TAFE NSW -Technical and Further Education Commission ENMAT101A Engineering Materials and Processes Associate Degree of Applied Engineering (Renewable Energy Technologies) Lecture 14 – The surface hardening of steels Flame Hardening

TAFE NSW -Technical and Further Education Commission The surface hardening of steels EMMAT101A Engineering Materials and Processes Reference TextSection Higgins RA & Bolton, Materials for Engineers and Technicians, 5th ed, Butterworth Heinemann Ch 14 Additional ReadingsSection

TAFE NSW -Technical and Further Education Commission The surface hardening of steels EMMAT101A Engineering Materials and Processes Note: This lecture closely follows text (Higgins Ch14)

TAFE NSW -Technical and Further Education Commission Principles of hardening (Higgins 14.1) EMMAT101A Engineering Materials and Processes READ HIGGINS 14.1 Many metal components require a hard outer skin and tougher inner core. E.g. Machine elements like shafts, bearings, gears, cams etc. There are two ways to achieve this; 1. Use low-carbon steel (tough) and add carbon to the outer skin. 2. Use carbon steel and heat only the surface before quenching.

TAFE NSW -Technical and Further Education Commission Case-hardening (Higgins 14.2) EMMAT101A Engineering Materials and Processes 1. Use low-carbon steel (tough) and add carbon to the outer skin. Higgins

TAFE NSW -Technical and Further Education Commission Case-hardening (Higgins 14.2) EMMAT101A Engineering Materials and Processes READ HIGGINS Carburising in solid media: (pack carburising) Higgins

TAFE NSW -Technical and Further Education Commission Case-hardening (Higgins 14.2) EMMAT101A Engineering Materials and Processes READ HIGGINS Carburising in liquid media (cyanide) Higgins

TAFE NSW -Technical and Further Education Commission Case-hardening (Higgins 14.2) EMMAT101A Engineering Materials and Processes READ HIGGINS Carburising by gaseous media Higgins

TAFE NSW -Technical and Further Education Commission Heat-treatment after carburising (Higgins 14.3) EMMAT101A Engineering Materials and Processes READ HIGGINS 14.3 Refining the core Refining the case Higgins

TAFE NSW -Technical and Further Education Commission Case-hardening steels (Higgins 14.4) EMMAT101A Engineering Materials and Processes READ HIGGINS 14.4 Higgins

TAFE NSW -Technical and Further Education Commission VIDEO: Crystals and Grain Structure BBC (1973) EMMAT101A Engineering Materials and Processes 1. What is a grain? 2. Recrystallisation Part 3: Heat Treatment Steel grains are too small to be visible - need a microscope approx 250 times magnification. Ferrite: Light coloured. Made of iron. Gives ductility to the steel Pearlite: darker coloured. Layers of Iron + Iron Carbide. Hardness and strength to the steel. 100% Pearlite: 0.83%C. Recrystallisation temperature 723C. Eutectic alloy. Normalising - cooled in air, grain size reduced and more uniform shape, toughness increased due to smaller grains Quenching - increases hardness. Not enough time for pearlite to form, so a needle like structure forms - martensite. Very hard and brittle. Tempering - (after quenching) restores toughness. Modifies the martensite needles with small flakes of carbon. This gives keeps most hardness, adds toughness. 0.1%C steel (Mild Steel). Recrystallisation 900C. Not enough carbon to produce martensite.

TAFE NSW -Technical and Further Education Commission Nitriding (Higgins 14.5) EMMAT101A Engineering Materials and Processes READ HIGGINS 14.5 Requires Steel with alloys that form carbides with N Lower temperature for diffusion (500 o C for 40 to 100 hours) Higgins

TAFE NSW -Technical and Further Education Commission Nitriding (Higgins 14.5) EMMAT101A Engineering Materials and Processes READ HIGGINS 14.5 Higgins

TAFE NSW -Technical and Further Education Commission Nitriding (Higgins 14.5) EMMAT101A Engineering Materials and Processes READ HIGGINS Heat treatment Advantages and disadvantages of nitriding Carbonitriding

TAFE NSW -Technical and Further Education Commission Ion Nitriding (Higgins 14.6) EMMAT101A Engineering Materials and Processes READ HIGGINS 14.6 Plasma nitriding and ion implantation.

TAFE NSW -Technical and Further Education Commission Flame-hardening (Higgins 14.7) EMMAT101A Engineering Materials and Processes READ HIGGINS 14.7 Localised heating/quenching Higgins

TAFE NSW -Technical and Further Education Commission Induction-hardening (Higgins 14.8) EMMAT101A Engineering Materials and Processes READ HIGGINS 14.8 Powerful, high frequency current induces eddy currents in the surface of the component, heating it locally. Higher frequencies heat to a shallower depth (skin effect). Induction Heating

TAFE NSW -Technical and Further Education Commission Summary (Higgins 14.9) EMMAT101A Engineering Materials and Processes Higgins

TAFE NSW -Technical and Further Education Commission Video: EMMAT101A Engineering Materials and Processes Heat Treatment: BBC: 1981 Heat treatment [videorecording] / producer Brian Davies. Video: Discusses the use of heat which changes the properties of metals. Outlines different techniques including hardening, tempering, annealing, normalising as well as a non-heat process, cold-working. Recommended viewing: All

TAFE NSW -Technical and Further Education Commission EMMAT101A Engineering Materials and Processes Handout Wikipedia: Online Resources. Teach yourself phase diagrams Heat Treatment: BBC: Heat treatment [videorecording] / producer Brian Davies. Heat treatment [videorecording] / producer Brian Davies. [B.B.C.], Video: Discusses the use of heat which changes the properties of metals. Outlines different techniques including hardening, tempering, annealing, normalising as well as a non-heat process, cold-working.

TAFE NSW -Technical and Further Education Commission GLOSSARY Carburising Plasma Ion Nitriding Pack carburising Cyanide hardening Gas-carburising Flame hardening Induction hardening Carbonitriding EMMAT101A Engineering Materials and Processes

TAFE NSW -Technical and Further Education Commission QUESTIONS Moodle XML: Some questions in Steel 1.Define all the glossary terms. 2.Describe why a part would need a hard skin and a soft core. 3.Use a table to summarise the advantages and disadvantages of the three carburising methods as shown in the video: Pack carburising, cyanide and plasma. 4.List advantages and disadvantages of nitriding EMMAT101A Engineering Materials and Processes