Assignement n°4 Group4 final

Group n°4 MTAD10 FALL 2010/2011

MATERIALS IN INDUSTRIAL APPLICATIONS

Home assignment n°4

Subject: Steel alloy

Group n°4

Thibault COUTURE

Amirhosein MASOUMI

Ghadir RAZAZ

Ruslan Sevastopolev

SUMMARY

I/ WELDOX 1300 and WELDOX 700

II/ Influence of alloying elements

IV/ WELDOX APPLICATIONS

V/ UDDEHOLM and production methods

VI/ SVERKER 21

VII/ Alloy composition

VIII/ OUTOKUMPU

IX/ Stainless steel is good for you

X/ SHAEFFLER DIAGRAM

XI/ Chemical composition of Stainless steels:

XII/ EN 1.4318, AISI 301LN

XIII/ Corrosion on stainless steels

XIV/ Pitting resistance


I/ WELDOX 1300 and WELDOX 700

WELDOX 1300 is the structural steel which has the best strength ever : 1300 MPa. The ratio strength/weight is equivalent to Al alloy.

Application: Arrows of cranes

Chemical composition in % max:

C Si Mn P S B Nb Cr V Cu Ti Al Mo Ni N

0.25 0.50 1.40 0.020 0.005 0.005 0.004 0.80 0.08 0.10 0.02 0.020 0.70 2.0 0.010

WELDOX 700 is a structural high strength steel : 700 MPa. The main advantages of this alloy is homogenous properties, easily weldable.

Application: Load carrying structures having high demands on low weight

Chemical composition in % max:

C Si Mn P S B Nb Cr V Cu Ti Al Mo Ni N

0.20 0.60 1.60 0.020 0.010 0.005 0.04 0.70 0.09 0.30 0.04 0.015 0.0 2.0 0.010


II/ Influence of alloying elementsA unique combination of alloying elements optimizes the mechanical properties of WELDOX structural steel plate and HARDOX wear plate. This combination governs the preheat and interpass temperature of the steel during welding, and can be used to calculate the carbon equivalent value. The carbon equivalent value is usually expressed as CEV or CET in accordance with the equations below.The alloying elements are specified in the inspection certificate of the plate and are stated in percent by weight in these formulas. A higher carbon equivalent usually requires a higher preheat and interpass temperature. Typical values of carbon equivalents are given in our product data sheets.

CEV= C+Mn6

+(Mo+Cr+V )

5+(¿+Cu)15

(%) CET= C+ (Mn+Mo)

10+(Cr+Cu)20

+¿40

(%)

Due to the low-alloyed chemical composition and the low carbon equivalent (CE) TMCP-steels are perfectly weld able. Especially the low carbon content results in excellent resistance against cold cracks after welding.

As you can see in the equation of CEV & CET , CEV is bigger than CET, therefor we use CEV for designing part because we need more safety in structural design as you can see in tables. Normally we need to be on the safe zone which is more realistic if we choose the bigger ratio. You should notice that we always use CEV for structural steels & design & in this article we have structural steel too.


The same yield strength level is possible on different CE levels depending on the delivery condition. Low carbon equivalent (CE) is most important for good weld - ability.

N Normalizing rolledQT Quenched and temperedTM Thermomechanically rolledACC Accelerated cooled

IV/ WELDOX APPLICATIONS

WELDOX 1300 is a general structural steel with minimum yield strength of 1300 MPa. It is stronger than ordinary steel. As a result, one need less material to achieve equivalent strengths in products. Consequently, products will be lighter.

The main application is load carrying applications.

The examples are:

different types of cranes, deck cranes and mobile cranes, extra long booms for excavators, where Weldox application resulted in increased lifting capacity and unchanged crane weight

trailers, where lower weight was achieved by Weldox application sailboat keels with improved weight distribution, static strength and fatigue properties concrete pumps.

Strength of WELDOX increases with increasing carbon content, Figure 1.

0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26400

600

800

1000

1200

1400

C content, wt%

Yie

ld s

tre

ng

th, M

Pa

WELDOX 100

WELDOX 960

WELDOX 1100

WELDOX 1300

Figure 1. Yield strength vs. carbon content in different WELDOX steels.


V/ UDDEHOLM and production methods

UDDEHOLM is a Swedish company founded in 1668. Nowadays, this international firm employ 4000 people around the world which work on the production of tool steel.

The production can be sum up in four main processes:

The conventional process

The conventional process consists of several steps:

Electric arc furnace:Recycled steel, ferroalloys and slag formers are loaded into an EAF-furnace and melted by electric energy transferred by arcs between three graphite electrodes and the steel scrap.

Ladle Furnace:Dissolved elements as H, N and O are removed by purging inert gas into the melt and exposing it to a low partial pressure. The strong mixing between high-basicity slag and the steel bath results in favorable conditions for the removal of sulphur and slag inclusions.

Up-hill casting:Casting into ingot moulds requires a close control of the melt temperature to avoid segregation and inclusion clustering

Hot working and heat treatment:Improves resistance against common failure mechanisms and increases overall performance

Electro Slag Remelting (ESR)

Process for high purity materials

In Electro Slag Remelting (ESR), the ingot is built up in a water-cooled mould by melting a consumable electrode immersed in a superheated process slag. An electrical current flowing through the liquid slag, which provides the electrical resistance, generates the heat.


Powder metallurgy

Process for PM tool steel and high-speed steel

High Alloy Steels will gain improved properties by increasing the solidification rate. This gives a fine microstructure and small, well-distributed carbides in the matrix. During Powder Metallurgy (PM), the melt stream is atomised by nitrogen gas into small droplets with an average size of 50-100 µm. The powder is filled into capsules directly in order to avoid contamination. With hot isostatic pressing (HIP), the powder is consolidated to 100% density.By using a special refining sequence, the cleanliness of the molten steel is improved prior to atomisation. This results in improved mechanical properties and an extremely low non-metallic inclusion level (SuperClean™).The HIP'ed PM capsules are hot forged and rolled to smaller bar sizes followed by heat treatment and machining.

PM steels are used in very demanding applications within cold work, plastic and cutting tools.

Granshot

Uddeholm Granshot granulated melting stock is produced according to a patented water granulation method in which liquid metal is split up to form droplets. The droplets are rapidly cooled in a water bath. After dewatering, the granules are completely dried in a heating unit and then subjected to oxide cleaning. This gives the product its consistent high quality in accordance with the agreed customer specifications.

The material is supplied to foundries, mainly investment casters and stainless steel manufacturers worldwide.


VI/ SVERKER 21The steel grade was developed around 1930 and is still going strong. Ledeburitic 12 % Cr-steels are still the most commonly used tool steel for cold work tooling all over the world. Uddeholm Sverker 21 is a tool steel with very good abrasive wear resistance but with rather limited cracking resistance. Being the bulk grade for cold work applications there are many advantages such as well established know-how concerning all types of treatments and tool processing. The risk with the popularity is, however, that the grade by routine is used in applications where the properties profile not is entirely appropriate. In such cases normally there are better alternatives like Uddeholm Sleipner, Uddeholm Caldie or Uddeholm Vanadis 4 Extra.

APPLICATIONSThe properties profile of Uddeholm Sverker 21 combine to give a steel suitable for the manufacture of medium run tooling for applications where abrasive wear is dominant and the risk of chipping or cracking is not so high, e.g. for blanking and forming of thinner, harder work materials.

GeneralUddeholm Sverker 21 is a high-carbon, high chromium tool steel alloyed with molybdenum and vanadium characterized by:• High wear resistance• High compressive strength• Good through-hardening properties• High stability in hardening• Good resistance to tempering-back

American Iron and Steel Institute (AISI)

Chemical Composition

Grade Standard C Si Mn Cr Mo V PS≤D2 ASTM 1.40-1.60 0.10-0.60 0.20-0.60 11.0-13.0 0.70-1.20 0.50-1.10 0.030

1.2379 DIN 1.45-1.60 0.10-0.60 0.20-0.60 11.0-13.0 0.70-1.00 0.70-1.00 0.030Cr12Mo1V1 GB 1.40-1.60 ≤0.60 11.0-13.0 0.70-1.20 0.50-1.10 0.030

SKD11 JIS 1.40-1.60 ≤0.40 ≤0.60 11.0-13.0 0.80-1.20 0.20-0.50 0.03


HardnessHRC

Compressive yield strength, Rc0,2

MPa ksi

62 2200 319

60 2150 312

55 1900 276

50 1650 239

VII/ Alloy composition

As we know Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight. With adding different elements in steel alloy we can improve the properties like strength and wear resistance. We should mention that alloys with high rating of Brinell(HB) has better wear resistance.

We give some examples below for increasing strength and hardness:

Increasing carbon content make steel with more strength and hardness In addition, Nickel and Manganese are Austenite forming elements which both increase strength in steel What's more by adding Chromium or molybdenum to low alloy steel the hardenability and strength will go up. After that the presence of phosphorus in stainless steel raises the strength. And vanadium is another element that increases hardness.

Ni Mn Cr Mo P V

Strength ↗ ↗ ↗ ↗ ↗

Wear resistanc

e↗ ↗ ↗

To respond to second part of question, the structure which can cover both high strength and wear resistance would be Martensite structure, as we know Martensite formed by rapid cooling (quenching) of austenite which traps carbon atoms that do not have time to diffuse out of the crystal structure.

In the martensite you can see bcc structure with needle appearance and the rate of hardness in martensite significantly depends on carbon content.

Martensite structure


http://en.wikipedia.org/wiki/Carbon

http://en.wikipedia.org/wiki/Iron

http://en.wikipedia.org/wiki/Alloy

VIII/ OUTOKUMPU

Stainless Steel Reinforcement Bars is used for concrete reinforcement.

Corrosion of steel reinforcement is the main cause of premature failure of concrete structures in the world today. The most straightforward, risk- and maintenance-free solution is to use Stainless Steel Reinforcement. Although it initially results in a higher cost than the normally used carbon steel, the long-term cost is often lower due reduced maintenance costs. Until recently, the only grades available are the austenitic grades 304 and 316L, the highly alloyed 2205 duplex or Outokumpu's lean duplex designation LDX2101.

IX/ Stainless steel is good for you

In this topic, OUTOKUMPU make advertising about use of stainless steel. They speak directly to the customer of aluminum film for food application.

Here you can find a summary about this web page:

Advantages:

resist different corrosion environments working conditions ensuring that factories are safe structures last longer and our food is hygienic used for in systems to clean up the exhaust gases from cars and power stations. recyclable: when scrapped, it can be re-melted to make something new.

Effect of Chromium :

The minimum chromium content of the standardised stainless steels is 10.5%.

Chromium makes the steel 'stainless' this means improved corrosion resistance, as can be seen in the chart.

The better corrosion resistance is due to a chromium oxide film that is formed on the steel surface.

Besides chromium, typical alloying elements are molybdenum, nickel and nitrogen. Nickel is mostly alloyed to improve the formability and ductility of stainless steel. Alloying these elements brings out different crystal structures to enable different properties in machining, forming, welding etc.


The four major types of stainless steel are:

Austenitic Ferritic Austenitic-Ferritic (Duplex) Martensitic

Austenitic is the most widely used type of stainless steel. It has a nickel content of at least of 7%, which makes the steel structure fully austenitic and gives it ductility, a large scale of service temperature, non-magnetic properties and good weldability. The range of applications of austenitic stainless steel includes housewares, containers, industrial piping and vessels, architectural facades and constructional structures.

Ferritic stainless steel has properties similar to mild steel but with the better corrosion resistance. The most common of these steels are 12% and 17% chromium containing steels, with 12% used mostly in structural applications and 17% in housewares, boilers, washing machines and indoor architecture.

Austenitic-Ferritic (Duplex) stainless steel has a ferritic and austenitic lattice structure - hence common name: duplex stainless steel. This steel has some nickel content for a partially austenitic lattice structure. The duplex structure delivers both strength and ductility. Duplex steels are mostly used in petrochemical, paper, pulp and shipbuilding industries.

Martensitic stainless steel contains mostly 11 to 13% chromium and is both strong and hard with moderate corrosion resistance. This steel is mostly used in turbine blades and in knives


X/ SHAEFFLER DIAGRAM

SCHAEFFLER DIAGRAM: CALCULATION OF STRUCTURE FOR STAINLESS STEELS

The Schaeffler diagram does evaluate the presence of austenite, ferrite, bainite and martensite depending on the chemical composition and the “proper cooling” (or heat treatment) after pouring.

The limits, for the chemical composition are:

C S Mn Mo Nb N Cr0,2 % 1 % 4 % 3 % 1,5 % 0,05

0,070,10

0 - 18 %18 - 25 %

> 25 %

These percentages are those of the element as present in the matrix, notin carbides or any other component as nitrides…

This diagram is interesting because, by quantifying the amount of types of structures (ferrite, martensiet, austenite), it does give an indication that the material will comply with the standard. This is possible at a time that the metal is still in the melting furnace because it does use the chemical composition that is taken before pouring. In this way corrections of the chemical composition are still possible. It is very useful for austenitic stainless steels because the amount of ferrite must be restricted (material becomes magnetic) and for martensitic stainless steels because the amount of delta-ferrite must be controlled. Another factor, which must be avoided, is the presence of carbides. The carbides do decrease the ductility but also the corrosion resistance (carbides remove chromium from the matrix). The carbides also lead to some magnetic behavior of austenitic stainless steels. It mostly concerns and the chemical composition and the cooling after pouring and if applicable, heat treatment. A stainless steel needs a minimum of 12 % of chromium in the matrix. Due to this condition, the part of the graph below a chromium-equivalent of 12 % is not applicable.

The latest version of Cr eq and Ni eq are:

Creq = % Cr + 1,0 (% Mo) + 0,5 (% Nb + % Ta) + 1,5 (% Si) + 2 (% Ti) + (% W + % V + % Al)Ni eq = % Ni + 30 (% C) + 0,5 (% Mn ) + 30 (% N) + 0,5 (%Co)

The carbides take carbon and chromium out of the matrix. In the special types of austenitic stainless steel, the carbon is equal or lower than 0,03 % and for these types nearly never carbides are formed. So we can estimate that this amount of carbon, at least, remains in the matrix.

Ferrite is important in avoiding hot cracking in during cooling from welding of austenitic stainless steels. 'Constitution diagrams' are used to predict ferrite levels from the composition by comparing the effects of austenite and ferrite stabilising elements. The Schaeffler and Delong diagrams are the original methods of predicting the phase balances in austenitic stainless steel welds.


The figure shows that chromium is a ferrite stabilizer and nickel is an austenite stabilizer.


XI/ Chemical composition of Stainless steels:

Steel stainless 316:

Carbon, C <= 0.080 %Chromium, Cr 16 - 18 %Iron, Fe 61.8 - 72.0 %Manganese, Mn <= 2.00 %Molybdenum, Mo 2.00 - 3.00 %Nickel, Ni 10.0 - 14.0 %Phosphorous, P <= 0.0450 %Silicon, Si <= 1.00 %Sulfur, S <= 0.0300 %

Stainless steel 304 :

Carbon, C <= 0.080 %Chromium, Cr 18.0 - 20.0 %Iron, Fe 66.345 - 74.0 %Manganese, Mn <= 2.0 %Nickel, Ni 8.0 - 10.5 %Phosphorous, P <= 0.045 %Silicon, Si <= 1.0 %Sulfur, S <= 0.030 %

Stainless steel 439:

Carbon, C 0.0700 %Chromium, Cr 18.0 %Iron, Fe 78.33 %Manganese, Mn 1.00 %Nickel, Ni 0.500 %Silicon, Si 1.00 %Titanium, Ti 1.10 %

Stainless steel 403:

Carbon, C <= 0.15 %Chromium, Cr 12.3 %Iron, Fe 86.0 %Manganese, Mn <= 1.0 %Phosphorous, P <= 0.040 %Silicon, Si <= 0.50 %Sulfur, S <= 0.030 %


S32950:

Carbon, C 0.0300 %Chromium, Cr 27.5 %Iron, Fe 63.52 %Manganese, Mn 2.00 %Molybdenum, Mo 2.00 %Nickel, Ni 4.35 %Silicon, Si 0.600 %

To investigate the place of alloy steel in Schaeffler diagram we should follow the formula below to

Count the equivalent chromium and Nickel:

Creq = % Cr + 1,0 (% Mo) + 0,5 (% Nb + % Ta) + 1,5 (% Si) + 2 (% Ti) + (% W + % V + % Al)Ni eq = % Ni + 30 (% C) + 0,5 (% Mn ) + 30 (% N) + 0,5 (%Co)

Alloys 316 304 439 403 S32950Creq 21 20.5 21.7 13.05 30.4Nieq 15.4 11.4 3.1 5 6.34

Colours: 316

304

439

403

S32950

As we can see in the schaeffler diagram the stainless steel 316 was placed in Austenit area,stain less steel 304 in Austenit & Ferrite area,stainless steel 439 in Ferrite area ,stainless steel 403 in Martensite &ferrite area and S32950 in Ferrite area.


XII/ EN 1.4318, AISI 301LN

EN 1.4318, AISI 301LN is a low carbon, high nitrogen austenitic stainless grade.

It is generally used for structural parts where high strength and toughness are needed beside a corrosion resistance. When hardened by cold working, the strength and corrosion resistance of this steel grade steel is utilized in structural applications, like in transportation vehicles.

The combination between ductility and toughness is excellent even at low temperatures.

The strength of the steels is controlled by the degree of work hardening. When the material is cold worked, it undergoes substantial strain hardening leading to significant strength enhancement. The strain-hardened austenite is also partially transformed to martensite. The larger the degree of deformation, the higher strength gets the steel.

Tensile strength levels in cold worked condition (2H) according to EN 10088-2:2005.

C means cold rolled, the following numbers mean the tensile strength.


XIII/ Corrosion on stainless steels:

Generally, the corrosion resistance of a stainless steel is dependent on a thin invisible film on the steel surface, the passive film. The passive film consists mainly of a chromium oxide that forms in reaction with oxygen in the air. Some alloys elements, for example molybdenum and nitrogen, improve the corrosion resistance in corrosive environments. The passive film can be broken down completely or partly with corrosion as a result

Some important Corrosion on stainless steel:

Uniform Corrosion: Uniform corrosion generally occurs on stainless steel in acid environments or hot alkaline solutions. The corrosion rate then develops at a rate determined by a combination of the alloy compositions and the corrosive environment like( hydrochloric or hydrofluoric). Actually, Uniform corrosion occurs when the passive layer on a stainless steel surface partly or completely breaks down Uniform corrosion rate is also affected if the acid contains oxidizing or reducing chemicals. Reducing impurities, for example hydrogen sulphide, may increase the corrosion rate. Higher alloyed stainless steel grades are more resistant to uniform corrosion than the lower alloyed stainless steel grades.

Galvanic corrosion: This corrosion happens When two dissimilar metals are connected electrically and immersed in a conductive liquid, an electrolyte, their corrosion performance might differ significally when compared with the metals, uncoupled. As a rule, the less noble material, the anode, is, more severely attacked, while the more noble metal, the cathode, is essentially protected from corrosion. This phenomenon is called galvanic corrosion. For example Two different stainless steel grades in the passive state, coupled in an electrolyte, are quite close in the galvanic series. And the amount of Galvanic corrosion dependent on temperature and the composition of conductive solution.


Pitting Corrosion:

Pitting is a form of localized corrosion and is known by attacks at small separated spots on the steel surface. Pitting occurs mainly in the presence of neutral or acidic solutions containing chlorides or other halides. Chloride ions facilitate a local breakdown of the passive layer, especially if there are defects in the metal surface. When the metal corrodes in the pit, dissolved metal ions generate an environment with low pH and chloride ions migrate into the pit to balance the positive charge of the metal ions. Thus the environment inside a growing pit gradually becomes more aggressive and repassivation becomes less likely. As a result, pitting attacks often entered at high rate, thereby causing corrosion failure in a short time higher chromium, molybdenum and nitrogen content in the steel increase the resistance to pitting.

Crevice corrosion:

Crevice corrosion is a form of localized corrosion and occurs. in neutral or acidic chloride solutions The corrosion attack starts more easily in a narrow crevice than on an unshielded surface, Crevices, that found at flange joints or at threaded connections, are critical sites to corrosion. Small amounts of dissolved metal ions inside the crevice cause a decrease of the solution pH and the presence of chlorides facilitates the break-down of the passive layer. Thus the environment inside the crevice gradually becomes more aggressive and repassivation becomes less likely. As a result, crevice corrosion attacks often develop at a high rate, thereby causing corrosion failure in a short time. A higher chromium, molybdenum and nitrogen content in the steel increases the resistance to crevice corrosion.

Intergranular corrosion:

This type of corrosion may occur if the area around the grain boundaries has less corrosion resistant than the matrix in the medium in question. The classical case is when chromium carbide is precipitated at the grain boundaries. The closer matrix will be empty of chromium and This narrow region around the grain boundary may have less corrosion resistant than the rest of the material. In modern stainless steels with lower carbon content, Intergranular corrosion is very seldom any problem in practical applications.


Stress corrosion Cracking:

It is the cracking made from the combined influence of tensile stress (or residual stresses)and a corrosive environment and the failure of material will accelerated by the combination of mechanical stress and corrosion environment. The most common type of SCC is trans-granular stress-corrosion cracking, SCC, that may develop in concentrated chloride-containing environments and The elevated temperature is vital for occurring the SCC. After that, alkaline solution at high temperature increases the possibility in SCC especially in low alloys steel.

Corrosion Fatigue:

It is well known that a material subjected to a cyclic load far below the ultimate tensile stress can fail, a process called fatigue.

If the metal at the same time exposed to a corrosive environment and loading, the failure can take place at even lower loads and shorter time.

Atmospheric Corrosion:

Atmospheric corrosion occurs on a steel surface in a thin wet film created by the humidity in the air in combination with impurities. Corrosive conditions for stainless steel can be the chloride depositions from a humid atmosphere on the steel surface .stainless steel is often chosen for decoration in buildings due to its aesthetic and you can see the atmospheric corrosion on building's surfaces easily. Atmospheric environments are most commonly divided into four categories: rural, urban, industrial and marine according to kind of environment. We should choose different types of stainless steels for example Molybdenum-alloyed grades of type 316 or comparable grades are normally specified for a marine atmosphere.


XIV/ Pitting resistance

Pitting resistanceas we know is a kind of corrosion in stainless steel alloys. Pitting resistance equivalent number(PRE) Is a theorical way to comparing the pitting resistance in different types of stainless steel grades.

The latest version to account the (PRE) is:

PRE = %Cr + 3.3 x( %Mo + 0.5 %W)+16 x %N

According to formula, stainless steel grades with high percentage in chromium

And particularly in molybdenum and nitrogen have more resistance in pitting corrosion.

The percentage of chromium and molybedenum in alloys to calculate:

S32950403439304316Stainless steel27.5%12.3%18%18-20%16-18%Chromium2%<=1%1%2%2%molybdenum

We ranked the alloys in pitting resistance:

Stainless steel S32950 316 304 439 403

PRE 34.1 27.9 26.6 21.3 15.6

As we can see from the result in the table S32950 has the best resistance corrosion that waslocated

in ferrite area as we saw in Schaeffler diagram and the stainless steel 403 has the lowest which is in

martensite and ferrite area.


Assignement n°4 Group4 final

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