1. What is the difference between the 300 and 400 stainless steel series?

The 300 series are the austenitic stainless steel, which are non-magnetic.
The 400 series are the ferritic stainless steel, which are magnetic.
The stainless steel from 400 series can be divided in two groups: the ferritic properly, which generally has a higher chrome and a lower carbon; and the Martensitic, in which predominates lower chrome and a higher carbon (compared with the ferritic).


2. Do the stainless steel mechanical proprieties change in high temperatures?

The carbon steel and the stainless steel both suffer a reduction in the values of their mechanical proprieties while working in high temperatures.
As a matter of fact, this is an attribute of metals and metallic alloys in general. In common steel, the loss in mechanical proprieties is more expressive than in the austenitic stainless steel, explaining the selection preference of these materials for high temperatures applications.
The equipments projects must consider this aspect, and that should not be forgotten while doing the material specification. However, in high temperatures, the anti-corrosion resistance is usual the most important factor in the material selection.
In high temperatures, the stainless steel is superior to the carbon steel, as for the anti-corrosion resistance and the mechanical proprieties.


3. What is the basic difference between the 304 and 430 steel series?

The 304 steel is austenitic non-magnetic steel, containing at least 18% of Chrome and 8% of Nickel.
The 430 is ferritic magnetic steel, with 16% of Chrome is his composition.
The austenitic and ferritic steels have a different behavior: The 304 has good fold ability, nice welding proprieties and an excellent anti-corrosion resistance. The 430 presents fragility in the welded parts, also has a good conformability (although lower than the 304’s), good anti-corrosion resistance (also lower than the 304’s).
Despite presenting general proprieties in a lower level than the 304’s specifications, the 430 steel can be perfectly applied to a large variety of utilities, like washing machine hampers, dishwasher parts, sinks (with not much large cavities), electric ovens, etc. 


4. Which precautions should be taken while welding stainless steel?

Some caution steps must be followed in the welding process of stainless steel:

1. Use additional material with chemical composition next to the material to be welded.

2. Avoid large fusion dots, they can cause solidification cracks in the welded parts.

3. The joints must be cleaned, by brushing process, face grinding or chemical decoupage (Isopropyl alcohol or acetone).
4. Use only brushes and cutters of stainless steel.

5. Do not use tools for procedures with stainless steel in procedures with carbon steel.

6. Finishing:
a) Remove the excess of arc welding material.
b) Correct the removing traces with a sandpaper belt that generates straight traces.
c) In the last finishing step, when the welded area will be equaled with the rest of the material, it's recommended the use of Scotch-Brite Strap (type SCM A-Gross) + Wheel for Metal (type A2-M) + Strap 3M 441D or 3M 441W # 120 or similar when the finishing number 3 is wanted and Scotch-Brite Strap (type SCM A - Medium) + Wheel for Metal (type A2-F) + Strap 3M 441D or 3M 441W # 150 or similar when the finishing number 4 is wanted.


5. How to bend stainless steel pipes?

In the operation of bending pipes is important to consider that a reduction in the section of the conformed pipe may occur. During the process, the external ray of the curve suffers a tractive effort, whereas the internal ray suffers an effort from compression.

This differential of tensions between the distended part and the compressed part is responsible for the reduction in the section of the conformed pipe.
This deformation depends of the pipe diameter, the thickness of the wall and the ray of bending. The bigger the diameter of the pipe is and minor is the bending ray; bigger will be the differential of tension and the deformation suffered by bending a pipe. Pipes with fine walls can snap in the bending operation.

It is recommended to fill the pipe to be bended with sand, lead or any another wadding material as form to minimize the effect of the deformation. This step can turn possible folding of pipes with fine walls and small rays of bending. The bending devices of modern pipes are endowed with mandrill that substitutes the wadding material. For pipes of diameter understood between 1” and 2” and ray of bending of approximately two times the diameter, the reduction of the section for the operation of bending is of the order of 2,5  to 3.0%.


6. Why does the stainless steel 416 have a better machining ability than the 304?

Although both the steel, ABNT 416 (stainless 416) and ABNT 304 (stainless 304) are of the family of stainless steel, they belong to different groups. The 416 Steel is of the group of Martensitic stainless steel and the 304 stainless steel is of the group of the austenitic ones. Additionally, steel 416 is generally machining workable when it is in the annealed condition of thermal treatment.

In this condition the microstructure is composed of ferrite carbons espheroidizades. In the other hand, the microstructure of steel 304 is permanently austenitic. This difference of microstructure enters steel by itself already confers to steel 416 one better machining ability. However, the great parcel of the difference of machining ability between them is on account of the shulphur level.

The stainless steel 416 is a re-sulphurated steel (minimum 0.15% of shulphur), already the steel 304 is not re-sulphurated (maximum 0.03% of sulphur). In summary, stainless steel 416 is a re-sulphurated, therefore projected steel to present good (high) machining ability, whereas the steel 304 was not projected with this characteristic.


7. I would like to know which are the inconveniences in binding by welding plates of different qualities. Example: aisi 304 to rst 37,2 or naval construction to a st 44,2; where will I be able to read about this subject?

In general, it is not recommended to bind the stainless steel to materials that would increase the possibility of a galvanic corrosion process, when in the presence of an electrolyte. This could be the case welding the 304 stainless steel to ST 37,2 or ST 44.2 steel. A form to prevent the galvanic corrosion, in case of electrolyte presence, could be to paint the carbon steel or the stainless steel after welding.


8. How to avoid the oxidation of the welded parts in stainless steel?

The recommendation is use a pickling gel (or pickling paste) and let it work for a while to remove the oxides and the contamination aggravated during the process f welding, doing immediately a nice wash with water. This way, the oxidation problems will be avoided in the welded parts. Remember, however, that the weld must be done with the adequate electrode for each kind of stainless steel.


9. Which is the best adhesive to fix stainless steel with stainless steel (plates)?

There is in the market a double face adhesive ribbon, produced by 3M, which may attend your necessity, depending of course, on the load that the plates to be fixed will be submitted.


10. Types of stainless steel for welding. Types of welds in inox. Weld process in inox. Problems in welding inox.

Introduction to the Processes of Welding of Stainless Steel:

There are diverse ways of if joining two metallic parts; between them it is the welding, that is an union process, using a heat source, with or without pressure application.

Characteristic of the Process of Welding:
- To produce energy to join two metals.
- To prevent the contact of the warm region with atmospheric air.
- To remove contaminations of the surfaces being joined.
- To control the transformations of welded phase in the together one.

The welding processes can in accordance with be classified the type of power plant or in accordance with the nature of the union. Industrially, the used processes of welding more are the ones that use the electricity as generation of energy to carry through the union.

The welding for resistance involves the following variants of process: welding the point, welding with sewing, welding top-the-top and welding with I stand out. Already the welding with electric arc can be subdivided between welding with consumable electrode and welding with not consumable electrode. In the first case the processes of welding with coated electrode are included, process of welding MIG/MAG, process of welding with tubular electrode and process of welding with submerged arc. The processes that use not consumable electrode are welding TIG and welding with plasma.

All the cited processes can be used for welding of stainless steel. The choice goes to depend on diverse factors that are boarded to follow.

The choice of the welding process involves four factors basically:
- The project of the together one (type, position, etc.).
- The thickness of the material.
- The nature of to be welded material.
- The manufacture cost (productivity, quality of the together one, durability of the product, etc.).

*Welding with coated electrode:
Process the electric arc produced between a coated electrode and the part to be welded.
Electrode: metallic soul + covering.

*Functions of the covering:
-Stabilizing the electric arc.
-Generate gases of protection of the fusing puddle.
-Produce slag that prevents contamination for the atmospheric air of the puddle of fusing and the weld lace.
-Add elements of league in the fusing puddle.
-Facilitate the welding is of position.
-Facilitate the manufacture of the coated electrodes.

*Advantages:
- Low cost of the equipment.
- Versatility.
- Welding in places of difficult access.
- Availability of consumable in the market.

* Limitations:
- Low productivity due the deposition tax.
- Necessity of slag removal.
- Dependent of the ability of the soldering iron.
- Production of  smokes and drips.
- Quality of the inferior lace to processes TIG, Plasma and MIG.
- Position of restricted welding.
- cannot be automatic.

TIG Welding:

The process of TIG (Tungsten Inert Gas) welding is defined as the welding process the established electric arc enters a not consumable electrode the tungsten base and the part to be welded. The fusing puddle is protected by an inert gas flow.

*Advantages:
- Welds of excellent quality.
- Finishing of the weld lace.
- Lesser heating of the welded part.
- Low sensitization to the intergranular corrosion.
- Absence of drips.
- It can be automatic.

*Limitations:
- Difficulty of use in draft presence.
- Inadequate for 6 plate welding of more than mm.
- Productivity low due to deposition tax.
- Cost of the equipment.
- Process depends on the ability of the soldering iron, when not automatic.

Gases of protection:

MIG Welding:

In the process of MIG (Metal Inert Gas) welding the electric arc is opened enters a fed wire continuously and the base metal. The casting region is protected by an inert gas or mixture of gases (argon, Co2, Helium or O2).

Advantages:
- Easiness of operation.
- High productivity.
- Automatic able Process.
- Low cost.
- Not form slag.
- Weld Lace with good finishing.
- Generates little amount of smoke.
- Welds of excellent quality.

Limitations:
- Regulation of the sufficiently complex process.
- It does not have to be used in draft presence.
- Position of limited welding.
- High Probability to generate porosity in the weld lace.
- Production of drips.
- More laborious Maintenance.


Welding for resistance:

In contrast of the other processes, the welding for electric resistance uses the heating for Joule effect to carry through the fusing of the common face between the two parts.
Joule effect occurs for the generation of heat through the electric chain ticket in a resistance. In the case of the plate welding, the biggest resistance is located accurately in the internal surface of plates, having used itself the correct conditions of welding. With application of the pressure for the copper electrodes and the posterior chain ticket, the fusing of this face occurs in common, forming the point.

Advantages:

- Very fine plate welding.
- Easiness of operation.
- Speed of the high process.
- Easiness for maintenance.
- It does not depend on the ability of the soldering iron.

Limitations:

- Not accepted parts with formats very complex and weighed.
- High Cost of the equipment and the maintenance.
- Demand of electric energy during the welding.


11. How is the stainless steel tempered? And which is the graph of treatment used in wanted temperatures?

The stainless steel family you tempered is known as maraging stainless steel. Equally to too much steel you tempered, they must be warm the high temperatures, called temperatures of austhenitization, from which if they submit the parts to a fast cooling until the temperature next to the environment, calling itself this operation of state of hardeness. The way of state of hardeness can be liquid (water, oil or polimerycs solutions) or gaseous (neutral air or gases). The diagram that guides the treatment of state of hardeness is the arched call of transformation, that can be isothermal (TTT) or of continuous cooling (TRC), more used.

One is about a map of the phases or microstructures (p.ex: perlita, bainita or martensita) foreseen in function of the temperature and the speed of cooling of the part. As this curve depends basically on the chemical composition, a diagram for each type of steel exists. Thus to answer accurately its question, we need to know which steel (degree) if wants to treat. Beyond the state of hardness conditions the graph called arched thermic treatment must also be used to determine which temperature to use to get itself the hardness desired after the thermic treatment.


12. I would like to know more about the stainless steel 429. How can I obtain it? Could you tell me the characteristics of this steel?

We know that it has 14% 16% of Chromium and the following typical properties:

Hardness - 156 HB max;
RT - 490 N/mm2;
Limit draining 310 N/mm2;
Allonge - 30%


13. I would like to have information about the stainless steel 303 S.S. That is, if I buy the stainless steel 304 will be the same thing?

No, it will not be the same thing of the point of view of factoring, that is the easiness of if manufacturing a part for processes that involve the metal removal for cut (mountain range, tilting, fresagem, etc). Of the point of view of resistance the corrosion will be very superior, especially the located corrosion, call of corrosion for pites (formation of small located punctures) that she is extremely dangerous and harmful to the component. In the normal condition of delivery in the solubilized state, the mechanical properties of the 304 are superior to the 303.
Normally the stainless steel of free cut contains sulphur (s), as in the stainless steel type 303. However sulphur cause a deterioration of the resistance the corrosion, restricting its application the not aggressive ways, beyond being able to modify the flavor of foods and drinks due to sulphur. In this case the application of inox 303 is restricted the applications without much responsibility of the point of view of aggressiveness of the way where it will go to operate. Of the point of view of factoring the 303 are insuperable.


14. We intend to manufacture sheaves for sportive use in scaling and rappel, also for rescue. I would like to know which is the type of stainless steel that has a greater mechanical resistance, as shear, traction, etc.

The common austenitic stainless steel do not possess high resistance mechanics, although good resistance the corrosion. In applications where if it needs good mechanical properties of resistance and tenacity and, simultaneously of good resistance the corrosion, must be used hardenable stainless steel for precipitation as the SOME 630, also known as 17-4 PH.
This steel, after thermal treatment of aging, presents resistance the traction above of 1000 MPa, depending on the employed cycle. This steel widely is used in the aeronautical, naval industry and in the manufacture of responsibility components, as axles.


15. I would like to know which are the inconveniences in binding weld plates of different former qualities. AISI 304 37,2 RST or naval construction ST 44.2.

In general, it is not recommendable to bind to the stainless steel the materials that will be able to promote the process of galvanic corrosion, when in the presence of an electrolyte. This could be the case to if joining for weld the stainless steel 304 to ST 37,2 or ST 44.2 steel. A form to prevent the galvanic corrosion, in case that it has the presence of the electrolyte, could be to paint the steel after stainless carbon or the weld.


16. The fixing through screws in stainless steel AISI-304 and AISI 420 (tempered/annealed) is recommended for application in which temperatures (minimum and maximum)? The fixing will be applied in a composition (wagon) for SUBWAY that probably will be subject to temperatures varying of approximately 0 to 50 ºC.

I do not see reasons for bigger concerns with the band of temperature esteem for the application in question.

Low temperature: exactly AISI 420 (that it presents one higher ductile-fragile transition temperature, compared to AISI 304) would not have the 0 contraindications to work degree Celsius.

High temperature: For 100 degrees Celsius, therefore 50 above of the esteem principle AISI 420 it has increased its tenacity to the impact, whereas for 304 AISI the effect most critical is the reduction of the LE in 20%.

Based in these data, I would simply advise the use of the usual factors of project security, which certainly already counts the effect of this narrow band of temperature on the mechanical properties of the materials in general.


17. I am doing a job and I need the cubical expansion coefficient of the stainless steel.

The coefficient of thermal expansion cubical "CETC" of the 304 stainless steel is approximately three times the value of the coefficient of thermal expansion linear "CETL".

Thus we have:

0 °C to 100 °C coefficient of linear thermal expansion °C is 17,2 X 10 -6/, that is, 0,0000172/°C, therefore 0 °C the 100 °C coefficient of cubical thermal expansion X 10 -6 will be approximately 51,6/°C, that is, 0,0000516/°C.

It fits to remember that:

(V - Vo)/Vo = "CETC" x (T - You); (V - Vo)/Vo = 0,0000516 x (T - > To), in the interval of 0°C the 100 °C
where, V is the volume in the T temperature and Vo is the original volume (initial) in the temperature To, the original one (initial).

Average coefficient of cubical thermal expansion (volumetric)

of 0 °C the 100 °C .......... 0,0000516 CETC =/°C
of 0 °C the 300 °C .......... 0.0000531 CETC =/°C
of 0 °C the 500 °C .......... 0,0000549 CETC =/°C
of 0 °C the 650 °C .......... 0.0000561 CETC =/°C


18. Which are the specific weights of the stainless steel 304 and 409?

The specific weights of steel 304 and 409 are the following ones:

Density in g/cm³ or kg/dm³:
steel 304: 8,0
steel 409: 7,8


19. Our client is having difficulties during the auto-broaching application of screws in AISI 420 tempered and annealing (it is believed that the hardness obtained of 43 to 45RC seems to be the problem). What is the maximum hardness that we will be able to get for AISI-410 and AISI-420?

Maximum hardness for steel AISI 410 and AISI 420 treated in the "standard" conditions:

Steel AISI 410
* Tempered in 1010 oil °C: typical 45,0 HRc
* Tempered as above + annealed the 300 °C: typical 43,5 HRc
* Tempered as above + annealed the 400 °C: typical 43,0 HRc

Steel AISI 420
* Tempered in 1040 oil °C: typical 52,0 HRc
* Tempered as above + annealed the 300 °C: typical 50,0 HRc
* Tempered as above + annealed the 400 °C: typical 49,0 HRc

Hardness a little bit superior (one or two points in the HRc scale) can eventually be obtained in these steel in its conditions of tempered, however, this would imply in superior temperatures of state of hardness the temperatures "standard". Superior temperatures of state of hardeness are not recommendable therefore cause loss of tenacity due the grain growth.


20. It would like to know if is it possible to know the temperature of the 420 stainless steel, without the use of thermometer for state of hardness in artisan knives and which would be the optimum procedure to obtain a good state of hardness?

We would like it to give some information on forging/annealing/state of hardness and thermic treatment of this steel.

Forging:

To heat slowly until 760oC and to wait that all the material reaches this temperature.
To uniformly continue then the heating up to 1100 to 1200ºC, to keep the enough time for complete homogenization, being remembered that extreme times in high temperatures take to a bigger oxidation of the material and eventual discarbonation.

To initiate the forging:

Not to forge below of 900ºC; after the forging to cool to the part in a warm oven 840ºC, if available. In case that not, to cool in warm leached ashes or dry whitewash. If cooled to air they can occur trincas in the parts. It after anneals cooling until the ambient temperature.

Annealing:

We suggest in its in case that to carry through a sub critical annealing to minimize the discarbonation. It uniformly heats the parts until 760 ºC and cools in the oven or calm air.

State of hardness:

To heat until 980 to1040 ºC to keep the sufficient to homogenize the temperature and to cool in oil; eventually we can think about cooling with blown air given its thicknesses to be small.

For control of the temperature of state of hardness we suggest the use of thermometry for contact thermocouple type K. Can in its lack be used an optic pyrometer or infra-red ray. One old technique of control of temperature without equipment use could be the table of colors. Had the narrow band of temperatures of state of hardeness, the use of colors for rightness of the temperature can be demonstrated inexact.

Thermic treatment:

To anneal soon the state of hardeness after, that is so soon the parts reach the ambient temperature. To keep the maximum hardness (about 52 HRC) and resistance the corrosion, to anneal between 150 and 200oC for one hour. Cool off in ambient temperature. The dimensional variation after state of hardness is between 1040 ºC to 200 ºC thermic treatment +0,0002 e + 0,0005 (m/m).


21. Can the stainless steel 430 be welded?

Yes, steel 430 can be welded, however its weld ability is inferior to the austenitic stainless steel (304, 316).