Steels for special applications: Steels for special applications EF420 lecture 7


This lecture covers: This lecture covers Deep drawing steel Structural steel Pressure equipment steel Pipeline steel


Sheet steel for deep drawing: Sheet steel for deep drawing Up to 3mm thick


Formable sheet steel: Formable sheet steel Motor body panels, whitegoods, etc Ductility for deep drawing, work hardened Pure ferrite, Interstitials controlled Carbon less than 0.10% Age hardening Strain aging


Age hardening: Age hardening Quenched low carbon steel C, N and O retained in super saturated solid solution Hardness raised from 130 to 180 HV on aging for 500 h at 20°C Intermediate carbides and nitrides (epsilon) are precipitated during aging Aging is more rapid when paint is baked


Strain aging: Strain aging On aging, interstitial elements migrate to dislocations, where they form solute atmospheres N, O and C in solution are responsible This locks mobile dislocations, leading to an increase in yield strength (upper yield) When the dislocations break away from the solute atmospheres, the flow strain is reduced (lower yield point) The brake-away from solute atmospheres is localised giving ugly stretcher-strains or Lüders lines


Yielding behaviour: Yielding behaviour Stress MPa Strain %


Lüders lines: Lüders lines


Prevention of strain aging: Prevention of strain aging Control interstitials Low carbon, aluminium killed Decarburised steels Anneal in wet hydrogen Expensive Deep draw immediately after rolling 2% temper rolling just before drawing Keep steel in cold storage after rolling


Structural and pressure equipment steels: Structural and pressure equipment steels Strength and toughness


Composition and properties: Composition and properties For Weldability Carbon 0.25% maximum Manganese 0.3 to 1.5% Carbon equivalent (IIW) often 0.45 maximum Strength specified minimum not exceeding 450MPa (normal grades) or 800MPa for quenched and tempered grades Some grades suitable for low temperature (impact tested)


Carbon equivalent formulae: Carbon equivalent formulae A measure of hardenability and weldability High CE, High risk of hydrogen induced cracking in HAZ. CEIIW widely used. Pcm preferred for microalloyed steel


Delivery conditions: Delivery conditions Plates, bars, rolled sections (bulb flats, angles, tees, columns and beams), tubes, forgings Hot rolled (as-rolled) Normalised Controlled rolled or TMCP


TMCP and TMCR steels: TMCP and TMCR steels Rolling carried out below recrystallisation temp Grain refined A + F rolling with accelerated cooling Microalloyed Rely on processing


As-rolled structural steel: As-rolled structural steel


As-rolled steel: As-rolled steel Mixed grain size Reasonable properties, not sufficient low temperature toughness for critical uses


Controlled rolled steel: Controlled rolled steel


Controlled rolled steel: Controlled rolled steel Finer and more even grain than as-rolled Higher strength, better toughness AS 1548-7-460T AS 3678 Grades 350, 400, 450 Offshore structural steels


Next step: Next step Work while between Ar1 and Ar3 Austenite + ferrite Even finer grains Accelerated cool necessary Or toughness poor


Examples: Examples High strength line pipe steels X80, X90 High strength steels to replace QT structural steels


Problems with TMCP steel: Problems with TMCP steel Effect of subsequent austenitisation Normalising, hot forming Destroys fine grain structure Loss of strength and toughness High arc energy welding Low strength HAZ CTOD inferior to normalised steel


Structural steels: Structural steels Buildings, bridges, etc designed to AS1538, AS3990 or AS4100 Carbon steel plates to AS3678 Grades 250, 300, 350, 400 Carbon steel hot rolled sections to AS 3679.1 same grades Formability and weldability important Can select impact tested grades


Pressure vessel steels: Pressure vessel steels Closed vessels under pressure. Designed to AS1210. Covered by regulation. Carbon steel plate to AS 1548. Better quality than structural. Killed steels Designation shows steelmaking practice Can select impact tested and normalised grades Weldability and formability important


Shipbuilding and offshore: Shipbuilding and offshore Classification authority specifications (Lloyds, DnV etc) Different quality than pressure vessel or structural Through-thickness properties can be important Weldability and formability Grades A through E, AH through EH


Pipe and tube products: Pipe and tube products Pipe intended to carry fluid at pressure Tube - structural shape May be cold formed Boiler tubes are carrying pressure and are fired Pipe fittings - valves, flanges, tees, elbows, reducers


Pipe manufacture: Pipe manufacture Welded pipe and tube ERW, SAW long lengths Seamless pipe and tube. Piercing a billet. Restricted to 12m lengths


Pipe sizes: Pipe sizes Standard throughout world Nominal bore and scheduled wall thickness Standard and extra strong ASTM A106 Grade B ASTM A333 Grade 6 “fine grain” impact tested at -46°C


Transmission line pipe: Transmission line pipe Cross country pressure pipe lines Strength is important as is weldability Sophisticated HSLA steels API (American Petroleum Institute) grades API 5L Grade B, API 5L X42, X46, X52, X56, X60, X65 and X70


Quenched and tempered plate: Quenched and tempered plate Structural (Bisalloy 60, 70, 80) AS1554 Part 4 (AS 3597, ASTM A514, A517) Pressure Vessel (Bisalloy 80PV) AS1210 (AS3597, ASTM A517) Military (BIS812EMA, HY80) Wear plates (Bisalloy 320, 360, 400, 500) HSLA micro alloyed with boron etc