HEAT TREATMENT DEPARTMENT

Transcription

1 HEAT TREATMENT DEPARTMENT VISION 1. To be seen as the primary Heat Treatment Company by which all other Heat Treatment Companies are judged with respect to: Metallurgical / Heat Treatment knowledge and experience. Quality of work Heat Treatment Diversity. 2. To be and remain a profitable company. 3. To supply a standard of heat treatment that meets all international quality criteria or specifications. 4. To supply service to our customers (internal and external) that cannot be matched by our competitors. The service entails:- A. Collection and delivery of components on time B. Doing the heat treatment correctly the first time C. Communicating good and bad news to our customers timeously. D. To build mutually rewarding long term relationship with our customers. Page 1 of 8

2 HEAT TREATMENT PROCESS RANGE: MACSTEEL Heat Treatment Plant is the largest most diversified heat treatment plant is. The heat treatment plant is divided into 3 departments, each specializing in a unique heat treatment process range. The heat treatment plant control instrumentation is computer driven and is on par with any similar system anywhere in the world. Batch Processes: o Annealing o Normalising o Sub-Critical Annealing o Stress Relieving o Harden and Temper (Both Water & Oil quench Facilities) Specialised Processes: o Case Hardening (Gas Carburising & Gas Nitriding) o Neutral Hardening o Vacuum Hardening and Tempering Continuous Processes: o Neutral Hardening o Austemper Process Furnaces & Ancilliary Equipment used in the Heat Treatment Plant Batch Processes: o 8 off Gas Fired Top Hat Furnaces that can handle up to 7m length bar stock o Water & Oil quench facilities o 2 Straightening Presses to straighten from 40mm dia to 320 dia. o 2 straightening Reelers to straighten 16mm dia to 40mm dia. Page 2 of 8

3 Specialised Processes: o 2 off Pit Retort Furnaces for gas carburising o 2 off Pit Retort Furnaces for neutral hardening o 2 off Sealed Quench Furnaces for neutral hardening and carburising o 2 Vacuum Furnaces o 1 Vacuum Temper Furnace o Shot and Bead Blasting facilities o Cryogenic freezing facilities Continuous Processes: o 2 off gas fired Shaker Hearth Furnaces o 1 off electric Shaker Furnace o Continuous & Batch Tempering furnaces o 1 Austemper Furnace THE REASONS FOR DOING HEAT TREATMENT Heat treatment of steel or components is usually intended to accomplish any one of the following objectives: To obtain the desired properties within a given steel To remove stresses in steel/components set up by cold working or to remove stresses set up by non-uniform cooling of hot metal objects. To refine the grain structure. A coarse grain size may result in premature cracking when the component is put into use. To decrease the hardness and increase the ductility. To increase the hardness so as to increase resistance to wear. To increase the toughness (The ability of a material to absorb energy & deform plastically before fracturing); that is to produce a steel or a component having both a high tensile strength and good ductility. To improve the machinability. To improve the electrical & magnetic properties. Page 3 of 8

4 HEAT TREATMENT PROCESSES Full Annealing: The purpose of full annealing may be to refine the grain, induce softness, improve electrical and/or magnetic properties and in some cases to improve machinability. The process consists of controlled heating to a suitable temperature, above transformation temperature (normally above 850 C) holding for sufficient time and then controlled cooling within the furnace. Sub critical annealing, stress relieving: The purpose of this treatment is primarily used for the removing of residual stresses introduced as a result of extensive cold working or extensive machining. Normalising: The purpose of normalising is to supply harder and stronger steel than full annealing. It may also be used to improve machinability, modify, refine and homogonise the grain structure to improve the response in further hardening operations.the process is similar to full annealing. The main difference is that the components are cooled in still air. Hardening: The hardening process is done to increase wear resistance. The process may be modified to supply a full through hardened component or a hard surface with a softer, tougher core. Tempering: Tempering is done as a necessary add on heat treatment after hardening. The purpose of tempering is to minimise the stresses induced by the quenching process. Its purpose is two-fold, to prevent cracking (high alloy / tool steels) and to achieve desired hardness levels. Page 4 of 8

5 Carburising: Carburising is normally carried out on low carbon steels/low carbon alloy steels that require a high surface hardness for wear resistance but still need high core toughness. The process entails heating the components up to between 900 C and 940 C in a carbon rich atmosphere. The carbon dissolves into the austenite to give a surface layer rich in carbon. The time, temperature and diffusion coefficient dictate the depth of case achieved. Nitriding: Nitriding is a case hardening operation done to components that are in the as-finished condition. Examples are camshafts and small precision gears. The process is a low temperature process (+ 550 C) and is a long cycle, typically 60 hours for gas nitriding. The process depends on the formation of nitrides in the steel by the reaction of nitrogen with certain alloying elements. Austempering: Austempering is applied to components requiring high hardness coupled with high impact resistance and greater ductility than can be achieved with a quench and temper. The process is achieved by heating the components to above the transformation temperature (normally 820 C to 880 C) and quenching into a salt bath of about 220 C to 400 C Page 5 of 8

6 HEAT TREATMENT FURNACES UTILISED AT MACSTEEL SPECIAL STEELS The Heat Treatment Processes can be performed in one or more furnace types. The selection of a furnace type is dependant on the process required, the size of the component / length of steel and the surface finish required. Pit Retort Furnaces Processes normally carried out are neutral hardening, gas carburising and gas nitriding. Annealing and normalizing under protective atmosphere can also be done. The furnaces use protective to slightly reactive atmospheres in the processes. Vacuum furnaces This furnace consists of a chamber in which a vacuum is drawn and then the furnace is heated. The heating, under vacuum, allows far greater control and precision as well as resulting in clean, non-oxidised component. After hardening the components are quenched in either an inert gas or oil. High value components of an intricate nature (tool dies) and which require a good surface finish & minimal deformation are ideally suited to these furnaces. Page 6 of 8

7 SPECIALISED HEAT TREATMENT Sealed Quench furnaces These furnaces, as the name implies, enables one to harden/carburise components and then quench them under a protective/reactive atmosphere without having to remove the components from the furnace and thus expose them to the atmosphere. The type of components that are heat treated in the Sealed Quench furnaces are high value components that need to be heat treated under atmosphere. Austemper Furnace (Continuous Line Process) This is a continuous belt fed furnace used for hardening (austempering) small components under a protective atmosphere. The components are moved along a belt through the hot atmosphere controlled zone and dropped into a molten salt bath. The components move through the salt bath on a conveyer into a washer and drier resulting in a complete and final product. Shaker hearth furnaces (Continuous Line process) These furnaces are specifically designed for neutral hardening (quenching and tempering) under protective atmosphere of small, high volume articles (e.g. fasteners, nails, and springs). Top Hat furnaces As the name applies these large box-type furnaces are placed on a bed which has steel billets/bars or components laid out on them. Heat treatment processes include stress relieving, normalizing, annealing and quench & temper. These furnaces are typically used in the Heat Treatment of small through to large items such as forgings, fabrications, bar stock which has been purchased in the untreated condition, round bar in coil form and castings. The atmosphere is not controlled, so some oxidation does occur. This is not normally serious as further machining is done on the components. Page 7 of 8

8 P O Box 6130, Dunswart mac.dun@mactrading.co.za LIST OF FURNACES AVAILABLE AT MACSTEEL SPECIAL STEELS Top Hat Furnaces WIDTH (m) LENGTH (m) HEIGHT (m) Types of Heat Treatment Processes Stress relieve, Temper, Sub Critical Anneal Water Quench, Oil Quench, Stress Relieve Oil Quench, Normalising, Annealing, Stress Relieving Normalising, Annealing, Tempering, Stress Relieving Oil Quench, Normalising, Annealing, Stress Relieving Normalising, Annealing, Tempering, Stress Relieving Oil Quench, Normalising, Annealing, Stress Relieving Oil Quench, Normalising, Annealing, Stress Relieving Pit Retort Furnaces WIDTH (m) LENGTH (m) HEIGHT (m) Types of Heat Treatment Processes Pit Ø Neutral Harden, Carburise, (Oil Quench Only) R1 Ø Carburise, Neutral Harden, (Oil and Water Quench) R2 Ø Carburise, Neutral Harden, (Oil Quench) R3 Ø Temper Furnace R4 Ø Temper Furnace R5 Ø Temper Furnace R6 Ø Temper Furnace R7 Ø Temper Furnace, Gas Nitriding Sealed Quench APP 0.5 APP 1.0 APP 0.45 Carburise, Neutral Harden, Oil Quench Vacuum Furnaces WIDTH (m) LENGTH (m) HEIGHT (m) Types of Heat Treatment Processes Degussa Nitrogen Gas Quench Ipsen Oil Quench and Nitrogen Gas Quench Vac Temper Vacuum Temper Continuous Furnaces Comp WIDTH Comp LENGTH Comp HEIGHT Shaker 1 Na 70mm 300mm 1.5 to 3 ton per 24 Hr period, depends on comp size Shaker 2 Na 70mm 300mm 1.5 to 3 ton per 24 Hr period, depends on comp size Shaker 3 Na 70mm 200mm Approx 2 Ton per 24 Hrs. Austem per Na 50mm 250mm Approx 2 Ton per 24 Hrs. Page 8 of 8