fields have important applications.Because the metal under the condition of the machining process must be, its organization status mainly depends on the organization in the process of evolution, heat treatment and strongly influence its performance.High temperature, therefore, the research of industrial pure titanium GR2 organization evolution behavior has important significance.In this paper, using the confocal laser scanning microscope (CLSM), optical microscope (OM), differential scanning calorimetry (DSC) method to study the isometric state of industrial pure titanium GR2 in organization evolution behavior in the process of heating, heat preservation and cooling, analyses and summarizes its organizational evolution law.In heating and heat preservation phase, bending part of alpha grain boundary migration and tend to be straight, short heating effect on alpha grain size is very Titaniumcn small.Temperature at the initial phase transition point T alpha/alpha + beta above multiple parallel "lenticular" in the same alpha beta strip around the intracrystalline nucleation and diffusion mechanism to gobble up alpha growing, with "tent" embossed on the surface of the form.Temperature more than completely alpha + beta phase transition point T/beta, alpha and beta phase change over, initial alpha beta article slices with crystal and to form a "group", continue to heat, the "group" "eat" to each other, eventually become the bulky shaft such as beta.The dynamics of beta grain grew up statistics and fitting calculation.From the state of the different cooling, different organization at room temperature.From the alpha + beta two-phase district cooling, such as organization revert to the original state axis, floating on the surface of convex disappear;From cooling, just completely into beta phase formation interface irregular alpha organizations;From cooling, axis beta groups such as alpha and beta and alpha phase change can be divided into grain boundary westergren alpha two phase nucleation and grain boundary first alpha in beta at grain boundary nucleation and growth to connect into a thin film of grain boundary alpha, then westergren alpha on the grain boundary alpha nucleation, and in the form of a layer of flake cluster to grew up in the beta phase, until full of beta grain, beta and alpha end of shift, forming a typical widmanstatten structure.Cooling rate equivalent shaft beta beta and alpha phase transition in the process of cooling effect is very big, the faster the cooling rate, grain boundary alpha and westergren alpha thickness is smaller, westergren alpha elongation the faster, the faster the phase transition.Under different cooling rate on the grain boundary of alpha broadening, the elongation and the thickness of the westergren alpha, and beta and alpha phase transformation kinetics of quantitative statistics, beta and alpha phase transformation kinetics of empirical formula is given.

Using the calculation method and differential scanning calorimetry and continuous heating metallographic method
Three kinds of method to calculate and determine the two-phase titanium alloy TC11 (alpha + beta)/beta phase transition point.Calculation method for each element and the influence of impurity element content on the phase transformation point value is within the scope of a content calculated value, thus calculated is close to the phase transition point and the measured values;Differential scanning calorimetry because of titanium alloy and chemical reaction of the crucible, produce transformation hysteresis phenomenon, cause the measured phase change temperature is too high;Metallographic method and continuous warming choose smaller due to the quenching temperature interval, measuring accuracy is higher, therefore more accurate measurement of TC11 titanium alloy phase transition temperature.Use the synchronous sTA449c thermal analyzer measurement titanium and titanium alloy phase transition temperature, the reference sample for 23 alo powder, 1 min to 10 ℃ temperature;The protection of argon flow for 45 m11min.Before test, should be first in the two samples in the crucible of 23 alo powder amount, measuring instrument baseline within the rules, can begin formal sample DSC curve.The phase transition temperature was evaluated by continuous heating metallographic method.The sample size to 10 mm x 10 mm x 10 mm;When heating sample to ensure heat through, time of heat preservation for 60 min.Quenching temperature range is 990 ~ 1040 ℃, quenching temperature interval of 10 ℃, and then water quenched sample.Of which the transfer speed of no more than 2 s.After quenching specimen made of metallographic observation, the optical microscope magnification of 500 times the sample organization change.2.1 calculation method according to the phase transition temperature of each element titanium phase transition point of the influence of the phase change temperature calculated formula is: / T + phase transformation point = 885 ℃ + Σ content of each element x (1) the effect of the elements of phase transformation point of the type of 885 ℃ for calculating the phase transition point of pure titanium.

The principle of titanium alloy and its Characteristics and shortcomings

The principle of titanium alloy TitaniumCN 
Titanium alloy is based on titanium to join other alloy elements.Titanium has two homogenous different crystal: under 882 ℃ to close the six-party alpha titanium structure, above 882 ℃ for body centered cubic beta titanium.
Alloying elements according to their influence on phase change temperature can be divided into three categories:
(1) a stable alpha, increase the temperature of the phase transition element for alpha stable elements, such as aluminum, carbon, oxygen and nitrogen.Including aluminum titanium alloy main alloy elements, it is to improve the alloy at room temperature and high temperature strength, reduce weight, increasing the elastic modulus have obvious effect.
(2) stable beta phase, to reduce the phase transition temperature elements for beta stable elements, and can be divided into two isomorphous and eutectoid type.
The application of titanium alloy products
The former are molybdenum, niobium, vanadium, etc.;The latter has a chromium, manganese, copper, iron, silicon, etc.
(3) the phase transition temperature impact elements to neutral elements, such as zirconium, tin.
Oxygen, nitrogen, carbon and hydrogen is the main impurity of titanium alloy.Oxygen and nitrogen in the alpha phase has larger solubility, to strengthen titanium alloy has a significant effect, but it is plastic.Usually prescribed titanium content of oxygen and nitrogen in under 0.15 ~ 0.2% and 0.04 ~ 0.05% respectively.Hydrogen in the alpha phase solubility is small, dissolve excess hydrogen yield in titanium alloy hydride, alloy become fragile.Usually controlled under 0.015% hydrogen content in titanium alloys.The dissolution of hydrogen in titanium is reversible and can be removed using a vacuum annealing.
disadvantages.
Titanium and titanium alloy limitation is mainly in high temperature and chemical reactivity with other materials.The nature of the force of titanium alloy and conventional refining, melting and casting technology is different, and often causes the damage of mold;As a result, make the price of titanium alloy is very expensive.So they began to use mostly in aircraft construction, aircraft, and used in the oil and chemical industry and other high-tech industries.But because of the space science and technology developed, people's quality of life has increased, so the titanium alloy also gradually used to make consumer goods, for the benefit of life of life, only these prices are still on the high side, belongs to the high price of the product, it is unable to carry forward the Achilles' heel of the biggest titanium alloy.
The main characteristics
Titanium alloy main features;Industrial pure titanium: pure titanium more than chemical pure titanium content of impurities, so its strength and hardness is high, its mechanical properties and chemical properties similar to stainless steel, compared with the strength of pure titanium, titanium alloy is better than that of austenitic stainless steel in terms of oxidation resistance, but poor heat resistance, TA1, TA2 and TA3 higher content of impurities, mechanical strength, hardness, in turn, enhanced, but the plastic toughness decline in turn.

Titanium alloy and Its development course

Titanium is developed in the 1950 s a kind of important structure of the metal, titanium alloy has high strength, good corrosion resistance and high heat resistance and is widely used in various fields.Many countries in the world is to know the importance of the titanium alloy material, carries on the research and development, and the practical application.50 ~ 60 s of the 20th century, mainly is the development of aviation engine with high temperature and the body with the structure of the titanium alloy, titanium alloy developed a batch of corrosion resistant titanium alloy in the 70 s, 80 s, to further corrosion resistant titanium alloy and high strength titanium alloy.Titanium alloy is mainly used to produce aircraft engine compressor components, followed by the rockets and missiles and high-speed plane structure.TitaniumCN

Titanium is developed in the 1950 s a kind of important structure of the metal, titanium alloy has high strength, good corrosion resistance and high heat resistance and is widely used in various fields.Many countries in the world is to know the importance of the titanium alloy material, carries on the research and development, and the practical application.
First practical titanium alloy is in 1954 the successful development of Ti 6 al 4 v alloy, because of its heat resistance, strength, plasticity, ductility, formability, weldability and corrosion resistance and biocompatibility are better, and become the industry in ace alloy, titanium alloy, the alloy usage has 75% ~ 85% of all titanium alloys.Many other titanium alloy can be regarded as Ti 6 al 4 v alloy modification.
50 ~ 60 s of the 20th century, mainly is the development of aviation engine with high temperature and the body with the structure of the titanium alloy, titanium alloy developed a batch of corrosion resistant titanium alloy in the 70 s, 80 s, to further corrosion resistant titanium alloy and high strength titanium alloy.Using the temperature of the heat resistance of titanium alloy has been in the 50 s to 400 ℃ up to 600 ~ 650 ℃ in the 90 s.A2 (Ti3Al) and r (TiAl alloy, the titanium in the use of the engine parts by the engine is cold end (fan and the compressor) to the hot end of engine (turbine) direction.Titanium alloy for high strength, high plastic structure, with high strength and high tenacity, high modulus and high damage tolerance direction.
In addition, since the 1970 s, the Ti, Ni, Ti - Ni - Fe - Ni - Nb, Ti shape memory alloy, and increasingly wide application in engineering.Has developed hundreds of titanium alloy in the world, the most famous of the alloy has 20 ~ 30 kinds, such as Ti 6 al 4 v, Ti - 5-2.5 Sn, Ti - 2 al - 2.5 - Zr, Ti - 32 Mo, Ti, Mo, Ni, Ti - Pd, SP - 700, Ti, Ti - 6242-10-5-3, Ti - 1023, BT9, BT20, IMI829, IMI834
According to relevant statistics, in 2012 China's chemical industry with titanium volume of 25000 tons, less than in 2011.This is since 2009, our country chemical industry with titanium market negative growth for the first time.In recent years, the chemical industry has always been the largest use of titanium processing material, its dosage in titanium has remained at more than 50% of the total amount accounted, the proportion is as high as 55% in 2011.But as the economic downturn, the chemical industry not only decreased significantly in new projects, at the same time will also face adjustment of industrial structure, the partial products new capacity controlled, backward production capacity will be phased out.Affected, its shrinking of titanium processing material consumption has become a natural.Before this, there is industry insiders predict chemical industry with titanium content peaked in 2013 ~ 2015 years.At the current market point of view, the weakness in the overall economy in 2012 is likely to make chemical recession ahead of titanium.

The blanking technology of the titanium alloy forging

                         Forging of titanium alloy forging (rolling) rods Titaniumcn, the alpha layer of the surface with a layer of hard brittle, die forging, need to get rid of this layer, so as to avoid forging billet caused by surface cracking.For less than 50 mm diameter rod, need to remove the surface layer of 3 mm thick, diameter greater than 50 mm, need to get rid of 5 mm.For extrusion bar, less than 50 mm diameter, can be car to 2 mm, greater than 50 mm in diameter, generally to 3 mm.After cutting, there are still defects, such as individual site, partial grinding can be eliminated, the grinding depth should not be greater than 0.5 mm.

Definite size titanium alloy forging blank available anode cutting machine, sawing machine, lathe, punching and shearing machine, grinding wheel cutting machine or cutting on the forging hammer or hydraulic press.The highest efficiency in the punching and shearing machine.
(1) the thickness of the disk saw cutting disc saw blade between 2 ~ 8 mm, suitable for cutting bar diameter is larger.Disk saw the linear velocity of about 30000 ~ 35000 mm/min, the feed amount of hours to get a clean face.To prevent metal bond tools, metal burns, can use suspension to reduce friction, cooling cutting tools.
(2) the cutting of titanium alloy anode, mechanical cutting, incision width of no more than 3 mm, with a concentration of 1.28 ~ 1.32 g/cm3 water as working fluid.Although anodic cutting cut cost less, but less rate is low.
(3) before the hammer or hydraulic press for cutting cutting, bar should be preheated to deformation began cutting temperature (or chop).Pure titanium in punching and shearing machine cold shearing.
(4) lathes cutting of titanium alloy car cutting, cutting speed should be within 25000 ~ 30000 mm/min, feed quantity is 0.2 ~ 0.3 mm/week.
Scalping remove the alpha layer, car to specification: the cutting rate of 15000 ~ 20000 mm/min.No alpha layer when turning the standard related to surface roughness: when the roughness Ra = 0.63 ~ 2.5, feed quantity is 0.08 ~ 0.1 mm/week;Ra = 1.25 ~ 5, the feed quantity is 0.1 ~ 0.2 mm/week;When Ra = 2.5 ~ 10, feed quantity is 0.3 ~ 0.4 mm/week., turning processing must be used when the lubricating coolant supply 1 ~ 1.5 MPa pressure.
(5) grinding wheel cutting of titanium alloy rod diameter less than 60 mm, appropriate is used grinding wheel cutting.When the diameter of the grinding wheel cutting more than 20 mm, should use the cooling fluid.Grinding wheel cutting efficiency is higher, but the life of the grinding wheel piece is shorter.
Blank after cutting, end of the acute Angle should be round.Otherwise end forging or heading on horizontal forging machine, may cause folding.The blank diameter of less than 50 mm, acute Angle round radius R is 1.5 ~ 2.0 mm;The blank diameter of more than 50 mm, acute Angle round radius R is 3 ~ 4 mm.

Forging of titanium

Titanium forging is on titanium TitaniumCN blank sheet (not including) the external force, make its produce plastic deformation, change the size, shape and improve performance, to manufacturing machinery parts, artifacts, tools or blank forming method.
According to the different forging temperature area, in view of the different quality of forgings and forging process requirements, can be divided into three cold forging, warm forging, hot forging forming temperature area.Originally this temperature region division, there is no strict boundaries, generally speaking, the recrystallization temperature region of the forging, called hot forging, no heating forging is called cold forging at room temperature.
When the cold forging, forging the size of the change is very small.Forging under 700 ℃, and less scale formation, and surface decarburization phenomenon.Therefore, as long as the deformation energy within the scope of the forming, cold forging is easy to get good dimensional accuracy and surface finish.As long as the good control of temperature and lubrication cooling, the temperature under 700 ℃ forging can also achieve good accuracy.Hot forging, due to the small deformation and deformation resistance, can be forged shape complicated large forgings.In order to get high dimensional precision forging, can be in 900-1000 ℃ temperature field using hot forging processing.Also, pay attention to improve working conditions for hot forging, die (2-5000 hot forging, warm forging 1-20000, cold forging 2-50000) compared with other temperature field of forging is shorter, but its degree of freedom is big, the cost is low.

To produce when in cold forging deformation and strain hardening, the forging die under high load, therefore, need to use the high strength of the forging die and using hard of lubricant to prevent wear and adhesive processing method.In addition, to prevent crack in billet, intermediate annealing when necessary to ensure deformation ability.To keep good lubrication condition, phosphating of billet.In a continuous process with bar and wire rod, and the current of cross section is not lubrication processing, are studying the possibility of phosphating lubrication method is used.

According to the movement of blank, forging can be divided into free forging, upsetting and extrusion, die forging, closed die forging, closed upset.Closed die forging and closed upset because there is no flash, material utilization ratio is high.With a process or a few process can complete complex forging finishing.Since there is no flash, forging stress area is reduced, the required load is also reduced.However, we should pay attention to not make blank completely is restricted, so we will strictly control the volume, control the relative position of forging die and measure of forgings, effort to reduce the wear and tear of forging.

The reason of chemical equipment from corrosion

With the development of economy, the increasing demand of chemical equipment, more and more the operation of the production equipment is beyond design ability, thus for global chemical enterprise at present, to prevent the corrosion of process equipment for the loss by the failure has become an urgent problem.Many experts agree that material protection and corrosion protection measures is to reduce maintenance costs and make the important guarantee of the safe and stable operation of the factory.In recent years, the chemical engineering construction in the field of competition, in order to reduce the bid price, the bid for the anti-corrosion measures, the use of high quality alloy, surface treatment technology, such as antiseptic coating (including)Titaniumcn
, cathodic protection and on-line corrosion monitoring system such as the importance of clear enough, this behaves particularly outstandingly in the developing world.The chemical industry for new and existing industrial artifacts protection and protection of the demand is higher and higher, people demand for coating and anticorrosion technology is growing rapidly.Corrosion damage everywhere, corrosion accidents occurred frequently, which in addition to corrosion itself has a spontaneous nature, largely because of corrosion harm to estimate shortage, not deep understanding of the importance of corrosion protection, the corrosion and protection they have no knowledge of science, no corrosion protection measures are taken, or improper anti-corrosion measures.The cause of the corrosion damage
(1) there are many in the chemical production has a certain corrosive medium, such as acid, alkali, salt, water, oxygen, and so on, this is one of the principal causes of corrosion.
(2) the operation of overtemperature and overpressure, chemical equipment management is not perfect, thought not value, and the corrosion is the main production
One of the reasons.
(3) chemical equipment equipment structure design is unreasonable, improper material selection, manufacturing process quality, welding residual, lack of anti-corrosion measures or inferior construction quality etc, provides the corrosive environment.The intrinsic factors of corrosion damage
(1) different metal for different media have different ability to resist corrosion.
(2) the metal of the coarse grains, the faster the corrosion.On the other hand, is slower, such as stainless steel is higher than the corrosion resistance of cast iron.
(3) the surface of the parts more rough, more prone to corrosion.The surface of oxide film is corrosion resistant.
(4) the shape of the equipment structure mutation place, such as openings, gaps, or corner position, rapid metal corrosion.
Corrosion damage caused by external factors
(1) the types of media,
Chemical composition, concentration, pH value, impurities, moisture and oxygen scene is the external cause of corrosion.
(2) the higher the temperature of the medium, the higher the pressure, the faster the corrosion, because corrosion is a kind of chemical reaction, every rise 10%, the corrosion speed increase
1 ~ 3 times _l J.Diffusion velocity increases as the temperature increases, and electrolyte resistance of corrosion, so quicken the reaction of corrosion cell.
(3) medium flow, the faster the more easy to corrosion, it will scour protection film, produced vortex, turbulence, cavitation and cause severe
The impact of the heavy wear and cavitation corrosion.
(4) components by external force or the greater the residual stress, the faster the corrosion.
(5) the influence of the stress and fatigue.Equipment stress produces on the one hand, is formed in the process of machining, such as cold working
Stress and organization stress of hot working;On the other hand in the work can also be under pressure or rotating parts of produce should be
Force.The results of the stress the role of causing distortion of the inner metal, reducing the area of the electrode potential, increase micro batteries
Corrosion.Anticorrosive technology of dalian petrochemical company since 1958 since the earliest using modified phenolic epoxy coating anticorrosive, anti-corrosion technology in me
The chemical industry has gained rapid development.The present anti-corrosion technology mainly include: development of corrosion resistant material, the surface corrosion protection technology, corrosion technology, electrochemical protection and so on.