Nitrocarburising is carried out at sub-critical temperatures and involves the diffusion of nitrogen and carbon into the surface of carbon steel to give a somewhat harder case and soft core with a very thin compound layer on the surface.

The compound layer is wear and corrosion resistant and yet is not brittle, unlike its counterpart in the nitriding process. Since it provides an essential part of the properties required from the process it must not be removed by subsequent machining. Below the compound layer, the thin case significantly enhances the fatigue resistance of the component.

QPQ Liquid NitridingHome/Services/QPQ Liquid Nitriding

 

QPQ Liquid nitriding (also known as salt bath nitriding) is a process for producing a thin, high-hardness case that is wear and corrosion resistant, with little or no distortion of the part during processing.

The resulting lustrous black finish is an effective alternative for both chrome and nickel plating.

Liquid nitriding is suitable for a wide variety of carbon steels, low alloy steels, tool steels, cast irons, and stainless steels. Because liquid nitriding is a relatively low-temperature form of case hardening, part distortion is minimal.

QPQ Liquid Nitriding – Process Capacities

EDMONTON

Up to 42” long, 28” diameter.,

800 lb.

Process Selection and quality Control

Liquid nitriding requires precise control of the treatment process. Thermex operates under an ISO Certified Registered Quality Management System. Process quality control measures include:

Complete control of process sequence, including salt bath temperature and composition, polishing, and post-treatment parts handling

Test coupons of matching material are run with all nitriding loads. Coupons can then be used for metallurgical analysis in Thermex’s in-house metals testing laboratory. Random microhardness case depth surveys ensure that process specifications are being met.

Contact Thermex for more information on our liquid nitriding services.

 Contact Us for more information on our full range of metal heat treating services.

http://www.thermexmetal.com/qpq-liquid-nitriding

Durferrit Asea Private Ltd manufactures following specialty Chemicals that are used for our own Processes like Sursulf®, ARCOR®, Tuftride®, Melonite® , Tenifer®, QPQ® & OPO®:

Nitriding Salts (Sursulf/ Tuftride/ Melonite)

Base Salt : CR4, CR8 & TF1 Regenerator Salt : CR2, CR9 & REG 1

Oxidising Salt

OX 1-2 OX-E

Other Heat Treatment Salts

Coating Chemicals like Tribomol (Solid film Lubricant)

Molten salts black oxide process

Molten salts process involves molten oxidizing salts, Oxygen of which reacts with iron atoms forming a film of black oxide.

A mixture of sodium nitrate (NaNO3) and potassium nitrate (KNO3) in equal quantities is used for the molten baths preparation. Melting point of such eutectic composition is about 485ºF (250ºC).

Typical operating temperatures of the molten salt baths are 550-650ºF (288-343ºC). Stainless steels may be treated at the melt temperature 900ºF (482ºC).

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Benefits of black oxide coating

Decorative black color. Required surface appearance (shiny, glossy or matte) may be obtained. The color is stable at increased temperatures.

Minor dimensional changes. Thickness of black oxide coating does not exceed 3*10-5 inch (0.75 µm), half of which is added to the part dimension and the second half penetrates into the part depth.

Strong adhesion between the coating and the substrate. Black oxide coating does not peel from the surface.

Good lubrication characteristics. Black oxide improves anti-galling properties. In addition to this after-finish oil/wax decreases coefficient of friction of the black oxide coated parts.

Low light reflection. Reduced light glare of moving parts, surgical instruments and hand tools coated with black oxide causes less eye fatigue.

No hydrogen embrittlement. Since Hydrogen is not evolved in the chemical process of black oxide coating, no hydrogen diffusion into the metal occurs.

Slight improvement of corrosion protection. Black oxide coating provides some corrosion protection for internally used parts (not in corrosive environments).

Cost effectiveness. Black oxide coating is less expensive than other types of coatings.

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Applications of black oxide coating

Fasteners; Machine and cutting tools; Machine parts (bearings, shafts, springs, etc.); Medical tools and equipment; Gauges; Automotive parts; Hand tools; Sport equipment.

The black oxide finish on steel is one of the most widely used black or blue-black finishes. Some of the advantages of this type of finish are (1) attractive black color; (2) no dimensional changes; (3) corrosion resistance, depending on the final finish dip used; (4) non-galling surface; (5) no flaking, chipping, or peeling because the finish becomes an integral part of the metal surface; (6) lubricating qualities due to its ability to absorb and adsorb the final oil or wax dips; (7) ease and economy of application; and (8) non electrolytic solutions and a minimum of plain steel tank equipment required.

The black oxide finish produced on steel is composed essentially of the black oxide of iron (Fe3O4), and is considered by many to be a combination of FeO and Fe2O3. It can be produced by several methods: the browning process, carbonia process, heat treatment, and the aqueous alkali-nitrate process. Each of these processes produces a black oxide of iron finish, although the finish produced by each particular process differs in some characteristics. The chemical dip aqueous alkali-nitrate process is the most widely used to apply a black oxide finish on steel.

Aqueous Alkali-Nitrate Process

In this process a blackening solution is used that is highly alkaline and that also contains strong oxidizing chemicals. Refinements such as penetrants and rectifiers are also used to promote ease of operation, faster blackening, and trouble-free processing. At specific concentrations and boiling temperatures, these solutions will react with the iron in the steel to form the black oxide of iron (Fe3O4).

Because the reaction is directly with the iron in the steel, the finish becomes an integral part of the metal itself and, therefore, cannot flake, chip, or peel. For all practical purposes, there are also no dimensional changes. In transforming iron to black iron oxide, it is correct to assume that there is a change in volume. However, because of the highly alkaline nature of the blackening solution and because of the operating temperature, the blackening solution will dissolve a small amount of iron. Therefore, the amount of iron lost in this manner is compensated for by the buildup in volume from the change of iron to iron oxide — resulting in, for all intents and purposes, no dimensional changes. Extremely close measurements have shown that the actual change amounts to a buildup of only about 5 millionths of an inch.

There are types and conditions of steel and many different products that may require special procedures or additional steps.

It is important that only steel or steel alloys be immersed in the solution because other metals such as copper, zinc, cadmium, and aluminum will contaminate it. Many improvements have been incorporated into some proprietary black oxide salts and the latest one will rectify approximately 50 times more contaminants than heretofore. This particular product causes the contaminants to boil to the top, from which they can be skimmed, or dragged out and rinsed away during processing.

After a black oxide blackening solution has been mixed, there is a "breaking-in" period that can run from 24 to 48 h, depending on the volume of blackening solution and the amount of work

being processed. During this period, if it occurs, erratic blackening may be encountered, resulting in some work being blackened and some remaining partially or totally unblackened.

Chemical black oxide finishes today are being used on a wide variety of consumer and military parts. Some of the most important applications are guns, firearms and components, metal stampings, toys, screws, spark plugs, machine parts, screw machine products, typewriter and calculating machine parts, auto accessories and parts, tools, gauges, and textile machinery parts. A black oxide finish can normally be used for indoor or semioutdoor applications on metal parts or fabrications that require an economical attractive finish, nominal corrosion resistance, and, in many cases, where "dimensional changes" cannot be tolerated.

Heat-Treatment Methods

These methods can be divided into three classes: (1) oven or furnace heating; (2) molten salt bath immersion; and (3) steam heat process.

Oven or Furnace Method

The parts are heated to a temperature of 316 to 371 °C at which temperature the metal surface is oxidized to a bluish-black color. The shade of color depends on the temperature and the analyses of the steel.

Molten Salt Bath Method

The oxide finish can be obtained in several ways, depending on the manufacturing or processing requirements:

1. In a molten salt bath composed essentially of nitrate salts maintained at 316 to 371°C, the pieces are first cleaned of any oils, greases, or objectionable oxides and then immersed in the molten bath. They will take on a blue-black finish, after which they are quenched in clean water and given a final oil dip.

2. In a molten nitrate bath in an austempering operation, the pieces are heated to the hardening temperature in a neutral salt hardening bath, after which they are quenched in the molten nitrate bath at 316 to 371°C. They are then removed, cleaned, and given a final oil dip.

Steam process

In this method, the steel is placed in a retort and heated to a minimum temperature of 316°C. The retort is then purged with steam. Under these conditions a black oxide is formed on the metal surface.

Browning Process

The browning process is commonly known as a rusting process. The pieces are first thoroughly cleaned and then swabbed with an acidic solution. After drying in a dry atmosphere at approximately 77°C, the pieces are then placed in an oven with an atmosphere of 100% humidity and temperature at around 77°C for about 1.5 h. They then become quite rusty and the surface is rubbed down to remove the loose rust.

This procedure is carried out three or four times, after which the surface will have taken on a bluish-black finish. The pieces are then given a final oil dip.

Carbonia Process

To apply a black oxide finish by this method, the pieces are placed in a rotary furnace heated to around 316 to 371°C. Charred bone or other carbonaceous material is placed in the furnace along with a thick oil known as carbonia oil. The floor or cover of the furnace is occasionally opened and closed to allow circulation of air. After the parts have been treated for approximately 4 h, they are removed and immersed in oil. This finish is essentially a black oxide of iron, but because the metal surface is in contact with carbonaceous material and oil, some black carbon penetrates into the metal surface.

Processes for Nonferrous Metals

Following are typical methods for applying black oxide coatings to nonferrous metals:

1. Stainless steel: aqueous alkali-nitrate and molten dichromate methods. In the aqueous alkali-nitrate method a solution is made up by using approximately 2.07 to 2.3 kg of blackening salt mixture to make up a gallon of blackening solution, which is operated at a boiling point of 124 to 127°C. The parts, after cleaning and acid pickling, are immersed in the boiling solution and will take on a black color. They are then given a rust-preventive oil dip. In the molten dichromate method a molten bath of sodium dichromate or a mixture of sodium and potassium dichromates is used at a molten temperature of 316 to 399°C. The parts are immersed in the molten bath until they take on a blue or blue-black color, after which they are removed and cooled in oil or water. They are then cleaned to remove the salt and oil (if cooled in oil), after which they are given a dip in a clean, rust-preventive oil.

2. Zinc, zinc plate, zinc-base die castings, and cadmium plate: hot molyb-date blackening method, chromate and black dye method, and the black nickel plate method.

3. Copper and copper alloys (brasses and bronzes): alkali-chlorite aqueous solution method, cuprammonium carbonate method, anodic oxidation method, and aryl-sulfone mono-chloramide-sodium hydroxide method.

http://www.en.paradowscy.pl/menu,10,nitriding

In 2007, AMP Paradowscy S.J. introduced to the domestic market and foreign markets motor valves hardened in the process of pulsed plasma nitriding, acc. Technology IMP - Warsaw. This process is most advanced in the world metal nitriding process. It is used for surface treatment of highly loaded surfaces of machine parts, equipment and tools using a glow discharge generated by a pulsating electric field.          

     

This process utilizes the phenomenon of lightning impulse in the diluted exhaust nitrogen saturation of the metal surface. Ion nitriding is a modern variation of gas nitriding, in which ammonia was replaced with nitrogen and hydrogen, posing no threat to the environment. The process is carried out at low temperatures (400 ° C, which is one of the many advantages of ion nitriding) and reduced pressure. The most important reason why this process is carried out is to obtain high hardness of nitrided layers.

Temperature range from 400 to 600 ° C to control the curing process. The highest hardness is obtained after nitriding in the range of 400 ÷ 500 ° C. Nitriding process is carried out in a vacuum vessel in the pressure range 1 ÷ 10 hPa. The processed input is the negative pole of the discharge (cathode), and the vessel wall - the positive pole (anode). Under the influence of an applied DC voltage (400 ÷ 700V) cathode surface emits electrons in an electric field acquire the energy necessary to ionize the gas molecules. As a result of collisions of ionized atoms and molecules are accelerated and hit the cathode surface. Surface ion bombardment causes depopulation of the iron atoms of alloying elements, carbon, nitrogen and electrons needed to sustain the glow discharge. Iron atoms combine with active nitrogen atoms and deposited on the surface in the form of nitrides and depleted of nitrogen in the subsurface layer diffusion process. As a result of ion nitriding layer of nitride is obtained from non-porous single-phase zone of ensuring uniformity of subsurface physicochemical conditions. It is possible to precisely control the layer structure, which allows for efficient machining of large components with high dimensional requirements, and ensures a high durability. Continually is expanding assortment of materials that can be cured by this method to give even a 5-fold increase in durability. Ion nitriding are extremely effective in increasing resistance to abrasion and seizure of nitrided layers. The use of ion nitriding technology in motor valves can increase their stability in the system valve stem - the guide

and to reduce the adhesion of carbon deposits in the zone disc. Using this technology allows for a layer resistant to corrosion and increase the overall durability of the valves. Test results for steel valve in the initial state and after nitriding measured straight-line exhibit of more than five times lower values of the nitrided steel consumption. Using the technology of plasma-ion nitriding, we can get valves with high mechanical properties - hardness, resistance to seizure, wear and tear. This technology has many advantages over previously used chromium and salt bath nitriding, also surpassing them in terms of a neutral impact on the environment.

 

If you are interested in the above service on a cooperative to provide you with any informationMr. Piotr DominaAMP Paradowscy s.j. Fabryczna 1 street27-415 KunowTel. / fax. +48 41 261 11 50+48 41 261 11 20Mobile: 0 609 450 027Email: piotr@paradowscy.pl

Technical Detail About Engine Valve (Atta and Brothers Lahore)

D = HEAD DIAMETERd  = STEAM DIAMETERL  = OVERALL LENGTH> = SEAT ANGLEHS = HEAD STYLESE  = STEM END

1- FLA

2- FLAT-RECESSED

3- DOME

4- TULIP

5- SEMI-TULIP

1 - CIRCULAR GROOVE2 - CIRCULAR GROOVES3 - CIRCULAR GROOVES4 - CIRCULAR GROOVES5 - CIRCULAR/RING GROOVE6 - TAPER GROOVE7 - REVERSE TAPER GROOVE8 - DOUBLE TAPER GROOVE9 - TAPER/RING GROOVE10- PARALLEL/TAPER GROOVE11- NARROW GROOVE12- PARALLEL GROOVE13- PARALLEL/RING GROOVE14- RING GROOVE15- DRILL HOLE

 EN 18 D  (40 Cr 4) NS LOW ALLOY CHROMIUM STEEL

EN 52 (x 45 Cr 9 Si 3) SC

HIGH ALLOY SILICON CHROMIUM STEEL.For High Stress Inlet & Low Stress Exhaust Valves.

EN 59  (x 80 Cr 20 Si 2 Ni 1) XBHIGH ALLOY SILICON CHROMIUM NICKEL STEEL.For High Stress Exhaust Valves

21 – 4 N(x 53 Cr 22 Mn 9 Ni 4 N)  TF HIGH ALLOY CHROMIUM NICKEL NITROGEN AUSTENITIC STEELFor High Strength Valves.

21 – 12 N (x 20 Cr 21 Ni 12 N) THHIGH ALLOY CHROMIUM NICKEL NITROGEN AUSTENITIC STEEL.For High Strength Valves

SUH.38  HIGH ALLOY SILICON CHROMIUM NICKEL STEEL.Heat Resistant Valve Steel

  BM

FRICTION WELDED TWO PIECE VALVE CONSISTING.HIGH ALLOY AUSTENITIC HEAD AND LOW ALLOY STEM